RADIOFREQUENCY CATHETER MODIFICATION OF SINUS PACEMAKER FUNCTION GUIDED BY INTRACARDIAC ECHOCARDIOGRAPHY

Background The sinus P wave arises from a pacemaker complex distribute d along the crista terminalis. We investigated the feasibility of modi fication of sinus pacemaker function using graded applications of radi ofrequency energy along the crista terminalis in dogs to achieve sinus rate control. Methods and Results Modification of sinus pacemaker fun ction (30+/-5% reduction in intrinsic heart rate with retention of a n ormal P-wave axis) was performed in 11 dogs (group 1). Total sinus pac emaker ablation (>50% reduction in intrinsic heart rate with developme nt of a low ectopic atrial or a junctional rhythm) was performed in 4 dogs (group 2). Intracardiac echocardiography was used to identify the crista terminalis as an anatomic marker of sinus node location. Sinus pacemaker modification caused a significant decrease in intrinsic hea rt rate (31% reduction, P<.001), heart rate responsiveness to isoprote renol (30% reduction, P<.0001), and average (20% reduction, P=.0002) a nd maximal (22% reduction, P=.0007) heart rates during 24-hour Holter monitoring. In 6 of the 11 animals, the targeted rate reduction of 30/-5% was accurately achieved (mean, 31.6+/-4.3%; P<.001), and in the o ther 5, significant reduction of intrinsic heart rate was achieved but with greater variation (28.0+/-17.3%, P<.005). Corrected sinus node r ecovery time was not prolonged. After modification, earliest activatio n was mapped to the crista terminalis inferior to the lesion in all an imals. In long-term follow-up (3.7+/-1.0 months), effects were maintai ned. After total sinus pacemacker ablation, junctional and low atrial escape pacemakers were unstable. Conclusions This study demonstrates t he feasibility of modification of sinus pacemaker function for sinus r ate control using catheter-based radiofrequency ablation guided by int racardiac echocardiography. This can be done while pacemaker stability and attenuated responsiveness to autonomic influences are preserved. Intracardiac echocardiography accurately defined the crista terminalis and provided a reliable means to anatomically localize catheter posit ion in relation to the sinus node.