VIRTUAL CATHODE EFFECTS DURING STIMULATION OF CARDIAC-MUSCLE - 2-DIMENSIONAL INVIVO EXPERIMENTS

被引:116
作者
WIKSWO, JP
WISIALOWSKI, TA
ALTEMEIER, WA
BALSER, JR
KOPELMAN, HA
RODEN, DM
机构
[1] VANDERBILT UNIV,MED CTR,SCH MED,DEPT PHARMACOL,NASHVILLE,TN 37232
[2] VANDERBILT UNIV,MED CTR,SCH MED,DEPT MED,NASHVILLE,TN 37232
关键词
VIRTUAL CATHODE; CARDIAC EXCITABILITY; LATENCY; CARDIAC PROPAGATION;
D O I
10.1161/01.RES.68.2.513
中图分类号
R5 [内科学];
学科分类号
1002 ; 100201 ;
摘要
We have found that when suprathreshold cathodal stimuli were applied to the epicardium of canine ventricle, impulse propagation originated at a "virtual cathode" with dimensions greater than those of the physical cathode. We report the two-dimensional geometry of the virtual cathode as a function of stimulus strength; the results are compared with the predictions of an anisotropic, bidomain model of cardiac conduction recently developed in our laboratories. Data were collected in six pentobarbital-anesthetized dogs by using a small plaque electrode sewn to the left ventricular epicardium. Arrival times at closely spaced bipolar electrodes oriented radially around a central cathode were obtained as a function of stimulus strength and fiber orientation. The dimensions of the virtual cathode were determined by linear back-extrapolation of arrival times to the time of stimulation. The directional dependence of the conduction velocity was consistent with previous reports: at 1 mA, longitudinal (0-degrees) and transverse (90-degrees) velocities were 0.60 +/- 0.03 and 0.29 +/- 0.02 m/sec, respectively. At 7 mA, the longitudinal velocity was 0.75 +/- 0.05 m/sec, whereas there was no significant change in the transverse velocity. In contrast to conduction velocity, the virtual cathode was smallest in the longitudinal orientation and largest between 45-degrees and 60-degrees. Virtual cathode size was dependent on both orientation and stimulus strength: at 0-degrees, the virtual cathode was small (approximately 1 mm) and relatively constant over the range of 1-7 mA; at oblique orientations (45-degrees-90-degrees), it displayed a roughly logarithmic dependence on stimulus strength, approximately 1 mm at 1 mA and approximately 3 mm at 7 mA. The bidomain, anisotropic model reproduced both the stimulus strength and the fiber-orientation dependence of the virtual cathode geometry when the intracellular and extracellular anisotropies were 10:1 and 4:1, respectively, but not when the two anisotropies were equal. We suggest that the virtual cathode provides a direct measure of the determinants of cardiac activation; its complex geometry appears to reflect the bidomain, anisotropic nature of cardiac muscle.
引用
收藏
页码:513 / 530
页数:18
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