IMPACT OF DENERVATED MYOCARDIUM ON IMPROVING RISK STRATIFICATION FOR SUDDEN CARDIAC DEATH
Michael E. Cain, M.D., University at Buffalo, NY, USA
The annual incidence of sudden cardiac death in the United States is between 184,000 and 462,000, with estimates that 50% to 70% of the deaths are due to VT or VF. Availability of therapies shown to reduce death in various at-risk groups, including beta-blockers, ACE- inhibitors, statins, aldosterone blockers, and the implantable cardiac defibrillator (ICD), underscore the need to accurately identify patients who will develop VT/VF and exclude those who will not. Multiple tests have been evaluated, but currently no optimal strategy for risk stratification exists. Left ventricular (LV) ejection fraction (EF) remains the single best predictor of benefit from an ICD. New evidence suggests myocardial sympathetic denervation may identify high-risk independently of EF. Positron emission tomography is being used to quantify myocardial sympathetic denervation (11C-meta-hydroxyephedrine, 11C-HED), perfusion (13N-ammonia, 13NH3) and viability (insulin-stimulated 18F-2-deoxyglucose, 18FDG) in patients with ischemic cardiomyopathy eligible for a primary prevention ICD. The primary outcome is sudden cardiac arrest or equivalent (SCAE) defined as arrhythmic death or ICD discharge for VT/VF >240 bpm. Based on data acquired so far, volumes of total denervated (p=0.001) and viable denervated myocardium (11C-HED-18FDG mismatch, p=0.03) predict SCAE, while hibernating (13NH3-18FDG mismatch) and infarcted myocardium do not. Denervated myocardium had a hazard ratio of 3.5 for SCAE (10.3%/year vs. 3.0%/year, p=0.001). Denervated myocardium quantified using 11C-HED PET strongly predicts risk of SCAE, and is independent of EF, infarct volume and other clinical variables. Thus, molecular imaging may improve risk stratification for current ICD candidates.