From the Division of Cardiovascular Disease, Departments of Medicine,
Biomedical Engineering, and Physiology and Biophysics, University of Alabama
at Birmingham.
Correspondence to Raymond E. Ideker, MD, PhD, Cardiac Rhythm Management Laboratory, B140 Volker Hall, 1670 University Blvd, Birmingham, AL 35294-0019. E-mail rei{at}crml.uab.edu
Abstract
Background—Theoretical models
suggest that an electrical stimulus causes regions of depolarization
and hyperpolarization on either side of a
myocardial discontinuity. This study determined experimentally whether
an artificial discontinuity gives rise to an activation front in
response to an electrical stimulus, consistent with the
creation of such polarized regions.
Methods and Results—After a thoracotomy in six dogs, a
504-unipolar-electrode plaque was sutured to the right
ventricular epicardium to map activations. From a line
electrode parallel to one side of the plaque, 10 S1 stimuli
were delivered, followed by S2 and S3 stimuli
(S1S1, S1S2,
S2S3 interval=300 ms). S1 and
S3 stimuli were 25 mA; 5-ms S2 stimuli of both
polarities were initially 25 mA and increased in 25 mA increments. The
plaque was removed, and a transmural incision was made through the
ventricular wall in the middle of the mapped region and
sutured closed. The plaque was replaced and the stimulation protocol
repeated. Before the incision, S2 stimuli directly
activated tissue only near the stimulation site. An activation
front arose at the border of the directly activated region and
propagated across the plaque. As the S2 stimulus strength
was increased, the size of the directly activated region
increased. After the incision, sufficiently large S2
stimuli caused direct activation of tissue adjacent to the transmural
incision as well as at the stimulation site. Activation fronts that
arose adjacent to the transmural incision either propagated proximally
toward the stimulation site and collided with the activation front
originating from the stimulation wire or propagated distally away from
the incision. Minimum S2 stimulus strengths activating
areas adjacent to the incision were only 45±14% (cathode) and
39±18% (anode) of the strengths required to directly activate
the same area before the incision was formed
(P<.05).
Conclusions—Myocardial discontinuities can give rise to
activation fronts after a stimulus, suggesting the presence of
polarized regions adjacent to the discontinuity.
© 1998 American Heart Association, Inc.
Basic Science reports
Myocardial Discontinuities
A Substrate for Producing Virtual Electrodes That Directly Excite the Myocardium by Shocks
Key Words: defibrillation • excitation • mapping • electrical stimulation
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