A new classification for the qualitative and quantitative electrophysiologic localization of atrioventricular (A-V) conduction defects based on His bundle (BH) recordings in 500 patients is proposed. This study demonstrates that the electrocardiographic manifestations of all three degrees of A-V block can result from conduction abnormalities present in either of these three regions, viz, A-V node, BH and the His-Purkinje system. Intraatrial conduction delays may also produce first degree A-V block. It is also suggested that first degree block in any of these four regions of the A-V conduction system may not be apparent in the standard electrocardiogram if the P-R interval is normal. The use of BH recordings in conjunction with standard electrocardiographic leads may be of great value in the diagnosis, therapy and prognosis of disease of the cardiac conduction system in man.
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