Ovariectomy Reduces the Arrhythmia Threshold Induced by Coronary Artery Occlusion in Conscious Rats

Abstract

Sudden cardiac death is the leading cause of death for men and women in industrially developed countries. The majority of these deaths result from tachyarrhythmias that culminate in ventricular fibrillation. Approximately 1% of the victims of cardiac arrest are resuscitated and survive to leave the hospital. Importantly, there are gender differences in cardiac physiology and in the types and severity of cardiac arrhythmias. Female sex hormones may be a contributing factor. Therefore, we tested the hypothesis that ovariectomy reduces the arrhythmia threshold induced by coronary artery occlusion. Female Wistar rats were ovariectomized or sham ovariectomized and instrumented with a radio-telemetry device for recording arterial pressure, ECG and body temperature. Six weeks later a Doppler ultrasonic flow probe was placed around the ascending aorta to measure cardiac output and a snare was placed around the left main coronary artery. After recovery, the response to coronary artery occlusion was determined in conscious intact and ovariectomized rats by pulling on the snare. Occlusion of the left main coronary artery in intact females resulted in tachyarrhythmias that culminated in ventricular fibrillation within 3.7 +/− 0.1 min. In contrast, occlusion of the left main coronary artery in ovariectomized females resulted in tachyarrhythmias that culminated in ventricular fibrillation within 2.4 +/− 0.1 min. These responses were associated with differences in cardiac autonomic tonus and electrophysiology. Supported by HL67713