Ventricular Parasystole in a Neonatal Rhesus Macaque (Macaca mulatta).

A 6-d-old Indian-origin female rhesus macaque (Macaca mulatta) presented with bradycardia shortly after sedation with ketamine. No other cardiac abnormalities were apparent. Approximately 2 wk after the initial presentation, the macaque was again bradycardic and exhibited a regularly irregular arrhythmia on a prestudy examination. ECG, echocardiography, blood pressure measurement, SpO2 assessment, and a CBC analysis were performed. The echocardiogram and bloodwork were normal, but the infant was hypotensive at the time of echocardiogram. The ECG revealed ventricular parasystole. Ventricular parasystole is considered a benign arrhythmia caused by an ectopic pacemaker that is insulated from impulses from the sinus node. Given this abnormality, the macaque was transferred to a short-term study protocol, according to veterinary recommendation. On the final veterinary exam, a grade 3 systolic murmur and a decrease in arrhythmia frequency were noted. Gross cardiac lesions were not identified at necropsy the following day. Cardiac tissue sections were essentially normal on microscopic examination. This infant did not display signs of cardiovascular insufficiency, and a review of the medical record indicated normal growth, feed intake and activity levels. This case demonstrates the importance of appropriate screening of potential neonatal and juvenile research candidates for occult cardiovascular abnormalities. Whether the arrhythmia diagnosed in this case was truly innocuous is unclear, given the documented hypotension and the development of a systolic heart murmur.

O Holter de 24 horas no diagnóstico diferencial da parassístole / Holter twenty-four monitoring in parasystole differential diagnosis

Os autores relatam um caso de parassístole ventricular registrada no Holter de 24 horas. Este diagnóstico foi possível devido à observação criteriosa do foco ectópico e por este exame disponibilizar longo tempo de monitorização. A gravação apresentou frequentes atividades atriais isoladas, mimetizando extra-sístoles atriais bloqueadas na condução atrioventricular, o que tornava difícil o correto diagnóstico. Após medidas precisas do traçado, observou-se, tratrem essas ectopias, de condução ventrículo-atrial do foco parassistólico ventricular, que, por apresentar bloqueio de saída, ocasionou a não-manifestação eletrocardiográfica do QRS. O Holter de 24 horas mostrou-se útil na detecção deste tipo de arritmia, que na maioria das vezes não é corretamente diagnosticada