Effects of mid-myocardial pacing on transmural dispersion of repolarization and arrhythmogenesis.
BACKGROUND
Epicardial (Epi) activation of the left ventricular (LV) wall increases transmural dispersion of repolarization (TDR), which creates a substrate for the development of ventricular arrhythmia. We hypothesize that pacing from the LV mid-myocardium may decrease the TDR and occurrence of arrhythmias.


RESULTS
A transmural electrocardiogram and transmembrane action potentials were simultaneously recorded from Epi, mid-myocardial (M), and endocardial (Endo) layers of the arterially perfused canine LV wedge preparations (n= 8). Transmural dispersion of repolarization varied when the preparations were paced at each layer, respectively (Endo pacing, 35.6 ± 6.6 ms; M pacing, 34.9 ± 7.3 ms; Epi pacing, 72.4 ± 4.9 ms; P< 0.001). A significant difference was noted in TDR between M pacing and Epi pacing (P< 0.001), but not between M pacing and Endo pacing (P= 0.831). This result was reproducible in the presence of ischaemia-reperfusion experiments (n= 8). Transmural dispersion of repolarization was amplified as compared with non-ischaemic experiments and differed when preparations were paced at each layer (Endo pacing, 62.8 ± 13.8 ms; M pacing, 63.3 ± 13.3 ms; Epi pacing, 111.1 ± 17.7 ms; P< 0.001). There was again no significant difference between Endo pacing and M pacing (P= 0.948). However, as pacing was shifted from M to Epi, there was a significant increase in TDR (P< 0.001). Ventricular arrhythmias were induced in two of eight ischaemic preparations during Epi pacing, but did not occur in either M or Endo pacing.


CONCLUSIONS
Mid-myocardial pacing can significantly decrease the TDR and prevent the occurrence of ventricular arrhythmias as compared with Epi pacing.
Department of Cardiology,  Shanghai Changzheng Hospital,  Second Military Medical University, Shanghai 200003,  People's Republic of China.
Tao
T
Xu
Hao
H
Wang
Jia-You
JY
Zhang
Yu
Y
Zhang
Ran
R
Zhang
Li-Qin
LQ
Jiang
Ji-Feng
JF
Zheng
Hang
H
Zhu
Zong-Gui
ZG
Wu
De-Ning
DN
Liao
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000209:etiology / Q000503:physiopathology*; D004285:Dogs; D004562:Electrocardiography / Q000295:instrumentation / Q000379:methods*; D006352:Heart Ventricles / Q000503:physiopathology*; D008564:Membrane Potentials / Q000502:physiology; D015427:Reperfusion Injury / Q000503:physiopathology