Stress-induced myocardial ischemia modifies phase analysis indices obtained from Tc-99m sestamibi gated single photon emission computed tomography myocardial perfusion imaging

Abstract

Purpose: Phase analysis of gated myocardial perfusion single photon emission computed tomography (GSPECT) images allows the assessment of left ventricle (LV) mechanical synchrony. The aim of our study was to determine whether stress-induced ischemia modifies the two most commonly used phase analysis synchrony parameters: Histogram bandwidth (HB) and Standard deviation (SD) obtained from Tc 99m sestamibi of GSPECT images and to evaluate the correlation between these indices and different amounts of ischemia. Methods: We included 92 consecutive ischemic patients defined by SDS≥2 who underwent a two-day stress-rest protocol Tc99 sestamibi GSPECT between August 2011 and July 2012 and we compared them to a group of 22 normal subjects defined as asymptomatic, without known coronary artery disease, with low pretest of coronary artery disease, and normal ECG, stress test, left ventricular function and perfusion (SSS: 0), who followed the same GSPECT protocol. Patients with left bundle branch block, ventricular pacing and fixed perfusion defects were excluded. Phase analysis indices HB and SD were obtained from stress and rest images in both groups. We obtained the change (stress minus rest) of SD and HB indices for each patient. The ischemic group was divided into moderate-to-severe ischemia (SDS≥5), and severe ischemia (SDS≥8). Results: The ischemic group had a mean age of 63±10 years, 47 were men, 21 had moderate-to-severe ischemia and 10 severe ischemia. Ischemic patients showed higher stress SD and HB values than normal subjects (SD 15.65 vs 11.76, p=0.0002 and HB 47.74 vs 38.04, p=0.002 respectively) and larger amounts of ischemia showed higher values: moderate to severe ischemia (SD 20.08 vs 11.76, p<0.001 and HB 59.61 vs 38.04 p=0.001 respectively) and severe ischemia (SD 19 vs 11.76, p<0.0001 and HB 60.4 vs 38, p<0.0001 respectively). Changes in SD and HB were significatively higher in ischemic patients than in normal subjects (SD -0.19 vs -0.58, p<0.0001; HB 1.27 vs -0.95, p=0.0002 respectively). These differences were even higher in moderate to severe ischemia (SD 2.49 vs -0.58, p=0,0002; HB 4.76 vs -0.95, p<0.0001) and severe ischemia (SD 2.42 vs -0.58, p=0,0001; HB 12.5 vs -0.95, p<0.0001). Conclusion: In our population left ventricular mechanical synchrony indices obtained by phase analysis of Tc99sestamibi GSPECT imaging, HD and SD are altered in the presence of myocardial ischemia. Larger amounts of ischemia are related to higher dyssynchrony values of the phase-derived indices HB and SD.