Impairment of baroreflex control of the sinoatrial node after cardiac operations with extracorporeal circulation in man

Abstract

The sensitivity of the baroreceptor reflex to transient hypertension was determined in 13 patients before (control) and after (72 hours) open cardiac operations with extracorporeal circulation (ECC). In all patients early postoperative values were appreciably decreased (p less than 0.01) as compared to the preoperative values. This decrease suggested severe impairment of baroreflex control of the sinoatrial node. These changes were not correlated with concurrent alterations in heart rate or systemic arterial, left atrial, or right atrial pressures. In addition, respiratory sinus node arrhythmia was absent in all subjects. In four patients, subsequent studies 4, 8, 10, and 12 months, respectively, after the operation revealed good recovery of baroreflex sensitivity and respiratory influences on beat-to-beat variation. No similar effects were observed in two patients studied before and after cardiac operations without ECC. It is possible that direct trauma to the nervous supply of the sinoatrial node is a major factor in that reversible dysfunction; in fact, in three patients evidence was obtained that while sinoatrial node responses were impaired, the reflex control of the atrioventricular region remained unaltered. These findings point to further impairment of the fine control of heart rate imposed by the conditions of cardiac operations with ECC in patients with previously curtailed cardiac reserve.