Implantable cardioverter-defibrillator therapy in the form of high-energy shock (HES) is associated with adverse effects. This study evaluated an alternative therapy to HES, including antitachycardia pacing (ATP) for very fast ventricular tachycardia (VFVT) and low-energy shock (LES) ≤5 J for ventricular tachycardia (VT) of any cycle length (CL). This multicenter study recruited 602 patients with standard indications for an implantable cardioverter-defibrillator. Programming was standardized into 3 zones: (1) ventricular fibrillation (VF) CL of <200 ms treated with HES; (2) VFVT defined within the VF zone (CL, 200 to 250 ms) treated with 2 ATP bursts, LES, and HES; and (3) fast ventricular tachycardia (CL, 251 to 320 ms) and slow VT (CL, >320 ms) treated with 3 ATP bursts, LES, and HES. The primary end point was ATP and LES efficacy and safety. After a mean follow-up of 19 ± 8 months, 2,815 device activations were recorded in 152 patients. Of 67 VFVT episodes, 34 reverted with combined ATP and LES (success rate 50.7%) with first and second ATPs successful in 36% and 13.8%, respectively. LES was used in 39 fast ventricular tachycardia and 60 slow VT episodes with success rates of 53.8% and 73.3%, respectively. Syncope occurred in 19.4%, 16.2%, and 1% of episodes because of VFVT, VF, and VT CL >250 ms, respectively. In conclusion, tiered ATP and LES therapy terminates >50% of VFVT episodes (CL, 200 to 250 ms), which otherwise would fall within the VF zone and be treated exclusively with HES. LES is efficacious and safe in patients with VT CL >250 ms with extremely low syncope rates. Limitation of ATP to a single burst in VFVT is recommended to minimize syncope.
Many ventricular arrhythmias (VAs) with cycle length (CL) of 200 to 250 ms are monomorphic and have prognostic significance when induced at electrophysiologic study as opposed to true ventricular fibrillation (VF). Previously, we have demonstrated that antitachycardia pacing (ATP) and low-energy shock (LES) can be used for very fast ventricular tachycardia (VFVT) CL of <250 ms in the setting of induced ventricular tachycardia (VT) at the time of implantable cardioverter-defibrillator (ICD) implant. However, traditional ICD programming for VFVT remains to be high-energy shock (HES). This study examined the effectiveness of ATP for VT CL of 200 to 250 ms and the use of LES when ATP fails for VT of any CL.
Methods
The Concept of Optimal Management of ventricular Fibrillation or very fast ventricular Tachycardia study was an Australian multicenter prospective study that recruited patients from 6 centers. Centers included Westmead Public and Private Hospitals, St Andrew’s War Memorial Hospital, Prince Charles Hospital, Royal Adelaide Hospital, and Wakefield Hospital. The primary end points were the efficacy and safety of ATP and LES for reverting VFVT (CL, 200 to 250 ms) and the efficacy and safety of LES when ATP fails in VT of any CL. Safety was assessed by evaluating acceleration rates, episode duration, syncope, first shock efficacy, and sudden death rates with reference to contemporary ICD studies. The study was approved by the local ethics review committee with informed consent obtained from each patient. A total of 602 patients with standard indications for ICD therapy were prospectively recruited from 2008 to 2010. Exclusions included patients with long QT or Brugada syndromes. All patients underwent implantation of a pectoral ICD system (Medtronic Australasia Pty Ltd, North Ryde, NSW, Australia) with a transvenous endocardial right ventricular lead. Device detection and therapy was standardized and into 3 zones ( Figure 1 ). (1) VF: required 18 of 24 RR intervals with CL of <250 ms. Treatment consisted of ≤6 HES. Any detection that had ≥1 of the previous 8 RR intervals <200 ms was classified as VF. (2) VFVT: defined within the VF zone for CL of 200 to 250 ms. First therapy was 2 ATP bursts (8-pulse burst pacing at 88% of the tachycardia CL). Second therapy was LES (5 J), with subsequent therapy HES. (3) Fast ventricular tachycardia (FVT [CL, 251 to 320 ms]) or slow VT (CL >320 ms) required 16 consecutive beats with CL of 251 to 360 ms. First therapy was 3 ATP sequences, second therapy LES, and subsequent therapies HES. For devices with an atrial lead, all supraventricular tachycardia discriminators were activated at the time of implant for CL >250 ms. To reduce unnecessary right ventricular pacing, backup pacing was set at 40 beats/min VVI (ventricular pacing, sensing and inhibition) for single-chamber devices and AAI-DDD (atrium and ventricular pacing, sensing and modulation) for devices with an atrial lead. Follow-up with device interrogation and diary review was at 1, 3, 6, and 12 months after implant, then 6 monthly thereafter until completion of the study. An independent committee comprising 3 electrophysiologists at a core laboratory reviewed adverse events and deaths as well as stored device data or electrograms in a blinded fashion. Temporal correlation was performed between episodes and symptoms recorded in patient diaries. The outcome of each individual therapy was classified as: (1) successful with termination of VA or (2) unsuccessful, which included change in VA CL. Acceleration was defined as ≥10% shortening of tachycardia CL.
With enrollment of 600 patients, it was expected that approximately 120 (20%) would have device activations during 12 months. Of these, approximately 24 (20%) were expected to have episodes within the VFVT zone. For inducible VFVT, the pilot study demonstrated a success rate of 30% for ATP and 86% for LES. We postulated that the success rate would be higher for spontaneous VT. Assuming at least 80% respond to the combination ATP ± LES, then the 95% confidence interval for the estimated response rate among the 24 subjects with VFVT would be no wider than ±16% about the estimated response rate. All analyses were performed using the Statistical Package for the Social Sciences for Windows (release 18.0, SPSS Inc., Chicago, Illinois). Analysis of variance was used to compare mean values or Kruskal-Wallis tests for continuous variables when normal distribution was not present. Cox regression backward stepwise analysis was used for predictors of survival. To account for multiple events within a patient, the generalized estimating equation was used for predictors of syncope during ICD activation. A 2-tailed p <0.05 was considered significant.
Results
A total of 602 patients underwent implantation of a Medtronic ICD with a single chamber, dual chamber, and cardiac resynchronization device implanted in 49%, 33%, and 18%, respectively. Baseline clinical and demographic characteristics are listed in Table 1 . Implant-related complications occurred in 6%, with no deaths related to device implantation. During a mean follow-up of 19 ± 8 months, 2,815 ICD detections occurred in 152 patients consisting of 2,580 (92%) true VAs and 235 (8%) inappropriately detected VAs. For analysis of therapy efficacy, only appropriate VA episodes requiring device therapy were included with VT storm episodes excluded. A total of 1,659 episodes were analyzed with 37 because of VF (2%), 67 because of VFVT (4%), 985 because of FVT (59%), and 570 because of slow VT (34%; Table 2 and Figure 2 ).
| Variable | Appropriate Activation | p | |
|---|---|---|---|
| Yes, n = 142 (%) | No, n = 460 (%) | ||
| Age, yrs (mean ± SD) | 64 ± 13 | 64 ± 12 | 0.69 |
| Men | 80 | 77 | 0.23 |
| Primary prevention ICD | 49 | 70 | 0.01 |
| Hypertension | 65 | 55 | 0.02 |
| Previous myocardial infarction | 58 | 64 | 0.09 |
| Diabetes mellitus | 25 | 31 | 0.08 |
| NYHA class | 0.49 | ||
| I | 54.5 | 46.4 | |
| II | 30.3 | 29.9 | |
| III | 11.7 | 22.9 | |
| IV | 3.4 | 0.9 | |
| β-Blocker therapy | 61 | 81 | <0.01 |
| Antiarrhythmic therapy ∗ | 33 | 25 | 0.07 |
| Left ventricular ejection fraction (mean ± SD) | 32 ± 12 | 32 ± 12 | 0.89 |
∗ Includes amiodarone, sotalol, verapamil, mexilitine, digoxin, and flecainide.
| Variable | VF (<200 ms; n = 19) | VFVT (200–250 ms; n = 28) | FVT (251–320 ms; n = 97) | VT (>320 ms; n = 65) | p |
|---|---|---|---|---|---|
| Episodes | 37 (2%) | 67 (4%) | 985 (59%) | 570 (34%) | |
| CL (ms), mean ± SD | 194 ± 30 | 237 ± 15 | 302 ± 20 | 357 ± 30 | <0.01 |
| Episode duration (s), median (IQR) | 11 (6) | 17 (14) | 7 (5) | 8 (8) | 0.03 |
| Syncope | 16.2% | 19.4% | 2.3% | 0.7% | <0.01 |
Of 67 VFVT episodes (28 patients), 34 (51%) reverted with the combined ATP and LES algorithm ( Table 3 and Figure 2 ). Episodes that failed 2 bursts of ATP went on to receive an LES with success in 5 of 9 patients (56%). Within individual patients, the combination ATP and LES was 100% successful in 14 patients, 0% successful in 7 patients, and ranged from 13% to 75% success rate in 7 patients. Therefore, combined ATP and LES algorithm prevented ≥1 HES in 21 of 28 patients (75%) with VFVT episodes. In the 28 patients, first ATP was 100% successful in 11 patients, 0% successful in 12 patients, and ranged from 20% to 75% success rate in 5 patients, thereby saving 16 of 28 patients (57%) from receiving ≥1 shock. VFVT episodes were monomorphic in 96% (64 of 67) and polymorphic in <5% (3 of 67). First ATP was successful in 38% of monomorphic VFVT versus 0% of polymorphic VFVT (p = 0.19). All episodes (n = 985) of FVT received ATP as the first treatment with 81% success ( Table 4 ). Thirty-nine episodes of FVT received LES with a 54% success rate. A small number of episodes, initially in the FVT zone, were redetected in the VFVT zone after ATP acceleration and subjected to further ATP and LES. In the 8 episodes that received LES after redetection in the VFVT zone, there was a 0% success rate. All episodes of slow VT received first ATP with 67% success rate ( Table 5 ). LES had a 73% success rate. Two episodes that accelerated after ATP were redetected in the VFVT zone and underwent LES with success in 1. Syncope occurred in an overall 48 episodes (3%; Table 2 ), with no related injuries or deaths. All VFVT episodes that failed ATP and LES combination were terminated by ≤2 HES. There was no significant difference in either episode duration (p = 0.62) or syncope rates (p = 0.45) for VFVT treated with ATP and LES versus VF treated with HES. During the follow-up period, 51 patients (9%) died. In 1 case, no information was available. In the other cases, death was noncardiac (27), nonarrhythmic cardiac (17), or arrhythmic where the ICD was intentionally deactivated (6). Predictors of mortality are listed in Table 6 .
| Variable | Success (n = 34) | Fail (n = 33) | Accelerate (n = 21) | p |
|---|---|---|---|---|
| ATP and LES combination, n (%) | 34 (51) | 33 (49) | ||
| Episode duration (s), median (IQR) | 9 (11) | 20 (15) | 0.03 | |
| Syncope | <1% | 36% | 0.01 | |
| First ATP | 24 (36%) | 26 (39%) | 17 (25%) | |
| Episode duration (s), median (IQR) | 7 (4) | 22 (9) | 19 (13) | <0.001 |
| Syncope | 0 | 31% | 29% | 0.011 |
| Second ATP | 4 (14%) | 21 (72%) | 4 (14%) | |
| Episode duration (s), median (IQR) | 16 (25) | 23 (9) | 27 (8) | 0.04 |
| Syncope | 0 | 33% | 50% | 0.01 |
| Variable | Success (n = 918) | Fail (n = 152) | Accelerate (n = 40) | p |
|---|---|---|---|---|
| First ATP | 793 (81%) | 152 (15%) | 40 (4%) | |
| Episode duration (s), median (IQR) | 7 (2) | 21 (23) | 26 (17) | <0.01 |
| Syncope | <1% | 4% | 30% | <0.01 |
| Second ATP | 78 (43%) | 77 (42%) | 25 (13%) | |
| Episode duration (s), median (IQR) | 15 (4) | 35 (35) | 26 (7) | 0.02 |
| Syncope | 1% | 8% | 24% | 0.01 |
| Third ATP | 26 (29%) | 58 (64%) | 6 (7%) | |
| Episode duration (s), median (IQR) | 25 (7) | 37 (39) | 38 (43) | 0.01 |
| Syncope | 0 | 12 | 50 | 0.01 |
| LES for FVT zone ∗ | 21 (54%) | 3 (8%) | 15 (39%) | |
| Episode duration (s), median (IQR) | 27 (12) | 63 (54) | 46 (19) | 0.01 |
| Syncope | 5 | 0 | 0 | 0.64 |
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