RIGHT ATRIAL FREE-WALL CONDUCTION-VELOCITY AND DEGREE OF ANISOTROPY IN PATIENTS WITH STABLE SINUS RHYTHM STUDIED DURING OPEN-HEART-SURGERY

Aims Although the perpetuation of several supraventricu lar arrhythmia s is critically dependent upon intra-atrial conduction, the literature lacks detailed information on normal values of conduction velocity an d degree of anisotropy. In order to explore these factors further, we have measured conduction velocities at the right atrial free wall duri ng sinus rhythm and during atrial pacing in four directions parallel a nd perpendicular to the atrioventricular groove in patients with norma l atria and stable sinus rhythm. Methods and Results Using a Bard Card iac Mapping System, atrial ECGs were recorded using a 3 x 4 cm electro de array with 56 equally spaced bipolar electrodes in 12 patients unde rgoing open heart surgery due to ischaemic heart disease or Wolff-Park inson-White syndrome. A bipolar pen probe connected to a Medtronic 532 8 stimulator was used for pacing at a 10% higher rate than sinus rhyth m. The local activation times were manually set and isochronal activat ion maps were created for each recording. The conduction velocities we re calculated from the activation maps over a distance ranging from 2. 2 to 4.2 cm. The majority of the activation maps showed no signs of an isotropy; the others had less than 15% spatial inhomogeneity of conduc tion. Mean conduction velocity, calculated from five consecutive beats , was 88 +/- 9 cm. s(-1) (mean +/- SD), ranging between 68 +/- 4 and 1 03 +/- 3 cm. s(-1) during sinus rhythm. Mean conduction velocity durin g atrial pacing was 81 +/- 16 cm. s(-1) at a propagation direction of 0 degrees, 74 +/- 14 cm. s(-1) at a 90 degrees direction, 79 +/- 12 cm . s(-1) at 180 degrees and 78 +/- 20 cm. s(-1) at 270 degrees, where 0 degrees was parallel to the atrioventricular groove in the cranial di rection and the angle increased counter-clockwise. Mean conduction vel ocity during sinus rhythm was significantly higher (P<0.05) than durin g atrial pacing at the 90 degrees and 180 degrees directions but not c ompared to atrial pacing at 0 degrees or 270 degrees. There was no sig nificant difference in mean conduction velocity in different direction s during atrial pacing. Conclusion Although anisotropy was documented during conduction velocity in individual cases, conduction velocity wa s not dependent on propagation direction at the epicardial right atria l free wall in patients with stable sinus rhythm. These findings do no t exclude the presence of internodal preferential pathways as these ar e located sub-epicardially and a marked transmural discordance in acti vation has previously been documented in the vicinity of such pathways .