EFFECTS OF VENTRICULAR ARRHYTHMIA ON THE CEREBRAL MICROCIRCULATION INCATS

To test the widely during ventricular arrhythmia are caused by a reduc ed cerebral blood supply, we examined the effects of single and multip le ectopic ventricular beats (or ventricular tachycardia of short dura tion) on the cerebral microcirculation. Six anaesthetized cats were us ed. Ectopic ventricular systoles of various sequences were produced by electrically stimulating the ventricle through a for 1 to 50 times at a rate of 300/min. The local cerebral blood volume (CBV) and blood fl ow (CBFLD) in the cortex were measured continuously employing the phot oelectric and laser Doppler methods. CBV reflects the cumulative dimen sions of the cerebrocortical microvessels. Ectopic ventricular contrac tions, 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 approxima tely 0.6-0.8 vol% for runs of 8 or more beats. The CBFLD reductions me asured with the laser Doppler flowmeter were 10-35%. The reductions in CBV and CBFLD during the ventricular arrhythmia could be attributed t o the abrupt and marked reductions in arterial blood pressure. Runs of ectopic the cerebral microcirculation, whether clinically apparent or not.