What's New in Hypertrophic Cardiomyopathy, With Gregory Weiss, MD

Gregory Weiss, MD

Hypertrophic cardiomyopathy or HCM is one of the most common genetic or congenital cardiac diseases. Affecting as many as 1 in 500 people HCM is characterized by large increases in cardiac mass, in particular, left ventricular mass.¹ Such enlargement predisposes seemingly healthy sufferers to sudden death at young ages. While HCM was first documented in the 1800s with quite a few scattered case reports to follow, it wasn’t until the late 1950s that Eugene Braunwald, MD, detailed the clinical characteristics, natural history, and hemodynamics of the condition.² Braunwald described the dynamic nature of the aortic outflow obstruction as well as the frequency of sudden death and its autosomal genetic transmission within families.² Finally in 1964, Braunwald along with his colleague Morrow published a lengthy monograph in Circulation that detailed their findings, including its pathophysiology as well as its medical and surgical treatment.³

Originally, the National Institutes of Health call this condition idiopathic hypertrophic subaortic stenosis. Without echocardiography in the beginning, the diagnosis was made purely based on history and physical exam with the mainstay of surgical treatment being open heart surgery for removal of excess muscle tissue. In 2020 the American College of Cardiology and the American Heart Association updated their 2011 guidelines for the diagnosis and treatment of patients with hypertrophic cardiomyopathy.⁴ While it is true that treatments for HCM have not changed very much in the last 50 years, strategies to manage it have made some important advances. Martin Maron, MD, director of the HCM Center at Tufts Medical Center, states,

“We're getting better and better at managing this disease – the risk of sudden cardiac death (SCD), arrhythmias, stroke prevention and reversal of refractory HF symptoms – and the new guideline explains all this.”

Among the take home points from the guideline update are strong recommendations for multi-disciplinary collaboration early on to catch the disease before sudden cardiac death (SCD) occurs.4 The guideline also recommends anticoagulation in patients with HCM and atrial fibrillation as these patients are a higher risk for stroke.4 Finally, the workgroup encourages an individualized approach to diagnosis and treatment especially when working with children at risk.4

So, what is new for the 2020 guidelines? Mihelle Kittleson, MD, PhD is the director of postgraduate education in heart failure and transplantation at Cedars-Sinai. Kittleson points to the guideline and states,

“What has been bumped up in importance is an ejection fraction (EF) less than 50%, the presence of an LV apical aneurysm, and the presence of extensive gadolinium enhancement, which also emphasizes the increased importance given to the role of MRI in risk stratification. MRI in risk stratification.”¹

The update further stresses that referrals for internal cardioverter defibrillator (ICD) implantation or septal reduction therapies are crucial and that risk stratification and patient selection are key to preventing sudden cardiac death (SCD).¹ Maron adds,

"Risk stratification in HCM has matured to the extent that we can identify almost all patients today who are at risk of SCD and provide them with protection in the form of an ICD. This is a remarkable statement to make and light years different from a time not that long ago when you gave a patient a beta-blocker and hoped you didn't get a phone call that they had died.”¹

Yet another important change in the recommendations for 2020 relates to exercise. Previously, only low-intensity exercise was recommended but it was found that SCD was rare during exercise and now moderate intensity aerobic exercise is not only allowed but encouraged for most patients with HCM.¹

While the guideline update is clearly important a new drug called Mavacamten is poised to steal the HCM show. Mavacamten is a first-in-class, cardiac-specific myosin inhibitor that acts by reducing the number of available actin-myosin cross-bridges thus reducing excessive myocardial contractility.⁵ Patients treated with Mavacamten during the trial saw improvement in symptoms with 37% reaching the primary endpoint of a greater than or equal to 1.5mL/kg/min increase in peak oxygen consumption (pVO2) and at least one NYHA class reduction in heart failure symptoms.⁵ Daniel Jacoby, MD, founder and director of the cardiomyopathy program at Yale Medical School heralds this news by saying,

“We have never in the 60-year history of this disease had a prospective, randomized, double-blind, placebo-controlled medication trial of this size showing this magnitude of benefit.”

While this is clearly good news it should be noted that two-thirds of the study patients did not improve.

Hypertrophic cardiomyopathy represents a rather common congenital heart condition with a truly devastating course that has seen little advancement in treatment over the last 50 years. However, with better understanding, prompt referrals for counseling and treatment, and new therapies like Mavacamten, progress is being made. This progress offers hope and a better chance for improved quality of life for patients with HCM.

References:

1. https://www.acc.org/latest-in-cardiology/articles/2021/07/01/01/42/hypertrophic-cardiomyopathy-in-2021-new-insights-new-strategies-and-possibly-a-new-treatment
2. Braunwald E. Hypertrophic cardiomyopathy: The first century 1869-1969. Glob Cardiol Sci Pract 2012;2012:5. doi:10.5339/gcsp.2012.5
3. Braunwald E, Lambrew CT, Rockoff SD, Ross J, Morrow AG. Idiopathic hypertrophic subaortic stenosis. I. A description of the disease based upon an analysis of 64 patients. Circulation 1964;30:SUPPL 4:3-119.
4. https://www.jacc.org/doi/10.1016/j.jacc.2020.08.045?_ga=2.196522532.947864656.1627386722-1297874215.1626701851&
5. Olivotto I, Oreziak A, Barriales-Villa R, et al. Mavacamten for treatment of symptomatic obstructive hypertrophic cardiomyopathy (EXPLORER-HCM): a randomized, double-blind, placebo-controlled, phase 3 trial. Lancet 2020;396:759-69.