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

Objective: to conduct a comparative analysis of the spectral indices of heart rate (HR) during the sixminute walk test (6MWT), depending on β-blocker intake, and to identify parameters capable of characterizing the contractile function and chamber sizes of the heart in chronic heart failure (CHF). Materials and methods. The study included patients with compensated CHF of ischemic or hypertensive origin: patients taking β-blockers (main group) and patients who had not taken β-blockers for more than 1 month prior to the 6MWT (comparison group). All participants underwent Doppler echocardiography and the 6MWT. At each stage of the 6MWT, spectral indices of HR were assessed in the frequency band [0; 1] Hz. The following were evaluated: the ratio of the most prominent frequencies in the spectrum for stages II and I (fII/I), stages II and IV (fII/IV) of the 6MWT, and the average HR recovery time. Results. In the main group of patients, no significant correlations were found between the ratios of the HR frequency composition, Doppler echocardiography parameters, and the functional class (FC) of CHF. In the comparison group, a higher left ventricular ejection fraction was associated with a greater fII/I ratio and a shorter HR recovery time. Conclusion. The frequency composition of HR during the 6MWT can serve as a marker of adherence to β-blocker therapy and can also indirectly characterize the contractile function and heart chamber sizes in CHF in the absence of β-blocker intake.