Abstract
BACKGROUND: Ablation of some myocardial substrates requires catheter-based radiofrequency delivery at the root of a great artery. We studied the safety and efficacy parameters associated with catheter-based radiofrequency delivery at the root of the aorta and pulmonary artery. METHODS: Thirty-six pigs underwent in-vivo catheter-based ablation under continuous contact-force and lesion index (power, contact-force, and time) monitoring during 60-s radiofrequency delivery with an open-irrigated tip catheter. Twenty-eight animals were allocated to groups receiving 40 W (n=9), 50 W (n=10), or 60 W (n=9) radiofrequency energy, and acute (n=22) and chronic (n=6) arterial wall damage was quantified by multiphoton microscopy in ex vivo samples. Adjacent myocardial lesions were quantified in parallel samples. The remaining 8 pigs were used to validate safety and efficacy parameters. RESULTS: Acute collagen and elastin alterations were significantly associated with radiofrequency power, although chronic assessment revealed vascular wall recovery in lesions without steam pop. The main parameters associated with steam pops were median peak temperature >42°C and impedance falls >23 ohms. Unlike other parameters, lesion index values of 9.1 units (interquartile range, 8.7-9.8) were associated with the presence of adjacent myocardial lesions in both univariate ( P=0.03) and multivariate analyses ( P=0.049; odds ratio, 1.99; 95% CI, 1.02-3.98). In the validation group, lesion index values using 40 W over a range of contact-forces correlated with the size of radiofrequency lesions (R(2)=0.57; P=0.03), with no angiographic or histopathologic signs of coronary artery damage. CONCLUSIONS: Lesion index values obtained during 40 W radiofrequency applications reliably monitor safe and effective lesion creation at the root of the great arteries.