Post operative AF,β-blockade & atrial electrophysiology. Introduction:We investigated whether post-cardiac surgery (CS) new-onset atrial fibrillation (AF) is predicted by pre-CS atrial cellular electrophysiology, and whether the anti-arrhythmic effect of β-blocker therapy may involve pre-CS pharmacological remodelling.

LVSD in patients in SR is independently associated with a shortening of the atrial cellular ERP, which may be expected to contribute to a predisposition to AF.

1 5-Hydroxytryptamine (5-HT) has been postulated to play a proarrhythmic role in the human atria via stimulation of 5-HT 4 receptors. 2 The aims of this study were to examine the effects of 5-HT on the L-type Ca 2 þ current (I CaL ) action potential duration (APD), the effective refractory period (ERP) and arrhythmic activity in human atrial cells, and to assess the effects of prior treatment with b-adrenoceptor antagonists. 3 Isolated myocytes, from the right atrial appendage of 27 consenting patients undergoing cardiac surgery who were in sinus rhythm, were studied using the whole-cell perforated patch-clamp technique at 371C. 4 5-HT (1 nM -10 mM) caused a concentration-dependent increase in I CaL , which was potentiated in cells from b-blocked (maximum response to 5-HT, E max ¼ 299712% increase above control) compared to non-b-blocked patients (E max ¼ 22076%, Po0.05), but with no change in either the potency (log EC 50 : À7.0970.07 vs À7.2670.06) or Hill coefficient (n H : 1.570.6 vs 1.570.3) of the 5-HT concentration -response curve. 5 5-HT (10 mM) produced a greater increase in the APD at 50% repolarisation (APD 50 ) in cells from b-blocked patients (of 37710 ms, i.e. 5897197%) vs non-b-blocked patients (of 1074 ms, i.e. 157754%; Po0.05). Both the APD 90 and the ERP were unaffected by 5-HT. 6 Arrhythmic activity was observed in response to 5-HT in five of 17 cells (29%) studied from b-blocked, compared to zero of 16 cells from the non-b-blocked patients (Po0.05). 7 In summary, the 5-HT-induced increase in calcium current was associated with a prolonged early plateau phase of repolarisation, but not late repolarisation or refractoriness, and the enhancement of these effects by chronic b-adrenoceptor blockade was associated with arrhythmic potential.