“ High-Intensity Interval Training in Patients With Heart Failure With Reduced Ejection Fraction

Ulrik Wisløff, PhD Carl J. Lavie, PhD, MD Øivind Rognmo, PhD To the Editor: In a clinical setting, high-intensity exercise is found to be an effective way to improve cardiorespiratory fitness,1 and several studies have shown that exercise using high-intensity interval training (HIIT) in comparison with moderate-intensity continuous training (MICT) is more effective for improving health outcomes, including cardiac adaptations. We acknowledge the SMARTEX Heart Failure Study (Study of Myocardial Recovery After Exercise Training in Heart Failure) Group for their recent study2 aiming to translate experience and findings from a small-scale study3 into a multicenter setting. The conclusion was that a 12-week program of HIIT was not superior to MICT in changing left ventricular remodeling or cardiorespiratory fitness in patients with heart failure. It was further stated that the multicenter trial did not confirm results from the small previous study.3 There is a lot to learn from SMARTEX as discussed in the article, but it still remains unclear whether HIIT is superior to MICT in such heterogeneous heart failure populations. The majority of the SMARTEX participants randomly assigned to exercise did not perform HIIT (62 of 77 exercised at too low intensity) or MICT (33 of 65 exercised at too high intensity) according to the prescribed intensity. Thus, in SMARTEX, only 47 (33%) of the patients trained at the designed intensity protocol (49% and 20% in MICT and HIIT, respectively). We acknowledge that it may be difficult to administrate HIIT, in particular, in patients with heart failure, despite having experience in cardiac rehabilitation. It is noteworthy that the same problems were experienced in SAINTEX-CAD study (A Multicentre Trial on the Effectiveness of Physical Rehabilitation of Patients With Coronary Artery Disease: Aerobic Interval Training Versus Moderate Continuous Training)4 where patients randomly assigned to MICT and HIIT ended up training at higher and lower exercise intensities than prescribed. According to our experience, successful HIIT depends on some key factors. As described in the referenced smallscale study,3 we emphasized continuous control throughout the study to secure that the training intensity was correct according to prescription, not only based on heart rate measures, but also on the use of the Borg scale of perceived exertion at every training session, and recording blood lactate levels during some sessions, as well. In addition, it would have been advisable to perform frequent checks to ensure that the absolute training workload increases throughout the study period. For instance, we3 and others (eg,5) observed an increase in workload that equaled ≈1 and 2 W per training session in MICT and HIIT, respectively. The corresponding increases in SMARTEX were 0.28 and 0.42 W per session. Thus, the low increase in workload in the SMARTEX study, in particular, in the HIIT group, could explain the moderate exercise response, and no difference between MICT and HIIT, as well. It is therefore our opinion that the conclusion: “HIIT was not superior to MICT in changing left ventricular remodeling or aerobic capacity. ” should be interpreted with caution, because the study did not succeed in adequately comparing the Letter by Wisløff et al Regarding Article, “High-Intensity Interval Training in Patients With Heart Failure With Reduced Ejection Fraction”