What is the treatment for left ventricular outflow obstruction due to subaortic stenosis?

Treatment for Left Ventricular Outflow Obstruction, Subaortic Stenosis

Surgical resection is recommended for adults with subaortic stenosis when the maximum gradient is ≥50 mm Hg or mean gradient is ≥30 mm Hg, and should also be performed for lower gradients when accompanied by symptoms, LV systolic dysfunction, or significant aortic regurgitation. 1

Primary Surgical Indications (Class I Recommendations)

Definite indications for surgery include:

• Peak instantaneous gradient ≥50 mm Hg or mean gradient ≥30 mm Hg on echocardiography-Doppler 1
• Symptomatic patients (dyspnea, chest pain, syncope) with maximum gradient ≥50 mm Hg 1
• Maximum gradient <50 mm Hg with heart failure or ischemic symptoms AND/OR LV systolic dysfunction attributable to subaortic stenosis 1
• Progressive aortic regurgitation with LV end-systolic diameter ≥50 mm OR LV ejection fraction <55% 1

Secondary Surgical Considerations (Class IIa/IIb Recommendations)

Surgery may be considered in specific clinical scenarios even with lower gradients:

• LV hypertrophy present with mean gradient ≥30 mm Hg 1
• Pregnancy being planned 1
• Patient plans to engage in strenuous/competitive sports 1
• Asymptomatic patients with at least mild AR and maximum gradient ≥50 mm Hg to prevent AR progression 1
• Abnormal blood pressure response on exercise testing with mean gradient ≥50 mm Hg 1

Medical Management

There is no specific medical therapy for subaortic stenosis. 1

• Endocarditis prophylaxis is recommended only for patients with prior history of infective endocarditis 1
• Beta-blockers have no role in discrete subaortic stenosis (unlike hypertrophic cardiomyopathy) 1

Surgical Technique

The standard surgical approach involves:

• Circumferential resection of the fibrous ring through a transaortic approach 1
• Resection of the muscular base along the left septal surface 1
• For fibromuscular or tunnel-type subaortic stenosis, more aggressive septal resection is required 1
• Severe long-segment LVOT obstruction may require a Konno procedure with extensive patch augmentation 1
• Concomitant aortic valve repair should be performed when moderate or severe AR is present 1

Important Surgical Risks

Potential operative complications include:

• Complete heart block (10-15% risk) 1
• Injury to aortic or mitral valves 1
• Creation of iatrogenic VSD 1
• Recurrence occurs in approximately 20% over 10 years, particularly when initial resection performed in childhood 1

Diagnostic Evaluation Before Surgery

Transthoracic 2D echocardiography-Doppler is the initial diagnostic method of choice to assess:

• LV outflow anatomy and severity of subaortic gradient 1
• Associated aortic valve abnormality and degree of AR 1
• LV hypertrophy and systolic/diastolic function 1
• Mitral valve involvement 1

TEE may add valuable anatomic detail preoperatively and intraoperatively 1

Exercise stress testing may be reasonable when indications for intervention are equivocal, to assess:

• Exercise capacity and symptoms 1
• ECG changes or arrhythmias 1
• Increase in LVOT gradient with exertion 1

When NOT to Operate (Class III)

Surgery is not recommended:

• To prevent AR in patients with trivial LVOT obstruction or trivial to mild AR 1
• In patients with Eisenmenger syndrome 2

Lifelong Follow-Up Requirements

All patients with subaortic stenosis require lifelong cardiology follow-up by an adult congenital heart disease specialist 1

Unoperated asymptomatic adults with stable LVOT obstruction (mean gradient <30 mm Hg) without LV hypertrophy or significant AR should be monitored yearly for:

• Increasing obstruction 1
• Development or progression of AR 1
• LV systolic and diastolic function 1

Postoperative follow-up must detect:

• Late restenosis (occurs in ~20% over 10 years) 1
• Progressive AR despite resection 1
• Arrhythmias and heart block 1

Critical Pitfalls to Avoid

The degree of subaortic stenosis may be underestimated in the presence of:

• LV systolic dysfunction (gradient may be <50 mm Hg due to low flow) 1
• VSD proximal to the subaortic stenosis 1

Discrete fibrous subaortic ring findings may be subtle on TTE unless:

• Good acoustic windows allow transducer positions perpendicular to the membrane 1
• LVOT obstruction is examined carefully with color flow Doppler 1

Catheter palliation has been performed experimentally but its efficacy has not been demonstrated 1