Microtransection of the His bundle with laser radiation through a pervenous catheter: Correlation of histologic and electrophysiologic data

Abstract This study describes microtransection of the His bundle with a pervenous laser catheter in a live dog. In an adult mongrel dog anesthetized with Nembutol®, administered intravenously, electrode catheters (No. 5Fr and 6Fr) were inserted through a femoral vein and positioned in the high right atrium for atrial pacing and in the His bundle region for recording of His bundle electrograms. The AH and HV intervals were measured during normal sinus rhythm and atrial pacing. Through another femoral vein, a laser fiber was inserted through a lumen catheter (No. 7Fr) with a preformed curved tip. Under fluoroscopic control, the laser fiber tip was positioned immediately next to the His bundle electrode catheter. During continuous His bundle recordings and fluoroscopic monitoring, short bursts (10 to 60 seconds) of argon laser were delivered (2.5 W) in order to produce His bundle interruption and complete heart block. Escape of a His bundle rhythm (cycle length = 1,100 ms) with QRS morphologic characteristics and duration similar to that of normal sinus rhythm was noted. “Split” His bundle potentials were recorded with an unchanged AH (50 ms) and an H'V interval of 20 ms. After the dog was killed, serial sections of the conduction system of the heart were analyzed. Histologic findings showed excellent correlation with electrophysiologic observations and validated “split” His bundle potentials. The laser radiation produced microtransection of the His bundle with a channel of tissue dissolution 0.2 to 0.3 mm wide in diameter. The latter passed through the His bundle at the junction of penetrating and branching segments, dividing it into superior and inferior portions that retained continuity with proximal and distal His bundle. Histologically, the atrioventricular node, proximal and distal His bundle segments and bundle branches were uninjured with laser radiation, and are consistent with an unchanged AH time, QRS duration and morphology. This study demonstrates that the His bundle can be precisely transected with a pervenous laser catheter technique.