Intracardiac electrode catheter recordings of atrioventricular bypass tracts in Wolff-Parkinson-White syndrome: Techniques, electrophysiologic characteristics and demonstration of concealed and decremental propagation

Atrioventricular bypass tract deflections were recorded in five patients with the Wolff-Parkinson-White syndrome using standard, closely spaced (5 mm) electrode catheters. Three right paraseptal and two left-sided Kent bundles were recorded at the level of the tricuspid valve on the His bundle catheter and in the coronary sinus, respectively. Characteristics of the bypass tracts were studied during atrial pacing, programmed premature atrial stimulation, induction of supraventricular tachycardias and programmed ventricular stimulation. During atrial pacing, as pre-excitation increased, the stimulus to bypass tract deflection time remained unchanged. In five patients normalization of the QRS complex coincided with loss of the bypass tract deflection during incremental atrial pacing. Two patients demonstrated fragmentation of the bypass tract deflection before block. In one patient fragmentation of the bypass deflection coincided with normalization of the QRS complex. The effective refractory periods of the bypass tracts coincided with loss of bypass tract deflections in three of the five patients. In one patient, the effective refractory period of the bypass tract at its ventricular insertion preceded that at its atrial insertion, whereas in the remaining patient, the effective refractory period of the bypass tract was not attained because of atrial refractoriness. During orthodromic supraventricular tachycardia, the bypass tract deflections disappeared in the anterograde limb in all patients. In one patient, the bypass tract deflection was recorded during atrial fibrillation with pre-excitation.In conclusion: 1) Bypass tract deflections can be recorded with a closely spaced electrode catheter. 2) Right paraseptal bypass tracts are located close to the His bundle. 3) The anterograde effective refractory period of the bypass tract usually reflects its atrial insertion, but concealment through the bypass tract can occur with block at the ventricular insertion. 4) Decremental conduction within the bypass tract can occur before block, suggesting concealed and overt Wenckebach block within the bypass tract. 5) Recordings of bypass tract deflections increase the potential of closed chest ablation of right paraseptal and left-sided bypass tracts