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Mickleborough LL. Surgical Treatment of Ventricular Arrhythmias.
In: Cohn LH, Edmunds LH Jr, eds. Cardiac Surgery in the Adult. New York: McGraw-Hill, 2003:12871292.

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Chapter 54

Surgical Treatment of Ventricular Arrhythmias

Lynda L. Mickleborough

ROLE OF REVASCULARIZATION
ANATOMICAL SUBSTRATE FOR VENTRICULAR ARRHYTHMIAS AND LESSONS LEARNED FROM MAPPING
ABLATION TECHNIQUE FOR CONTROL OF VENTRICULAR TACHYCARDIA
LEFT VENTRICULAR RECONSTRUCTION
RESULTS OF SURGERY FOR VENTRICULAR ARRHYTHMIAS: COMPARISON WITH OTHER TREATMENT MODALITIES
CURRENT RECOMMENDATIONS
REFERENCES

?? INTRODUCTION
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In the 1990s the number of patients referred for surgery for control of ventricular arrhythmias dramatically decreased. Alternative approaches gained in popularity, particularly implantable cardioverter-defibrillator (ICD) insertion and radiofrequency catheter ablation. I believe, however, that in selected patients with coronary artery disease, surgery still has an important role to play. This is particularly true in view of the recent resurgence of interest in left ventricular surgical remodelling or restoration as a potential treatment for congestive heart failure.1 As ventricular arrhythmias are often a component of the clinical presentation in these cases, I think it is important at this time to review lessons learned from earlier experience with surgical ventricular tachycardia (VT) ablation.

In patients with ventricular arrhythmias due to coronary artery disease, ICD implantation has proven very effective for preventing sudden death. However, in such patients, electrical instability is only one manifestation of a complex problem. Other sequelae of coronary artery disease include the potential for recurrent ischemia and in many cases progressive heart failure related to poor left ventricular function and dilatation with or without mitral insufficiency. Optimal treatment in these patients would prevent further episodes of the arrhythmia, reverse ischemia, and restore left ventricular size, shape, and geometry towards normal. ICD insertion does not prevent recurrent arrhythmia episodes nor does it address ongoing ischemia or heart failure. A surgical procedure that can correct the underlying structural cardiac abnormality as much as possible may not only prevent arrhythmia recurrence but also offer additional improvements in quality of life as well as prolonged survival.


?? ROLE OF REVASCULARIZATION
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In patients with coronary artery disease and ventricular arrhythmias, revascularization should be considered whenever possible to relieve symptoms of ischemia, to eliminate ischemia as a possible trigger for ventricular arrhythmias, and to improve prognosis.

In those with relatively good ventricular function who present with exercise-induced arrhythmias clearly associated with demonstrable ischemia, revascularization alone may be an effective treatment.24 Following aortocoronary bypass grafting, repeat exercise testing and an electrophysiologic study (EPS) can be used to separate those who are noninducible and unlikely to have an arrhythmia recurrence from those still at risk in whom an ICD can be inserted as a staged procedure.

Most patients with coronary artery disease and clinical ventricular arrhythmias have dilated hearts and poor left ventricular function.5 In these patients the arrhythmia is inducible by programmed stimulation and is due to reentry in a fixed anatomical substrate.


?? ANATOMICAL SUBSTRATE FOR VENTRICULAR ARRHYTHMIAS AND LESSONS LEARNED FROM MAPPING
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Preoperative catheter mapping and intraoperative mapping using handheld roving electrodes or computerized multiple electrode arrays have been used to try to determine the arrhythmogenic site of origin in patients with ventricular tachycardia. Techniques involving handheld probes and sequential acquisition of data are time consuming and require a sustained monoform VT for appropriate analysis.6,7 Endocardial mapping is performed through a ventriculotomy incision that often renders the tachycardia noninducible.810 Such techniques therefore often provide incomplete mapping data, and ablation attempts relying on these data result in a higher inducibility rate at postoperative EPS and are associated with increased arrhythmias or sudden death during follow-up.11,12

Our group introduced a transatrial approach to mapping in the intact beating heart that has allowed us and others to obtain extensive mapping data in all patients within a relatively short period of time.13 We used a multiple-balloon electrode array and a computer-generated flashing light display (Fig. 54-1), which demonstrates the endocardial activation sequence. Cox et al developed a different system for data analysis that allows rapid generation of serial potential distribution maps.14 Whether the information derived is displayed as a series of color-coded isochrone maps, a real-time video light display of the activation sequence, or a dynamic color-coded potential map display is largely a matter of preference and availability.



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FIGURE 54-1 Diagram of transatrial approach to mapping. The balloon is inserted via a small left atrial incision and passed across the mitral valve. When positioned in the LV, it is inflated to achieve good electrode contact with the endocardium. Intraballoon pressure is monitored to prevent overinflation and possible subendocardial ischemia. (Reproduced with permission from Mickleborough LL: Surgery for ventricular arrhythmias following myocardial infarction, in David TE (ed): Mechanical Complications of Myocardial Infarction. Austin, TX, RG Landes Company, 1993; p 211.

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After extensive mapping experience, three basic patterns of activation have been observed.13 Based on our understanding of these patterns, ablation efforts have been directed not only towards the earliest site of activation, but also towards critical areas of the reentry circuit (Fig. 54-2). Results of mapping studies show that the substrate for inducible VT is usually located at the borderzone between viable myocardium and scar and corresponds to sheets of surviving muscle fibers mixed with areas of fibrosis.15 In most cases at least part of the reentry circuit is subendocardial in location. In a small number of cases a mid myocardial circuit has been implicated.16



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FIGURE 54-2 Patterns of activation observed with transatrial balloon mapping technique. (A) Monoregional. Endocardial activation radiates from well-defined focus indicated by asterisk. Shaded area (A1) corresponds to target area identified from video display. Surgical ablation techniques encompassed this region of interest. (B) Figure-of-8 pattern. Earliest site of endocardial activation indicated by asterisk lies to one side of two areas of block. Endocardial activity radiates in two directions around arcs of block in figure-of-8 pattern. An area of slow conduction can be identified between two areas of block that appears to lead up to site of earliest endocardial activation. We believe that this narrow corridor between two areas of block represents a reentry pathway. Target area as indicated by shading (B1) was chosen to include both presumed reentry pathway and earliest site of endocardial activity observed. (C) Circle (complete or incomplete). A large portion of myocardium is involved in sweeping circular front of activation. Earliest site of endocardial activation is indicated by asterisk. There is a spacial and temporal gap in upper right hand quadrant of circle and presumed pathway of reentry in this area is indicated by broken arrows. Shaded area (C1), which includes both presumed reentry circuit and earliest site of endocardial activation, indicates target area chosen for surgical ablation. (Reproduced with permission from Mickleborough LL, Harris L, Downar E, et al: A new intraoperative approach for endocardial mapping of ventricular tachycardia. J Thorac Cardiovasc Surg 1988; 95:271.)

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The majority of patients with coronary artery disease and poor left ventricular function who present with ventricular arrhythmias have an area of anteroapical scar (akinetic or dyskinetic), which often extends over the apex in cases of a wraparound left anterior descending (LAD) artery. In such patients mapping studies showed that the arrhythmogenic area almost always lies on the scarred septum.11,17

Because mapping is time consuming and requires specialized equipment and expertise, many centers have advocated a visually directed approach to VT ablation. Their approach is to resect areas of subendocardial scarring, and in cases of anteroapical infarcts such operations have been quite successful.11,12,18,19 In less frequent cases of prior inferior myocardial infarction and a posterior aneurysm, results of VT ablation, even when guided by extensive mapping information, have been less successful.11,20 Resection of endocardial scar and repair of the aneurysm may be hampered in this location by proximity of the posterior papillary muscle. Some centers have advocated resection and reimplantation of the papillary muscle or mitral valve replacement as a means of improving control of the arrhythmia, but such aggressive ablation procedures often result in decreased long-term survival21 and in general results of VT surgery in cases of posterior aneurysm have been less satisfactory.


?? ABLATION TECHNIQUE FOR CONTROL OF VENTRICULAR TACHYCARDIA
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Various techniques have been advocated for control of VT foci. All techniques involve destruction of tissue at the borderzone between scar and viable muscle and as such have potential negative effects on left ventricular structure and function. Some techniques such as encircling ventriculotomy have largely been abandoned because of their harmful effects on LV function.22,23 In the late 1980s the most frequently used ablation techniques included endocardial excision (removal of visible endocardial scar) and cryoablation.6,11,20,24 The depth of tissue injury achieved with cryoablation is critically dependent on the heat sink of the underlying tissue. Cryoablation using a 15-mm probe cooled to -60?C and applied for 2 minutes will result in depth of injury of only 2 to 3 mm in a well-perfused area of the heart but could result in much more extensive injury (6 mm or more) if applied in the heart under cold cardioplegia conditions. Other techniques for ablation that have been used at the time of surgery to control VT include direct shock ablation,24 laser photoablation, or radiofrequency ablation.25 In general, the more extensive the ablation procedure carried out, the less likely it is that inducible arrhythmias will appear on the postoperative EPS, but the more chance there is to have a negative effect on LV function or to damage surrounding structures including the papillary muscle apparatus. Such deleterious effects of the ablation procedure may have a negative effect on long-term survival.26


?? LEFT VENTRICULAR RECONSTRUCTION
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In patients with coronary artery disease, ventricular arrhythmias, and poor left ventricular function, an important part of the surgical approach is to address poor LV function and associated mitral insufficiency in addition to revascularization and ablation of the arrhythmogenic focus. Following VT ablation in patients with akinetic or dyskinetic scar, LV reconstruction or remodelling should be undertaken to restore LV size and geometry towards normal.24 We have advocated use of a modified linear closure technique that can be combined with septoplasty when there is significant aneurysmal involvement of the septum or when the septum has been thinned following extensive endocardial excision for control of VT.27 Dor has popularized his approach utilizing an endoventricular patch plasty.28 Both techniques have been associated with excellent results. The aim is to resect or exclude all nonfunctioning portions of the ventricle, thereby restoring ventricular cavity size and shape towards normal as much as possible. Potential benefits include decreased wall stress and decreased oxygen consumption in the surrounding myocardium as well as potential improvements in fiber orientation that may result in increased contractility.27 Mechanical unloading with decreased stretch of remote ventricular wall may also help prevent recurrent arrhythmias.29 Mitral regurgitation (MR) may be improved by LV remodelling, but intraoperative transesophageal echocardiography should be used to rule out residual MR for which additional valvuloplasty procedures may be indicated.


?? RESULTS OF SURGERY FOR VENTRICULAR ARRHYTHMIAS: COMPARISON WITH OTHER TREATMENT MODALITIES
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In the 1980s results of surgery for control of ventricular tachycardia improved over time as experience was accumulated with various mapping and ablation techniques. Clearly, results achieved with respect to operative mortality, control of VT, and long-term survival will depend on many factors including patient selection, accuracy of mapping data if used, and type and extent of ablation technique employed. Most reported surgical series for control of VT include patients at high risk, i.e., those with extensive coronary artery disease, poor preoperative ejection fraction, and symptoms of congestive heart failure. By the late 1980s, average ejection fraction in most reported series ranged from 25% to 30%.6,7,11,24 Operative mortality with map-directed or visually directed surgery was in the range of 2% to 10%.7,11,24 Patients with a positive postoperative EPS were generally treated with either amiodarone or an ICD. Recurrence of clinical arrhythmias was low, ranging from 10% to 20%, and freedom from sudden death during follow-up was usually over 90%.6,7,11,24 Long-term survival at 5 years was in the range of 70% to 80%. Factors associated with increased risk of surgery for control of VT included advanced age, decreased ejection fraction, and severe symptoms of congestive heart failure.11,24,3032 Decreased success of surgical VT ablation was reported in patients with an inferior infarct.11 These results will be compared to results obtained with other treatment modalities.

Catheter ablation has been reported to successfully ablate the target VT in 82% of cases.33 The procedural mortality is low (1.8%), but there is an 8% chance of major complications including stroke, transient ischemia attack, or tamponade.34 Perhaps more importantly, when used in a patient population with a mean ejection fraction of 32% ? 11%, the 5-year survival following catheter ablation was only 49% with the recurrence rate of VT at 4 years of 72%.33 Clearly, the results of catheter ablation are inferior to those achieved with surgical ablation in patients with coronary artery disease and poor LV function.

Thousands of ICDs have been employed in patients with coronary artery disease and ventricular arrhythmias. Most patients with an ICD do receive shocks, and if shocks are frequent they have a definite negative effect on quality of life.35 It has recently been established in large randomized prospective trials in patients with prior VT or VF arrest (secondary prevention trials) that ICD treatment is superior to drug therapy including amiodarone with respect to prevention of sudden death and improving overall survival.33 In these studies, survival benefit due to ICD increased with increasing patient risk, i.e., increasing age, decreasing ejection fraction, and increasing symptoms of heart failure. In the Antiarrhythmics Versus Implantable Defibrillators (AVID) series, the Canadian Implantable Defibrillator Study (CIDS) series, and the Cardiac Arrhythmic Suppression Trial (CAST) series, the mean ejection fraction was 30% to 45% and the average annual death rate ranged between 8% and 12%.36,37 If the results in patients with an ejection fraction of less than 35%, which are comparable to surgical VT series, are analyzed, the 5-year survival rate was only 60%.38 In the AVID registry the 3-year survival in patients with an ejection fraction less than 25% was only 55%.39 Clearly, in patients with previous documented clinical ventricular arrhythmias and decreased ejection fraction, the 5-year survival following ICD implantation is less than that reported in patients with similar ejection fractions following surgical ablation for VT.


?? CURRENT RECOMMENDATIONS
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Based on past experience and results reported with VT ablation surgery, we would currently recommend revascularization in patients with coronary artery disease, poor left ventricular function, and ventricular arrhythmias, if there is an area of anteroapical scarring (akinesis or dyskinesis) with no significant thinning of the wall.40 If arrhythmias recur or are still inducible postoperatively, the patient should be treated with amiodarone or considered for an ICD.

We would recommend left ventricular remodelling in patients with coronary artery disease, poor left ventricular function, and ventricular arrhythmias, if the area of anteroapical scarring (akinesis or dyskinesis) corresponds to a region of significant thinning. At the time of surgery, the septum should be examined for scarring. We would recommend excision of all visible endocardial septal scar with cryoablation at the periphery of the excision as the strategy for control of VT.27 A postoperative electrophysiologic study should be performed. If ventricular arrhythmias are still inducible, amiodarone therapy should be instituted. In our experience with this approach, ventricular arrhythmias have rarely been a problem during long-term follow-up and ICD use in our series has been low.27 Further studies are needed to confirm effectiveness of this approach in patients with poor left ventricular function and dilated hearts. In such patients we believe symptoms of congestive heart failure, mitral insufficiency, and ventricular arrhythmias are all markers of advanced ischemic disease. Surgery should be undertaken early before progressive dilatation and adverse ventricular remodelling result, leaving transplantation as the only reasonable option.


?? REFERENCES
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  1. Cox JL: Ventricular shape and function in health and disease. Semin Thorac Cardiovasc Surg 2001; 13:297.
  2. Berntsen RF, Gunnes P, Lie M, Rasmussen K: Surgical revascularization in the treatment of ventricular tachycardia and fibrillation exposed by exercise-induced ischemia. Eur Heart J 1993; 14:1297.[Abstract/Free?Full?Text]
  3. Lee JF, Folsom DL, Biblo LA, et al: Combined internal cardioverter-defibrillator implantation and myocardial revascularization for ischemic ventricular arrhythmias: optimal cost-effective strategy. Cardiovasc Surg 1995; 3:393.[Medline]
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  35. Heller SS, Ormont MA, Lidagoster LC, et al: Psychosocial outcomes after ICD implantation: a current perspective. Pacing Clin Electrophysiol 1998; 127:978.
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  40. Mickleborough LL, Carson S, Tamariz M, Ivanov J: Results of revascularization in patients with severe left ventricular dysfunction. J Thorac Cardiovasc Surg 2000; 119:550.[Abstract/Free?Full?Text]




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