Recording of diastolic slope with catheters during junctional rhythm in humans.

Junctional diastolic slopes were recorded in 11 of 15 patients (73.3%) with junctional rhythm that occurred spontaneously, after intravenous administration of atropine (1 mg), or during carotid sinus massage. The diastolic slopes were recorded through a unipolar lead consisting of a terminal of an electrode catheter placed in the His bundle area paired with an indifferent terminal on the superior vena cava. The slope of these diastolic deflections -0.18 +/- 0.06 m V/sec (mean +/- SD). Overdrive atrial and ventricular stimulations were followed by slowing of the junctional rate and decrease in the diastolic slope. Strong negative correlations (r values from -.71 to -.95) were found between the junctional cycle lengths and the diastolic slopes after atrial or ventricular pacing. Carotid sinus massage decreased the junctional rate and the junctional diastolic slope, whereas atropine increased the junctional rate and the junctional diastolic slope. Since prolongation of junctional cycle lengths after atrial pacing did not depend on frequency of impulse penetration into the His bundle, we postulate that the junctional pacemaker responsible for the junctional rhythm in some of our patients was in the N region of the AV node. Application of this recording method should help in the identification and characterization of automatic junctional pacemakers.