Tridimensional activation patterns of acquired torsade-de-pointes tachycardias in dogs with chronic AV-block.
BACKGROUND
Dogs with chronic AV block exposed to type-III antiarrhythmic agents develop polymorphic ventricular tachycardias (PVT). Controversy exists regarding PVT mechanism and underlying pathophysiology.


RESULTS
In dogs with acute (n = 10, AAVB) or chronic AV block (n = 14, CAVB, 62 +/- 5 days after AV-node ablation) 60 pins (12 mm long, 4 bipolar electrodes) were inserted into both ventricles. QT intervals and effective refractory periods (ERP) at 56 +/- 22 randomly selected sites (extrastimulus technique, 800 ms basic cycle length) were determined before and after Almokalant (0.34 micromol/kg). A multiplexer mapping system was used to reconstruct 3D activation patterns. The heart-to-body-weight index (HBWI) was obtained after the experiments. CAVB led to a significant increase in HBWI (11.3 +/- 1.5 vs. 9 +/- 1.2 g/kg BW, p < 0.001), and a significant increase in ERP (280 +/- 28 ms vs. 260 +/- 37 ms, p < 0.05) and QT interval (339 +/- 16 vs. 288 +/-12 ms, p < 0.05). Dispersion (DISP) of ERP was similar for AAVB and CAVB dogs. No AAVB dog, but 9 of 14 CAVB dogs developed PVTs in response to Almokalant. All PVTs originated from an endocardial focus. Consecutive beats continued to reveal centrifugal activation patterns in 8 of 10 episodes. In only 2 episodes was reentrant activation evident.


CONCLUSIONS
Myocardial hypertrophy associated with CAVB predisposes the canine heart to drug induced PVTs. This seems to be primarily linked to prolonged repolarization. PVTs in this model are not only initiated, but also perpetuated by a centrifugal spread of activation.
Schreiner
Kirsten D
KD
University of Heidelberg, Department of Cardiology, Bergheimerstr 58, 69115, Heidelberg, Germany. Dr.Mark.Schreiner@telemed.de
Voss
Frederik
F
Senges
Julia C
JC
Becker
Ruediger
R
Kraft
Patrizia
P
Bauer
Alexander
A
Kelemen
Kamilla
K
Kuebler
Wolfgang
W
Vos
Marc A
MA
Schoels
Wolfgang
W
D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000009:adverse effects*; D006332:Cardiomegaly / Q000150:complications / Q000503:physiopathology; D004285:Dogs; D004562:Electrocardiography; D006327:Heart Block / Q000150:complications / Q000503:physiopathology; D006329:Heart Conduction System / Q000503:physiopathology*; D023421:Models, Animal; D011412:Propanolamines / Q000009:adverse effects*; D016171:Torsades de Pointes / Q000139:chemically induced* / Q000503:physiopathology*
D000889:Anti-Arrhythmia Agents; D011412:Propanolamines; C074334:almokalant