Abstract 4119554: Septal Thickness has a Variable Effect on Shock Incidence Rate by ICD Indication in Hypertrophic Cardiomyopathy.

Introduction: Hypertrophic cardiomyopathy (HCM) is the most common cardiomyopathy. People with HCM are at risk of cardiac arrest. ACC/AHA guideline-supported indications for ICD placement include cardiac arrest or VT, family history of sudden cardiac death in a close relative ≤50, massive septal hypertrophy (MSH - septal thickness ≥30mm), apical pouch, and non-sustained ventricular tachycardia (NSVT). Methods: People attending any Mayo Clinic site on > 1 occasion who underwent ICD placement for HCM who had documented cardiac magnetic resonance (CMR) results were included in the study from time of ICD placement to last device interrogation. Outcome was incidence rate of first appropriate shock. Multivariable cox regression was used to examine the association between septal thickness and shock rate, controlling for current age, sex and secondary vs primary prevention device. An interaction term for association between septal thickness and each ICD indication in turn was incorporated into regression, and stratum specific estimates produced using linear computation. Results: 326 people were included in the study, of whom 50 experienced at least one appropriate ICD shock over 1,487.95 person years (incidence rate 3.36 per 100 person years, NNT 29.76 per year). MSH was strongly associated with shock rate (HR 2.29 [1.19 to 4.40], p=0.013). In people without MSH, there was a 50% reduction in shocks where a subjective measure (syncope or family history of sudden cardiac death) was present (table 1). In this cohort, NSVT resulted in a threefold increase in incidence of shock (HR 3.15 [1.446 to 6.47], p=0.003). In the presence of MSH, there was a four-fold increase in shock rate in people who underwent ICD insertion for family history of sudden cardiac death or for syncope (table 2). There was no difference in shock rates in people with NSVT prior to ICD placement based on septal thickness (HR 0.76 [0.21 to 2.74], p=0.679). There was strong evidence of interaction between NSVT and MSH on shock rates (LR χ2 =6.94, p=0.008), such that presence of both risk factors did not increase shock rate. Concurrent presence of late gadolinium enhancement (LGE) >15% on CMR and MSH was associated with a significant increase in shock rate (3.58 [1.43 to 8.98], p=0.006). Conclusion: MSH is a helpful indicator of who will benefit from ICD placement among people with a pre-existing indication for a device, particularly among those with a more subjective indication for a device.