doi:10.1510/mmcts.2005.001081
Concomitant ablation of atrial fibrillation during mitral surgery Stefano Benussi*, Ottavio Alfieri Division of Cardiac Surgery, S Raffaele University Hospital, via Olgettina 60, 20132 Milan, Italy Left atrial ablation with bipolar radiofrequency using the epicardial approach is described. After dissection of the pericardial reflections and of the Marshall fold, electrical isolation of the right and left pulmonary veins and that of the left appendage are carried out through epicardial ablation. After aortic cross clamping, through standard atriotomy, the connecting lines are then performed. The possible options for the mitral connecting ablation are discussed. At completion of the ablation procedure the base of the left appendage is sutured from inside.
Keywords: Atrial fibrillation; Bipolar radiofrequency; Cardiac surgery; Mitral valve disease; Radiofrequency ablation. Introduction First reported in 1999 w1x, epicardial ablation has been described by many groups for the concomitant treatment of atrial fibrillation (AF) w2–5x and also as a possible option for curing lone AF w3,6x. Diverse unipolar ablating systems have been used for epicardial ablation on the beating heart, with variable success rates w4,5,7x. The major limitation of unipolar devices is that, due to the convective cooling of blood flowing through the atria and depending on the composition of the diseased atrial wall, they do not predictably yield epicardial transmural lesions w4,8x. Bipolar devices seem a promising way to obviate such problems: the first experimental trials demonstrated that bipolar radiofrequency (RF) ablation can reliably produce continuous transmural linear scars w9,10x. We report our ablation technique and initial results with bipolar RF. * Corresponding author: Tel.: q39-02-2643 7127; fax: q39-02-2643 7125. E-mail: [email protected] 䉷 2005 European Association for Cardio-thoracic Surgery
Perioperative management To decrease the risk of intracavitary thrombus formation upon admission, oral anticoagulant medications are discontinued and a continuous heparin infusion is administered until 6 h before surgery. Preoperative transesophageal echocardiography is performed in all patients no longer than 24 h before surgery to exclude left atrial thrombosis. A continuous heparin drip is started after cessation of postoperative bleeding and is continued until effective anticoagulation is reached with oral medications. In the absence of indications other than AF, patients with stable sinus rhythm (SR) at G3 months after surgery are instructed to discontinue the use of anticoagulant medications, following the echocardiographic demonstration of a recovered significant (Awave 10 cm/s) left and right atrial contraction. Antiarrhythmic prophylaxis is carried out on a routine basis. Amiodarone is used as the first-choice drug: an intravenous bolus of 300 mg, followed by a continuous infusion of 1200 mg/24 h until the first postoperative day is generally administered. In the absence of A-V block greater than 1 degree or of unstable SR, 1
S. Benussi and O. Alfieri / Multimedia Manual of Cardiothoracic Surgery / doi:10.1510/mmcts.2005.001081
Video 1. The two ablating inserts are mounted on the opposing jaws of a stainless steel clamp and are moistened with saline before use. Different shapes of the clamp can be employed based on the site of ablation and on the surgeon’s preference.
Video 2. After blunt dissection of the pericardial reflections, generally after institution of full CPB, isolation of the right pulmonary veins couple is carried out. The device is clamped on the left atrial wall around the orifices of the veins and not on the veins themselves, to prevent pulmonary vein stenosis. Care is taken in making sure that all the atrial wall is within the ablating surface of the device. In particular, the very tip of the clamp behind the heart must be free from atrial tissue. Folding of the atrial walls within the clamp should be prevented since an uneven thickness of the ablated tissue can increase the probability of leaving gaps within the encircling line.
Video 3. The table is then slightly tilted to the right of the heart and the heart is lifted towards the surgeon. The Marshall fold is then exposed by gently pulling the left pulmonary artery. It is then interrupted with diathermy. The pericardial reflections around the left pulmonary veins are then easily interrupted, generally through blunt dissection only. Schematic 1. Simplified lesion scheme for the concomitant treatment of atrial fibrillation using the bipolar ablator only. RPVs: right pulmonary veins; LPVs: left pulmonary veins; LA: left appendage; MV: mitral valve.
oral administration of 200 mg of amiodarone, every 8 h until discharge, followed by a maintenance regimen of 200 mg/day is then continued. Patients with contraindications to amiodarone are administered sotalol, propaphenon or do not receive any antiarrhythmic medication. After discharge such medications are continued for 3 to 6 months, and are then generally tapered off.
Surgical technique The ablations are performed using a bipolar RF ablation device (Cobra Bipolar – MMCTSLINK 75). Two 64-mm long ablating inserts are mounted on the opposing faces of the jaws of a stainless steel clamp (Video 1). Each insert is made of two electrodes 2
lodged in a polyester cover. Each electrode has a thermocouple mounted on both ends. RF current is delivered for 40–45 s at 35–40 W, with a preset temperature of 90 8C. In our initial experience with bipolar RF, the mitral line was omitted because of concern about injuring a major coronary artery branch in the A-V groove (Schematic 1). The epicardial ablations are generally performed on cardiopulmonary bypass (CPB) at 37 8C. After dissection of pericardial reflections, the bipolar device is clamped around the atrial cuff containing the inflow of the right pulmonary veins. Then RF energy is deployed yielding an encircling lesion (Video 2). The heart is then lifted, the Mashall fold interrupted (Video 3), and a similar encircling lesion is performed on the left pulmonary vein cuff (Video 4). Based on recent evidence w11–13x, to increase the chance of an effective isolation of the pulmonary
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Video 4. The ablating device is then clamped on the atrial wall around the left pulmonary veins orifices and an encircling ablation is performed in a similar manner to that described for isolation of the right pulmonary veins.
Video 5. An epicardial connecting ablation with the tip of the clamp pinching the left encircling line and the base ending in the body of the left appendage can be performed – an optional alternative is that of performing this connecting line endocardially, through the left atriotomy, by clamping the device with one jaw in the left appendage and the other in one of the left pulmonary veins.
Schematic 2. Complete left atrial lesion scheme for the concomitant treatment of atrial fibrillation by adding to the set of bipolar ablations a mitral connecting line performed with a unipolar device. RPVs: right pulmonary veins; LPVs: left pulmonary veins; LA: left appendage; MV: mitral valve.
The left atrial appendage (LAA) is then ablated at its base. At this time the ablating piece must be kept away from the A-V groove (around the upper portion of the base of the appendage) thus is preventing injury to a major coronary artery. After aortic cross clamping through a standard left atriotomy, the bipolar device can be used in the endo/ epicardial mode (one jaw inside the heart and the other outside) to perform a connecting line between the two encirclings (Video 6).
Video 6. After cross-clamping the connecting lines are then completed. One jaw of the clamp is inserted in the left atrium with the tip in the upper left pulmonary vein or in the appendage, while the other jaw is outside, in the transverse sinus of pericardium. Alternatively, the inner jaw is directed to the lower left pulmonary vein (or to the appendage) and the outer jaw is placed in the oblique sinus, parallel to the A-V groove. If the left atriotomy does not intersect the right encircling ablation – a frequent occurrence in the case of left atriomegaly – a short additional connecting line is performed between the atriotomy and the right encircling ablation as shown.
veins, it is advisable to either validate the encircling lines with intraoperative conduction block assessment, or at least to double such ablation lines. The appendage is then ablated at its base and connected to the left encircling by means of an additional epicardial ablation (Video 5).
In order to reduce the chance of a reentry circuit around the mitral annulus to sustain left flutter, the described ablation procedure has been recently revised (Schematic 2) by reintroducing a left isthmus ablation line, performed with a unipolar linear catheter (Video 7). As previously described w14x, the site of such line is chosen based on coronary anatomy (Photo 1). After the ablations the LAA is sutured, generally from inside.
Results Clinical experience Starting in February 1998, we performed concomitant AF ablation in 492 patients undergoing open heart 3
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Video 7. A left isthmus line can finally be performed by connecting the left appendage (like in the video) or the atriotomy with the mitral annulus with a unipolar device. A temperature-controlled unipolar RF catheter is utilized in the recorded case, but different tools can be utilized including a reusable cryoprobe. The safest site in which to place this line is chosen based on coronary anatomy (see Photo 1). Finally the base of the left appendage is sutured from inside. A double layer of running 4-0 polypropylene is utilized (mattress followed by over-and-over), to ensure a watertight exclusion.
surgery. We report our experience in the first 100 patients (from February 2003 onward), scheduled for mitral surgery, who had the ablation procedure performed with bipolar RF. The indications for concomitant ablation were continuous AF (lasting at least 6 months) in 83 patients, and symptomatic intermittent AF refractory to antiarrhythmic medications or to prior percutaneous ablation in 17 patients. Preoperative data are summarized in Table 1. All patients had mitral valve disease as the main indication to surgery. Fifty-two patients had mitral valve replacement, 43 had mitral repair, 5 had commissurotomy. Sixty-two patients had other associated cardiac procedures: tricuspid repair in 53 cases, aortic valve replacement in 12, correction of an atrial septal defect in 8, CABG in 5, and other procedures in 3. The time spent ablating during aortic occlusion never exceeded 2 min. No complication related to bipolar ablation was recorded. Four patients required re-exploration for bleeding. Overall, intensive care unit stay was 3"3 days and postoperative hospital stay was 8"6 days. One elderly woman died due to rectus muscles hematoma, leading to acute renal failure and respiratory insufficiency. Fourty-four patients experienced some form of sustained supraventricular arrhythmia during hospital stay. At discharge 62/99 patients were in normal sinus rhythm. During follow-up no thromboembolic event was recorded. No patient died. Graph 1 depicts the trend 4
Photo 1. Tailoring of the ablation set based on coronary anatomy. Three different coronary anatomical situations (left coronary angiogram in the right anterior oblique projection) are outlined together with the corresponding suggested routes of the mitral line (arrow): (A) From the appendage to the lateral half of the posterior annulus in patients with a strongly dominant right coronary artery. (B) From the appendage to the medial portion of the posterior annulus, crossing the AV groove perpendicularly, in patients with a mildly dominant right coronary artery. (C) From the right encircling to the medial commissure, close to the interatrial septum in patients with a left dominant coronary circulation. Dotted line s ablations; solid line s surgical incision; arrow s mitral line. (LA s sutured left appendage; LPVs s left pulmonary veins; MV s mitral valve; RPVs s right pulmonary veins.) Reprinted from Ref. w14x with permission from the Society of Thoracic Surgeons.
of rhythm status. Two patients experienced typical counterclockwise right atrial flutter 3 months after surgery and they were successfully treated by percutaneous RF isthmus ablation. Seven patients developed left atrial flutter, all of them within 3 months of mitral Table 1. Preoperative data-values are expressed as number and (percentage) for discreet variables and as number (S.D.) for continuous variables Patients n
100
Age (years) NYHA I–II (patients) NYHA III–IV (patients) Ejection fraction (%) Left atrial diameter (mm) Intermittent AF (patients) Continuous AF (patients) Duration of continuous AF (months)
63"9 61 39 57"10 54"10 17 83 39"50
NYHA: New York Heart Association functional class; AF: atrial fibrillation.
S. Benussi and O. Alfieri / Multimedia Manual of Cardiothoracic Surgery / doi:10.1510/mmcts.2005.001081 to surgical time and it increases operative risk w17x. Furthermore, a concomitant maze carries a G20% risk of postoperative pacemaker implantation w16x. In the search of the simplest ablation procedure to be combined with concomitant open heart surgery, PV isolation alone was first reported by Melo in 1997 w18x. But the AF cure rate of such procedure in this context is in the range of 60 to 70% at 1–2 years w18,19x.
Graph 1. Rhythm after surgery. SR: sinus rhythm; AF: atrial fibrillation.
surgery. Two of them underwent an electrophysiological study with transseptal approach at three months. Both studies showed an optimal isolation of the pulmonary veins encirclings. In both cases a reentry circuit around the mitral valve annulus was documented and interrupted through a left isthmus RF ablation line. Both patients recovered SR during the procedure. Of the remaining patients with left flutter, 1 recovered SR with medications, 1 needed DC-shock, 3 are waiting for the electrophysiological assessment. Two patients are presently waiting to be admitted for electrophysiological assessment. No perioperative variable was related to postoperative left atrial flutter. All transthoracic echo-Doppler controls carried out three months or more after surgery, in patients in SR, showed an effective contraction (A-wave 10 cm/s) of both atria. Conduction block validation During PV pacing performed in 12 patients during surgery, 2/12 showed a residual conduction from 1 PV couple after a single bipolar RF ablation. All patients showed total right and left PV isolation after a repeat parallel ablation.
Discussion The 90% efficacy of Cox’s original cut and sew maze are still unequalled today w15,16x. Nevertheless, such a technique has never become popular in the context of concomitant AF ablation, since it adds significantly
More recently, after the first report by Sueda in 1996 w20x, most of the surgeons dealing with AF embraced the so-called ‘left ablation approaches’, generally sharing pulmonary vein isolation and the connecting lines proper of the left part of the maze procedure w2,21,22x. By granting a success rate of approximately 80–90% at 1 year and around 75% at 3 years after surgery w7,21,23x, such approaches have emerged as a cost-effective option for concurrent intraoperative ablation of AF. Cox has recently defined some of the lines of the original maze III operation – including all the right-sided lines except the cavo-tricuspid isthmus connection – as superfluous in most cases w24x. The rate of SR maintenance 18 months after concomitant surgical treatment of AF through bipolar RF left atrial ablation was 81% in our experience. Such a figure is coherent with the very promising results recently reported by other groups with intraoperative bipolar RF ablation w11,12,25x. When considering only reports on left atrial ablation approaches (PV isolation q connecting lines), other author’s and our results with bipolar RF are in line with the 79 to 92% success rate reported after unipolar ablation w7,20–23x. In a comparable earlier series of patients treated at our institution with unipolar RF, in which the same lesion set was completed by a mitral connecting line, freedom from AF at 18 months was 79% w7x. So, the replacement of unipolar RF ablation catheters with modern bipolar devices, in our experience, translated itself into similar mid-term AF cure rates despite the temporary adoption of a lesser lesion set. Although infrequent and quite easy to cure through percutaneous ablation, typical right atrial flutter can occur after left atrial ablation for AF. Therefore, the addition of a cavo-tricuspid line during surgery, should probably be considered based on the programmed open heart procedure (need for right atriotomy) and on the available technology and expertise. 5
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Damage to the surrounding structures related to the use of physical means to ablate AF can be of two types:
w11x and confirm the efficacy of bipolar RF. It is safe to assume that in the absence of any validation system, epicardial isolation of the pulmonary veins can be predictably achieved with the described bipolar RF device by performing two parallel ablations. This generally takes less than a couple of minutes for each pulmonary vein pair.
1. Damage to the structures surrounding the heart (esophagus and bronchial tree);
Mitral line
Controversial issues Collateral damage
2. Injury to a major coronary artery in the A-V groove. The first types have only been reported after ablation with ‘heating’ unipolar devices, generally following endocardial ablation, since in this case the heat spreads from the endocardium outward. Keeping away from the posterior wall of the left atrium can help in preventing such problems w14x. With the advent of bipolar devices, however, this type of complication will become very unlikely, since bipolar ablation renders thermal spread negligible. Thermal damage to the coronary arteries has been described both after ablation with heating devices and following cryoablation. It can theoretically be reduced by keeping blood flow within the vessel while ablating (i.e. beating heart or cardioplegia administration). Therefore, a clamping device, which by definition would interrupt blood flow across the ablation line, does not seem to be the safest way to overcome the problem. One effective way to prevent coronary injury is to reach the A-V groove in a coronary-free area w14x. Transmurality Data on transmurality of epicardial ablation with unipolar devices are all but satisfactory. Both microwave and RF can fail to accomplish electrical isolation even after repeat ablations on the beating heart w4,8x. Failure to provide a transmural scar has been found to be related to the composition and to the thickness of the atrial wall w8x. The major obstacle to the inward progression of the lesion is the convective cooling exerted by intracavitary blood flow on the subendocardial atrial layer. Bipolar systems are specifically designed to work epicardially. The clamping mechanism abates convective cooling of the endocardium and reduces tissue thickness by compression. Bipolar RF atrial ablations have been shown to be transmural both acutely and after 3 months in pigs w9x. In our series, pacing threshold assessment showed a complete conduction block in 92% of the pulmonary vein couples after a single ablation and in 100% after one repeat ablation. These data are similar to those described by Gillinov with a different clamping device 6
Compared with our prior experience with unipolar RF w7x, the elimination of the mitral line did not turn into worse SR recovery rates. A possible explanation can be found in the superior efficacy of bipolar devices. But the 7% rate of postoperative left atrial flutter registered in this series is worrisome. Left flutter in fact is not easily managed by medications, and it frequently requires complex transseptal left atrial ablation procedures. Interestingly, in our earlier experience with unipolar RF the incidence of left flutter/tachycardia was around 1% w7x. A possible explanation is that the omission of the mitral line, in order not to injure a major coronary branch during bipolar ablation in the A-V groove, has left the substrate for a left isthmus reentry unaddressed. It is noteworthy that a reentry circuit around the mitral valve annulus was found in both patients with left atrial flutter undergoing electrophysiological study in this series. Even if such arrhythmia is generally dealt with in the electrophysiology laboratory, at present such ablation procedures require a considerable expertise with transseptal mapping and ablation. Therefore, especially if a specific electrophysiological expertise is not available, omitting the mitral line may not be the best option when using bipolar RF. Some authors support the feasibility and safety of the mitral connection by clamping the bipolar device right across the A-V groove. As a preferable alternative we suggest performing the mitral line with a different unipolar device such as a reusable cryoprobe when this is available. Left atrial appendage exclusion Routine obliteration of the LAA in high risk patients as a possible prophylaxis of thromboembolic complications of AF has been proposed.
S. Benussi and O. Alfieri / Multimedia Manual of Cardiothoracic Surgery / doi:10.1510/mmcts.2005.001081 A number of physiologic functions of the LAA have been ascertained: due to its major compliance, the LAA functions as a volume reservoir. Its exclusion in patients undergoing surgery for coronary disease and for mitral insufficiency has been found to increase transmitral and pulmonary flow velocities as well as left atrial pressure and size w26x. The LAA contractility and its contribution to ventricular filling has been related to a significant increase in cardiac output in the isolated guinea pig heart w27x. The LAA is then implicated in mediating the thirst reflex as a response to volume depletion in the sheep w28x. Finally, the LAA plays a role in mediating diuretic and natriuretic responses by releasing atrial natriuretic peptide under volume expansion w29x. But whatever the physiologic function played by the LAA in patients with stable SR, it is probably outweighed by its role in enhancing thrombus formation in patients with AF. The LAA is in fact the apparent source of left atrial thrombi in 57% of patients with AF secondary to rheumatic disease and in 91% of patients with nonrheumatic AF w30x. Its exclusion during mitral surgery appears to reduce the rate of late embolism in high-risk patients w31x. Therefore, ligation of the LAA during mitral surgery seems a sound option in all patients with AF undergoing cardiac surgery. Even when AF ablation is combined, in fact, the significant rate of early and late rhythm disturbances and the frequent need of DC shock cardioversions make elimination of the LAA advisable. When excluding the LAA meticulous watertight closure must be attained. Incomplete surgical exclusion, in fact, can occur in as many as 10–36% w31,32x of the patients and it has been associated with an increased risk of thrombus formation and of systemic embolization.
Conclusions Left atrial ablation with bipolar RF is highly effective in eliminating AF after open-heart surgery. Epicardial ablation with bipolar RF allows to predictably achieve acute electrical isolation. The safety profile and the negligible addition of time makes bipolar RF an extremely suitable option for the concomitant treatment of AF even in the most complex cases. Based on our experience a left atrial set of ablations, possibly including a connecting line to the mitral annulus, can be indicated in virtually all patients with AF undergoing cardiac surgery.
Acknowledgement We are grateful to Lorenzo Arcobasso for his invaluable help with editing the video material.
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pulmonary veins: a chronic animal study. Ann Thorac Surg 2003;76:836–841. Bonanomi G, Schwartzman D, Francischelli D, Hebsgaard K, Zenati MA. A new device for beating heart bipolar radiofrequency atrial ablation. J Thorac Cardiovasc Surg 2003;126: 1859–1866. Gillinov AM, McCarthy PM. Atricure bipolar radiofrequency clamp for intraoperative ablation of atrial fibrillation. Ann Thorac Surg 2002;74: 2165–2168. Gaynor SL, Diodato MD, Prasad SM, Ishii Y, Shuessler RB, Bailey MS, Damiano NR, Bloch JB, Moon MR, Damiano RJ. A prospective, singlecenter clinical trial of a modified Cox maze procedure with bipolar radiofrequency ablation. J Thorac Cardiovasc Surg 2004;128:535–541. Benussi S, Nascimbene S, Calori G, Denti P, Ziskind Z, Kassem S, La Canna G, Pappone C, Alfieri O. Surgical ablation of atrial fibrillation using a novel bipolar radiofrequency device. J Thorac Cardiovasc Surg 2005;130:491–497. Benussi S, Nascimbene S, Calvi S, Alfieri O. A tailored anatomical approach to prevent complications during left atrial ablation. Ann Thorac Surg 2003;75:1979–1981. Cox JL, Jaquiss RDB, Schuessler RB, Boineau JP. Modification of the maze procedure for the treatment of atrial flutter and fibrillation. I. Rationale and surgical results. J Thorac Cardiovasc Surg 1995;110:473–484. Prasad SM, Maniar HS, Camillo CJ, Schuessler RB, Boineau JP, Sundt TM 3rd, Cox JL, Damiano RJ Jr. The Cox maze III procedure for atrial fibrillation: long-term efficacy in patients undergoing lone versus concomitant procedures. J Thorac Cardiovasc Surg 2003;126:1822–1828. Kawaguchi AT, Kosakai Y, Sasako Y, Eishi K, Kiyoharu N, Kawashima Y. Risks and benefits of combined maze procedure for atrial fibrillation associated with organic heart disease. J Am Coll Cardiol 1996;28:985–990. Melo JQ, Neves J, Adragao P, Ribeiras R, Ferreira MM, Bruges L, Canada M, Ramos T. When and how to report results of surgery on atrial fibrillation. Eur J Cardiothorac Surg 1997;12:739– 745. Sueda T, Imai K, Orihashi K, Okada K, Ban K, Hamamoto M. Midterm results of pulmonary vein isolation for the elimination of chronic atrial fibrillation. Ann Thorac Surg 2005;79:521–525. Sueda T, Nagata H, Shikata H, Orihashi K, Morita S, Sueshiro M, Okada K, Matsuura Y. Simple left atrial procedure for chronic atrial fibrillation
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Concomitant ablation of atrial fibrillation during mitral surgery Stefano Benussi*, Ottavio Alfieri Division of Cardiac Surgery, S Raffaele University Hospital, via Olgettina 60, 20132 Milan, Italy Left atrial ablation with bipolar radiofrequency using the epicardial approach is described. After dissection of the pericardial reflections and of the Marshall fold, electrical isolation of the right and left pulmonary veins and that of the left appendage are carried out through epicardial ablation. After aortic cross clamping, through standard atriotomy, the connecting lines are then performed. The possible options for the mitral connecting ablation are discussed. At completion of the ablation procedure the base of the left appendage is sutured from inside.
Keywords: Atrial fibrillation; Bipolar radiofrequency; Cardiac surgery; Mitral valve disease; Radiofrequency ablation. Introduction First reported in 1999 w1x, epicardial ablation has been described by many groups for the concomitant treatment of atrial fibrillation (AF) w2–5x and also as a possible option for curing lone AF w3,6x. Diverse unipolar ablating systems have been used for epicardial ablation on the beating heart, with variable success rates w4,5,7x. The major limitation of unipolar devices is that, due to the convective cooling of blood flowing through the atria and depending on the composition of the diseased atrial wall, they do not predictably yield epicardial transmural lesions w4,8x. Bipolar devices seem a promising way to obviate such problems: the first experimental trials demonstrated that bipolar radiofrequency (RF) ablation can reliably produce continuous transmural linear scars w9,10x. We report our ablation technique and initial results with bipolar RF. * Corresponding author: Tel.: q39-02-2643 7127; fax: q39-02-2643 7125. E-mail: [email protected] 䉷 2005 European Association for Cardio-thoracic Surgery
Perioperative management To decrease the risk of intracavitary thrombus formation upon admission, oral anticoagulant medications are discontinued and a continuous heparin infusion is administered until 6 h before surgery. Preoperative transesophageal echocardiography is performed in all patients no longer than 24 h before surgery to exclude left atrial thrombosis. A continuous heparin drip is started after cessation of postoperative bleeding and is continued until effective anticoagulation is reached with oral medications. In the absence of indications other than AF, patients with stable sinus rhythm (SR) at G3 months after surgery are instructed to discontinue the use of anticoagulant medications, following the echocardiographic demonstration of a recovered significant (Awave 10 cm/s) left and right atrial contraction. Antiarrhythmic prophylaxis is carried out on a routine basis. Amiodarone is used as the first-choice drug: an intravenous bolus of 300 mg, followed by a continuous infusion of 1200 mg/24 h until the first postoperative day is generally administered. In the absence of A-V block greater than 1 degree or of unstable SR, 1
S. Benussi and O. Alfieri / Multimedia Manual of Cardiothoracic Surgery / doi:10.1510/mmcts.2005.001081
Video 1. The two ablating inserts are mounted on the opposing jaws of a stainless steel clamp and are moistened with saline before use. Different shapes of the clamp can be employed based on the site of ablation and on the surgeon’s preference.
Video 2. After blunt dissection of the pericardial reflections, generally after institution of full CPB, isolation of the right pulmonary veins couple is carried out. The device is clamped on the left atrial wall around the orifices of the veins and not on the veins themselves, to prevent pulmonary vein stenosis. Care is taken in making sure that all the atrial wall is within the ablating surface of the device. In particular, the very tip of the clamp behind the heart must be free from atrial tissue. Folding of the atrial walls within the clamp should be prevented since an uneven thickness of the ablated tissue can increase the probability of leaving gaps within the encircling line.
Video 3. The table is then slightly tilted to the right of the heart and the heart is lifted towards the surgeon. The Marshall fold is then exposed by gently pulling the left pulmonary artery. It is then interrupted with diathermy. The pericardial reflections around the left pulmonary veins are then easily interrupted, generally through blunt dissection only. Schematic 1. Simplified lesion scheme for the concomitant treatment of atrial fibrillation using the bipolar ablator only. RPVs: right pulmonary veins; LPVs: left pulmonary veins; LA: left appendage; MV: mitral valve.
oral administration of 200 mg of amiodarone, every 8 h until discharge, followed by a maintenance regimen of 200 mg/day is then continued. Patients with contraindications to amiodarone are administered sotalol, propaphenon or do not receive any antiarrhythmic medication. After discharge such medications are continued for 3 to 6 months, and are then generally tapered off.
Surgical technique The ablations are performed using a bipolar RF ablation device (Cobra Bipolar – MMCTSLINK 75). Two 64-mm long ablating inserts are mounted on the opposing faces of the jaws of a stainless steel clamp (Video 1). Each insert is made of two electrodes 2
lodged in a polyester cover. Each electrode has a thermocouple mounted on both ends. RF current is delivered for 40–45 s at 35–40 W, with a preset temperature of 90 8C. In our initial experience with bipolar RF, the mitral line was omitted because of concern about injuring a major coronary artery branch in the A-V groove (Schematic 1). The epicardial ablations are generally performed on cardiopulmonary bypass (CPB) at 37 8C. After dissection of pericardial reflections, the bipolar device is clamped around the atrial cuff containing the inflow of the right pulmonary veins. Then RF energy is deployed yielding an encircling lesion (Video 2). The heart is then lifted, the Mashall fold interrupted (Video 3), and a similar encircling lesion is performed on the left pulmonary vein cuff (Video 4). Based on recent evidence w11–13x, to increase the chance of an effective isolation of the pulmonary
S. Benussi and O. Alfieri / Multimedia Manual of Cardiothoracic Surgery / doi:10.1510/mmcts.2005.001081
Video 4. The ablating device is then clamped on the atrial wall around the left pulmonary veins orifices and an encircling ablation is performed in a similar manner to that described for isolation of the right pulmonary veins.
Video 5. An epicardial connecting ablation with the tip of the clamp pinching the left encircling line and the base ending in the body of the left appendage can be performed – an optional alternative is that of performing this connecting line endocardially, through the left atriotomy, by clamping the device with one jaw in the left appendage and the other in one of the left pulmonary veins.
Schematic 2. Complete left atrial lesion scheme for the concomitant treatment of atrial fibrillation by adding to the set of bipolar ablations a mitral connecting line performed with a unipolar device. RPVs: right pulmonary veins; LPVs: left pulmonary veins; LA: left appendage; MV: mitral valve.
The left atrial appendage (LAA) is then ablated at its base. At this time the ablating piece must be kept away from the A-V groove (around the upper portion of the base of the appendage) thus is preventing injury to a major coronary artery. After aortic cross clamping through a standard left atriotomy, the bipolar device can be used in the endo/ epicardial mode (one jaw inside the heart and the other outside) to perform a connecting line between the two encirclings (Video 6).
Video 6. After cross-clamping the connecting lines are then completed. One jaw of the clamp is inserted in the left atrium with the tip in the upper left pulmonary vein or in the appendage, while the other jaw is outside, in the transverse sinus of pericardium. Alternatively, the inner jaw is directed to the lower left pulmonary vein (or to the appendage) and the outer jaw is placed in the oblique sinus, parallel to the A-V groove. If the left atriotomy does not intersect the right encircling ablation – a frequent occurrence in the case of left atriomegaly – a short additional connecting line is performed between the atriotomy and the right encircling ablation as shown.
veins, it is advisable to either validate the encircling lines with intraoperative conduction block assessment, or at least to double such ablation lines. The appendage is then ablated at its base and connected to the left encircling by means of an additional epicardial ablation (Video 5).
In order to reduce the chance of a reentry circuit around the mitral annulus to sustain left flutter, the described ablation procedure has been recently revised (Schematic 2) by reintroducing a left isthmus ablation line, performed with a unipolar linear catheter (Video 7). As previously described w14x, the site of such line is chosen based on coronary anatomy (Photo 1). After the ablations the LAA is sutured, generally from inside.
Results Clinical experience Starting in February 1998, we performed concomitant AF ablation in 492 patients undergoing open heart 3
S. Benussi and O. Alfieri / Multimedia Manual of Cardiothoracic Surgery / doi:10.1510/mmcts.2005.001081
Video 7. A left isthmus line can finally be performed by connecting the left appendage (like in the video) or the atriotomy with the mitral annulus with a unipolar device. A temperature-controlled unipolar RF catheter is utilized in the recorded case, but different tools can be utilized including a reusable cryoprobe. The safest site in which to place this line is chosen based on coronary anatomy (see Photo 1). Finally the base of the left appendage is sutured from inside. A double layer of running 4-0 polypropylene is utilized (mattress followed by over-and-over), to ensure a watertight exclusion.
surgery. We report our experience in the first 100 patients (from February 2003 onward), scheduled for mitral surgery, who had the ablation procedure performed with bipolar RF. The indications for concomitant ablation were continuous AF (lasting at least 6 months) in 83 patients, and symptomatic intermittent AF refractory to antiarrhythmic medications or to prior percutaneous ablation in 17 patients. Preoperative data are summarized in Table 1. All patients had mitral valve disease as the main indication to surgery. Fifty-two patients had mitral valve replacement, 43 had mitral repair, 5 had commissurotomy. Sixty-two patients had other associated cardiac procedures: tricuspid repair in 53 cases, aortic valve replacement in 12, correction of an atrial septal defect in 8, CABG in 5, and other procedures in 3. The time spent ablating during aortic occlusion never exceeded 2 min. No complication related to bipolar ablation was recorded. Four patients required re-exploration for bleeding. Overall, intensive care unit stay was 3"3 days and postoperative hospital stay was 8"6 days. One elderly woman died due to rectus muscles hematoma, leading to acute renal failure and respiratory insufficiency. Fourty-four patients experienced some form of sustained supraventricular arrhythmia during hospital stay. At discharge 62/99 patients were in normal sinus rhythm. During follow-up no thromboembolic event was recorded. No patient died. Graph 1 depicts the trend 4
Photo 1. Tailoring of the ablation set based on coronary anatomy. Three different coronary anatomical situations (left coronary angiogram in the right anterior oblique projection) are outlined together with the corresponding suggested routes of the mitral line (arrow): (A) From the appendage to the lateral half of the posterior annulus in patients with a strongly dominant right coronary artery. (B) From the appendage to the medial portion of the posterior annulus, crossing the AV groove perpendicularly, in patients with a mildly dominant right coronary artery. (C) From the right encircling to the medial commissure, close to the interatrial septum in patients with a left dominant coronary circulation. Dotted line s ablations; solid line s surgical incision; arrow s mitral line. (LA s sutured left appendage; LPVs s left pulmonary veins; MV s mitral valve; RPVs s right pulmonary veins.) Reprinted from Ref. w14x with permission from the Society of Thoracic Surgeons.
of rhythm status. Two patients experienced typical counterclockwise right atrial flutter 3 months after surgery and they were successfully treated by percutaneous RF isthmus ablation. Seven patients developed left atrial flutter, all of them within 3 months of mitral Table 1. Preoperative data-values are expressed as number and (percentage) for discreet variables and as number (S.D.) for continuous variables Patients n
100
Age (years) NYHA I–II (patients) NYHA III–IV (patients) Ejection fraction (%) Left atrial diameter (mm) Intermittent AF (patients) Continuous AF (patients) Duration of continuous AF (months)
63"9 61 39 57"10 54"10 17 83 39"50
NYHA: New York Heart Association functional class; AF: atrial fibrillation.
S. Benussi and O. Alfieri / Multimedia Manual of Cardiothoracic Surgery / doi:10.1510/mmcts.2005.001081 to surgical time and it increases operative risk w17x. Furthermore, a concomitant maze carries a G20% risk of postoperative pacemaker implantation w16x. In the search of the simplest ablation procedure to be combined with concomitant open heart surgery, PV isolation alone was first reported by Melo in 1997 w18x. But the AF cure rate of such procedure in this context is in the range of 60 to 70% at 1–2 years w18,19x.
Graph 1. Rhythm after surgery. SR: sinus rhythm; AF: atrial fibrillation.
surgery. Two of them underwent an electrophysiological study with transseptal approach at three months. Both studies showed an optimal isolation of the pulmonary veins encirclings. In both cases a reentry circuit around the mitral valve annulus was documented and interrupted through a left isthmus RF ablation line. Both patients recovered SR during the procedure. Of the remaining patients with left flutter, 1 recovered SR with medications, 1 needed DC-shock, 3 are waiting for the electrophysiological assessment. Two patients are presently waiting to be admitted for electrophysiological assessment. No perioperative variable was related to postoperative left atrial flutter. All transthoracic echo-Doppler controls carried out three months or more after surgery, in patients in SR, showed an effective contraction (A-wave 10 cm/s) of both atria. Conduction block validation During PV pacing performed in 12 patients during surgery, 2/12 showed a residual conduction from 1 PV couple after a single bipolar RF ablation. All patients showed total right and left PV isolation after a repeat parallel ablation.
Discussion The 90% efficacy of Cox’s original cut and sew maze are still unequalled today w15,16x. Nevertheless, such a technique has never become popular in the context of concomitant AF ablation, since it adds significantly
More recently, after the first report by Sueda in 1996 w20x, most of the surgeons dealing with AF embraced the so-called ‘left ablation approaches’, generally sharing pulmonary vein isolation and the connecting lines proper of the left part of the maze procedure w2,21,22x. By granting a success rate of approximately 80–90% at 1 year and around 75% at 3 years after surgery w7,21,23x, such approaches have emerged as a cost-effective option for concurrent intraoperative ablation of AF. Cox has recently defined some of the lines of the original maze III operation – including all the right-sided lines except the cavo-tricuspid isthmus connection – as superfluous in most cases w24x. The rate of SR maintenance 18 months after concomitant surgical treatment of AF through bipolar RF left atrial ablation was 81% in our experience. Such a figure is coherent with the very promising results recently reported by other groups with intraoperative bipolar RF ablation w11,12,25x. When considering only reports on left atrial ablation approaches (PV isolation q connecting lines), other author’s and our results with bipolar RF are in line with the 79 to 92% success rate reported after unipolar ablation w7,20–23x. In a comparable earlier series of patients treated at our institution with unipolar RF, in which the same lesion set was completed by a mitral connecting line, freedom from AF at 18 months was 79% w7x. So, the replacement of unipolar RF ablation catheters with modern bipolar devices, in our experience, translated itself into similar mid-term AF cure rates despite the temporary adoption of a lesser lesion set. Although infrequent and quite easy to cure through percutaneous ablation, typical right atrial flutter can occur after left atrial ablation for AF. Therefore, the addition of a cavo-tricuspid line during surgery, should probably be considered based on the programmed open heart procedure (need for right atriotomy) and on the available technology and expertise. 5
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Damage to the surrounding structures related to the use of physical means to ablate AF can be of two types:
w11x and confirm the efficacy of bipolar RF. It is safe to assume that in the absence of any validation system, epicardial isolation of the pulmonary veins can be predictably achieved with the described bipolar RF device by performing two parallel ablations. This generally takes less than a couple of minutes for each pulmonary vein pair.
1. Damage to the structures surrounding the heart (esophagus and bronchial tree);
Mitral line
Controversial issues Collateral damage
2. Injury to a major coronary artery in the A-V groove. The first types have only been reported after ablation with ‘heating’ unipolar devices, generally following endocardial ablation, since in this case the heat spreads from the endocardium outward. Keeping away from the posterior wall of the left atrium can help in preventing such problems w14x. With the advent of bipolar devices, however, this type of complication will become very unlikely, since bipolar ablation renders thermal spread negligible. Thermal damage to the coronary arteries has been described both after ablation with heating devices and following cryoablation. It can theoretically be reduced by keeping blood flow within the vessel while ablating (i.e. beating heart or cardioplegia administration). Therefore, a clamping device, which by definition would interrupt blood flow across the ablation line, does not seem to be the safest way to overcome the problem. One effective way to prevent coronary injury is to reach the A-V groove in a coronary-free area w14x. Transmurality Data on transmurality of epicardial ablation with unipolar devices are all but satisfactory. Both microwave and RF can fail to accomplish electrical isolation even after repeat ablations on the beating heart w4,8x. Failure to provide a transmural scar has been found to be related to the composition and to the thickness of the atrial wall w8x. The major obstacle to the inward progression of the lesion is the convective cooling exerted by intracavitary blood flow on the subendocardial atrial layer. Bipolar systems are specifically designed to work epicardially. The clamping mechanism abates convective cooling of the endocardium and reduces tissue thickness by compression. Bipolar RF atrial ablations have been shown to be transmural both acutely and after 3 months in pigs w9x. In our series, pacing threshold assessment showed a complete conduction block in 92% of the pulmonary vein couples after a single ablation and in 100% after one repeat ablation. These data are similar to those described by Gillinov with a different clamping device 6
Compared with our prior experience with unipolar RF w7x, the elimination of the mitral line did not turn into worse SR recovery rates. A possible explanation can be found in the superior efficacy of bipolar devices. But the 7% rate of postoperative left atrial flutter registered in this series is worrisome. Left flutter in fact is not easily managed by medications, and it frequently requires complex transseptal left atrial ablation procedures. Interestingly, in our earlier experience with unipolar RF the incidence of left flutter/tachycardia was around 1% w7x. A possible explanation is that the omission of the mitral line, in order not to injure a major coronary branch during bipolar ablation in the A-V groove, has left the substrate for a left isthmus reentry unaddressed. It is noteworthy that a reentry circuit around the mitral valve annulus was found in both patients with left atrial flutter undergoing electrophysiological study in this series. Even if such arrhythmia is generally dealt with in the electrophysiology laboratory, at present such ablation procedures require a considerable expertise with transseptal mapping and ablation. Therefore, especially if a specific electrophysiological expertise is not available, omitting the mitral line may not be the best option when using bipolar RF. Some authors support the feasibility and safety of the mitral connection by clamping the bipolar device right across the A-V groove. As a preferable alternative we suggest performing the mitral line with a different unipolar device such as a reusable cryoprobe when this is available. Left atrial appendage exclusion Routine obliteration of the LAA in high risk patients as a possible prophylaxis of thromboembolic complications of AF has been proposed.
S. Benussi and O. Alfieri / Multimedia Manual of Cardiothoracic Surgery / doi:10.1510/mmcts.2005.001081 A number of physiologic functions of the LAA have been ascertained: due to its major compliance, the LAA functions as a volume reservoir. Its exclusion in patients undergoing surgery for coronary disease and for mitral insufficiency has been found to increase transmitral and pulmonary flow velocities as well as left atrial pressure and size w26x. The LAA contractility and its contribution to ventricular filling has been related to a significant increase in cardiac output in the isolated guinea pig heart w27x. The LAA is then implicated in mediating the thirst reflex as a response to volume depletion in the sheep w28x. Finally, the LAA plays a role in mediating diuretic and natriuretic responses by releasing atrial natriuretic peptide under volume expansion w29x. But whatever the physiologic function played by the LAA in patients with stable SR, it is probably outweighed by its role in enhancing thrombus formation in patients with AF. The LAA is in fact the apparent source of left atrial thrombi in 57% of patients with AF secondary to rheumatic disease and in 91% of patients with nonrheumatic AF w30x. Its exclusion during mitral surgery appears to reduce the rate of late embolism in high-risk patients w31x. Therefore, ligation of the LAA during mitral surgery seems a sound option in all patients with AF undergoing cardiac surgery. Even when AF ablation is combined, in fact, the significant rate of early and late rhythm disturbances and the frequent need of DC shock cardioversions make elimination of the LAA advisable. When excluding the LAA meticulous watertight closure must be attained. Incomplete surgical exclusion, in fact, can occur in as many as 10–36% w31,32x of the patients and it has been associated with an increased risk of thrombus formation and of systemic embolization.
Conclusions Left atrial ablation with bipolar RF is highly effective in eliminating AF after open-heart surgery. Epicardial ablation with bipolar RF allows to predictably achieve acute electrical isolation. The safety profile and the negligible addition of time makes bipolar RF an extremely suitable option for the concomitant treatment of AF even in the most complex cases. Based on our experience a left atrial set of ablations, possibly including a connecting line to the mitral annulus, can be indicated in virtually all patients with AF undergoing cardiac surgery.
Acknowledgement We are grateful to Lorenzo Arcobasso for his invaluable help with editing the video material.
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