Assessment of Responsiveness to Cardiac Resynchronization Therapy: A Novel and Simple Exercise Approach

In this work, the heart rate recovery index (HRRI), a novel exercise test parameter, was evaluated as a potential predictor of cardiac resynchronization therapy response (CRT). We hypothesize that ET may be practical and applicable to study by analyzing the time ratio between the acceleration and deceleration of heart rate. Following implantation and every six months after that, patients who received a CRT device consecutively were monitored. The minimum and maximum heart rates, as well as the acceleration and deceleration periods, were used to measure an effort test (ET). The ratio of acceleration to deceleration time (AT/DT), or HRRI, was calculated and compared to the result. We used logistic regression to assess the predictive value of HRRI for responders and non-responders to CRT. The area under the curve (AUC) was computed to distinguish between positive and negative outcomes. A total of 109 patients (74 men, mean age 63.3 ± 9.8 years) were analyzed; permanent long-term fusion CRT pacing was possible in 65 patients. Patients were assigned to two groups: responders and non-responders (98/11 patients). During a mean follow-up of 36 months, 545 ETs were performed. HRRI was significantly higher in responders versus non-responders (3.16 ± 2 vs. 1.4 ± 0.5, p < 0.001). The optimal cutoff value for HRRI as a predictor of CRT response was 1.51 (area under the receiver operating characteristic (ROC) curve = 0.844). Responders had significant left-ventricular (LV) reverse remodeling (LV end-diastolic volume = 240 ± 90 mL vs. 217 ± 89 mL, p < 0.001) and higher LV ejection fraction (26 ± 5.8% vs. 35 ± 8.7%, p < 0.001). HRRI computation during routine ET is useful for the evaluation of responsiveness to CRT. The present study is the first to evaluate a novel parameter HRRI using HR behavior after cessation of exercise in patients with CRT; baseline and maximal HR could not predict CRT response, but the analysis of ET graphs in responders versus non-responders showed a better outcome corelated with improved response in heart HRR.