This is a case report of a 52-year-old man who was referred to our institution for radiofrequency (RF) catheter ablation of typical atrial flutter (AFL). The patient was an otherwise healthy man, who presented with palpitations beginning two years prior to the date of ablation. These episodes were initially infrequent and sporadic, but were associated with exertional dyspnea and fatigue. Over the ensuing months, however, there was an increasing frequency of symptoms, and the patient eventually presented to the emergency room in sustained AFL with rapid ventricular response. He was electrically cardioverted, but due to underlying bradycardia, antiarrhythmic drug therapy was not initiated. A Holter monitor was obtained, which revealed episodes of AFL with a rapid ventricular response in excess of 120 bpm. The patient was therefore referred to our institution for RF catheter ablation of his AFL. At presentation, the patient was noted to be otherwise healthy and in no acute distress. His vital signs were normal with a blood pressure of 110/78 mmHg, and heart rate of 82 bpm. The remainder of the physical examination was unremarkable, including the cardiovascular exam, with the exception of an irregular rhythm. A 12-lead ECG revealed an abnormal rhythm consistent with type 1 AFL, with a classic saw-tooth F-wave pattern in the inferior limb leads II, III, with upright F-waves in V1, and inverted F-waves in V6. The atrial rate was 240 bpm, with a ventricular rate of 80 bpm. A 2D echocardiogram obtained on the day of the procedure revealed mild global left ventricular hypokinesis, with an ejection fraction of 50%, mild bi-atrial enlargement and moderate tricuspid regurgitation. It was concluded that the patient was in incessant AFL, and he was scheduled for RF catheter ablation expeditiously. On the day of ablation, the patient presented in AFL with a variable ventricular response. A transesophageal echocardiography was performed due to a sub-therapeutic INR observed during the three weeks prior to the procedure date. The patient agreed to enroll in the Boston Scientific EPT-1000XP Cardiac Ablation System clinical trial, evaluating large 8- and 10-mm tip electrode radiofrequency ablation catheters, combined with a high power RF generator capable of delivering up to 100 watts. Upon intravenous administration of moderate sedation and local anesthesia at the catheter entry sites, diagnostic catheters were placed under fluoroscopic guidance as follows: A decapolar catheter was positioned in the coronary sinus (CS) via a 6 French (Fr) sheath in the right internal jugular vein. A quadripolar steerable mapping/ablation catheter (Blazer II XP catheter, Boston Scientific, Natick, Massachusetts), with a 10 mm tip, was positioned in the right atrium via an 8 Fr sheath in the right femoral vein. A quadripolar, steerable, mapping catheter (Navistar, Biosense Webster, Inc., Diamond Bar, California) was positioned in the right atrium via a second 8 Fr sheath in the right femoral vein. The patient underwent electro-anatomical contact mapping using the CARTO mapping system (Biosense Webster, Inc.), which confirmed the presence of type 1 counterclockwise AFL (Figure 1). The tachycardia cycle length was 292 ms. Pacing was performed via the ablation catheter (Blazer II XP) placed in the tricuspid valve-inferior vena cava (TV-IVC) isthmus, while the mapping catheter (Navistar) was placed in the high-to-low configuration in the low lateral right atrium (LLRA). Concealed entrainment was demonstrated, confirming the isthmus dependence of the AFL. Radiofrequency catheter ablation of the TV-IVC isthmus was then performed using the 10-mm tip investigational ablation catheter (Blazer II XP catheter, Boston Scientific). Initially, the Blazer II XP catheter was positioned in the 6 o clock position on the TV annulus. A continuous line of ablation was created by withdrawing the ablation catheter from the TV annulus toward the Eustachian ridge approximately 0.5 cm every 60 seconds. A total of only 3 radiofrequency energy applications were delivered, ranging from 19 to 103 seconds in duration, at peak watts of from 51-75, achieving temperatures in the 42-60 ºC range. Atrial flutter terminated during the second energy application and was no longer inducible after completion of the ablation procedure. After a waiting period of 30 minutes following ablation, bi-directional TV-IVC isthmus conduction block was demonstrated by electro-anatomical mapping during pacing from the CS ostium (Figure 2A) and the LLRA (Figure 2B). Additionally, rapid atrial pacing from the CS ostium and LLRA down to a cycle length of 200 ms failed to induce any further AFL. There were no complications during the procedure. The total fluoroscopy time for the procedure was 25.3 minutes, of which only 3.9 minutes was required for ablation. The total procedure time was 90 minutes. The patient was monitored for eight hours following the procedure with ECG telemetry. There were no complications observed following ablation. A 2-dimensional echocardiogram was repeated after the procedure prior to discharge, which revealed no changes from baseline. After discharge, the patient was followed up with weekly scheduled trans-telephonic event monitor recordings, and was instructed to transmit a trans-telephonic recording in the event of any symptoms suggesting arrhythmia recurrence. The patient was evaluated in the clinic at the 1-, 3-, and 6-month intervals following ablation, and by telephone call at the 1- and 2-year intervals post-ablation. The patient reported no recurrence of symptoms and remains arrhythmia-free. The patient returned to his pre-treatment exercise regimen within a few days of his ablation and reports recovery of normal exercise capacity. This case report demonstrates the successful ablation of type 1 atrial flutter in a highly symptomatic patient using a new large-tip ablation catheter (10 mm) and high-power (100 watt) RF generator. Although great advances have been made in radiofrequency catheter ablation of isthmus dependent type 1 AFL, using standard 5-mm electrode-tip ablation catheters and standard 50-watt RF generators, the acute success rate is still only 80-90% with recurrence rates ranging from 10-20%. Furthermore, achieving bi-directional isthmus block with standard 5-mm electrode tip ablation catheters may require numerous ablation attempts resulting in a prolonged procedure and fluoroscopy times. More recently, with the development of chilled-tip ablation catheters and 8 mm tip-electrode ablation catheters, acute success rates have improved to 90-95%. The greater efficacy of large-tip electrode catheters is likely due to the larger surface area of the ablation electrode and reduced impedance, which results in the ability to disperse larger amounts of energy into the myocardium without overheating the tissue and producing coagulum. By allowing delivery of larger amounts of energy, a larger lesion may be created. This case demonstrated that a large, 10-mm tip electrode can produce TV-IVC isthmus block with very few energy applications, resulting in a short procedure without complications. Acknowledgments. We would like to thank Linda Tone, RN and Christine Feller, RN for their help in preparing the manuscript and figures.