Atrial flutter (AFl) commonly occurs after surgical

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1 Prevention of Atrial Flutter With Cryoablation May Be Proarrhythmogenic Peter Lukac, MD, PhD, Vibeke E. Hjortdal, MD, PhD, Anders K. Pedersen, MD, DMSc, Peter T. Mortensen, MD, Henrik K. Jensen, MD, PhD, and Peter S. Hansen, MD, PhD Departments of Cardiology and Cardio-Thoracic Surgery, Skejby University Hospital, Aarhus, Denmark Background. Atrial flutter is a serious problem after surgery for congenital heart disease. Methods. We performed an intraoperative linear oneminute cryolesion between a right atriotomy and the tricuspid annulus to prevent atrial flutter in 17 consecutive adult patients undergoing surgery for congenital heart disease. Coronary angiography and electrophysiology study using an electroanatomic mapping system to assess the conduction across the line and to try to induce atrial flutter were performed three months after the operation in 15 patients. Results. Eleven patients had bidirectional block in the cryolesion, four patients did not, and two patients refused the electrophysiology study and coronary angiography. All patients with terminal temperature below 151 C had bidirectional block, while only one patient with terminal temperature above 151 C had bidirectional block. No patient with bidirectional block and all patients without bidirectional block had inducible or spontaneous atrial flutter (p ). No lesion of the right coronary artery was detected at coronary angiography. Conclusions. The success rate was suboptimal and the intervention is potentially proarrhythmogenic in patients without block. Preventive strategies targeting atrial flutter should be validated with regard to the block rate achieved. (Ann Thorac Surg 2007;83: ) 2007 by The Society of Thoracic Surgeons Atrial flutter (AFl) commonly occurs after surgical correction of congenital heart disease [1, 2]. The incidence of AFl early after the correction of atrial septal defect, a frequent operation involving a right atriotomy, depends on the age at operation and may be as high as 39% in patients operated on after the age of 60 years [3]. Atrial flutter complicates mitral valve surgery using the superior transseptal approach, which also involves a right atriotomy, in 35% of patients [4]. An incision in the right atrial wall predisposes to AFl [5] and forms the central obstacle of incisional atrial tachycardia (Fig 1). The AFl and incisional atrial tachycardia represent three quarters of tachycardia circuits after a right atriotomy and after mitral valve surgery using the superior transseptal approach [6]. Both AFl and incisional atrial tachycardia require passage of the activation wavefront through the channel between a right atriotomy and the tricuspid annulus (TA). A blocking lesion spanning this channel was effective in prevention of AFl in a Fontan model [7]. The propensity of certain patient populations to develop AFl is increasingly recognized and preventive strategies aimed at AFl are being employed to surgical practice, frequently in addition to procedures aimed to prevent and treat atrial fibrillation [8]. In this prospective study, we tested the feasibility of a Accepted for publication Jan 12, Address correspondence to Dr Lukac, Department of Cardiology, Skejby Hospital, Brendstrupgaardsvej, DK-8200 Aarhus N, Denmark; lukacpe2@hotmail.com. prophylactic intraoperative linear cryolesion spanning the channel between a right atriotomy and TA to prevent AFl. Patients and Methods Patient Selection Consecutive patients operated on in the Department of Cardiac Surgery, Skejby University Hospital were included. Inclusion criteria were the following: (1) clinical indication for corrective operation for congenital heart disease involving a right atriotomy; (2) age greater than 18 years; and (3) ability to consent. The only exclusion criterion was acute operation. All patients gave written informed consent. The Ethics Committee for Aarhus County approved the study on September 18, Operation and Postoperative Care Two linear endocardial one-minute cryolesions connecting the right lateral atriotomy with the TA anteriorly and the crista terminalis posteriorly were performed (Fig 1). The ablations were performed with a malleable 60-mm or 100-mm cryoprobe (SurgiFrost; Endocare Inc, Irvine, CA) that uses argon as its cooling source and is capable of reaching temperatures of 160 C. Both lesions were completed after cardiopulmonary bypass and cardioplegic arrest. The right atrium was opened using either a right lateral atriotomy or the superior septal incision. In the last two patients, the duration of freezing was extended to 90 seconds. Two pairs of epicardial electrodes 2007 by The Society of Thoracic Surgeons /07/$32.00 Published by Elsevier Inc doi: /j.athoracsur

2 1718 LUKAC ET AL Ann Thorac Surg PREVENTION OF ATRIAL FLUTTER WITH CRYOABLATION 2007;83: Fig 1. Schematic of the cryolesion in the right atrium. (AFL circuit of atrial flutter; CT crista terminalis; IAT circuit of the incisional atrial tachycardia; IVC inferior vena cava; SVC superior vena cava; TA tricuspid annulus.) were placed on the atrium between the incision and the TA, 1.5 cm cranially and caudally from the cryolesion at the end of the repair. They were brought out together on to the thorax on the patient s right side. Subsequently, the thorax was closed in the usual way. Measurement of Conduction Time On the second postoperative day, the conduction time was measured by pacing the electrode pair on one side of the cryolesion between the incision and the TA and sensing the unipolar signals on the other side (Fig 2). Signals were recorded at 100 mm/second on a commercially available electrocardiograph (ECG). In patients 16 and 17, the epicardial electrodes were placed at the start of the procedure and two additional intraoperative measurements of the conduction interval were made; before the atriotomy and the cryolesion were made and after the cryolesion was created and the atriotomy was sutured. of intracardiac electrograms filtered at 50 to 500 Hz and 12-lead surface ECGs were stored digitally (Prucka CardioLab 2000; GE Medical Systems, Milwaukee, WI). An electroanatomic map (CARTO; Biosense Webster) was constructed during pacing with special emphasis on the region of surgical scar and cryolesion to judge conduction across the cryolesion. Then, the active fixation lead was repositioned to the opposite side of the cryolesion near the Navistar catheter, which was placed with the help of the already constructed electroanatomic map. Another electroanatomic map was created under pacing from this second site to judge the completeness of the cryolesion in the other direction. Afterwards, attempts at induction of atrial arrhythmias were made. These included rapid atrial pacing with 20 stimuli starting from a cycle length of 400 ms with 20 ms decrements down to a cycle length of 200 ms, and single and double extra stimuli at 400 ms cycle length down to atrial refractoriness. Isoproterenol was not used during the study. Safety Assessment of the Intervention All adverse events were recorded. Relation of adverse events to study intervention was determined by consensus of the participating investigators. Statistical Analysis All calculations were carried out using the statistical software Intercooled Stata Release 8 (Stata Corp, College Station, TX). Comparison of continuous variables was performed using the Student s t-test or the Wilcoxon rank sum test, as appropriate. Comparison of proportions was performed using the Fisher s exact test. Median (interquartile range) or mean standard deviation is reported, as appropriate. Electrophysiology Study and Coronary Angiography Electrophysiology study and coronary angiography were carried out three months after the operation. Patients were free of antiarrhythmic agents at the time of the study. Coronary angiography was performed with the usual technique using the femoral approach. Then, a 7-French quadripolar deflectable ablation catheter with a 4-mm tip electrode (Navistar; Biosense Webster, Diamond Bar, CA) was advanced through the right femoral vein into the right atrium for mapping and radiofrequency catheter ablation. An active fixation lead (Sweet Picotip; Guidant, St. Paul, MN) was screwed into the lateral right atrial wall near the TA and the cryolesion and was used for pacing. Simultaneous recordings Fig 2. Measurement of conduction delay. The time from the pacing spike until the local unipolar electrogram on the contralateral side of the cryolesion was measured on a commercially available electrocardiograph. (A local unipolar electrogram; QRS far field QRS complex; S pacing spike.)

3 Ann Thorac Surg LUKAC ET AL 2007;83: PREVENTION OF ATRIAL FLUTTER WITH CRYOABLATION Table 1. Clinical Characteristics Patient Gender Age (Years) Heart Disease Previous Operation History of Arrhythmia 1 F 59 ASD ostium secundum 0 AF 2 M 58 Pulmonary regurgitation Aortic coarctation repair AF, AFL 3 F 46 VSD, split MV Common AV canal repair AF 4 M 48 ASD sinus venosus, anomalous 0 No PV-drainage 5 F 32 ASD ostium secundum 0 No 6 F 65 ASD ostium secundum 0 No 7 M 50 ASD ostium secundum 0 AF 8 F 18 ASD ostium secundum 0 No 9 F 18 ASD ostium secundum 0 No 10 F 70 ASD ostium secundum, VSD 0 No 11 F 47 ASD ostium secundum 0 No 12 F 43 Stenosis of artificial TV 1. ASD closure, 2. PVR AFL TV repair, 3. TVR 13 F 25 ASD ostium secundum 0 AF 14 M 51 ASD ostium secundum 0 No 15 M 51 ASD sinus venosus 0 AF 15 F 26 ASD ostium secundum 0 No 17 M 58 ASD sinus venosus 0 No 1719 AF atrial fibrillation; AFL atrial flutter; ASD atrial septal defect; MV mitral valve; PV pulmonary vein; PVR pulmonary valve replacement; TV tricuspid valve; TVR tricuspid valve replacement; VSD ventricular septal defect. Results Seventeen consecutive patients were included; six were men (Table 1). Median age was 48 (32 to 58) years. The majority had atrial septal defect. Several patients had a history of paroxysmal or persistent atrial fibrillation. Patients 2 and 12 had a history of AFl. No patient had sinus node dysfunction. Apart from patient 3 all patients were free of antiarrhythmic agents during the study period. No patient was treated with class I or III antiarrhythmic drugs. Table 2. Surgical Procedures and Electrophysiologic Measurements Patient Surgical Procedure Distance Incision-TV (mm) Minimum Temperature ( C) Minimum Delay (ms) Block 1 ASD closure, cryo-pv isolation (superior transseptal Yes atriotomy a ) 2 PVR, cryo-pv isolation (superior transseptal atriotomy) n.r. n.r. n.r. Yes 3 VSD closure, MV repair through LA incision b No 4 ASD closure, anomalous PV-drainage correction Yes 5 ASD closure Yes 6 ASD closure Yes 7 ASD closure Refused 8 ASD closure Yes 9 ASD closure Yes 10 ASD and VSD closure, cryo-pv isolation through ASD Yes 11 ASD closure Yes 12 TVR, cryo-pv isolation through LA incision Refused 13 ASD closure, cryo-pv isolation through ASD Yes 14 ASD closure No 15 ASD closure, cryo-pv isolation through ASD No 16 ASD closure Yes 17 ASD closure No a The superior transseptal approach was begun anteriorly in the right atrium and continued superiorly and continued onto the septum and the superior portion of the left atrium. b 350 ms in the opposite direction. ASD atrial septal defect; LA left atrium; MV mitral valve; n.r. data was not registered; PV pulmonary vein; PVR pulmonary valve replacement; refused patient refused coronary angiography and electrophysiology study; TVR tricuspid valve replacement; VSD ventricular septal defect.

4 1720 LUKAC ET AL Ann Thorac Surg PREVENTION OF ATRIAL FLUTTER WITH CRYOABLATION 2007;83: Fig 3. Conduction block in the cryolesion between the incision and TA in superior-inferior direction in patient 3 after radiofrequency ablation. Electroanatomic map of the right atrium is shown in the right anterior oblique (left panel) and left anterior oblique (right panel) projection. Activation sequence is coded in color from red through yellow, green, blue, to purple. Pacing site is located on the superior side of the cryolesion. Cryolesion is depicted by the blue dots representing double potentials, pacing site by the yellow dot, and ablation site by the red dot. The impulse must go the whole way around the scar (visible in the left panel) and TA (right panel), respectively, to reach the caudal aspect of the cryolesion, demonstrating complete block. (PS pacing site; RF radiofrequency ablation site; SCAR scar at the site of the atriotomy; TA tricuspid annulus.) Operation The procedural data are summarized in Table 2. The mean distance between the TA and the atriotomy, and thus the mean length of the anterior cryolesion, was mm. The terminal temperature during cryolesion formation between the incision and the TA was available for 16 patients and ranged from 126 C to 161 C. Operative Data in Patients 16 and 17 The minimum temperature achieved was 152 C in patient 16 and 150 C in patient 17; in both, the temperature did not decrease during the last 40 seconds. The conduction delay, measured intraoperatively after the cryolesion was made and the patient was off bypass, was 150 ms in patient 16 and 140 ms in patient 17. Conduction Delay on the Second Postoperative Day Conduction delay between the two pairs of epicardial electrodes two days after the operation could be measured in all but one patient (Table 2). The shortest delay was 50 ms and the longest was 230 ms. Postoperative Course and Complications Patient 3 developed incessant AFl, which was judged to be a sequel of an incomplete cryolesion. Patient 12 developed an embolic stroke, which was judged not Fig 4. Figure-of-eight intraatrial reentry tachycardia in patient 3, demonstrating conduction across the cryolesion between the incision and TA in the superior inferior direction. Electroanatomic map of the right atrium is shown in the right lateral (left panel) and left lateral (right panel) projection. Activation sequence is coded in color as in Figure 3. One wavefront is coming clockwise around the incision (left panel) and the other counter clockwise around TA (right panel; we look through the TA at the scar at the lateral wall from the inside). Both merge to pass through the common channel between the atriotomy and TA. Cryolesion is depicted by the blue dots representing double potentials. (SCAR scar at the site of the atriotomy; TA tricuspid annulus.)

5 Ann Thorac Surg LUKAC ET AL 2007;83: PREVENTION OF ATRIAL FLUTTER WITH CRYOABLATION Fig 5. Minimal temperature reached during cryolesion formation between the incision and the tricuspid annulus in patients with bidirectional conduction block and no bidirectional block. related to the cryolesion. Patient 2 developed symptomatic sick sinus syndrome postoperatively and had a pacemaker implanted. This complication also was declared not related to the cryolesion. No other complications related to the cryolesion and specifically no lesions of the right coronary artery were noted immediately after the operation or during follow-up. Electrophysiology Study Patients 7 and 12 refused electrophysiology study and coronary angiography. Bidirectional block in the cryolesion between the incision and the TA was present in 11 patients (Fig 3), and bidirectional conduction across the cryolesion was present in three (patients 14, 15, and 17). Patient 3 had block in the inferior superior direction and conduction in the superior inferior direction (Fig 4). Fractionated electrograms were found at the site of the cryolesion in all patients without bidirectional block. The posterior cryolesion to the crista terminalis was not visualized in any patient. The median terminal temperature reached during cryolesion formation was 158 C ( 159, 156 C) in patients with bidirectional conduction block and 148 C ( 150, 136 C) in patients without bidirectional block (p 0.016; Fig 5). All patients without bidirectional block had temperatures above 151 C and all with bidirectional block with the exception of one had terminal temperatures below 151 C. Mean conduction time between the epicardial electrodes was ms in patients with conduction block and ms in patients without block (p ). Atrial Flutter None of the 11 patients with bidirectional block in the cryolesion between the atriotomy and TA had AFl, spontaneous or induced. All four patients without bidirectional block had AFl, two spontaneous and two induced (p ). Patient 3 developed incessant AFl on day 2. Attempts at overdrive termination were not successful because AFl recurred after the first sinus beat. The patient was treated with digoxin and a beta-blocker. The AFl persisted with adequate ventricular rate until the electrophysiology study at three months. The mechanism was a figure-ofeight atrial tachycardia with one wavefront coming clockwise around the incision and the other counter clockwise around the TA (Fig 4). The cryolesion was mapped as a line of progressively less-separated double potentials that merged at a point with fractionated potential. A radiofrequency application at this point resulted in termination of the tachycardia, noninducibility, and bidirectional block across the cryolesion (Fig 3). Patient 14 had inducible AFl at electrophysiology study and was treated with ablation of the cavotricuspid isthmus. Two months later he developed spontaneous atrial tachycardia with the central obstacle formed by the atriotomy together with the ostium of superior vena cava. This atrial tachycardia was treated by completion of the cryolesion. Afterwards, the patient had no inducible atrial arrhythmia. Patients 15 and 17 had inducible AFl and were treated with ablation of the cavotricuspid isthmus. A line of fractionated potentials was found at the site of the cryolesion. After the ablation of AFl, atrial tachycardia (where the right lateral atriotomy formed the central obstacle) was induced in both patients 15 and 17. A gap between the incision and inferior vena cava with fractionated potential was targeted with radiofrequency catheter ablation, and this lesion terminated the tachycardia. Afterwards, both patients had block of conduction between the atriotomy and the inferior vena cava and through the cavotricuspid isthmus, and no inducible atrial arrhythmia. Coronary Angiography No lesion of the right coronary artery was detected in the 15 patients who had coronary angiography after the operation. Comment 1721 The present study tested the feasibility of a prophylactic linear cryolesion spanning the channel between a right atriotomy and TA to prevent AFl. We were not able to reliably create a complete line of block with the equipment used. The reason probably was failure to achieve sufficiently low temperature. While none of the patients with bidirectional block developed AFl, incomplete block was associated with AFl in all the patients. Previous Studies Animal experiments involving the connection of the right lateral atriotomy with the tricuspid anulus in a Fontan model using cryoablation eliminated the inducibility of AFl [7]. However, a randomized short-term study based on this work failed to show benefit of such intervention [9]. Only two of 42 included patients (median age, 2.4 to 2.7 years), both in the control group, had spontaneous or induced AFl.

6 1722 LUKAC ET AL Ann Thorac Surg PREVENTION OF ATRIAL FLUTTER WITH CRYOABLATION 2007;83: Design of Preventive Lines We chose the corridor between the right atriotomy and the TA as the site of the preventive intervention because of the following: (1) It is crucial for the perpetuation of AFl and incisional atrial tachycardia, which form the majority of AFl and tachycardias irrespective of the surgical substrate [6]; (2) this region is easily accessible for the surgeon; and (3) a blocking lesion spanning this channel was effective in the prevention of AFl and tachycardia in a Fontan model [7]. We performed an additional cryolesion posteriorly from the incision toward the crista terminalis because of the theoretical possibility that the AFl circuit would use this pathway in the lateral wall. When mapping the region, we did not see a line of block in this location in any patient. On the basis of our data we cannot comment on the necessity of this lesion and further studies are needed to address this issue. Two other isthmuses are potential targets for preventive lines, but both of them eliminate only one of the two most frequent circuits; AFl or incisional atrial tachycardia. One is the isthmus between the atriotomy and the inferior vena cava, the other one is the cavotricuspid isthmus. The isthmus between the atriotomy and the inferior vena cava is crucial for the perpetuation of incisional atrial tachycardia [10]. However, continuation of the incision toward the inferior vena cava, although preventing incisional atrial tachycardia, may increase the risk of AFl because of creation of a longer posterior line of block [11]. Factors Responsible for Incomplete Block Terminal temperature below 151 C was associated with bidirectional block in all the patients and only one of five patients with terminal temperature above 151 C had a bidirectional block. Other factors than temperature, such as the contact of the cryoprobe to the atrium and the presence of a contiguous cryolesion completely down to the TA, might have affected the achievement of the block. However, care was taken to avoid these other potential sources of failure. Furthermore, the site is easily accessible and the effects of the freezing were clearly visible on the epicardium in all the patients. Proarrhythmogenicity All four patients with incomplete lesions developed AFl. A significantly higher propensity toward AFl (spontaneous or induced) in the patients without bidirectional block than in the patients with bidirectional block proves that the outcome of the cryolesion has an effect on the tachycardia substrate: protective in patients with bidirectional block and (or) proarrhythmogenic in patients without bidirectional block. The proportion of patients after a right atriotomy with inducible AFl three months after the surgery is unknown, but it is difficult to argue against classifying AFl in patient 3 as a proarrhythmia. The explanation for the possible proarrhythmogenic effect may be the conduction properties of the incompletely ablated tissue. Unidirectional block, demonstrated in patient 3, is one of the prerequisites of reentry. Fractionated potentials found at the site of the cryolesion in all four patients suggest slow and inhomogeneous impulse conduction [12]. In patient 3 a clear delay across the cryolesion with a distinct localized gap was demonstrated. Zones of slow conduction may act proarrhythmogenic by shortening the wavelength of a reentry circuit and by predisposing to unidirectional block [13, 14]. Avoiding Incomplete Block The success rate of the presented technique was suboptimal, especially when considering the possible proarrhythmogenicity of the incomplete lesion. Very similar intervention aimed at the cavotricuspid isthmus is routinely used to prevent and treat AFl concomitant with endocardial cryoablation of atrial fibrillation [8]. Our data show that before these interventions can be used clinically the efficacy with regard to the rate of complete block has to be established. Unfortunately, we do not know how to avoid incomplete block. An intraoperative measurement of conduction delay to detect patients without bidirectional block immediately after starting cardiac perfusion to allow the surgeon to supplement an additional lesion does not solve the problem, as immediate measurement was not predictive of chronic block in one of two patients. A longer application time did not lead to further decrease in temperature (patients 16 and 17) and did not solve the problem of incomplete block (patient 17). The value of techniques other than cryoablation (surgical incision, radiofrequency ablation) has to be determined. A surgical incision that had been brought to the atrioventricular groove with a single 90-second cryothermal lesion in the majority of cases was not proarrhythmogenic [9]. The efficacy of this intervention with regard to the percentage of bidirectional block is, however, unknown. Complications Apart from the proarrhythmogenic effect of the cryolesion, the cryolesion in the described location was safe. A right-sided cryolesion cannot explain an embolic stroke (patient 12) and sick sinus syndrome (patient 2) is a known complication of the superior transseptal incision [15]. No other complications related to the cryolesion, and specifically no lesions of the right coronary artery, were noted immediately after the operation or during follow-up. In conclusion, the success rate was suboptimal and the intervention is potentially proarrhythmogenic in patients without block. Preventive strategies targeting AFl should be validated with regard to the block rate achieved. Dr Peter Lukac has been supported by a Training Fellowship of the European Society of Cardiology, the Slovak Society of Cardiology, by the Danish Research Agency, Ejnar and Aase Danielsen s Fund, Dagmar Marshall s Fund, and Grant No B38-A of the Danish Heart Foundation.

7 Ann Thorac Surg LUKAC ET AL 2007;83: PREVENTION OF ATRIAL FLUTTER WITH CRYOABLATION References 1. Garson A Jr, Bink-Boelkens M, Hesslein PS, et al. Atrial flutter in the young: a collaborative study of 380 cases. J Am Coll Cardiol 1985;6: Murphy JG, Gersh BJ, McGoon MD, et al. Long-term outcome after surgical repair of isolated atrial septal defect. Follow-up at 27 to 32 years. N Engl J Med 1990;323: Berger F, Vogel M, Kramer A, et al. Incidence of atrial flutter/fibrillation in adults with atrial septal defect before and after surgery. Ann Thorac Surg 1999;68: Lukac P, Hjortdal VE, Pedersen AK, Mortensen PT, Jensen HK, Hansen PS. Atrial incision affects the incidence of atrial tachycardia after mitral valve surgery. Ann Thorac Surg 2006;81: Frame LH, Page RL, Boyden PA, Fenoglio JJ Jr, Hoffman BF. Circus movement in the canine atrium around the tricuspid ring during experimental atrial flutter and during reentry in vitro. Circulation 1987;76: Lukac P, Pedersen AK, Mortensen PT, Jensen HK, Hjortdal V, Hansen PS. Ablation of atrial tachycardia after surgery for congenital and acquired heart disease using an electroanatomic mapping system: which circuits to expect in which substrate? Heart Rhythm 2005;2: Rodefeld MD, Gandhi SK, Huddleston CB, et al. Anatomically based ablation of atrial flutter in an acute canine model of the modified Fontan operation. J Thorac Cardiovasc Surg 1996;112: Mack CA, Milla F, Ko W, et al. Surgical treatment of atrial fibrillation using argon-based cryoablation during concomitant cardiac procedures. Circulation 2005;112:I1 I Collins KK, Rhee EK, Delucca JM, et al. Modification to the Fontan procedure for the prophylaxis of intraatrial reentrant tachycardia: short-term results of a prospective randomized blinded trial. J Thorac Cardiovasc Surg 2004; 127: Nakagawa H, Shah N, Matsudaira K, et al. Characterization of reentrant circuit in macroreentrant right atrial tachycardia after surgical repair of congenital heart disease: isolated channels between scars allow focal ablation. Circulation 2001;103: Shah D, Jais P, Haissaguerre M. Electrophysiological evaluation and ablation of atypical right atrial flutter. Card Electrophysiol Rev 2002;6: Gardner PI, Ursell PC, Fenoglio JJ Jr, Wit AL. Electrophysiologic and anatomic basis for fractionated electrograms recorded from healed myocardial infarcts. Circulation 1985; 72: Cranefield PF, Wit AL, Hoffman BF. Conduction of the cardiac impulse. 3. Characteristics of very slow conduction. J Gen Physiol 1972;59: Rensma PL, Allessie MA, Lammers WJ, Bonke FI, Schalij MJ. Length of excitation wave and susceptibility to reentrant atrial arrhythmias in normal conscious dogs. Circ Res 1988; 62: Lukac PL, Hjortdal VE, Pedersen AK, Mortensen PT, Jensen HK, Hansen PS. The superior transseptal approach to mitral valve is associated with a higher need for pacemaker implantation than the left atrial approach. Ann Thorac Surg 2007;83: INVITED COMMENTARY There has been an explosion in the number of operations directed at treating atrial arrhythmias and more specifically atrial fibrillation. This has been aided by technological advances and the availability of new energy sources substituted for the cut and sew technique as developed by Cox in the 1980s. These new energy sources have in turn led to the development of the so-called minimally invasive approaches by some surgeons toward treating atrial fibrillation. Regardless of the surgical approach and the energy source used, the lesions set created have to be transmural to ensure success of the operation and curing the patient. After all, the high success rate of the gold standard cut and sew technique was due to its 100% transmurality of the surgical incisions. In the current issue, Lukac and colleagues [1] have looked at the subject of pro-arrhythmogenicity of nontransmural cryolesions in the right atrium in adult patients undergoing surgical repair of congenital heart defects, predominantly atrial septal defect. In their sophisticated electrophysiological studies they noted fractionated electrograms at the site of the cryolesion in all patients who did not have bidirectional block. This is an important point and something that all surgeons involved with treatment of atrial arrhythmias need to consider when using new technology and energy sources to avoid unintended consequences of nontransmural lesions. Transmurality of the lesion and complete block across the lesion should be verified intraoperatively if we are going to match the cure rate offered by surgical incisions. Using either custom made or commercially made available devices, surgeons should try to confirm the presence of complete block across the lesions intraoperatively. Lukac and colleagues [1] should be congratulated on a nice study. G. Hossein Almassi, MD Division of Cardiothoracic Surgery Medical College of Wisconsin 9200 W Wisconsin Ave Milwaukee, WI halmassi@mcw.edu Reference 1. Lukac P, Hjortdal VE, Pedersen AK, Mortensen PT, Jensen HK, Hansen PS, et al. Prevention of atrial flutter with cryoablation may be proarrhythmogenic. Ann Thorac Surg 2007;83: by The Society of Thoracic Surgeons /07/$32.00 Published by Elsevier Inc doi: /j.athoracsur