Review on sudden death risk reduction after septal reduction therapies in hypertrophic obstructive cardiomyopathy.

Treatment of left ventricular outflow tract (LVOT) obstruction in hypertrophic obstructive cardiomyopathy (HOCM) with septal reduction, either with myectomy or alcohol septal ablation, is aiming to reduce the LVOT gradient and improve symptoms in patients who are refractory to or do not tolerate medical treatment. Apart from contributing to the evolution to heart failure, LVOT obstruction is considered a risk factor for sudden cardiac death (SCD). Both septal reduction treatments have been proven effective in reducing symptoms and seem to improve survival, which has been shown equal to the expected in the normal population. SCD is probably reduced after septal reduction, implying that LVOT obstruction is a major factor predisposing to ventricular tachyarrhythmias. Although available algorithms for SCD stratification have not been tested in patients after septal reduction treatments, effective treatment improves SCD risk profile substantially. Furthermore, high-risk patients with already implanted implantable cardioverter defibrillators (ICDs) before septal reduction show very low appropriate ICD shock rate after effective treatment. It should be noted, however, that the best outcomes for septal myectomy or ablation have been reported in HOCM patients treated in high-volume centres, which substantiates the need to refer patients to centres with high procedural expertise.