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Left ventricular (LV) myocardial stunning is a phenomenon described decades ago as a transient acute systolic dysfunction secondary to myocardial ischemia. The pathogenesis of myocardial stunning involves disruption of calcium homeostasis and oxygen-free radical injury. In patients with normal myocardial perfusion, LV myocardial contractility increases during stress testing, whether exercise or pharmacologic, with correspondent increase in LV ejection fraction (EF). This is most evident during stress echocardiography where live stress imaging shows augmented contractility of myocardial segments. In patients with significant coronary artery disease (CAD), supply demand mismatch during stress testing results in myocardial perfusion abnormality followed by abnormal segment contractility, an energy-dependent phenomenon, causing transient stunning of the myocytes. While this is more common with exercise or dobutamine, vasodilator stress testing can also induce myocardial ischemia (steal-phenomenon). If the ischemic burden is significant, global LVEF may decrease at peak stress in up to half of patients. The best predictor of this post-stress stunning is the ischemic burden. However, it is important to point out that factors other than myocardial ischemia, such as hemodynamics and myocardial innervation, play a key role in the lack of augmentation of LVEF with vasodilator stress. Stress-induced new wall motion abnormality is highly specific for CAD and ischemia with imaging modalities that focus on myocardial motion such as echocardiography and cardiac magnetic resonance imaging. With gated Tc-99m single-photon emission computed tomography (SPECT), reversible regional wall motion abnormalities with exercise have a specificity of 100% to detect significant CAD ([ 70% epicardial stenosis of a coronary artery on angiogram), with good correlation with coronary artery jeopardy score (R = 0.49, P\ 0.0001), although with limited sensitivity (53%). After adjusting for Duke Treadmill Score and other covariates, reversible wall motion abnormality on stress gated SPECT remains an independent predictor of severe CAD. Similarly, worsening of LVEF with vasodilator 201-Thallium-gated SPECT has a high specificity for significant CAD, albeit with low sensitivity. In addition to global LVEF, assessment of regional wall motion is also feasible with gated SPECT myocardial perfusion imaging (MPI) although quantification and scoring are not routinely performed and reported. The visual assessment of segment thickening is subjective and sometimes limited by the tracer count, frame rate, and attenuation artifact. Another tool provided by gates images is mechanical synchrony using phase analysis. This valuable tool is automated, reproducible, repeatable, and transcends the 8 to 16 frame rate of the gated images though a complex Fourier transformation giving it an apparent frame rate of 1/64th frames/cycle. Moreover, phase analysis provides regional synchrony and onset of mechanical contractility for each myocardial segment. During stress testing, the Reprint requests: Fadi G. Hage, MD, FASNC, Division of Cardiovascular Disease, Department of Medicine, University of Alabama at Birmingham, 306 Lyons-Harrison Research Building, 701 19th Street South, Birmingham, AL 35294-0007; fadihage@uab.edu J Nucl Cardiol 2019;26:841–4. 1071-3581/$34.00 Copyright 2017 American Society of Nuclear Cardiology.

Myocardial stunning by gated SPECT: An old tool reinvented in a stunning turn