Aims Cardiac optical mapping is the gold standard for measuring complex electrophysiology in ex vivo heart preparations. However, new methods for optical mapping in vivo have been elusive. We aimed at developing and validating an experimental method for performing in vivo cardiac optical mapping in pig models. Methods and results First, we characterized ex vivo the excitation-ratiometric properties during pacing and ventricular fibrillation (VF) of two near-infrared voltage-sensitive dyes (di-4-ANBDQBS/di-4-ANEQ(F)PTEA) optimized for imaging blood-perfused tissue (n = 7). Then, optical-fibre recordings in Langendorff-perfused hearts demonstrated that ratiometry permits the recording of optical action potentials (APs) with minimal motion artefacts during contraction (n = 7). Ratiometric optical mapping ex vivo also showed that optical AP duration (APD) and conduction velocity (CV) measurements can be accurately obtained to test drug effects. Secondly, we developed a percutaneous dye-loading protocol in vivo to perform high-resolution ratiometric optical mapping of VF dynamics (motion minimal) using a high-speed camera system positioned above the epicardial surface of the exposed heart (n = 11). During pacing (motion substantial) we recorded ratiometric optical signals and activation via a 2D fibre array in contact with the epicardial surface (n = 7). Optical APs in vivo under general anaesthesia showed significantly faster CV [120 (63–138) cm/s vs. 51 (41–64) cm/s; P = 0.032] and a statistical trend to longer APD90 [242 (217–254) ms vs. 192 (182–233) ms; P = 0.095] compared with ex vivo measurements in the contracting heart. The average rate of signal-to-noise ratio (SNR) decay of di-4-ANEQ(F)PTEA in vivo was 0.0671 ± 0.0090 min−1. However, reloading with di-4-ANEQ(F)PTEA fully recovered the initial SNR. Finally, toxicity studies (n = 12) showed that coronary dye injection did not generate systemic nor cardiac damage, although di-4-ANBDQBS injection induced transient hypotension, which was not observed with di-4-ANEQ(F)PTEA. Conclusions In vivo optical mapping using voltage ratiometry of near-infrared dyes enables high-resolution cardiac electrophysiology in translational pig models.

Thermodynamic Evaluation of 4 Open-Irrigated Catheters. Introduction: New generation open-irrigated catheters aim to improve irrigation efficiency. This may change lesion patterns, challenging operators. Indeed, safety issues have recently arisen. We aimed to experimentally assess 4 open-irrigated catheters, comparing lesion size, safety, and heat transfer. Methods: The thigh lesion model was employed in 6 anesthetized pigs to assess the morphology of perpendicular and tangential lesions (n = 140) created by the newer catheters ThermoCool R SF, CoolFlex TM , and Blazer TM Open-Irrigated, and the standard ThermoCool R , at a constant power of 30 W (60 seconds). To evaluate the propensity for deep-tissue overheating, a set of 120 applications were performed at 50 W (180 seconds) comparing pop rates. Thermal assessment of the lesion generation process (20 W, 60 seconds, n = 32) was performed with an infrared camera on bovine ventricular tissue.Results: At 30 W, the newer catheters showed lower temperature readings compared with the ThermoCool R . No major efficacy or safety differences were found at tangential applications; however, at perpendicular applications: (1) the SF at 17 mL/min better preserved the superficial layers and focused its maximum thermal effect deeper, but at recommended flow rates (8 mL/min) it generated the largest superficial lesions; (2) CoolFlex TM created smaller lesions than SF and readily induced steam pops at 50 W without temperature control; and (3) no major differences were found comparing Blazer TM Open-Irrigated and ThermoCool R .Conclusions: The lower temperature readings in the newer catheters make them more prone to deliver the maximum programmed power. Under experimental conditions, the SF catheter focuses its maximum effect deeper and the CoolFlex TM can be more prone to induce steam pops at high power settings.