Analysis of Cardiac MRI Based Regional Timing of Left Ventricular Mechanical Contraction as a Biomarker for Electrical Dyssynchrony in Heart-Failure Patients

Abstract

Cardiac resynchronization therapy (CRT) is relatively new treatment for symptoms associated with congestive heart failure (HF) which is achieved by simultaneously pacing both the left and right ventricles of the heart. Current clinical guidelines support the use of CRT in moderate or severe HF patients with a left ventricular (LV) ejection fraction of ≤35% and a prolonged QRS interval (≥120 ms), characteristic of electrical dyssynchrony. Several clinical studies have reported high non-response rates to CRT and have questioned the accuracy of currently practiced patient-selection criteria for this therapy. In this study we demonstrate the translational application of medical imaging biomarkers of phase of ventricular contraction quantified from cardiac magnetic resonance (CMR) imaging, in defining correlations between mechanical dysynchrony (MD) and electrical dyssynchrony, in an effort to identify a means to relate the best-practices for positioning an LV pacing lead (viz. localized to the latest mechanically activating, non-scarred regions) with the clinical guidelines for electrical dyssynchrony in a cohort of heart failure (HF). We retrospectively examine two cohorts of HF patients with different electrical conduction characteristics: a) Left bundle branch block (LBBB) and wide QRS interval – defining the Class I indication for CRT – characteristic of electrical dyssynchrony as evidenced from electrocardiograms; and b) HF with large antero-apical aneurysms and scarring but narrow QRS interval. Indices of mean and standard deviation in phase of regional contraction were examined across the entire LV of each patient, including scarred territories. Additionally, contraction timing delay between the septal and lateral cardiac walls were also examined in the basal LV territories which were free from adverse remodelling and scar. The results from this pilot study show that MD assessment using CMR imaging based biomarkers of phase of LV contraction is highly accurate in predicting electrical dyssynchrony defined by QRS duration ≥150 ms, with receiver operator characteristics evidencing close to perfect accuracy when MD was analyzed in LV territories which excluded scar.