Author - James P. MacNamara, M.D., M.S.C.S.
”The HIIT-HCM trial is the first study to show that patients with HCM can safely improve their fitness with high-intensity exercise.” – James P. MacNamara, M.D., M.S.C.S.
Hypertrophic cardiomyopathy (HCM) is a common, inherited condition defined by abnormal thickening of the heart muscle. For many years, participation in competitive sports was discouraged for patients with HCM due to a concern for sudden cardiac arrest, and conventional practice was to recommend patients with HCM avoid exercise altogether. Recent data has challenged this paradigm. The RESET-HCM trial demonstrated that moderate-intensity exercise was safe and effective for patients with HCM. In 2020, the AHA/ACC guidelines (co-authored by two UT Southwestern faculty, Jose Joglar, M.D., and Mark Link, M.D.) liberalized the recommendations regarding exercise training in patients with HCM and emphasized a shared decision-making process about the risks and benefits of high-intensity training. Many patients with HCM, particularly those with minimal symptoms, may want to perform high-intensity exercise to maintain fitness, but little data are available to guide the decision-making process.
At #AHA22, we presented the results of the randomized controlled HIIT-HCM trial, which I led in conjunction with Benjamin Levine, M.D., at the Institute for Exercise and Environmental Medicine (IEEM) and UT Southwestern. We evaluated the efficacy and safety of high-intensity exercise training (HIT) compared to moderate-intensity exercise training (MIT) in 15 patients with HCM. To assess safety, patients were continuously monitored for arrhythmias by an implantable loop recorder or pre-existing implantable cardiac defibrillator (ICD). We found that exercise, regardless of intensity, was safe and effective with an increase in fitness (measured bypeak oxygen consumption), no adverse clinical events, and no increase in arrythmias, including ventricular tachycardia. Patients who did HIT had a 40% greater improvement in fitness compared to MIT, though the overall response was variable among patients. Importantly, we found no evidence that exercise led to progressive left ventricular hypertrophy in patients with HCM; indeed, the hearts showed positive signs of exercise-induced eccentric remodeling after training.
The HIIT-HCM trial is the first study to show that patients with HCM can safely improve their fitness with high-intensity exercise. The gains in fitness from HIT were less than we would expect in a healthy adult, and larger studies will be needed to fully understand the risk of high-intensity exercise in patients with HCM. We are currently designing a new study to evaluate the mechanisms of how exercise training improves fitness in HCM to find the most effective approach to improving fitness for these patients. While the data presented at AHA are exciting, we caution that all patients with HCM should discuss their individual circumstances with their health care provider before starting an exercise program.
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