Observations on the regulation of cerebral blood flow in complete heart block.

Abstract

The simultaneous effects of right ventricular pacing on cerebral blood flow (CBF) and cardiac function in complete heart block have not been reported. Catheters in the jugular bulb, right ventricle, and pulmonary and brachial arteries of five patients, aged 49 to 78 years, allowed studies at initial rates of 30 to 40 and during the tenth minute of pacing at 60, 70, 90, and 100 per minute. Mean initial cardiac output (CO) was 2.8 L per minute and increased 29% to 3.6 at a rate of 60 per minute ( P <0.01). Simultaneous mean control CBF was also low, but rose to 118% of control with pacing ( P <0.05). Systemic, cerebral, and pulmonary vascular resistances declined with these increases in flow as the elevated mean venous and arterial pressures remained stable. Mean arterial oxygen and carbon dioxide tensions and pH were normal at all rates. The parameters measured were not materially altered by pacing at rates above 60 per minute. The changes in CBF were well correlated with those of CO (r=0.81, P <0.01) and unrelated to simultaneous mean arterial or cerebral perfusion pressures. The alterations in CO were also unrelated to these pressures. The data clearly demonstrate a disturbance in CBF autoregulation, which may be a function of the low CO state.