Dual Evaluation of Vagal Activity with Exercise Testing

Abstract

PURPOSE: Heart rate recovery (HRR), a recognized surrogate of vagal activity, has been shown to strongly predict all cause mortality. However, it only takes into account the physiological and autonomic changes that occur after exercise. We postulate that by considering the rate of heart rate increase during the 1st third of exercise and HRR, the prognostic power would be stronger. We therefore developed the heart rate slope (HR slope), denned as the slope of the linear relation between the initial increase in work rate and heart rate (vagal release). With this, our aim was to determine if the HR slope and HRR together have a better prognostic power than wither alone. METHODS: 1,415 consecutive patients undergoing treadmill testing for clinical reasons from 1997 to 2002 were studied. Heart rate and METs estimated from the ramp work rate were calculated during the first 3 minutes and regressed to calculate the HR slope. RESULTS: After a mean follow-up of 2.8± 1.8 years, there were 110 deaths. Age-adjusted HR slope was both univariately and multivariatley predictive of all cause mortality (multivariate HR = 1.24, 95% CI=1.08–1.42, p = 0.04. The combination of an HR slope >30 beats/MET and HRR <22 beats/MET at 2 minutes in recovery was particularly powerful in predicting mortality (hazard ratio 3.9, 95% CI 2.0–7.7, p<0.0001) with an annual mortality of 6.6%.FigureCONCLUSIONS: A dual evaluation of heart rate response to and after recovery from exercise has a better prognostic power than either alone.