Are all Non-sustained Ventricular Tachycardia the Same in Hypertrophic Cardiomyopathy Risk Stratification for Sudden Cardiac Death?Mohamad Khaled Sabeh MD1, Marwan M. Refaat MD21Cardiac Arrhythmia Service, Massachusetts General Hospital, Boston, Massachusetts - USA2Division of Cardiology, Department of Internal Medicine, American University of Beirut Medical Center Beirut, LebanonRunning Title: NSVT in HCM SCD Risk StratificationWords (excluding references): 664Disclosures: NoneFunding: NoneKeywords: Hypertrophic Cardiomyopathy, Non-sustained Ventricular Tachycardia, Cardiac Arrhythmias, Cardiovascular DiseasesCorrespondence:Marwan M. Refaat, MD, FACC, FAHA, FHRS, FASE, FESC, FACP, FRCPAssociate Professor of MedicineDirector, Cardiovascular Fellowship ProgramDepartment of Internal Medicine, Cardiovascular Medicine/Cardiac ElectrophysiologyDepartment of Biochemistry and Molecular GeneticsAmerican University of Beirut Faculty of Medicine and Medical CenterPO Box 11-0236, Riad El-Solh 1107 2020- Beirut, LebanonFax: +961-1-370814Clinic: +961-1-350000/+961-1-374374 Extension 5800Office: +961-1-350000/+961-1-374374 Extension 5353 or Extension 5366 (Direct)Email: [email protected] with reduced systolic function predispose to sudden cardiac death (SCD) and many studies helped in decreasing that risk by Implantable Cardioverter Defibrillator (ICD) implantation and pharmacologic management (1-4). Many types of cardiomyopathies with preserved systolic function, including hypertrophic cardiomyopathy (HCM), can predispose to malignant ventricular arrhythmias and SCD. HCM is the most common inherited cardiac disease that affects 1 in 200 live births (5,6). SCD remains one of the main causes of death in HCM and the SCD rate peaks in early adulthood (7-14). Data from ICDs suggest that SCD in HCM is most commonly caused by ventricular fibrillation (VF) (15). One major clinical challenge is identifying patients at risk for SCD. Multiple studies showed that non-sustained ventricular tachycardia (NSVT) is a risk actor for SCD (16,17). However the strength of the data was variable across these studies due to difference in populations and the low sensitivity of Holter ECG. Moreover, other studies looked at the rate and duration of the ventricular arrhythmias and their relationship to SCD in HCM (17-19) yet the effect of the morphology of NSVT on SCD has not been well investigated.In this single center study Adduci et al . explore the prognostic impact of different NSVT morphologies in a cohort of 109 consecutive HCM patients. The study included patients who had an ICD implanted in the authors’ institution from January 2001 to December 2018. The ICDs were mostly implanted for primary prevention in HCM patient with 1) one or more risk factor including maximal LV thickness ≥30 mm, family history of SD in at least 1 first-degree relative <50 years of age, non-sustained ventricular tachycardia (NSVT), recent (≤ 6 months) unexplained syncope, 2) hypotensive blood pressure during exercise with at least one additional major risk factor for SD 3) end-stage HCM regardless of other established risk markers of SCD. Devices were interrogated on evaluation every 3 to 6 months and the data was assessed for appropriate or inappropriate ICD therapies. Two independent electrophysiologists analyzed the ICD near field and far field EGMs from the ventricular tachycardia runs. They classified the VTs as either monomorphic (MMVT) or polymorphic (PMVT).During a mean follow up of 71+/- 48 months, 377 NSVT episodes of NSVT were retrieved from ICD memory in 46 patients; of these episodes, 7(2%) were polymorphic and 370 (98%) were monomorphic (MM). The mean HR of The MM NSVT had an average HR of 171+/- 32 BPM and lasted for 17 +/- 12 beats while the PMVT were faster at 241BPM +/- and longer at 28+/- 16 beats. The appropriate intervention rate was 5.1% per year and interestingly NSVT did not predict the occurrence of ICD therapy. However patients with polymorphic NSVT had a statistically higher risk for ICD intervention as compared to monomorphic NSVT. Further analysis noted a trend for increased risk of ICD therapy with patients with >1 NSVT morphology. Moreover 75% of the treated VTs had been previously observed as NSVT.Risk stratification is very important in this young patient population; decreasing the risk threshold for ICD implants leads to missed arrhythmias and bad outcomes while increasing it increases the risk for complications from unnecessarily implanted devices. There are several types of ICDs: Transvenous ICD, Subcutaneous ICD and Extravascular ICD. The results of this study suggest that the risk of SCD in patients with PMVT and/or NSVT with multiple morphologies is different from that of patients with a MMVT, and that the presence of short MMVT doe not predict the future ICD therapies. As such, one may consider a conservative approach in low-risk patients with short bursts of slow MM NSVT, and a more aggressive approach in patients with frequent, rapid rate burst of PMVT. Although this study suggests that different NSVT morphologies affect the prognosis in HCM patients, the low number of events lacked the statistical power to redefine ICD candidacy. Larger multicenter studies are needed to confirm these findings and to help delineate the “at risk patients” who would truly benefit from ICDs.