Cellular electrophysiologic properties of old canine atria provide a substrate for arrhythmogenesis.
OBJECTIVE
The incidence of atrial fibrillation increases with age. We hypothesized that aging-associated changes in the atrial action potential (AP) and conduction velocity provide a substrate for abnormal conduction and arrhythmogenesis.


METHODS
We used microelectrode techniques to record AP from the endocardium of the right atrial wall of dogs aged 1-5 (adult) and >8 years (old). Conduction velocity was measured between two microelectrodes 3-10 mm apart. Histological study was carried out to assess fibrosis.


RESULTS
Whereas resting potential, AP amplitude and V(max) did not differ with age, the plateau was more negative and AP duration was longer in old tissue. The L-type calcium current (I(Ca,L)) agonist Bay K8644 (10(-8)-10(-6) mol/l) elevated the plateau and shortened APD more in old than in adult, such that AP contour in old atria approached that of adult. In contrast, the I(Ca,L) blocker nisoldipine (10(-8)-10(-5) mol/l) depressed the plateau in adult and had no effect in old. There was no difference between the two groups in conduction velocity of normal beats, whereas for early premature impulses, reduced conduction velocity and a wider time window manifesting slow conduction were detected in old in comparison to adult tissue. A twofold increase in the amount of fibrous tissue was detected in old atria.


CONCLUSIONS
Our data show significant differences in contour of AP in adult and old atria. The responses to Bay K8644 and nisoldipine suggest a decreased I(Ca,L) in old atrial tissue. The alterations in AP contour and increased fibrosis may be responsible for slower conduction of early premature beats in old atria. The age-related changes in conduction of premature beats are consistent with those observed in patients with paroxysmal atrial fibrillation and may contribute to the greater propensity to atrial fibrillation in the aged.
Anyukhovsky
Evgeny P
EP
Department of Pharmacology, Center for Molecular Therapeutics, College of Physicians and Surgeons of Columbia University, 630 West 168th Street, PH 7 West-321, New York, NY 10032, USA.
Sosunov
Eugene A
EA
Plotnikov
Alexei
A
Gainullin
Ravil Z
RZ
Jhang
Jeffrey S
JS
Marboe
Charles C
CC
Rosen
Michael R
MR
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000375:Aging; D000818:Animals; D001281:Atrial Fibrillation / Q000473:pathology / Q000503:physiopathology*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004285:Dogs; D004562:Electrocardiography; D006321:Heart / Q000503:physiopathology*; D006325:Heart Atria / Q000473:pathology; D008839:Microelectrodes; D015737:Nisoldipine / Q000494:pharmacology
D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D015737:Nisoldipine; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester