What is the mortality benefit of surgery in a patient with Hypertrophic Obstructive Cardiomyopathy (HOCM)?

Mortality Benefit of Surgery in HOCM

Surgical septal myectomy in patients with hypertrophic obstructive cardiomyopathy (HOCM) and severe drug-refractory symptoms is associated with a 43% reduction in long-term mortality and adverse cardiac events compared to conservative management, with an operative mortality of less than 1% at experienced centers. 1, 2

Evidence for Mortality Benefit

The strongest evidence comes from a large observational study of 1,530 HOCM patients with severe left ventricular outflow tract (LVOT) obstruction followed for 8.1 years. 1 In this cohort:

• Surgery reduced the composite endpoint of cardiac death and/or ICD discharge by 43% (hazard ratio 0.57, P<0.01) when used as a time-dependent covariate in multivariable analysis 1
• 990 patients (65%) underwent surgical relief of LVOT obstruction with 0% 30-day mortality 1
• Surgical decision-making was based on intractable symptoms (73% were NYHA class II or greater) and impaired exercise capacity 1

At the Mayo Clinic, where over 3,000 septal myectomies have been performed since 1993, operative mortality for isolated septal myectomy is less than 1%—comparable to elective mitral valve repair—with dramatic symptomatic improvement in more than 90% of patients. 2

Who Benefits Most from Surgery

Guideline-Defined Eligibility Criteria

Surgery should only be performed in patients meeting ALL three criteria: 3

1. Clinical: Severe dyspnea or chest pain (NYHA class III-IV) or exertional syncope that interferes with daily activities despite optimal medical therapy 3

2. Hemodynamic: Dynamic LVOT gradient ≥50 mmHg at rest or with provocation, associated with septal hypertrophy and systolic anterior motion of the mitral valve 3

3. Anatomic: Sufficient anterior septal thickness to perform the procedure safely in the judgment of an experienced operator 3

Expanding Indications at Comprehensive Centers

Select patients with fewer symptoms but significant hemodynamic impairment may benefit from earlier surgery at comprehensive HCM centers (those with >90% success rates and <1% mortality). 3 Surgery can:

• Improve progressive pulmonary hypertension 3
• Reverse left atrial enlargement 3
• Decrease subsequent atrial and ventricular arrhythmias 3
• Ameliorate occult gastrointestinal bleeding 3
• Improve outcomes in those with marked exercise impairment 3

Surgical vs. Alcohol Septal Ablation

Surgical septal myectomy is the first-line invasive therapy and should be the primary consideration for most eligible patients. 3

When to Choose Surgery:

• Younger patients (especially <40 years old) 3
• Patients with marked septal hypertrophy (>30 mm) 3
• Concomitant cardiac disease requiring surgical correction (CAD, intrinsic mitral valve disease, valvular aortic stenosis) 3
• Patients with paroxysmal atrial fibrillation (can add pulmonary vein isolation/maze procedure) 3

When Alcohol Septal Ablation Becomes Preferred:

When surgery is contraindicated or risk is unacceptably high due to serious comorbidities or advanced age, alcohol septal ablation becomes the preferred invasive strategy. 3

However, alcohol septal ablation has higher rates of:

• Permanent pacemaker requirement 3
• Need for reintervention 3

Critical Requirements for Mortality Benefit

Center Experience Matters Profoundly

Septal reduction therapy must be performed at experienced centers with comprehensive HCM programs to achieve mortality benefit. 3 The 2024 guidelines emphasize that:

• Previously, procedural mortality was 5-10% at less experienced centers 3
• This high mortality rate persists in the recent era at HCM centers with less surgical experience 3
• Experienced operators are defined as: Individual with ≥20 procedures OR working in a dedicated HCM program with ≥50 cumulative procedures 3

Contraindications to Surgery

Septal reduction therapy should NOT be performed in: 3

• Asymptomatic patients with normal exercise tolerance 3
• Patients whose symptoms are controlled on optimal medical therapy 3
• Centers without dedicated longitudinal HCM programs 3

Common Pitfalls

1. Performing surgery at inexperienced centers negates the mortality benefit and may actually increase mortality risk to 5-10% 3

2. Operating on inadequately medically optimized patients: All patients must have failed optimal medical therapy with beta-blockers or non-dihydropyridine calcium channel blockers, with consideration of adding disopyramide or myosin inhibitors before proceeding to surgery 3, 4

3. Choosing mitral valve replacement over septal myectomy: This should not be performed when septal reduction therapy is an option, as it exposes patients to prosthetic valve complications without superior outcomes 3