[Importance of the "proximity effect" in recording intracardiac electrograms]

Intracardiac "local" electrograms were recorded and studied in 73 dogs. When unipolar macroelectrode (to 1 mm in diameter) approaches immediately the main conduction pathway the resistance between them disappears, the "proximity effect" takes place and simultaneously the quick and synchronous spread of the excitation wave through the corresponding preferential pathways may be recorded as a spike. Spike potential of the sinus node, atria of the bundle of His obvious during the "proximity effect"; in absence of the latter the above spikes are recorded as rudimentary spikes. The moment of the sinus impulse generation occurs in a form of a spike of this node which precedes by 10--30 msec the onset of P wave on the body surface ECG. The atrial depolarization appears in the intracardiac right atrium ECG in the form of a slow wave A and three superimposed spikes. Genesis of these spikes and the influence of the heart valves upon the amplitude of H potentials and atrial wave A, are discussed.