LAUSR

Left ventricular mechanical dyssynchrony (LVMD) by phase analysis of gated single-photon emission computed tomography (SPECT) was initially introduced by Chen et al in 2005 as a simple reliable tool that is reproducible and repeatable, performed retrospectively on previously acquired gated images, and without the need for additional imaging. LVMD has been used to identify patients with cardiomyopathy who would benefit from cardiac resynchronization therapy (CRT) beyond electrical dyssynchrony and ejection fraction criteria, and based on phase standard deviation cut-offs, contraction patterns (U versus non-U shape), and concordance of LV lead placement with site of latest mechanical contraction. The software, now commercially available, has also been used to differentiate ischemic versus nonischemic cardiomyopathy 8 and for many other clinical indications. Furthermore, it is a powerful prognostic tool validated in different cohorts. There have been many studies evaluating a potential role for LVMD in patients with coronary artery disease (CAD). Indeed, Gimelli et al showed that 38% of patients with extensive CAD have significant LVMD which is dependent on the presence of myocardial perfusion abnormalities and LV end-systolic volume. In the current manuscript, Hämäläinen et al from Kuopio University Hospital, Finland, evaluated LVMD in 326 patients with CAD. LVMD was assessed with the phase analysis of ECG-gated myocardial SPECT and LVMD was described with phase histogram bandwidth, standard deviation or entropy values above limit of the highest normal using a control group as a reference. Almost a third of patients with CAD had LVMD. The size of the myocardial scar (fixed perfusion defect) and ischemia (reversible perfusion defect) correlated significantly with all dyssynchrony indices (P\ 0.001 for all). Furthermore, on multivariate analysis, independent predictors of LVMD were myocardial infarction scar (P = 0.004), ischemia extent (P = 0.003), and QRS duration (P = 0.003). In a subgroup analysis, Hämäläinen et al also showed that patients with abnormal MPI in 2 or more vessel territories had more extensive LVMD. The effect of stress testing on LVMD is interesting. It has been postulated that significant stress-induced ischemia may cause myocardial stunning that translates into new or worsening LVMD on stress-gated images. Indeed, Hida et al nicely demonstrated that early post-stress worsening of LVMD identified patients with multivessel ischemia. However, few controversial issues remain regarding the significance of stress-induced changes in LVMD. First, the detection of stunning might be problematic with Tc-99m SPECT as imaging occurs 30-60 min after injection of the tracer, unlike Tl-201 imaging. Second, other studies have shown that LVMD indices tend to be smaller on stress imaging as opposed to rest imaging, independent of perfusion defect, and likely attributed to the higher tracer dose/uptake on stress images and more noise on rest images. Third, vasodilator stress testing which was performed on all patients in the study by Hämäläinen et al (few had hybrid testing with low-level exercise) is less likely to cause myocardial stunning and induce ischemia as opposed to exercise stress testing. Still, the association between LVMD and abnormal myocardial perfusion imaging remains interesting and valuable. In one of the largest studies, Hess et al evaluated 1244 patients with CAD undergoing gated SPECT Funding None. Reprint requests: Wael AlJaroudi, MD, FASNC, Division of Cardiovascular Medicine, Clemenceau Medical Center, Beirut, Lebanon; [email protected] J Nucl Cardiol 2021;28:3021–4. 1071-3581/$34.00 Copyright 2020 American Society of Nuclear Cardiology.