TY - JOUR
T1 - Near-threshold field stimulation
T2 - Intramural versus surface activation
AU - Zemlin, Christian W.
AU - Mironov, Sergey
AU - Pertsov, Arkady M.
N1 - Funding Information:
We thank Olivier Bernus, Marcel Wellner, and Arvydas Matiukas for useful discussions and Marcel Wellner and Charles Danko for carefully reading the manuscript. Research in this article has been supported by AHA grant #0325458T and by NIH grants 5P01HL039707, 5R01HL071635, and 5R01HL071762.
PY - 2006/1
Y1 - 2006/1
N2 - Objective: The mechanism by which an electric field terminates arrhythmias continues to puzzle investigators. Existing experimental methods provide information about epicardial manifestations of electrical cardioversion, yet little is known about field effects deep inside the myocardium. Here we combine specially designed optical mapping experiments and computer modeling to separate the intra-myocardial and surface field effects. Methods: We used isolated coronary perfused and superfused slabs of pig right ventricular wall (n = 6) stained with di-4-ANNEPS. A uniform transmural field was produced via two parallel planar (5 x 5 cm) transparent mesh electrodes aligned with the endocardial and epicardial surfaces. Low-intensity shocks (≤ 3.3 V/cm) were applied during diastole. The electrical activity under both electrodes was recorded simultaneously using two CCD cameras at 800 frames/s. Shock responses were also simulated using a bidomain Luo-Rudy model. Results: We discovered that during the near-threshold diastolic field stimulation, when surface polarization should be dominant, the early activation occurs not at the cathodal surface, as might be expected, but deep inside the myocardium. Comparison of epi- and endocardial activation delays suggests that the sites of early activation are located closer to the endocardium. Our experimental observations could be reproduced computationally by assuming large resistive heterogeneities inside the myocardial wall. Conclusions: Surface polarization plays a minor role during field stimulation. Intramural virtual electrodes produced even by weak fields are sufficiently strong to initiate intra-myocardial excitation. Significant heterogeneities in tissue resistivity may explain the strength of the virtual electrodes.
AB - Objective: The mechanism by which an electric field terminates arrhythmias continues to puzzle investigators. Existing experimental methods provide information about epicardial manifestations of electrical cardioversion, yet little is known about field effects deep inside the myocardium. Here we combine specially designed optical mapping experiments and computer modeling to separate the intra-myocardial and surface field effects. Methods: We used isolated coronary perfused and superfused slabs of pig right ventricular wall (n = 6) stained with di-4-ANNEPS. A uniform transmural field was produced via two parallel planar (5 x 5 cm) transparent mesh electrodes aligned with the endocardial and epicardial surfaces. Low-intensity shocks (≤ 3.3 V/cm) were applied during diastole. The electrical activity under both electrodes was recorded simultaneously using two CCD cameras at 800 frames/s. Shock responses were also simulated using a bidomain Luo-Rudy model. Results: We discovered that during the near-threshold diastolic field stimulation, when surface polarization should be dominant, the early activation occurs not at the cathodal surface, as might be expected, but deep inside the myocardium. Comparison of epi- and endocardial activation delays suggests that the sites of early activation are located closer to the endocardium. Our experimental observations could be reproduced computationally by assuming large resistive heterogeneities inside the myocardial wall. Conclusions: Surface polarization plays a minor role during field stimulation. Intramural virtual electrodes produced even by weak fields are sufficiently strong to initiate intra-myocardial excitation. Significant heterogeneities in tissue resistivity may explain the strength of the virtual electrodes.
KW - Defibrillation
KW - Excitation
KW - Optical mapping
KW - Virtual electrodes
KW - Voltage-sensitive dyes
UR - http://www.scopus.com/inward/record.url?scp=29144495657&partnerID=8YFLogxK
U2 - 10.1016/j.cardiores.2005.08.012
DO - 10.1016/j.cardiores.2005.08.012
M3 - Article
C2 - 16226236
AN - SCOPUS:29144495657
SN - 0008-6363
VL - 69
SP - 98
EP - 106
JO - Cardiovascular Research
JF - Cardiovascular Research
IS - 1
ER -