Case 15 — Comparison Case

Four-trace ECG from an 11-year-old male standard poodle with syncope. Top: SVT at 250 bpm. Second: carotid sinus massage breaks rhythm. Third: response to IV verapamil. Fourth: restored sinus rhythm with first-degree AV block.
Four-trace ECG from an 11-year-old standard poodle with syncope and pericardial effusion.

This ECG was recorded from an 11-year-old male standard poodle examined after two syncopal episodes. He had a grade IV/VI left apical holosystolic murmur. Echocardiogram showed pericardial effusion, left atrial and ventricular enlargement, and normal myocardial function.

The top trace (lead II, 50 mm/s) shows SVT at 250 bpm with normal QRS complexes and no identifiable P waves. In the second trace, carotid sinus massage produced a “break.” The third trace shows response to IV verapamil (0.1 mg/kg over 5 minutes). The fourth trace shows restored sinus rhythm with first-degree AV block (drug effect).

The dog improved clinically but continued to deteriorate. Pericardiocentesis yielded very bloody fluid (PCV 28%). A 5-mm left atrial wall tear was identified at necropsy. The arrhythmia most likely originated from this site.

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