When Vomiting Causes Collapse: A Case of Situational Syncope in a Cat

Vomiting is an unusual trigger for syncope in cats, but a reported case highlights an important cardiac association. A 14-year-old spayed female mixed-breed cat developed transient loss of consciousness exclusively after vomiting, with Holter monitoring subsequently revealing paroxysmal high-grade second-degree atrioventricular block. 

The vomiting and associated syncopal episodes had begun 104 days before referral and had progressively increased in frequency. During an episode, the cat became completely recumbent without tonic-clonic seizure activity and returned to normal consciousness after approximately 10 seconds^[1]. 

When Vomiting and Collapse Occur Together 

Syncope results from transient global cerebral ischemia. In neurally mediated syncope, a vagal reflex can trigger bradyarrhythmia or hypotension. Situational syncope is a form of neurally mediated syncope associated with specific activities or situations, including urination, defecation, swallowing, and coughing^[1],[2]. 

Vomiting-associated syncope has rarely been reported, including in humans. In this cat, the consistent sequence was particularly important: Vomiting occurred first, followed by collapse, and the cat recovered within seconds^[1]. 

A Normal Routine Examination Did Not Exclude an Arrhythmia^[2] 

At presentation, the cat was in good general condition. The femoral pulse was 156 bpm, with no pulse irregularities, while cardiac and respiratory auscultation revealed no abnormalities. 

Complete blood count and biochemical analyses were within normal limits. Serum feline pancreatic-specific lipase, symmetric dimethylarginine, thyroxine, and high-sensitivity cardiac troponin I were also within normal limits. 

Thoracic radiographs showed no abnormalities in cardiac size or lung fields. Echocardiography revealed no obvious chamber enlargement, valvular abnormalities, cardiac shunts, intracardiac structures, or abnormal endocardial echogenicity. Six-lead ECG showed sinus rhythm with low QRS amplitude. 

The absence of abnormalities during routine assessment did not explain the intermittent episodes. 

Holter ECG Captured the Critical Finding 

Because the syncopal episodes occurred only after vomiting, home Holter electrocardiography was performed. It demonstrated paroxysmal high-grade second-degree atrioventricular block consistent with the clinical episodes. 

The ECG pattern also showed mild, progressive prolongation of the PP interval before the block. The PR interval was prolonged immediately before the atrioventricular block. These changes occurred in association with the block and were not observed during sinus rhythm. 

Prolonged PR intervals can occur with vagal tone in humans and dogs with Mobitz type 1 atrioventricular block. Similar ECG features have been described in neurally mediated syncope and respiratory arrhythmias, suggesting changes in autonomic balance, particularly enhanced vagal tone^[1],[3]. 

Reducing the Trigger Reduced the Episodes 

No gastrointestinal abnormality was identified, and the underlying cause of vomiting remained unclear. Antiemetic treatment with famotidine and metoclopramide markedly reduced the frequency of vomiting, with a corresponding reduction in syncopal episodes. 

Metoclopramide was discontinued after approximately two weeks, while famotidine was continued. Vomiting subsequently occurred approximately once every 1–2 weeks, while syncopal episodes occurred approximately once every six months. Approximately 624 days after the initial visit, no further syncopal events were observed. 

Clinical Takeaway 

When a cat repeatedly collapses only after vomiting, the temporal relationship between the two events can provide an important diagnostic clue. A normal physical examination, echocardiogram, or routine ECG may not capture an intermittent conduction abnormality. 

In this case, the combination of vomiting-associated collapse and Holter-documented paroxysmal high-grade atrioventricular block supported a diagnosis of situational syncope triggered by vomiting. 

The diagnosis had limitations: electrophysiological testing was not performed, and postmortem examination was unavailable to confirm abnormalities within the electrical conduction system. Nevertheless, the case highlights the value of careful event history and prolonged ECG monitoring when transient collapse is repeatedly associated with a specific trigger.

References:

1. Hirao D, Kato R, Sakaguchi K, Ohmori T, Morita S, Hasegawa H, Yoshimura A, Fukushima R. Situational syncope caused by vomiting in a cat. Journal of Veterinary Medical Science. 2024;86(12):1233-6. https://www.jstage.jst.go.jp/article/jvms/86/12/86_24-0058/_pdf
2. Freeman R, Wieling W, Axelrod FB, Benditt DG, Benarroch E, Biaggioni I, Cheshire WP, Chelimsky T, Cortelli P, Gibbons CH, Goldstein DS. Consensus statement on the definition of orthostatic hypotension, neurally mediated syncope and the postural tachycardia syndrome. Autonomic Neuroscience. 2011 Apr 26;161(1-2):46-8. https://www.academia.edu/download/73465936/j.autneu.2011.02.00420211023-19395-ysq5zf.pdf
3. Zyśko D, Gajek J, Koźluk E, Mazurek W. Electrocardiographic characteristics of atrioventricular block induced by tilt testing. Europace. 2009 Feb 1;11(2):225-30. https://academic.oup.com/europace/article-pdf/11/2/225/7272901/eun299.pdf