Effects of ventricular arrhythmia on the cerebral microcirculation in cats

To test the widely believed but poorly proved hypothesis that the cerebral symptoms observed during ventricular arrhythmia are caused by a reduced cerebral blood supply, we examined the effects of single and multiple ectopic ventricular beats (or ventricular tachycardia of short duration) on the cerebral microcirculation. Six anesthetized cats were used. Ectopic ventricular systoles of various sequences were produced by electrically stimulating the ventricle through a bipolar needle-type electrode for 1 to 50 times at a rate of 300/min. The local cerebral blood volume (CBV) and blood flow (CBFLD) in the cortex were measured continuously employing the photoelectric and laser Doppler methods. CBV reflects the cumulative dimensions of the cerebrocortical microvessels. Ectopic ventricular contractions, as confirmed by electrocardiograms, always reduced the CBV and arterial blood pressure in a total of 104 attempts. The CBV reductions ranged from 0.20 +/- 0.03 vol% for a single ectopic beat to approximately 0.6-0.8 vol% for runs of 8 or more beats. The CBFLD reductions measured with the laser Doppler flowmeter were 10-35%. The reductions in CBV and CBFLD during the ventricular arrhythmia could be attributed to the abrupt and marked reductions in arterial blood pressure. Runs of ectopic ventricular beats have significant effects on the cerebral microcirculation, whether clinically apparent or not.