September 1971

Premature Atrial Contraction

Author Affiliations


From the Indiana University Medical Center, Krannert Institute of Cardiology, Indianapolis.

Arch Intern Med. 1971;128(3):453-455. doi:10.1001/archinte.1971.00310210129017

As was described last month for premature ventricular beats, the interaction of the basic heart rate, the degree of prematurity, and electrophysiologic properties of refractoriness and conduction determine what follows in the wake of any premature impulse. The fact that discharge of a premature atrial contraction (PAC) originates in the atrium affords the impulse greater opportunity to reach the sinus node before the latter can fire. Therefore, a PAC most often disturbs the timing of the sinus node by discharging it and causing the next impulse to begin from that point. One would surmise that this would make the interval between the PAC (P') and the next normal P wave (P'-P) exactly the same as a normal P-P interval. However, two factors prevent this from occurring. First, the P'-P interval may be lengthened by the time it takes the impulse to discharge the atrium and then travel to, and discharge

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