1. Verapamil does not affect atrial or anomalous bypass tract conduction characteristics, but selectively lengthens both refractoriness and conduction time of the AV node (Spurrell;et al; Zipes and Fischer, 1974). In all 3 patients verapamil prevented slow pathway conduction at AMA2 values less than the refractory period of the fast pathway thus preventing the resumption of conduction at close atrial coupling intervals and abolishing the gap phenomenon,1974
2. Anterograde gap phenomena produced by block distal to the AV node are generally masked by fast basic pacing rates and by drugs such as betablockers (Wit;Akhtar;et al; and verapamil which increase AV nodal functional refractoriness. These manoeuvres cannot, therefore, be used to distinguish gap phenomena related to AV nodal duality from those produced by inhomogeneous refractoriness along the length of a single AV nodal-His Purkinje pathway,1970
3. Agha, A. S., Befeler, B., Castellanos, A. M., Sung, R. J., Castillo, C. S., Myerbury, R. J., and Castellanos, A. (1976).
4. Bipolar catheter electrograms for study of retrograde atrial activation pattern in patients without pre-excitation syndromes;British Heart Journal
5. Type I, type II and type III gaps in bundle-branch conduction;Agha, A.S.; Castellanos, Jr., A.; Wells, D.; Ross, M.D.; Befeler, B.; Myerburg, R.J.;Circulation,1973