Methadone blockade of IK1promotes both long QT and Brugada-like arrhythmias: Mechanistic insights from computational modeling

Methadone blockade of IK1 promotes both long QT and Brugada-like arrhythmias: Mechanistic insights from computational modeling | bioRxiv /* */ /* */ <!-- <!-- /*! * yepnope1.5.4 * (c) WTFPL, GPLv2 */ (function(a,b,c){function d(a){return"[object Function]"==o.call(a)}function e(a){return"string"==typeof a}function f(){}function g(a){return!a||"loaded"==a||"complete"==a||"uninitialized"==a}function h(){var a=p.shift();q=1,a?a.t?m(function(){("c"==a.t?B.injectCss:B.injectJs)(a.s,0,a.a,a.x,a.e,1)},0):(a(),h()):q=0}function i(a,c,d,e,f,i,j){function k(b){if(!o&&g(l.readyState)&&(u.r=o=1,!q&&h(),l.onload=l.onreadystatechange=null,b)){"img"!=a&&m(function(){t.removeChild(l)},50);for(var d in y[c])y[c].hasOwnProperty(d)&&y[c][d].onload()}}var j=j||B.errorTimeout,l=b.createElement(a),o=0,r=0,u={t:d,s:c,e:f,a:i,x:j};1===y[c]&&(r=1,y[c]=[]),"object"==a?l.data=c:(l.src=c,l.type=a),l.width=l.height="0",l.onerror=l.onload=l.onreadystatechange=function(){k.call(this,r)},p.splice(e,0,u),"img"!=a&&(r||2===y[c]?(t.insertBefore(l,s?null:n),m(k,j)):y[c].push(l))}function j(a,b,c,d,f){return q=0,b=b||"j",e(a)?i("c"==b?v:u,a,b,this.i++,c,d,f):(p.splice(this.i++,0,a),1==p.length&&h()),this}function k(){var a=B;return a.loader={load:j,i:0},a}var l=b.documentElement,m=a.setTimeout,n=b.getElementsByTagName("script")[0],o={}.toString,p=[],q=0,r="MozAppearance"in l.style,s=r&&!!b.createRange().compareNode,t=s?l:n.parentNode,l=a.opera&&"[object Opera]"==o.call(a.opera),l=!!b.attachEvent&&!l,u=r?"object":l?"script":"img",v=l?"script":u,w=Array.isArray||function(a){return"[object Array]"==o.call(a)},x=[],y={},z={timeout:function(a,b){return b.length&&(a.timeout=b[0]),a}},A,B;B=function(a){function b(a){var a=a.split("!"),b=x.length,c=a.pop(),d=a.length,c={url:c,origUrl:c,prefixes:a},e,f,g;for(f=0;f<d;f++)g=a[f].split("="),(e=z[g.shift()])&&(c=e(c,g));for(f=0;f<b;f++)c=x[f](c);return c}function g(a,e,f,g,h){var i=b(a),j=i.autoCallback;i.url.split(".").pop().split("?").shift(),i.bypass||(e&&(e=d(e)?e:e[a]||e[g]||e[a.split("/").pop().split("?")[0]]),i.instead?i.instead(a,e,f,g,h):(y[i.url]?i.noexec=!0:y[i.url]=1,f.load(i.url,i.forceCSS||!i.forceJS&&"css"==i.url.split(".").pop().split("?").shift()?"c":c,i.noexec,i.attrs,i.timeout),(d(e)||d(j))&&f.load(function(){k(),e&&e(i.origUrl,h,g),j&&j(i.origUrl,h,g),y[i.url]=2})))}function h(a,b){function c(a,c){if(a){if(e(a))c||(j=function(){var a=[].slice.call(arguments);k.apply(this,a),l()}),g(a,j,b,0,h);else if(Object(a)===a)for(n in m=function(){var b=0,c;for(c in a)a.hasOwnProperty(c)&&b++;return b}(),a)a.hasOwnProperty(n)&&(!c&&!--m&&(d(j)?j=function(){var a=[].slice.call(arguments);k.apply(this,a),l()}:j[n]=function(a){return function(){var b=[].slice.call(arguments);a&&a.apply(this,b),l()}}(k[n])),g(a[n],j,b,n,h))}else!c&&l()}var h=!!a.test,i=a.load||a.both,j=a.callback||f,k=j,l=a.complete||f,m,n;c(h?a.yep:a.nope,!!i),i&&c(i)}var i,j,l=this.yepnope.loader;if(e(a))g(a,0,l,0);else if(w(a))for(i=0;i (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0];var j=d.createElement(s);var dl=l!='dataLayer'?'&l='+l:'';j.src='//www.googletagmanager.com/gtm.js?id='+i+dl;j.type='text/javascript';j.async=true;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-M677548'); Skip to main content Home About Submit ALERTS / RSS Search for this keyword Advanced Search New Results Methadone blockade of I K1 promotes both long QT and Brugada-like arrhythmias: Mechanistic insights from computational modeling View ORCID Profile Zhaoyang Zhang , J.T. Green , Mark C. Haigney , View ORCID Profile Kalyanam Shivkumar , Alan Garfinkel , View ORCID Profile Zhilin Qu doi: https://doi.org/10.1101/2025.03.01.641012 Zhaoyang Zhang 1 Department of Physics, School of Physical Science and Technology, Ningbo University , Ningbo, Zhejiang 315211, China Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Zhaoyang Zhang J.T. Green 2 Department of Medicine, Uniformed Services University of the Health Sciences , Bethesda, MD 20814 Find this author on Google Scholar Find this author on PubMed Search for this author on this site Mark C. Haigney 2 Department of Medicine, Uniformed Services University of the Health Sciences , Bethesda, MD 20814 Find this author on Google Scholar Find this author on PubMed Search for this author on this site Kalyanam Shivkumar 3 UCLA Center for Interventional Programs and Department of Medicine (Cardiology), David Geffen School of Medicine, University of California , Los Angeles, CA 90095, USA Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Kalyanam Shivkumar Alan Garfinkel 3 UCLA Center for Interventional Programs and Department of Medicine (Cardiology), David Geffen School of Medicine, University of California , Los Angeles, CA 90095, USA 4 Department of Integrative Biology and Physiology, University of California , Los Angeles, CA 90095, USA Find this author on Google Scholar Find this author on PubMed Search for this author on this site Zhilin Qu 3 UCLA Center for Interventional Programs and Department of Medicine (Cardiology), David Geffen School of Medicine, University of California , Los Angeles, CA 90095, USA 5 Department of Computational Medicine, David Geffen School of Medicine, University of California , Los Angeles, CA 90095, USA Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Zhilin Qu For correspondence: zqu{at}mednet.ucla.edu Abstract Full Text Info/History Metrics Preview PDF Abstract Background Methadone is widely used for chronic pain relief and in the maintenance therapy of opioid use disorder, however, it also increases the risk of ventricular arrhythmias and sudden cardiac death. Methadone blocks several ionic currents with different half-maximal inhibitory concentrations (IC 50 ), including the rapid component of the delayed rectifier potassium current (I Kr ), the inward rectifier potassium current (I K1 ), the L-type calcium current (I Ca,L ), and the late component of the sodium current (I NaL ). Despite the well-known proarrhythmic effect of I Kr blockade, the effects of blocking other ionic currents on arrhythmogenesis remain less well understood. Methods Computer simulations were used to explore the proarrhythmic effects of methadone by investigating how its blocking effects on ionic currents act alone or together in arrhythmogenesis. Results The major findings are: 1) blocking I K1 potentiates QT prolongation-related arrhythmogenesis by enhancing a tissue-scale dynamical instability for the spontaneous genesis of ectopic excitations. Blocking I K1 and I Kr together results in a synergistic effect, greatly increasing the arrhythmia propensity, much larger than that of blocking either one alone; 2) blocking I K1 in combination with lowering I Ca,L potentiates phase-2 reentry caused by spike-and-dome action potential morphology, an arrhythmia mechanism of Brugada syndrome. Blocking I Kr exhibits little effect for this mechanism of arrhythmias; and 3) hypoxia, often comorbid in methadone populations, can potentiate QT prolongation-related arrhythmias at high sympathetic activity and phase-2 reentry at low or basal sympathetic activity, mainly via its effect on I Ca,L. Conclusions These simulation results provide mechanistic insights into the genesis of QT prolongation-related Torsades de Pointes and Brugada-like ECG related arrhythmias caused by methadone use. Introduction Methadone is a drug widely used for chronic pain relief and in the maintenance treatment of opioid use disorder, however, it is also associated with increased risk of ventricular arrhythmias and sudden cardiac death 1 - 7 . Methadone users may exhibit abnormal ECG signs, including QT prolongation, Brugada-like ECG patterns, elevated U waves, etc. Experimental studies have shown that methadone blocks the rapid component of the delayed rectifier potassium (K + ) current (I Kr ) 8 - 13 , encoded by the human ether-a-go-go-related gene (hERG). Blocking I Kr causes drug-induced long QT syndrome (LQTS) and Torsades de pointes (TdP), which agrees with methadone’s proarrhythmic profile of QT prolongation and TdP promotion. However, biophysical studies have shown a wide range of half-maximal inhibitory concentrations (IC 50 ) of methadone on I Kr , from 3 to 10 μM 8 - 13 . In an analysis of clinical trial data 14 , <5% of patients manifested peak methadone concentrations exceeding 3 μM. Due to extensive protein binding, free methadone concentrations may well be <1 μM. If the IC 50 is much higher than 1 μM, the I Kr blocking effect may not be as large as anticipated. A recent study by Klein et al 13 showed that methadone also blocks the inward rectifier K + current (I K1 ) with an IC 50 of 1.5 μM, suggesting that its blocking effect on I K1 may play a key role in arrhythmogenesis. In addition to blocking I Kr and I K1 , experimental studies have shown that methadone also blocks the L-type Ca 2+ current (I Ca,L ) and the late component of the sodium (Na + ) current (I NaL ) at high concentrations (5.5 μM and 8.5 μM, respectively) 12 , 15 , which agrees with the observations that methadone shortens action potential (AP) duration (APD) at high doses 13 . A recent study by Solhjoo et al 16 showed that methadone users have lower oxygen levels during sleep, which may cause hypoxia-induced electrophysiological changes to affect arrhythmogenesis. Despite the well understood role of blocking hERG in prolonging QT interval and promoting TdP, how the multiple ion channel blocking effects of methadone integrate together to impact arrhythmogenesis remains to be elucidated 17 . Moreover, it is unclear why most methadone-related deaths occur during sleep 1 , 16 , 18 . In this study, we use computer simulations to investigate the mechanisms of arrhythmogenesis caused by methadone. Our major findings are: 1) Blocking I K1 potentiates APD- or QT prolongation-related arrhythmogenesis by enhancing the tissue-scale dynamical instability for spontaneous PVCs. Blocking I K1 and I Kr together results in a synergistic effect, greatly increasing the arrhythmia propensity, much larger than that of blocking either one alone; 2) Blocking I K1 in combination with lowering I Ca,L potentiates phase-2 reentry (P2R) caused by spike- and-dome AP morphology. Blocking I Kr exhibits little effect for this mechanism of arrhythmias; and 3) Hypoxia, often comorbid in methadone populations, for example with underlying sleep apnea, can potentiate APD prolongation-related arrhythmias at high sympathetic activity and P2R at low or basal sympathetic activity, mainly via its effect on I Ca,L . We discuss implications of the mechanistic insights from the computer simulations to arrhythmogenesis caused by methadone. Methods PVCs in tissue Early afterdepolarizations (EADs) in isolated cardiac myocytes are often cited as the cause of tissue-level PVCs, which then propagate through ventricular tissue and become triggers of arrhythmias. However, our computer simulations showed that while cellular- level EADs can cause tissue-level PVCs under the right conditions 19 , 20 , repolarization gradient (RG)-induced PVCs arising from tissue-scale dynamical instabilities might be the major mechanism of PVCs, which is supported by experimental observations 21 - 24 . These PVCs, dubbed “R-from-T” 25 , 26 , can degenerate spontaneously into reentrant arrhythmias under the right tissue conditions. Therefore, to assess the proarrhythmic effects of methadone, we looked for PVC induction in tissue as our marker for arrhythmogenesis. 1D Cables Based on our previous work, we found that a one-dimensional (1D) cable is a sufficient test for the genesis of these tissue-level PVCs and allows fast enough computer simulations. In our simulations, the 1D cable was composed of 200 cells (3 cm), the first half endocardium and the second half epicardium. We used four AP models, i.e., the 1994 Luo and Rudy (LRd) guinea pig model 27 , the 2004 ten Tusscher at al (TP04) human model 28 , the O’Hara et al (ORd) human model 29 , and the modified ORd model by Tomek et al. (ToRORd) 30 . The endocardial versions of the human models were used. For simplicity, we altered the slow component of the delayed rectifier K + channel (I Ks ) to model the endo-epi heterogeneity. We also added I to to the epicardium. Populations of Models To take into account inter-individual variabilities, we generated 1D cable model populations using random parameters and preset filters. The LRd, TP04, and ORd models were used for the model populations. (The ToRORd model behaves very similarly to the ORd model.) We multiply the maximum conductance of the major ionic currents with a factor drawn randomly from a preset interval. We carried out 1D cable simulations with the randomly selected parameter sets and measured APD at both the endocardium and epicardium. We first dropped the cases that exhibited PVCs and the cases that gave rise to too short an APD in the epicardium (due to a too strong I to ). After these filters, we obtained a model population with a wide raw APD distribution. We then assigned a Gaussian distribution (the QTc distribution of healthy human is close to a Gaussian distribution 31 ) within this raw APD distribution for the endocardium as the target APD distribution, and then dropped parameter sets randomly to achieve the targeted Gaussian APD distribution. The retained parameter sets then form the normal control model population. Modeling channel block The blocking effect of methadone on an ionic current was modeled by multiplying the current by a Hill function, i.e., for an ionic current I m , the formulation is: where [M] is the methadone concentration, IC 50 is the half-maximal inhibitory concentration, and n is the Hill coefficient. I m represents I Kr , I K1 , I Ca,L , or I NaL . For I Kr , we used n=0.8 and IC 50 =2.9 μM (Klein et al 13 and Tran et al 12 ). For I K1 , we used n=0.7 and IC 50 =1.5 μM (Klein et al 13 ). For I Ca,L , we used n=1.1 and IC 50 =5.5 μM (Tran et al 12 ). For I NaL , we used n=0.9 and IC 50 =8.5 μM (Tran et al 12 ). Results Effects of blocking I Kr or I K1 on PVC genesis To relate the effects of blocking I Kr or I K1 on APD to their effects on PVC genesis, we first explored the effects of blocking I Kr or I K1 on APD for the four AP models simulated in this study ( Fig.1 ). In all four models, reducing I K1 by 50% results in roughly a 5% increase in APD but reducing I Kr by 50% causes a larger APD increase, as expected. However, their responses to blocking I Kr are very different, with the ORd and ToRORd models exhibiting a much larger change in APD than did the other two models. Download figure Open in new tab Figure 1. Effects of blocking I Kr and I K1 on APD prolongation. Showing are APD versus percentage of the control value of G Kr (circle) or G K1 (square) for the LRd model (A), the TP04 model (B), the ORd model (C), and the ToRORd model (D). To investigate the effects of blocking I Kr or I K1 on PVC genesis, we performed simulations of 1D cables, scanning for what combinations of the maximum conductance of I Kr or I K1 and I Ca,L produced PVCs. To model repolarization heterogeneity, we reduced G Ks in the endocardial region and added I to in the epicardial region. We first used cables based on the LRd model to show PVC genesis in more detail ( Fig.2 ) and then cables based on TP04, ORd, and ToRORd models (Fig.S1) to verify and compare with the LRd model results. EAD- and Repolarization Gradient-mediated PVCs For the LRd model, we first excluded I to in the epicardial layer to avoid I to -mediated PVCs ( Fig.2A ). In this case, PVCs are promoted by enhancing I Ca,L and blocking I K1 or I Kr (light blue regions). In other words, for a fixed G K1 or G Kr , PVCs occur once G Ca,L is above a certain threshold, or for a high enough G Ca,L , PVCs can occur by reducing G K1 or G Kr . These PVCs are mediated by early afterdepolarizations (EADs) in the long APD region or by the Repolarization Gradient (RG) between endocardium and epicardium (see an example of RG-mediated PVC in Fig.2D ), as shown in previous studies 19 , 20 . Although blocking I K1 increases APD less than does blocking I Kr ( Fig.1A ), it causes a faster reduction of the threshold I Ca,L for PVC genesis than blocking I Kr . For example, a 50% reduction of I Kr from its control value reduces the I Ca,L threshold from 4.5 to 3.9 fold (red arrow in right panel in Fig.2A ) of its control value, while a 50% reduction in I K1 reduces the threshold from 4.5 to 3 fold (red arrow in left panel in Fig.2A ). This indicates that although I K1 only exhibits a small effect on APD and EADs at the cellular scale 32 , it plays a critical role at the tissue scale to promote PVCs. This is because both EAD- and RG-mediated PVCs are tissue-scale phenomena driven by tissue-scale dynamical instabilities 19 , 20 , and I K1 plays a critical role in promoting these dynamical instabilities in tissue . Phase-2 Reentry-mediated PVCs We then added I to to the epicardial layer and observed qualitative difference in PVC genesis ( Fig.2B ). Adding I to created a spike-and-dome AP morphology in the epicardial layer ( Fig.2C ) but had only a small effect on RG-mediated PVCs, i.e., the light blue regions at high G Ca,L in Figs. 2 A and B are similar. However, a new PVC region emerged at low G Ca,L (magenta regions and insets in Fig.2B). The mechanism of this type of PVCs is via phase-2 reentry (P2R) caused by the I to -induced spike-and-dome AP morphology 33 - 35 . As shown in Fig.2E, the AP in the epicardial layer became very short (a spike), facilitating the formation of a PVC. The PVC region of this mechanism reduces as G K1 increases until it completely disappears. In other words, blocking I K1 promotes P2R. In general, P2R is promoted by decreasing inward currents or increasing outward currents. It is non-intuitive that blocking I K1 , an outward current, promotes P2R. This is because similar to the RG-mediated PVCs, the PVCs caused by P2R are also a result of a tissue-scale instability 36 that depends on I K1 strength. Note that the P2R region is insensitive to I Kr changes (the width of the PVC region only changes slightly with G Kr ), agreeing with that shown in our previous studies that P2R is not sensitive to changes of G Kr and G Ks 35 , 37 . Download figure Open in new tab Figure 2. Effects of I K1 and I Kr on PVC genesis in a 1D cable with the LRd model. A . RG- mediated PVC regions (light blue) in the G K1 and G Ca,L parameter plane (left) and the G Kr and G Ca,L parameter plane (right) when no I to is present in the epicardial region (G to =0). G Ks is 0.3 folds of control in the endocardium and 2 folds in the epicardium. Red arrows mark the changes in I Ca,L threshold for a 50% block of I Kr from control. B . Same as A but when I to is present in the epicardial region (G to =1.75 mS/cm 2 ). The RG-mediated PVC regions are colored light blue and the P2R- medtaed PVC regions are colored magenta. The three symbols mark the parameter locations for the examples shown in C-E. Insets are expanded views of the P2R-mediated PVC regions. C . Time-space-voltage plot of a case with no PVC (triangle, G K1 is 1 fold and G Ca,L 1.1 folds of their control values). D . Time-space-voltage plot of a RG-mediated PVC caused by reducing I K1 and increasing I Ca,L (diamond, G K1 is 0.7 folds and G Ca,L 3.7 folds of control). * marks the spontaneous PVC. E . Time-space-voltage plot of P2R-mediated PVC caused by reducing both I K1 and I Ca,L (circle, G K1 is 0.7 folds and G Ca,L 0.9 folds of control). * marks the spontaneous PVC. Note that the stimulated AP in the epicardial layer is an abbreviated spike due to lowering G Ca,L , which allows the spike-and-dome AP in the middle layer to initiate a PVC in epicardial layer. As shown in our previous simulation studies of 2D tissue 19 , 35 , 37 or 3D heart 25 models, the RG-mediated or P2R-mediated PVCs can maintain as multi-beat focal excitations or degenerate into reentrant arrhythmias, depending on the tissue conditions. Therefore, in this study, we used the 1D cable model as our test platform, and the genesis of spontaneous PVCs as a marker for arrhythmogenesis. We compared the results of the LRd model to those of the other three AP models (see SI Fig.S1). The results are similar despite some quantitative differences. In summary, blocking I Kr and/or I K1 combined with increasing I Ca,L conductance promotes RG-mediated PVCs, and blocking I K1 combined with decreasing I Ca,L conductance promotes P2R- mediated PVCs. Although blocking I K1 only exhibits a small effect on prolonging APD and promoting EADs in single cells, it exhibits a much larger effect on promoting PVCs in tissue, a tissue-scale phenomenon that cannot be revealed by single-cell studies. Arrhythmogenesis promoted by methadone In general, we can infer, from the results shown in Figs.1 , 2 and S1, that among the proarrhythmic effects of methadone, blocking I Kr and I K1 prolongs APD and promotes arrhythmias under high I Ca,L via RG-mediated PVCs and that blocking I K1 promotes arrhythmias at low I Ca,L via P2R-mediated PVCs. However, methadone also blocks other currents and causes hypoxia during sleep; how these effects of methadone integrate together to affect arrhythmogenesis is unclear. Secondly, in the general population, there is substantial inter-individual variability: individual parameter sets will differ from one person to another. This inter-individual variability results in individuals having different responses to a specific drug, including different responses to different drug doses. The results shown in Figs.1 and 2 are based on a single set of control parameters for each model, which is not representative of the diversity of the general population. To take into account inter-individual variability, we generated model populations using randomly selected parameter sets and APD filters (see Methods). This randomization-plus-filtering resulted in Gaussian-like distributions of APD from the endocardium of the normal control populations for the LRd model ( Fig.3A ), the TP04 model (Fig.S2A), and the ORd model (Fig.S3A). To differentiate the contributions of methadone’s blocking effects on different ionic currents, we also used different combinations of its blocking effects. For example, we might include only its I K1 or I Kr blocking effect alone or a combination of the two, etc. Effects of Methadone on APD We first used the model populations to assess the effects of methadone on APD under normal control conditions. Fig.3B shows average APDs and standard deviations for different methadone concentrations and different combinations of methadone blocking effects, marked by different colors, for the LRd model. In general, the responses of the average APD of the model populations (see also SI Figs. S2B and S3B) to methadone agree with the results shown in Fig.1 : 1) blocking I K1 alone (yellow) only lengthens APD slightly; 2) blocking I Kr alone (red) has a bigger effect on prolonging APD than does blocking I K1 ; 3) blocking I K1 and I Kr together (blue) results in stronger effects on lengthening APD than did blocking I Kr alone; and 4) the APD lengthening effects due to blocking I K1 and I Kr are attenuated by blocking I Ca,L and I NaL (green and purple). Arrhythmogenesis in high sympathetic conditions We then used the model populations to simulate the arrhythmogenic effects of methadone in the setting of high sympathetic activity, modeled by increased G Ca,L . We chose to modify only G Ca,L because, although β-adrenergic stimulation increases the amplitudes of both I Ca,L and I Ks , the amplitude of I Ca,L increases much faster than that of I Ks 38 , and thus in the early phase of sympathetic stimulation, the main effect is the increase of I Ca,L strength. Fig.3C shows the percentages of individuals in the population exhibiting PVCs for the LRd model. When methadone only blocks I Kr (red bars), the PVC risk, although it increases with methadone dose, is very low. If methadone blocks I K1 only (yellow bars), the risk increases with dose to a higher percentage than by blocking I Kr alone. Interestingly, when methadone blocks both I Kr and I K1 together (blue bars), the risk becomes much higher, indicating that blocking I Kr and I K1 synergistically promotes arrhythmias. The TP04 model (Fig.S2C) behaves similarly to the LRd model. The ORd model (Fig.S3C) exhibits some differences from the other two models. In the ORd model, blocking I K1 exhibits almost no effects while blocking I Kr exhibits a large effect. But again, blocking both I Kr and I K1 together exhibits a much larger effect, demonstrating that the synergistic effects of blocking both I Kr and I K1 still occur as observed in the other two models. For all three models, as anticipated, blocking I Ca,L reduces PVCs (green bars), which is substantiated at high doses of methadone. Due to its high IC 50 , the effect of I NaL on PVC genesis is small (purple bars) with a larger effect occurring in the ORd model. To correlate APD to PVC risk under different conditions of methadone blocking effects, we plotted the percentage of the population exhibiting PVCs versus averaged baseline APD for different conditions of methadone blocking effects ( Fig.3D ). Specifically, we plotted the percentage exhibiting PVCs (under high sympathetic activity) against the averaged APD shown in Fig.3B (under control). Blocking I Kr alone lengthens APD but does little in promoting PVCs (red). Blocking I K1 alone increases APD slightly but has a large effect on promoting PVCs (yellow, steep curve). Blocking both I K1 and I Kr together, the curve is less steep than for blocking I K1 alone but extends to longer APDs and higher percentages due to the synergy effect. The TP04 model behaves similarly to the LRd model (Fig.S2D) while the ORd model behaves differently when blocking I Kr or I K1 alone (Fig.S3D). However, all three models demonstrated that blocking I Kr and I K1 together greatly enhanced the arrhythmia risk. Arrhythmogenesis in low sympathetic conditions Finally, we simulated the effects of methadone under low sympathetic activity (control I Ca,L ) for the LRd model ( Fig.4 ) and the TP04 model (SI Fig.S4). We simulated two scenarios: with or without hypoxia. Since we simulated low sympathetic activity, we used the effects of hypoxia on ionic currents under basal condition used by Gaur et al 39 , in which I Ca,L was reduced. In the absence of hypoxia ( Fig.4A ), when methadone blocks I K1 and/or I Kr but does not block I Ca,L and I NaL , it exhibits almost no effects on PVC genesis (color bars do not show up in graph). When methadone also blocks I Ca,L and I NaL (green and purple bars), the PVC risk increases with methadone concentration quickly due to its I Ca,L blocking effect. Blocking I NaL only enhances the risk slightly. In the presence of hypoxia ( Fig.4B ), blocking I K1 increases the arrhythmia risk (yellow) but blocking I Kr with or without blocking I K1 does not affect the risk of arrhythmia (red and blue bars). If methadone also blocks I Ca,L and I NaL (green and purple bars), the PVC risk decreases with methadone concentration due to too high an I Ca,L blockade at high methadone concentrations. Role of I ca , L Since I Ca,L is the current affected by sympathetic stimulation, hypoxia, and methadone, it plays a key role in methadone-induced arrhythmias. To give broader view of the effects of I Ca,L combined with I K1 and I Kr blocking effects, we recorded the percentage of PVCs versus I Ca,L strength for a fixed methadone concentration (3 μM) with methadone blocking I Kr (red boxes) or I K1 (yellow boxes) alone or both together (blue boxes) for the LRd model ( Fig.5 ). For reference, we also plot the percentage of PVCs in the absence of methadone. In all cases, the PVC risk is low in the intermediate I Ca,L strength range. For high I Ca,L , PVCs are caused by APD prolongation, and the risk increases with the strength of I Ca,L . For low I Ca,L , PVCs are caused by spike-and-dome AP morphology via P2R, which occurs in a narrow range of I Ca,L strength. Blocking I K1 greatly increases the risk of PVCs, but blocking I Kr exhibits little effects. Discussion In this study, we used computational simulation to investigate the multiple ion channel blocking effects of methadone on arrhythmogenesis, beyond its role as a hERG blocker. Our major findings are: Blocking I K1 does not prolong APD significantly but can substantially increase the occurrence of RG-mediated PVCs at high sympathetic activity via tissue-scale instabilities. Blocking I K1 works synergistically with blocking I Kr to greatly increase the susceptibility to arrhythmias. Blocking I Ca,L (and I NaL ) at high methadone concentrations can attenuate the risk of arrhythmias, as anticipated. Blocking I K1 promotes P2R at low or basal sympathetic activity, which is potentiated by the I Ca,L blocking action of methadone. Blocking I Kr has little effect on this mechanism of arrhythmias. Hypoxia may promote RG-mediated PVCs at high sympathetic activity by enhancing I Ca,L and I NaL and also promote P2R at basal or low sympathetic activity by suppressing I Ca,L . The insights from the computer simulations reveal the important roles of I K1 in both RG-mediated and P2R-mediated PVCs and the mechanisms of methadone-induced arrhythmogenesis, as discussed below. I K1 blockade and its synergy with I Kr blockade in APD prolongation and arrhythmogenesis It is well understood that blocking I Kr lengthens APD and promotes EADs, which are associated with QT prolongation and arrhythmogenesis in the inherited LQTS type 2 and most cases of drug-induced LQTS. Blocking I K1 gives rise to a small increase in APD ( Fig.1 ) and thus its contribution to QT prolongation is small. But on the other hand, our present and previous studies 19 , 20 showed that although blocking I K1 plays only a small role in APD prolongation ( Fig.1 ) and in EAD genesis 32 , it plays a much greater role in promoting PVCs in tissue ( Figs.2 and 3 ). We showed that the RG-mediated (or phase-2 EAD-mediated) PVCs originate from a tissue-scale dynamical instability caused by RG and enhanced I Ca,L 19 , 20 , 36 , and I K1 potentiates this instability without affecting the APD or the RG per se. Therefore, the main effect of I K1 on PVC genesis is at the tissue level by promoting dynamical instability in tissue, while the effect of I Kr is mainly at the single-cell level by prolonging APD and promoting EADs . Effect on DADs Because I K1 plays a key role in stabilizing the resting potential, reducing I K1 increases the amplitude of DADs and promotes DAD-mediated triggered activity creating arrhythmogenesis 40 , 41 . Phase-3 EADs For the same reason, I K1 is thought to be important for the genesis of phase- 3 EADs 17 , which have been observed in Purkinje fibers 42 - 44 and in mouse and rat ventricular myocytes 45 , 46 . However, our survey of the literature showed that no phase-3 EADs had been observed in isolated ventricular myocytes of large animals and humans 32 . Computer simulations showed that to generate phase-3 EADs in ventricular myocytes of large animal or human models, drastic changes in ionic current conductance are needed 47 , and these large changes in parameters may well be unphysiological. Therefore, whether blocking I K1 promotes TdP via promoting phase- 3 EADs or not remains unclear. More intuitively, reducing I K1 makes the resting potential or phase-3 repolarization of the AP less stable, allowing spontaneous occurrence of depolarizations (thus PVCs) in the RG region. Note that phase-3 EADs may be rarely observed in isolated ventricular myocytes but can be observed in tissue 22 due to electronic coupling and the tissue-scale genesis of PVCs. For example, in Fig.2D , one can record a phase-3 EAD in the middle of the cable (the RG region) while there are no EADs in the long and short APD regions at all. Synergy between I K1 and I Kr blockade Another important finding is that blocking I K1 works in synergy with blocking I Kr to promote PVCs. In the cases shown in Figs.3 , S2 and S3, when only I Kr was blocked, increasing the methadone concentration from 0 to 5 μM increased the PVC risk from 0 to 0.18% in the LRd model, to 0% in the TP04 model, and to 4.1% in the ORd model. When only I K1 was blocked, the PVC risk increased from 0% to 9.36%, 3.58%, and 0%, respectively. However, when both were blocked, the PVC risk increased from 0% to12.56%, 23.54%, and 20.06%, respectively. Therefore, blocking both I Kr and I K1 causes an increase in PVC risk that is disproportionate to the sum of blocking them alone, indicating a strong synergistic effect. Download figure Open in new tab Figure 3. Effects of methadone on APD and arrhythmia risk in the LRd model. A . APD histogram of the model population under the control condition. B . Bar graph showing averaged APD () and standard deviation (σ) versus methadone concentration. C . Bar graph showing percentage of individuals exhibiting PVCs versus methadone concentration under 5 different conditions of methadone blocking effects (see labels in the inset). The I Ca,L is strength is 5 folds of control for the LRd model. D . Dependence of percentage of individuals exhibiting PVCs on baseline under the first 4 conditions of methadone effects. The baseline was obtained at control I Ca,L as in B and the PVCs are obtained with the same I Ca,L as in C. The synergy can be understood as follows. Blocking I Kr prolongs APD and enhances RG while blocking I K1 does not prolong APD or enhance RG but destabilizes the system. When the two work together, they work cooperatively or synergistically, amplifying the effect on PVC genesis. This synergistic effect may explain the experimental 48 and clinical 49 observations that when I Kr and I K1 are reduced simultaneously, arrhythmia events increase disproportionately compared to reducing either one alone. Specifically, in the study by Hornyik et al 48 , they showed that the arrhythmia rate was 50%. However, there were little effects in the wild type or LQT5 rabbits with the same treatment. In the clinical study by Mazzanti et al 49 , they showed that in Andersen-Tawil Syndrome Type 1 patients (where Kir2.1 mutation reduces I K1 ), treatment with the I Kr blocker amiodarone (a class III antiarrhythmic drug) caused a >40-fold increase in arrhythmia risk compared to treatments with β-blockers or class 1c antiarrhythmic drugs. I K1 and I Ca,L blockade in P2R-mediated arrhythmogenesis P2R is a term used to describe a PVC or reentry caused by the spike-and-dome morphology induced by I to 33 , 34 or by altered Na + channel kinetics 37 . It has been proposed as one mechanism of arrhythmogenesis in Brugada syndrome (BrS). In general, BrS and P2R are promoted by reducing inward currents and/or increasing outward currents, in contrast to LQTS. For example, our simulations showed that P2R is promoted by increasing I to ( Figs. 2 and S1) or by reducing I Ca,L (Fig.5). A non-intuitive observation from our simulation is that blocking I K1 , an outward current, can greatly increase the risk of PVCs ( Figs. 4 , 5 , and S4). Blocking I K1 also promotes P2R caused by altered Na + channel kinetics 37 . Here, the role of I K1 is the same as its role in promoting RG- mediated PVCs, i.e., by promoting tissue-scale dynamical instabilities 36 or by making the resting potential and phase-3 repolarization less stable. Download figure Open in new tab Figure 4. Effects of methadone on PVC genesis (P2R) at low sympathetic activity (low I Ca,L strength) in the LRd model. A . Percentage of individuals in the population exhibiting PVCs versus methadone concentration under 5 different conditions of methadone blocking effects (see labels in the inset) for the control G Ca,L without hypoxia. B . Same as A but for the control G Ca,L with hypoxia. Effects of hypoxia on ionic current conductance are modeled as follows (From Gaur et al with zero isoproterenol 39 ): I Na → 0.9 I Na , I NaL → 1.5 I NaL , I Ca,L → 0.75 I Ca,L , and I Ks → 0.73 I Ks . Download figure Open in new tab Figure 5. Percentage of PVCs versus I Ca,L strength. Shown are percentage of individuals exhibiting PVCs versus G Ca,L for the LRd model under no methadone action and three different conditions of methadone effects as labeled in the inset. The methadone concentration is 3 μM. The open boxes almost completely overlap with the red boxes. Roles of hypoxia in QT prolongation and P2R mediated arrhythmogenesis Based on the mathematical formulation by Gaur et al 39 , hypoxia alters I Na , I NaL , I Ca,L and I Ks and their responses to isoproterenol. For example, in the mathematical formulation by Gaur et al 39 , I Ca,L → Isofactor × I Ca,L with for the normal condition and for hypoxic condition. For low isoproterenol (e.g., for Iso=0, Isofactor=1 for the normal condition and 0.75 for hypoxia), I Ca,L is lower under hypoxia than under the normal condition. For intermediate or high isoproterenol (e.g., for Iso=1.6, Isofactor=1.69 for the normal condition and 2.25 for hypoxia), I Ca,L is higher under hypoxia than under the normal condition. Therefore, at low sympathetic activity or basal condition, hypoxia reduces I Ca,L , but at normal or high sympathetic activity, it increases I Ca,L . The consequence is that hypoxia promotes arrhythmias at both low and high sympathetic activity via promoting P2R-mediated and RG- mediated PVCs, respectively. Arrhythmogenetic effects of methadone QT prolongation has been shown for methadone use 13 , 14 , 50 , 51 with high risk of TdP 7 . Like many other LQTS or TdP-genic drugs, methadone also blocks I Kr and thus causes QT prolongation and TdP as widely anticipated. However, biophysical studies showed a wide range of IC 50 , from around 3 to 10 μM 8 , 10 - 13 or even higher 9 . For example, for a methadone concentration of 1 μM and an IC 50 3 μM, I Kr is only blocked by ∼25%. If the IC 50 becomes 10 μM, only ∼10% I Kr is blocked. Therefore, the I Kr blocking effect may not be sufficient to explain methadone’s proarrhythmic effect. On the other hand, it has been shown that methadone blocks I K1 with an IC 50 of 1.5 μM 13 . Our simulations showed that blocking I K1 alone, although it only has a small effect on prolonging APD or the QT interval, can increase the risk of RG-mediated PVCs. More interestingly, blocking I K1 and I Kr simultaneously results in a synergistic effect which increases the risk of arrhythmias many-fold more than blocking either one alone. In other words, moderately blocking I Kr combined with blocking I K1 increases QT moderately, but the synergistic effect of blocking the two greatly increases the TdP risk, making methadone a drug causing a high incidence of TdP with moderate QT prolongation. Methadone and Brugada Syndrome-like arrhythmias While the major focus of methadone effect is on QT prolongation and TdP, BrS-like ECGs have also been observed in methadone users 5 , 52 - 55 . Our simulations in this study showed that methadone’s I K1 blocking effect combined with its I Ca,L blocking effect can promote P2R at low or basal sympathetic activity, agreeing with arrhythmogenesis in patients with BrS. Note that unlike QT prolongation, BrS-like ECGs are not persistent even in the same patient and thus cannot be easily or widely detected. Clinically, Na + channel blockers are often used to unmask BrS. Furthermore, our simulation showed that blocking I Kr prolongs QT but has little effect on either promoting or suppressing P2R, and thus QT prolongation can still be a dominant ECG marker, but the mechanism of arrhythmias can be P2R as for BrS. Therefore, the prevalence of BrS-related arrhythmias in methadone users might be highly underestimated. U-waves Elevated U-waves are another ECG feature in methadone users 5 , 6 , which agrees with methadone’s I K1 blocking effect 13 , 56 . Although the exact mechanism of the U-wave is unclear, it is related to phase-3 repolarization and phase-4 depolarization, where I K1 becomes important. One of the links of U-waves to arrhythmias is via DAD-mediated arrhythmogenesis 57 , 58 in which reducing I K1 lowers the threshold for a DAD to trigger an AP for arrhythmogenesis 40 , 59 . DADs are caused by spontaneous intracellular calcium release events, which can be triggered by high sympathetic activity 60 . Hypokalemia Besides its ion channel blocking effects, another arrhythmia risk factor for methadone use is hypokalemia 6 , 61 - 63 . One of the effects of hypokalemia is reduction of I K1 conductance, and lowering I K1 is a key parameter for arrhythmias in all three mechanisms, as discussed above. Therefore, in the case of methadone use, I K1 is already lowered by the drug action and hypokalemia makes it even worse. Effects of sleep Finally, our simulation results may provide insights into the observation that most methadone deaths occur during sleep 1 , 16 , 18 . It is known that cardiac arrhythmias for LQTS occur during physical or emotional stress except for LQT3 where the cardiac events occur mainly during sleep 64 , 65 . For catecholaminergic polymorphic ventricular tachycardia (CPVT), arrhythmias occur in the afternoon to evening due to higher physical activity 66 , and for BrS, most arrhythmias occur in the nighttime due to low sympathetic activity 67 . Our simulations show that blocking I K1 combined with lowering I Ca,L caused by low sympathetic activity and methadone- related ion channel blockade and hypoxia during sleep promotes P2R for arrhythmogenesis. This agrees with the observations that BrS-like ECGs occur in methadone users and that methadone- related deaths mainly occur during sleep. Furthermore, serum K + concentration is lower in the nighttime (bottoming around 9pm) 68 - 70 , which can further increase the likelihood of arrhythmias during sleep. Limitations Several limitations are worth mentioning. First, we simulated only 1D cable models for spontaneous genesis of PVCs, to allow for a large number of simulations, but arrhythmias are tissue-level phenomena in the three-dimensional heart. To model arrhythmias, two- or three- dimensional tissue models are needed. Furthermore, the shape of the geometry of the heterogeneous region in higher dimensions than 1D may also be nontrivial for arrhythmogenesis. However, as shown previously 26 , 35 , 37 , once a spontaneous PVC occurs, it may exhibit as an ectopic beat or degenerate into reentrant arrhythmias, depending on properties of the heterogeneous region. Therefore, the propensity of spontaneous PVCs in the 1D cable is a good measure of propensity for arrhythmias in higher dimensional tissue. Second, we used one fixed IC 50 for each current and combinations of inclusion and exclusion of currents for methadone action to assess arrhythmogenesis related to methadone use. In reality, the IC 50 for methadone action may differ in different experimental conditions, in different species, as well as in different individuals. These differences may give rise to different conclusions for the contributions of different ionic currents caused by methadone. Third, we modeled sympathetic activity by altering I Ca,L only. It is known that β-adrenergic stimulation causes strong increases of both I Ca,L and I Ks . Since the maximum I Ca,L strength elevates much faster than that of I Ks in response to β-adrenergic stimulation 38 , there is a time window in which I Ca,L enhancement is the dominant effect. Fourth, although we simulated 4 AP models and obtained generally consistent results, there are still differences between models, such as the roles of I Kr and I K1 . Nevertheless, the computer simulation results in this study provide mechanistic insights into methadone-induced arrhythmogenesis and sudden cardiac death. Conclusions Methadone blocks multiple ionic currents, which alone or in combination can promote arrhythmias via LQTS related arrhythmias (TdP) and BrS related arrhythmias (P2R). In particular, its I K1 blockade effect can work synergistically with its action of blocking other currents, such as I Kr and I Ca,L , to greatly increase the propensity of arrhythmias and sudden cardiac death. References 1. ↵ Chugh SS , Socoteanu C , Reinier K , Waltz J , Jui J , Gunson K. A Community-Based Evaluation of Sudden Death Associated with Therapeutic Levels of Methadone . Am J Med . 2008 ; 121 : 66 – 71 . OpenUrl CrossRef PubMed 2. Andrews CM , Krantz MJ , Wedam EF , Marcuson MJ , Capacchione JF , Haigney MC . Methadone-induced mortality in the treatment of chronic pain: Role of QT prolongation . Cardiol J . 2009 ; 16 : 210 – 217 . OpenUrl PubMed 3. Kao DP , Haigney MCP , Mehler PS , Krantz MJ . Arrhythmia associated with buprenorphine and methadone reported to the food and drug administration . Addiction . 2015 ; 110 : 1468 – 1475 . OpenUrl CrossRef PubMed 4. Marzec LN , Katz DF , Peterson PN , Thompson LE , Haigney MC , Krantz MJ . Torsade de pointes associated with high-dose loperamide ingestion . J Innov Card Rhythm Manage . 2015 ; 6 : 1897 – 1899 . OpenUrl 5. ↵ Alinejad S , Kazemi T , Zamani N , Hoffman RS , Mehrpour O. A systematic review of the cardiotoxicity of methadone . EXCLI J . 2015 ; 14 : 577 – 600 . OpenUrl PubMed 6. ↵ Krantz MJ , Palmer RB , Haigney MCP . Cardiovascular Complications of Opioid Use . J Am Coll Cardiol . 2021 ; 77 : 205 – 223 . OpenUrl CrossRef PubMed 7. ↵ Wang L , Volkow ND , Berger NA , Davis PB , Kaelber DC , Xu R. Cardiac and mortality outcome differences between methadone, buprenorphine and naltrexone prescriptions in patients with an opioid use disorder . J Clin Psychol . 2023 ; 79 : 2869 – 2883 . OpenUrl CrossRef PubMed 8. ↵ Katchman AN , McGroary KA , Kilborn MJ , Kornick CA , Manfredi PL , Woosley RL , Ebert SN . Influence of opioid agonists on cardiac human ether-a-go-go-related gene K+ currents . J Pharmacol Exp Ther . 2002 ; 303 : 688 – 694 . OpenUrl Abstract / FREE Full Text 9. ↵ Kornick CA , Kilborn MJ , Santiago-Palma J , Schulman G , Thaler HT , Keefe DL , Katchman AN , Pezzullo JC , Ebert SN , Woosley RL , Payne R , Manfredi PL . QTc interval prolongation associated with intravenous methadone . Pain . 2003 ; 105 : 499 – 506 . OpenUrl CrossRef PubMed Web of Science 10. ↵ Eap CB , Crettol S , Rougier J-S , Schläpfer J , Sintra Grilo L , Déglon J-J , Besson J , Croquette-Krokar M , Carrupt P-A , Abriel H. Stereoselective Block of hERG Channel by (S)-Methadone and QT Interval Prolongation in CYP2B6 Slow Metabolizers . Clin Pharmacol Ther . 2007 ; 81 : 719 – 728 . OpenUrl CrossRef PubMed Web of Science 11. Zünkler BJ , Wos-Maganga M. Comparison of the Effects of Methadone and Heroin on Human ether-à-go-go-Related Gene Channels . Cardiovasc Toxicol . 2010 ; 10 : 161 – 165 . OpenUrl CrossRef PubMed 12. ↵ Tran PN , Sheng J , Randolph AL , Baron CA , Thiebaud N , Ren M , Wu M , Johannesen L , Volpe DA , Patel D , Blinova K , Strauss DG , Wu WW . Mechanisms of QT prolongation by buprenorphine cannot be explained by direct hERG channel block . PLoS One . 2020 ; 15 : e0241362 . OpenUrl CrossRef PubMed 13. ↵ Klein MG , Krantz MJ , Fatima N , Watters A , Colon-Sanchez D , Geiger RM , Goldstein RE , Solhjoo S , Mehler PS , Flagg TP , Haigney MC . Methadone Blockade of Cardiac Inward Rectifier K+ Current Augments Membrane Instability and Amplifies U Waves on Surface ECGs: A Translational Study . J Am Heart Assoc . 2022 ; 11 : e023482 . OpenUrl CrossRef PubMed 14. ↵ Florian J , Garnett CE , Nallani SC , Rappaport BA , Throckmorton DC . A Modeling and Simulation Approach to Characterize Methadone QT Prolongation Using Pooled Data From Five Clinical Trials in MMT Patients . Clin Pharmacol Ther . 2012 ; 91 : 666 – 672 . OpenUrl CrossRef PubMed 15. ↵ Kuryshev YA , Bruening-Wright A , Brown AM , Kirsch GE . Increased Cardiac Risk in Concomitant Methadone and Diazepam Treatment: Pharmacodynamic Interactions in Cardiac Ion Channels . J Cardiovasc Pharmacol . 2010 ; 56 : 420 – 430 . OpenUrl CrossRef PubMed 16. ↵ Solhjoo S , Punjabi NM , Ivanescu AE , Crainiceanu C , Gaynanova I , Wicken C , Buckenmaier III C , Haigney MC . Methadone Destabilizes Cardiac Repolarization During Sleep . Clin Pharmacol Ther . 2021 ; 110 : 1066 – 1074 . OpenUrl CrossRef PubMed 17. ↵ Eckhardt LL . Arrhythmogenesis and Prolonged Repolarization From Synthetic Opioids: Finally Sorted? J Am Heart Assoc . 2022 ; 11 : e025778 . OpenUrl CrossRef PubMed 18. ↵ Caplehorn JRM , Drummer OH . Fatal methadone toxicity: signs and circumstances, and the role of benzodiazepines . Australian and New Zealand Journal of Public Health . 2002 ; 26 : 358 – 362 . OpenUrl CrossRef PubMed 19. ↵ Huang X , Kim TY , Koren G , Choi B-R , Qu Z. Spontaneous initiation of premature ventricular complexes and arrhythmias in type 2 long QT syndrome . Am J Physiol Heart Circ Physiol . 2016 ; 311 : H1470 – H1484 . OpenUrl CrossRef PubMed 20. ↵ Zhang Z , Liu MB , Huang X , Song Z , Qu Z. Mechanisms of premature ventricular complexes caused by QT prolongation . Biophys J . 2021 ; 120 : 352 – 369 . OpenUrl CrossRef PubMed 21. ↵ Liu J , Laurita KR . The mechanism of pause-induced torsade de pointes in long QT syndrome . J Cardiovasc Electrophysiol . 2005 ; 16 : 981 – 987 . OpenUrl CrossRef PubMed Web of Science 22. ↵ Maruyama M , Lin SF , Xie Y , Chua SK , Joung B , Han S , Shinohara T , Shen MJ , Qu Z , Weiss JN , Chen PS . Genesis of phase 3 early afterdepolarizations and triggered activity in acquired long-QT syndrome . Circ Arrhythm Electrophysiol . 2011 ; 4 : 103 – 111 . OpenUrl Abstract / FREE Full Text 23. Alexander C , Bishop MJ , Gilchrist RJ , Burton FL , Smith GL , Myles RC . Initiation of ventricular arrhythmia in the acquired long QT syndrome . Cardiovasc Res . 2023 ; 119 : 465 – 476 . OpenUrl CrossRef PubMed 24. ↵ Renard E , Haïssaguerre M , Bear LR , Bernus O. Origin of ventricular fibrillation triggers in a model of localized repolarization heterogeneity . Heart Rhythm . 2024 ;(in press) 25. ↵ Liu MB , Vandersickel N , Panfilov AV , Qu Z. R-from-T as a common mechanism of arrhythmia initiation in long QT syndromes . Circ Arrhythm Electrophysiol . 2019 ; 12 : e007571 . OpenUrl CrossRef PubMed 26. ↵ Qu Z , Liu MB , Olcese R , Karagueuzian H , Garfinkel A , Chen P-S , Weiss JN . R-on-T and the initiation of reentry revisited: Integrating old and new concepts . Heart Rhythm . 2022 ; 19 : 1369 – 1383 . OpenUrl CrossRef PubMed 27. ↵ Luo CH , Rudy Y. A dynamical model of the cardiac ventricular action potential: I. simulations of ionic currents and concentration changes . Circ. Res . 1994 ; 74 : 1071 – 1096 . OpenUrl Abstract / FREE Full Text 28. ↵ ten Tusscher KH , Noble D , Noble PJ , Panfilov AV . A model for human ventricular tissue . Am J Physiol Heart Circ Physiol . 2004 ; 286 : H1573 – 1589 . OpenUrl CrossRef PubMed Web of Science 29. ↵ O’Hara T , Virag L , Varro A , Rudy Y. Simulation of the undiseased human cardiac ventricular action potential: model formulation and experimental validation . PLoS Comput Biol . 2011 ; 7 : e1002061 . OpenUrl CrossRef PubMed 30. ↵ Tomek J , Bueno-Orovio A , Passini E , Zhou X , Minchole A , Britton O , Bartolucci C , Severi S , Shrier A , Virag L , Varro A , Rodriguez B. Development, calibration, and validation of a novel human ventricular myocyte model in health, disease, and drug block . eLife . 2019 ; 8 : e48890 . OpenUrl CrossRef PubMed 31. ↵ Gallagher MM , Magliano G , Yap YG , Padula M , Morgia V , Postorino C , Di Liberato F , Leo R , Borzi M , Romeo F. Distribution and prognostic significance of QT intervals in the lowest half centile in 12,012 apparently healthy persons . Am J Cardiol . 2006 ; 98 : 933 – 935 . OpenUrl CrossRef PubMed Web of Science 32. ↵ Huang X , Song Z , Qu Z. Determinants of early afterdepolarization properties in ventricular myocyte models . PLoS Comput Biol . 2018 ; 14 : e1006382 . OpenUrl CrossRef PubMed 33. ↵ Di Diego JM , Antzelevitch C. Pinacidil-induced electrical heterogeneity and extrasystolic activity in canine ventricular tissues . Does activation of ATP-regulated potassium current promote phase 2 reentry? Circulation . 1993 ; 88 : 1177 – 1189 . OpenUrl PubMed 34. ↵ Lukas A , Antzelevitch C. Phase 2 reentry as a mechanism of initiation of circus movement reentry in canine epicardium exposed to simulated ischemia . Cardiovasc Res . 1996 ; 32 : 593 – 603 . OpenUrl CrossRef PubMed Web of Science 35. ↵ Zhang Z , Chen P-S , Weiss JN , Qu Z. Why is only type 1 electrocardiogram diagnostic of Brugada syndrome? Mechanistic insights from computer modeling . Circ Arrhythm Electrophysiol . 2022 ; 15 : e010365 . OpenUrl CrossRef PubMed 36. ↵ Zhang Z , Qu Z. Life and death saddles in the heart . Phys Rev E . 2021 ; 103 : 062406 . OpenUrl PubMed 37. ↵ Zhang Z , Brugada P , Weiss JN , Qu Z. Phase 2 Re-Entry Without Ito: Role of Sodium Channel Kinetics in Brugada Syndrome Arrhythmias . JACC: Clin Electrophysiol . 2023 ; 9 : 2459 – 2474 . OpenUrl CrossRef PubMed 38. ↵ Liu GX , Choi BR , Ziv O , Li W , de Lange E , Qu Z , Koren G. Differential conditions for early after-depolarizations and triggered activity in cardiomyocytes derived from transgenic LQT1 and LQT2 rabbits . J Physiol . 2012 ; 590 : 1171 – 1180 . OpenUrl CrossRef PubMed 39. ↵ Gaur N , Rudy Y , Hool L. Contributions of Ion Channel Currents to Ventricular Action Potential Changes and Induction of Early Afterdepolarizations During Acute Hypoxia . Circ Res . 2009 ; 105 : 1196 – 1203 . OpenUrl Abstract / FREE Full Text 40. ↵ Liu MB , Ko CY , Song Z , Garfinkel A , Weiss JN , Qu Z. A Dynamical Threshold for Cardiac Delayed Afterdepolarization-Mediated Triggered Activity . Biophys J . 2016 ; 111 : 2523 – 2533 . OpenUrl CrossRef PubMed 41. ↵ Liu MB , Priori SG , Qu Z , Weiss JN . Stabilizer Cell Gene Therapy: A Less-Is-More Strategy to Prevent Cardiac Arrhythmias . Circ Arrhythm Electrophysiol . 2020 ; 13 : e008420 . OpenUrl CrossRef PubMed 42. ↵ Damiano BP , Rosen MR . Effects of pacing on triggered activity induced by early afterdepolarizations . Circulation . 1984 ; 69 : 1013 – 1025 . OpenUrl Abstract / FREE Full Text 43. Roden DM , Hoffman BF . Action potential prolongation and induction of abnormal automaticity by low quinidine concentrations in canine Purkinje fibers . Circ. Res . 1985 ; 56 : 857 – 867 . OpenUrl Abstract / FREE Full Text 44. ↵ Bailie DS , Inoue H , Kaseda S , Ben-David J , Zipes DP . Magnesium suppression of early afterdepolarizations and ventricular tachyarrhythmias induced by cesium in dogs . Circulation . 1988 ; 77 : 1395 – 1402 . OpenUrl Abstract / FREE Full Text 45. ↵ Edwards AG , Grandi E , Hake JE , Patel S , Li P , Miyamoto S , Omens JH , Heller Brown J , Bers DM , McCulloch AD . Non-Equilibrium Reactivation of Na+ Current Drives Early Afterdepolarizations in Mouse Ventricle . Circ Arrhythm Electrophysiol . 2014 46. ↵ Tazmini K , Frisk M , Lewalle A , Laasmaa M , Morotti S , Lipsett DB , Manfra O , Skogested J , Aronsen JM , Sejersted OM , Sjaastad I , Edwards AG , Grandi E , Niederer SA , Øie E , Louch WE . Hypokalemia Promotes Arrhythmia by Distinct Mechanisms in Atrial and Ventricular Myocytes . Circ Res . 2020 ; 126 : 889 – 906 . OpenUrl CrossRef PubMed 47. ↵ Zhang Z , Qu Z. Mechanisms of phase-3 early afterdepolarizations and triggered activities in ventricular myocyte models . Physiol Rep . 2021 ; 9 : e14883 . OpenUrl PubMed 48. ↵ Hornyik T , Castiglione A , Franke G , Perez-Feliz S , Major P , Hiripi L , Koren G , Bősze Z , Varró A , Zehender M , Brunner M , Bode C , Baczkó I , Odening KE . Transgenic LQT2, LQT5, and LQT2-5 rabbit models with decreased repolarisation reserve for prediction of drug-induced ventricular arrhythmias . Br J Pharmacol . 2020 ; 177 : 3744 – 3759 . OpenUrl CrossRef PubMed 49. ↵ Mazzanti A , Guz D , Trancuccio A , Pagan E , Kukavica D , Chargeishvili T , Olivetti N , Biernacka EK , Sacilotto L , Sarquella-Brugada G , Campuzano O , Nof E , Anastasakis A , Sansone VA , Jimenez-Jaimez J , Cruz F , Sánchez-Quiñones J , Hernandez-Afonso J , Fuentes ME , Sredniawa B , Garoufi A , Andršová I , Izquierdo M , Marinov R , Danon A , Expósito-García V , Garcia-Fernandez A , Muñoz-Esparza C , Ortíz M , Zienciuk-Krajka A , Tavazzani E , Monteforte N , Bloise R , Marino M , Memmi M , Napolitano C , Zorio E , Monserrat L , Bagnardi V , Priori SG . Natural History and Risk Stratification in Andersen-Tawil Syndrome Type 1 . J Am Coll Cardiol . 2020 ; 75 : 1772 – 1784 . OpenUrl CrossRef PubMed 50. ↵ Fareed A , Patil D , Scheinberg K , Blackinton Gale R , Vayalapalli S , Casarella J , Drexler K. Comparison of QTc Interval Prolongation for Patients in Methadone Versus Buprenorphine Maintenance Treatment: A 5-Year Follow-Up . J Addict Dis . 2013 ; 32 : 244 – 251 . OpenUrl CrossRef PubMed 51. ↵ Chou R , Weimer MB , Dana T. Methadone Overdose and Cardiac Arrhythmia Potential: Findings From a Review of the Evidence for an American Pain Society and College on Problems of Drug Dependence Clinical Practice Guideline . J Pain . 2014 ; 15 : 338 – 365 . OpenUrl CrossRef PubMed 52. ↵ Sheibani M , Zamani N , Hassanian-Moghaddam H. Electrocardiographic Findings in Mortalities Due to Pure Methadone Toxicity . Cardiovasc Toxicol . 2019 ; 19 53. Srivatsa U , Hoppe B , Lu J , Feld GK . Sequential appearance of both Brugada and long QT patterns on EKG in a single patient receiving methadone . Heart Rhythm . 2005 ; 2 : S50 . OpenUrl 54. Guay DRP . Cardiotoxicity of Oral Methadone as an Analgesic–Recommendations for Safe Use . Clin Med Ther . 2009 ; 1 :CMT.S3041. 55. ↵ Mancia E , Dendramis G , Carollo C , Guarino L , Guarneri M , Calandra L , Cottone S , Mulè G. Brugada pattern in heroin addiction: Syndrome or phenocopy? Euromediterr Biomed J . 2021 ; 16 56. ↵ Postema PG , Ritsema van Eck HJ , Opthof T , van Herpen G , van Dessel PFHM , Priori SG , Wolpert C , Borggrefe M , Kors JA , Wilde AAM . IK1 modulates the U-wave: insights in a 100-year-old enigma . Heart Rhythm . 2009 ; 6 : 393 – 400 . OpenUrl CrossRef PubMed Web of Science 57. ↵ Aizawa Y , Komura S , Okada S , Chinushi M , Aizawa Y , Morita H , Ohe T. Distinct U wave changes in patients with catecholaminergic polymorphic ventricular tachycardia (CPVT) . Int Heart J . 2006 ; 47 : 381 – 389 . OpenUrl CrossRef PubMed Web of Science 58. ↵ Morita H , Zipes DP , Morita ST , Wu J. Mechanism of U wave and polymorphic ventricular tachycardia in a canine tissue model of Andersen-Tawil syndrome . Cardiovasc Res . 2007 ; 75 : 510 – 518 . OpenUrl CrossRef PubMed 59. ↵ Liu MB , de Lange E , Garfinkel A , Weiss JN , Qu Z. Delayed afterdepolarizations generate both triggers and a vulnerable substrate promoting reentry in cardiac tissue . Heart Rhythm . 2015 ; 12 : 2115 – 2124 . OpenUrl CrossRef PubMed 60. ↵ Myles RC , Wang L , Kang C , Bers DM , Ripplinger CM . Local β-Adrenergic Stimulation Overcomes Source-Sink Mismatch to Generate Focal Arrhythmia . Circ Res . 2012 ; 110 : 1454 – 1464 . OpenUrl Abstract / FREE Full Text 61. ↵ Krantz MJ , Lewkowiez L , Hays H , Woodroffe MA , Robertson AD , Mehler PS . Torsade de Pointes Associated with Very-High-Dose Methadone . Annals of Internal Medicine . 2002 ; 137 : 501 – 504 . OpenUrl CrossRef PubMed Web of Science 62. Lopez OJ , Othon D , Ng-Wong YK , Sleiman J. The Perfect Storm: Abnormal Baseline QT With Chronic Methadone Use and Serious Hypokalemia . J Investig Med High Impact Case Rep . 2024 ; 12 : 23247096241286373 . OpenUrl CrossRef PubMed 63. ↵ Velkova IK , Jovanoski M , Bojovski I , Nastevska EG , Taravari H , Celikic A , Boshev M. QT prolongation and ventricular arrhythmia in methadone user presenting with severe hypokalemia . KNOWLEDGE-International Journal . 2022 ; 55 : 539 – 544 . OpenUrl 64. ↵ Takigawa M , Kawamura M , Noda T , Yamada Y , Miyamoto K , Okamura H , Satomi K , Aiba T , Kamakura S , Sakaguchi T , Mizusawa Y , Itoh H , Horie M , Shimizu W. Seasonal and Circadian Distributions of Cardiac Events in Genotyped Patients With Congenital Long QT Syndrome . Circ J . 2012 ; 76 : 2112 – 2118 . OpenUrl CrossRef PubMed Web of Science 65. ↵ Stramba-Badiale M , Priori SG , Napolitano C , Locati EH , Vinolas X , Haverkamp W , Schulze-Bahr E , Goulene K , Schwartz PJ . Gene-specific differences in the circadian variation of ventricular repolarization in the long QT syndrome: a key to sudden death during sleep? Italian Heart Journal . 2000 ; 1 : 323 – 328 . OpenUrl PubMed 66. ↵ Miyake CY , Asaki SY , Webster G , Czosek RJ , Atallah J , Avasarala K , Rao SO , Thomas PE , Kim JJ , Valdes SO . Circadian variation of ventricular arrhythmias in catecholaminergic polymorphic ventricular tachycardia . JACC: Clin Electrophysiol . 2017 ; 3 : 1308 – 1317 . OpenUrl Abstract / FREE Full Text 67. ↵ Takigawa M , Noda T , Shimizu W , Miyamoto K , Okamura H , Satomi K , Suyama K , Aihara N , Kamakura S , Kurita T. Seasonal and circadian distributions of ventricular fibrillation in patients with Brugada syndrome . Heart Rhythm . 2008 ; 5 : 1523 – 1527 . OpenUrl CrossRef PubMed 68. ↵ Schmidt ST , Ditting T , Deutsch B , Schutte R , Friedrich S , Kistner I , Ott C , Raff U , Veelken R , Schmieder RE . Circadian rhythm and day to day variability of serum potassium concentration: a pilot study . J Nephrol . 2015 ; 28 : 165 – 172 . OpenUrl CrossRef PubMed 69. Sennels HP , Jørgensen HL , Goetze JP , Fahrenkrug J. Rhythmic 24-hour variations of frequently used clinical biochemical parameters in healthy young males – The Bispebjerg study of diurnal variations . Scand J Clin Lab Invest . 2012 ; 72 : 287 – 295 . OpenUrl CrossRef PubMed 70. ↵ Gumz ML , Rabinowitz L. Role of Circadian Rhythms in Potassium Homeostasis . Seminars in Nephrology . 2013 ; 33 : 229 – 236 . OpenUrl CrossRef PubMed View the discussion thread. Back to top Previous Next Posted March 07, 2025. Download PDF Email Thank you for your interest in spreading the word about bioRxiv. NOTE: Your email address is requested solely to identify you as the sender of this article. Your Email * Your Name * Send To * Enter multiple addresses on separate lines or separate them with commas. You are going to email the following Methadone blockade of IK1 promotes both long QT and Brugada-like arrhythmias: Mechanistic insights from computational modeling Message Subject (Your Name) has forwarded a page to you from bioRxiv Message Body (Your Name) thought you would like to see this page from the bioRxiv website. Your Personal Message CAPTCHA This question is for testing whether or not you are a human visitor and to prevent automated spam submissions. Share Methadone blockade of I K1 promotes both long QT and Brugada-like arrhythmias: Mechanistic insights from computational modeling Zhaoyang Zhang , J.T. Green , Mark C. Haigney , Kalyanam Shivkumar , Alan Garfinkel , Zhilin Qu bioRxiv 2025.03.01.641012; doi: https://doi.org/10.1101/2025.03.01.641012 Share This Article: Copy Citation Tools Methadone blockade of I K1 promotes both long QT and Brugada-like arrhythmias: Mechanistic insights from computational modeling Zhaoyang Zhang , J.T. Green , Mark C. Haigney , Kalyanam Shivkumar , Alan Garfinkel , Zhilin Qu bioRxiv 2025.03.01.641012; doi: https://doi.org/10.1101/2025.03.01.641012 Citation Manager Formats BibTeX Bookends EasyBib EndNote (tagged) EndNote 8 (xml) Medlars Mendeley Papers RefWorks Tagged Ref Manager RIS Zotero Tweet Widget Facebook Like Google Plus One Subject Area Pharmacology and Toxicology Subject Areas All Articles Animal Behavior and Cognition (7622) Biochemistry (17650) Bioengineering (13871) Bioinformatics (41881) Biophysics (21424) Cancer Biology (18566) Cell Biology (25461) Clinical Trials (138) Developmental Biology (13365) Ecology (19866) Epidemiology (2067) Evolutionary Biology (24290) Genetics (15590) Genomics (22476) Immunology (17713) Microbiology (40331) Molecular Biology (17148) Neuroscience (88473) Paleontology (666) Pathology (2827) Pharmacology and Toxicology (4816) Physiology (7635) Plant Biology (15114) Scientific Communication and Education (2044) Synthetic Biology (4286) Systems Biology (9815) Zoology (2268)