Early post-stress LV dyssynchrony: A new marker for significant CAD

Abstract

Single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) remains one of the most commonly ordered tests for the detection of ischemia and significant coronary artery disease (CAD). 1 A coronary artery territory perfused by a significantly narrowed vessel has limited coronary flow reserve; hence, during peak stress, there are less blood flow and tracer uptake in that region as compared to normal myocardial. The detection of reversible perfusion defect, therefore, depends on the relative flow between myocardial territories. 2 In patients with multivessel disease, the coronary flow reserve is reduced in all territories leading to what has been described as balanced ischemia phenomenon. 3 The latter poses a challenge as patients with multi-vessel CAD may have ''normal'' MPI and could be miss-diagnosed or more commonly assumed to have less extensive CAD. 3 However, other complementary tools have helped recognize the presence of high ischemic burden even when the perfusion images say otherwise. Among them, transient ischemic dilation (TID), 4 increased lung uptake of 5 and left ventricular (LV) stunning (i.e., decrease in early post-stress LV ejection fraction [EF]). These tools, nevertheless, have limitations: the diagnostic accuracy of TID is low; Tl-201 is rarely used and has been replaced by Tc-99m; and LV stunning is often missed or underestimated since imaging with SPECT does not occur at peak stress giving enough time for LV recovery. 6 LV mechanical dyssynchrony indices have been proposed as additional tools to help detect myocardial stunning and ischemia-induced dyssynchronous contraction. The technique was developed by Chen 7 almost a decade ago. It calculates a phase value for each of sampled regions ([600) that represent the onset of mechanical contraction. The standard deviation (phase SD) and 95% bandwidth (histogram bandwidth) represent the LV dyssynchrony indices: the bigger the numbers, the greater the dyssychrony. These indices are derived retrospectively from prior acquired and saved images, with no additional radiation burden or cost. They are automated, reproducible with small inter and intra-observer variability, 8 repeatable, 9 and have been validated against two 10 and three-dimensional echocardiography. 11 The initial application of the technique was in identifying the optimal patients with cardiomyopathy who would derive most benefit from cardiac resynchronization therapy. 12 Since then, the technique proved not only to be a valuable tool in detecting mechanical dyssynchrony, but also providing prognostic information and risk stratifying patients with various co-morbidities (ischemic, 13 non-ischemic cardiomyopathy, 14 implantable defibrillators, 15 end-stage renal disease 16,17 ). More recently, the technique has been used to detect ischemiainduced myocardial dyssynchrony and multi-vessel CAD by comparing stress and rest indices [18][19][20] (Table 1).The concept of stress-induced changes in LV dyssynchrony is not new. In patients with normal MPI undergoing gated...

Ventricular synchrony is not significantly determined by absolute myocardial perfusion in patients with chronic heart failure: A 13N-ammonia PET study

“…Finally, it is worth considering that either if mechanical synchrony is viewed as a marker of disease, 27,28 a risk factor, 4 or as an addressable substrate for therapy (CRT), 29 further understanding of the hierarchical structure of its determinants is desirable, and we consider that the present report is a discrete contribution to this horizon.…”

Phase analysis of gated PET in the evaluation of mechanical ventricular synchrony: A narrative overview

“…Notably, the characterization of this interaction seems to be suitable for the application of PET due to the fact that myocardial perfusion studies are typically acquired during conditions of peak-stress (in contrast to the poststress evaluation with SPECT imaging). Phase synchrony evaluation has therefore been proposed as a marker in the detection of myocardial stunning and ischemia-induced dyssynchrony 24. Specifically, synchrony differences in between rest and stress acquisitions have been demonstrated.…”

Normal values of cardiac mechanical synchrony parameters using gated myocardial perfusion single-photon emission computed tomography: Impact of population and study protocol

“…LVD assessed by the GMPS has been recognized as an essential and additional criterion for response to cardiac resynchronization therapy (CRT) in heart failure patients. [ 3 4 ] Aljaroudi[ 5 ] outlined other potential clinical applications of LVD including prognostication and risk stratification of patients with ischemic,[ 6 ] nonischemic cardiomyopathy,[ 7 ] implantable defibrillators,[ 8 ] and end-stage renal disease. [ 9 10 ]…”