[Role of accessory atrioventricular pathways in the genesis of permanent junctional tachycardia. Apropos of 2 cases].

Electrophysiological studies were performed in two patients with permanent junctional tachycardias. In both cases, the heart rate was 160/mn and standard ECG showed negative P waves in leads D2, D3 and AVF, isobiphasic or negative P waves in the left precordial leads and a PR interval of 0.12 and 0.13 secs. respectively. The tachycardia started without lengthening of the PR interval or preceding extrasystoles. Shortening of the sinus cycle before the tachycardia was inconstant. The reciprocating mechanism was shown by stimulation studies. Premature ventricular depolarisations not conducted to the atria were capable of terminating the attacks. Proof of His bundle bypass was obtained by the recording of the early atrial activity after ventricular stimulation at the time of His bundle depolarisation. The emergence of retrograde excitation in the left atrium in one of the cases was strongly suggestive of an accessory AV pathway. Atrial participation in the reentry loop was shown in both patients by premature atrial stimulation during tachycardia. This resulted in an earlier appearance of the His potential and QRS complex without affecting the reentrant excitation of the opposite atrium. The present study shows that accessory AV pathway with long retrograde conduction times may play a role in the initiation of permanent reciprocating junctional tachycardia. The functional characteristics of such pathways are suggestive of the presence of tissue with properties similar to that of the AV node. This data adds to our present knowledge of the mechanism of supraventricular tachycardia.