Journal
AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY
Volume 294, Issue 4, Pages H1753-H1766Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpheart.01400.2007
Keywords
propagation patterns; excitation mapping
Funding
- NCRR NIH HHS [P41-RR12553, P41 RR012553, P41 RR012553-09] Funding Source: Medline
- NIGMS NIH HHS [P41 GM103545] Funding Source: Medline
- NATIONAL CENTER FOR RESEARCH RESOURCES [P41RR012553] Funding Source: NIH RePORTER
- NATIONAL INSTITUTE OF GENERAL MEDICAL SCIENCES [P41GM103545] Funding Source: NIH RePORTER
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Published studies show that ventricular pacing in canine hearts produces three distinct patterns of epicardial excitation: elliptical isochrones near an epicardial pacing site, with asymmetric bulges; areas with high propagation velocity, up to 2 or 3 m/s and numerous breakthrough sites; and lower velocity areas (< 1 m/s), where excitation moves across the epicardial projection of the septum. With increasing pacing depth, the magnitude of epicardial potential maxima becomes asymmetric. The electrophysiological mechanisms that generate the distinct patterns have not been fully elucidated. In this study, we investigated those mechanisms experimentally. Under pentobarbital anesthesia, epicardial and intramural excitation isochrone and potential maps have been recorded from 22 exposed or isolated dog hearts, by means of epicardial electrode arrays and transmural plunge electrodes. In five experiments, a ventricular cavity was perfused with diluted Lugol solution. The epicardial bulges result from electrotonic attraction from the helically shaped subepicardial portions of the wave front. The high-velocity patterns and the associated multiple breakthroughs are due to involvement of the Purkinje network. The low velocity at the septum crossing is due to the missing Purkinje involvement in that area. The asymmetric magnitude of the epicardial potential maxima and the shift of the breakthrough sites provoked by deep stimulation are a consequence of the epi-endocardial obliqueness of the intramural fibers. These results improve our understanding of intramural and epicardial propagation during premature ventricular contractions and paced beats. This can be useful for interpreting epicardial maps recorded at surgery or inversely computed from body surface ECGs.
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