Laser catheter-induced atrioventricular nodal delays and atrioventricular block in dogs: Acute and chronic observations

Selective modification of atrioventricular (AV) nodal conduction, that is, induction of varying degrees of AV nodal delays or block (second or third degree), or both, was achieved with a pervenous laser catheter technique. In six adult mongrel dogs anesthetized with pentobarbital (Nembutal), 5F leads were placed through femoral and external jugular veins and placed into the right atrium and His bundle region. Through another femoral vein, a 200 μm optical fiber was inserted by way of a 7F catheter with a preformed curved tip. Guided by fluoroscopy and His bundle electrograms, the fiber's tip was positioned in the AV nodal region. After autonomic blockade was achieved with intravenous propranolol (5 mg) and atropine (1 mg), AV conduction was analyzed. An argon laser delivered 3 to 4 watts into the fiber in bursts of 10 seconds' duration until the desired degree of AV nodal delay or block (second or third degree) was manifested. Monitoring of His bundle electrograms was continued for 2 hours. Four weekly serial electrocardiograms were recorded, after which electrophysiologic studies were repeated. Acute post-lasing studies showed that: 1) in all six dogs, the mean PR interval was prolonged from 116 ms (range 100 to 135) to 153 ms (range 120 to 185), with the prolongation being caused exclusively by AH lengthening from 68 ms (range 50 to 90) to 105 ms (range 65 to 140); 2) the mean effective refractory period of the AV node increased from less than 185 ms (range <150 to <200) to 215 ms (range 190 to 280); and 3) the mean atrial pacing cycle length, at which second degree AV nodal block was manifested, increased from 210 ms (range 160 to 260) to 261 ms (range 205 to 320). The PA, H and HV intervals and QRS complex remained constant. In two of the six dogs, additional radiation produced second and eventually third degree AH block with an escape junctional rhythm, HV interval and QRS complex identical to those during control normal sinus rhythm. After 2 hours, the junctional rhythm was replaced by a distal rhythm that persisted for the next 4 weeks. In the remaining four dogs, persistence of AV nodal delays was noted when the dogs were restudied at 4 weeks. None of the dogs exhibited any complications during the acute or chronic observations. The potential application of this technique to slow AV nodal conduction for management of supraventricular tachyarrhythmias in human beings merits further clinical investigation.