Efficacy of a cooled bipolar epicardial radiofrequency ablation probe for creating transmural myocardial lesions.

OBJECTIVE: Creation of transmural myocardial lesions with epicardial surgical devices to treat atrial fibrillation is difficult. A new cooled bipolar radiofrequency ablation probe was used to create transmural myocardial lesions under controlled conditions. METHODS: The Coolrail (AtriCure, Inc, West Chester, Ohio) is a handheld probe with 2 parallel 30-mm long radiofrequency conductors. Conductors are cooled by water irrigation. Lesions were delivered to epicardial surface of isolated bovine myocardium sliced 3- to 8-mm thick, with blood flow beneath tissue at 0 or 0.4 m/s. Contact pressure between probe and tissue was either 450 g or 900 g. Tissue temperatures were measured. Tissue was sectioned every 5 mm along lesion long axis to determine lesion dimensions. RESULTS: For 80 experiments with 450-g contact pressure, epicardial lesion length was 31.3 mm (interquartile range, 30.1-32.8 mm); endocardial lesion length was 14.1 mm (interquartile range, 0.0-22.6 mm). Average lesion depth was 4.2 +/- 0.74 mm. Temperature at probe interface was 81 degrees C +/- 21 degrees C; that at blood pool interface was 53 degrees C +/- 12 degrees C. Lesions were always transmural when tissue thickness was 4.0 mm or less. Endocardial blood flow did not influence lesion depth. With 900-g contact pressure, increased depth was always transmural at 4.8-mm tissue thickness or less. CONCLUSIONS: This irrigated bipolar radiofrequency probe consistently produced transmural lesions in tissue 4 mm or thinner under controlled conditions in vitro. Lesion depth was increased by greater pressure on probe and not affected by blood flow. Endocardial lesions were smaller than epicardial dimensions.

Long-term outcomes after catheter ablation of cavo-tricuspid isthmus dependent atrial flutter: a meta-analysis.

BACKGROUND: Despite the success of catheter ablation of cavotricuspid isthmus-dependent atrial flutter (AFL), important postablation outcomes are ill-defined. The purpose of our study was to analyze long-term outcomes after catheter ablation of cavotricuspid isthmus-dependent AFL. METHODS AND RESULTS: A meta-analysis was performed of articles reporting clinical outcomes after catheter ablation of AFL published between January 1988 and July 2008. The analysis included 158 studies comprising 10 719 patients (79% men, 59.8+/-0.5 years old, 46% left atrial enlargement, 46% heart disease, 42% with history of atrial fibrillation, 14.3+/-0.4 months of follow-up). The overall acute success rate adjusted for reporting bias was 91.1% (95% CI, 89.5 to 92.4), 92.7% (95% CI, 90.0 to 94.8) for 8- to 10-mm tip/or irrigated radiofrequency catheters, and 87.9% (95% CI, 84.2 to 90.9) for 4- to 6-mm tip catheters (P>0.05). Atrial flutter recurrence rates were significantly reduced by use of 8- to 10-mm tip or irrigated radiofrequency catheters (6.7% versus 13.8%, P<0.05) and by use of bidirectional cavotricuspid isthmus block as a procedural end point (9.3% versus 23.6%, P<0.05). The AFL recurrence rate did not increase over time. The overall occurrence rate of atrial fibrillation after AFL ablation was 33.6% (95% CI, 29.7 to 37.3) but was 52.7% (95% CI, 47.8 to 57.6) in patients with a history of atrial fibrillation before ablation and 23.1% (95% CI, 17.5 to 29.9) in those without atrial fibrillation before ablation (P<0.05). The incidence of atrial fibrillation increased over time in both groups; however, 5 years after ablation, the incidence of atrial fibrillation was similar in those with and without atrial fibrillation before ablation. The acute complication rate was 2.6% (95% CI, 2 to 3). The mortality rate during follow-up was 3.3% (95% CI, 2.4 to 4.5). Antiarrhythmic drug use after ablation was 31.6% (95% CI, 25.6 to 37.8). The long-term use of coumadin was 65.9%, (95% CI, 43.8 to 82.8). Quality of life data were very limited. CONCLUSIONS: AFL ablation is safe and effective. Ablation technology and procedural end points have greater influences on AFL recurrences than on acute ablation success rates. Atrial fibrillation is common after AFL ablation. Almost one third of patients take antiarrhythmic drugs after AFL ablation. Atrial fibrillation before AFL ablation may indicate a more advanced state of electric disease.

Effect of electrode orientation on lesion sizes produced by irrigated radiofrequency ablation catheters.

BACKGROUND: Irrigated radiofrequency (RF) ablation catheters may produce different lesion sizes dependent upon the electrode orientation to the tissue. This study examined the effect of irrigated electrode orientation on the lesion size and explores a potential mechanism for this effect. METHODS AND RESULTS: Lesions were created in isolated porcine myocardium using an open irrigation, closed irrigation, and nonirrigated RF catheter (all 3.5-4 mm tips). Lesions were created with the electrodes with all permutations of electrode orientation (vertical or horizontal), contact pressure (6 or 20 g), and saline superfusate flow (0.2 or 0.4 m/sec) over tissue interface. The effect of electrode irrigation without RF delivery on tissue temperature was assessed with intramyocardial temperature probes and infrared thermal imaging. For both irrigated catheters, the horizontal orientation produced 25-30% smaller lesion volumes than the vertical orientation despite equal or greater power deliveries. The horizontal orientation produced larger lesion volumes for the nonirrigated catheter. Higher superfusate flow rates were associated with decreased lesion volumes for the irrigated catheters but greater lesion volumes for the nonirrigated catheter. Catheter irrigation alone without RF delivery reduced intramyocardial temperatures up to 4.9 degrees C and the horizontal orientation produced a 2-fold greater area of tissue cooling than the vertical orientation. CONCLUSION: Horizontal electrode orientations reduce lesion volumes for irrigated RF catheters. This effect may be in part due to greater areas of active tissue cooling in the horizontal orientation.

Comparison of lesion sizes produced by cryoablation and open irrigation radiofrequency ablation catheters.

INTRODUCTION: The relative lesion sizes created by large electrode cryoablation catheter and irrigated radiofrequency (RF) ablation are not known. The purpose of this study was to directly compare lesion sizes created by cryoablation and irrigated RF under controlled conditions. METHODS AND RESULTS: Ablation lesions were created in freshly harvested porcine left ventricular myocardium in a blood-filled tissue bath using an 8-mm-tip cryoablation catheter and a 3.5-mm-tip open-irrigated RF ablation catheter. Lesions were created under all permutations of the following conditions: electrode orientation vertical (perpendicular) or horizontal (parallel) to the tissue, electrode contact pressure at 6 or 20 g, and blood flow at 0.2 or 0.4 m/s over the electrode-tissue interface. The largest lesion volumes created with cryoablation were 961 +/- 103 mm(3), compared with the largest lesions volumes created with RF of 680 +/- 48 mm(3) (P < 0.001). The 3-way interactions among electrode orientation, contact pressure, and superfusate blood velocity accounted for the variation in lesion volumes for both catheters (both r(2)= 0.97, both P < 0.0001). The greater contact pressure increased lesion size for both cryoablation and RF. For cryoablation, lesion sizes were increased by the horizontal orientation and by the lower blood flow velocity. For open-irrigated RF, lesion sizes were significantly reduced by the horizontal orientation, however. CONCLUSIONS: Depending on conditions of electrode orientation, contact pressure, and blood velocity, either 8-mm-tip cryoablation or open-irrigated RF may produce the larger lesion volumes. Open-irrigated RF lesion sizes are reduced in the horizontal catheter orientation.

Site localization and characterization of pain during radiofrequency ablation of the pulmonary veins.

BACKGROUND: Characteristics of radiofrequency (RF) lesions producing pain with an 8-mm catheter during pulmonary vein (PV) ablation have not been prospectively studied. METHODS: We studied 46 (30 men, age 56 +/- 10 years) patients with AF who underwent RF ablation of PVs. PV isolation was achieved by using an 8F, 8-mm Biosense ablation catheter (Biosense Webster, Diamond Bar, CA, USA) guided by intracardiac echocardiography (ICE). An electroanatomic map was used to document the location of all RF lesions and the time; PV location and maximum temperature of every lesion were recorded. Location of the esophagus was determined by magnetic resonance imaging prior to the procedure and by both ICE and barium swallows during procedure. RESULT: A total of 1,448 (33 +/- 12) RF lesions were delivered to 180 veins. Thirty-nine patients (85%) had at least one lesion associated with pain (mean: 8 +/- 5 lesions) during ablation. The RF generator setting during lesions resulting in pain sensation was 48.6 +/- 7.0 Watts and 51.5 +/- 2.9 degrees C. Maximum temperature attained at the time of pain sensation was 45.7 +/- 4.2 degrees C. By logistic regression analysis the left superior PV (OR 1.54, CI 1.06-2.24, LS vs RI, P < 0.05) and left inferior PV (OR 2.74, CI 1.79-4.19, LI vs RI, P < 0.001) location were both positively correlated with the production of pain. The location of lesions associated with pain was not near the esophagus during any of the pain-producing lesions. CONCLUSION: Pain sensation is relatively common during RF ablation of PVs. There was no correlation between pain and the location of esophagus. Pain was more common during RF ablation of left inferior and left superior PVs.

Time to electrode rewarming after cryoablation predicts lesion size.

INTRODUCTION: There are no methods in clinical use to assess tissue cooling during catheter cryoablation. Cryoablation electrode temperature may be a poor predictor of lesion size. The purpose of this study was to determine whether the time necessary for the cryoablation electrode to cool to target temperature or to rewarm after cryoablation can predict lesion size. METHODS AND RESULTS: Cryoablation was performed on live porcine left ventricle in a saline bath (37 degrees C) using 8-mm-tip catheter. Cryoablation was given for 300 seconds under all permutations of the following conditions: electrode orientation vertical or horizontal, contact pressure 6 or 20 g, superfusate flow over electrode-tissue interface at 0.2 or 0.4 m/s (N = 10 each condition set, total 80 experiments). The time intervals necessary to cool the electrode to the target temperature of -75 degrees C and to rewarm to + 30 degrees C after termination of cryoablation were recorded. Lesion volume was predicted best by the time necessary to rewarm the electrode to +30 degrees C (r2 = 0.65, P < 0.0001), followed by electrode temperature (r2 = 0.28, P < 0.0001) and time to cool the electrode to -75 degrees C (r2 = 0.24, P < 0.0001). Time to +30 degrees C and time to -75 degrees C were associated with superfusate flow rate, contact pressure, and electrode orientation (r2 = 0.80 and 0.61, respectively, both P < 0.0001). Superfusate flow rate, contact pressure, and orientation were also highly predictive of lesion volume (r2 = 0.93, P < 0.0001). CONCLUSIONS: Time to cryoablation electrode rewarming is a better predictor of cryoablation lesion size than is electrode temperature. Time to cryoablation electrode rewarming reflects important determinants of cryoablation lesion formation--convective warming, contact pressure, and electrode orientation--that are not ascertainable during clinical ablation procedures.