Chronotropic incompetence predictors in a Cardiac Rehabilitation Program following myocardial infarction

Abstract Background Chronotropic incompetence (CI) has been described in many patients after myocardial infarction (MI) and can negatively affect physical capacity, especially if negative chronotropic therapy (NCT) is prescribed. Prediction of CI after MI could be useful for tailored medical therapy and exercise training prescription. Purpose We aim to predict CI on initial exercise ECG testing (ExECG) in MI patients submitted to a Cardiac Rehabilitation Program (CRP). Methods Patients with ST-segment elevation MI (STEMI) or occlusion MI (OMI) submitted to our CRP were prospectively included. After an initial follow-up phase of clinical stabilization and medical therapy optimization, ExECG (conventional or cardiopulmonary) was performed. Peak VO2 and chronotropic reserve index [(maximum heart rate – resting heart rate) / ([220-age] – resting heart rate)] were measured. Chronotropic incompetence was defined as <80% chronotropic reserve index (≤62% in patients treated with NCT). Pharmacological therapy with NCT was registered in absolute and equivalent doses per bisoprolol 2.5mg units (B2.5EU). The effect of NCT on CI was studied by ANOVA test, and predictors of CI by binary logistic regression analysis. The model was tested by area under the curve (AUC) analysis in receiver operating characteristic curves. A p<0.05 was considered statistically significant. Results The cohort comprised 143 patients, mostly middle-aged (mean 60.3±15.8 years) males (85.3%) with anterior or inferior MI (44.8% and 44.8%, respectively). Mean left ventricular ejection fraction (LVEF) was 52.4±10.6% and 36.4% depicted LVEF<50%. NCT was prescribed in most patients (n=125, 87.4%), and median equivalent dose was 1 [0.5-1] B2.5EU. CI was noted on more than half of the population on initial ExECG (n=75, 52.4%). Higher NCT doses per B2.5EU associated with worse mean chronotropic reserve indexes: 72.8±24.4% in patients without NCT; 71.7±18.7% in patients with 0.5 B2.5EU; 62.8±18.2% in patients with 1 B2.5EU; and 58.7±16.9% in patients with ≥2 B2.5EU (ANOVA p=0.04). On binary logistic regression analysis, only two variables were independent predictors of CI: diabetes mellitus (HR 3.02 [1.26-7.23], p=0.01) and LVEF (0.97 [0.94-0.99] per increased %, p=0.04). However, the predictive power of the model was poor (AUC 0.62 [0.53-0.71], p=0.01). Conclusions Chronotropic incompetence after a MI is associated with lower LVEF, diabetes mellitus, and higher doses of NCT. Although significant interindividual variability exists in chronotropic response in the post-infarction period, these factors could be taken into consideration for tailored prescription (or deprescription), especially in patients who may not derive any prognostic benefit from NCT.Chronotropic incompetence in CRP