Transmural Dispersion of Myofiber MechanicsImplications for Electrical Heterogeneity In Vivo
Hiroshi Ashikaga, MD*, ,*,
Benjamin A. Coppola, BS*,
Bruce Hopenfeld, PhD,
Eric S. Leifer, PhD ,
Elliot R. McVeigh, PhD and
Jeffrey H. Omens, PhD*
* *Department of Medicine and Bioengineering, University of California, San Diego, La Jolla, California
Laboratory of Cardiac Energetics
Office of Biostatistics Research, National Heart, Lung, and Blood Institute, Bethesda, Maryland
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Figure 1 Schematic Representation of the Heart
The transmural bead set was implanted between the first (D1) and the second (D2) diagonal branch of the left anterior descending coronary artery (LAD) to measure finite deformation of the myocardial tissue across the wall. Endo = endocardium; Epi = epicardium; LCx = left circumflex coronary artery; LV = left ventricle.
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Figure 3 Transmural Fiber Orientation
Values are mean ± SD (n = 14). Fiber angles were measured with reference to the positive circumferential direction. Abbreviations as in Figure 1.
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Figure 4 Time Course of Transmural Fiber Strains
(A) Entire cardiac cycle. Different colors represent the percent wall depth from the epicardial surface. Open circles = onset of myofiber shortening; open squares = onset of myofiber relaxation. (B) A closer look at TDShort. (C) A closer look at TDRelax. AoP = central aortic pressure; ECG = electrocardiogram; LAP = left atrial pressure; LVP = left ventricular pressure; TDRelax = transmural dispersion of myofiber relaxation; TDShort = transmural dispersion of myofiber shortening.
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Figure 5 Transmural Dispersion of Myofiber Mechanics
Values are mean and error bars indicate SD (n = 14). Open circles = onset of myofiber shortening; open squares = onset of myofiber relaxation. Endo = endocardium; Epi = epicardium; TDRelax = transmural dispersion of myofiber relaxation; TDShort = transmural dispersion of myofiber shortening.
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Figure 2 Bipolar Electrograms From Plunge Electrodes
Red and blue dots mark the time points of steepest portion of initial bipolar QRS waveforms and end of the T wave, respectively. Note the endocardial-to-epicardial direction of depolarization, whereas no clear transmural dispersion of repolarization is observed.
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Figure 6 Electrical Activation and the Onset of Myofiber Shortening Versus Mean Wall Depth
Open triangles = electrical activation (n = 4) mean value at each depth (mm); open circles = onset of myofiber shortening (n = 14) mean value at each depth (mm). Abbreviations as in Figure 1.
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Figure 7 Electrical Repolarization and the Onset of Myofiber Relaxation Versus Mean Wall Depth
Closed triangles = electrical repolarization (n = 4) mean value at each depth (mm); open squares = onset of myofiber shortening (n = 14) mean value at each depth (mm). Abbreviations as in Figure 1.
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Figure 8 Transmural Tissue Coupling
Red and green lines = strains in epicardial (0% wall depth) and endocardial (90% wall depth) layers, respectively. Solid and broken lines = fiber and cross-fiber strains, respectively. AoP = central aortic pressure; ECG = electrocardiogram; IVC = isovolumic contraction; IVR = isovolumic relaxation; LAP = left atrial pressure; LVP = left ventricular pressure.
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