CAROTID-ARTERY STENOSIS AND TACHYARRHYTHMIAS - REGIONAL CEREBRAL BLOOD-FLOW DURING HIGH-RATE VENTRICULAR PACING AFTER ONE VESSEL OCCLUSION IN RATS

The aim of the present study was to investigate the effect of hypotensive tachycardias on cerebral blood flow (CBF) in the presence of significant carotid stenosis. The experiments were performed in 57 spontaneously breathing rats during arterial normoxia and normocapnia anesthetized with thiobarbital. CBF was determined with radiolabeled microspheres during control conditions (normofrequent sinus rhythm, normotension; group A; n = 15), during high-rate left ventricular pacing (660-840 ppm) at normotension (group B-1; n = 13), borderline hypotension (group B-2; n = 15) and severe hypotension (group B-3; n = 7). In addition, CBF measurements were performed during borderline hypotension induced by hemorrhage (group C; n = 7). Global CBF was 1.09 +/- 0.29 ml g(-1) min(-1) in group A, 0.93 +/- 0.40 in group B,, 0.68 +/- 0.31 in group B-2 (P < 0.05 vs. A), 0.42 +/- 0.16 in group B-3 (P < 0.05 vs. A) and 0.83 +/- 0.2 in group C. The highest CBF values were found in the cerebellum (A; 1.43 +/- 0.5 ml g(-1) min(-1)) and the lowest in the postocclusive tissue of the ipsilateral hemisphere (A; 0.74 +/- 0.2 ml g(-1) min(-1)). In all groups a 15% mean CBF reduction in the right hemispherical cerebrum in comparison to the left hemisphere was observed (P < 0.01). In contrast, hemispherical CBF of the cerebellum did not differ. The CBF blood pressure relationship shifted to lower CBF values, the threshold of CBF regulation shifted to higher blood pressure values in the tissue regions distal to the occluded vessel during hypotensive tachycardias. One carotid artery occlusion and high rate ventricular pacing seem to be a reliable model for quantifying cerebral hemodynamics during arrhythmias in the presence of carotid stenoses. Using this experimental approach it was demonstrated that hypotensive tachycardias and obstructions within the ectracranial carotid vascular bed such as arterial vessel stenoses and occlusions have an additive effect on CBF reduction.