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BySteven Lome, MD
Fact checked byErik Swain

Hypertrophic Cardiomyopathy Topic Review

BySteven Lome, MD
Fact checked byErik Swain

The hypertrophic cardiomyopathies include several diseases with different etiologies, all of which are characterized by abnormal thickening of the myocardium, most commonly in the interventricular septum.

These etiologies have a common pathology of “myocardial disarray” upon microscopic inspection.

Hypertrophic cardiomyopathy (HCM) is relatively common, with an estimated prevalence of 1 in 200 to 1 in 500 in the general population; however, only 10% to 20% of cases are clinically diagnosed. [Maron BJ, et al. J Am Coll Cardiol. 2022;2a; Ommen SR, et al. J Am Coll Cardiol. 2024;2331b] HCM can manifest clinically with heart failure (HF), life-threatening arrhythmias, atrial fibrillation (AF), mitral regurgitation and sudden cardiac death (SCD). Formerly considered an unrelenting disease with few treatment options and a grim prognosis, more sophisticated diagnostics and clinical advances have transformed HCM into a treatable condition with comparatively low morbidity and mortality if diagnosed in a timely manner. [Maron BJ, et al. J Am Coll Cardiol. 2022;2b; Maron BJ, et al. J Am Coll Cardiol. 2022-2;2a] In fact, the decline in recent years of SCD in patients with HCM has shifted focus to HF and complications from AF as the predominant morbidity and mortality concerns in this population. [Ommen SR, et al. J Am Coll Cardiol. 2024;2334b]

In 50% to 60% of cases, HCM is considered an autosomal dominant genetic disorder; it is the most common genetic cardiovascular disease. [Hurst’s The Heart 14th edition;1484a,c] More than 1,500 mutations in a number of different genes are known to be involved in the pathogenesis of HCM. [Hurst’s The Heart 14th edition;1484e] The majority of affected genes (40% to 60%) encode sarcomere proteins in the contractile apparatus of the myocardial cells. Most (75% to 80%) of HCM-related sarcomere protein gene mutations are found in MYBPC3 (which encodes the cardiac myosin binding protein C) and MYH7 (which encodes the cardiac beta-myosin heavy chain). [Hurst’s The Heart 14th edition;1484a,1485a] Some 5% to 10% of HCM cases are caused by mutations in other pathways or by non-genetic causes, including inborn errors of metabolism, neuromuscular or mitochondrial disease, malformation syndromes, amyloidosis and other causes. Significantly, 25% to 30% of cases do not yet have a known cause. [Hurst’s The Heart 14th edition;1485a] The 2024 American Heart Association/American College of Cardiology/Multisociety Guideline for the Management of Hypertrophic Cardiomyopathy estimates that 30% to 60% of patients with HCM have an identifiable or likely pathogenic genetic variant. [Ommen SR, et al. J Am Coll Cardiol. 2024;2333b,2334a]

In patients with HCM, the myocardial muscle is abnormally thickened by fibrous tissue. As a result of interstitial and replacement fibrosis, the myocytes are not able to align properly; “myocardial disarray” is the typical pathological description of HCM heart specimens. [Hurst’s The Heart 14th edition;1485c,1486c:]

Enlarge 
Example of myocardial disarray observed in patients with HCM.
Image: Adobe Stock

The highly variable natural history of HCM reflects its complex multifactorial etiology. [Hurst’s The Heart 14th edition;1497a] Functional left ventricular (LV) outflow obstruction during systole is common, and results in increased LV systolic pressure, which in turn causes an array of pathophysiological processes (including high wall stress, ventricular relaxation prolongation, impaired LV filling, LV diastolic pressure elevation, secondary mitral regurgitation, myocardial ischemia and cardiac output reduction). [Nishimura RA, et al. Circ Res. 2017;2b] Approximately two-thirds of HCM cases are obstructive HCM; about one-third will have hemodynamic LV outflow obstruction and one-third has “latent” obstruction that becomes apparent with provocation, while the remaining third do not have LV outflow obstruction and are therefore termed nonobstructive HCM. [Nishimura RA, et al. Circ Res. 2017;2c] Distinguishing between obstructive HCM and nonobstructive HCM is important because effective treatment options (eg, septal reduction, mavacamten, etc) exist for oHCM, while options are more restricted for nHCM. [Nishimura RA, et al. Circ Res. 2017;2d]

In a minority (approximately 5%) of patients, HCM may progress over time into systolic HF, defined by a LV ejection fraction (LVEF) below 50%; this phase is called “burnt out HCM” and carries a poor prognosis, with a high risk for SCD or death from HF. [Hurst’s The Heart 14th edition;1498b]

Diagnosis

The clinical diagnosis of HCM is typically made with direct imaging of the hypertrophied interventricular septum; echocardiography and cardiac magnetic resonance (CMR) are synergistic imaging modalities for diagnosis. [Maron BJ, et al. J Am Coll Cardiol. 2022;2a,4a] Echocardiography is used to characterize systolic anterior motion, mechanical impedance and other mechanisms of LV outflow obstruction. [Maron BJ, et al. J Am Coll Cardiol. 2022;4b] Because of its high spatial and temporal resolution and quantitative contrast capacity, CMR (in centers with the technical capacity and experience) possesses additional advantages as a diagnostic modality; it is particularly helpful when echocardiographic images are suboptimal, allowing for a more detailed quantification of LV mass and function and more informative patient risk stratification. [Maron BJ, et al. J Am Coll Cardiol. 2022;6b,7a] An LV thickness or 15 mm or greater is consistent with HCM in most age groups; in young children, an LV thickness of 13 mm or greater (or a strong deviation from the mean value) would be consistent with HCM. In borderline cases (eg, an LV thickness of 13 mm to 14 mm in adolescents or adults), additional information may be required for a positive diagnosis, including family history of HCM, typical dynamic outflow obstruction and an abnormal ECG. [Maron BJ, et al. J Am Coll Cardiol. 2022;4a-b]

A standard 12-lead ECG should be included in the initial evaluation of HCM. [Maron BJ, et al. J Am Coll Cardiol. 2022;4a] The vast majority of patients with HCM (approximately 95%) have an abnormal ECG, although there is no typical common pattern. Repolarization abnormalities — such as ST-segment depression and T-wave inversion — are the most common findings. Other common abnormalities include left-axis deviation (up to 30% of patients), pathologic Q waves (25% to 30% of patients) and increased QRS voltage (estimates of 30% to 75% of patients). [Hurst’s The Heart 14th edition;1489a] Repolarization changes and other ECG abnormalities offer diagnostic clues in relatives of patients with HCM or in mutation carriers even before hypertrophy develops; ECG may thus be a useful modality in screening for “prehypertrophic” patients. [Hurst’s The Heart 14th edition;1492a]

Below are links to two ECG examples of obstructive HCM.

  1. Hypertrophic Obstructive Cardiomyopathy (HOCM) ECG (Example 1)
  2. Hypertrophic Obstructive Cardiomyopathy (HOCM) ECG (Example 2)

Physical Examination

Despite advanced imaging and clinical genetics, the physical examination remains an important part of the initial evaluation for HCM. [Maron BJ, et al. J Am Coll Cardiol. 2022;2b] Characterizing the murmur of obstructive HCM (LV outflow tract obstruction) has important clinical implications. The murmur is a high-pitched, crescendo-decrescendo, mid-systolic murmur usually heard best at the left lower sternal border; it typically ends before the second heart sound. The murmur of obstructive HCM does not radiate to the carotids like that of aortic stenosis (AS), but may radiate to the base and apex of the heart. The important auscultatory features of obstructive HCM that distinguish it from AS and mitral regurgitation relate to dynamic auscultation. [Hurst’s The Heart 14th edition;1489b-c]

Dynamic auscultation involves assessing the effects of increasing or decreasing venous return to the heart on the amplitude and duration of the systolic outflow murmur. During the strain phase of the Valsalva maneuver, the murmur of obstructive HCM increases. The strain phase decreases venous return and thus decreases LV filling, resulting in more severe LV outflow tract obstruction and a louder murmur in patients with obstructive HCM. However, this response depends on the patient’s ability to perform the Valsalva properly, and may not occur in all patients. [Hurst’s The Heart 14th edition;1489d]

As an alternative, the response to the stand-squat-stand position may be more diagnostically reliable. [Hurst’s The Heart 14th edition;1489d] Rapidly squatting from a standing position increases venous return and decreases the obstructive HCM murmur. Promptly standing up from the squatting position results in sudden pooling of blood in the legs, decreasing venous return with an increase in the obstructive HCM murmur. [Hurst’s The Heart 14th edition;1489d] In contrast, with aortic valvular stenosis, the murmur will get softer with Valsalva or standing from squatting because less blood is being ejected through the aortic valve.

A post-premature ventricular contraction (PVC) beat with a compensatory pause will prolong LV filling time. This has a similar effect to increased venous return, resulting in decreased intensity of the murmur of obstructive HCM.

Treatment

Clinical profiles and management strategies

A 2022 review published by a panel of experts in the Journal of the American College of Cardiology (JACC ) subdivides HCM into four distinct “adverse pathways”, each of which is associated with a specific management strategy. These include: [Maron BJ, et al. J Am Coll Cardiol. 2022-2;3a]

  • Sudden death (prevention)
  • Progressive HF (obstructive)
  • Progressive HF (nonobstructive)
  • AF

Most patients with HCM fall into just one of the above categories, with only approximately 10% concurrently falling into two or more. [Maron BJ, et al. J Am Coll Cardiol. 2022-2]

Enlarge 
HF algorithm from the 2024 ACC/AHA/Multisociety Guideline for the Management of Hypertrophic Cardiomyopathy.
Source: Ommen SR, et al. J Am Coll Cardiol. 2024;doi:10.1016/j.jacc.2024.02.014. Published with permission.

Historically, SCD has been the most devastating outcome in younger patients with HCM; in recent decades, great progress has been made in reducing the incidence of SCD in HCM, based primarily on better risk assessment and stratification, and the introduction of implantable cardioverter defibrillator (ICD) devices. [Maron BJ, et al. J Am Coll Cardiol. 2022-2;3b;4a-b] The JACC-recommended SCD prevention algorithm consists of assessing for AHA/ACC risk factors (more information in the ICD section below), with the following management strategies: [Maron BJ, et al. J Am Coll Cardiol. 2022-2;5a]

  • In patients without risk factors, risk assessment should be performed annually but no ICD implantation is required [Maron BJ, et al. J Am Coll Cardiol. 2022-2;5a]
  • In patients with one or more major risk factors, an ICD should be implanted for the primary prevention of SCD [Maron BJ, et al. J Am Coll Cardiol. 2022-2;5a]
  • In patients who fall into a risk “grey area”, an ICD may be implanted following a shared discussion taking into consideration both the physician’s assessment and the patient’s perception of risk [Maron BJ, et al. J Am Coll Cardiol. 2022-2;5a]
  • In patients with prior cardiac arrest or sustained ventricular tachyarrhythmia, an ICD should be implanted for the secondary prevention of SCD (no risk assessment is required) [Maron BJ, et al. J Am Coll Cardiol. 2022-2;5a]

The 2024 AHA/ACC guideline recommendations on ICD placement are similar. The guideline states that ICDs should be implanted for patients with HCM and prior cardiac arrest or sustained ventricular tachyarrhythmia; that it is reasonable to implant an ICD in a patient with HCM and at least one major risk factor for SCD; that an ICD may be considered in patients with HCM and extensive late gadolinium enhancement by contrast-enhanced CMR imaging or nonsustained ventricular tachyarrhythmia present on ambulatory monitoring; that an ICD should not be implanted in a patient with HCM but no risk factors for SCD; that an ICD should not be implanted in a patient with HCM for the sole purpose of participating in competitive athletics; and that shared decision-making should be performed at every step of the process. [Ommen SR, et al. J Am Coll Cardiol. 2024;2360-61]

The management of progressive HF in patients with HCM depends on whether the disease is obstructive or nonobstructive. For obstructive HCM, the JACC expert panel recommends the following management strategies: [Maron BJ, et al. J Am Coll Cardiol. 2022-2;4a]

  • In patients who are asymptomatic, no pharmacologic or other therapy is required; although some pediatric cardiologists use beta-blockers prophylactically, there is little evidence to support this practice [Maron BJ, et al. J Am Coll Cardiol. 2022-2;4a,12b]
  • In patients with symptoms of HF, such as exertional dyspnea or fatigue, pharmacological therapy is indicated; beta-blockers are the first-line therapy, but other negative inotropic drugs including verapamil and disopyramide are also useful; the recommendations of the panel pre-date the approval of mavacamten (Camzyos, Bristol Myers Squibb), which is currently approved for use in this setting (more information in the Medical Therapy section below) [Maron BJ, et al. J Am Coll Cardiol. 2022-2;4a,12c]
  • In patients who progress to drug-refractory symptoms, mechanical therapy (more details in the Mechanical Therapy section below) at an experienced center is recommended, including surgical myectomy and, in patients who have advanced age, major comorbidities or a strong aversion to surgery, alcohol septal ablation. [Maron BJ, et al. J Am Coll Cardiol. 2022-2;4a]

Options for patients with nonobstructive HCM are more limited. For the distinct minority (5% to 10%) of patients with nonobstructive HCM who progress to severe (NYHA class III/IV) HF symptoms, cardiac transplantation offers the most effective option. [Maron BJ, et al. J Am Coll Cardiol. 2022-2;16a,18b] The JACC expert panel recommends the following management strategies for patients with nonobstructive HCM: [Maron BJ, et al. J Am Coll Cardiol. 2022-2;4a]

  • In patients who are asymptomatic (the vast majority of patients with nonobstructive HCM), no drug therapy is required [Maron BJ, et al. J Am Coll Cardiol. 2022-2;4a,18b]
  • Patients with mild symptoms (NYHA class I-II) and preserved EF can be managed pharmacologically with beta-blockers or verapamil [Maron BJ, et al. J Am Coll Cardiol. 2022-2;4a,18b]
  • Patients with preserved EF who progress to NYHA class III-IV symptoms should be pharmacologically managed with diuretics [Maron BJ, et al. J Am Coll Cardiol. 2022-2;4a]
  • Patients with reduced EF (< 50%) – end-stage HCM – should be pharmacologically managed with ACE inhibitors/angiotensin II receptor blockers, beta-blockers, spironolactone and diuretics [Maron BJ, et al. J Am Coll Cardiol. 2022-2;4a,18b]
  • Patients with end-stage HF (with or without systolic dysfunction) should be considered for cardiac transplantation as the only definitive approach to restore an acceptable quality of life; an ICD may be implanted as a bridge to transplant [Maron BJ, et al. J Am Coll Cardiol. 2022-2;4a,18b,19a-b]

Although comparatively more common in patients with HCM than in the general population, AF carries a low mortality risk in HCM and can be effectively managed with pharmacologic agents, catheter ablation or a surgical maze procedure. [Maron BJ, et al. J Am Coll Cardiol. 2022-2;19b] The JACC expert panel recommends the following for the management of AF in patients with HCM: [Maron BJ, et al. J Am Coll Cardiol. 2022-2;6a]

  • In patients with paroxysmal or persistent AF that is asymptomatic or mildly symptomatic, beta-blockers and/or calcium channel blockers should be used to achieve rate control [Maron BJ, et al. J Am Coll Cardiol. 2022-2;6a]

In patients with moderately to severely symptomatic AF with infrequent paroxysmal episodes, the management strategy depends on the frequency of paroxysmal episodes:

  • Infrequent paroxysmal episodes can be managed with rate control using beta-blockers and/or calcium channel blockers [Maron BJ, et al. J Am Coll Cardiol. 2022-2;6a]
  • Frequent paroxysmal episodes or persistent AF should be managed with antiarrhythmic drugs (amiodarone, disopyramide, sotalol or dofetilide) and/or with ablation (typically catheter ablation or a maze procedure if surgical myectomy for heart failure symptoms is also planned) [Maron BJ, et al. J Am Coll Cardiol. 2022-2;6a,16b,20a]

The 2024 AHA/ACC guideline makes the following recommendations for management of AF in patients with HCM: [Ommen SR, et al. J Am Coll Cardiol. 2024;2370-71]

  • In patients with HCM and clinical AF or subclinical AF lasting 24 hours or more, anticoagulation is recommended (class 1 recommendation), with direct oral anticoagulants as the first-line option and vitamin K antagonists as the second-line option, regardless of CHA2DS2-VASc score.
  • Patients with HCM and AF who require rate control should have a beta-blocker, verapamil or diltiazem (class 1 recommendation).
  • In patients with HCM and subclinical AF lasting more than 5 minutes but less than 24 hours, anticoagulation may be considered (class 2a recommendation), with direct oral anticoagulants as the first-line option and vitamin K antagonists as the second-line option, regardless of CHA2DS2-VASc score.
  • In patients with HCM and poorly tolerated AF, a rhythm control strategy with cardioversion or antiarrhythmic drugs may be considered (class 2a recommendation).
  • In patients with HCM and poorly tolerated AF needing a rhythm control strategy, catheter ablation may be considered if antiarrhythmic drugs are ineffective, contraindicated or not preferred by the patient (class 2a recommendation).
  • In patients with HCM and AF undergoing surgical myectomy, a concomitant surgical AF ablation procedure can be beneficial for rhythm control (class 2a recommendation).

Treatment modalities: Implantable cardioverter defibrillator

Many young patients with HCM have an elevated risk for sudden cardiac death. Historically, the rate of sudden death has been approximately 0.9% per year. The introduction of ICDs at the turn of the 21st century changed the SCD prevention paradigm, and SCD incidence has dropped to the current level of approximately 0.5% per year. [Maron BJ, et al. J Am Coll Cardiol. 2022-2;4a,5a] Implantation of an ICD is not recommended in all patients with HCM, however; the decision is complex and requires careful risk assessment; the 2024 HCM guideline recommends patients actively participate in the decision-making process, and that a “thorough and balanced discussion of the evidence, benefits and estimated risks” take place. [Maron BJ, et al. J Am Coll Cardiol. 2022-2;5a; Ommen SR, et al. J Am Coll Cardiol. 2024;2355]

The JACC expert panel recommends implantation of ICD for SCD prevention if any of the following risk factors are present: [Maron BJ, et al. J Am Coll Cardiol. 2022-2;5b]

  • Recent unexplained syncope (with or without outflow obstruction)
  • History of SCD related to HCM in a close relative
  • Thin-walled akinetic or dyskinetic LV apical aneurysm with regional scarring
  • Repeated and/or prolonged episodes of nonsustained ventricular tachycardia on ambulatory monitoring
  • Extensive fibrosis as indicated by late gadolinium enhancement, including end-stage progression
  • LV wall thickness ≥ 30 mm

Note that none of the above six risk factors is present in every patient at risk of SCD. [Maron BJ, et al. J Am Coll Cardiol. 2022-2;5b]

The 2024 HCM guideline recommends (Class 1 recommendation) that patients with HCM and a previous cardiac arrest or sustained ventricular tachycardia receive an ICD. It states that it is reasonable (Class 2a recommendation) to offer an ICD to patients with HCM and at least one of the following major risk factors: definite or probable SCD due to HCM in at least one close relative aged 50 years or younger, massive LV hypertrophy (≥ 30 mm) in any LV segment, at least one recent episode of syncope suspected to be due to an arrhythmic cause, an LV apical aneurysm with transmural scar or late gadolinium enhancement or LV systolic dysfunction (defined as EF < 50%). [Ommen SA, et al. J Am Coll Cardiol. 2024;2355]

Implantation of an ICD may also be useful as a bridge to heart transplantation in patients with end-stage HCM. [Maron BJ, et al. J Am Coll Cardiol. 2022-2;19b]

Treatment modalities: Medical therapy

Medical therapy is the mainstay of HF symptom control in patients with both obstructive and nonobstructive HCM. [Maron BJ, et al. J Am Coll Cardiol. 2022-2;4a] There are no large randomized clinical trials available to evaluate different drug therapies in symptomatic patients with HCM. Since most symptoms of obstructive HCM are related to LV outflow tract obstruction, which occurs during systole, medical therapy is aimed at lowering the heart rate to allow better diastolic filling and using negative inotropic agents to decrease the force of contractility. In nonobstructive HCM, pharmacologic heart rate reduction and prolongation of LV filling to improve diastolic function are both beneficial. [Maron BJ, et al. J Am Coll Cardiol. 2022-2;12b]

Non-dihydropyridine calcium channel blockers such as verapamil are commonly used. These drugs slow the heart rate and decrease the inotropic force of LV contraction, relieving the symptoms of HCM.

Beta-blockers act via a mechanism similar to that of non-dihydropyridine calcium channel blockers, and are the usual first-line therapy for HF symptom control. Combining verapamil and beta-blockers is not recommended because of the potential for excessive bradycardia and hypotension. [Maron BJ, et al. J Am Coll Cardiol. 2022-2;15a]

Disopyramide has been used as a pharmacologic treatment option for HCM for over 4 decades. [Maron BJ, et al. J Am Coll Cardiol. 2022-2;12b] It has significant negative inotropic effects but is clinically considered an antiarrhythmic drug. It is typically used for HF symptom control if symptoms persist despite calcium channel blocker and beta-blocker therapy. [Verlinden NJ, et al. Phamacotherapy. 2015;1a] Because disopyramide enhances atrioventricular (AV) nodal conduction, if AF/flutter develop, it may be associated with rapid ventricular response rates. Accordingly, patients on disopyramide should take a non-dihydropyridine calcium channel blocker or beta-blocker concomitantly. [Verlinden NJ, et al. Phamacotherapy. 2015;5b] Disopyramide may also be used for rhythm control in the context of HCM-associated AF. [Maron BJ, et al. J Am Coll Cardiol. 2022-2;6a,21a]

Disopyramide can prolong the QT interval, resulting in polymorphic ventricular tachycardia in some patients. There are significant anticholinergic side effects including xerostomia (dry mouth), urinary retention, visual disturbances and decreased perspiration.

Mavacamten is a promising new drug for obstructive HCM. Mavacamten received FDA approval in April 2022, and is currently indicated for the treatment of adult patients with NYHA class II-III obstructive HCM to improve functional capacity and symptoms. [Camzyos package insert;1a,2a,9b; Keam SJ. Drugs. 2022;2a] It is a small molecule with strong negative inotropic effects that allosterically inhibits the cardiac myosin ATPase. This reduces myosin-actin crosslink formation and sarcomere hypercontractility which characterizes HCM. [Keam SJ. Drugs. 2022;2a; Maron BJ, et al. J Am Coll Cardiol. 2022-2;12a]

The pivotal phase 3 efficacy and safety trial of mavacamten in patients with obstructive HCM was EXPLORER-HCM, which randomly assigned a total of 251 patients (18 years or older) to either mavacamten (starting oral dose 5 mg once daily, titrated to a final oral dose of 2.5 mg, 5 mg, 10 mg or 15 mg once daily; 123 patients) or a matching placebo (128 patients). Importantly, eligibility criteria included a LV ejection fraction of 55% or greater and NYHA class II or III symptoms. [Olivotto I, et al. Lancet. 2020;3a,5a] Mavacamten treatment resulted in comparative symptomatic and functional improvement: In the mavacamten group, 37% of patients achieved the primary endpoint (a composite endpoint of ≥ 1.5 mL/kg/min increase in peak oxygen consumption and ≥ 1 NYHA class reduction or ≥ 3.0 mL/kg/min increase in peak oxygen consumption and no increase of NYHA class), compared with 17% of patients in the placebo group (P = .0005). [Olivotto I, et al. Lancet. 2020;4a,5b] Mavacamten was generally well tolerated in EXPLORER-HCM, with a safety profile similar to that of placebo. [Olivotto I, et al. Lancet. 2020;10a-b] A long-term (5 year) safety and efficacy trial of mavacamten, MAVA-LTE, is currently ongoing; MAVA-LTE will include patients from EXPLORER-HCM and MAVERICK-HCM, a phase 2 trial in patients with nonobstructive HCM. [Keam SJ. Drugs. 2022;3b,6b]

The 2024 HCM guideline states (Class 1 recommendation) that cardiac myosin inhibitors can be added to therapy for patients who have persistent symptoms attributable to LV outflow tract obstruction despite use of beta-blockers or nondihydropyridine calcium channel blockers; other options for these patients include disopyramide plus an AV nodal blocking agent; or septal reduction therapy. [Ommen SA, et al. J Am Coll Cardiol. 2024;2360]

Treatment Modalities: Mechanical therapy

The two mechanical therapies to treat obstructive HCM are surgical myomectomy and catheter-based alcohol septal ablation, collectively known as septal reduction therapy.

The JACC expert panel recommends mechanical therapy for obstructive HCM when symptoms of HF persist despite optimal medical therapy. [Maron BJ, et al. J Am Coll Cardiol. 2022-2;4a]. The 2024 HCM guidelines recommend (Class 1 recommendation) septal reduction therapy performed at an experienced HCM center for patients with obstructive HCM who remain symptomatic despite optimal medical therapy, and state it may be considered (Class 2b recommendation) for patients who remain symptomatic but do not want to escalate medical therapy.

In surgical myectomy, also known as septal myectomy, the surgeon removes a hypertrophied segment of the interventricular septum, relieving the outflow tract obstruction. In most cases, this entails a transaortic resection of a limited amount of muscle from the proximal to mid-septal region. [Hurst’s The Heart 14th edition;1498d] If there is mid-cavity obstruction, a more extensive myectomy may be required, sometimes including papillary muscle reduction. [Hurst’s The Heart 14th edition;1498e] Complications are rare, but may include a ventricular septal defect (if too much tissue is removed), LV dysfunction (if other myocardial segments are damaged during surgery) or the development of complete heart block (due to injury of the AV node). Mortality is below 1% in experienced centers. [Hurst’s The Heart 14th edition;1498f]

Alcohol (ethanol) septal ablation (ASA) is a catheter-based, minimally invasive intervention during which the septal perforator coronary arteries are identified and intra-coronary alcohol is infused, resulting in thrombosis and infarction of the interventricular septum. The infarcted tissue remodels to become thinner, thus relieving the outflow tract obstruction. [Hurst’s The Heart 14th edition;1499a] Complications can be serious and may include complete heart block, ventricular arrhythmias, sudden cardiac death, coronary dissection/perforation resulting in pericardial effusion and LV systolic dysfunction. [Hurst’s The Heart 14th edition;1500d]

As yet, no direct randomized trial data comparing the above two procedures are available, though in a retrospective study of 3,859 patients with obstructive HCM who underwent one of the procedures at three centers from 1998 to 2019, ASA was linked with increased long-term mortality vs. surgical myectomy [Cui H, et al. J Am Coll Cardiol. 2022;1a]. Observational data suggest that ASA has more variable results, with some patients achieving excellent results and others showing no benefit. Cardiovascular complications (complete heart block) are lower with surgical myectomy, but surgical complications (infection) are higher. Both procedures similarly improve symptoms of HF. ASA is more likely to result in the need for a second procedure. Because of these factors, the JACC expert panel recommends surgical myectomy over ASA, except in older patients at risk for surgical complications, those with multiple high-risk comorbidities, or strong aversion to open-heart surgery. [Maron BJ, et al. J Am Coll Cardiol. 2022-2;4a,18a]

In the VALOR-HCM trial of patients with obstructive HCM who met guideline criteria for septal reduction therapy, mavacamten reduced the proportion of patients meeting the criteria after 16 weeks compared with placebo (Desai MY, et al. J Am Coll Cardiol. 2022;1a).

References:


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obstructive hypertrophic cardiomyopathy
heart failure
mitral regurgitation
arrhythmia
diastolic dysfunction
 

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