Studies of intra-atrial conduction with bipolar atrial and His electrograms.

With the use of His bundle electrograms, intra-atrial conduction delay has been found to be a cause offirstdegree heart block. Twenty-one patients with evidence of atrioventricular conduction defects or dysrhythmias were studied with His bundle electrograms and 2 were found to have delayed intra-atrial conduction while in sinus rhythm. A further 3 patients had normal PA intervals during sinus rhythm but prolonged StA intervals during atrial pacing. The significance of this is discussed. In view of the difficulty in timing the onset of atrial depolarization from the surface electrocardiogram, a bipolar electrogram from the high right atrium recorded simultaneously with the His electrogram was used to time intra-atrial conduction in II patients. This interval wasfound to be significantly greater than the PA interval measured from the surface electrocardiogram. It is suggested that this be done routinely during recording of His bundle electrograms.