Left atrial pacing induces memory and is associated with atrial tachyarrhythmias.
OBJECTIVE
Transiently altering the atrial activation sequence induces atrial memory, manifested as an altered atrial gradient as measured in electrocardiographic XYZ leads. We hypothesized that protracted periods of left atrial impulse initiation alter the atrial gradient in a manner predictive of arrhythmias.


METHODS
A total of 12 chronically instrumented mongrel dogs in complete heart block were paced AV sequentially from the left or right atrium for 7-28 days, and then recovered in normal sinus rhythm for 21 days. Rate histograms were recorded during the entire period, and electrophysiological studies were conducted to note changes in the atrial gradient, effective refractory period and atrial rhythm. No atrial arrhythmias were seen in eight control animals that were instrumented but not paced.


RESULTS
Left atrial pacing was associated with a decreased atrial gradient and occurrence of atrial tachycardias that appeared during pacing and persisted during recovery from pacing. In contrast, right atrial pacing did not alter the atrial gradient significantly. Atrial tachycardias occurring during right atrial pacing disappeared after cessation of pacing, when dogs recovered in sinus rhythm. The effective refractory period did not change in either group.


CONCLUSIONS
Pacing-induced impulse initiation from the left atrium alters the atrial gradient and is associated with atrial tachycardias. These changes in atrial gradient occur in the absence of ERP changes and may be early predictors of an arrhythmogenic substrate.
Chandra
Parag
P
Departments of Pharmacology and Pediatrics and Center for Molecular Therapeutics, College of Physicians and Surgeons of Columbia University, 630 West 168th Street, PH7West-321, New York, NY, USA.
Rosen
Tove S
TS
Herweg
Bengt
B
Danilo
Peter
P
Rosen
Michael R
MR
D000818:Animals; D016279:Atrial Function, Left; D002304:Cardiac Pacing, Artificial; D004285:Dogs; D004562:Electrocardiography; D005260:Female; D006325:Heart Atria / Q000503:physiopathology; D006327:Heart Block; D013610:Tachycardia / Q000209:etiology* / Q000503:physiopathology