Improving Exercise Capacity in Recent Heart Transplant Recipients: Can a “HIT” Result in a Home Run?

Abstract

Heart transplantation is an established life-saving treatment for individuals with end-stage refractory heart failure. Although heart transplant recipients’ peak exercise oxygen uptake (Vo . 2peak) improves after surgery, it remains 40% to 50% lower than healthy age-matched control values.1 The lower Vo . 2peak after heart transplantation is the result of both central (cardiac denervation, diastolic dysfunction) and peripheral (vascular dysfunction, reduced skeletal muscle oxidative fibers, enzymes, and capillarity) abnormalities that limit O2 delivery and extraction by the exercising skeletal muscles.1 Decreased exercise tolerance may also have important prognostic implications, because heart transplant recipients with a median Vo . 2peak <19.6 mL/kg per minute have reduced long-term posttransplantation survival.2 Accordingly, an important goal of therapy in the early posttransplantation period is to optimize the exercise rehabilitation program to maximize improvements in Vo . 2peak. Randomized controlled exercise intervention trials performed to date have demonstrated that aerobic training performed alone or combined with strength training significantly increases Vo . 2peak in heart transplant recipients. 1 The magnitude of increase in Vo . 2peak can depend on the intensity of exercise training performed. 1,3 For example, high-intensity interval training (HIT) has been shown to be safe and timeefficient, and it elicits superior improvements in Vo . 2peak compared with traditional moderate-intensity continuous training in patients with cardiometabolic disorders,4 coronary artery disease,5 and heart failure.6 Completing multiple bouts of higherintensity exercise allows for a greater physiological stimulus and adaptations than moderate-intensity continuous training, which may be particularly beneficial for patients with an impaired cardiac output response to exercise.7,8 The HIT approach also produces greater improvements in cardiac and vascular function and skeletal muscle metabolism and has been shown to be more enjoyable than moderateintensity continuous training, which may encourage long-term adherence.9 Currently, no study has examined the safety, feasibility, and efficacy of HIT initiated in the early period after heart transplantation. In this issue of Circulation, Nytrøen and colleagues10 aimed to fill this important knowledge gap by assessing whether HIT introduced early after heart transplantation surgery was safe and effective for increasing Vo . 2peak and healthrelated quality of life and whether these improvements were superior to traditionally prescribed moderate-intensity continuous training. To achieve this aim, the authors conducted a multicenter, prospective, randomized controlled exercise intervention trial that included 81 clinically stable heart transplant recipients recruited from 3 medical centers (Copenhagen, Denmark; Gothenburg, Sweden; and Oslo, Norway). © 2019 American Heart Association, Inc.