Abstract 18148: CMR Mapping of Mechanical Activation Time in Patients with Heart Failure and Left Bundle Branch Block: Methods and Initial Results
Introduction: The nonresponse rate to cardiac resynchronization therapy (CRT) in patients with heart failure (HF) is 30-50% using current clinical indicators and implementation methods. A frequent cause of CRT nonresponse is suboptimal positioning of the left ventricular (LV) lead, which should be located in a late-activated region of the LV. In contrast to the the current trend to measure time to peak strain to identify late contraction, we aimed to develop and evaluate MRI strain imaging for mapping the onset of mechanical activation in the LV in CRT patients.
Methods: Cine DENSE MRI was performed in 18 patients with HF and left bundle branch block (LBBB) and in 6 healthy subjects. Circumferential strain was computed using previously described semiautomatic methods. Circumferential strain as a function of time and LV segment was refined using singular value decomposition (SVD), and an active contour was used to find the time of the onset of contraction (Fig. 1A), which was defined as the mechanical activation time.
Results: The mean time of latest mechanical activation was 56 ± 23 ms in HF-LBBB patients and 19 ± 9 ms in healthy subjects (p<0.05). In all HF-LBBB patients, activation times in the septal segments occurred within the first 17 ms of the imaging ECG trigger, whereas varying degrees of delayed activation were detected in LV free wall (Fig. 1A-B). The latest activated LV free wall segment could be either anterolateral (61%) or posterolateral (39%) (Fig. 1C).
Conclusions: Assessment of regional strain onset in heart failure can be determined using SVD of cine DENSE circumferential strain. Mechanically late-activated regions were identified in all 18 patients with HF and LBBB, with significant variability in the site of latest LV free wall activation. This heterogeneity of late-activated segments in LBBB suggests that activation mapping holds potential for pre-procedure identification of optimal LV lead implantation sites for individual patients undergoing CRT.
Author Disclosures: D.A. Auger: None. S.X. Cui: None. X. Chen: None. K.C. Bilchick: None. F.H. Epstein: None.
- © 2014 by American Heart Association, Inc.