High-septal pacing reduces ventricular electrical remodeling and proarrhythmia in chronic atrioventricular block dogs.
OBJECTIVE
This study was designed to analyze the relevance of ventricular activation patterns for ventricular electrical remodeling after atrioventricular (AV) block in dogs.


BACKGROUND
Bradycardia is thought to be the main contributor to ventricular electrical remodeling after complete AV block. However, an altered ventricular activation pattern or AV dyssynchrony may also contribute.


METHODS
For 4 weeks, AV block dogs were either paced from the high-ventricular septum near the His bundle at lowest captured rate (n = 9, high-septal pacing [HSP]) or kept at idioventricular rate without controlled activation (n = 14, chronic AV block [CAVB]). Multiple electrocardiographic and electrophysiological parameters were measured under anesthesia at 0 and 4 weeks. Proarrhythmia was tested at 4 weeks by I(Kr) block (25 mug/kg dofetilide intravenous).


RESULTS
At 0 weeks, the 2 groups were comparable, whereas after 4 weeks of similar bradycardia, QT duration at unpaced conditions had increased from 300 +/- 5 to 395 +/- 18 ms in CAVB (+32 +/- 6%) and from 307 +/- 8 ms to 357 +/- 11 ms in HSP (+17 +/- 4%; p < 0.05). Frequency dependency of repolarization was less steep in HSP compared to CAVB dogs after 4 weeks remodeling. Beat-to-beat variability of repolarization, a proarrhythmic parameter, increased only in CAVB from 0 to 4 weeks. Torsades de pointes arrhythmias were induced at 4 weeks in 44% HSP versus 78% CAVB dogs (p = 0.17). Cumulative duration of arrhythmias per inducible dog was 87 +/- 36 s in CAVB and 30 +/- 21 s in HSP (p < 0.05).


CONCLUSIONS
High-septal pacing reduces the magnitude of ventricular electrical remodeling and proarrhythmia in AV block dogs, suggesting a larger role for altered ventricular activation pattern in the generation of ventricular electrical remodeling than previously assumed.
Winckels
Stephan K G
SK
Department of Medical Physiology, Heart Lung Center Utrecht, University Medical Center Utrecht, Utrecht, the Netherlands. s.k.g.winckels@umcutrecht.nl
Thomsen
Morten B
MB
Oosterhoff
Peter
P
Oros
Avram
A
Beekman
Jet D M
JD
Attevelt
Nico J M
NJ
Kretzers
Leo
L
Vos
Marc A
MA
D000200:Action Potentials; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000517:prevention & control*; D001919:Bradycardia / Q000503:physiopathology; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D004195:Disease Models, Animal; D004285:Dogs; D022062:Electrophysiologic Techniques, Cardiac; D006327:Heart Block / Q000503:physiopathology* / Q000628:therapy; D006329:Heart Conduction System / Q000503:physiopathology*; D006352:Heart Ventricles / Q000294:innervation / Q000503:physiopathology*; D020257:Ventricular Remodeling / Q000502:physiology*