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Heart rate as a measure of cardiac function.


 Cenizal, Arleen F,
 Brillo, Peachy,
 Chua, William,
 Mapua, Cynthia A,
 Ong-Garcia, Helen

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Philippine Heart Association 36th Annual Convention


BACKGROUND: With all the physiologic adjustments that take place in the body during exercise, we feel that the heart rate response supersedes them all to maintain adequate cardiac output in the face of increased oxygen demand. How much does it contribute to the compensatory mechanisms of the heart? Is it dependent on the underlying cardiac condition? Studies have shown that the heart rate response especially during exercise is diagnostic and reflective of cardiac function. Lack of heart rate response during exercise has been associated with signs and symptoms of heart failure and a poorer prognosis
OBJECTIVE: This study aims to determine variability in heart rate response to exercise among a cohort of patients with and without heart failure and with and without significant coronary artery disease based on the results of treadmill stress test, echocardiograms and coronary angiogram
METHOD: The cohort of patients was derived from 189 consecutive adults aged 20 to 80 referred for coronary angiography at SLMC from the year 2000 to 2004 who underwent baseline treadmill stress test and echocardiography. Patients were grouped into those with and without heart failure based on an ejection fraction value of d" 40 percent, with and without coronary artery disease based on the Dukes prognostic criteria. Patients with pacemakers, arrhythmia, anti-arrhythmic medications, beta-blockers, congenital and valvular heart disease were excluded. Symptom-limited treadmill testing was performed according to standard protocols. At each stage of exercise, resting heart rate, peak heart rate, heart rate at different workloads, heart rate during recovery, and estimated workload in metabolic equivalents (METS, where 1 MET = 3.5 ml/kg/min of oxygen consumption) were recorded. Chronotropic incompetence was assessed as failure to achieve 85 percent of the age-predicted maximum heart rate as well as by calculating the ratio of heart rate reserve (HRR) used to metabolic reserve (MR) used at peak exercise otherwise called "chronotropic index". The results were presented as means +/- SD. Differences between groups were assessed by analysis of variance (ANOVA) followed by Scheffe multiple comparisons test. Results were considered significant at p0.001 and p0.05 respectively
RESULTS: The resting heart rate was not significantly different among groups. Peak heart rate was significantly lower in patients with CAD and CHF and higher in normal and cardiomyopathic groups with the lowest heart rate seen in patients with heart failure and highest in cardiomyopathic group. The workload achieved, heart rate increase during exercise, and heart rate recovery was highest in the normal group followed by the myopathic, the CAD and lastly the CHF group. In terms of chronotropic incompetence, more patients with ischemic heart failure have chronotropic incompetence than the CAD and normal patients while all patients in the cardiomyopathic group do not have chronotropic incompetence. Patients with chronotropic incompetence have a lower heart rate response to exercise. However, even in patients without incompetence, our results are the same with the heart failure and CAD group having the lowest heart rate response compared to the normal and the myopathic group. Lastly, the presence of diabetes does not affect the heart rate response of patients to exercise
CONCLUSION: At rest, heart rate of the four groups under study do not have any significant difference. With increasing workload, at peak heart rate and during the recovery period, heart rate response is variable dependent on the etiology and severity of cardiac dysfunction. Normal and cardiomyopathic patients have higher heart rates than patients with ischemic heart disease. The lowest heart rate is noted in patients with ischemic heart failure. Chronotropic incompetence occurs more frequently in patients with CAD and ischemic heart failure and may be responsible for the attenuated heart rate response to exercise in these subsets of patients. Overall, knowing the heart rate response of a patient during treadmill exercise gives us an idea of the etiology as to whether the heart is normal, ischemic or non-ischemic and the severity of cardiac dysfunction as to whether it is in failure or not. (Author)

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