Heart Rate Recovery Index as a Novel Marker in Heart Failure Assessment: A Comparative Analysis of Heart Rate Deceleration During Exercise Testing.

Purpose: Heart rate recovery, measured during exercise testing, is an important marker of cardiovascular function. The Heart Rate Recovery Index, a recently proposed parameter derived from heart rate recovery, has shown predictive outcomes in patients undergoing cardiac resynchronization therapy. However, its role in heart failure identification remains unexplored. This study aimed to assess differences in the heart rate recovery index between patients with heart failure and individuals without heart failure undergoing exercise testing. Patients and Methods: 194 patients (mean age 58.3 ± 11.7 years; 57.7% men) with heart failure or other cardiovascular conditions requiring exercise testing were prospectively enrolled and underwent cycle ergometer testing. The index was calculated as the ratio between heart rate acceleration and deceleration time during exercise testing. Differentiation ability was assessed using receiver operating characteristic curve analysis. Subgroup and two-step cluster analyses examined heart rate recovery index differences across heart failure phenotypes and severity. Results: Heart Rate Recovery Index was significantly lower in heart failure patients compared to those without (1.87 ± 0.68 vs 2.65 ± 1.08, p < 0.01). An optimal HRRI cut-off of 2.225 identified heart failure, while a lower cut-off of 1.555 differentiated patients with mildly reduced and reduced ejection fraction from those with preserved ejection fraction (AUC = 0.647). The index correlated significantly with systolic and diastolic parameters on echocardiography. In multivariable analysis, it remained an important predictor of heart failure (p < 0.01). Cluster analysis identified four phenotypic groups, with the index helping to differentiate early or less severe from advanced heart failure, according to the ejection fraction. Conclusion: HRRI is a simple parameter that distinguishes the heart failure status and provides discrimination across its phenotypes. Its strong correlation with echocardiographic and functional markers supports its potential role in the assessment and characterization of heart failure.