Original ArticleAssociation between left ventricular mechanical dyssynchrony with myocardial perfusion and functional parameters in patients with left bundle branch block
Introduction
Previous studies identified left ventricular mechanical dyssynchrony (LVMD) as independent predictor for a favorable response to cardiac resynchronization therapy1 and also for all-cause death in patients with advanced coronary artery disease (CAD) and reduced LV function not undergoing cardiac resynchronization therapy.2
LVMD can be evaluated by ECG gated single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI), a technique enabling the assessment of both perfusion and LV functional parameters with low inter- and intraobserver variability in a single investigation.1,3,4 Furthermore, SPECT MPI allows the quantification of mechanical dyssynchrony through phase analysis, based on the Fourier phase histogram of the left ventricle, in which the parameters bandwidth and standard deviation (SD) have been identified as valid markers of LVMD.1
In a recent study of a patient population with severely reduced ejection fraction (≤35%), Samad et al5 showed that LVMD was relatively common, and was independently predicted by declining left ventricular ejection fraction (LVEF), the severity and extent of myocardial scaring, as well as by an increased QRS duration. But also patients with left bundle branch block (LBBB) and normal LVEF can present with LVMD,6 indicating that a long QRS duration reflecting electrical dyssynchrony, is not necessarily associated with the presence of LVMD.
Up to now there is an incomplete understanding of the underlying interactions between electrical dyssynchrony, perfusion defects, wall motion abnormalities, and the appearance of LVMD, which ultimately leads to deterioration of LVEF and heart failure. Thus, we aimed in the present study at identifying predictors of mechanical dyssynchrony in a cohort of patients with known electrical dyssynchrony and both normal and reduced LVEF.
Section snippets
Study Population
We identified consecutive patients with LBBB (QRS duration ≥ 120 ms) and suspected or known CAD, who were referred to the Department of Nuclear Medicine of the University of Munich for MPI. We excluded patients with implanted cardiac resynchronization therapy (CRT) devices and those in whom ECG triggering failed because of the presence of severe arrhythmia arising from any other cause. Patients with known CAD received medical therapy according to current guidelines.7 Relevant comorbid medical
Results
We excluded four patients in whom ECG triggering failed because of absolute arrhythmia. The final study cohort consisted of 81 patients (74% male; 70.1 ± 9.6 years old) with LBBB (mean QRS duration 158 ± 24 ms, LVEF 49.5% ± 16.1%). 60 of the 81 patients (74%) had known CAD, 35/81 (42%) had prior MI, and 41/81 (51%) had two or more out of five cardiac risk factors (diabetes mellitus, familiar predisposition, hypertension, smoking, or high cholesterol). The baseline characteristics and other
Discussion
In a cohort of 81 consecutive patients with LBBB investigated by means of ECG gated SPECT MPI including phase analysis, only global wall thickening, as expressed by the STS, was identified as independent predictor for the appearance of LVMD. In addition, univariate analysis showed also significant correlation between the appearance of LVMD and perfusion parameters like SRS and SSS. This is to the best of our knowledge the first study investigating a patient cohort with individual LBBB extending
Conclusions
In patients with LBBB, the occurrence of LVMD as assessed by gated SPECT phase analysis is mainly influenced by reduced myocardial contractility as expressed by the STS. As a consequence, careful discrimination between LVMD arising from known electrical conduction delay as opposed to areas of MI causing reduced regional contractility seems to be mandatory for therapy planning in patients with LVMD.
Acknowledgment
None.
Disclosures/Funding
Cedars-Sinai Medical Center receives royalties for the licensure of software used in the quantitative assessment of function, perfusion, and viability, a portion of which is distributed to some of the authors of this article.
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