AIMS: Based on European guidelines, alcohol septal ablation (ASA) for hypertrophic obstructive cardiomyopathy (HOCM) is indicated only in patients with interventricular septum (IVS) thickness >16 mm. The aim of this study was to evaluate the short- and long-term outcomes in ASA patients with mild hypertrophy (IVS ≤ 16 mm).

METHODS AND RESULTS: We retrospectively evaluated 1505 consecutive ASA patients and used propensity score to match 172 pairs (344 patients) in groups IVS ≤ 16 mm or IVS > 16 mm. There was no occurrence of post-ASA ventriculoseptal defect in the whole cohort (n = 1505). Matched patients had 30-day mortality rate 0% in IVS ≤ 16 mm group and 0.6% in IVS > 16 mm group (P = 1). Patients in IVS ≤ 16 mm group had more ASA-attributable early complications (16% vs. 9%; P = 0.049), which was driven by higher need for pacemaker implantation (13% vs. 8%; P = 0.22). The mean follow-up was 5.4 ± 4.3 years and the annual all-cause mortality rate was 1.8 and 3.2 deaths per 100-patient-years in IVS ≤ 16 group and IVS > 16 group, respectively (log-rank test P = 0.04). There were no differences in symptom relief and left ventricular (LV) gradient reduction. Patients with IVS ≤ 16 mm had less repeated septal reduction procedures (log-rank test P = 0.03).

CONCLUSION: Selected patients with HOCM and mild hypertrophy (IVS ≤ 16 mm) had more early post-ASA complications driven by need for pacemaker implantation, but their long-term survival is better than in patients with IVS >16 mm. While relief of symptoms and LV obstruction reduction is similar in both groups, a need for repeat septal reduction is higher in patients with IVS > 16 mm.