Triggered firing in pulmonary veins initiated by in vitro autonomic nerve stimulation

BACKGROUND Rapid firing within pulmonary vein sleeves frequently initiates atrial fibrillation. The role of the autonomic nervous system in facilitating spontaneous firing is unknown. OBJECTIVES The purpose of this study was to determine if autonomic nerve stimulation within canine atrium and pulmonary vein sleeves initiates arrhythmia formation. METHODS Extracellular bipolar and intracellular microelectrode recordings were obtained from isolated superfused canine pulmonary veins (N = 28) and right atrium (N = 5) during local autonomic nerve stimulation. RESULTS Autonomic nerve stimulation decreased pulmonary vein sleeve action potential duration (APD(90) = 160 ± 17 to 92 ± 24 ms; P < .01) and initiated rapid (782 ± 158 bpm) firing from early afterdepolarizations in 22 of 28 pulmonary vein preparations. The initial spontaneous beat had a coupling interval of 97 26 ins. Failure to induce arrhythmia was associated with a failure to shorten APD(90) (151 ± 18 to 142 ± 8 ms; P = .39). Muscarinic receptor blockade (atropine: 3.2 x 10(-8) M) prevented APD90 shortening in 8 of 8 preparations and suppressed firing in 6 of 8 preparations, whereas β(1)-adrenergic receptor blockade (atenolol: 3.2 x 10(-8) M) suppressed firing in 8 of 8 preparations. Suppression of the Ca transient with ryanodine (10(-5) M) completely suppressed firing in 6 of 6 preparations. Inhibition of forward Na/Ca exchange by a transient increase in [Ca+2](o) completely suppressed firing in 4 of 6 preparations. The same stimulus trains produce atropine-suppressed APD(90) shortening in superfused right atrial free wall but fail to produce triggered arrhythmia. CONCLUSIONS The data demonstrate triggered firing within canine pulmonary veins with combined parasympathetic and sympathetic nerve stimulation. Both an enhanced Ca transient and increased Na/Ca exchange may be required for arrhythima formation.