Low chronotropic response in post-myocardial infarction exercise test predicts worse prognosis in patients with preserved or mildly reduced left ventricular ejection fraction

Abstract

Abstract Background Chronotropic incompetence is common in post-myocardial infarction (MI) patients and is associated with reduced exercise capacity. However, its prognostic significance and a determination of threshold values for prognosis remain unclear. Methods & Results We assessed 96 post-MI patients 4 weeks after their initial event with left ventricular ejection fraction (LVEF) ≥ 40%. All patients underwent combined stress echocardiography and cardiopulmonary exercise tests. The chronotropic response was measured as a percent of the maximal predicted heart rate at peak exercise (%MPHR). Exclusion criteria included patients with exercise limitations for pulmonary or peripheral reasons and those who declined to complete the study. Follow-up was conducted in 86 patients. The primary outcome measured was a composite of all-cause mortality or hospitalization for ischemic heart disease events (acute MI, unstable angina, or revascularization procedures) or heart failure exacerbation. The median follow-up duration was 4.0 (IQR 2, 5.6) years. The median patient age was 60 (IQR 53, 65) years, 64% of patients were males, and 84% were on beta-blockers. Median LVEF was 57 (IQR 51, 62)%, and median peak VO2 was 19 (IQR 15, 22) mL/kg/min. There were 15 composite end-point events, including 3 deaths, during the follow-up period. The %MPHR threshold of 67% had the best predictive value with an area under the curve (AUC) of 77% for predicting the primary outcome (PPV 31%, NPV 97%, sensitivity 93%, specificity 55%). A significant difference (p = 0.0022) in the occurrence of the composite end-point was noted between patients with a %MPHR below versus above this threshold (Figure. Kaplan-Meier curves for survival free of primary outcome). In the multivariate Cox regression analysis adjusting for demographic, clinical variables, and beta-blocker doses, only chronotropic response and current smoking correlated with the primary end-point (Table. The Cox proportional hazards regression model for prediction of the primary outcome). Conclusions A low chronotropic response to exercise is a negative prognostic marker in post-myocardial infarction patients with either preserved or mildly reduced left ventricular ejection fraction.Figure.Table.