Effect of brief periods of paced ventricular tachycardia on coronary blood flow in dogs before and after graded coronary stenosis.

The effect of short bouts (1 min) of electrically induced ventricular tachycardias (VT) of increasing rates (160-240/min) was studied in 8 anesthetized dogs before and after graded constrictions of the left anterior descending (LAD) and the circumflex (CCA) coronary arteries. In the absence of coronary stenosis, paroxysmal VT caused a significant decrease in tension-time index (TTI), coronary blood flow (CBF) and coronary vascular resistance (CVR). Single and combined coronary stenosis caused relatively small alterations of the VT-induced depression of the systemic hemodynamics but reversed the effect of paroxysmal VT on the CVR. In the presence of single 90% LAD stenosis, VT resulted in an increase in CVR-LAD and a decrease in F-LAD associated with a fall in CVR-CCA and a rise in F-CCA. Combination of 90% LAD plus 70% CCA stenosis abolished the compensatory fall of CVR-CCA resulting in a pronounced reduction of F-CCA during VT. The results support the concept that in the presence of severe coronary stenosis brief paroxysmal ventricular tachycardias do increase myocardial nutritional demand but rather decrease nutritional supply.