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Electromechanical decoupling with multisite onset of mechanical contraction in patients with different underlying heart diseases derived to gated-SPECT


 
 
 Varying degrees of left ventricle (LV) mechanical dyssynchrony have been detected in some patients without electrical dyssynchrony. However, the site of onset of ventricular mechanical contraction as part of the electromechanical coupling process has not been fully described.
 
 
 
 To characterize LV contractile dynamics associated with multisite onset of mechanical contraction (OMC).
 
 
 
 Phase histograms at rest were obtained in a sample of consecutive patients referred to 99mTc-MIBI gated-SPECT (radiotracer dose at rest: 925 MBq). Visual interpretation was performed through a semi-quantitative perfusion scale from 0 to 4 in a 17-segment model. Automated analysis included segmental summed rest, stress and difference scores (SRS, SSS and SDS), and also rest and post-stress functional parameters. Applying SyncTool from Emory Cardiac Toolbox® we obtained peak amplitude (PA), standard deviation (PSD) and phase bandwidth (PBW) indexes from resting phase histogram, detecting the site of OMC in LV. Then, we detected the patients with multisite (“multipoint”) OMC, defined as the onset in at least 3 of 17 segments. Latest site of mechanical contraction was recorded in last 10–30 degrees of phase. Histogram indexes were compared with a control group from our sample (n=24) and with controls reported by Chen J (n=90) by paired t test (p=0.05, two tailed).
 
 
 
 Multisite OMC was found in 19/137 patients (14%); affected from chronic coronary artery disease (n=13), hypertensive heart disease (n=2), inflammatory cardiomyopathy (n=1), hypertrophic cardiomyopathy (n=1) and nonischemic dilated cardiomyopathy (n=2). ECG showed left bundle branch block in one case and biventricular pacing in another. Multisite OMC was associated with diabetes (47.3%), lower LVEF (44.2±15.3%) and higher cavitary volumes (104.5±61.4 ml), SRS (17.0±10.7%) and incidence of fixed defects attributed to old infarct (77.8%); p<0.05 for all comparisons. Subjects with multisite OMC and chronic coronary disease (n=13) were 63±13 years old, 54% diabetic, LVEF=39.9±13.6%, telesystolic LV volume=112.4±64.9 ml, SRS=12.5% and SDS=4.2%. All patients with multisite OMC exhibited marked mechanical dyssynchrony at rest (PA=121.7±16.3, PSD=47.6±19.8, PBW=148.3±64.2 degrees (p<0.05 for the comparisons of PSD and PBW with sample controls and for the comparisons of all indexes with reported controls). In 4 of them (21%) a multisite late mechanical contraction was also detected.
 
 
 
 Electromechanical decoupling with “multipoint” OMC is not infrequently found in patients referred to gated-SPECT, even in the absence of wide QRS complex. This subpopulation of patients is characterized by several functional high risk markers. Additional prognostic implications of this mechanical substrate, that seems to be common to several heart diseases, deserves further evaluation in large series subjected to prolonged clinical and physiological follow-up.
 
 
 
 Type of funding source: None
