Fatunde, Bade

Abstract Introduction Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disorder with a pathogenic mutation identified in approximately 50% of cases. The MYH7 and MYBPC3 genes account for over half of these cases, while dozens of other genes can be pathogenic(1). Genetic test results are not independently used to determine which people with HCM benefit from implanted cardiac defibrillators (ICDs)(2, 3). Little is known about the additive role of genetic testing results to existing indications for ICD insertion. Purpose This study aims to examine the interaction between genetic testing results and existing ICD indications and imaging results on defibrillator discharge rates in HCM. Methods Patients who underwent an ICD for HCM, who underwent a cardiac magnetic resonance (CMR) study and who underwent genetic testing were included across 3 sites. The outcome was the incidence rate of appropriate ICD discharges, calculated using cox regression controlling for current age and primary vs secondary prevention. Interaction analysis between genetic risk factors and existing ICD indications, and with CMR quantification of LGE and septal thickness, was performed, and stratum specific estimates calculated using linear computation. Results 177 patients were included in the study, of whom 70 (39.55%) had a pathogenic mutation, 5 (2.82%) had a variant likely pathogenic (VLP), 44 (24.86%) had a variant of undetermined significance (VUS) and 58 (39.55%) had no identifiable mutation. The event rate was 3.32 {2.28 to 4.84) per 100 person years. There was no association between genetic variables and ICD discharge rate. There was an 80% reduction in ICD discharge rate in people who underwent ICD insertion exclusively for family history of sudden cardiac death or for syncope who had no pathogenic or likely pathogenic mutation, however this change was not statistically significant (table 2). Conclusion There is no strong association between genetic characteristics and ICD discharge rates among people with hypertrophic cardiomyopathy with an existing ICD indication. There is a nonsignificant trend towards fewer ICD discharges among people who underwent ICD insertion for family history alone or for a history of syncope and did not have a pathologic variant.Table 1 Table 2

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.