Long-Term Efficacy of Implantable Cardioverter Defibrillator in Repaired Tetralogy of Fallot　― Role of Anti-tachycardia Pacing ―

Abstract

Background: Tetralogy of Fallot (TOF) is one of the common congenital heart diseases (CHD) in implantable cardioverter defibrillator (ICD) recipients, but few studies have reported the long-term outcomes of and the anti-tachycardia pacing (ATP) efficacy in repaired TOF.

Methods and Results: Twenty-one repaired TOF patients with an ICD implanted between April 2003 and March 2015 were investigated retrospectively. ICD therapy and clinical outcome were analyzed. Mean patient age was 39±11 years; 62% were male; and mean age at repair surgery was 9.4±6.8 years. During a median follow-up of 5.6 years (range, 2.6–8.4 years), no patients died. Appropriate ATP were delivered in 11 patients (52%), with appropriate shocks in 5 patients (24%) and inappropriate shocks in 5 patients (24%). The success rate of ATP was 98% for fast ventricular tachycardia (VT; cycle length ≤320 ms) and 98% for slow VT (cycle length >320 ms). ATP effectiveness increased from 81.5% with the first ATP attempt to 93.7% with the second ATP attempt, to 97.5% with the third ATP attempt, and to 98.6% with the fourth or successive ATP attempt (P<0.0001, Cochran-Armitage trend test).

Conclusions: ATP was highly effective in repaired TOF regardless of VT cycle length. Multiple ATP attempts could have an important role in VT termination, and the novel subcutaneous ICD without ATP capability should be used carefully.

Patients with tetralogy of Fallot (TOF), one of the common congenital heart diseases (CHD), are at risk of sudden cardiac death due to malignant ventricular arrhythmias, and they are the most common recipients of implantable cardioverter defibrillators (ICD) among CHD patients.^1–4 Previous studies have investigated the incidence of appropriate shock and the effectiveness of shock in TOF patients with ICD for primary and secondary prevention,^1–6 but few have described the long-term effectiveness of ICD and the role of anti-tachycardia pacing (ATP) in repaired TOF.^2,6 Moreover, the efficacy of ATP in TOF patients is still unknown. Previous data suggest that the prevalence of serious arrhythmia is low in Japanese TOF patients compared with those from Western countries,⁷ but there has been no study on the prognosis in Japanese TOF patients with ICD. The aim of this study was therefore to evaluate the efficacy of appropriate ATP in Japanese repaired TOF patients with ICD for primary and secondary prevention. The secondary outcome studied was mortality.

Methods

Subjects

This was an observational retrospective cohort study. The subjects consisted of surgically repaired TOF patients who underwent ICD or cardiac resynchronization therapy defibrillator (CRTD) implantation at the Tokyo Women’s Medical University Hospital (Tokyo, Japan). Between April 2003 and March 2015, all repaired TOF patients who underwent ICD or CRTD implantation were reviewed. Secondary prevention was defined as ICD implantation after sustained ventricular tachyarrhythmia and/or resuscitated cardiac arrest. This study was approved by the local institutional ethics board, and all patients gave written, informed consent.

Baseline Characteristics

Demographic data, surgical history, laboratory data, surface 12-lead electrocardiogram, echocardiographic data, cardiac magnetic resonance imaging, cardiac catheterization, and electrophysiology studies were retrospectively analyzed from electronic medical records. The most recent data preceding ICD implantation were analyzed, with a maximum acceptable time interval of 6 months. Echocardiographic parameters were obtained from the most recent echocardiogram prior to ICD implantation. Echocardiographic data included left and right ventricular (LV and RV) function, chamber size, and degree of valvular function. LV ejection fraction (LVEF) was calculated using the Teichholz formula. RV systolic function was assessed on visual estimation as normal (EF ≥50%), mildly (EF 40–49%), moderately (EF 30–39%), or severely (EF <30%) impaired. Surgical characteristics included type of repair and the presence of ventriculotomy (non-transannular RV outflow patch; transannular RV outflow patch; pulmonary valve implantation; and extracardiac RV to pulmonary artery conduit).

ICD Programming

Device programing was left to the discretion of the implanting physician in the present study. In general, device programming was as follows. The ventricular fibrillation (VF) zone detected ventricular events faster than 176–230 beats/min, and initial therapy was ≥30 J (maximum energy of the device). The ventricular tachycardia (VT) zone detected ventricular events faster than 150–181 beats/min, and multiple sequences of ATP were initially attempted before shock. In the case of documented slow ventricular tachyarrhythmia, a detection zone <150 beats/min was sometimes programmed. ATP consisted of 2–4 bursts (8–15 pulse bursts pacing trains at 80–90% of the VT cycle length), followed by 1–4 bursts or ramps (8–15 pulse bursts or ramp pacing trains at 80–91% of the VT cycle length). In most patients who received their devices before 2011, ATP during charging in the VF zone was not available. The ICD devices were manufactured by Biotronik (Berlin, Germany), Medtronic (Minneapolis, MN, USA), or St. Jude Medical (Minneapolis, MN, USA).

ICD-Related Data

All tachyarrhythmia episodes requiring therapy, either ATP or shock, were reviewed. For each episode, the date, time, mean tachyarrhythmia cycle length, and number of ATP and shock episodes were reviewed. ATP or shock episodes that could not be classified as appropriate or inappropriate by the first investigator, were adjudicated by at least 2 physicians. Treated arrhythmias were classified as appropriate if adjudicated as VT or VF and resulted in ATP and/or shock. Inappropriate ICD therapies were categorized according to the type of the most probable underlying rhythm (noise interference or oversensing, sinus tachycardia, atrial tachyarrhythmia, non-sustained VT). Acceleration was defined as reduction in cycle length >10% after therapy. Slow VT was defined as cycle length >320 ms, and fast VT was defined as cycle length 250–320 ms. All physicians had long-term experience with ICD therapy and cardiac electrophysiology. The term “appropriate ATP” in this analysis refers to ATP-only therapy that was triggered for a single rhythm event, regardless of the total number of ATP treatments required to satisfy the criteria for termination of tachycardia by the ICD. If a tachycardia episode triggered ICD shocks as well as ATP, this episode was classified as an appropriate shock episode. ATP therapy was viewed as successful when the post-therapy rhythm was not a ventricular tachyarrhythmia.⁸

Follow-up

Follow-up data were obtained from review of all cardiac implantable electronic device interrogations and clinical follow-up medical records. Outcome data included all-cause death, appropriate shock, appropriate ATP, and inappropriate shock.

Statistical Analysis

Data are presented as mean±SD or median (IQR). Differences between continuous data were assessed using unpaired 2-tailed t-test for normally distributed continuous variables, Mann-Whitney test for skewed variables, and chi-squared test (with Fisher’s exact test) for nominal variables. Cox proportional hazards model was used to identify predictors of appropriate therapy. All preprocedural potential confounders were entered into the model on the basis of known clinical relevance and significance <0.05 on univariate analysis. Differences between the number of ATP attempts were analyzed using Cochrane-Armitage test for trend for proportions and analysis of variance for continuous measures. Kaplan-Meier analysis was used to determine the incidence of appropriate shock, appropriate ATP, and inappropriate shock. Statistical analysis was carried out with JMP Pro version 12.1.0 (SAS Institute, Cary, NC, USA).

Results

Between April 2003 and March 2015, a total of 21 repaired TOF patients (62% male) underwent ICD implantation. Patient baseline characteristics are listed in Table 1. Enrolled patients had a mean age of 39±11 years, QRS duration ≥180 ms in 33%, and LVEF ≤35% in 14%. The initial implantation procedure was single-chamber ICD in 3 patients (14%), dual-chamber ICD in 16 patients (76%), and CRTD in 2 patients (10%). Thirteen patients (62%) had a single-coil lead. All devices were implanted in the pre-pectoral position. Defibrillation threshold testing was performed in 18 patients (86%), and the mean defibrillation threshold was 12.5±6.0 J. All patients achieved an adequate safety margin (≥10 J below the maximum output of the device). Baseline surgical characteristics are listed in Table 2. There were no intraprocedural complications.

Table 1. Baseline Subject Characteristics

Clinical variable	All patients (n=21)	Appropriate therapy (n=11)	No appropriate therapy (n=10)	P-value
Age at ICD implantation (years)	39±11	36±8	42±14	0.22
Male	13 (62)	7 (63)	6 (60)	0.86
BMI (kg/m2)	22.8±3.6	23.5±3.7	21.9±3.6	0.32
NYHA class	1.3±0.6	1.2±0.4	1.4±0.7	0.38
Documented CAD	0 (0)	0 (0)	0 (0)	–
Documented AT	5 (24)	2 (18)	3 (30)	0.52
β-blockers	15 (71)	7 (63)	8 (80)	0.40
ACEI or ARB	9 (43)	4 (36)	5 (50)	0.52
Amiodarone or sotalol	9 (43)	5 (45)	4 (40)	0.80
SBP (mmHg)	112±15	108±9	116±18	0.18
BNP (pg/dL)	154±200	74±58	243±262	0.051
Serum creatinine (mg/dL)	0.79±0.18	0.79±0.19	0.77±0.20	0.76
QRS duration (ms)	160±31	158±27	162±35	0.72
QTc interval (ms)	477±36	477±36	477±37	0.98
Moderate-severe RV dysfunction	5 (24)	2 (20)	3 (30)	0.60
LVEF (%)	49±11	52±13	45±8	0.16
Moderate-severe PR	5 (24)	2 (18)	3 (30)	0.52
Moderate-severe TR	3 (14)	1 (9)	2 (20)	0.47
Secondary prevention	19 (90)	10 (90)	9 (90)	0.94
Resuscitated cardiac arrest	3 (14)	1 (9)	2 (20)
Sustained VT	16 (76)	9 (81)	7 (70)
Primary prevention	2 (10)	1 (9)	1 (10)	0.94
Symptomatic non-sustained VT	2 (10)	1 (9)	1 (10)

Data given as mean±SD or n (%). ACEI, angiotensin-converting enzyme inhibitor; AT, atrial tachyarrhythmia; BMI, body mass index; BNP, B-type natriuretic peptide; CAD, coronary artery disease; LVEF, left ventricular ejection fraction; NYHA, New York Heart Association; PR, pulmonary regurgitation; RV, right ventricle; SBP, systolic blood pressure; TR, tricuspid regurgitation; VT, ventricular tachycardia.

Table 2. Surgical Characteristics

Clinical variable	All patients (n=21)	Appropriate therapy (n=11)	No appropriate therapy (n=10)	P-value
Age at corrective surgery (years)	9±7	7±5	12±8	0.14
Time from corrective surgery to ICD (years)	30±8	29±6	31±10	0.62
Prior palliative surgery	10 (48)	3 (27)	7 (70)	0.046
Blalock-Taussig shunt	6 (29)	2 (18)	4 (40)	0.26
Central shunt	2 (10)	1 (9)	1 (10)	0.94
Unifolization of MAPCA	2 (10)	0 (0)	2 (20)	0.073
Ventriculotomy	21 (100)	11 (100)	10 (100)	–
Corrective surgery	21 (100)	11 (100)	10 (100)	–
Non-transannular RVOT patch	3 (14)	3 (27)	0 (0)	0.037
Transannular RVOT patch	10 (48)	6 (54)	4 (40)	0.50
No patch	4 (19)	0 (0)	4 (40)	0.008
Extracardiac RV to PA conduit	2 (10)	1 (9)	1 (10)	0.94
Unknown	2 (10)	1 (9)	1 (10)	0.94
Cardiac surgery (n)	1.4±0.6	1.5±0.5	1.3±0.6	0.36

Data given as mean±SD or n (%). ICD, implantable cardioverter defibrillator; MAPCA, major aortopulmonary collateral artery; PA, pulmonary artery; RV, right ventricle; RVOT, right ventricular outflow tract.

Appropriate Therapy

During a median follow-up of 5.6 years (range, 2.6–8.5 years), 11 patients (52%) had one or more appropriate treatments. Appropriate ATP were delivered in 11 patients (52%), with appropriate shock in 5 patients (24%). Kaplan-Meier curves for freedom from appropriate shock, and appropriate ATP are shown in Figure 1. Freedom from appropriate shock was 95.2% at 1 year, 82.9% at 3 years, and 75.4% at 5 years (Figure 1A). Freedom from appropriate ATP was 71.4% at 1 year, 58.4% at 3 years, and 58.4% at 5 years (Figure 1A). To analyze the predictors of appropriate therapy, univariate analysis was performed using a Cox proportional hazards model. No clinical variables were associated with appropriate therapy.

Figure 1.

Kaplan-Meier analysis of (A) freedom from appropriate shock or appropriate anti-tachycardia pacing and (B) freedom from inappropriate shock. ATP, anti-tachycardia pacing; ICD, implantable cardioverter defibrillator.

ATP Effectiveness

During follow-up, 11 patients (52%) had a total of 382 appropriate treatments. Five patients had 24 appropriate treatments (6%) that were terminated by shock, and 11 patients had 358 appropriate treatments (94%) that were terminated by ATP. Of 382 appropriate treatments, 363 were ATP, of which 358 (98%) were successful. Acceleration occurred in 4 treatments (1.1%). Nineteen appropriate treatments involved shock without ATP. The mean period from ICD implantation to the initial appropriate treatment was 1.9±2.3 years. Therapy type distribution is shown in Figure 2. There was no difference in the termination of VT stratified by VT cycle length (Figure 3). ATP terminated 59 of 60 (98%) fast VT episodes (cycle length 250–320 ms) and 296 of 300 (98%) slow VT episodes (cycle length >320 ms), whereas cycle length in 3 episodes was unknown. The distribution of ATP attempts is shown in Figure 4. The first burst of ATP was effective in 81.5% of cases (296 of 363 episodes). As a result of programming successive bursts of ATP, ATP effectiveness increased to 93.7% with the second ATP attempt, to 97.5% with the third ATP attempt, and to 98.6% with the fourth or successive ATP attempt (P<0.0001, Cochran-Armitage trend test; Figure 5).

Figure 2.

Treatment type vs. ventricular tachycardia cycle length. ATP, anti-tachycardia pacing.

Figure 3.

Anti-tachycardia pacing (ATP) efficacy vs. ventricular tachycardia (VT) cycle length.

Figure 4.

Distribution of anti-tachycardia pacing (ATP) attempts.

Figure 5.

Effect of increasing number of anti-tachycardia pacing (ATP) bursts on effectiveness of ATP. Effectiveness of the first ATP was 81%, and it increased to 98% with successive ATP bursts (P<0.0001, for Cochran-Armitage trend test). Data presented are unadjusted rates. 1, 1-2, and 1-2-3, number of ATP bursts.

Inappropriate Therapy and Lead Complications

During follow-up, 5 patients (24%) had 7 inappropriate shocks, and 4 patients (19%) had 18 inappropriate ATP. The inappropriate shocks were delivered due to atrial tachyarrhythmia in 4 patients, and non-sustained VT in 1 patient. The inappropriate ATP were delivered due to atrial tachyarrhythmia in 3 patients, and non-sustained VT in 2 patients. Freedom from inappropriate shock was 90.5% at 1 year, 84.0% at 3 years, and 77.5% at 5 years (Figure 1B). Freedom from inappropriate ATP was 90.5% at 1 year, 90.5% at 3 years, and 90.5% at 5 years. Two patients had lead failure because of a recalled lead (Medtronic Sprint Fidelis lead). No inappropriate treatments were caused by this lead dysfunction.

Overall Survival

During a median follow-up of 5.6 years (range, 2.6–8.5 years), no patients died. One patient required surgical reoperation due to tricuspid regurgitation 4 months after ICD implantation. In this patient, right ventriculography showed a dilated RV (RV end-diastolic volume index, 147 mL/m²) with normal RV systolic function. Six patients required device replacement during the study period, which was due to elective replacement indicators (n=4), lead failure of a recalled lead (n=1), or upgrade to a dual-chamber ICD and lead failure of a recalled lead (n=1).

Reintervention After Repair Surgery

Six patients (28.5%) required surgical reoperation after repair surgery. The median period from repair surgery to reoperation was 18.2 years (range, 11.7–29.6 years). The reasons for surgical reoperation were pulmonary valve stenosis and regurgitation (n=1), tricuspid regurgitation (n=1), RV-pulmonary artery conduit stenosis (n=1), aortic regurgitation and subaortic stenosis (n=1), infective endocarditis (n=1), and residual ventricular septal defect (n=1).

Discussion

There are several important clinical observations that need to be made. First, ATP was successful in terminating 98% of VT episodes, and the success did not depend on VT cycle length in repaired TOF patients. The programming of multiple ATP attempts was associated with a clinically relevant reduction in high-energy shocks. Second, Japanese repaired TOF patients with ICD had a good prognosis.

ATP is recognized as an effective therapy for the termination of fast VT episodes. It is well established that ATP reduces painful high-energy shocks and improves quality of life.⁹ Traditionally, a single burst pacing sequence has been used in fast VT. Several recent studies have shown that multiple burst pacing sequences for fast VT (cycle length 250–320 ms) are safe and effective in ICD recipients.^10–12 Sivagangabalan et al showed that ATP efficacy was low in very fast VT (cycle length 200–250 ms).¹³ The safety of ATP delivery needs to be considered in very fast VT. The electrophysiological mechanism responsible for VT after surgically repaired TOF is typically a macro re-entrant RV circuit within the RV around scar tissue or prosthetic materials used during surgical repair.^2,14,15 Theoretically, any re-entrant VT can be terminated by a critically timed pacing stimulus that depolarizes the excitation gap. The duration of the excitation gap and the conduction time from the pacing stimulus site to the re-entrant circuit are the main factors influencing penetration of the excitation gap and termination of the arrhythmia.¹⁶ In repaired TOF patients with an ICD, the pacing stimulus site is RV, and the re-entrant circuit is typically RV. Polymorphic VT or VF could occur in approximately 20% of ventricular arrhythmia events in repaired TOF patients.² Schoels et al showed that ATP could significantly terminate monomorphic VT more often than polymorphic VT.¹⁷ Tuan et al showed that a smaller morphological variation, which means monomorphic VT, correlated with a higher probability of a successful ATP.¹⁸ In the present study, >70% of the patients had β-blockers, and more than 40% of the patients had either amiodarone or sotalol. Therefore, the present incidence of polymorphic VT might be lower than in previous studies, and high ATP efficacy is expected in repaired TOF patients. Few studies, however, have investigated the role of ATP in repaired TOF patients. Koyak et al noted that ATP was effective in 5 of 26 repaired TOF patients.³ In contrast, Witte et al found that ATP was highly effective in 4 of 4 repaired TOF patients.⁵ In the present study, ATP was highly effective in 9 of 11 patients in whom ATP was attempted. Additionally, there have been no previous studies on the efficacy of ATP in repaired TOF. In the present study, multiple ATP attempts were highly effective, independent of VT cycle length. The incidence of appropriate treatment is between 19% and 31% for follow-up periods of 1.9–5.5 years.^1–3,5,6 In the present study, the incidence of appropriate treatment was high (52%), because of the higher proportion of patients with secondary prevention than in previous studies, as well as the longer follow-up period. The incidence of appropriate shock, however, is in line with previous results. Some patient groups may benefit from multiple ATP attempts.

All-cause mortality is between 2% and 15% for follow-up periods of 1.9–5.5 years.^1–3,5,6 The main causes of death were congestive heart failure and sudden cardiac death. In the present study, the mortality was lower than in the previous reports. In Japan, conotruncal repair with small RV outflow patching, which was reported by Kurosawa et al, has been used for primary repair of TOF.¹⁹ This technique may have resulted in a shorter QRS duration and a lower incidence of RV dysfunction in the present study than in previous studies.^1,2,5 Additionally, in the present study, 6 patients required cardiac surgery in the mean period of 20.9 years from repair surgery. Previous data suggest that the need for reintervention increases after the second decade.²⁰ In Japan, Mizuno et al showed that pulmonary stenosis and pulmonary regurgitation are the most common reasons for reoperation.²¹ In the present study, surgical intervention was indicated at an appropriate time because all patients had regular follow-up with a cardiologist and a pediatric cardiologist with expertise in adult CHD. Thus, the all-cause mortality in the present study might be low.

The incidence of inappropriate shock is between 15% and 41% for follow-up periods of 1.9–5.5 years, predominantly because of atrial tachyarrhythmias.^1,2,5,6 Witte et al noted an incidence of inappropriate ATP of 20%.⁵ In the present study, inappropriate shock occurred in 24% of patients, and inappropriate ATP in 19% of patients. The incidence of inappropriate shock and ATP is in line with previous reports. Therefore, ICD device programming to reduce inappropriate shocks caused by atrial tachyarrhythmias should be considered.²² Atrial tachyarrhythmia ablation should be considered, not only in patients with documented atrial tachyarrhythmias before ICD implantation, but also in patients with atrial arrhythmia detected after ICD implantation.²³ The most prevalent implantation-related complication was lead failure. In patients with CHD, a high incidence of lead-related complications has been previously reported.^1,24,25 Implantation of an entirely subcutaneous ICD (S-ICD) may be considered in patients who do not require cardiac pacing, but experience in CHD is limited.²⁶ The present study has shown that multiple ATP may be highly effective in repaired TOF. Therefore, use of S-ICD without ATP capability should be carefully considered in repaired TOF patients.

Study Limitations

There are several limitations to the present study. First, this was a retrospective study with a small number of patients. Second, there was variation among operators in implantation technique. Third, ATP protocols and detection rates for ICD shock were not uniformly programmed, which introduces the potential for detection bias.

Conclusions

ICD was highly effective in repaired TOF patients despite the relatively large number of ICD treatments for each patient in this study. ATP could have an important role in the termination of malignant ventricular arrhythmias in this specific patient group. When an ICD is implanted, multiple ATP should be programmed for all VT episodes, regardless of cycle length. Additionally, use of the novel S-ICD without ATP capability should be carefully considered.

Acknowledgments

None.

Disclosures

The authors declare no conflicts of interest.

References

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