Slow ventricular response atrial fibrillation and J wave in a hypothermic dog.

A 9-year-old, outdoors, Italian hound dog was referred for severe hypothermia that had occurred after vomiting and diarrhea. At presentation, the electrocardiogram showed a slow ventricular response atrial fibrillation with an instantaneous heart rate ranging from 20 to 115 beats/min. The QRS complexes were mildly enlarged and followed by a J wave. The QT interval was prolonged (360 msec). Multiple wide QRS complexes with various bizarre morphologies, either singular or in couples, indicative of ventricular ectopic beats, were also observed. The dog was hospitalized and actively rewarmed; the rhythm spontaneously converted to sinus rhythm with respiratory sinus arrhythmia.