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PRECLINICAL STUDY: CARDIAC PHYSIOLOGY

Transmural Dispersion of Myofiber Mechanics

Implications 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, National Heart, Lung, and Blood Institute, Bethesda, Maryland
Office of Biostatistics Research, National Heart, Lung, and Blood Institute, Bethesda, Maryland

Manuscript received April 26, 2006; revised manuscript received July 5, 2006, accepted July 10, 2006.

^_* Reprint requests and correspondence: Dr. Hiroshi Ashikaga, Laboratory of Cardiac Energetics, NIH/NHLBI, 9000 Rockville Pike, Building 10/B1D416, Bethesda, Maryland 20892. (Email: ha8000{at}gmail.com).

OBJECTIVES: We investigated whether transmural mechanics could yield insight into the transmural electrical sequence.

BACKGROUND: Although the concept of transmural dispersion of repolarization has helped explain a variety of arrhythmias, its presence in vivo is still disputable.

METHODS: We studied the time course of transmural myofiber mechanics in the anterior left ventricle of normal canines in vivo (n = 14) using transmural bead markers under biplane cineradiography. In 4 of these animals, plunge electrodes were placed in the myocardial tissue within the bead set to measure transmural electrical sequence.

RESULTS: The onset of myofiber shortening was earliest at endocardial layers and progressively delayed toward epicardial layers (p < 0.001), resulting in transmural dispersion of myofiber shortening of 39 ms. The onset of myofiber relaxation was earliest at epicardial layers and most delayed at subendocardial layers (p = 0.004), resulting in transmural dispersion of myofiber relaxation of 83 ms. There was no significant transmural gradient in electrical repolarization (p = NS).

CONCLUSIONS: Despite lack of evidence of significant transmural gradient in electrical repolarization in vivo, there is transmural dispersion of myofiber relaxation as well as shortening.

Abbreviations and Acronyms   AoP = central aortic pressure   ECG = electrocardiogram   LA = left atrial   LAD = left anterior descending coronary artery   LAP = left atrial pressure   LCx = left circumflex coronary artery   LV = left ventricular   LVP = left ventriclar pressure   RMANOVA = repeated-measures analysis of variance   TDRelax = transmural dispersion of myofiber relaxation   TDRepol = transmural dispersion of repolarization   TDShort = transmural dispersion of myofiber shortening   3-D = 3-dimensional

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