Po-04-072 thermochromic heart phantom to model radiofrequency ablation

We have previously developed a conductive hydrogel for use as an intermediate between heart tissue and catheter tips in cardiac ablation, providing a more uniform and precisely shaped lesion with the goal of minimizing the occurrence of steam pops and repeat procedures in arrythmia patients. Characterization of the gel has involved the repeated use of porcine hearts for an approximation of ablation behavior in human models. As this gel will require testing and iterative development to characterize its performance in ablation, a more conservative, safe, and affordable model of the heart is paramount. The heart phantom is to mimic the visible formation of lesions in ventricular myocardial tissue upon contact with a catheter that imparts radiofrequency (RF) energy. To predict lesion formation as mediated with the hydrogel, we seek to produce a heart model with similar thermally conductive properties as myocardial tissue. Various gel materials were prepared and evaluated for similarity to physiological myocardium, visual appeal, and ease of use for multiple trials, among other factors. Each gel was mixed with a thermochromic pigment (transition temperature of 60 C) and placed in a water bath of normal saline at 37 C for at least ten minutes for temperature equilibration. Preliminary tests were conducted with bare catheters alone instead of with hydrogel. An RF generator was set to 30 then 50 Watts, then Thermocool SF non-irrigated catheters were lightly applied to the gel surface in the saline bath for thirty seconds (Fig 1C). Lesions (white) are formed as shown in the figure for tests with silicone and black pigment, the most successful material combination thus far (Fig 1A and 1B). Compared to lesions formed in prior ex vivo experiments with ventricular myocardial tissue, the width and depth of the lesions formed in the gel model varied up to 22% and 76% from the ex vivo values, respectively. A thermochromic phantom heart for lesion characterization is feasible. Further development of this model seeks to better mimic myocardial tissue by selecting or synthesizing a material that matches the heart's experimental thermal conductivity and designing the phantom to contain similar anatomical compartments as in the left ventricular region. Once the phantom material displays lesions approximately equal in size to those formed in heart tissue, it may be used as a substitute for further characterization of the conductive hydrogel.