Significance of Heart Rate Profile during Treadmill Stress Test - A Critical Appraisal

Several studies have tried to correlate heart rate profile during treadmill stress test with presence and severity of coronary artery disease and long term prognosis. These studies have concluded that higher resting heart rate, inability to increase heart rate commensurate with increase in work load (chronotropic incompetence), and inadequate decline in heart rate after stopping exercise (abnormal heart rate recovery) are all associated with increased long term mortality. Detailed evaluation, however, shows that these studies had important limitations e.g.(i) failure to exclude subclinical myocardial ischemia and/or left ventricular dysfunction (ii) failure to exclude subclinical systemic diseases by thorough clinical and laboratory evaluation (iii) not excluding symptomatic patients (iv) failure to correlate heart rate parameters with clinical and electrocardiographic parameters (v) failure to correlate their observation with echocardiographic and angiographic findings (vi) failure to perform multivariate analysis to find independent significance of heart rate parameters. Therefore, these studies do not provide any conclusive evidence of any diagnostic or prognostic significance of various heart rate parameters observed during treadmill stress test. Well-designed studies are needed.