Which approach to exercise intensity prescription provides better outcomes of cardiac rehabilitation - percentage of heart rate reserve or ventilatory thresholds?

Abstract Background Exercise intensity prescription in cardiac rehabilitation (CR) is determined by calculating the training heart rate (THR) as percentage of heart rate reserve (HRR) using the Karvonen formula or by using metabolic zones (VT zone) based on ventilatory thresholds (VT) obtained during a cardiopulmonary exercise test (CPET). While the methods for determining THR are theoretically equivalent, they may differ significantly in cardiac patients. Purpose The aim of the study was to assess the differences in exercise capacity changes after CR between subgroups of patients training with exercise intensity determined according to HRR and VT zone. Methods From a single-center registry of 518 patients, 51 post-cardiac surgery patients and 186 inpatient rehabilitation subjects were excluded. Patients who completed 24 outpatient interval training sessions with telemonitoring according to a progressive regimen were included. The HRR subgroup was defined as THR in the range of 40–69% of HRR, while the VT zone subgroup as THR in the aerobic zone determined on the basis of VT in CPET (from the first VT to 50% of HR between first and second VT). The inclusion criteria included presence of twice CPET during CR. Data regarding training sessions and changes in CPET parameters before and after CR were analyzed. Results In comparison to the VT zone subgroup (n = 39, 32 male), HRR patients (n = 89, 63 male) were older - Table 1. There was no difference in the duration of daily training between HRR and VT zone. After calculating the THR for all analyzed patients, a significantly lower range of THR was found in the VT zone subgroup than in the HRR zone. No significant differences were noted in the upper THR between subgroups. The VT zone subgroup showed greater improvement in exercise capacity than the HRR subgroup expressed as greater change in median peak VO2, peak oxygen pulse (VO2/HR), percent of predicted value of peak VO2 and peak VO2/HR, OUES and achieving lower RER and breathing reserve during CPET after CR - Table 1. The first VT was observed later (at greater HR and VO2) during second CPET when CR based on VT zone. No significant differences were found in duration of CPET, workload, ventilation parameters and HR at peak exercise. Conclusions Despite the same load of training sessions in CR program, patients recommended to train according to VT zone, in comparison to those prescribed based on HRR, presented greater improvement in exercise capacity.For image description, please refer to the figure legend and surrounding text.