An animal model of spontaneous syncope and sudden death
Branch, C.E.; Robertson, B.T.; Beckett, S.D.; Waldo, A.L.; James, T.N.
Journal of Laboratory and Clinical Medicine 90(4): 592-603
1977
ISSN/ISBN: 0022-2143 PMID: 903692 Document Number: 116474
A particular line of purebred pug dogs displayed spontaneous episodes of syncope characterized by sudden collapse, no detectable heart beat, cyanosis, and dilated pupils. The tendency for syncope and sudden death was transmitted through four generations. Measurements of blood electrolytes and routine PM and histological examination did not explain the attacks or sudden deaths. Histological examination of the cardiac conduction system revealed abnormal narrowing of the midportion of the His bundle. Monitoring the ECG for 4 to 6 h by radiotelemetry showed that 15 pugs had a higher frequency of nonconducted atrial beats due to second-degree AV heart block (8.02/h) than did 11 normal mongrels (0.36/h). The AV block was related to the respiratory cycle and was prevented by atropine. Eight of the pugs and four mongrels were monitored continuously by radiotelemetry for 2 to 6 weeks with the use of combinations selected from myocardial electrograms, surface ECG, arterial blood pressure, respiration, ECG, and surface laryngeal EMG. An automatic system was used to retain data associated with the absence of ventricular activation. Episodes of total cardiac standstill for 6 to 15 sec without the appearance of escape pacemakers were recorded from all the pug dogs. The episodes of cardiac standstill were of two distinct types. The first type appeared as an exaggerated sinus arrhythmia. The second type was a sudden transition from a moderate tachycardia to cardiac standstill. Simultaneous time-lapse video monitoring of selected pugs revealed that the first type occurred when the dogs were resting or asleep. The second type occurred when they were awake, and was associated with the syncopal attacks.