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Ann Thorac Surg 2005;80:2263-2270
© 2005 The Society of Thoracic Surgeons

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Original article: Cardiovascular

Irrigated Radiofrequency Ablation With Transmurality Feedback Reliably Produces Cox Maze Lesions In Vivo

^a Division of Cardiovascular Surgery, Mayo Clinic, Rochester, Minnesota
^b Medtronic, Inc, Minneapolis, Minnesota

Accepted for publication June 3, 2005.

^_* Address correspondence to Dr Schaff, Division of Cardiovascular Surgery, Mayo Clinic, 200 First St SW, Rochester, MN 55905 (Email: schaff{at}mayo.edu).

BACKGROUND: Irrigated bipolar radiofrequency ablation has been used to replicate Cox maze surgical scars in pig hearts ex vivo. Impedance monitoring accurately predicted complete transmurality for all lesions. This study aimed to assess the feasibility and reliability of irrigated radiofrequency ablation and impedance monitoring to produce electrically isolating Cox maze lesions in vivo.

METHODS: A modified Cox maze procedure was performed in 8 adult sheep during cardiopulmonary bypass using irrigated bipolar and unipolar radiofrequency ablation. For bipolar radiofrequency ablation, atrial tissues were clamped between opposing electrodes; ablation was terminated at the plateau in impedance decline. Unipolar radiofrequency ablation lesions were painted on the endocardium, and transmurality was assessed visually. Animals survived 30 days.

RESULTS: Bipolar lesions (n = 48) were thinner (7.4 ± 2.4 mm versus 12.7 ± 3.2 mm) and required less time (14.1 ± 3.4 seconds versus 41.4 ± 21.8 seconds) and energy (377.5 ± 99.2 W · s versus 995.1 ± 547.1 W · s) to create despite being longer (31.7 ± 8.6 mm versus 19.2 ± 5.6 mm) than unipolar lesions (n = 26). The left atrial pacing threshold across selected bipolar lesions increased at least fivefold above baseline (1.6 ± 0.2 mA) at 1 hour (18.4 ± 4.6 mA; n = 8; p < 0.001) and 30 days (17.2 ± 5.2 mA; n = 6; p < 0.001), indicating functional conduction block. Bipolar lesions had no adherent thrombus or endocardial defects. Cross-section examination confirmed transmurality in 100% of bipolar lesions and 98.7% of unipolar lesions.

CONCLUSIONS: Irrigated bipolar radiofrequency ablation with impedance monitoring safely and reliably produces electrically isolating, transmural Cox maze lesions in vivo.

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