Noninvasive methods for recording bundle of his activity

The electrode catheter technique for recording electrical activity from various parts of the atrioventricular (A-V) conducting system (particularly bundle of His activity) has significantly contributed to understanding of a variety of A-V conduction and rhythm disturbances occurring within the human heart. Understanding of these events is further enhanced when electrode catheter recordings are made in conjunction with atria1 and ventricular pacing procedures. The information derived from the many reported His bundle studies performed in several laboratories has clearly demonstrated both the value and limitations of standard 12 lead electrocardiographic recordings in reflecting underlying electrophysiologic events. It is obvious that not all patients who manifest either a transient or fixed alteration in A-V conduction or rhythm require intracardiac recordings from the specialized A-V conduction system. However, in some patients, bundle of His recordings are indispensable for proper diagnosis and treatment. At present, His bundle electrography is primarily a clinical research procedure although it is relatively simple and safe to perform. The obvious disadvantages of the procedure as currently performs. 1 relate to: (1) its invasive nature and the conseque t possibility of complications, however minimal; (2) the requirement for catheterization laboratory facilities and equipment, including fluoroscope, multichannel recorder, standby defibrillator; (3) the need to have in attendance two or more physicians and a clinical nurse; and (4) the constant need for awareness of potential electrical hazards. Perhaps the greatest limitation of the electrode catheter technique relates to the inability to perform repeated sequential studies. ‘T‘hus, the development of a reliable noninvasive method for recording electrical activity of the specialized conducting system of the heart from the surface of the chest would be a welcome event. The report by Flowers and associates,’ appearing in this issue of the Journal, represents an initial attempt toward the realization of this goal. These investigators succeeded in recording, from the surface of the chest wall of dogs, activity within the P-R segment of the surface electrocardiogram which they have cautiously termed “blips” and which appear to bear a temporal relation to intracardiac recordings of bundle of His activity. It is obvious that the individual surface recorded “blips” need to be better defined in terms of onset, duration and amplitude. The indefiniteness of some of the “blips” can best be appreciated when the surface recordings are viewed independently of the intracardiac electrograms. Undoubtedly the quality of the surface recordings will improve as technical advances or modifications in the recording apparatus are developed. Additional validation procedures also need to be applied to define more precisely the origin of the successive “blips” as well as the less conspicuous, low amplitude undulations that are also occurring within the P-R segment. It is important to know whether the surface recorded “blips” represent electrical activity of the right side of the heart exclusively, or whether leftsided activity is also included in these recordings. If the latter is true, then consideration must be given to the effects of cancellation and summation on the configurations and timing of surface recordings. Experiments in which multiple internal recordings of various parts of the His-Purkinje system are made in conjunction with surface recordings under different conditions of A-V conduction and A-V block would substantially assist in the interpretation of the several blips recorded within the P-R segment.