Effect of increased parasympathetic and sympathetic tone on internal atrial defibrillation thresholds in humans

Although changes in autonomic tone affect ventricular defibrillation, littl e is known about the effect of increased parasympathetic or sympathetic ton e on the atrial defibrillation threshold. Methods: To evaluate the effect o f reflexly increased parasympathetic and increase alpha- and beta-adrenergi c tone on the atrial defibrillation threshold (ADFT), atrial fibrillation w as induced in 14 patients. ADFTs, right atrial refractory period (RARP), an d monophasic action potential duration (MAPD) were determined before and af ter autonomic intervention. ADFTs were determined with a step-up protocol u sing 3/3-ms biphasic shocks delivered through decapolar catheters in the ri ght atrial appendage and coronary sinus. Two groups were studied. Group I ( N = 8) had ADFTs determined at baseline, after receiving phenylephrine (PE) , and with PE plus atropine (A). Group 2 (N = 6) had ADFTs determined at ba seline and after receiving isoproterenol (ISO). Results: Group I: PE signif icantly increased sinus cycle length (SR-CL) compared to baseline (742 +/- 123 to 922 +/- 233 ms) without significantly changing RARP, MAPD, or ADFT ( 2.3 +/- 1.3 j vs 2.3 +/- 0.8 J). With PE + A, SR-CL significantly decreased (529 +/- 100 ms vs 742 +/- 123 ms) and MAPD shortened (231 +/- 41 ms vs 27 9 +/- 49 ms) without altering RARP or ADFT (1.94 +/- 0.9 J vs 2.25 +/- 1.25 J). Group 2: ISO decreased SR-CL (486 +/- 77 ms vs 755 +/- 184 ms) and MAP D (169 +/- 37 ms vs 226 + 58 ms) but not RARP or ADFT (2.25 +/- 1.21 J vs 2 .33 +/- 1.75 J). Conclusions: Increasing parasympathetic, alpha-, or beta-a drenergic tone does not affect the ADFT despite causing significant electro physiological changes in the atria.