Wedensky facilitation. Electrotonic potentiation during complete A-V block.

The electrocardiogram recorded from a patient with third degree A-V block reflected almost regular A-V junctional escape rhythm. Some of the R-R cycles were slightly shorter than the basic escape cycle. A QRS complex ending such a relatively short R-R interval was always preceded by a sinus P wave, and had a QRS configuration which was minimally different from that of the escape complexes. The His bundle recording demonstrated that these minimally premature complexes were associated with an H-V interval which was shorter than that of the escape complexes. This indicates that the premature QRS complex could not be a capture beat. The relationship between the slightly premature QRS complex and the preceding sinus P-waves is explained on the basis of electrotonic potentiation or modulation to due Wedensky facilitation.