Cardiac Magnetic Resonance Assessment of Dyssynchrony and Myocardial Scar Predicts Function Class Improvement Following Cardiac Resynchronization Therapy
Kenneth C. Bilchick, MD, FACC*,
Veronica Dimaano, MD*,
Katherine C. Wu, MD*,
Robert H. Helm, MD*,
Robert G. Weiss, MD*,
Joao A. Lima, MD*,
Ronald D. Berger, MD, PhD*,
Gordon F. Tomaselli, MD, FAHA, FACC, FHRS*,
David A. Bluemke, MD, PhD, FAHA ,
Henry R. Halperin, MD, FAHA*, ,,
Theodore Abraham, MBBS, MD*,
David A. Kass, MD, FAHA*,, ,
Albert C. Lardo, PhD, FACC, FAHA*,,,*
* Department of Medicine, Division of Cardiology, Johns Hopkins University School of Medicine, Baltimore, Maryland
Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland
Department of Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland
Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland
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Figure 1 Quantification of Circumferential Mechanical Dyssynchrony from MR-MT Strain Map
Calculation of the circumferential uniformity ratio estimate (CURE) for mechanical dyssynchrony using Fourier analysis with extreme examples of spatial distribution of strain for synchrony (straight line) versus dyssynchrony (sine wave pattern). S0 is the zero-order or constant term of the Fourier transform, and S1 is the first-order term, representing low frequency changes at a given time. The CURE for a given short-axis slice is generated first by determining instantaneous circumferential strains at 24 equally spaced segments in a short-axis slice at each time point, then subjecting this strain v. segment data to Fourier analysis with determination of the ratio of first- to zero-order power. MR-MT = magnetic resonance-myocardial tagging.
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Figure 2 MR-MT Temporal and Spatial Circumferential Strain Maps for a Normal Subject and a Subject With Cardiomyopathy and Dyssynchrony
In the normal subject, the progression of the strain versus time (negative strain represents systole) is uniform in each of the 24 segments in each slice (A), and there is synchronous negative strain for each segment along the circumference of the left ventricle (B). In the subject with dyssynchrony and cardiomyopathy, the strain versus time maps show variable timing of contraction (blue arrows = negative strain) and stretch (orange arrows = positive strain) in septal versus lateral segments (C). In this subject, some segments have positive strain (stretch) and others have negative strain (contraction) during systole (D). See Online Video. Abbreviation as in Figure 1.
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Figure 3 Correlations for MR-MT Circumferential Dyssynchrony (CURE), TDI Septal-Lateral Delay, and QRSd
The modest correlation between CURE and QRS duration (QRSd) is shown (r = –0.58, p < 0.001) for all 43 subjects in the cardiac resynchronization therapy heart failure (CRT-HF) and multimodality cohorts (A). For the multimodality cohort only (B), CURE and the tissue Doppler imaging (TDI) septal-lateral delay are shown versus QRSd. As expected (based on prior published data), there is no correlation between TDI and QRSd (r = 0.04, p = 0.83), but there is a significant correlation between CURE and QRSd (r = –0.60, p = 0.001) (B). The CURE-QRSd correlation is also shown (C) for the CRT-HF cohort only (r = –0.40, p = 0.08). Abbreviations as in Figure 1.
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Figure 4 Clinical Response to CRT Based on CMR Findings
These plots show data for individual improvement in function class for patients in the CRT-HF cohort based on baseline characteristics such as QRSd (A), CURE (B), and percent left ventricular scar volume by delayed enhancement-cardiac magnetic resonance (DE-CMR) (C). Those with function class improvement are shown in the left column of each panel, and those without improvement are shown in the right column of each panel. The QRSd (A) has no association with improvement in function class. MR-MT (B) has better accuracy (90%) than DE-CMR (78%) and (C) MR-MT and DE-CMR combined have superior accuracy (95%). This highlights the superior accuracy of CURE for predicting function class improvement. Abbreviations as in Figures 1 and 3.
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Figure 5 CRT Nonresponse Due to Extensive Scar
Scar imaging from a subject with significant circumferential dyssynchrony but CRT nonresponse shows extensive left ventricular scar on long-(A) and short-axis (B) images. This underscores the importance of CMR relative to echocardiography in the assessment of CRT candidates. Not only does MR-MT provide a very accurate measure of dyssynchrony, but the scar imaging data provide important information regarding the myocardial substrate such as extent and distribution of scar. Abbreviations as in Figures 1 and 3.
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