PRECLINICAL STUDIES
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
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.
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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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