Systolic time intervals in induced atrial fibrillation in the dog: effects of ectopic ventricular activation.

Electrocardiogram, atrial electrogram, phonocardiogram, aortic pressure, and left ventricular pressure were recorded during periods of induced atrial fibrillation in dogs anesthetized with a combination of morphine sulfate and pentobarbital sodium. Data were accumulated by selecting 50 cardiac cycles which terminated in ectopic ventricular electrical complexes, and comparing systolic time intervals (STI) following these beats with STI Following 50 normal ventricular complexes. Ectopic ventricular activation prolonged left ventricular pre-ejection period and external isovolumic contraction time, and reduced duration of left ventricular ejection time. These events resemble changes in STI observed following induction of atrial fibrillation from a sinus rhythm, but they are of significantly greater magnitude than the effects of atrial fibrillation alone.