Clinical implications of the P wave duration and dispersion: relationship between atrial conduction defects and abnormally prolonged and fractionated atrial endocardial electrograms.

Atrial conduction disease provides a suitable substrate for reentry and appears to be a major predisposing factor for the development of atrial fibrillation. It was demonstrated that when depressed conduction was observed in recordings from human atrial muscle, the ultra-structure was usually abnormal. Areas of poorly coupled fibers in diseased atrial tissue with progressive fibro-degenerative changes may lead to abnormal electrophysiological characteristics. Structural inhomogeneity or local differences in electrophysiological or ultra-structural properties are considered to play a major role in the initiation of reentrant circuits due to the increased likelihood of unidirectional block of the premature impulse. The P wave of the electrocardiogram may show alterations that can be associated with atrial arrhythmias. It was shown that there is a statistical association between the low resting membrane potential and a prolonged P wave duration. Also a prolonged inter-atrial conduction time was significantly related to abnormal P wave morphology. In the evaluation of patients with altered P waves in the electrocardiogram, it is very important to keep in mind that, patients who have a great susceptibility to develop AF possess abnormally prolonged and fractionated atrial endocardial electrograms in sinus rhythm within the right atrium, a significantly longer P wave duration, a significantly longer intra-atrial and inter-atrial conduction time of sinus impulses; and a significantly greater sinus node dysfunction and higher incidence of induction of sustained atrial fibrillation. Awareness of this strong association may lead to a better therapeutic management in individual patients.