LOW-FREQUENCY EXTRACELLULAR POTENTIALS RECORDED FROM THE SINOATRIAL NODE

Objective: To study the morphology of small extracellular potentials l ocalized to the sinoatrial (SA) node and to elucidate its potential us efulness in evaluating SA node dysfunction. Methods: Extracellular pot entials were recorded from the endocardial surface of the SA node in i solated right atrial preparations of rabbits through custom-made modif ied bipolar electrodes with high-gain amplification and a low-frequenc y (0.5-30 Hz) filter setting. Results: The potentials in and around th e SA node under control conditions showed a variety of morphologies. I n a small area near the leading pacemaker site, slow primary negative deflections were preceded by a gradual increase of the negativity (73. 5+/-5.6 mu V in amplitude, n=12). In the periphery of the SA node cran ial and caudal to the leading pacemaker site, slow positive/negative d eflections were recorded. In the septal side of the SA node showing ve ry slow conduction, the electrograms showed slow primary positive defl ections. Transient pacemaker shifts induced by atrial stimulation or v agal nerve stimulation were reflected well in morphologies of the extr acellular potentials. In the presence of 20 mu M TTX, wide and slow ne gative deflections were observed in the center and periphery of the SA node in association with extremely slow conduction restricted to a co rridor-like area along the crista terminalis, whereas the atrial muscl e surrounding the area was made inexcitable. In the presence of 1 mu M nifedipine, the leading pacemaker site was shifted to the periphery o f the SA node close to the crista terminalis. The negative deflection in the center and septal side of the SA node disappeared reflecting no excitation of the area. Conclusion: The endocardial extracellular ele ctrograms recorded in and around the SA node under appropriate conditi ons reflect two dimensional activation sequences. They would provide u seful information in recognizing the leading pacemaker site and altera tions of the conductivity and excitability. (C) 1998 Elsevier Science B.V. All rights reserved.