Dynamic characteristics of heart rate during a functional six-minute walk test in patients with Chronic heart failure

Objective: to perform a comparative analysis of heart rate (HR) spectral indices during the six-minute walk test (6MWT), considering β-blocker intake, and to determine parameters capable of characterizing cardiac contractility and chamber dimensions in chronic heart failure (CHF). Materials and Methods. The study involved patients with stable CHF of either ischemic or hypertensive etiology: those receiving β-blockers (the main group) and those who had refrained from β-blocker use for over one month before undergoing the 6MWT (the control group). All participants completed Doppler echocardiography and the 6MWT. Spectral indices of HR within the frequency range [0; 1] Hz were measured at every stage of the 6MWT. Evaluated parameters included the ratio of predominant frequencies in the spectrum for stages II vs. I (fII/I), stages II vs. IV (fII/IV) of the 6MWT, and mean HR recovery time. Results. No statistically significant correlations were identified between HR frequency composition ratios, Doppler echocardiography metrics, and the NYHA class of CHF in the main group. However, in the control group, a larger left ventricular ejection fraction correlated positively with increased fII/I ratios and reduced HR recovery times. Conclusion. The spectral characteristics of HR during the 6MWT could serve as markers of compliance with β-blocker treatment and might indirectly indicate cardiac contractility and chamber size in CHF patients not currently using β-blockers.