To examine patients with hypertrophic obstructive cardiomyopathy (HOCM) before and after septal alcohol ablation, to investigate the effect of the treatment in regards to changes in myocardial function, perfusion, invasive hemodynamics and exercise tolerance.

Patients with HOCM who develop symptoms of heart failure are treated initially with non-vasodilating ß-blockers or verapamil to decrease myocardial contractility and heart rate. A substantial part of patients remain symptomatic despite medical treatment. In these patients interventional or surgical treatments (septal reduction therapies (SRT)) to reduce left ventricular outflow tract obstruction (LVOTO) is considered in the presence of moderate to-severe symptoms (New York Heart Association - functional class (NYHA) III-IV) and/or recurrent exertional syncope and an LVOTO gradient ≥50 mm Hg. In some centers, invasive therapy is also considered in patients with mild symptoms (NYHA Class II) who have a resting or maximum provoked gradient of ≥50 mm Hg (with exercise or Valsalva's maneuver) and moderate-to-severe mitral valve regurgitation. Advanced treatment options are alcohol septal ablation (ASA) or surgical myectomy often combined with mitral valve reconstructive surgery. These treatments have similar outcomes in terms of gradient reduction, symptom improvement and exercise capacity

No previous trials have examined the effect of ASA in HOCM with respect to changes in central hemodynamics and myocardial performance during exercise.

24 HOCM patients will be examined prior to ASA, and approximately six-nine months after ASA.

The examination set-up consists of simultaneous 1) transthoracic echocardiography (TTE), 2) right heart catheterization (RHC) and 3) cardiopulmonary exercise test (CPX).

Inclusion Criteria:

• Left ventricular wall thickness ≥ 15 mm in one or more myocardial segments that is not explained by loading conditions
• LVOT gradients ≥ 30 mmHg at rest and/or ≥ 50 mmHg at Valsalva's maneuver or exercise
• NYHA ≥ III

Exclusion Criteria:

• < 18 years
• Fertile women who do not use anti-contraceptives
• Pregnancy
• Patients are allowed to have a pacemaker (eg. an implantable cardioverter defibrillator (ICD)) but cannot be pace-dependent
• Amiodarone treatment
• Persistent or permanent atrial fibrillation/flutter
• Previous SRT
• Alcohol or drug abuse
• Significant co-morbidity (judged by the investigator)
• Patients who cannot give valid consent (e.g. mental illness or dementia) or who do not understand Danish.