Catheter ablation for ventricular arrhythmias

Morton F Arnsdorf, MD John Kall, MD

Mar 28, 2000

Pharmacologic therapy has been the cornerstone of treatment for symptomatic and life-threatening ventricular arrhythmias. However, alternative nonpharmacologic therapy has received increasing attention because of the high failure rate, common proarrhythmic actions, and frequent toxicity of the antiarrhythmic drugs. Included in this group are the implantable defibrillator, catheter ablation, and, at times, cardiac surgery. (See "Treatment of nonsustained ventricular tachycardia").

This card will review the role of catheter ablation in the treatment of ventricular arrhythmias. Most studies of ablative therapy have used electrical catheter ablation; in comparison, laser and chemical ablative techniques have only been used in small series of selected patients.

There are two types of electrical catheter ablation: the application of high energy direct current (DC) shock and, more recently, radiofrequency current. DC shock causes thermal injury and, more importantly, barotrauma due to the formation and expansion of vapor at the surface. Barotrauma can result in a number of potentially serious complications including rupture of the myocardium, low cardiac output, pulseless electrical activity (electromechanical dissociation) and death [1]. In contrast, radiofrequency current heats the myocardial tissue and causes local necrosis without barotrauma or remote damage [2]. It produces a much more localized injury than DC shock, so the mechanism of the arrhythmia must be defined more precisely.

SINGLE VENTRICULAR PREMATURE BEATS — Although isolated ventricular premature beats (VPB) are frequently encountered in clinical practice, they generally have no prognostic importance and are often asymptomatic or associated with only mild symptoms. However, there is a small group of patients with drug refractory VPBs who are very symptomatic. (See "Clinical significance and treatment of ventricular premature beats"). Radiofrequency ablation may be an effective approach for these patients; in one study of 12 patients who did not have spontaneous or inducible sustained ventricular tachycardia, radiofrequency ablation of an isolated focus was successful in 11 patients [3]. During a 25 month follow-up, two patients had recurrent symptoms that were controlled with a previously ineffective drug.

MICROREENTRANT VENTRICULAR TACHYCARDIA — Catheter ablation has been primarily used in three types of VT: microreentrant VT; bundle branch block reentrant VT; and idiopathic VT in which the arrhythmia is not associated with underlying structural heart disease. The vast majority of microreentrant ventricular tachycardias that have been treated with ablation are of the sustained monomorphic form.

Site of ablation — A number of reports have reviewed the methods that have been advocated to locate the site of VT [4,5,6,7,8]. During reentrant types of VT accompanying ischemic heart disease, low amplitude signals detected by electrophysiology testing usually allow the identification of the orthodromic and antidromic areas of conduction and indicate the area of interest for ablation [9,10,11]. The use of a 32-site bipolar catheter allows for more rapid endocardial mapping, shortening the time that patients need to remain in VT (show figure 1) [12]. A novel noncontact mapping system utilizing a 64 electrode balloon catheter uses inverse mathematics to simultaneous calculate and record several thousand virtual electrograms; this may be particularly useful for mapping ventricular tachycardia that is not hemodynamically stable [13,14].

  •  Areas with isolated mid-diastolic potentials which cannot be dissociated from the tachycardia by pacing, often represent a vulnerable portion of the reentrant circuit and predict a good response to ablation [9]. Figure 2, for example, shows ECG leads I, III, and V1, a high right atrial electrogram, His electrograms, and localized electrograms, one of which showed diastolic potentials; this site was ablated, eliminating the VT (show figure 2).

  •  The best ablation site can, in about 50 percent of cases, be further defined by entrainment, without evidence for fusion, in an area of slow conduction [9,10,11,15,16]. This results in an acceleration of the ventricular tachycardia to the pacing cycle length, with a QRS complex that is identical to that of the spontaneous VT (entrainment with concealed fusion) and that has a long stimulus to QRS duration. Upon termination of pacing, there is resumption of the ventricular tachycardia with the cycle length present prior to pacing.

  •  Also attractive in concept is pace mapping, in which left and right endocardial ventricular pacing is performed during sinus rhythm in an attempt to mimic the QRS complex of the spontaneous arrhythmia (show figure 3A-3B). The correlation between the site of stimulation and the resultant point of epicardial emergence of activation may be poor, however, and there is concern about the frequency of both false negative and false positive results [16,17,18].

A new nonfluoroscopic catheter-based electroanatomic mapping system, CARTO, has a magnetic field emitter and sensor and can create a replica of the anatomy of the cardiac chamber in which the tachycardia focus is located, permitting more precise localization of the arrhythmia focus [19]. Electroanatomic mapping images also allow identification of areas of interest around an arrhythmia focus (show figure 4 and show figure 5).

Efficacy of ablation — The experience with catheter ablation remains small, and has been primarily performed with DC shock ablation [10,11,20,21,22,23,24,25,26]. It is difficult to summarize the data because of differences in patient populations, details of the mapping and ablation, and number of patients. We will therefore summarize a few of the larger or, in our view, better studies.

  •  One report evaluated 33 patients with recurrent monomorphic VT who had been resistant to drug therapy [11]. Twenty-two had coronary artery disease, six had other types of heart disease, and five had no structural heart disease. The site was identified by endocardial mapping, and pace mapping was successful in 26 patients. One to four shocks of 100 to 300 joules were used. Ablation was successful in 15 patients (45 percent) as defined by no recurrence of VT either on no antiarrhythmic therapy or on the same regimen that was ineffective before ablation. Follow-up averaged about 16 months with a range of five to 35 months. There were no fatalities, but one patient had sustained VT immediately after the shock and ventricular fibrillation on days five and six after ablation, two had neurologic deficits, two developed atrioventricular block, and one had brachial artery thrombosis.

  •  The success rate was also approximately 45 percent in another study of 70 high-risk patients with low cardiac output [26]. However, five patients died during or as a result of the DC shock ablation. Another seven patients died during an average follow-up of 38 months; three of these deaths were sudden.

  •  More modest success rates have been reported in other studies [9,23]. The Percutaneous Catheter Mapping and Ablation Registry reported that only about one-third of subjects remained free of arrhythmia while the mortality rate, including mortality related to the procedure itself, was 25 percent [21].

Less information is at present available with radiofrequency current ablation, although this procedure is being used with increasing frequency [27,28,29,30,31,32,33]. One group published two reports on the use of radiofrequency ablation for ventricular arrhythmias [28,29]. In the larger study, 136 patients with coronary disease who had one configuration of sustained monomorphic VT underwent either radiofrequency ablation (72 patients) or DC current ablation (64 patients) [29]. The mapping procedure included pace mapping during sinus rhythm, endocardial activation mapping, identification of isolated mid-diastolic potentials, and pacing interventions during VT. The success rate (74 versus 77 percent) and complication rate (10 versus 14 percent) were similar with the two procedures. Tamponade with death occurred in one patient in each group, both of whom had severe hemodynamic compromise prior to the procedure. Two patients with radiofrequency and three with DC ablation had transient second- or third-degree atrioventricular (AV) block that required external pacing for as long as 24 hours. One patient had a cerebral embolism after DC shock. The investigators point out that their patients were highly selected, representing about 20 percent of patients with VT who were referred to this laboratory. This may account for the higher success rate than found in the studies described above.

Two other studies of patients with ventricular tachycardia and coronary heart disease noted initial success rates of approximately 80 percent with recurrence occurring in none of fifteen and nine of twenty patients, respectively [30,31]. Even better results were noted in another report (25 of 26 VTs ablated) when concealed entrainment was used in association with other mapping criteria, particularly an isolated mid-diastolic potential that cannot be dissociated from the tachycardia [27]. After an 8.7 month follow-up, no patient experienced a recurrence of sustained symptomatic VT.

In addition to accurate mapping, other determinants of success are the ability to induce a well arrhythmia that can be mapped [34] and ablation of all hemodynamically tolerated arrhythmias that are induced. In one series of 35 patients with postinfarction ventricular tachycardia, the clinical arrhythmia was successfully ablated in 30 (86 percent) [32]. At a mean follow-up of 12 months, 10 of 11 patients with no inducible arrhythmia were free of recurrent arrhythmia. In contrast, recurrent arrhythmia occurred in 10 of 19 patients who had inducible "nonclinical" arrhythmia.

A second study evaluated 52 patients with a prior myocardial infarction and arrhythmia recurrence despite antiarrhythmic drugs including amiodarone; all inducible monomorphic ventricular tachycardias that allowed mapping (average of 3.6 per patient) were ablated [33]. More than one ablation session was required in 31 percent of patients and complications occurred in 10 percent. The three-year survival rate was 70 percent and the risk of ventricular tachycardia recurrence was 33 percent, primarily in patients with prior drug failure. Ablation was largely an adjunctive therapy in this series since 59 percent of patients were receiving amiodarone and 45 percent had an ICD implanted.

  Unmappable ventricular tachycardia — In many patients, mapping to localize the origin of the ventricular tachycardia cannot be achieved because there are multiple morphologies of ventricular tachycardia, the arrhythmia is hemodynamically unstable, or ventricular tachycardia cannot be induced. In one study of 16 patients with unimorphic unmappable ventricular tachycardia, bipolar catheter mapping was performed during a supraventricular rhythm using the CARTO system; normal endocardium was defined by an electrogram amplitude of >1.5 mV while dense scar was identified by a voltage <0.5 mV (show figure 5)  [35]. Using radiofrequency energy, lesions were created, extending linearly from the dense scar to anatomic boundaries or normal endocardium. After a median follow-up of eight months, 75 percent of patients were free of recurrent ventricular tachycardia.

Adjunct to implantable cardioverter-defibrillator — A substantial number of patients with an implantable cardioverter-defibrillator (ICD) require concomitant therapy with antiarrhythmic drugs to decrease the recurrence of the clinical arrhythmia and the frequency of ICD shocks. (See "Nonpharmacologic therapy in survivors of sudden cardiac death: Role of surgery and radiofrequency ablation"). An alternative approach is radiofrequency ablation. One study of 21 patients with frequent ICD shocks despite antiarrhythmic drugs found that ablation was effective in 76 percent of patients [36]. At 11 month follow-up, the frequency of ICD shocks per month decreased from 60 to 0.1.

  Cost-effectiveness — The cost-effectiveness over five years was calculated for radiofrequency ablation relative to amiodarone therapy in patients an ICD who have recurrent episodes of ventricular tachycardia in a report that estimated event probabilities from 107 patients entered into a prospective randomized trial of ablation versus antiarrhythmic drug, the literature, and a consensus panel [37]. The five year costs were higher for ablation compared to amiodarone ($21,795 versus $19, 075), but the quality of life was greater for ablation. This yielded a cost effectiveness ratio of $20,923 per quality-adjusted life-years gained for ablation compared to amiodarone. The incremental cost effectiveness ratio was $6028 for patients with a good left ventricular ejection fraction with a first episode of ventricular tachycardia.

BUNDLE BRANCH REENTRANT VENTRICULAR TACHYCARDIA — BBRVT is a special form of sustained monomorphic VT involving abnormal conduction through normally present structures: the bundle of His and the bundle branches. It occurs with both ischemic and nonischemic heart disease. Up to six percent of inducible VT is due to bundle branch reentry but the arrhythmia is generally difficult to induce. Treatment is necessary as the arrhythmia is often hemodynamically significant but resistant to drug therapy. (See "Bundle branch reentrant ventricular tachycardia"). The site of ablation for VT due to bundle branch reentry with the most common left bundle branch block pattern is the right bundle branch [38].

Efficacy of ablation — Catheter ablation has been very successful in BBRVT due to bundle branch reentry that characteristically has a left (rarely a right) bundle branch morphology [38,39,40,41]. In one report, for example, DC current ablation of the right bundle branch in seven patients resulted in abolition of the arrhythmia in all patients; there were no recurrences on follow-up [38]. Similar findings were noted in a larger study of ablation in 28 patients [40]. These results suggest that ablation therapy is the treatment of choice for this type of VT.

IDIOPATHIC VENTRICULAR TACHYCARDIA — VT not associated with structural organic heart disease usually arises in the right ventricular outflow tract. These arrhythmias most commonly have an electrocardiographic pattern of left bundle branch block with right axis deviation, presumably arising from the right ventricular outflow tract [42]. Less commonly, idiopathic VT presents with a right bundle branch block pattern with a leftward axis, presumably arising from the inferoapical region of the left ventricle [43]. Both forms of this arrhythmia (called right and left ventricular tachycardia, respectively) can be precipitated by catecholamines or exercise, and terminated by verapamil or adenosine.

Site of ablation — Idiopathic VT probably results from a mechanism other than reentry, most likely being triggered by activity from a very localized area of myocardium. Pace mapping is a useful means to identify the best sites for ablations in idiopathic VT arising from the right ventricular outflow tract [42]. On the other hand, the target for ablation in idiopathic left ventricular VT (which originates in the apicoseptal portion of the left ventricle) is often best defined as site with the earliest local electrogram and identification of a Purkinje potential [43,44].

Efficacy of ablation — A number of ablation studies of modest size have now been reported in idiopathic VT [42,43,44,45,46,47,48,49,50]. Initial success rates range from 75 to 100 percent for tachycardias that originate in the right ventricular outflow tract, and 50 to 90 percent for those that originate at other sites. In addition, success may be lower when the site of origin is not endocardial and not definitively identified during mapping. One study of 75 patients found that the inability to identify a focus, and hence the success rate, correlated with the QRS duration; the success rate was 95 percent when the QRS complex in V2 during pacing mapping was 160 ms in duration, while the success rate was only 54 percent if the QRS duration was <160 ms [51].

There is limited information on long-term follow-up. In one study of 20 patients with idiopathic left ventricular tachycardia, the initial success rate was 85 percent and there were no recurrences at 7 ± 8 months [50]. Six patients underwent a repeat electrophysiologic study; none were inducible. A second study of 13 patients with right ventricular outflow tract VT reported that all tachycardias were successfully ablated; during a 28 month follow-up only one patient had a recurrence [52].

Another review of 13 patients with idiopathic left ventricular VT reported success in 92 percent; among 35 patients with idiopathic right ventricular outflow tract VT,14 percent had a recurrence after a follow-up of 30 months [53]. A good pacemap was more important than the earliest local endocardial electrogram in those with right ventricular VT, while both an optimal pacemap and the earliest endocardial electrogram were important for successful ablation of left ventricular VT. Factors predictive of unsuccessful ablation were greater than one induced VT morphology, a delta wave-like beginning of the QRS, and a match between the clinical VT and pacemap in less than 11 of 12 leads.

OTHER FORMS OF VT — The role of ablation in arrhythmogenic right ventricular dysplasia and tetralogy of Fallot remains to be defined. (See "Sustained monomorphic ventricular tachycardia in nonischemic heart disease"). Preliminary evidence suggests that radiofrequency catheter ablation may be successful in some patients with sustained VT and dilated cardiomyopathy [54].

LASER AND CHEMICAL ABLATION — Laser techniques were used as part of intraoperative ablation in one study of 17 patients [55]. Follow-up at six to 18 months was encouraging. A more recent series evaluated nine patients with postinfarction VT in whom laser energy was delivered to the site of earliest epicardial activation without the need for ventriculotomy [56]. Seven patients remained free of recurrent VT after a follow-up of 17 months.

Transcoronary chemical ablation has been used in selected patients. One study treated patients with incessant VT in whom other therapeutic options had failed [57]. Sterile ethanol was injected into the coronary artery supplying the myocardium which contained the arrhythmogenic focus in three patients; the arrhythmia was cured in two and suppressed in one until new collateral blood supply developed and the arrhythmia returned. Repeat treatment was successful. The same group more recently reported follow-up on 10 patients, seven of whom were alive from two to 44 months later with six remaining free of tachycardia [58].

RECOMMENDATIONS — Catheter ablation for the treatment of ventricular tachycardia has been variably successful depending upon the type and etiology of the arrhythmia.

  •  Catheter ablation is curative in virtually all patients with bundle branch reentry and we consider it the treatment of choice.

  •  Catheter ablation has been quite successful in patients with idiopathic VT. It should be considered in patients with symptomatic VT refractory to medical management and in patients in high risk occupations (such as airline pilots and heavy equipment operators.

  •  Catheter ablation has been modestly successful in reentrant tachycardias, particularly in the presence of coronary disease. The recurrence of potentially fatal VT is sufficiently frequent that catheter therapy should be considered adjunctive and palliative to other forms of treatment such as the implantable defibrillator in the high-risk patient. Improved techniques for identifying suitable sites for radiofrequency ablations and new catheters are being developed.

  •  Chemical ablation may have a small niche in patients who fail pharmacologic and ablative therapy and who can not tolerate the implantation of an implantable defibrillator.

Catheter ablation for ventricular arrhythmias

Morton F Arnsdorf, MD John Kall, MD

Mar 28, 2000

Pharmacologic therapy has been the cornerstone of treatment for symptomatic and life-threatening ventricular arrhythmias. However, alternative nonpharmacologic therapy has received increasing attention because of the high failure rate, common proarrhythmic actions, and frequent toxicity of the antiarrhythmic drugs. Included in this group are the implantable defibrillator, catheter ablation, and, at times, cardiac surgery. (See "Treatment of nonsustained ventricular tachycardia").

This card will review the role of catheter ablation in the treatment of ventricular arrhythmias. Most studies of ablative therapy have used electrical catheter ablation; in comparison, laser and chemical ablative techniques have only been used in small series of selected patients.

There are two types of electrical catheter ablation: the application of high energy direct current (DC) shock and, more recently, radiofrequency current. DC shock causes thermal injury and, more importantly, barotrauma due to the formation and expansion of vapor at the surface. Barotrauma can result in a number of potentially serious complications including rupture of the myocardium, low cardiac output, pulseless electrical activity (electromechanical dissociation) and death [1]. In contrast, radiofrequency current heats the myocardial tissue and causes local necrosis without barotrauma or remote damage [2]. It produces a much more localized injury than DC shock, so the mechanism of the arrhythmia must be defined more precisely.

SINGLE VENTRICULAR PREMATURE BEATS — Although isolated ventricular premature beats (VPB) are frequently encountered in clinical practice, they generally have no prognostic importance and are often asymptomatic or associated with only mild symptoms. However, there is a small group of patients with drug refractory VPBs who are very symptomatic. (See "Clinical significance and treatment of ventricular premature beats"). Radiofrequency ablation may be an effective approach for these patients; in one study of 12 patients who did not have spontaneous or inducible sustained ventricular tachycardia, radiofrequency ablation of an isolated focus was successful in 11 patients [3]. During a 25 month follow-up, two patients had recurrent symptoms that were controlled with a previously ineffective drug.

MICROREENTRANT VENTRICULAR TACHYCARDIA — Catheter ablation has been primarily used in three types of VT: microreentrant VT; bundle branch block reentrant VT; and idiopathic VT in which the arrhythmia is not associated with underlying structural heart disease. The vast majority of microreentrant ventricular tachycardias that have been treated with ablation are of the sustained monomorphic form.

Site of ablation — A number of reports have reviewed the methods that have been advocated to locate the site of VT [4,5,6,7,8]. During reentrant types of VT accompanying ischemic heart disease, low amplitude signals detected by electrophysiology testing usually allow the identification of the orthodromic and antidromic areas of conduction and indicate the area of interest for ablation [9,10,11]. The use of a 32-site bipolar catheter allows for more rapid endocardial mapping, shortening the time that patients need to remain in VT (show figure 1) [12]. A novel noncontact mapping system utilizing a 64 electrode balloon catheter uses inverse mathematics to simultaneous calculate and record several thousand virtual electrograms; this may be particularly useful for mapping ventricular tachycardia that is not hemodynamically stable [13,14].

  •  Areas with isolated mid-diastolic potentials which cannot be dissociated from the tachycardia by pacing, often represent a vulnerable portion of the reentrant circuit and predict a good response to ablation [9]. Figure 2, for example, shows ECG leads I, III, and V1, a high right atrial electrogram, His electrograms, and localized electrograms, one of which showed diastolic potentials; this site was ablated, eliminating the VT (show figure 2).

  •  The best ablation site can, in about 50 percent of cases, be further defined by entrainment, without evidence for fusion, in an area of slow conduction [9,10,11,15,16]. This results in an acceleration of the ventricular tachycardia to the pacing cycle length, with a QRS complex that is identical to that of the spontaneous VT (entrainment with concealed fusion) and that has a long stimulus to QRS duration. Upon termination of pacing, there is resumption of the ventricular tachycardia with the cycle length present prior to pacing.

  •  Also attractive in concept is pace mapping, in which left and right endocardial ventricular pacing is performed during sinus rhythm in an attempt to mimic the QRS complex of the spontaneous arrhythmia (show figure 3A-3B). The correlation between the site of stimulation and the resultant point of epicardial emergence of activation may be poor, however, and there is concern about the frequency of both false negative and false positive results [16,17,18].

A new nonfluoroscopic catheter-based electroanatomic mapping system, CARTO, has a magnetic field emitter and sensor and can create a replica of the anatomy of the cardiac chamber in which the tachycardia focus is located, permitting more precise localization of the arrhythmia focus [19]. Electroanatomic mapping images also allow identification of areas of interest around an arrhythmia focus (show figure 4 and show figure 5).

Efficacy of ablation — The experience with catheter ablation remains small, and has been primarily performed with DC shock ablation [10,11,20,21,22,23,24,25,26]. It is difficult to summarize the data because of differences in patient populations, details of the mapping and ablation, and number of patients. We will therefore summarize a few of the larger or, in our view, better studies.

  •  One report evaluated 33 patients with recurrent monomorphic VT who had been resistant to drug therapy [11]. Twenty-two had coronary artery disease, six had other types of heart disease, and five had no structural heart disease. The site was identified by endocardial mapping, and pace mapping was successful in 26 patients. One to four shocks of 100 to 300 joules were used. Ablation was successful in 15 patients (45 percent) as defined by no recurrence of VT either on no antiarrhythmic therapy or on the same regimen that was ineffective before ablation. Follow-up averaged about 16 months with a range of five to 35 months. There were no fatalities, but one patient had sustained VT immediately after the shock and ventricular fibrillation on days five and six after ablation, two had neurologic deficits, two developed atrioventricular block, and one had brachial artery thrombosis.

  •  The success rate was also approximately 45 percent in another study of 70 high-risk patients with low cardiac output [26]. However, five patients died during or as a result of the DC shock ablation. Another seven patients died during an average follow-up of 38 months; three of these deaths were sudden.

  •  More modest success rates have been reported in other studies [9,23]. The Percutaneous Catheter Mapping and Ablation Registry reported that only about one-third of subjects remained free of arrhythmia while the mortality rate, including mortality related to the procedure itself, was 25 percent [21].

Less information is at present available with radiofrequency current ablation, although this procedure is being used with increasing frequency [27,28,29,30,31,32,33]. One group published two reports on the use of radiofrequency ablation for ventricular arrhythmias [28,29]. In the larger study, 136 patients with coronary disease who had one configuration of sustained monomorphic VT underwent either radiofrequency ablation (72 patients) or DC current ablation (64 patients) [29]. The mapping procedure included pace mapping during sinus rhythm, endocardial activation mapping, identification of isolated mid-diastolic potentials, and pacing interventions during VT. The success rate (74 versus 77 percent) and complication rate (10 versus 14 percent) were similar with the two procedures. Tamponade with death occurred in one patient in each group, both of whom had severe hemodynamic compromise prior to the procedure. Two patients with radiofrequency and three with DC ablation had transient second- or third-degree atrioventricular (AV) block that required external pacing for as long as 24 hours. One patient had a cerebral embolism after DC shock. The investigators point out that their patients were highly selected, representing about 20 percent of patients with VT who were referred to this laboratory. This may account for the higher success rate than found in the studies described above.

Two other studies of patients with ventricular tachycardia and coronary heart disease noted initial success rates of approximately 80 percent with recurrence occurring in none of fifteen and nine of twenty patients, respectively [30,31]. Even better results were noted in another report (25 of 26 VTs ablated) when concealed entrainment was used in association with other mapping criteria, particularly an isolated mid-diastolic potential that cannot be dissociated from the tachycardia [27]. After an 8.7 month follow-up, no patient experienced a recurrence of sustained symptomatic VT.

In addition to accurate mapping, other determinants of success are the ability to induce a well arrhythmia that can be mapped [34] and ablation of all hemodynamically tolerated arrhythmias that are induced. In one series of 35 patients with postinfarction ventricular tachycardia, the clinical arrhythmia was successfully ablated in 30 (86 percent) [32]. At a mean follow-up of 12 months, 10 of 11 patients with no inducible arrhythmia were free of recurrent arrhythmia. In contrast, recurrent arrhythmia occurred in 10 of 19 patients who had inducible "nonclinical" arrhythmia.

A second study evaluated 52 patients with a prior myocardial infarction and arrhythmia recurrence despite antiarrhythmic drugs including amiodarone; all inducible monomorphic ventricular tachycardias that allowed mapping (average of 3.6 per patient) were ablated [33]. More than one ablation session was required in 31 percent of patients and complications occurred in 10 percent. The three-year survival rate was 70 percent and the risk of ventricular tachycardia recurrence was 33 percent, primarily in patients with prior drug failure. Ablation was largely an adjunctive therapy in this series since 59 percent of patients were receiving amiodarone and 45 percent had an ICD implanted.

  Unmappable ventricular tachycardia — In many patients, mapping to localize the origin of the ventricular tachycardia cannot be achieved because there are multiple morphologies of ventricular tachycardia, the arrhythmia is hemodynamically unstable, or ventricular tachycardia cannot be induced. In one study of 16 patients with unimorphic unmappable ventricular tachycardia, bipolar catheter mapping was performed during a supraventricular rhythm using the CARTO system; normal endocardium was defined by an electrogram amplitude of >1.5 mV while dense scar was identified by a voltage <0.5 mV (show figure 5)  [35]. Using radiofrequency energy, lesions were created, extending linearly from the dense scar to anatomic boundaries or normal endocardium. After a median follow-up of eight months, 75 percent of patients were free of recurrent ventricular tachycardia.

Adjunct to implantable cardioverter-defibrillator — A substantial number of patients with an implantable cardioverter-defibrillator (ICD) require concomitant therapy with antiarrhythmic drugs to decrease the recurrence of the clinical arrhythmia and the frequency of ICD shocks. (See "Nonpharmacologic therapy in survivors of sudden cardiac death: Role of surgery and radiofrequency ablation"). An alternative approach is radiofrequency ablation. One study of 21 patients with frequent ICD shocks despite antiarrhythmic drugs found that ablation was effective in 76 percent of patients [36]. At 11 month follow-up, the frequency of ICD shocks per month decreased from 60 to 0.1.

  Cost-effectiveness — The cost-effectiveness over five years was calculated for radiofrequency ablation relative to amiodarone therapy in patients an ICD who have recurrent episodes of ventricular tachycardia in a report that estimated event probabilities from 107 patients entered into a prospective randomized trial of ablation versus antiarrhythmic drug, the literature, and a consensus panel [37]. The five year costs were higher for ablation compared to amiodarone ($21,795 versus $19, 075), but the quality of life was greater for ablation. This yielded a cost effectiveness ratio of $20,923 per quality-adjusted life-years gained for ablation compared to amiodarone. The incremental cost effectiveness ratio was $6028 for patients with a good left ventricular ejection fraction with a first episode of ventricular tachycardia.

BUNDLE BRANCH REENTRANT VENTRICULAR TACHYCARDIA — BBRVT is a special form of sustained monomorphic VT involving abnormal conduction through normally present structures: the bundle of His and the bundle branches. It occurs with both ischemic and nonischemic heart disease. Up to six percent of inducible VT is due to bundle branch reentry but the arrhythmia is generally difficult to induce. Treatment is necessary as the arrhythmia is often hemodynamically significant but resistant to drug therapy. (See "Bundle branch reentrant ventricular tachycardia"). The site of ablation for VT due to bundle branch reentry with the most common left bundle branch block pattern is the right bundle branch [38].

Efficacy of ablation — Catheter ablation has been very successful in BBRVT due to bundle branch reentry that characteristically has a left (rarely a right) bundle branch morphology [38,39,40,41]. In one report, for example, DC current ablation of the right bundle branch in seven patients resulted in abolition of the arrhythmia in all patients; there were no recurrences on follow-up [38]. Similar findings were noted in a larger study of ablation in 28 patients [40]. These results suggest that ablation therapy is the treatment of choice for this type of VT.

IDIOPATHIC VENTRICULAR TACHYCARDIA — VT not associated with structural organic heart disease usually arises in the right ventricular outflow tract. These arrhythmias most commonly have an electrocardiographic pattern of left bundle branch block with right axis deviation, presumably arising from the right ventricular outflow tract [42]. Less commonly, idiopathic VT presents with a right bundle branch block pattern with a leftward axis, presumably arising from the inferoapical region of the left ventricle [43]. Both forms of this arrhythmia (called right and left ventricular tachycardia, respectively) can be precipitated by catecholamines or exercise, and terminated by verapamil or adenosine.

Site of ablation — Idiopathic VT probably results from a mechanism other than reentry, most likely being triggered by activity from a very localized area of myocardium. Pace mapping is a useful means to identify the best sites for ablations in idiopathic VT arising from the right ventricular outflow tract [42]. On the other hand, the target for ablation in idiopathic left ventricular VT (which originates in the apicoseptal portion of the left ventricle) is often best defined as site with the earliest local electrogram and identification of a Purkinje potential [43,44].

Efficacy of ablation — A number of ablation studies of modest size have now been reported in idiopathic VT [42,43,44,45,46,47,48,49,50]. Initial success rates range from 75 to 100 percent for tachycardias that originate in the right ventricular outflow tract, and 50 to 90 percent for those that originate at other sites. In addition, success may be lower when the site of origin is not endocardial and not definitively identified during mapping. One study of 75 patients found that the inability to identify a focus, and hence the success rate, correlated with the QRS duration; the success rate was 95 percent when the QRS complex in V2 during pacing mapping was 160 ms in duration, while the success rate was only 54 percent if the QRS duration was <160 ms [51].

There is limited information on long-term follow-up. In one study of 20 patients with idiopathic left ventricular tachycardia, the initial success rate was 85 percent and there were no recurrences at 7 ± 8 months [50]. Six patients underwent a repeat electrophysiologic study; none were inducible. A second study of 13 patients with right ventricular outflow tract VT reported that all tachycardias were successfully ablated; during a 28 month follow-up only one patient had a recurrence [52].

Another review of 13 patients with idiopathic left ventricular VT reported success in 92 percent; among 35 patients with idiopathic right ventricular outflow tract VT,14 percent had a recurrence after a follow-up of 30 months [53]. A good pacemap was more important than the earliest local endocardial electrogram in those with right ventricular VT, while both an optimal pacemap and the earliest endocardial electrogram were important for successful ablation of left ventricular VT. Factors predictive of unsuccessful ablation were greater than one induced VT morphology, a delta wave-like beginning of the QRS, and a match between the clinical VT and pacemap in less than 11 of 12 leads.

OTHER FORMS OF VT — The role of ablation in arrhythmogenic right ventricular dysplasia and tetralogy of Fallot remains to be defined. (See "Sustained monomorphic ventricular tachycardia in nonischemic heart disease"). Preliminary evidence suggests that radiofrequency catheter ablation may be successful in some patients with sustained VT and dilated cardiomyopathy [54].

LASER AND CHEMICAL ABLATION — Laser techniques were used as part of intraoperative ablation in one study of 17 patients [55]. Follow-up at six to 18 months was encouraging. A more recent series evaluated nine patients with postinfarction VT in whom laser energy was delivered to the site of earliest epicardial activation without the need for ventriculotomy [56]. Seven patients remained free of recurrent VT after a follow-up of 17 months.

Transcoronary chemical ablation has been used in selected patients. One study treated patients with incessant VT in whom other therapeutic options had failed [57]. Sterile ethanol was injected into the coronary artery supplying the myocardium which contained the arrhythmogenic focus in three patients; the arrhythmia was cured in two and suppressed in one until new collateral blood supply developed and the arrhythmia returned. Repeat treatment was successful. The same group more recently reported follow-up on 10 patients, seven of whom were alive from two to 44 months later with six remaining free of tachycardia [58].

RECOMMENDATIONS — Catheter ablation for the treatment of ventricular tachycardia has been variably successful depending upon the type and etiology of the arrhythmia.

  •  Catheter ablation is curative in virtually all patients with bundle branch reentry and we consider it the treatment of choice.

  •  Catheter ablation has been quite successful in patients with idiopathic VT. It should be considered in patients with symptomatic VT refractory to medical management and in patients in high risk occupations (such as airline pilots and heavy equipment operators.

  •  Catheter ablation has been modestly successful in reentrant tachycardias, particularly in the presence of coronary disease. The recurrence of potentially fatal VT is sufficiently frequent that catheter therapy should be considered adjunctive and palliative to other forms of treatment such as the implantable defibrillator in the high-risk patient. Improved techniques for identifying suitable sites for radiofrequency ablations and new catheters are being developed.

  •  Chemical ablation may have a small niche in patients who fail pharmacologic and ablative therapy and who can not tolerate the implantation of an implantable defibrillator.