High intensity interval training for heart failure with preserved ejection fraction: High hopes for intense exercise

Example of high intensity interval training and moderate continuous training protocols. In HIIT, a 5–10 min warm-up at moderate intensity (50–60% of peak VO2, 50–70% of peak heart rate) is followed by four intervals of 4 min at high training intensity (80–90% of peak VO2, 90–95% of peak heart rate), interspaced by 3 min active recovery at moderate intensity. In MCT, moderate intensity is maintained continuously throughout the training session. When comparing both modalities, the duration of MCT is prolonged to match the energy expenditure of a HIIT session. HIIT: high intensity interval training; MCT: moderate continuous training; VO2: oxygen uptake It took several decades before exercise training was considered as a therapy for patients with cardiovascular disease, let alone high intensity exercise. HIIT was first introduced in coronary artery disease (CAD) patients and chronic heart failure patients in the 1990s by Katharina Meyer in Germany’s Bad Krozingen.1,2 A new wave of curiosity and excitement started after scientists from Trondheim (Norway) showed a spectacular superior cardiovascular effect of HIIT in the first prospective randomized clinical trials.3,4 A 12-week HIIT protocol was more effective than moderate continuous training (MCT) matched for energy expenditure, increasing aerobic capacity in CAD and heart failure patients, and improving left ventricular remodelling, endothelial function and quality of life in heart failure patients. These superior effects of HIIT were also translated to non-cardiovascular diseases: HIIT showed improvement in metabolic, cognitive and parameters, but all in small single-centre studies.5,–7 In an attempt to confirm these initial results, European multicentre randomized clinical trials were started. The Study of MyocArdial Recovery afTer EXercise training in HF (SMARTEX-HF) included more than 200 heart failure patients with reduced ejection fraction (HFrEF), and adopted the same HIIT protocol, but could not confirm the spectacular results. HIIT and MCT equally improved aerobic capacity at 12 weeks, an improvement which was unfortunately not maintained up to 52 weeks.8 Using the same protocol in 200 patients with CAD and normal ejection fraction, the multicentre Study on Aerobic INTerval EXercise training in CAD (SAINTEX-CAD) showed that HIIT and MCT equally improved aerobic exercise capacity, endothelial function and quality of life.9 In these and other studies training patients with normal ejection fraction, HIIT appeared to be safe and well-tolerated.4,9 Meta-analyses only add to the confusion, confirming the small benefit in aerobic capacity for HIIT versus MCT seen in small studies, but refuting superiority on other endpoints.10,11 Heart failure patients with preserved ejection fraction (HFpEF) is a third group deserving our attention to measure the effect of HIIT. Most of these patients exhibit several pathophysiological abnormalities, including cardiac (diastolic dysfunction, reduced cardiac output reserve, atrial fibrillation, and coronary artery disease) and non-cardiac aspects (reduced vasodilation, arterial stiffness, ventilatory dysfunction, skeletal myopathy, and renal dysfunction).12 HFpEF patients are characterized by marked exercise intolerance, dyspnoea and reduced quality of life which are of comparable magnitude with what is found in HFrEF patients.13 To date, standard pharmacological therapy has failed to improve prognosis in HFpEF, but aerobic exercise has demonstrated a consistent benefit in aerobic capacity and quality of life.14 In this issue of the journal, Donelli da Silveira et al. show that in their centre, HIIT induces a superior improvement of aerobic capacity in HFpEF patients compared with MCT.15 Although this trial was small (19 patients) and non-controlled, this study puts HIIT forward as a potential exercise modality for HFpEF patients. The authors have to be congratulated for their excellent results in protocol adherence: patients in the MCT group exercised at 67% ± 4% relative training intensity, compared with 88% ± 4% in the HIIT group (p < 0.001).15 Over 80% of the training sessions were performed at the prescribed intensity. Poor adherence to the prescribed protocol has been the most frequently cited reason why the large SMARTEX-HF and SAINTEX-CAD trials failed to show a superior effect of HIIT. HFpEF patients are often elderly and have many comorbidities, thus they are a challenging population to provide exercise training to. These patients have often been sedentary for a very long time, are frequently obese, and have motion-limiting comorbidities. This is proven again in this study: the authors screened 445 patients but could only randomize 24. During training, another five patients (20% of the study population) had to abandon training. Thus, it is safe to say the superior effect of HIIT on aerobic capacity is found in a highly selected population of HFpEF patients. Also, let us not forget that patients with heart failure, whether with reduced or preserved ejection fraction, are usually not interested in maximal exercise capacity. Their goal is to perform sub-maximal activities in daily life without getting short of breath. So, in the meantime, let us improve their quality of life by combining their cardiorespiratory training with strength training of both skeletal and respiratory muscles.16,17 Altogether, it seems that in CAD and HFrEF, the ‘high hopes’ set by small trials were substantially downsized by subsequent large randomized clinical trials. Let us hope that the recently completed large multicentre Optimising Exercise Training in Prevention and Treatment of Diastolic Heart Failure trial will, this time, confirm the ‘high hopes’ for HIIT in HFpEF patients.18 The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. The author(s) received no financial support for the research, authorship, and/or publication of this article.