Abstract
Background
Ventricular tachycardia (VT) recurrence after catheter ablation for electrical storm is commonly seen in patients with ischemic cardiomyopathy (ICM).
Hypothesis
We hypothesized that VT recurrence can be predicted and be related to the all‐cause death after VT storm ablation guided by remote magnetic navigation (RMN) in patients with ICM.
Methods
A total of 54 ICM patients (87% male; mean age, 65 ± 7.1 years) presenting with VT storm undergoing acute ablation using RMN were enrolled. Acute complete ablation success was defined as noninducibility of any sustained monomorphic VT at the end of the procedure. Early VT recurrence was defined as the occurrence of sustained VT within 1 month after the first ablation.
Results
After a mean follow‐up of 17.1 months, 27 patients (50%) had freedom from VT recurrence. Sustained VT recurred in 12 patients (22%) within 1 month following the first ablation. In univariate analysis, VT recurrence was associated with incomplete procedural success (hazard ratio [HR]: 6.25, 95% confidence interval [CI]: 1.20‐32.47, P = 0.029), lack of amiodarone usage before ablation (HR: 4.71, 95% CI: 1.12‐19.7, P = 0.034), and a longer procedural time (HR: 1.023, 95% CI: 1.00‐1.05, P = 0.05). The mortality of patients with early VT recurrence was higher than that of patients without recurrence (P < 0.01).
Conclusions
Inducibility of any VT at the end of procedure for VT storm guided by RMN is the strongest predictor of VT recurrence. ICM patients who have early recurrences after VT storm ablation are at high risk of all‐cause death.
Keywords: Electrical Storm, Remote Magnetic Navigation, Ventricular Tachycardia
1. INTRODUCTION
Electrical storm (ES) due to ventricular tachycardia (VT) in patients with ischemic cardiomyopathy (ICM) is difficult to control with medical therapy and is associated with poor short‐ and long‐term prognoses.1, 2, 3 Catheter ablation targeting the tachycardia substrate has been reported to effectively suppress ES.4, 5, 6 The challenge however, is that VT recurrence after ablation is still commonly seen in this cohort. Multiple factors are related to VT recurrence in patients with structural heart disease.7, 8, 9, 10 For this study, remote magnetic navigation (RMN) was chosen because of several advantages. These advantages included better catheter stability and less fluoroscopy time.11 Also, the improved maneuverability of the RMN catheter may overcome the challenge of accessing some difficult anatomic substrates during VT ablation.12 Available evidence on the prediction and prognosis of VT recurrence of ES treated by ablation with RMN is still limited. Therefore, this study attempts to define the predictors and prognostic significance of VT recurrence after ablation for VT storm guided by RMN.
2. METHODS
2.1. Study population
In this prospective observational study, 54 patients with a confirmed diagnosis of ES due to VT were consecutively included at the Rigshospitalet, University of Copenhagen, between January 2008 and February 2014. All patients signed an informed consent before the procedure. ES was defined as the occurrence of ≥3 episodes of sustained VT, separated by 5 min, during a 24‐h period, or the presence of incessant VT (defined as persistent sustained VT or continuous episodes of VT separated by brief bouts of normal rhythm).13 Intravenous antiarrhythmic therapy was withheld before procedure. Due to the relative urgency of the ablation procedure, it was not possible to withdraw oral antiarrhythmic drugs, such as amiodarone, for 5 half‐lives before the procedure. A coronary angiogram was performed if acute ischemia was a potential cause of arrhythmia. If acute ischemic events were present, these patients were excluded from the study.
2.2. Electrophysiological study
A 6‐F steerable catheter (Inquiry; St. Jude Medical, Minneapolis, MN) and a 5‐F quadripolar catheter (Medtronic, Minneapolis, MN) were positioned within the coronary sinus and at the apex of right ventricle via the left femoral vein. A transseptal puncture was performed in the left anterior oblique radiographic position during pressure monitoring. An open‐irrigated magnetic ablation catheter (NaviStar RMT ThermoCool; Biosense Webster Inc., Diamond Bar, CA) was introduced into the left ventricular (LV) cavity using a steerable sheath (Agilis; St. Jude Medical). A single bolus of 50 to 100 IU/kg body weight of heparin was administrated after transseptal puncture. Additional heparin was administrated to maintain an activated clotting time between 250 and 300 s as required. Surface ECG and endocardial electrograms were continuously monitored and recorded. If present, implantable cardioverter‐defibrillators (ICDs) were turned off and programmed to VVI mode.
2.3. Electroanatomical mapping and ablation
The ablation catheter was connected with the CARTO 3D mapping system (Biosense Webster) and the RMN Niobe II system or Niobe ES (Stereotaxis Inc., St. Louis, MO) to perform 3D LV electroanatomic mapping and ablation. The detailed information of this technique was discussed in our previous study.14 Substrate mapping followed by activation mapping was performed in patients with initial sinus rhythm and well‐tolerated VT. A programmed stimulation protocol from multiple right ventricular/LV sites at the 500‐ and 400‐ms drive cycle with up to 3 extrastimuli decrementally to 200 ms or ventricular refractoriness was applied to induce VT. If incessant VT was still present after catheter placement, activation and substrate mapping were performed simultaneously. If patients had poorly tolerated VT in this clinical setting, restricted activation mapping was performed after substrate mapping in sinus rhythm.
Bipolar isovoltage maps of LV were constructed to delineate the scar and border zone areas. Areas with potential amplitudes ≥1.5 mV were defined as normal and those with amplitudes between 0.5 mV and 1.5 mV as border zone.15 The scar area was defined during sinus rhythm by electrograms with an amplitude ≤0.5 mV. Regions with fragmented, abnormal electrograms and late potentials were annotated using color tags. Points with QRS morphology during pace‐mapping identical to those seen during documented VT were also annotated. Entrainment‐mapping techniques were applied trying to characterize the arrhythmic circuit in patients with well‐tolerated VTs.
Radiofrequency energy was delivered in the temperature control mode with target catheter temperature of <45 to 48°C. Power was set at 30 W to 40 W with a flush rate of 10 to 25 mL/min. Radiofrequency lesions were delivered either during VT or during sinus rhythm in the regions identified or judged to be critical for sustaining clinical or inducible VTs. After VT was terminated by ablation (whether induced or incessant), further ablation, targeting local late potential during sinus rhythm, was performed. After catheter ablation, the same stimulation protocol mentioned above was applied to induce tachycardia. Any induced sustained monomorphic VT was targeted with further ablation, and the inducible protocol of VT was repeated subsequently until no further VT was inducible.
2.4. Study endpoints
The procedural endpoint was ablation of any clinical and nonclinical inducible VTs. VT morphology was defined as “clinical” if it had been documented previously by a 12‐lead electrocardiogram (ECG).5 Nonclinical VTs were defined as those presenting different morphology and/or cycle length from any spontaneous episode documented in 12‐lead ECG. Therefore, complete procedural success was defined as noninducibility of any VT except polymorphic VT or ventricular fibrillation (VF). Incomplete success represented inducibility of nonclinical VT and/or clinical VT. The primary study endpoint was the time to first recurrence of any sustained VT after ablation. The secondary endpoint was mortality after ablation.
2.5. Complications
Complications were divided into 2 categories, major and minor. Major complications included cardiac tamponade, acute myocardial infarction, stroke, major bleeding, and exacerbation of heart failure (HF) during the procedure or 30 days after the procedure. Minor complications were defined as pericarditis and inguinal hematoma.
2.6. Follow‐up
All patients without previous ICD implantation were implanted, regardless of acute procedural outcome before discharge. Patients were monitored for ≥48 h in‐hospital before discharge. After VT ablation, patients were typically seen 1 month postprocedure and every 3 months thereafter, or were followed using remote monitoring systems, to assess VT recurrences. Any sustained VT during follow‐up, whether symptomatic or treated by ICD or not, was considered a recurrence of VT. Early recurrence was defined as any sustained VT that recurred within the first month after ablation. Mortality data were confirmed during hospitalization, telephone contact via remote monitoring, or national health registry system. Each patient was followed for >3 months unless the patient died before then.
2.7. Statistical analysis
Continuous variables were expressed as mean ± SD and categorical variables as numbers and percentages. An unpaired Student t test was used to compare the continuous variables from the 2 groups. Categorical data were analyzed using χ2 test analysis or Fisher exact test where appropriate. Univariate logistic regression analysis was performed to identify predictors of VT recurrence. Survival functions were estimated by Kaplan–Meier analysis and compared by the log‐rank test. A value of P < 0.05 was considered statistically significant. The statistical package SPSS version 19.0 (IBM Corp., Armonk, NY) was used for all analyses.
3. RESULTS
3.1. Baseline clinical characteristics
Fifty‐four ICM patients with VT storm undergoing ablation with RMN were included. All patients had evidence of monomorphic VT on a 12‐lead ECG and/or stored ICD electrograms. All patients were treated with a first ablation procedure for VT. Patient characteristics are summarized in Table 1. The population was predominantly male (47/54, 87%) with a mean age of 65 ± 7.1 years. Average LV ejection fraction (LVEF) was 26.6%. All the patients received β‐blocker agents according to HF treatments. Forty‐one patients were on amiodarone therapy before ablation. One‐third of all patients had multiple monomorphic VTs recorded by ECG or ICD. Average VT cycle length (VT‐CL) was 393 ms. A total of 48/54 (89%) patients already had an ICD implanted. Prior to ablation procedure, the number of ICD antitachycardia pacing (ICD‐ATP) attempts per year and ICD shocks per year in individuals were 47 ± 78 and 5.4 ± 12, respectively.
Table 1.
Baseline clinical characteristics
| Characteristic | Total |
|---|---|
| No. of patients | 54 |
| Mean age, y | 65 ± 7.1 |
| Sex, M/F | 47/7 (87/13) |
| NYHA class | 2.49 ± 0.75 |
| I + II/III + IV, n | 25/29 |
| LVEF, % | 26.6 ± 9.0 |
| LVEF ≤30% | 40 (74) |
| Amiodarone therapy before ablation, Y/N | 41 (76)/13 (24) |
| Multiple clinical VTs | 18 (33) |
| Clinical VT‐CL, ms | 393 ± 62 |
| ICD recipients: ICD‐VVI/ICD‐DDD/CRT‐D, n | |
| Before ablation | 20/12/16 |
| After ablation | 24/14/16 |
| ICD ATP episodes per patient per year | 47 ± 78 |
| ICD shock per patient per year | 5.4 ± 12 |
Abbreviations: ATP, antitachucardia pacing; CRT‐D, cardiac resynchronization therapy‐defibrillator; F, female; ICD, implantable cardioverter‐defibrillator; LVEF, left ventricular ejection fraction; M, male; N, no; RF, radiofrequency; RMN, remote magnetic navigation; SD, standard deviation; VT, ventricular tachycardia; VT‐CL, ventricular tachycardia cycle length; Y, yes.
Data are presented as n (%) or mean ± SD.
3.2. Procedural outcomes of ablation with RMN
Most of the procedures in this studied population were performed with local anesthesia. Five patients underwent general anesthesia during the VT ablation procedure. Electrophysiological and procedural outcomes are listed in Table 2. In this population, at least one type of monomorphic sustained VT, whether clinical or nonclinical, was incessant or could be induced in each of the patients during the procedure. The frequency of multiple induced VTs during the procedure was higher than that documented at baseline (36/54 vs 18/54; P < 0.01) (Tables 1 and 2). The average CL of inducible clinical and nonclinical VTs was not statistically different from baseline (380 ± 63 ms vs 393 ± 62 ms; P > 0.05). LV endocardial mapping was performed via transseptal approach in all patients. None of the patients underwent epicardial mapping and ablation. All of the monomorphic sustained VTs were targeted for ablation. Complete success for noninducible sustained VTs using ablation was achieved in 43 (80%) patients (Table 2). Eight patients (15%) still had inducible nonclinical VTs, but ES was controlled by ablation. Three patients (5%) failed RF ablation treatment and still had inducible clinical VT during the procedure. Additional medications for ES including antiarrhythmic drugs and sedation were needed after the procedure. No procedure required manual crossover from RMN in this study. The total procedure and fluoroscopy times were 104 ± 21 min and 7.2 ± 4.6 min, respectively. The duration of RF ablation was 976 ± 419 s.
Table 2.
Electrophysiological and procedural outcomes of acute RMN catheter ablation
| Parameters | Results |
|---|---|
| Multiple induced VTs | 36 (67) |
| Induced VT‐CL, ms | 380 ± 63 |
| Acute success of catheter ablation | |
| Noninducibility of any VT | 43 (80) |
| Noninducibility of clinical VT (nonclinical VT persists) | 8 (15) |
| RF ablation failure (inducible clinical VT persists) | 3 (5) |
| Procedure time, min | 104 ± 21 |
| Fluoroscopy time, min | 7.2 ± 4.6 |
| RF ablation time, sec | 976 ± 419 |
Abbreviations: RF, radiofrequency; RMN, remote magnetic navigation; SD, standard deviation; VT, ventricular tachycardia; VT‐CL, ventricular tachycardia cycle length.
Data are represented as n (%) or mean ± SD.
There were no major complications in this studied population. None of the patients underwent acute exacerbation of HF during or after catheter ablation.
3.3. VT recurrence and predictors
During a mean follow‐up of 17.1 ± 16.6 months, 27 patients (50%) had no recurrence of any sustained VT. Comparative results of clinical and procedural characteristics in relation to VT recurrence are summarized in Table 3. The LVEF of patients with VT recurrence was 15% lower than those without recurrence (P = 0.16). A higher proportion of nonrecurrent VT patients (89%) reported taking amiodarone before ablation, compared with recurrent VT patients (63%). This was a strong trend, but not statistically significant (P = 0.056). No difference between groups (patients with and without VT recurrence) was seen in clinical or induced VT‐CL times (P = 0.25 and P = 0.42, respectively). Compared with patients without recurrence, the total procedural time of VT recurrent patients was significantly higher, by 14% (P = 0.04). A statistically significantly higher proportion of nonrecurrent VT patients achieved acute complete success, compared with the recurrent VT patients (93% vs 67%, respectively; P = 0.04). Kaplan–Meier curves of time to first recurrence of sustained VT with complete and incomplete procedural success are illustrated in Figure 1. The total follow‐up months of the patients without complete success was similar to the patients with complete success (21.0 ± 21.9 vs 16.1 ± 15.2; P = 0.38). Within 1 month after ablation, 22% (12/54) of patients had early VT recurrence.
Table 3.
Comparison of clinical and procedural characteristics in relation to VT recurrence
| Characteristic | No Recurrence, n = 27 | Recurrence, n = 27 | P Value |
|---|---|---|---|
| Mean age, y | 65 ± 9.3 | 65 ± 9.4 | 0.87 |
| Male sex | 23 (85) | 24 (89) | 1.0 |
| NYHA class | 0.59 | ||
| I/II | 14 (52) | 11 (41) | |
| III/IV | 13 (48) | 16 (59) | |
| LVEF, % | 28.7 ± 10.9 | 24.4 ± 11.3 | 0.16 |
| LVEF ≤30% | 19 (70) | 21 (78) | 0.76 |
| Amiodarone therapy before ablation, n | 24/3 | 17/10 | 0.056 |
| ICD recipients: ICD‐VVI/ICD‐DDD/CRT‐D, n | |||
| Before ablation | 12/5/6 | 8/7/10 | 0.36 |
| After ablation | 14/7/6 | 10/7/10 | 0.43 |
| Multiple clinical VTs | 9 (33) | 9 (33) | 0.77 |
| Clinical VT‐CL, ms | 407 ± 76 | 380 ± 90 | 0.25 |
| Multiple induced VTs | 16 (59) | 20 (74) | 0.63 |
| Induced VT‐CL, ms | 390 ± 82 | 372 ± 88 | 0.42 |
| Procedural time, min | 97 ± 25 | 111 ± 27 | 0.04 |
| RF ablation time, sec | 892 ± 409 | 1060 ± 582 | 0.23 |
| Acute complete success rate, % | 93 | 67 | 0.04 |
Abbreviations: CRT‐D, cardiac resynchronization therapy‐defibrillator; ICD, implantable cardioverter‐defibrillator; RF, radiofrequency; RMN, remote magnetic navigation; SD, standard deviation; VT, ventricular tachycardia; VT‐CL, ventricular tachycardia cycle length.
Data are represented as n (%) or mean ± SD.
Figure 1.
Kaplan–Meier for time to first recurrence of sustained VT according to complete procedural success. Abbreviations: VT, ventricular tachycardia
Incomplete procedural success (hazard ratio [HR]: 6.25, 95% CI: 1.20‐32.47, P = 0.029) was the strongest predictor of VT recurrence. Lack of amiodarone use before ablation procedure (HR: 4.71, 95% CI: 1.12‐19.7, P = 0.034), and a longer procedural time (HR: 1.023, 95% CI: 1.00‐1.05, P = 0.05) were other predictors of VT recurrence.
3.4. Mortality on follow‐up
During the follow‐up period, a total of 11 patients (20%) died. There were no procedure‐related deaths. One patient died of cardiogenic shock and severe congestive HF (LVEF = 10% before ablation) after coronary artery bypass grafting surgery during hospitalization. Eight out of 10 of the remaining deaths were due to end‐stage HF. Two patients died of noncardiac causes.
3.5. Impact of VT recurrence on mortality
The mortality of the VT‐recurrent patients was higher than that of the patients without VT recurrence after ablation (9/27 vs 2/27, P = 0.04). In the subgroup analysis, the patients with early VT recurrence (within 3 months after ablation) had the highest mortality when compared with the patients with late recurrence and without recurrence (Figure 2A). Kaplan–Meier curves of the secondary endpoint of mortality are shown in Figure 2B.
Figure 2.
Kaplan–Meier time‐to‐death curves
4. DISCUSSION
To our knowledge, the current study is one of the largest ones describing the predictors of VT recurrence and the impact of VT recurrence on survival after catheter ablation with RMN for VT storm in ICM patients. The main findings of this study are as follows: (1) catheter ablation of VT with RMN effectively controlled ES and resulted in acceptable long‐term clinical outcomes; (2) noninducibility of any VT after ablation was associated with improved freedom from VT recurrence; (3) despite the failure to control ES before ablation, administration of amiodarone still had an effect in preventing early VT recurrence after ablation; and (4) early VT recurrence after ablation for ES in ICM patients was associated with increased mortality during long‐term follow‐up.
4.1. Potential of RMN in ischemic VT storm ablation
It is well known that the main advantages of RMN‐guided ablation include improved catheter stability, reduced fluoroscopy time, and relatively lower occurrence of mechanical complications.11 Also, the improved maneuverability of RMN catheter may overcome the challenges in accessing difficult anatomic substrates during VT ablation. Our previous study and other studies have provided evidence that the use of RMN to ablate VT in patients with ICM can achieve acute success rates ranging from 71% to 83%.14, 15, 16, 17 However, some operators are still concerned that the floppy soft‐tip catheters used in RMN systems may produce insufficient lesions, and thus lead to higher arrhythmia recurrence rates. Interestingly, recurrence rates of VT ablation using RMN ranged from 14% to 50%, which was similar to the recurrence rate reported after manual ablation.18, 19 In the present study, at a mean follow‐up of 17.1 months, there is an acceptable VT recurrence rate but no further improvement compared with published data. Several reasons may explain this result. First, all the selected patients had ES before ablation. A history of VT storm has been reported to be associated with early VT recurrence.7 Second, the majority of these patients (74%) presented with markedly reduced LVEF (≤30%). A recent study demonstrated that the VT recurrence rate reached >60% in patients with severely depressed LVEF (≤30%) at 1‐year follow‐up.20 Other reasons, such as antiarrhythmic drugs administration, follow‐up period, and mode, may influence the VT recurrence rate. Thus, the data for RMN for ischemic VT storm ablation are promising, but larger randomized clinical studies are needed to further compare this technique with manual ablation.
4.2. Predictors of VT recurrence
The predictors of VT recurrence after VT ablation in structural heart disease vary by studies. Noninducibility of any VT at the study end was the strongest predictor of VT recurrence in a series of manual‐navigation ischemic VT ablation studies.21 However, VT recurrence is commonly seen even in the patients with noninducibility as a procedural endpoint after ablation in these above‐mentioned studies. To date, few studies have described the predictors of VT recurrence after ablation guided by RMN. In this study, incomplete procedural success was the strongest predictor of VT recurrence (HR: 6.25, 95% CI: 1.20‐32.47, P = 0.029). However, 18 patients (33%) with complete success (noninducibility of any VT) did experience VT recurrence during follow‐up. This finding is consistent with the observations of others that programmed electric stimulation has a limited ability to predict outcome.
Of note in the current study, no use of amiodarone before ablation was another predictor of VT recurrence (HR: 4.71, 95% CI: 1.12‐19.7, P = 0.034) by univariate regression analysis. Although intravenous amiodarone was withheld before procedure, it was not possible to withdraw amiodarone for 5 half‐lives before the procedure due to the relative urgency of the VT storm ablation. Of 12 patients who underwent early VT recurrence within 1 month after ablation, 6 patients did not receive amiodarone administration before the procedure. It is described that amiodarone has a relatively long half‐life. These interesting findings may indicate that amiodarone still played a role in the prevention of VT recurrence even though VT storm was refractory to amiodarone before ablation. However, the data from this study cannot come to a conclusion as to whether and how long amiodarone should be administrated after VT storm ablation.
4.3. Impact of VT recurrence on mortality
Catheter ablation has been reported to acutely control ES and reduce ICD therapies, and thus possibly improve quality of life. However, this strategy was not shown to significantly decrease mortality in some earlier reports.22 To date, the impact of VT storm ablation with RMN on mortality is still limited. In this study, the patients with early VT recurrence had higher mortality than did those without VT recurrence during follow‐up (Figure 2). However, the mortality was not significantly different between the patients with late recurrence and those without recurrence. These findings raise the possibility that other management besides ablation to attempt to reduce early VT recurrences may improve outcomes. For example, renal sympathetic denervation has been reported to control ES23 and be associated with reduced arrhythmic burden, with no procedure‐related complications in patients with ICDs and refractory ventricular arrhythmias.24 Further studies are needed to determine whether additional therapies, such as renal denervation, can prevent early VT recurrence and then reduce mortality, especially in patients without complete abolition of inducible VT at the end of the ablation procedure.
4.4. Study limitations
There are several limitations in the current study. First, epicardial ablation was not performed in this study. Although endocardial ablation is often sufficient to eliminate local abnormal ventricular activities from the epicardium and may be used first to reduce the risk of epicardial ablation,25 incomplete procedural success may be caused by lack of epicardial ablation. Second, data on the impact of amiodarone or other antiarrhythmic drugs after ablation on VT recurrence were not analyzed. In addition, this study included a population with a major proportion of severe HF (mean LVEF, 26.6%; LVEF ≤30% in 74% of patients). The acute procedural success rate and long‐term outcomes of patients with preserved LVEF may be different from those presented in this study.
5. CONCLUSION
Catheter ablation of VT with RMN is an acutely effective method to control ES. Incomplete procedural success is the strongest predictor of VT recurrence, which indicated that noninducibility of any sustained monomorphic VT is an important procedural endpoint during the VT storm ablation procedure guided by RMN. Early VT recurrence after ablation for ES in ICM patients is associated with increased mortality during long‐term follow‐up. Therefore, it is critical to develop novel strategies to prevent early VT recurrence, especially for the ES patients ablated without complete procedural success.
Conflicts of interest
The authors declare no potential conflicts of interest.
Jin Q, Jacobsen P. K, Pehrson S, Chen X. Prediction and prognosis of ventricular tachycardia recurrence after catheter ablation with remote magnetic navigation for electrical storm in patients with ischemic cardiomyopathy. Clin Cardiol. 2017;40:1083–1089. 10.1002/clc.22773
Funding information Chinese National Natural Science Foundation Grant, Grant/Award number: 81470450, 81470451; Shanghai Municipal Education Commission‐Gaofeng Clinical Medicine Grant, Grant/Award number: 20161404.
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