Diurnal Changes of Heart Rate and Sympathovagal Activity for Temporal Patterns of Transient Ischemic Episodes in 24-Hour
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Research Article Diurnal Changes of Heart Rate and Sympathovagal Activity for Temporal Patterns of Transient Ischemic Episodes in 24-Hour Electrocardiograms A. Smrdel and F. Jager Faculty of Computer and Information Science, University of Ljubljana, 1000 Ljubljana, Slovenia Received 26 April 2006; Revised 27 October 2006; Accepted 11 January 2007 Recommended by Maurice Cohen We test the hypothesis that different temporal patterns of transient ST segment changes compatible with ischemia (ischemic episodes) are a result of different physiologic mechanisms responsible for ischemia. We tested the hypothesis using records of the Long-Term ST Database. Each record was divided into three intervals of records: morning, day, and night intervals; and was inserted into one of three sets according to the temporal pattern of ischemia: salvo, periodic, and sporadic pattern. We derived timeand frequency-domain parameters of the heart rate time series in selected intervals in the neighborhood of ischemic episodes. We used the adaptive autoregressive method with a recursive least-square algorithm for consistent spectral tracking of heart rate time series and to study frequency-domain sympathovagal behavior during ischemia. The results support the hypothesis that there are at least two distinct populations, which differ according to mechanisms and temporal patterns of ischemia. Copyright © 2007 A. Smrdel and F. Jager. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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INTRODUCTION
Ischemia is one of the most common heart diseases. It is caused by the insufficient supply of the heart muscle with the oxygen, which can cause part of the heart muscle to become electrically inactive, and can in turn lead to acute myocardial infarction, and consequently death. To further complicate the matter, up to 95% of ischemic episodes may be silent [1], while others are symptomatic. Ischemia occurs in different ischemic syndromes, such as coronary artery disease, stable angina pectoris, unstable angina, Prinzmetal’s angina, transmural angina, and syndrome X [2]. The most commonly ischemia appears in patients with stable coronary artery disease. In these patients, ischemia is usually preceded with a marked increase in heart rate, and majority of episodes appear to be caused by a physical exertion, where patophysiology is connected to increased oxygen demand associated with increased myocardial contractility and blood pressure. Less common are ischemic episodes which are not preceded by an increase in heart rate. These episodes usually appear due to mental stress, where patophysiology is connected to reduced oxygen supply due to coronary vasoconstrictions. This group includes ischemic episodes of Prinzmetal’s angina due
to vasospasms, of unstable angina due to thrombosis, and of microvascular angina. Determining the type of ischemia (increased demand or reduced supply) for a given patient
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