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Ablation index (AI) is a widely used variable incorporating power, time, and contact force for predicting lesion size for radiofrequency ablation (RFA). Its utility for guiding ablation in ventricular tissue, and particularly in clinically relevant scar tissue, has not been studied.
To examine the utility and limitations of AI for predicting lesions dimensions in healthy and scarred ventricular tissue.
This study included three steps: 1) In an ex-vivo bath model of fresh porcine hearts, RFA was performed using Thermocool STSF® (Biosense Webster) at a fixed power of 30W and an AI value range of 400-1200 at increments of 100; 2) In an in-vivo beating heart model of healthy porcine, RFA was performed at an AI value range of 500-900 at increments of 100; 3) in an in-vivo beating heart model of healed anterior wall infarction, RFA at an AI value range of 600-900 was performed at scar border zone defined by low voltage and abnormal electrograms. The relationship between AI and lesions dimensions was analyzed.
In ex-vivo hearts, lesion width and depth had positive correlation with AI values (R=0.97, P<0.01; R=0.96, P<0.01, respectively). The relationship between lesion width and depth was linear between AI values of 400-900 (Width 1.4mm/100; Depth 0.9mm/100) but became flatter at 900-1200 (Width 0.05mm/100; Depth 0.28mm/100) as shown in Figure 1. In healthy beating ventricles, a similar positive correlation between AI values and lesions width and depth was observed (R=0.99, P<0.01; R=0.97, P<0.01, respectively) with 90% of lesion depth achieved at an AI value of 900. In contrast, AI did not correlate with lesion depth at infarcted myocardium (R=-0.23, P=0.74). Furthermore, lesion architecture was influenced by the spatial relationship between viable and scarred myocardium, with lesion growth-restricted predominantly to viable myocardium superficial to the infarct. Figure 2 shows gross pathological examples of lesions at variable AI values in healthy and scarred ventricular myocardium.