Pre‐P (Sino‐Atrial Node Region) Activity Recording from the Right Atrial Cavity by Signal Averaging*

A mobile instrumentation and noninvasive method developed recently for external His bundle recording and employing the signal averaging technique was applied for intra-atrial recording of the pre-P (sino-atrial node region) activity. Recordings were obtained in ten anesthetized dogs and five patients at the time of right heart catheterization. A bipolar intra-atrial lead was used for triggering of the averaging process and a unipolar intra-atrial lead was used for signal recording. Direct bipolar epicardial recordings were obtained for comparison from the sino-atrial (S-A) node area in experimental animals. In animals studies, the averaged intra-atrial recording showed 30 muV amplitude deflections beginning 40-45 ms prior to the onset of P wave and were preceded by a slow rise and lower frequency and amplitude deflections arising 60-70 ms earlier. There was good correlation between the pre-P activity recorded intra-atrially and from the epicardium. Deflections of similar configuration but smaller amplitude (1 muV) were recorded in human studies. They preceded the onset of large atrial activity deflections (P wave) in the reference electrocardiogram by 40-80 ms. The exact source of these pre-P activity potentials has not been definitely established, but they appear to originate from the S-A node region, based on their similarity to the direct epicardial recordings and time relationship to the preceding T and following P wave.