The Local Atrial Deflection.Introduction: As a wave front passes unfiltered bipolar recording electrodes, the point of local depolarization is marked by a maximal change in voltage, i.e., the intrinsic deflection. However, during electrophysiologic studies, the depolarization (A) on the lead recording the His‐bundle potential traditionally has been measured at the first rapid reproducible deflection on a filtered electrogram. This methodology permits considerable latitude for subjective interpretation. The purpose of this study was to assess the timing of the atrial electrogram using the intrinsic deflection of relatively unfiltered electrograms (0.1‐4.0 to 1,250 Hz) or the equivalent on filtered recordings.Methods and Results: To do this we studied 70 patients without evidence of atrial or atrioventricular (AV) nodal disease, documenting the difference in timing between the A wave as traditionally measured and as measured at its peak local deflection (AL) determined from simultaneously recorded filtered and relatively unfiltered electrograms. New ranges based on the ALwere established for timing of intra‐atrial and AV nodal conduction intervals. The P‐A (41 ± 11 msec) was significantly shorter than the P‐AL(55 ± 12) and the A‐H (80 ± 20) was longer than the AL‐H (66 ± 21 msec), both P<0.001. Interobserver differences in measurements were smaller when using the local (AL) rather than traditional criteria.Conclusions: Conventional measurement of the A deflection provides only a rough estimate of local depolarization of the atrium near the AV node. The criteria proposed in the present article may (1) provide a better estimate of the timing of local depolarization; (2) have application in computerized timing of intervals; and (3) decrease technical problems and
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