Primary prevention of sudden cardiac death in in hypertrophic cardiomyopathy: are we calibrating arrhythmic risk correctly?

Introduction

Sudden cardiac death (SCD) risk stratification amongst hypertrophic cardiomyopathy (HCM) population remains challenging. Current guideline-recommended risk models show modest discrimination for SCD risk, potentially exposing individuals either to arrhythmic fatal events or unnecessary implantable cardioverter defibrillator (ICD) related complications.

Purpose

To assess the burden of ventricular arrhythmias in a real-world cohort of HCM patients undergoing ICD implantation for primary prevention of SCD.

Methods

We performed a retrospective observational single centre analysis on HCM individuals accompanied at a dedicated tertiary centre who underwent ICD implantation in primary prevention of SCD. Data were gathered through medical records review. The primary outcome was the occurrence of appropriate ICD therapies, defined as anti-tachycardia pacing or shock for ventricular tachyarrhythmias.

Results

From an initial cohort of 165 pts with HCM, 26 pts (15.8%) with an ICD were identified, including 24 with an ICD and 2 pts with a cardiac resynchronization therapy with ICD. Of these, 22 pts were included for analysis under the defined inclusion criteria.

Most were male (n=12, 54.5%), with HCM diagnosis at routine cardiac screening (n=15, 68.2%) at mean age 41 ± 21 years. Almost half were genotype-positive (n=10, 45.5%), with predominant variants in sarcomeric genes (n=8, 80%). 72.7% had an asymmetrical septal morphology and 31.8% had left intraventricular obstruction physiology. 68.2% had concomitant atrial fibrillation.

ICD implantation decision was based on European Society of Cardiology 5-year SCD-risk stratification tool and additional features, including reduced or mildly reduced (R/MR) left ventricular systolic function and extensive late gadolinium enhancement (LGE). 55.5% had a SCD-risk score ≥ 4%, 37.4% had a R/MR LV systolic function and 59.1% with LGE ≥ 15%.

Over a median FUP of 11 (IQR 12) years, 18.2% (n=4) experienced ICD appropriate therapies – all of which with appropriate ICD shocks, none with only-ATP treated ventricular arrhythmias. No ICD-related complications were reported.

Conclusion

In this real-world cohort of HCM patients undergoing primary prevention ICD implantation, almost one-fifth experienced appropriate ICD therapies, persistent risk of malignant ventricular arrhythmias in this population. Nevertheless, a substantial proportion of patients did not receive any appropriate ICD therapy, underling the limitations of SCD risk models and the need for its refinement, possibly including additional imaging features.