Intracardiac electrocardiography and its usefulness for the assessment of conduction disturbance of the heart

Recordings of electrical potentials of the bundle of His as well as other specialized conduction tissues (A-V node, right and left bundle branches) were accomplished in 76 patients during the period between May 1972 and October 1973. Using bipolar electrode catheters the intracardiac electrograms were recorded from the right ventricular endocardial surface alone, in 46, from the left ventricular endocardial surface alone, in 8 and simultaneously from both right and left surfaces in 20 patients. In the remaining 2 patients, the recording was accomplished from the root of the aorta and the right ventricular endocardial surface simultaneously. Atrial pacing was carried out in 24 patients and His bundle (HB) pacing was done in 11 patients for validation of the His bundle electrograms (HBEs). The electrograms were analysed and evaluated for 6 component parts: P-A interval (internodal or intraatrial conduction time); A-H interval (approximation of A-V nodal conduction time); H duration; H-V interval (His Purkinje system conduction time); right bundle branch (RB) and left bundle branch (LB) durations; and RB-V and LB-V intervals. The interatrial conduction time was determined by simultaneous recording of right and left atrial electrograms and internodal conduction time was further assessed by simultaneous recordings of high atrial electrogram and a HBE from the tricuspid valve area. The normal A-V conduction times (mean ± ISD) at various parts of the heart as determined by the right ventricular approach were P-A 27 ± 6; A-H 74 ± 11; H 19 ± 2; H-V 44 ± 6; RB 15 ± 2; RB-V 23 ± 4 msec; and those by the left ventricular approach were P-A 28 ± 7; A-H 76 ± 16; H 19 ± 3; H-V 45 ± 6; LB 15 ± 3; and LB-V 25 ± 3 msec. The recording of HB potential could localize the site of heart block of various forms. This was especially useful in the evaluation of second degree A-V block with 2:1 conduction, providing a guide for the use of artificial pacemakers. Moreover, the intracardiac electrograms permitted rapid and precise analysis of some complex arrhythmias. Determination of the origin of ectopic beats and tachycardias and differentiation between supraventricular beats with aberration and beats that originated in the ventricle could easily be carried out. Individual cases were demonstrated and the value of the intracardiac electrograms was emphasized. Electrophysiology of the heart was also briefly reviewed.