The independent prognostic value of left ventricular dyssynchrony.

Stress Gated SPECT myocardial perfusion imaging (MPI) provides powerful prognostic information that is incremental to myocardial perfusion pattern including left ventricular ejection fraction (LVEF), transient ischemic dilation, exercise-specific parameters (functional capacity, heart rate response and recovery and electrocardiographic changes), vasodilator-specific parameters (inability to exercise, heart rate response and electrocardiographic changes), and absolute quantitation of myocardial blood flow. MPI, using phase analysis, can also assess the synchrony of LV contraction. The development of this technique, its validation, and the advantages it provides to the field has been reviewed elsewhere. Although phase analysis has been used primarily to guide resynchronization therapy, there has been recent interest in the prognostic information provided by its parameters. This has been fueled by the realization that LV mechanical dyssynchrony is common even in patients with narrow QRS on electrocardiography and in those with normal or only mildly depressed LVEF. Studies have shown that dyssynchrony on phase analysis is associated with worse outcomes in patients with heart failure and in those with end-stage renal disease. In this issue of the Journal, Zafrir et al. examine whether LV dyssynchrony is associated with worse cardiac outcomes in all patients studied at a single universityaffiliated laboratory over a 2-year period. After excluding 86 patients due to incomplete data, they report findings on a cohort of 787 patients (42% exercise, 45% dipyridamole, 9% rest only) followed for 18.3 ± 6.2 months. During this time, 55 patients died (26 from cardiac causes), 16 patients were hospitalized with heart failure, and three were hospitalized with ventricular tachycardia or fibrillation. Patients with cardiac events (composite of cardiac death and hospitalization for heart failure or ventricular tachycardia or fibrillation) had wider phase standard deviation (SD) and bandwidth (BW) than those without events but this association was not statistically significant after multivariate adjustment. NYHA functional class, diabetes, and LVEF\50% were the only independent predictors of the composite outcome of cardiac events. In contrast, phase SD (hazard ratio for 10 increase 1.2, 95% CI 1.01-1.45, P = .043) and NYHA, but not LVEF, were the independent predictors of cardiac death. When an abnormal phase SD cutoff was used (40 ), composite cardiac events occurred in 12.4% of patients with abnormal phase SD and 3.5% of patients with normal phase SD (P\ .001). The respective numbers for cardiac deaths were 7.8% and 1.9% (P \ .001). In a separate report, Pazhenkottil et al. studied 202 consecutive patients (197 patients with follow-up) who underwent 1 day adenosine stress-rest MPI for evaluation of known or suspected coronary artery disease at a university hospital. During 3.2 ± 1.2 years of follow-up, 62 major adverse cardiac events (a composite of cardiac death, hospitalization for cardiac reason including heart failure, nonfatal myocardial infarction, unstable angina, and coronary revascularization occurring after 30 days of the index MPI) occurred in 41 patients including 5 cardiac deaths. LV dyssynchrony, based on previously derived cutoffs, was associated with major adverse cardiac events in univariate (hazard ratio 3.6, 95% CI 1.9-6.8, P \ .001) and multivariate analyses (hazard ratio 2.0, 95% CI 1.0-4.2, P \ .05) that adjusted for age, gender, cardiovascular risk factors, myocardial perfusion, and LVEF. Reprint requests: Fadi G. Hage, MD, FASH, FACC, Division of Cardiovascular Disease, University of Alabama at Birmingham, Lyons Harrison Research Building 314, 1900 University BLVD, Birmingham, AL 35294; fadihage@uab.edu J Nucl Cardiol 2014;21:541–3. 1071-3581/$34.00 Copyright 2014 American Society of Nuclear Cardiology.