Endocardial and His bundle electrocardiograms.

Endocardial electrocardiograms permit the analysis of auricular depolarization and contribute to the study of ventricular activation. Direct recording of auriculograms from the right atrium and indirect recording of the left auriculograms through the coronary sinus and pulmonary artery, show the different auricular activation pathways in common atrial flutter, atrial tachycardia and in case of retrograde atrial depolarization (via the AV node, septal or parietal accessory pathway). His bundle electrograms obtained via the femoral vein or, less easy, via the brachial vein, has introduced an essential mark in the analysis of intracardiac activation enabling us to precisely locate lesions of the AV conduction system, making easier differential diagnosis between aberrant ventricular conduction and ventricular ectopic rhythms and contributing to the study of ventricular preexcitation. Endocavitary stimulation at increasing rate and by the single extrastimulus technique is the complement of intracardiac electrocardiography in evaluating sinus node function, conduction times and refractory periods at different levels, electrophysiological properties of accessory pathways and studies of the antiarrhythmic drugs. Programmed stimulation allows the recognition of reentry as the mechanism of many tachyarrhythmias. The recording of monophasic action potential by the suction--electrode technique is another step in the intracavitary electrophysiological investigation.