[An experimental study on the selective ablation of AV node].

26 dogs were divided into two equal groups. Each dog was anesthetized, and a tetrapolar electrode was inserted transvenously to the area of AV junction. Unipolar leads of HBE were recorded with each of the four electrodes. The electrode where the highest H wave was recorded was considered to the contiguous to the His bundle, and the first or the second electrode proximal to the above-mentioned one was considered as in the vicinity of the AV node. These electrodes were used as cathodes, and electric discharges were performed with an external defibrillator. Two dogs in each group died of VF during discharge. Complete AV blocks were produced in all the other dogs. After discharge, in each of the 11 dogs in His bundle ablation group, the H wave disappeared, the escaping rhythm was slower and irregular, the QRS interval was wide, multiple ventricular extrasystoles or VT occurred, and 4 dogs died due to cardiac arrest within 3 days. These manifestations denoted that the block was situated in the His bundle, and the escaping rhythm focus located within the bundle branch or the ventricle. In contrast, the H waves still existed in 9 dogs of the AV node ablation group, the A waves dissociated with the H waves, the relationship between H waves and V waves was fixed, and H-V intervals were the same as before discharge. In all the 11 dogs, the morphology and the width of QRS did not change in comparison with those before discharge, the escaping rhythm was quicker and regular, and the incidence of ventricular extrasystole was low.(ABSTRACT TRUNCATED AT 250 WORDS)