Acute and sudden death secondary to cardiac tamponade during anesthetic recovery in a 21 year old Draft mule.

Summary: This case report is of educational value and contributes to the literature because it describes a unique death after anaesthesia due to cardiac tamponade from a rare cardiac neoplasm. In trying to diagnose the origin of chronic sinusitis, a geriatric mule mare was anesthetized and during recovery, died acutely. Post mortem and histopathology revealed the cause of death as cardiac tamponade due to a pericardial leiomyosarcoma. Title: Acute and sudden death secondary to cardiac tamponade during anesthetic recovery in a 21 year old Draft mule. Authors: Anna Carroll, DVM; Jane Quandt, DVM, MS, DACVAA, DACVECC; Stephanie Dantino DVM, DACVAA Affiliations: University of Georgia Veterinary Teaching Hospital, Athens, Georgia, USA Summary: This case report is of educational value and contributes to the literature because it describes a unique death after anaesthesia due to cardiac tamponade from a rare cardiac neoplasm. In trying to diagnose the origin of chronic sinusitis, a geriatric mule mare was anesthetized and during recovery, died acutely. Post mortem and histopathology revealed the cause of death as cardiac tamponade due to a pericardial leiomyosarcoma.

cardiac tamponade, sudden death, peri-anaesthetic mortality, cardiac neoplasm

Horses undergoing general anaesthesia, have a perioperative mortality rate that is currently around 1% (Laurenza et al., 2019). This death rate is attributed to high American Society of Anaesthesiologists (ASA) Physical Status rating cases, post operative colics, and catastrophic fractures. The rate is much lower, around 0.6%, for elective diagnostic procedures (Gozalo-Marcilla et al., 2021). This report describes a sudden death during recovery in a mule mare due to cardiac tamponade from complications related to a rare cardiac neoplasm. Case history: An aged Draft mule mare, estimated to be about 21 years old and weighing 528 kg, presented to the University of Georgia Veterinary Teaching hospital for evaluation of chronic left sided sinusitis and epiphora, reduced appetite, and progressive weight loss. Prior to arrival, the referral veterinarian performed a full dental flotation and removed the 209 molar, packing the space with polymethyl methacrylate (PMMA). It was recommended that the mare undergo general anaesthesia for a CT scan of the skull to assess the condition of the teeth and investigate a possible oronasal fistula. Clinical findings: The anaesthesia team’s physical exam results were largely unremarkable. No cardiac murmurs or arrhythmias were appreciated, and thoracic auscultation was normal. It was noted that the mare had a body condition score (2/5) with reduced epaxial and hindquarter muscling. Bloodwork revealed lymphopenia (0.64 * 10 3 /μl), neutropenia (2.3 *10 3 /μl), and slight anaemia (5.92 * 10 6 /μl), likely attributed to chronic disease. Thirty minutes prior to induction, the mare received 0.01 mg/kg Acepromazine intravenously. After walking into the induction stall, she was administered 0.7 mg/kg Xylazine and 0.04 mg/kg Hydromorphone IV, then induced with 2.2 mg/kg Ketamine and 0.1 mg/kg Midazolam IV. The induction process was smooth and intubation was performed uneventfully. Transportation to the CT scanner via a mechanical hoist was achieved without complication and the patient was placed in dorsal recumbency. Pulse oximetry and heart rate monitoring, as well as regular assisted ventilation with a demand valve, was provided during the CT scan, and values remained within normal limits. Maintenance of anaesthesia was achieved with “top up” provisions of Ketamine (1.1 mg/kg) and Xylazine (0.5 mg/kg). The length of the procedure was 27 minutes. Spontaneous ventilation resumed four minutes after return to the induction stall. After extubation, respiratory rate and effort were normal. First movement from the mare occurred 20 minutes later. After four attempts to lift the head along with weakened abdominal effort, the respiratory rate and effort suddenly increased to 36 brpm. Anaesthesia personnel entered the stall, observed no nystagmus, and assisted the mare into sternal position. After attaining sternal position the mare stood in one attempt, then buckled at the knees and fell forward onto her face, crashing against the induction stall wall. The anaesthesia team moved the mare into lateral position, observed pale white mucus membranes and obtained a pulse oximetry saturation of 60%. The mare was immediately intubated and ventilation was provided with a demand valve. Cardiac auscultation revealed a heart rate of 80 bpm which increased to 140 over approximately three minutes. Rapid venous blood sampling showed a lactate of 11.4 mmol/L, pH 7.2, and a p0 2 of 10 mmHg. One litre of IV hypertonic saline and five litres of LRS were initiated, but lack of PLR and pulses were confirmed within moments and all treatments were discontinued. A quick T-FAS and A-FAS scan did not show evidence of a ruptured aorta or other apparent cause of collapse. Due to the rapid onset of death and no clear indication for cause, the body was submitted for post mortem examination. Post-mortem findings: On gross pathology, the thoracic cavity contained approximately 3.5 litres of serosanguineous fluid. The heart had multiple clots attached to the pericardial sac and a focal haemorrhagic lesion of the mesentery of the pericardial sac near the apex of the heart (Figure 1). The dorsal colon was full of sand and an oronasal fistula was confirmed at 209. No other significant gross changes were observed. Histopathology of the pericardium showed an unencapsulated, infiltrating neoplasm consisting of spindle cells with scant to moderate eosinophilic cytoplasm, poor cellular borders, within a thick fibrovascular stroma. Degeneration of elastin fibres and tunica media thickening was seen in surrounding vasculature adjacent to the sarcoma. Immunohistochemistry classified the tumour as a leiomyosarcoma based on its immunoreactivity for alpha smooth muscle actin and vimentin V9. The pathology report was performed by a board certified pathologist at UGA. Diagnosis: Pericardial vascular rupture with acute, marked haemothorax. Cause of death attributable to cardiac tamponade secondary to ruptured pericardial leiomyosarcoma.

This is the first published report of acute death in a horse attributed to cardiac tamponade from a pericardial neoplasm. Pericardial effusion, considered to be rare in horses, can develop secondary to viral or bacterial infection, septicaemia, trauma/vessel rupture, neoplasia or in conjunction with primary pleural effusion or pleuropneumonia (Worth and Reef, 1998). In retrospective studies, consistent physical findings included tachycardia, lethargy, anorexia, ventral edema, jugular venous distention and diminished heart sounds (Worth and Reef, 1998). In cases of pericarditis idiopathic or septic in origin, roughly half of the horses resolved with pericardiocentesis, and returned to original function (Worth and Reef, 1998, Freestone et al., 1987, Malalana et al., 2011). There are two major ways that cardiac tamponade develops. In one instance, rapid accumulation of a small volume of fluid (one litre or greater) can result in a severe increase in pericardial pressure and impede cardiac output. Large volumes of fluid can accumulate over a long period of time with little effect on diastolic filling of the heart, due to gradual stretching of the pericardium (Abuzaid, 2014). Whether acute or chronic, fluid accumulation will increase the intrapericardial pressure until the tipping point when right and left ventricular diastolic pressures become equal and cardiac flow decreases abruptly. Impedance of filling then results in collapse, tachycardia, peripheral vasoconstriction, and eventually cardiogenic shock and death (Abuzaid, 2014). In this case, we suspect that during the anaesthetic event, blood from the heart based neoplasm began leaking into the pericardial space, distending it and causing cardiac tamponade. Considering the physicality of the equine induction process and the hoisting of the mule, the pressure of dorsal recumbency worsened by the sand filled colon pressing against the diaphragm, it is likely that the tamponade was acute in origin. This is also supported by the histopathology reporting on the low elasticity of the pericardium. Tamponade likely occurred when the mare stood, and the pericardial rupture and subsequent haemothorax was due to the force of the fall. Previously, cardio-respiratory arrest and aortic rupture has been reported more commonly in colic patients (Román Durá et al., 2025). In general, cardiac complications and mortality are associated with higher ASA status, increased age, and lateral recumbency (Laurenza et al., 2019). Draft mule breeds can have risk associated with anaesthesia complications (O’Donovan et al., 2023). Leiomyosarcomas are smooth muscle neoplasms that are considered very rare in occurrence (Kawabata et al, 2019). Currently in the literature, there are individual equine case reports confirming leiomyosarcomas in urogenital tracts and vestibulo -vaginal locations, in metastatic cases relating to CNS disease, and in the jejunum and uvea (Kawabata et al., 2016, Hurcombe et al., 2008, Grosås et al., 2017, Oreff et al., 2018, Husby et al., 2019). There is one report of a pericardial leiomyosarcoma found in a dog, but nothing that has been published reporting this finding in a horse (Fews et al., 2008). This report uniquely describes an unexpected cause of death from a rare neoplasm and cardiac complication. In hindsight, it is difficult to say if further initial diagnostics could have alerted us to the potential for a fatal cardiac event in this patient. The history of lethargy, inappetence, along with bloodwork abnormalities are not uncommonly seen with chronic dental issues, but they also indicate the possibility of systemic disease as well (Dixon and Dacre, 2005, Wright et al., 2023). Even though no murmurs or arrhythmias were appreciated prior to anaesthesia, this patient may have benefited from an echocardiogram due to her age, signalment, and history of lethargy. Geriatric equines with chronic dental issues can ingest large amounts of sand substrate if they are fed mostly grain from the ground (Niinistö et al., 2019). Possibly, taking abdominal radiographs to identify the presence of sand in the large colon prior to anaesthesia may have been beneficial in deciding whether or not this patient was a good anaesthetic candidate. Declarations: These authors declare no conflict of interest.

ABUZAID, A. 2014. Cardiac tamponade, a clinical challenge Ahmed Abuzaid, MD; Mohamed Elkashab, MD; Marwan Saad, MD Creighton University, Internal Medicine department, Omaha, NE, USA. John H Stroger Hospital of Cook County, Cardiology department, Chicago, IL, USA. Trinitas Regional Medical Center / Seton Hall University, Internal Medicine department, NJ, USA. JCIC, 1.DIXON, P. M. & DACRE, I. 2005. A review of equine dental disorders. Vet J, 169 , 165-87.FEWS, D., SCASE, T. J. & BATTERSBY, I. A. 2008. Leiomyosarcoma of the Pericardium, with Epicardial Metastases and Peripheral Eosinophilia in a Dog. Journal of Comparative Pathology, 138 , 224-228.FREESTONE, J. F., THOMAS, W. P., CARLSON, G. P. & BRUMBAUGH, G. W. 1987. Idiopathic effusive pericarditis with tamponade in the horse. Equine Veterinary Journal, 19 , 38-42.GOZALO-MARCILLA, M., BETTSCHART-WOLFENSBERGER, R., JOHNSTON, M., TAYLOR, P. M. & REDONDO, J. I. 2021. Data Collection for the Fourth Multicentre Confidential Enquiry into Perioperative Equine Fatalities (CEPEF4) Study: New Technology and Preliminary Results. Animals (Basel), 11.GROSåS, S., ØSTEVIK, L., REVOLD, T., OTTESEN, N. & ROPSTAD, E. O. 2017. Uveal myxoid leiomyosarcoma in a horse. Clin Case Rep, 5 , 1811-1818.HURCOMBE, S. D., SLOVIS, N. M., KOHN, C. W. & OGLESBEE, M. 2008. Poorly differentiated leiomyosarcoma of the urogenital tract in a horse. J Am Vet Med Assoc, 233 , 1908-12.HUSBY, K. A., HUBER, M. J., PHILLIPS, I. & HEIDEL, J. R. 2019. Vestibulovaginal leiomyosarcoma in a mare. Equine Veterinary Education, 31 , 126-129.KAWABATA, A., DEL PIERO, F., CASERTO, B. G. & LANGOHR, I. 2016. Metastatic Leiomyosarcoma Causing Ataxia in a Horse. Journal of Equine Veterinary Science, 43 , 23-27.LAURENZA, C., ANSART, L. & PORTIER, K. 2019. Risk Factors of Anesthesia-Related Mortality and Morbidity in One Equine Hospital: A Retrospective Study on 1,161 Cases Undergoing Elective or Emergency Surgeries. Front Vet Sci, 6 , 514.MALALANA, F., BARDELL, D. & MCKANE, S. 2011. Idiopathic aseptic pericardial effusion with cardiac tamponade in a horse. Equine Veterinary Education, 23 , 64-68.NIINISTö, K. E., MääTTä, M. A., RUOHONIEMI, M. O., PAULANIEMI, M. & RAEKALLIO, M. R. 2019. Owner-Reported Clinical Signs and Management-Related Factors in Horses Radiographed for Intestinal Sand Accumulation. J Equine Vet Sci, 80 , 10-15.O’DONOVAN, K. A., AARNES, T. K., HUBBELL, J. A. E., PARKER, E. M., MOLLENKOPF, D., LERCHE, P., RICCO PEREIRA, C. H., BINI, G. & BEDNARSKI, R. M. 2023. Risk of anesthesia-related complications in draft horses: a retrospective, single-center analysis. Veterinary Anaesthesia and Analgesia, 50 , 157-162.OREFF, G. L., TATZ, A. J., DAHAN, R., VALENTINE, B. A. & KELMER, G. 2018. Successful removal of jejunal leiomyosarcoma in a Quarter Horse mare. Equine Veterinary Education, 30 , e458-e462.ROMáN DURá, B., DUNHAM, O., GRULKE, S., SALCICCIA, A., DUPONT, J. & SANDERSEN, C. 2025. A Retrospective Study on Pre- and Intraoperative Predictors on the Recovery Quality of Horses After General Anesthesia. Vet Sci, 12.WORTH, L. T. & REEF, V. B. 1998. Pericarditis in horses: 18 cases (1986–1995). Journal of the American Veterinary Medical Association, 212 , 248-253.WRIGHT, A. L., EARLEY, E. T., AUSTIN, C. & ARORA, M. 2023. Equine odontoclastic tooth resorption and hypercementosis (EOTRH): microspatial distribution of trace elements in hypercementosis-affected and unaffected hard dental tissues. Sci Rep, 13 , 5048. Figure 1 Legend: Left image shows an opening of the pericardial sac with sanguinous fluid, suggesting tamponade as likely cause of death. Right image shows the cross section of the same heart with areas of focal hemorrhage and the blue arrow indicating a lesion of the mesentery of the pericardial sac near the apex of the heart. Supplementary Material File (figure 1.docx) - Download - 3.07 MB Information & Authors Information Version history Copyright This work is licensed under a Non Exclusive No Reuse License.

Authors Metrics & Citations Metrics Article Usage 220views 129downloads Citations Download citation Anna Carroll, Jane Quandt, Stephanie Dantino. Acute and sudden death secondary to cardiac tamponade during anesthetic recovery in a 21 year old Draft mule.. Authorea. 18 November 2025. DOI: https://doi.org/10.22541/au.176347274.48737056/v1 DOI: https://doi.org/10.22541/au.176347274.48737056/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu.