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(Circulation. 2001;103:455.)
© 2001 American Heart Association, Inc.

Basic Science Reports

Cardiac Memory in Canine Atrium

Identification and Implications

Bengt Herweg, MD¹; Fang Chang, PhD, MD¹; Parag Chandra, MD; Peter Danilo, Jr, PhD; Michael R. Rosen, MD

From the Departments of Pharmacology (B.H., F.C., P.C., P.D., M.R.R), Pediatrics (M.R.R.), and Medicine (B.H., F.C.) and the Center for Molecular Therapeutics (P.D., M.R.R.), College of Physicians and Surgeons of Columbia University, New York, NY.

Correspondence to Michael R. Rosen, MD, Gustavus A. Pfeiffer Professor of Pharmacology, Professor of Pediatrics, College of Physicians and Surgeons of Columbia University, Department of Pharmacology, 630 West 168 St, PH7W-321, New York, NY 10032. E-mail mrr1{at}Columbia.edu

Background—Memory is a diverse biological phenomenon whose importance in the ventricle has been demonstrated. We hypothesized its occurrence in the atrium, contributing to the modulation of cardiac rhythm.

Methods and Results—We analyzed P and Ta waves in conscious chronically instrumented dogs with complete heart block. Animals were atrioventricularly sequentially paced at 5% greater than the sinus rate from the lateral right atrium (RA) during control, followed by 2 periods of 1-hour test pacing at 50% greater than the sinus rate, or by equivalent test pacing from the left atrial appendage (LAA) at 5% or 50% greater than the sinus rate. Recovery RA pacing periods of 20- and 30-minute duration, respectively, succeeded each test pacing period. RA test pacing at either rate did not affect the variables measured, but changing the pacing site from RA to LAA altered the P and Ta waves. Displacement of the spatial atrial gradient vector occurred during recovery from LAA pacing, was more marked at rapid pacing rates, and manifested accumulation and resolution consistent with cardiac memory. Concurrently, the right effective refractory period decreased.

Conclusions—Memory is demonstrable in canine atrium, showing rapid onset, accumulation during successive pacing periods, and resolution on cessation of pacing. Given its association with a reduced effective refractory period, it may contribute to the substrate for atrial arrhythmias.

Key Words: electrophysiology • pacing • atrium • remodeling

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