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Updates to national guidelines for the management of hypertrophic cardiomyopathy (HCM) endorse cardiac myosin inhibitor use in certain cases, greenlight more intensive physical activity, and expand treatment options for young patients.

The American College of Cardiology (ACC) and the American Heart Association (AHA) published the guideline in the and , respectively.

"Recommendations for physical activity continue to evolve with research," Guideline Committee Chair Steve R. Ommen, MD, director of the Mayo Hypertrophic Cardiomyopathy Clinic in Rochester, Minnesota, said in a press release from the two organizations. "As part of a healthy lifestyle, patients with HCM are now encouraged to engage in low-to-moderate intensity physical activities. We're seeing how vigorous physical activities can be reasonable for some individuals. With shared decision-making between the clinician and the patient, some patients may even be able to return to competitive sports."

The updated document added a clear statement that "universal restriction from vigorous physical activity or competitive sports is not indicated." A class 2a recommendation said that vigorous recreational activities were reasonable after an annual checkup and shared decision-making with an "expert professional." A class 2b recommendation noted that competitive sports are OK to consider after a specialist with experience managing athletes with HCM reviews the patient's case, conducts an annual comprehensive evaluation, and weighs in on shared decision-making to balance potential benefits and risks.

"Challenging treatment decisions -- where reasonable alternatives exist, where the strength of recommendation is weak (e.g., any decision relying on a Class of Recommendation 2b) or is particularly nuanced (e.g., interpretation of genetic testing; primary prevention implantable cardioverter-defibrillator decision-making), and for HCM-specific invasive procedures -- may critically benefit from involving specialized HCM centers," the guideline authors noted.

In terms of treatment, cardiac myosin inhibitors were added as one of the class 1 options for patients with symptomatic obstructive HCM who do not get adequate symptom relief from first-line drug therapy (beta blockers or nondihydropyridine calcium channel blockers), although this only applied to adults. The guidelines caution that cardiac myosin inhibitors should be discontinued for HCM patients who develop persistent systolic dysfunction with a left ventricular ejection fraction under 50%.

However, the authors noted that this new class is monitored under the FDA's Risk Evaluation and Mitigation Strategies (REMS) program, "which may create additional steps and time for both the clinician and the patient. Clinicians require special training to prescribe the medication, and patients require regular screenings."

Several updates to the guidelines were also made for younger patients.

For those ages 45 and younger, valsartan was recommended to be considered (class 2b) for slowing adverse cardiac remodeling in patients with nonobstructive HCM due to a pathogenic or likely pathogenic cardiac sarcomere genetic variant.

The guidelines had previously recommended shared decision-making for consideration of implantable cardioverter defibrillators in HCM patients with one or more major risk factors for sudden cardiac death if they were at least 16 years old, but that age criterion was removed.

A new recommendation for pediatric HCM patients advised exercise stress testing to determine functional capacity and prognostication, regardless of symptom status, given that children may not describe symptoms readily. "New risk calculators, specific to children and adolescents, have been validated and can help young patients and their families contextualize their estimated risk of sudden cardiac death," the guideline authors wrote.

In addition, a contraindication warning was added for mavacamten (Camzyos) during pregnancy due to potential teratogenic effects.

In addition to the ACC and AHA, the guideline was developed in collaboration with and endorsed by the American Medical Society for Sports Medicine, the Heart Rhythm Society, the Pediatric & Congenital Electrophysiology Society, and the Society for Cardiovascular Magnetic Resonance.

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