Effect of Electrode Orientation on Lesion Sizes. Background: Irrigated radiofrequency (RF)ablation catheters may produce different lesion sizes dependent upon the electrode orientation to the tissue. This study examined the effect of irrigated electrode orientation on the lesion size and explores a potential mechanism for this effect.Methods and Results: Lesions were created in isolated porcine myocardium using an open irrigation, closed irrigation, and nonirrigated RF catheter (all 3.5-4 mm tips). Lesions were created with the electrodes with all permutations of electrode orientation (vertical or horizontal), contact pressure (6 or 20 g), and saline superfusate flow (0.2 or 0.4 m/sec) over tissue interface. The effect of electrode irrigation without RF delivery on tissue temperature was assessed with intramyocardial temperature probes and infrared thermal imaging. For both irrigated catheters, the horizontal orientation produced 25-30% smaller lesion volumes than the vertical orientation despite equal or greater power deliveries. The horizontal orientation produced larger lesion volumes for the nonirrigated catheter. Higher superfusate flow rates were associated with decreased lesion volumes for the irrigated catheters but greater lesion volumes for the nonirrigated catheter. Catheter irrigation alone without RF delivery reduced intramyocardial temperatures up to 4.9 • C and the horizontal orientation produced a 2-fold greater area of tissue cooling than the vertical orientation.Conclusion: Horizontal electrode orientations reduce lesion volumes for irrigated RF catheters. This effect may be in part due to greater areas of active tissue cooling in the horizontal orientation

Background-The lethal isotherm for radiofrequency catheter ablation of cardiac myocardium is widely accepted to be 50°C, but this has not been directly measured. The purpose of this study was to directly measure the tissue temperature at the edge of radiofrequency lesions in real time using infrared thermal imaging. Methods and Results-Fifteen radiofrequency lesions of 6 to 240 seconds in duration were applied to the left ventricular surface of isolated perfused pig hearts. At the end of radiofrequency delivery, a thermal image of the tissue surface was acquired with an infrared camera. The lesion was then stained and an optical image of the lesion was obtained. The thermal and optical images were electronically merged to allow determination of the tissue temperature at the edge of the lesion at the end of radiofrequency delivery. By adjusting the temperature overlay display to conform with the edge of the radiofrequency lesion, the lethal isotherm was measured to be 60.6°C (interquartile ranges, 59.7°to 62.4°C; range, 58.1°to 64.2°C). The areas encompassed by the lesion border in the optical image and the lethal isotherm in the thermal image were statistically similar and highly correlated (Spearman ϭ0.99, PϽ0.001). The lethal isotherm temperature was not related to the duration of radiofrequency delivery or to lesion size (both PϾ0.64). The areas circumscribed by 50°C isotherms were significantly larger than the areas of the lesions on optical imaging (Pϭ0.002). Conclusions-By direct measurement, the lethal isotherm for cardiac myocardium is near 61°C for radiofrequency energy deliveries Ͻ240 seconds in duration. A 50°C isotherm overestimates lesion size. Accurate knowledge of the lethal isotherm for radiofrequency ablation is important to clinical practice as well as mathematical modeling of radiofrequency lesions. (Circ Arrhythm Electrophysiol. 2011;4:373-378.)

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The identification of strategies to assemble nanostructured films with engineered properties on solid supports can lead to the development of innovative functional materials. In particular, the self-assembly of electroactive multilayers from simple molecular building blocks on metallic electrodes can offer the opportunity to regulate the exchange of electrons between the underlying substrate and solution species. In this context, we designed an experimental protocol to prepare electroactive films from bipyridinium bisthiols. Specifically, we found that a compound incorporating two bipyridinium dications at its core and terminal thiol groups self-assembles into remarkably stable multilayers on polycrystalline gold. The surface coverage of the resulting films can be regulated by adjusting the exposure time of the gold substrate to the bipyridinium solution. Control experiments with appropriate model compounds demonstrate that both bipyridinium dications as well as both thiol groups must be present in the molecular skeleton to encourage multilayer growth. The resulting films transport electrons efficiently from the electrode surface to the film/solution interface. Indeed, they mediate the reduction of Ru(NH(3))(6)(3+) in the electrolyte solution but prevent the back oxidation of the resulting Ru(NH(3))(6)(2+). Furthermore, these polycationic bipyridinium films capture electrostatically Fe(CN)(6)(4-) tetraanions, which can also be exploited to transport electrons across the interfacial assembly. In fact, electrons can travel through the bipyridnium(2+/1+) couples to redox probes in solution and then back to the electrode through the Fe(CN)(6)(4/3-) couples. Thus, our original approach to self-assembling multilayers can produce stable electroactive films with unique electron transport properties, which can be regulated with a careful choice of the anionic components.

The supramolecular association of tetrathiafulvalene (TTF) donors and bipyridinium acceptors is employed routinely to direct the formation of host/guest complexes and interlocked molecules in bulk solution. We have reproduced these donor/acceptor interactions at electrode/solution interfaces and demonstrated their pronounced influence on heterogeneous electron transfer. Specifically, we have synthesized a TTF with an oligomethylene arm terminated by a thiol group and assembled monolayers of this compound on gold. We have observed that the cyclic voltammogram of the immobilized TTF donors varies significantly upon addition of benzyl viologen, tetracyanoquinodimethane (TCNQ), or tetracyanoethylene (TCNE) acceptors to the electrolyte solution. Indeed, the supramolecular association of the complementary donors and acceptors results in a pronounced current decrease for the TTF redox waves. Consistently, the electrochemical response of the acceptors changes dramatically in the presence of TTF donors on the electrode surface. Instead, hexadecanethiolate monolayers, lacking the TTF donors at the termini of the oligomethylene chains, have a marginal influence on the voltammograms of the acceptors. Impedance measurements indicate that the charge-transfer resistance (R CT) for the reduction of the acceptors increases from less than 0.3 kΩ, at bare gold, to 324, 24, and 43 kΩ for benzyl viologen, TCNQ, and TCNE, respectively, at TTF-coated electrodes. By contrast, the electrode coating has a negligible influence on the cyclic voltammogram and impedance response of ferrocene, which cannot sustain donor/acceptor interactions with the immobilized TTFs. Thus, our results demonstrate that the interfacial complexation of complementary donors and acceptors has a dramatic effect on the heterogeneous electron transfer to and from the associated components.