Measurement of the inducing rate of arrhythmia
Programmed electrical stimulation
(S1S2S3) and burst
pacing (S1S1) were used sequentially to
induce arrhythmia at baseline, after drug administration, or during
LL-ES of ARVGP. Atrial arrhythmia was provoked first by
S1S2S3at the base of the
left atrial appendage, and ventricular arrhythmia was induced at the
left ventricular via bipolar screw-in pacing with leads fixed
epicardially[8]. Each two-burst pacing protocol was performed with a
10 min interval in-between to allow for recovery from the rapid pacing
to occur via atrial remodeling. The programmed stimulation protocol was
set at basic cycle lengths of 400 and 300 ms with up to two extra
stimuli (S3). All stimuli were monitored on a 64-channel
electrophysiological recorder (Henan Huanan Medical Science &
Technology Co., Zhengzhou, China). The first extra stimulus
(S2) was introduced with an
S1-S2 interval 30 ms longer than the
atrial effective refractory period, and the coupling interval was
shortened in 10 ms decrements. If the
S1-S2 extra stimuli failed to induce
arrhythmia, a second extra stimulus (S3) was introduced
at 10 ms scanning decrements during an
S1-S2 interval set at 80% of the basic
cycle length. If programmed stimulation failed to induce arrhythmia,
burst pacing at a cycle length of 200 ms for 30 seconds was applied to
provoke arrhythmia, and the cycle length was subsequently decreased to
160 and 120 ms if 200 ms was ineffective. The above electrical
stimulation procedure was repeated twice. A successful endpoint was
defined as arrhythmia started either by
S1S2S3, by a subsequent
S1S1, or both if either procedure
failed. Arrhythmiais defined as atrial or ventricular tachycardia
(sustained>10sec), atrial fibrillation
(sustained>30sec), or ventricular flutter or fibrillation.
If malignant arrhythmia occurred (persistent ventricular tachycardia
over 5 min or ventricular flutter or fibrillation), epicardial
electrical conversion (50J) was performed immediately to recover a
stable internal environment.
Measurement of VERP, stroke volume of the LV, and
ejection fraction of the
LV
VERP was measured at baseline and after treatment with a placebo, drugs,
and LL-ES, respectively. It was recorded using the extra stimulus
technique (basic cycle length of 400 ms and final extra stimulus steps
of 5 ms; Electrophysiological Recorder, 64 channels, Henan Huanan
Medical Science & Technology Co., Zhengzhou, China).
Furthermore,transthoracic
echocardiography was performed with dogs in the left lateral decubitus
position, breathing slowly, using aphased-array probe(Vivid E9, GE,
USA). The LV endocardial surface was detected using the Simpson′s method
from the apical four-chamber view and the apical right heart two-chamber
view to measure LVEDV and LVESV. Then, LVSV and LVEF were obtained at
baseline and after 1 week of treatment with a placebo, drug, and LL-ES,
respectively.