With the real-time guidance of TTE, a radiofrequency electrode needle was percutaneously inserted via the transapical intramyocardial approach into the hypertrophied septum for thermal ablation. Intraoperative TTE and 12-lead electrocardiographic monitoring were employed to assess the ablation extent and prevent vascular and cardiac conduction bundle injury. The success of ablation was confirmed by evaluating contrast medium perfusion defects in the ablated areas and comparing them with the preprocedural hypertrophied septum.

Major adverse cardiovascular events including but not limited to:

1. All-cause death;
2. Arrhythmic events: resuscitated cardiac arrest or ventricular tachycardia/fibrillation, appropriate implantable cardioverter-defibrillator discharge, atrioventricular block, pacemaker implantation and atrial fibrillation;
3. Acute heart failure: acute pulmonary edema, new-onset NYHA class Ⅲ-IV symptoms, and heart failure-related hospitalization;
4. Cardiogenic shock: cardiac disorder that results in a systolic blood pressure <90 mmHg for ≥30 min (or the need for vasopressors, inotropes or mechanical circulatory support to maintain systolic blood pressure ≥90 mmHg) with evidence of hypoperfusion;
5. Severe systolic anterior motion: the proximal portion of the anterior mitral leaflet moved excessively close to the septum, resulting in extreme LVOT obstruction and acute haemodynamic collapse;
6. Cerebrovascular events: all stroke (ischemic or hemorrhagic) and transient ischemic attacks.

Any instrument or procedure-related complications, including but not limited to death, emergency surgery, pericardial tamponade requiring pericardiocentesis or surgery, bleeding, procedure-related stroke.

Maximum septal thickness as measured by echocardiography.

Left ventricular outflow tract gradient as measured by echocardiography.

The New York Heart Association Classification involved 4 classes. I-No limitation of physical activity, II-Slight limitation of physical activity, III-Marked limitation of physical activity, IV-Unable to carry on any physical activity without discomfort. A higher grade means worse heart function.