Atrial Preexcitation Research Articles

Further observations on the ventricular echo phenomenon elicited in the human heart. Is the atrium part of the echo pathway?

In order to answer the question whether the atrium is a link in the pathway of ventricular reciprocation or whether the A-V node itself is the reflection point of the echo, a special stimulation program was followed in six patients in whom ventricular echo beats with stable time relations could be elicited by regular pacing of the right ventricle or by the application of appropriately timed right ventricular premature beats during regular pacing of the right ventricle. In these experiments the atrial septum was stimulated earlier than the expected arrival at the atrium of the retrograde impulse in the course of the echo sequence. The influence of stepwise (steps of 5 msec) advancing of this atrial "preexcitation" on the timing of the ventricular echo beat was studied. We found that the atrial septum could be preexcited without interfering with the ventricular echo beat time relations over a time interval less than 5 msec in one patient, less than 10 msec in one, less than 20 msec in two, and less than 30 msec in two cases. When the time interval needed for the stimulated atrial impulse to reach the atrionodal margin is taken into account, it seems likely that the atrium participated in the echo pathway in the four cases with minimal atrial preexcitation intervals of 20 msec or less, and that in the two cases with a minimal atrial preexcitation interval of 30 msec the echo reflection point was localized in the upper part of the A-V node.

Retrograde activation of the His bundle during intermittent paired ventricular stimulation in the human heart.

Intermittent paired ventricular pacing was performed in five patients, one of them with Wolff-Parkinson-White (WPW) syndrome. Retrograde activation of the His bundle and of the atria was observed in all patients. Bipolar leads with interelectrode distances of 1 mm seemed to be slightly better than the conventional ones (10 mm apart) for the identification of His (H) deflections buried inside the QRS complexes. Diagnosis of retrograde atrial activation was enhanced by the use of a high bipolar right atrial lead. In cases 1 and 2, V 2 -A 2 and V 2 -H 2 intervals consistently lengthened as the V 1 -V 2 interval was reduced. In two other patients, previously present retrograde P waves disappeared as the V 1 -V 2 interval was reduced. Yet at even shorter intervals, retrograde conduction to the His bundle and to the atria was seen. Ventricular echoes occurred in two cases, and reciprocating tachycardia in one. In these instances the His bundle was engaged in both retrograde and forward conduction. Finally in the patient with WPW syndrome A 2 preceded H 2 at a given coupling interval, suggesting retrograde atrial pre-excitation through an extra-Hisian pathway.