Hemodynamic sequelae of ventricular tachyarrhythmias on cerebral blood flow

The present experiments were designed to compare the behavior of cerebral blood flow (CBF) during acute moderate and severe hypotensive episodes induced by either ventricular tachycardias (VT) or by hemorrhage. Using the microsphere method CBF was determined in 20 Sprague-Dawley rats during sinus rhythm (Group A), in 28 animals during high-rate VT (Group B) and in 10 animals after hemorrhage (Group C). According to the decrease in blood pressure and with respect to the lower threshold of cerebral autoregulation Group B was divided into 2 subgroups (B1: 80-130 mmHg; B2: 50-80 mmHg) retrospectively. While CBF remained constant in Group B1 (0.98 +/- 0.3 ml g-1 min-1 vs. 1.01 +/- 0.32 in controls, NS), CBF decreased markedly during severely hypotensive VT in Group B2 (0.52 +/- 0.2 ml g-1 min-1, p < 0.001 vs. A; p < 0.05 vs. C) and during hypovolemic hypotension in Group C (0.77 +/- 0.22 ml g-1 min-1 vs. A; NS). Cerebrovascular resistance and autoregulation indices indicated a maintenance of CBF regulation during hypovolemic hypotension and a failure during normovolemic hypotension. These findings indicate that the autoregulatory ability of the brain is substantially more stable during hypovolemic hypotension than during normovolemic hypotension. Therefore, the hemodynamic sequelae of acute hypotensive episodes on CBF depend on the underlying cause of hypotension.