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Introduction: Previous studies have shown that electrical stimulation of the ganglionated plexi (GP) on the right pulmonary artery (RPA), the so-called “3rd fat pad (FP)” causes slowing of the sinus rate and AV conduction. Ablation of this GP prevents induction of atrial fibrillation (AF) caused by vagosympathetic nerve (VNS) stimulation and atrial premature beats (APBs). Methods: Eleven dogs anesthetized with Na-pentobarbital were subjected to a right thoracotomy at the 4 th intercostal space. The RPA at the upper lobe of the right lung was dissected and the distal end tied in order to insert and stabilize an 8 Fr. Sheath into the RPA. A small basket electrode catheter, consisting of 5 splines, each spline containing 3 pairs of bipolar electrodes, was inserted into the RPA underneath the superior vena cava (SVC). A Lasso catheter, inserted through a sheath in the right jugular vein was positioned in the SVC contacting the sleeve of myocardium at the SVC-right atrial (RA) junction. Octapolar electrode catheters were sutured against the right superior, inferior pulmonary veins (PVs), RA and RA appendage. Through a left sided thoracotomy, similar placements of recording electrode catheters were made at the left superior, inferior PVs and left atrium (LA) body and appendage. Right and left vagosympathetic nerve stimulation (VNS, frequency, 20 Hz; stimulus duration, 0.01 ms; voltage 1.5– 4.5 Volts) slowed the heart rate (HR) by 50% or induced 2:1 AV block. The RPA GP was also stimulated to achieve similar effects on HR and AV block. Results: RPA GP stimulation consistently and significantly reduced the threshold for AF inducibility (control 8±3; RPA GP stimulation 3.2±1.5 volts, p<0.01) whereas after RPA GP ablation, the averaged voltage to induce AF was increased to 11.5±1.5 although 7 of 11 showed non-inducibility at the maximum voltage used (12 volts). The inducibility threshold at the other atrial and PV sites were unchanged by RPA GP stimulation before or after RPA GP ablation (p=NS). Moreover, there was a loss of HR slowing and AV block with VNS stimulation. Conclusion: RPA GP stimulation which markedly decreased HR or AV conduction selectively suppressed AF inducibility at the myocardial sleeve of the SVC but did not affect AF inducibility at other atrial sites.

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