Response to Letter Regarding Article “Comparison of Electrode Cooling Between Internal and Open Irrigation in Radiofrequency Ablation Lesion Depth and Incidence of Thrombus and Steam Pop”
We thank Drs Saul and Haemmerich for their comments regarding our article,1 but we respectfully disagree. Using the open-irrigation electrode in clinical practice in the “temperature control” mode with an adequate irrigation flow rate (17 mL/min at ≤30 W and 30 mL/min at 31 to 50 W) infrequently results in reaching the target electrode temperature (ET, 40°C to 45°C). Therefore, radiofrequency (RF) energy is delivered continuously at the power limit (ie, 30 W). This is essentially “power control.”
Thrombus did not occur when the closed-loop electrode was used in the 8 RF applications with ET ≤40°C in high blood flow. However, in low blood flow, thrombus occurred in 3 (60%) of the 5 RF applications with peak ET ≤40°C, indicating inadequate interface cooling. The higher risk of thrombus with the closed-loop electrode has been suggested in clinical studies.2,3 Stroke or transient ischemic attack occurred in 5 (3.1%) of the 163 patients undergoing ablation of atrial fibrillation using the closed-loop electrode with target ET ≤35°C.2 In the same study, adding intracardiac echocardiography to detect microbubbles for titrating RF power eliminated embolic complications in the next 152 patients. Significantly, there was no correlation between microbubble formation and ET. Type 2 microbubbles, indicating high interface temperature (IT) and risk of thrombus, were observed in 20%, 22%, 15%, and 11% of RF applications using the closed-loop electrode at ET of 36°C to 40°C, 31°C to 35°C, 26°C to 30°C, and 20°C to 25°C, respectively.2
We agree that our study1 demonstrates greater interface cooling with the open-irrigation electrode. However, we disagree with statement by Drs Saul and Haemmerich that using the temperature control mode with both electrodes would lead to similar rates of thrombus. Thrombus does not occur until IT reaches 80°C.4 In our study and in previous studies, IT did not reach 80°C using the open-irrigation electrode when an adequate irrigation flow rate was used.5 Therefore, the risk of thrombus will still be smaller with the open-irrigation electrode. One of the important points from this study is that there is no significant relationship between ET and IT for both closed-loop and open-irrigation electrodes.
Finally, we respectfully disagree that greater power and lesion size would occur with the closed-loop electrode when both are used within “clinical guidelines” (temperature control). Because lesion size is determined by the power delivered to the tissue and the similar impedance with the 2 electrodes, similar power (and lesion size) will be delivered through both electrodes until the target ET is reached.4 The target ET will be reached first with the closed-loop electrode, especially in low blood flow, limiting lesion size. The findings in our study and previous studies using the thigh muscle preparation have correlated with clinical experience.4,5
Sources of Funding
Drs Nakagawa and Jackman have received research grants from Biosense Webster.
Dr Nakagawa is a consultant for Biosense Webster, Inc, St Jude Medical, Inc, and Boston Scientific, Japan, and has received honoraria from Biosense Webster, Inc, and St Jude Medical, Inc. Dr Wittkampf is a consultant for St Jude Medical, Inc. Dr Jackman is a consultant for Biosense Webster, Inc, and has received honoraria from Biosense Webster, Inc. The other authors report no conflicts.
Yokoyama K, Nakagawa H, Wittkampf FH, Pitha JV, Lazzara R, Jackman WM. Comparison of electrode cooling between internal and open irrigation in radiofrequency ablation lesion depth and incidence of thrombus and steam pop. Circulation. 2006; 113: 11–19.
Marrouche NF, Martin DO, Wazni O, Gillinov AM, Klein A, Bhargava M, Saad E, Bash D, Yamada H, Jaber W, Schweikert R, Tchou P, Abdul-Karim A, Saliba W, Natale A. Phased-array intracardiac echocardiography monitoring during pulmonary vein isolation in patients with atrial fibrillation impact on outcome and complication. Circulation. 2003; 107: 2710–2716.
Calkins H, Epstein A, Packer D, Arria AM, Hummel J, Gilligan DM, Trusso J, Carlson M, Luceri R, Kopelman H, Wilber D, Wharton JM, Stevenson W. Catheter ablation of ventricular tachycardia in patients with structural heart disease using cooled radiofrequency energy: results of a prospective multicenter study. J Am Coll Cardiol. 2000; 35: 1905–1914.
Nakagawa H, Wittkampf FHM, Yamanashi WS, Pitha JV, Imai S, Campbell B, Arruda M, Lazzara R, Jackman WM. Inverse relationship between electrode size and lesion size during radiofrequency ablation with active electrode cooling. Circulation. 1998; 98: 458–465.