Heart Rate Variability and Arrhythmia Occurrence in Isolated Hearts before and after Ischemia/Reperfusion Injury

Heart rate variability (HRV) is a measure of the variation of instantaneous heart rate or cardiac cycle [1-3]. It has become a measure that is associated with susceptibility to lethal arrhythmias following myocardial infarction. HRV is thought to reflect both sympathetic and vagal tones in the heart [2, 4-6]. Although HRV is regulated by autonomic function, it is still present in heart transplant patients [4, 7] and in isolated hearts [4, 6, 7], where autonomic intervention has been interrupted. The presence of HRV in isolated hearts may be due to remaining catecholamines or some innate cardiac electrophysiologic mechanism. For this study, I investigated HRV in intact isolated guinea pig hearts. I sought to determine whether HRV was indeed present in the isolated heart and whether it changed with ischemia and catecholamine blockers. Alterations in HRV may have important implications for the development of arrhythmias and may be indicative of compromised cardiac function. In this study, data was collected from guinea pig hearts prepared according to the Langendorff method and retrogradely perfused with a modified Krebs-Ringer\u27s solution. Atrial electrogram, ventricular electrogram, and left ventricular pressure (LVP) recordings were taken at regular intervals throughout the experiments where hearts were subjected to ischemia and reperfusion in combination with a variety of pharmacologic agents. Each experiment consisted of episodes of baseline, drug infusion, global ischemia, and reperfusion during which electrogram and pressure recordings were made. Three separate drugs were tested: control (no drug), atropine, and esmolol. The overall objective of this study was to measure variability in atrial, ventricular and LPV events during a variety of normal and ischemic conditions. However, in order to estimate the variability of the events in each of the three types of recordings, a novel computer algorithm for accurately and automatically identifying cardiac events needed to be developed. Thus, the first part of this thesis describes the research involved in developing an automated, computerized event detection scheme. Four event detection algorithms were developed and compared in terms of their sensitivities and specificities. The algorithm that offered the best combination of sensitivity and specificity was then used on all recordings to automatically detect cardiac events (atrial, ventricular or LVP)..