Meta-analysis of catheter ablation as an adjunct to medicaltherapy for treatment of ventricular tachycardia in patientswith structural heart diseaseJaya Mallidi, MD, MHS,* Girish N. Nadkarni, MD, MPH,* Ronald D. Berger, MD, PhD, FHRS,†
Hugh Calkins, MD, FHRS,† Saman Nazarian, MD*†
From the *Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, and†Division of Cardiology/Cardiac Arrhythmia, Johns Hopkins University School of Medicine, Baltimore, Maryland.
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BACKGROUND Most studies of catheter ablation for the treatment ofventricular tachycardia (VT) are relatively small observational trials.
OBJECTIVE The purpose of this study was to define the relativerisk of VT recurrence in patients undergoing catheter ablation asan adjunct to medical therapy versus medical therapy alone in apooled analysis of controlled studies.
METHODS Randomized and nonrandomized controlled trials of pa-tients who underwent adjunctive catheter ablation of VT versus med-ical therapy alone were sought. MEDLINE, EMBASE, the Cochranecentral register of controlled trials (CENTRAL), and Web of Sciencewere searched from 1965 to July 2010. Supplemental searches in-cluded Internet resources, reference lists, and reports of arrhythmiaexperts. Three authors independently reviewed and extracted the dataregarding baseline characteristics, ablation methodology, medicaltherapy, complications, VT recurrences, mortality, and study quality.
RESULTS Five studies were included totaling 457 participantswith structural heart disease. Adjunctive catheter ablation was
herapy alone for VT. Complications of catheter ablation includedeath (1%), stroke (1%), cardiac perforation (1%), and completeeart block (1.6%). Using a random-effects model, a statisticallyignificant 35% reduction in the number of patients with VTecurrence was noted with adjunctive catheter ablation (P�.001).here was no statistically significant difference in mortality.
ONCLUSIONS Catheter ablation as an adjunct to medical ther-py reduces VT recurrences in patients with structural heart dis-ase and has no impact on mortality.
performed in 58% of participants, whereas 42% received medical All rights reserved.
IntroductionVentricular tachycardia (VT) is a significant contributor tomorbidity and mortality among patients with structural heartdisease. Several clinical trials have proved the efficacy ofimplantable cardioverter-defibrillators (ICDs) in reducing therisk of sudden death from VT.1,2 Despite their unquestionablebenefits, ICD shocks are painful, can lead to decreased qualityof life,3 and appear to be associated with increased mortal-ity.4–7 Therefore, additional therapies for treatment of VT areoften necessary. Antiarrhythmic medications have limited ef-ficacy at reducing shocks and may result in severe adverseeffects.8 Catheter ablation of VT is an alternative approach thattargets the critical zone(s) in VT circuits. Catheter ablationfor VT in the setting of structural heart disease is currently
Dr. Nazarian is funded by a National Heart, Lung, and Blood InstituteCareer Development Award (K23HL089333). Address reprint requestsand correspondence: Saman Nazarian, M.D., Johns Hopkins Hospital,Carnegie 592C, 600 North Wolfe Street, Baltimore, Maryland 21287.E-mail address: [email protected]. (Received August 24, 2010; accepted
indicated for VT storm and symptomatic sustained VT thatrecurs despite antiarrhythmic drug therapy.9,10 Most studiesof catheter ablation for treatment of VT, however, are rel-atively small uncontrolled observational trials.11–14 To de-
ne the magnitude of benefit associated with catheter abla-ion of VT, we sought to perform a meta-analysis combiningll prospective randomized controlled trials and nonran-omized trials with control groups. This meta-analysisested the null hypothesis that the number of patients withT recurrences is equal among those with structural heartisease undergoing catheter ablation as an adjunct to med-cal therapy versus medical therapy alone.
MethodsThe Preferred Reporting Items for Systematic Reviews andMeta-Analyses (PRISMA) checklist was used for our meta-analysis.15 Randomized controlled trials and nonrandomizedcontrolled trials evaluating the efficacy of catheter ablation asan adjunct to medical therapy versus medical therapy alone for
Data sources and searchesA comprehensive literature search was conducted in MED-LINE, EMBASE, the Cochrane central register of controlledtrials (CENTRAL), and Web of Science, using the MeSHterms “ventricular tachycardia” and “catheter ablation.” Nolimits of either language or date were applied to the search.Bibliographies of the retrieved articles and systematic reviewson the topic were searched for other relevant studies. Thewebsite www.theheart.org was used to search for related presen-ations at any of the major scientific meetings. The search wasonducted in the third week of July 2010. The July issues of allajor scientific journals were reviewed, as the latest articles might
ot be available in the databases. Arrhythmia experts were con-acted to identify additional potential studies not identified byatabase searches. The National Institutes of Health Clinical Trialsatabase was also searched for any recent completed trials com-aring catheter ablation to medical therapy.
Study selectionThree reviewers (J.M., G.N., and S.N.) independently re-viewed all identified publications and abstracts for inclusionusing predetermined criteria. The inclusion criteria were (1)randomized controlled trials and (2) nonrandomized controlledstudies, where catheter ablation was used to treat VT and a controlgroup received medical therapy only. Given the limited number ofstudies, there were no exclusions based on patient inclusion cri-teria, mapping and ablation methodology, or type of catheter used.
Data extraction and quality assessmentThree independent authors (J.M., G.N., and S.N.) assessed thepotential for systematic bias in studies selected for inclusion.Each reviewer assessed every candidate study for risk of biasand methodological quality. The specific criteria to assess therisk of bias are summarized below: (1) study design, (2) inclu-sion criteria, (3) length of follow-up, (4) definition of VTrecurrences and method for primary outcome assessment, (5)proportionate and acceptable amount of loss to follow-up, and (6)study funding. The answers to specific questions in each categorywere tabulated (Table 1). The tables from each reviewer werecompared, and disagreements were resolved by discussion.
Data from included studies were extracted independently bytwo reviewers (J.M., G.N.) and confirmed in duplicate by athird reviewer (S.N.). Extracted data included baseline patientcharacteristics, number of patients screened and enrolled, VTmapping and ablation technique and equipment, number of pa-tients allocated to each group, complications, number of patientswith VT recurrences, electrical storm events, and deaths.
The primary outcome was the number of patients with VTrecurrences. VT recurrences were most commonly defined asICD interventions that included both appropriate ICD shocksand antitachycardia pacing. In studies in which only VT recur-rences were mentioned, we made the assumption that VTrecurrences and ICD interventions for VT represent the sameinformation. The secondary outcomes were complications,
electrical storm events, and all-cause mortality. w
Data synthesis and analysisIntent-to-treat data were used for all randomized studies. Theprincipal summary measure was relative risk. Pooled relativerisks with 95% confidence intervals were calculated usingfixed-effects models with Mantel-Haenszel and inverse vari-ance weighting. If the fixed-effects models showed statisticalsignificance, DerSimonian Laird random-effects analyses werealso performed. Results obtained from random-effects analysiswere then compared with results of the fixed-effects model toascertain the effect of heterogeneity. I2 statistics were calcu-ated to further assess for heterogeneity. Repeating the analysisith data only from the randomized clinical trials was used to
ssess sensitivity to nonrandomized results. All statistical anal-ses were performed using STATA 10 statistical softwareStataCorp., College Station, TX). Two-sided P-values �.05ere considered statistically significant.
ResultsSearch resultsAmong a total of 1,944 studies that were obtained using theMeSH terms from different databases and three other studiesselected from bibliographies of scientific meetings and discus-sion with arrhythmia experts, 154 potential studies were se-lected by review of titles (Figure 1). Out of the total 154potential studies, 149 studies were excluded after assessmentof the full text. Review articles, letters to editors, observationalstudies without a control group of patients, case reports, caseseries, and studies comparing ablation technologies without agroup of patients allocated to medical therapy were excluded.Of the randomized trials, two were excluded because theirobjective was to compare electroanatomic versus standard flu-oroscopic mapping and no patients were assigned to medicaltherapy.16,17 Another registry and planned randomized studyfrom Poland was excluded owing to failure to enroll patientsinto the randomized portion of the study.18 The studies selectedfor final meta-analysis included two published randomizedclinical trials,19,20 two randomized trials that are only availablen abstract format,21,22 and an observational study with a pa-ient group that did not undergo ablation.23
Studies of catheter ablation as an adjunct tomedical therapy versus medical therapy alone for VTTable 1 provides an outline of the quality assessment for eachstudy. Four studies were randomized clinical trials.19–22 Thefirst randomized trial, conducted by Epstein et al,21 was aubstudy (available in abstract format only) of the Cooled RFulti-Center Investigators Group,11 comparing adjunctive
catheter ablation to medical therapy alone. The other unpub-lished (abstract format only) randomized trial, conducted bySchreieck et al,22 was a single-center study in Germany com-paring adjunctive catheter ablation to medical therapy alone.The third randomized trial, conducted by Reddy et al,19 was athree-center study done in the United States randomizing pa-tients to catheter ablation as an adjunct to beta-blockers versusmedical therapy with beta-blockers alone. The latest random-ized trial, conducted by Kuck et al20 and published in 2010,
as a 16-center trial from Europe that randomized patients to
Study site United States Germany United States Japan Europe
Publication status Abstract Abstract Manuscript Manuscript Manuscript
Inclusion criteria Patients with structural heartdisease and (1) �2 episodesof sustained VT within 2months of enrollment; (2)hemodynamically stablespontaneous VT; and (3)failure of at least twoantiarrhythmic agents(extracted from parentstudy11)
Patients with post–myocardialinfarction VT
Patients with post–myocardialinfarction VT
Patients with history ofcongestive heart failureand spontaneoussustained ornonsustained (�5beats) VT/ventricularfibrillation
Patients ages 18–80years with stableclinical VT, previousmyocardialinfarction, and leftventricular ejectionfraction �50%
Follow-up period inmonths, mean(standarddeviation)
6 11.3 (8.9) 22.5 (5.5) 31 (22) 22.5 (9)
Outcomeassessment
Not provided ICD arrhythmia logs ICD arrhythmia logs ICD arrhythmia logsand sudden deaths inpatients without ICDs
ICD arrhythmia logs
Lost to follow-up,n (%)
Not provided Not provided 2 (1.6) Not provided 1 (0.9)
Funding Source Cardiac PathwaysCorporation, Sunnyvale, CA(extracted from parentstudy11)
Not provided National Institutes of Health Not provided St. Jude MedicalCorporation, St.Paul, MN
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adjunctive catheter ablation versus medical therapy alone withantiarrhythmic therapy left to investigator discretion in botharms. The nonrandomized study, conducted by Niwano et al,23
was a single-center observational study conducted in Japanwith five study groups: (1) acute successful ablation, (2) acutefailed ablation, (3) ablation not attempted, (4) ventricular fi-brillation, and (5) no inducible VT/ventricular fibrillationgroups. For the purposes of our analysis, the acute successfuland failed ablation groups (groups 1 and 2) were combined asthe arm allocated to adjunctive catheter ablation and theirlong-term outcomes compared with the ablation not attemptedgroup (group 3). Both groups received medical therapy withbeta-blockers. Sensitivity to nonrandomized results was as-sessed by performing the meta-analysis with and without theresults of this trial. All studies enrolled patients with structuralheart disease and were thus immune to bias resulting fromenrollment of patients with idiopathic and focal VT. All studiesreported at least 180 days of follow-up. All studies reportedutcome assessment through ICD arrhythmia logs with the ex-
Figure 1 Flow diagram of liter
eption of Epstein et al21 and Niwano et al’s studies,23 where v
ot all participants had ICDs. Loss to follow-up was mini-al when reported but unavailable in three studies.21–23
The data of included studies are outlined in Table 2. A totalof 457 participants were enrolled across all five studies. Ofthese, 266 (58%) patients were in the intervention group and191 (42%) in the control group. The mean age was between 60and 70 years in all trials. The majority of patients in all studieswere male. Three studies enrolled only patients with ischemiccardimyopathy.19,20,22 However, the populations of Epsteint al21 and Niwano et al’s23 studies included patients with bothschemic and nonischemic cardiomyopathy. The average ejec-ion fraction for all studies was approximately 30%–35%.
Complications of catheter ablation for VTData regarding complications related to catheter ablation wereavailable from three studies and have been detailed in Table2.19–21 Pooling data from all three studies resulted in a 6.3%omplication rate as a result of catheter ablation for VT. Majoromplications included death (1%), stroke/transient ischemicttack (1%), cardiac perforation (1%), and third-degree atrio-
arch and study selection process.
entricular block (1.6%).
Table 2 Data of included studies
Epstein et al,199821 Schreieck et al, 200422
Reddy et al,200719
Niwano et al,200823 Kuck et al, 201020
No. screened Not provided Not provided Not provided 864 Not providedNo. allocated to:
Ablation group 73 19 64 58 (success andfailure groups)
Cooled or large tip radiofrequency Standard 4-mm tipor 3.5 mmirrigatedradiofrequency
Not provided Not provided
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Epstein et al, 199821Schreieck et al,200422 Reddy et al, 200719
Niwano et al,200823 Kuck et al, 201020
Medical therapy:Ablation group Not provided Not provided Beta-blocker (94%) Beta-blocker (78%) Beta-blocker (75%) and
Amiodarone (35%)Control group Beta-blocker (% Not
provided)Beta-blocker (98%) Beta-blocker (70%) Beta-blocker (75%) and
Amiodarone (35%)Complications:
Ablation group 7 (2 deaths, 1 stroke, 1perforation, and 3 third-degree atrioventricular blocks)
Not provided 3 (1 pericardialeffusion, 1congestive heartfailure exacerbation,1 deep veinthrombosis
Not provided 6 (2 from ablation: 1transient ST elevation,1 transient ischemicattack; 4 from ICD: 2lead dislodgement, 2generator defects)
Control group Not provided Not provided 9 (all from ICD: 2 leaddislodgement, 3generator defects, 2dislodged ICDgenerators, 1 T-waveoversensing, 1 leadinsulation damage, 1twiddler’s syndrome, 1system infection)
events (%):Ablation group Not provided Not provided 4 (6) Not provided 13 (25)Control group 12 (19) 17 (31)
No. of deaths (%):Ablation group Not provided Not provided 6 (9) 9 (16) 5 (10)Control group 11 (17) 4 (20) 4 (7)
Note: Carto: electroanatomic mapping system, Biosense Webster, Diamond Bar, CA; Ensite: noncontact mapping system, St. Jude Medical, St. Paul, MN.
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VT recurrencesDuring a follow-up period ranging from 6 to 22.5 months(Table 1), 93 (35%) of 266 patients with catheter ablationexperienced VT recurrence, compared with 105 (55%) of 191patients in the control group. The pooled relative risk using aMantel-Haenszel fixed-effects model revealed a statisticallysignificant 38% reduction in the number of patients with VTrecurrence associated with adjunctive catheter ablation (rela-tive risk 0.62; 95% confidence interval 0.51–0.76; P �.001).
he estimated relative risk was similar when using inverseariance fixed-effects and DerSimonian Laird random-effectsodels (relative risk for both models 0.65; 95% confidence
nterval 0.54–0.79; P �.001). Figure 2A shows the pooledelative risk of VT recurrence after adjunctive catheter ablationompared with medical therapy alone with all five studiesncluded. The results were similar in magnitude and directionhen the analysis was repeated with only randomized con-
rolled trials, excluding the single nonrandomized trial (Man-el-Haenszel pooled relative risk 0.64, 95% confidence interval.52–0.79; P �.001; inverse variance pooled relative risk 0.67,5% confidence interval 0.55–0.82; P �.001; and DerSimo-ian Laird random-effects pooled relative risk 0.67, 95% con-dence interval 0.55–0.82; P �.001; Figure 2B).
Electrical storm eventsThe incidence of electrical storm was reported in two stud-ies.19,20 Electrical storm occurred in 17 (15%) of 116 patientsassigned to adjunctive catheter ablation and 29 (24%) of 119
Figure 2 A: Forest plot of relative risk of VT recurrences after catheterablation versus medical therapy, all studies included. B: Forest plot ofrelative risk of VT recurrences after catheter ablation versus medicaltherapy, randomized controlled trials only. C: Forest plot of relative risk ofmortality after catheter ablation versus medical therapy. Relative risks inthis figure were calculated using the fixed-effects Mantel-Haenszel method.
patients assigned to medical therapy. The pooled relative risk o
using a fixed-effects model revealed a trend toward reductionof electrical storm among patients allocated to adjunctive cath-eter ablation (Mantel-Haenszel pooled relative risk 0.61, 95%confidence interval, 0.36–1.03; P � .066; inverse variance pooledrelative risk 0.65, 95% confidence interval 0.38–1.11; P � .115).
MortalityData regarding long-term mortality after catheter ablation ofVT were available from three studies.19,20,23 Mortality oc-urred in 20 (12%) of 174 patients allocated to adjunctiveatheter ablation compared with in 19 (14%) of 139 patients inhe control group. The pooled relative risk using a fixed-effectsodel revealed reduced mortality with catheter ablation; how-
ver, this difference was not statistically significant (Mantel-aenszel pooled relative risk 0.76, 95% confidence interval.41–1.38; P � .37; inverse variance pooled relative risk 0.76;5% confidence interval 0.41–1.40; P � .37; Figure 2C). Causesf death included congestive heart failure (ablation 4, control 7),rrhythmic deaths (ablation 5, control 1), noncardiac causes (ab-ation 7, control 5), and unknown (ablation 4, control 6).
DiscussionTo the best of our knowledge, this is the first meta-analysis ofstudies regarding catheter ablation for VT. To avoid the risksassociated with publication bias, we conducted a rigoroussearch with a detailed protocol to include both published andunpublished studies. We also assessed the sensitivity of ouranalysis to the inclusion of nonrandomized studies. The resultsof this meta-analysis show that among patients with structuralheart disease and VT, catheter ablation as an adjunct to medicaltherapy reduces the number of patients with VT recurrencesduring follow-up and has no impact on mortality.
Recurrent VT episodes may result in sudden death despitethe presence of an ICD,24 and recurrent shocks can reducequality of life3,25 and appear to be associated with increased
ortality.4–7 Antiarrhythmic medications have limited efficacyand can have severe adverse effects. With the availability ofnew technologies and strategies for ablation of hemodynami-cally unstable VT during sinus rhythm, catheter ablation ap-pears to be a promising technique for prevention of VT recur-rences. Based on the results of prior studies included in thismeta-analysis,19,20,22 some experts favor the use of “prophy-actic” catheter ablation at the time of ICD implantation forecondary prevention of VT. Such an approach appears veryromising and may be considered in individuals with a highikelihood of VT recurrence. However, given the small number ofontrolled trials, limited follow-up data, and relatively high pro-edural complication rate (6.3%), current recommendations toeserve catheter ablation for patients experiencing multiple VTecurrences that are not responsive to antiarrhythmic medicationsppear well justified.9,10 The results of this meta-analysis, how-ver, underscore the utility of adjunctive catheter ablation whenatients experience VT recurrences despite medical therapy.
Our meta-analysis has several limitations. First, a small num-er of studies were included. This reflects the paucity of controlledrials assessing the efficacy of catheter ablation for VT. There are
nly two published randomized controlled trials to date. Two
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additional randomized trials included in the current meta-analysiswere only published in abstract format. Inclusion of data reportedin conference abstracts has potential limitations such as a lack ofthe rigorous peer review required for manuscript format publica-tions. However, greater than half of trials reported in conferenceabstracts never reach full publication, and those that are eventuallypublished are more likely to show a positive association betweenthe subject under study and outcome.26 Therefore, randomizedtudies in abstract format have been included to reduce the risk ofublication bias in this meta-analysis. Second, it is important toote that the included studies were conducted among differentopulations and two studies included patients with ischemic andonischemic cardiomyopathy. There were also differences in VTapping strategies, ablation technologies, methodologies of col-
ecting information regarding VT recurrences, and length of fol-ow-up. Importantly, given the variation in the length of follow-upetween studies, we had to make the assumption that the relativeisk for VT recurrence is stable over time. Metaregression ortratification by study characteristics could not be performed ow-ng to the low number of available studies. However, random-ffects analyses did not significantly alter the results of the fixed-ffects models, and the between-study heterogeneity was notignificant with respect to VT recurrence (I2 � 0%; P � .42) or
mortality (I2 � 0%; P � .54) endpoints. Therefore, although theincluded studies had different characteristics, the pooled relativerisk estimates are likely reasonable. Finally, the studies wereprimarily performed in tertiary care centers; therefore, the reportedefficacy and complications rates may not be generalizable to othersettings and populations not included in the meta-analysis.
Data regarding the efficacy of catheter ablation for VTare limited, and many questions remain unanswered. De-spite finding a reduction in VT recurrences, in the one studyin which quality of life measures were collected, no differ-ence was found between the ablation and control groups.20
Also, data regarding mortality after catheter ablation of VTare sparse. Since mortality was not the primary outcome ofincluded studies,19,20,23 and arrhythmic death was likelyrevented by ICDs in the majority of included patients,dditional studies are necessary to assess this importantndpoint. These unresolved issues clearly indicate the needor more sufficiently powered randomized trials and multi-enter registry studies of catheter ablation for VT.
In summary, catheter ablation of VT as an adjunct toedical therapy reduces the number of patients with struc-
ural heart disease who experience VT recurrences. Notatistically significant mortality benefit or detriment wasssociated with catheter ablation. Future randomized con-rolled studies to assess mortality and quality of life asso-iated with catheter ablation of VT are warranted.
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