Reversal of atrial mechanical dysfunction after cardioversion of atrial fibrillation: implications for the mechanisms of tachycardia-mediated atrial cardiomyopathy.
BACKGROUND
Atrial mechanical "stunning" develops after cardioversion of atrial fibrillation (AF) and is implicated in the genesis of thromboembolic complications. However, the mechanisms responsible for this phenomenon are poorly understood. Whether atrial mechanical dysfunction caused by AF can be reversed by pacing at increased rates or by pharmacological agents is unknown.


RESULTS
Twenty-six patients with AF undergoing cardioversion were dichotomized prospectively on the basis of the duration of arrhythmia as short-duration (1 to 6 months) or long-duration (> or =3 years) AF. Left atrial appendage emptying velocities (LAAEVs) and spontaneous echocardiographic contrast (LASEC) were assessed by transesophageal echocardiography during AF, after reversion to sinus rhythm, during atrial pacing at cycle lengths of 750 to 250 ms, after a postpacing pause, and with isoproterenol. In patients with short-duration AF, LAAEV decreased (42.0+/-2.7 to 18.5+/-2.0 cm/s; P<0.0001) and LASEC increased (0.9+/-0.3 to 2.2+/-0.3; P<0.01) with termination of AF; pacing increased LAAEV (48.3+/-4.1 cm/s; P<0.0001) and decreased LASEC (1.5+/-0.3; P<0.01); isoproterenol increased LAAEV (73.3+/-7.8 cm/s; P<0.0001) and decreased LASEC (0.3+/-0.2; P<0.01); and the postpacing pause increased LAAEV (68.3+/-3.8 cm/s; P<0.0001). In contrast, patients with long-duration AF demonstrated a significantly attenuated response of atrial mechanical function at each time point. With termination of AF, LAAEV decreased (19.1+/-2.6 to 8.2+/-1.0 cm/s; P=0.003) and LASEC increased (2.0+/-0.2 to 3.3+/-0.2; P<0.01); pacing increased LAAEV (18.4+/-2.7 cm/s; P<0.0001) and decreased LASEC (2.3+/-0.2; P<0.01); isoproterenol increased LAAEV (26.1+/-3.9 cm/s; P=NS to equivalent atrial rate) and decreased LASEC (1.0+/-0.3; P<0.01); and the postpacing pause increased LAAEV (27.2+/-2.4 cm/s; P=0.007).


CONCLUSIONS
Atrial pacing at increased rates and isoproterenol can reverse atrial mechanical stunning associated with short-duration AF. In contrast, long-duration AF is associated with an attenuated response to these maneuvers. These findings suggest a functional contractile apparatus in the mechanically remodeled atrium caused by AF; however, with longer durations of AF, additional factors may determine atrial mechanical function.
Sanders
Prashanthan
P
Department of Cardiology, Royal Melbourne Hospital, Melbourne, Australia.
Morton
Joseph B
JB
Kistler
Peter M
PM
Vohra
Jitendra K
JK
Kalman
Jonathan M
JM
Sparks
Paul B
PB
D000318:Adrenergic beta-Agonists / Q000627:therapeutic use; D001281:Atrial Fibrillation / Q000150:complications / Q000503:physiopathology* / Q000628:therapy*; D002304:Cardiac Pacing, Artificial; D009202:Cardiomyopathies / Q000209:etiology* / Q000503:physiopathology; D002908:Chronic Disease; D017548:Echocardiography, Transesophageal; D004554:Electric Countershock; D004562:Electrocardiography; D005500:Follow-Up Studies; D006325:Heart Atria / Q000000981:diagnostic imaging / Q000187:drug effects / Q000503:physiopathology*; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D007545:Isoproterenol / Q000627:therapeutic use; D017682:Myocardial Stunning / Q000209:etiology / Q000628:therapy; D011446:Prospective Studies; D013610:Tachycardia / Q000503:physiopathology / Q000628:therapy; D013995:Time; D016896:Treatment Outcome
D000318:Adrenergic beta-Agonists; D007545:Isoproterenol