The purpose of this study was to test the feasibility of
neodymium-
yttrium-aluminum-garnet (
Nd-YAG) laser photocoagulation of the atrioventricular (AV) node to control the ventricular rate during rapid atrial rhythms without creating
AV block. In 12 dogs on normothermic
cardiopulmonary bypass, short
laser pulses were delivered to an area between the coronary sinus orifice and the site of the most proximally recorded His deflection until second degree
AV block occurred at a paced atrial rate of 200 beats/min. Long-term effects on AV node function were followed up for 3 months. Three animals developed chronic high grade
AV block. In nine animals with preserved 1:1 conduction, the mean (+/- SEM) critical atrial cycle length resulting in AV node Wenckebach periodicity increased from 183 +/- 6 to 261 +/- 24 ms (+43%), the mean RR interval during induced
atrial fibrillation increased from 248 +/- 14 to 330 +/- 27
ms (+32%) and the shortest RR interval during
atrial fibrillation increased from 215 +/- 11 to 275 +/- 20
ms (+28%).
Laser effects were not reversed by
isoproterenol infusion. Histologic examination of the irradiated area showed fibrotic changes in the AV node and fatty metamorphosis. This study suggests that 1) graded
Nd-YAG laser photocoagulation of the AV node region in dogs results in long-term modification of anterograde AV node transmission properties; 2) 1:1 conduction during sinus rhythm usually remains preserved, but ventricular rate during rapid atrial rhythms is chronically reduced; and 3) progression to high grade
AV block occurs in a minority of animals.(ABSTRACT TRUNCATED AT 250 WORDS)