Heterogeneous shortening of the atrial effective refractory period (AERP) and increased dispersion of refractoriness (disp_A) predispose to recurrent episodes of atrial fibrillation (AF).
Aim: To evaluate the effects of stimulation and blockade of the autonomic nervous system (ANS) on atrial refractoriness in patients with > or = 1 year clinical history of lone paroxysmal AF (PAF).
Methods: Ten patients (6 men, aged 55 +/- 14 years) underwent electrophysiological study while off medication. AERP was assessed at 5 sites--right atrial appendage (RAA) and low lateral right atrium (LRA), high interatrial septum (IAS), proximal (pCS) and distal (dCS) coronary sinus in basal conditions, during handgrip (HG) and carotid sinus massage (CSM), and after ANS blockade (ANSB) (atropine 0.04 mg/kg + propranolol 0.15 mg/kg). The AERP was taken as the longest S1-S2 interval that failed to initiate a response. Disp_A was calculated as the difference between the longest and shortest AERP.
Results: RR intervals were 853 +/- 68 ms, 724 +/- 73 ms, 928 +/-131 ms and 856 +/-81 ms in basal conditions, HG, MSC and ANSB respectively (p < 0.05 for basal vs. HG). Systolic blood pressure (BP) increased significantly during HG (from 126 +/- 8 mmHg to 135 +/- 10 mmHg, p < 0.05), but there were no significant differences in BP values during CSM and ANSB. The AERPs were 208 +/- 15 ms, 212 +/- 22 ms, 252 +/- 43 ms, 256 +/- 37 ms and 246 +/- 31 ms, in RAA, LRA, IAS, pCS and dCS respectively (RAA vs. IAS and pCS, p < 0.05). AERPs decreased significantly in LRA during CSM, and increased in dCS after ANSB. Disp_A was 70 +/- 39 ms in basal conditions, 71 +/- 34 ms during HG, 75 +/- 46 ms with CSM, and 54 +/- 37 ms after ANSB (p < 0.05 for ANSB vs. all others). Patients with inducible AF had greater disp_A (70 +/- 15 ms vs. 44 +/- 20 ms, p < 0.05) and a larger reduction of AERP in RAA during HG (11 +/- 9% vs. 2 +/- 4%, p = 0.02), with no significant differences in basal AERP.
Conclusion: In patients with PAF, ANS stimulation alters AERP, whereas ANSB increases AERP in dCS and decreases disp_A. Patients with inducible AF show greater disp_A and shorter AERP in RAA during sympathetic stimulation. These findings highlight the complexity of the influence of the ANS on alterations in refractoriness related to vulnerability to AF.