Ventricular tachycardia ablation and substrate modification in ICD patients with electrical storm

Minglong Chen

Section of Electrophysiology, Division of Cardiology, the First Affiliated Hospital of Nanjing Medical University, Nanjing,Jiangsu 210029, China.

Ventricular tachycardia ablation and substrate modification in ICD patients with electrical storm

Minglong Chen?

Section of Electrophysiology, Division of Cardiology, the First Affiliated Hospital of Nanjing Medical University, Nanjing,Jiangsu 210029, China.

The electrical storm (ES) is defined as a state of electrical instability with three or more sustained ventriculararrhythmias (VAs) occurring within twenty-four hours, which needs intravenous antiarrhythmic medications andfrequent defibrillation. Recently, radiofrequency catheter ablation evolved as a sole therapy to terminate ES inpatients with ICD, and the survival has been reported to be improved with successful ablation during follow-up.In this review, we briefly summarize substrate mapping and substrate ablation strategy in patients with ES, anddiscuss the reason of recurrence after ablation.

electrical storm, ventricular tachycardia, substrate, ablation

Implantable cardioverter defibrillator (ICD) has beenrecommended for primary or secondary prevention ofsudden cardiac death in patients with ischemic or nonischemiccardiomyopathy and life-threatening cardiacrhythm disorders[1-3]. Electrical storm (ES) is definedas a state of electrical instability, with three or moresustained ventricular arrhythmias (VAs) occurringwithin twenty-four hours, which needs intravenousantiarrhythmic medications and frequent defibrillationtherapies (≥ 3 episodes and separated by 5 minutesin 24 hours). The estimated incidence of ES is approximately4% or 20% in primary or secondary prophylacticICDs[4,5], respectively. Recently, more studies demonstratedthe significant association between ES eventsand death5-7. Patients with ES are estimated from caseseries to survive 1-year, varying from 5% to 35%[1,2].The most common cause of death in patients with ICDESis related to heart failure because of frequent storms.Recurrent shocks also can reduce quality of life[8].

Radiofrequency catheter ablation may be a sole therapyto terminate ES in patients with ICD and survivalhas been reported to be improved with successful ablationduring follow-up[7,9]. The individualized patientprofile can yield a different mapping strategy and thecorresponding ablation strategy. Recently, a systematicreview elucidated that the most common mechanismof ES seen in 83% patients was scar-related reentry in atotal of 471 ES patients from thirty-nine publications[10].According to this meta-analysis, substrate guided mappingand ablation is a reasonable strategy in ES patientswith unstable hemodynamic VT or non-inducible VTduring the procedure[11-14]. Substrate mapping can identify,by three dimensional mapping (NavX or CARTOsystem), the possible reentry circuit. This is based onlow-voltage and fragmental potential which can be analyzedduring stable sinus or paced rhythm. However,this strategy is less precise for localization of the reentrycircuit and needsmore extensive ablation over a relativelylarge area within the scar.Based on the substrate geometry,radiofrequency lesions can then be placed roughly parallelto the low-voltage region border;linear perpendicularto the border,extending through the exit region into the dense scar region[12].Areas of late and fragmentlow-voltage potentials observed during sinus orpaced rhythm would also be targeted forablation[13]. The goaland idealproceduralendpointwas complete elimination of localabnormal ventricular activities, including fractionated,double orlate potentials and no capture of ablation area with maximaloutput(amplitude=20 mA and pulse width=10 ms)[15,16].The most common mapping and radiofrequency ablation region was leftorrightendocardium.A combination ofendocardialand epicardialmapping was applied in patients with recurrence afterthe firstprocedure orinitially failed endocardially[17,18].

A prospective evaluation of radiofrequency catheter ablation in 95 patients with medication-refractory ES showed that ES was acutely suppressed in allpatients; 92%of the patients were free of ES and 66%were free of VT after a median follow-up of 22 months. Epicardial mapping and ablation was performed in ten patients;19%ofthe patients required repeatcatheter ablation.Eightpercentofthe patientshad ES recurrence at5±7 months,fourofwhom died.In total,12%ofthe patients died of cardiac causes,the remaining seven deaths originating from refractory heartfailure[7].In a retrospective study of52 patientsexperiencing theirfirst ES,the patientswere divided the catheterablation group (n=23)and drug therapy group(n=29)according to the operatorˊs preference and the time of occurrence. There was no statistically significantmortality difference between the two groups.The recurrence of ES wasalso similar(38%in ablation vs.57%in medication, P=0.29),and the 38%recurrentpatientsin the ablation group were proved to have lower LVEF(＜25%). Patients with a higher LVEF(＞25%)in the ablation group had a lower ES recurrence compared to the medicalgroup(21%vs.62%,P=0.002).However,82.6% ofthe ablated patients were on antiarrhythmic medications.Anotherinteresting finding was thatno difference was noticed in the estimated mortality in ablated and non-ablated patients(47%vs.32%,P=0.039)[19].In an observationalstudy of a multihospitalnetwork to facilitate VT ablation for 37 ES patients,five patients with ES died prior to ablation,29 patients had monomorphic VT and there were 3 patients with ventricular fibrillation.Among the 32 patients,27 underwentablation within 24 hours after transfer and five underwent emergentablation within 8 hours.Acute success was achieved in 11 of the 17 patients with ischemic cardiomyopathy and 8 of the 14 patients with nonischemic cardiomyopathy during the ablation procedure;one patientdied during the procedure.After a mean follow-up of15 months,3 patients died,10 had recurrent VA and 2 had recurrent ES.Although the result of catheter ablation to suppress ES is encouraging,the effectof this multihospitalnetwork on proceduralsuccess rates and mortality cannotbe determined withouta control group[18].A meta-analysis evaluating 471 patients presenting with ES demonstrated 68%with ischemic cardiomyopathy,17%with idiopathic-dilated cardiomyopathy,5%with ARVD/C,and 6%without structuralheart disease.ES was from monomorphic VT in 77%,polymorphic VT in 7%and VF in 11% (45%of patients with VF had no structuralheartdisease).The cumulative data demonstrated an acute ablation success rate for ES,with 91%patients having elimination ofclinicalventricular arrhythmia and 72% with allinducible VT with a 0.6%procedure-related mortality rate.During follow-up,only 6%ofthepatients had recurrence of ES and 17%mortality over61±37 weeks of follow-up,with 10%of the deaths owing to progressive heartfailure and 4%of the deaths due to recurrentVA.Patients with nonischemic cardiomyopathy orincessantVA tended to have a worse outcome[10]. However,this meta-analysis excludes large trials of catheterablation,such as the Multi-Center ThermoCool trial20,the Euro-VT trial[21]and a study of epicardial ablation[22],because these studies did not report the effectofventricularsubstrate map and ablation on survivalfor ES patients.Another meta-analysis study of catheter ablation as an adjunctto medicaltherapy for VT in patientswith structuralheartdisease[23]found that VT recurrence had a significantreduction(35%)in the ablation group compared to the medical group(P＜0.001),although there was no statistically significant difference in mortality between the two groups. However,in this meta-analysis[23],the authorcombined two studies to analyze the differentstrategies to treat ES.In 116 patients with ICD,ES occurred in 40%of the patients[24,25];17 of the patients were assigned to adjunctive ablation and 29 patients were assigned to medicaltherapy.The results implied thatthe ablation group showed a trend toward reduction of ES compared to medicaltherapy(Mantel-Haenszelpooled relative risk 0.61,P=0.066).

Recently,a novel substrate ablation strategy for unmappable VT with ES was reported[16].The study found that electrical isolation of the entire substrate was feasible and appeared to be an effective treatment in patients with ES.Isolation was defined as the presence of both an entrance and exit block within the entire low-voltage area border-zone.In this study, twelve patients(54±8 years,LVEF 32±13%)underwent catheter ablation for sustained VT.Seven patients had ES and recurrent defibrillator shocks. Substrate isolation was achieved in seven patients through endocardialmapping and ablation(including one transient isolation patient),three of which had a focaldischarge within the isolated area.During a mean follow-up of 479 days,eightpatients remained free of VT recurrence after the first procedure;five patients in the entire isolation group had no recurrence of VT.

There mightbe many factors in baseline characteristics and the ablation procedure thatcan predicta higher risk ofdeath orES recurrence.However,no singlefactor in the baseline can significantly predict this poor result. Even the LVEF appeared to have a smallassociation with mortality.Some studies supported this[7,26];but other studies argued the opposite relationship[27].The published systematic meta-analysis[10]demonstrated that storm in patients with incessant VA predicted poor outcomes compared with frequent VA;patients with VF and polymorphic VT also had significantly lowerrecurrence compared with monomorphic VT.The successful ablation procedure suggests a favorable long-term result;however,ES patients with failed ablation procedure mighthave moderate increase in mortality.

In conclusion,catheter ablation is a suitable and useful strategy for treating recurrent VT with ES. However,a successful procedure does not mean an improved survivalrate because many of these patients still die of progressive heart failure.

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?Corresponding author: Minglong Chen, M.D., Section of Electrophysiology, Division of Cardiology, the First Affiliated Hospital of Nanjing Medical University, 300 Guangzhou Road,Nanjing 210029, China. Tel/Fax: +0086-25-8371-7168/+0086-25-8371-7168,E-mail:chenminglong@njmu.edu.cn.

Received 19 December 2014, Accepted 28 December 2014, Epub 15January 2015

The author reported no conflict of interests

?2015 by the Journal of Biomedical Research. All rights reserved.

10.7555/JBR.29.20140165