Background. The increase in heart rate during exercise is considered to be attributed to sympathetic system activation combined with parasympathetic withdrawal. The prognostic importance of the chronotropic response to exercise and heart rate recovery 1 minute after exercise has already been established. The purpose of this study was to evaluate heart rate recovery as an index of myocardial ischemia, by correlating heart rate recovery with known parameters of myocardial ischemia. Methods and Results. Included in the study were 304 consecutive patients (73% men), aged 34 to 82 years. Patients whose heart rate recovery value or myocardial perfusion imaging could have been influenced by factors other than ischemic disease were excluded from the study. The patients underwent single photon emission computed tomography myocardial perfusion imaging combined with symptom-limited exercise testing with thallium 201 or technetium 99m tetrofosmin. The value for heart rate recovery was defined as the decrease in heart rate from peak exercise to 1 minute after termination of exercise. For semiquantitation of the scintigram, the uptake of the radiotracer was graded on a scale from 0 to 4. Twenty-one beats per minute was defined as the lowest normal value for heart rate recovery. We found 74 patients (24%) with an abnormal value. We also found a significant correlation between heart rate recovery 1 minute after exercise and stress myocardial perfusion score. In addition, there was a statistically significant relationship between heart rate recovery and chronotropic variables. Patients with an abnormal value of heart rate recovery were generally of an older age, were more likely men, had a higher frequency of risk factors for coronary artery disease, were mostly taking cardioactive medications, had lower efficiency during treadmill testing, and had more pathologic findings on the scintigram. Conclusions. Myocardial ischemia, as assessed by myocardial perfusion imaging, is an important correlate of heart rate recovery. There is a significant correlation between chronotropic variables during exercise testing and heart rate recovery 1 minute after exercise. It seems that. the heart rate recovery value 1 minute after peak exercise may be considered a reliable index of the severity of myocardial ischemia.
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