Regional cardiac mechanical activation times using cine DENSE strain imaging strongly predict electrical activation times in cardiac resynchronization therapy
Daniel A Auger1, Kenneth C Bilchick2, and Frederick H Epstein1,3

1Department of Biomedical Engineering, University of Virginia, Charlottesville, VA, United States, 2Department of Medicine, Cardiovascular Medicine, University of Virginia, Charlottesville, VA, United States, 3Radiology and Medical Imaging, University of Virginia, Charlottesville, VA, United States

Synopsis

A widely held goal in cardiac resynchronization therapy (CRT) is to implant the left-ventricular (LV) pacing lead in a late-activating region. Time to peak shortening (TPS) has been used to image mechanical activation; however electrical activation time is directly related to the time of onset of contraction rather than TPS. Using cine DENSE in heart failure patients, we show that the time of onset of shortening (TOS) shows a strong correlation with electrical activation time, whereas a lower correlation was found using TPS. Cine DENSE of TOS is a promising method for the detection of late-activating segments in CRT patients

Purpose

A widely held goal in cardiac resynchronization therapy (CRT) is to implant the left-ventricular (LV) pacing lead in a late-activating region [1]. Speckle tracking echocardiography (STE) typically uses regional time to peak myocardial strain [2] rather than onset of strain to characterize regional dyssynchrony; however, electrical activation is directly related to the onset of contraction rather than the time to peak contraction. Preclinical MR strain imaging studies using myocardial tagging have demonstrated that strain MRI effectively detects the time of onset of circumferential shortening (TOS) [3]. The present study applied cine DENSE (Displacement Encoding with Stimulated Echoes) MR strain imaging [4] in CRT patients to test the hypothesis that the TOS correlates better with the electrical activation time compared with the time to peak circumferential shortening (TPS).

Methods

Data were acquired from 50 patients with heart failure (HF) and left bundle branch block (LBBB) who met the standard criteria for CRT based on established clinical guidelines. Patients with and without myocardial scar were included. Cine DENSE imaging was performed on a 1.5T MRI system in three standard short-axis planes. Circumferential strain (Ecc) was computed using semiautomatic methods [5], and Ecc data were arranged into matrix form as a function of cardiac phase and LV segment. TPS was defined as the time point where Ecc reached its minimum value, and an active contour (AC) method was applied to the strain matrix to automatically detect the regional TOS, which was defined as the time point where dEcc/dt first becomes negative (Fig. 1A, B). During the CRT implantation procedure, the electrical activation time from QRS onset to the electrogram at the LV lead implantation site (QLV) was measured. MRI and fluoroscopy registration methods were used to determine the LV lead position on the MR images [6]. The TOS and TPS were recorded for the LV segment corresponding to the LV lead position and then compared with the corresponding electrical activation time at the site of LV lead implantation.

Results

Fig. 1(B) shows an Ecc matrix from a mid-ventricular slice for a CRT patient with HF-LBBB and no scar. The figure illustrates the AC, which depicts regions of early and delayed onset of Ecc. Also evident is heterogeneity in the time to minimum Ecc. In the corresponding bull’s eye plots of TOS and TPS shown in Fig. 1(C, D), delayed TOS and TPS are observed in the lateral wall of the LV, and the CRT LV lead position is shown (black dot). Fig. 2 shows the correlations between electrical activation time and the mechanical parameters TOS (A, B) and TPS (C, D). In the datasets with no scar shown in Fig. 2(A, C), the R2 was 0.78 (p<0.0001) for TOS versus electrical activation time, but only 0.32 (p = 0.004) for TPS versus electrical activation. In datasets with patients having the LV lead placed in a region containing scar shown in Fig. 2(B, D), the R2 was 0.8 (p<0.0001) for TOS versus electrical activation time, but only 0.38 (p = 0.019) for TPS versus electrical activation time. We also observed that the slope of the regression line for TOS versus electrical activation is greater when the lead is placed in regions containing scar, as shown in Fig 2(B), versus without scar, as shown in Fig 2(A), consistent with scar-associated delays in electromechanical coupling.

Discussion and Conclusion

Regional mechanical activation times assessed using MRI cine DENSE TOS are strongly correlated with invasively measured electrical activation times, but this association was much weaker using MRI TPS. Cine DENSE imaging of TOS is a promising method for the noninvasive detection of late-activating segments in HF patients referred for CRT, which provides a distinct advantage for cine DENSE MRI over commonly used echocardiography methods.

Acknowledgements

AHA Grant-in-Aid 12GRNT12050301, Siemens Medical Solutions, NIH RO1 EB 001763

References

1. Bilchick et al. J Am Coll Cardiol. 2014;63(16):1657-1666. 2. Tanaka et al. Am J Cardiol, 2010; 105:235-42 3. McVeigh et al. Magn Reson Med. 1998; 39(4):507–13. 4. Kim et al. Radiology, 2004; 230:862-71 5. Spottiswoode et al. MIA, 2009; 13:105–15. 6. Parker et al. PACE, 2014; 37:757-67.

Figures

Figure 1: (A) Ecc curve indicating the definitions of TOS and TPS. (B) Strain matrix showing region of delayed activation as per TOS depicted by an active contour. (C, D) Bull’s-eye plots showing DENSE TOS and TPS maps respectively. Black dots represent the location of the CRT LV lead.

Figure 2: Correlation of mechanical and electrical activation times. (A) TOS vs. QLV. (B) TOS vs. QLV where the LV lead was placed in a region containing scar. (C) TPS vs. QLV. (D) TPS vs. QLV where the LV lead placed in a region containing scar.



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
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