RELATIONSHIP OF VENTRICULAR-TACHYCARDIA TO SLEEP WAKEFULNESS IN A MODEL OF SUDDEN CARDIAC DEATH/

Death from some childhood disorders such as sudden infant death syndro me and the congenital long QT syndrome are associated with specific be haviors such as sleep or emotional stress. We studied young German she pherd dogs that die suddenly during presumed sleep. These dogs have in herited ventricular tachycardia (VT) which is most frequent during sin us bradycardia and sinus arrhythmia. We hypothesized that the number o f VT complexes (three or more consecutive ectopic complexes) would be greatest during sleep. Moreover, we hypothesized that pauses in the si nus rhythm of greater than 1000 ms would be greatest in the behavior w ith the most frequent VT. Behavioral states [excited, ambulatory, sitt ing, lying, rapid eye movement (REM) sleep] were quantified from 24-h video recordings of seven dogs. VT and pauses were quantified for each behavior using simultaneously recorded ECGs. A multivariate model was used to analyze the results. After controlling for time of day, lying , and REM sleep were significantly (p < 0.02) associated with VT, wher eas more active behaviors were not. Time of day also independently aff ected the number of VT complexes. However, behavior and time of day di d not account for all of the variability in the number of VT complexes . Pauses were significantly associated with behavior, with the highest number of pauses occurring during lying and REM sleep. However, pause s were not always associated with VT, indicating that a pause was a ne cessary, but not sufficient, condition for the development of VT. Thes e results suggest that modulation of VT incidence in these animals is multifactorial and that the highest number of VT complexes is associat ed with the bradycardia that accompanies REM sleep.