Atrial Fibrillation in an Unroofed Coronary Sinus

A 43-year-old nulliparous female patient of Japanese descent presented to clinic with intermittent palpitations. The palpitations were fast and irregular, lasting seconds with no associated presyncope or syncope. The episodes occurred every few weeks with no obvious precipitant. Examination was unremarkable. Body mass index was normal at 23. Past medical history included endometriosis. Family history was unremarkable for cardiac disease. They did not smoke and consumed alcohol socially. The patient was active but did not engage in endurance sports. On examination, blood pressure was 110/80 mm Hg, heart rate was 80 bpm, and oxygen saturation was 99% on room air. Heart sounds were dual with no audible murmurs, and chest was clear. Electrocardiogram demonstrated sinus rhythm, right-axis deviation, and a premature atrial contraction. Given infrequent symptoms, a 28 day ambulatory electrocardiogram was performed. This demonstrated sinus rhythm with occasional atrial ectopy, atrial couplets, and nonsustained atrial runs lasting up to 27 seconds. It also showed occasional AF and atrial flutter with intermittent rapid ventricular response up to 194 beats per minute. Transthoracic echocardiogram (TTE) demonstrated normal left ventricular size and systolic function but a severely enlarged right ventricle (RV; right ventricular base, 5 cm) with preserved systolic function (tricuspid annular plane systolic excursion 20, right ventricular S′ 11; Figures 1 and 2 , Videos 1-3 ). The right atrium (RA) was also enlarged, but pulmonary pressures were normal. A shunt was not appreciated on this initial study. Considering these findings, cardiac computed tomography (CCT) was performed ( Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Videos 4-9 ), revealing a completely unroofed coronary sinus (CS) with left-to-right shunting. The CS was severely dilated. The ostium measured 19 × 36 mm. The RA (4-chamber right atrial area 29 cm 2 vs left atrial area 20 cm 2 ), RV (4-chamber RV: right ventricular basal dimension ratio >2), and main pulmonary artery (28 mm, pulmonary artery: aorta ratio >1) were also severely dilated. Pulmonary venous drainage was normal, and there was a single right-sided superior vena cava. A repeat dedicated TTE also demonstrated a deficient left atrial “floor.” Color-flow Doppler confirmed flow from the left atrium to the CS ( Figure 8 , Figure 9 , Figure 10 , Videos 10-12 ). Right heart catheterization demonstrated a significant left-to-right shunt with a Qp:Qs of 2.5:1 and normal pulmonary artery pressures (mean gradient, 14 mm Hg; Figure 11 ). Oxygen saturation increased significantly in the RA (SaO 2 96%) compared to the superior vena cava (SaO 2 74%) and inferior vena cava (SaO 2 83%), consistent with a shunt at the atrial level. An electrophysiology study was considered. However, previous reports have postulated that in patients with an unroofed CS, AF arises from the ostium of the dilated CS. Thus, it was felt that surgical correction of the unroofed CS might mitigate AF. The patient proceeded to have successful surgery through a median sternotomy. The RA was opened obliquely, and the interatrial septum was exposed. The large CS defect was seen and measured approximately 2.0 cm × 2.0 cm. A fresh patch of autologous pericardium was used to close the defect. The left atrial appendage was then closed with a 35 mm clip. A MAZE procedure was considered, but the patient elected not to proceed with this given the risk of complete heart block. Five months postsurgery, the patient remains asymptomatic with no further palpitations. Ambulatory event monitor demonstrated no further episodes of AF; TTE demonstrated normal biventricular and biatrial size. Figure 1 Two-dimensional TTE, apical 4-chamber diastolic view, demonstrates a dilated RV and RA with abnormal septal position consistent with right ventricular volume overload. Figure 2 Two-dimensional TTE, apical 4-chamber systolic view, demonstrates a dilated RV and RA with abnormal septal position consistent with right ventricular volume overload. Figure 3 Cardiac computed tomography, oblique sagittal plane, cardiac mid-LV short-axis view, demonstrates a dilated RV (arrow) with abnormal septal position consistent with right ventricular volume-overload. Figure 4 Cardiac computed tomography, oblique axial plane, cardiac 4-chamber view, demonstrates a dilated RV with abnormal septal position consistent with right ventricular volume overload. Figure 5 Cardiac computed tomography, oblique sagittal plane, cardiac basal-LV short-axis view demonstrates a completely unroofed CS with an unrestricted LA-CS communication (star) . Figure 6 Cardiac computed tomography, oblique sagittal plane, cardiac 2-chamber view, demonstrates the absence of inferior LA “floor” (arrow) with LA-CS communication and severely dilated CS (star) . Figure 7 Cardiac computed tomography in multiple different planes ( red line : apical 4-chamber; green line : apical 3-chamber; purple line : apical 2-chamber) demonstrates that the 2-chamber view best demonstrates the unroofed CS. Figure 8 Two-dimensional TTE, parasternal right ventricular inflow view, demonstrates a dilated right heart with dilated CS (star) . Figure 9 Two-dimensional TTE, apical 2-chamber systolic view, demonstrates the dilated CS with a deficient LA floor (star) . Figure 10 Two-dimensional TTE, apical 2-chamber systolic view with color-flow Doppler, demonstrates the dilated CS with a deficient LA floor (star) and laminar flow connecting these chambers (arrow) . Figure 11 Schematic representation of the hemodynamic findings during right heart catheterization, including oxygenation levels in each of the cardiac chambers, demonstrates the left-to-right shunt-induced step-up. Two-dimensional TTE, apical 4-chamber diastolic view, demonstrates a dilated RV and RA with abnormal septal position consistent with right ventricular volume overload. Two-dimensional TTE, apical 4-chamber systolic view, demonstrates a dilated RV and RA with abnormal septal position consistent with right ventricular volume overload. Cardiac computed tomography, oblique sagittal plane, cardiac mid-LV short-axis view, demonstrates a dilated RV (arrow) with abnormal septal position consistent with right ventricular volume-overload. Cardiac computed tomography, oblique axial plane, cardiac 4-chamber view, demonstrates a dilated RV with abnormal septal position consistent with right ventricular volume overload. Cardiac computed tomography, oblique sagittal plane, cardiac basal-LV short-axis view demonstrates a completely unroofed CS with an unrestricted LA-CS communication (star) . Cardiac computed tomography, oblique sagittal plane, cardiac 2-chamber view, demonstrates the absence of inferior LA “floor” (arrow) with LA-CS communication and severely dilated CS (star) . Cardiac computed tomography in multiple different planes ( red line : apical 4-chamber; green line : apical 3-chamber; purple line : apical 2-chamber) demonstrates that the 2-chamber view best demonstrates the unroofed CS. Two-dimensional TTE, parasternal right ventricular inflow view, demonstrates a dilated right heart with dilated CS (star) . Two-dimensional TTE, apical 2-chamber systolic view, demonstrates the dilated CS with a deficient LA floor (star) . Two-dimensional TTE, apical 2-chamber systolic view with color-flow Doppler, demonstrates the dilated CS with a deficient LA floor (star) and laminar flow connecting these chambers (arrow) . Schematic representation of the hemodynamic findings during right heart catheterization, including oxygenation levels in each of the cardiac chambers, demonstrates the left-to-right shunt-induced step-up.

The authors declare that the work described has been carried out in accordance with The Code of Ethics of the World Medical Association (Declaration of Helsinki) for experiments involving humans.

Complete written informed consent was obtained from the patient (or appropriate parent, guardian, or power of attorney) for the publication of this study and accompanying images.

The authors declare that this report did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Unroofed CS is a rare congenital abnormality. Diagnosis should be considered in patients with an unexplained dilated RV. Atrial fibrillation in unroofed CS typically occurs with right heart dilatation and has been postulated to arise from the ostium of the CS rather than the pulmonary veins. Cardiac computed tomography, CMR, and/or TEE are helpful for diagnosing unroofed CS due to the posterior location. Mainstay treatment for unroofed CS is surgery. Pulmonary vein isolation may not be effective in these patients.

The authors reported no actual or potential conflicts of interest relative to this document.

Unroofed CS is a rare congenital abnormality, accounting for <1% of all atrial septal defects. 3 Unroofed CS was first described in 1965 and is characterized by rupture or complete absence of the CS wall, resulting in communication between the CS and left and right atria. 4 In most cases, unroofed CS is associated with other congenital heart defects; 75% are associated with a persistent left-sided superior vena cava (LSVC). 4 Other associations include mitral, pulmonary, or tricuspid atresia, atrial isomerism, atrioventricular septal defect, mitral stenosis, and tetralogy of Fallot. 3 , 4 There are 4 types of unroofed CS. Type 1 is characterized by a completely unroofed CS with an LSVC. Type 2 is defined by a completely unroofed CS without an LSVC. Type 3 is characterized by a partially unroofed midportion, and type 4 by a partially unroofed terminal portion. Isolated unroofed CS (type 2), as in our case, is extremely rare. Clinical manifestations are nonspecific and can include exertional dyspnea, fatigue, and signs of heart failure. Syncope, peripheral edema, and recurrent respiratory infections have also been described. 4 Atrial fibrillation tends to occur in older patients with unroofed CS. 5 Only a few cases of AF in unroofed CS have been described in the literature. Tsuji et al. 5 describe a case of AF in a 74-year-old woman who was found to have an unroofed CS. This was successfully managed with a pulmonary vein isolation and CS ablation. Miyashita and Suzuki 6 describe a 75-year-old man with AF and mitral regurgitation, who was found to have an unroofed CS. In this case, the CS defect was surgically repaired. Watanabe et al. 7 describe a 67-year-old woman who presented with AF and was also found to have an unroofed CS. Nishimura et al. 8 describe a similar case in a 55-year-old man who was treated with surgery. Interestingly, all patients were of Japanese descent. We describe the youngest case of AF in an unroofed CS. The exact mechanism of AF in patients with an unroofed CS remains elusive. Previous case reports have postulated that AF arises from the ostium of the dilated CS, rather than the pulmonary veins. Tsuji et al. 5 describe sustained AF due to premature contractions from the CS ostium after wide circumferential pulmonary vein isolation. Upon ablation of the ostial region of the CS floor, AF was no longer inducible. Furthermore, in patients who have developed recurrent AF after unroofed CS repair and concomitant MAZE procedure, CS ablation has been shown to be effective. Diagnosis of unroofed CS can be challenging, particularly when coexistent with another cyanotic cardiac malformation. 9 A large number of unroofed CSs are still diagnosed intraoperatively. 10 Unroofed CS can be diagnosed on TTE but is often missed due to its posterior location, as in our case initially. Cardiac computed tomography has superior temporal and spatial resolution and can better evaluate the venous system and extracardiac structures. Cardiac computed tomography also allows three-dimensional visualization of anatomy. 9 Other imaging modalities include transesophageal echocardiography (TEE) and cardiovascular magnetic resonance imaging (CMR). Transesophageal echocardiography is particularly helpful for identifying posterior structures and has superior spatial resolution. 10 Transesophageal echocardiography is also helpful for determining direction of blood flow without the need for contrast. 11 Three-dimensional TEE has been found to further enhance accuracy in delineating anatomical relationships with adjacent structures. 12 A TEE was organized in our case but did not eventuate given the diagnosis was already established on CCT. Cardiovascular magnetic resonance imaging allows visualization of all cardiac and extracardiac manifestations and can also be used to determine functional information. Right heart catheterization can be used to confirm presence of the defect and to determine the Qp:Qs ratio. Surgical patch repair is the mainstay treatment of unroofed CS. 10 Transcatheter closure using an Amplatzer septal occluder or covered stent has also been described as a treatment option in type 2 and 3 unroofed CS with adequate rims. 4 , 10

Atrial fibrillation (AF) is less common in middle adulthood. 1 Diagnosis should prompt investigation for underlying causes such as cardiomyopathy, valvular heart disease, or structural heart disease. Family history should also be considered. 2 In those below the age of 45, without structural abnormalities, genetic testing should also be considered. 1