EFFECTS OF INTRACAVITARY BLOOD-FLOW AND ELECTRODE-TARGET DISTANCE ON RADIOFREQUENCY POWER REQUIRED FOR TRANSIENT CONDUCTION BLOCK IN A LANGENDORFF-PERFUSED CANINE MODEL

Objectives, We sought to quantify the effects of electrode-target dist ance and intracavitary blood how on radiofrequency (RF) pow er require d to induce transient conduction block, using a Langendorff-perfused c anine ablation model. Background. Given the thermally mediated nature of RF catheter ablation, cooling effects of intracavitary blood flow a nd electrode-target distance will influence lesion extension and geome try and electrophysiologic effects. Methods. In eight Langendorf-perfu sed canine hearts, the right ventricular free wall was opened, and the right bundle branch (RBB) carefully localized by multielectrode activ ation mapping, The right atrium was paced at cycle length of 500 ms, P roximal and distal electrodes were attached at the endocardial aspect of the RBB, and the perfused heart was submerged in heparinized blood at 37 degrees C, A standard 4-mm tip ablation electrode was positioned at a constant contact pressure of 5g between the two electrodes at th e site of maximal RBB potential (0 mm) and 2 and 4 mm distant from thi s site along a line perpendicular to the RBB, RF pulses (500 kHz) were delivered for 30s at 0.5-W increments until transient bundle branch b lock, In four hearts, intracavitary flow was simulated by directing a 30-cm/s jet of blood parallel to the septum at the ablation site, and the protocol was repeated to assess the effects on power required for block In one heart, the effect of variable flow was assessed (0, 15 an d 30 cm/s). Results. An exponential distance related increase was seen in power required for block, from 1.8 +/- 0.9 W (mean +/- SD) at 0 mm to 5.4 +/- 1.1 W at 4 mm. In the presence of 30-cm/s flow, an increas e to 3.9 +/- 0.8 W at 0 mm and 13.1 +/- 2.4 W at 2 mm was seen. At 4 m m, coagulum formation invariably occurred before block could be induce d, For 15-cm/s flow, less power was required: 3 and 7 W at 0 and 2 mm, respectively. Conclusions. Increasing the ablation electrode-target d istance causes an exponential increase in power required for conductio n block; this relation is profoundly influenced by intracavitary flow, Given the geometry of endomyocardial RF lesions, these findings are p articularly relevant for directly subendocardial ablation targets. (C) 1998 by the American College of Cardiology.