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Managing cardiac arrhythmias with catheter ablation requires positioning electrodes in contact with myocardial tissue. Objective measures to assess contact and effective coupling of ablation energy are sought. An electrical coupling index (ECI) was devised using complex impedance at 20 kHz to perform in the presence of RF ablation and deliver information about electrical interactions between the tip electrode and its adjacent environment. ECI was derived and compared with clinical judgment, pacing threshold, electrogram amplitude, and ablation lesion depth and transmurality in a porcine model. ECI was also compared with force and displacement using ex vivo bovine myocardial muscle. Mean noncontact ECI was 97.2 ± 14.3 and increased to 145.2 ± 33.6 (p <; 0.001) in clinician assessed (CLIN) moderate contact. ECI significantly improved CLIN's prediction of the variance in pacing threshold from 48.7% to 56.8% ( ). ECI was indicative of contact force under conditions of smooth myocardium. Transmural lesions were associated with higher pre-RF (109 ± 17 versus 149 ± 25, ) and during-RF (82 ± 9 versus 101 ± 17, ) ECI levels. ECI is a tip specific, robust, correlate with contact and ablation efficacy, and can potentially add to clinical interpretation of electrical coupling during electrophysiology procedures.

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OBJECTIVE: : Autonomic ganglionated plexi (GP) in fat pads near the pulmonary veins may contribute to initiation and maintenance atrial fibrillation (AF). We attempted to localize these plexi in a canine model, and evaluate the efficacy of microwave ablation in eliminating their vagal reflexes. METHODS: : 8 Mongrel dogs (25-31 kg), underwent cervical vagal trunk stimulation to produce AV nodal block and sustained AF. Sternotomy was performed and the epicardial fat on the posterior left atrium and pulmonary veins was locally stimulated at high-frequency (20 Hz, 3-5 mA). Locations that produced a vagal response were identified and in 7 dogs ablated using the Flex 4 epicardial microwave ablation probe (Guidant Corp) at 65 watts/90 sec. One animal was a control and not ablated. Vagal responses were retested with local stimulation as well as stimulation of the cervical vagal trunks. The presence of AV block and duration of sustained AF was recorded. RESULTS: : Baseline cervical vagal stimulation produced AV block and AF in all the animals. Local high-frequency stimulation (HFS) elicited vagal responses at the junction of the inferior vena cava and the middle pulmonary vein (IVC-MPV) in 8 animals, the base of the left pulmonary veins/ligament of Marshall (LoM) in 5 animals, and between the upper and lower right pulmonary veins (RPV) in 2 animals. Microwave ablation at the IVC-MPV eliminated the vagal response upon local fat pad HFS. Cervical vagal trunk stimulation yielded less AV block (n = 2) or no AV block (n = 5) after microwave ablation of the IVC-MPV alone (n = 4) or in conjunction with LoM area ablation (n = 3). The average duration of AF during cervical vagal stimulation decreased significantly from baseline (52.7 ± 27.0 sec) versus after fat pad ablation (13.8 ± 20.3 sec, p = 0.004). CONCLUSIONS: : In a canine model we found the primary epicardial autonomic ganglionated plexi to be at the junction of the IVC-MPV. Epicardial microwave ablation of this GP eliminated the vagal response during local fat pad stimulation; and attenuated or eliminated AV block and induction of sustained AF during cervical vagal trunk stimulation. Epicardial microwave ablation of the ganglionated plexi in epicardial fat pads is feasible and can eliminate vagal reflexes that maybe important in atrial fibrillation.

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Chronic rapid atrial pacing (RAP) leads to changes that perpetuate atrial fibrillation (AF). Chronic atrial dilatation due to mitral regurgitation (MR) also increases AF inducibility, but it is not clear whether the underlying mechanism is similar. Therefore, we have investigated atrial electrophysiology in a canine MR model (mitral valve avulsion, 1 mo) using high-resolution optical mapping and compared it with control dogs and with the canine RAP model (6-8 wk of atrial pacing at 600 beats/min, atrioventricular block, and ventricular pacing at 100 beats/min). At followup, optical action potentials were recorded using a 16 x 16 photodiode array from 2 x 2-cm left atrial (LA) and right atrial (RA) areas in perfused preparations, with pacing electrodes around the field of view to study direction dependency of conduction. Action potential duration at 80% repolarization (APD(80)) was not different between control and MR but was reduced in RAP atria. Conduction velocities during normal pacing were not different between groups. However, the MR LA showed increased conduction heterogeneity during pacing at short cycle lengths and during premature extrastimuli, which frequently caused pronounced regional conduction slowing. Conduction in the MR LA during extrastimulation also displayed a marked dependence on propagation direction. These phenomena were not observed in the MR RA and in control and RAP atria. Thus both models form distinctly different AF substrates; in RAP dogs, the decrease in APD(80) may stabilize reentry. In MR dogs, regional LA conduction slowing and increased directional dependency, allowing unidirectional conduction block and preferential paths of conduction, may account for increased AF inducibility.

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