1328 OKAMURA H et al.

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1 1328 OKAMURA H et al. Circulation Journal ORIGINAL ARTICLE Official Journal of the Japanese Circulation Society Arrhythmia/Electrophysiology Right Parasternal Lead Placement Increases Eligibility for Subcutaneous Implantable Cardioverter Defibrillator Therapy in Adults With Congenital Heart Disease Hideo Okamura, MD; Christopher J. McLeod, MD, PhD; Christopher V. DeSimone, MD, PhD; Tracy L. Webster; Crystal R. Bonnichsen, MD; Martha Grogan, MD; Sabrina D. Phillips, MD; Heidi M. Connolly, MD; Naser M. Ammash, MD; Carole A. Warnes, MD; Paul A. Friedman, MD Background: The subcutaneous implantable cardioverter defibrillator (S-ICD) provides an attractive option for patients with congenital heart disease (CHD) in whom a transvenous defibrillator is contraindicated. Given the unusual cardiac anatomy and repolarization strain, the surface electrocardiogram (ECG) is frequently abnormal, potentially increasing the screen failure rate. Methods and Results: We prospectively screened 100 adult CHD patients regardless of the presence of clinical indication for ICD utilizing a standard left sternal lead placement, as well as a right parasternal position. Baseline patient and 12-lead ECG characteristics were examined to assess for predictors of screen failure. Average patient age was 48±14 years, average QRS duration was 134±37 ms, and 13 patients were pacemaker dependent. Using the standard left parasternal electrode position, 21 patients failed screening. Of these 21 patients with screen failure, 9 passed screening with the use of right parasternal electrode positioning, reducing screening failure rate from 21% to 12%. QT interval and inverted T wave anywhere in V2 V6 leads were found to be independent predictors of left parasternal screening failure (P=0.01 and P=0.04, respectively). Conclusions: Utilization of both left and right parasternal screening should be used in evaluation of CHD patients for S-ICD eligibility. ECG repolarization characteristics were also identified as novel predictors of screening failure in this group. (Circ J 2016; 80: ) Key Words: Congenital heart disease; Right parasternal screening; Screening; Subcutaneous implantable cardioverter defibrillator; T wave The population of adults with congenital heart disease (CHD) continues to grow and, despite the substantial advances in management over the last several decades, ventricular arrhythmia remains an important cause of mortality. 1,2 Consequently, many adults with CHD undergo implantable cardioverter defibrillator (ICD) implantation for primary or secondary prevention. 2 6 The subcutaneous implantable cardioverter defibrillator (S-ICD) provides an alternative in these patients when the traditional transvenous implant is commonly contraindicated or unfeasible secondary to venous anomalies or intracardiac shunts that introduce a risk of systemic thromboembolism from transvenous lead thrombus. Due to the absence of an electrode in contact with the myocardium, T-wave oversensing leading to inappropriate shock is a specific concern for the S-ICD. Screening using a modified electrocardiogram (ECG) with patches positioned over planned electrode sites (due to the equivalence of skin and subcutaneous electrodes) is required to ensure that the R-wave/ T-wave ratio is sufficiently large to avoid T-wave oversensing To detect ventricular arrhythmias, the S-ICD uses 1 of the 3 subcutaneous electrograms acquired between the 2 electrodes embedded in the subcutaneous lead and the defibrillator can. If the patient does not pass the screening ECG test in any of the 3 ECG vectors, S-ICD implantation is contraindicated due to the high risk of inappropriate shock. This T/R ratio is the major determinant of screening. The pass rate in non-congenital patients is generally reported at around 85 95%. 8,10,11 Although the S-ICD is especially well-designed for certain CHD syndromes, many patients may fail screening due to the unique anatomy and resultant surface ECG characteristics found in CHD. 2 The aim of this study was to investigate the screening failure rate in a series of adult patients with CHD. Additionally, given the variation in cardiac anatomy in these patients, Received February 14, 2016; revised manuscript received March 15, 2016; accepted March 21, 2016; released online April 22, 2016 Time for primary review: 17 days Division of Cardiovascular Diseases, Mayo Clinic, Rochester, MN, USA Mailing address: Christopher J. McLeod, MBChB, PhD, Department of Cardiovascular Medicine, Mayo Clinic, 200 First Street SW, Rochester, MN 55902, USA. mcleod.christopher@mayo.edu ISSN doi: /circj.CJ All rights are reserved to the Japanese Circulation Society. For permissions, please cj@j-circ.or.jp

2 Eligibility for SICD in CHD 1329 Figure 1. Positioning of the 3 electrodes. (Left) Left parasternal position: (1) (LA), 2 cm left of xiphoid process; (2) (RA), straight up 14 cm from (1) along the left side of the sternum; (3) (LL): left-side chest wall, mid-axillary line around the 5 6 intercostal space. (Right) Right parasternal position: (1) (LA), 2 cm right of xiphoid process; (2) (RA), straight up 14 cm from (1) along the right side of the sternum; and (3) (LL), same as the left parasternal position. Three electrocardiogram vectors: primary (III), secondary (II) and alternative (I) were recorded using 3 electrodes. LA, left arm electrode; LL, left leg electrode; RA, right arm electrode. which can manifest on surface ECG as large T waves with vectors directed to the left of the sternum, we hypothesized that a right parasternal lead position may reduce screening failure rate. Methods Patients We prospectively screened 100 adult CHD patients regardless of the presence of clinical indication for ICD in the Adult Congenital Clinic at Mayo Clinic, Rochester, between March and July We included patients with previously implanted pacemaker or ICD. Patients <18 years old were excluded. All patients consented for participation and the study was approved by the Mayo Clinic institutional review board (IRB ). Screening ECG Test for S-ICD Screening ECG were recorded using a proprietary programmer provided by Boston Scientific (Marlborough, MA, USA). Electrodes were placed at 3 positions: (1) 2 cm to the left of the xiphoid process; (2) 14 cm directly above position 1; and (3) left mid-axillary line at approximately the 5 6 intercostal space (Figure 1, left panel, left parasternal position). These positions correspond to the S-ICD electrode positions after device implantation, and are routinely used for implant screening for potential S-ICD recipients. Utilizing these 3 electrode positions, 3 vectors were evaluated in both the supine and standing positions and ECG were recorded. In addition, ECG were also recorded after placement of 2 electrodes on the right side of the xiphoid process (Figure 1, right panel, right parasternal position). This was performed to determine whether a right-sided implant would pass the screening test. When it was difficult for patients to stand for ECG recording, ECG was obtained in the sitting position instead. Eligibility for S-ICD was judged using the screening tool provided by Boston Scientific. Data Collection Demographic data such as age, gender, diagnosis, body weight and body mass index (BMI) were obtained from electronic medical records. The complexity of the underlying CHD was defined according to the task force statement on CHD published in ,12 Additionally, ECG parameters, such as QRS width, QT interval, and dependency on ventricular pacing were obtained from the patients most recent 12-lead ECG when available. Bundle branch block in patients with QRS >120 ms was defined based on the standard definition. 13 Statistical Analysis Categorical data are expressed as percentages and were analyzed using chi-squared test or Fisher s exact test when appropriate. Continuous variables are expressed as mean ± SD and compared between groups using Student s t-test. Mann- Whitney U-test was applied when the data were not normally distributed. Potential predictors of screen failure in left parasternal screening were assessed on univariate logistic regression analysis. Factors associated with screening failure with P<0.05 were implemented in a multivariate analysis model. With at least 10 outcomes required for each to be included as an independent variable in the model, only 2 of 5 univariately significant variables (QT interval and inverted T wave anywhere in leads V2 V6) were used. Given that 4 of them (QRS width, QRS >120 ms, inverted T wave anywhere in leads V2 V6 and dependency on ventricular pacing) were highly correlated, inverted T wave anywhere in leads V2 V6 was selected based on clinical significance to be included in the multivariate logistic regression model. Receiver operating characteristics (ROC) analysis was used to evaluate the optimal cut-offs for predicting left-side screening failure. All tests were 2-sided, and P<0.05 was considered statistically significant. Data were analyzed using JMP (version , SAS, Cary, NC, USA).

3 1330 OKAMURA H et al. Table 1. Congenital Heart Disease Background Congenital heart disease n Great complexity Single ventricle 6 Transposition of great arteries 7 Pulmonary atresia 4 Tricuspid atresia 3 Truncus arteriosus 1 Subtotal 21 Simple or moderate severity Bicuspid aortic valve 12 Coarctation of the aorta 5 Atrial septum defect 10 Pulmonary stenosis 9 Ventricular septum defect 2 Patent ductus arteriosus 1 Tetralogy of Fallot 22 Ebstein s anomaly 11 Atrioventricular canal defects 4 Anomalous pulmonary venous drainage 1 Sinus venosus atrial septal defect 2 Subtotal 79 Total 100 Results Patient Characteristics Composition of CHD and complexity are listed in Table 1. Twenty-one patients were defined as having complex CHD. Baseline subject characteristics are listed in Table 2. Twentytwo patients had a pacemaker or ICD, and 13 patients were dependent on ventricular pacing. In 1 patient with pulmonary stenosis accompanied with dextrocardia, electrodes in the screening ECG as well as the 12-lead ECG were positioned right and left reversed supposing the device implantation on the right-side chest, which resulted in pass on both sides. Screening ECG Table 3 summarizes the results of the screening ECG both on the left and right parasternal electrode position. Standard left parasternal screening failed in 21 patients (21%), but 9 of these patients subsequently passed right parasternal screening, and thus decreased the failure rate from 21% to 12%. Figure 2 shows a typical screening surface ECG from a patient who failed left parasternal lead position in all ECG vectors, but passed right parasternal screening both in the supine and in the standing positions. Predictors of Failure on Screening ECG Table 2 also lists the clinical characteristics for patients who passed left parasternal screening (n=79) vs. those who failed (n=21). QRS and QT duration were significantly longer in the subgroup who failed screening compared with those who passed (165.7±28.4 ms vs ±35.1 ms, P<0.001; and 466.2±34.3 ms vs ±45.4 ms, P<0.01, respectively). There was a significant difference in patients who failed vs. those who passed standard left-sided screening for QRS duration >120 ms (95% vs. 46%, P<0.001), but the distribution of bundle branch block pattern in patients with QRS >120 ms was not significantly different (P=0.59). In addition, there were more patients in the failed subgroup with inverted T wave anywhere in leads V2 V6 (90% vs. 63%, P=0.02) and dependency on ventricular pacing (29% vs. 9%, P=0.03). The results of both univariate and multivariate analysis for comparison of factors associated with left screening failure are given in Table 4. We identified 5 univariate significant predictors but, due to the limited number of patients who failed standard screening (n=21), only 2 parameters could be tested using a multivariate logistic regression model. With 4 of them (QRS duration, QRS >120 ms, inverted T wave anywhere in leads V2 V6 and dependency on ventricular pacing) being Table 2. Patient Characteristics vs. Pass for Left Parasternal Screening All patients (n=100) Pass (n=79) Fail (n=21) P-value Age (years) 48.0± ± ± Male 58 (58) 48 (61) 10 (48) 0.28 BW (kg) 82.4± ± ± BMI (kg/m 2 ) 27.8± ± ± Diseases of great complexity 21 (21) 18 (23) 3 (14) 0.38 QRS (ms) 134.2± ± ±28.4 <0.001 (n=99) (n=78) (n=21) QRS >120 ms 56 (56) 36 (46) 20 (95) <0.001 CLBBB CRBBB NSIVCD QT (ms) 440.8± ± ±34.3 <0.01 (n=99) (n=78) (n=21) Inverted T wave between V2 and V6 68 (69) 49 (63) 19 (90) 0.02 (n=99) (n=78) (n=21) Existing pacemaker/icd 22 (22) 15 (19) 7 (33) 0.17 Dependent on ventricular pacing 13 (13) 7 (9) 6 (29) 0.03 Data given as n (%) or mean ± SD. No. patients for whom data were available. BMI, body mass index; BW, body weight; CLBBB, complete left bundle branch block; CRBBB, complete right bundle branch block; ICD, implantable cardioverter defibrillator; NSIVCD, non-specific interventricular conduction disturbance.

4 Eligibility for SICD in CHD 1331 correlated, based on clinical significance, QT interval and inverted T wave anywhere in leads V2 V6 were selected for implementation in the multivariate logistic regression model. After adjusting for each other, QT interval (OR, 23.19; 95% CI: , P=0.01) and inverted T wave anywhere in leads V2 V6 (OR, 4.16; 95% CI: , P=0.04) were still independently associated with screening failure. On ROC analysis, QT interval >422 ms predicted left-side screening failure with an area under curve (AUC) of 0.714, sensitivity of 95.2%, and specificity of 61.2%; and inverted T wave anywhere between V2 and V6 leads predicted left-side screening failure with an AUC of 0.638, sensitivity of 90.5% and specificity of 72.3% (Figure 3). In contrast, patients who failed the right parasternal screening (n=24) were lighter (74.3±4.3 vs. 85.0±2.4 kg, P=0.02), had smaller BMI (25.2±1.3 vs. 28.6±0.7 kg/m 2, P=0.02) and had wider QRS (152.8±7.4 vs ±4.2 ms, P<0.01) than those who passed the right parasternal screening (n=76). On multivariate logistic regression modeling, QRS was the only independent predictor for right parasternal screening failure. Discussion In this prospective investigation, we found that a substantial number of adult CHD patients (21%) are ineligible for S-ICD based on standard left-sided screening. Table 3. Screening ECG Results Left pass Left failure Total Right pass Right failure Total ECG, electrocardiogram; Left, left parasternal screening; Right, right parasternal screening. The high rate of screen failure is most likely secondary to the altered cardiac anatomy such as chamber enlargement, mechanical strain and augmented repolarization, cardiac position in the chest and relation to standard ECG positioning, all of which may result in prominent and/or non-traditional T-wave morphology. 2,14 The presence of inverted T wave anywhere in V2 V6 (often seen in patients with bundle branch block or dependent on ventricular pacing), appears to be predictive of such failure. Importantly, a significant number of patients who failed leftsided screening were found to remain as candidates for S-ICD implantation if a right-sided lead position was performed. This may be explained by the smaller repolarization vector found from the right side of the sternum, thus lowering the risk of T-wave oversensing on screening ECG. Figure 2. Typical case of effective right parasternal screening. The patient (44-year-old woman with Ebstein s anomaly) had failed left parasternal screening in all electrocardiogram vectors (arrows) but passed right parasternal screening both in the supine and standing positions.

5 1332 OKAMURA H et al. Table 4. Significant Factors of Screening Failure Factor Univariate logistic regression Multivariate logistic regression OR 95% CI P-value OR 95% CI P-value Age (per 10 years) Sex (male) BW (per 10 kg) BMI (per 10 kg/m 2 ) Diseases of great complexity QRS duration (per 10 ms) <0.001 QRS >120 ms <0.001 QT interval (per 20 ms) < Inverted T wave between V2 and V < Existing pacemaker/icd Dependent on ventricular pacing Abbreviations as in Table 2. Figure 3. Receiver operating characteristics (ROC) analysis for left-side screening failure: (A) QT interval; (B) T-wave inversion anywhere in lead V2 V6. (A) Area under the curve (AUC) was 0.714, and QT interval cut-off >422 ms predicted left-side screening failure with a sensitivity of 95.2% and specificity of 61.2%. (B) T-wave inversion anywhere in lead V2 V6 had an AUC of 0.638, sensitivity of 90.5% and specificity of 72.3%. There are several unique and important considerations regarding implantation of an ICD in patients with CHD. These patients are relatively young compared with most ICD recipients, and therefore the patient s vasculature will be exposed to foreign material for years, and be at risk for infection, erosion, vascular stenosis, and thrombosis. In addition, with transvenous systems in young patients, the lead will be exposed to the repetitive and damaging effects of cardiac motion for years. 15 Furthermore, implanted leads are also typically exposed to mechanical trauma given the higher levels of activity in this younger age group, and therefore have a higher incidence of lead fracture This patient group also will require more generator replacements over the course of a lifetime, and thus have an increased chance of pocket or bloodstream infection, along with the resultant higher likelihood of requiring device system extraction. 19 Furthermore, transvenous lead implantation via a standard superior vena cava route may not be possible due to the absence of a connection to the right ventricle (eg, following a Glenn or bicavopulmonary anastomosis) or may be contraindicated due to the presence of intracardiac shunting, which can result in thromboembolic stroke from lead thrombus. 2,20,21 For these reasons, the S-ICD, which does not require transvenous lead placement, provides an attractive treatment option for many CHD patients. Given that the lead is placed outside the thoracic cage, it is subject to much gentler and less frequent excursions of respiration. That, combined with a rugged design (due to the lack of a lumen because the lead does not navigate the vascular space and does not require stylets), results in anticipated longevity of the device lead. Moreover,

6 Eligibility for SICD in CHD 1333 when infections occur in patients with S-ICD, they have not resulted in sepsis (a particularly threatening condition in congenital patients with conduits and/or prosthetic valves), because the entire system is extravascular. Recognizing the caveat that this approach does not provide chronic pacing support, the efficacy of S-ICD has been proven in multiple studies Eligibility in CHD Patients for S-ICD The potential eligibility of CHD patients for S-ICD has been reported in a small 30-patient cohort that screened 10 patients with tetralogy of Fallot, 10 patients with transposition of great arteries and 10 patients with single ventricle/fontan circulation. 14 This screening was compared with 10 control patients without CHD, and it was found that 87% of CHD patients vs. 100% of the controls met S-ICD eligibility. These authors found a non-significant difference between the 2 groups. In contrast to the present study, patients with permanent pacing were excluded. In the present study, the failure rate for screening ECG was found to be 21%, and those with permanent pacing were also included to provide a more real world insight, given that patients with CHD frequently require pacing and that S-ICD devices have been implanted in patients with pacemakers in place. 29 Furthermore, the present cohort encompassed a wide variety of CHD syndromes, including 13 patients with ventricular paced rhythms. Importantly, 6 patients (46%) with ventricular pacing failed the screening; 3 of those patients were eligible for a right-sided system. The failure rate of 21% was significant in this cohort of 100 patients, and is higher than in other reports on acquired heart disease (approximately 10%). 8,10,11 Efficacy of Right Parasternal Lead Placement In this study, we evaluated right-sided electrode placement for T-wave sensing. The only independent predictor for right-side screening failure was wider QRS, which could differentiate the results from left-side screening. The addition of this preemptive screening step substantially reduced the failure rate from 21% to 12%. Evaluation of the ECG vector from these right-sided oriented leads is not known to reduce the sensitivity of R-wave detection and chiefly affects over-detection of the T wave. The efficacy of right parasternal lead position in patients with hypertrophic cardiomyopathy has been previously reported. 30 In that study in a small cohort, 2 of 5 patients who failed left parasternal screening during exercise and 8 of 28 patients who failed with paced complexes passed screening with right parasternal electrodes. This decreased the failure rate by 10 and 20%, respectively. Figure 4 shows a chest X-ray (after S-ICD implantation) in a patient who failed left parasternal screening but who passed right parasternal screening and subsequently underwent S-ICD implantation with the defibrillation lead along the right side of the sternum. Defibrillation testing during the procedure was successful with a 65-J shock terminating ventricular fibrillation (VF). Chan et al reported a case in which the right parasternal position resolved the tall T wave detected in the left parasternal position. 31 In that study, VF was also successfully converted with 65-J standard polarity shock during the procedure. S-ICD Eligibility in Patients Requiring Cardiac Pacing Patients who require permanent pacing support are not candidates for isolated S-ICD implantation but, in patients with CHD, it is not rare to encounter patients with longstanding epicardial pacing systems who develop an ICD indication, or Figure 4. Chest X-ray in a patient in whom the defibrillation coil was placed along the right side of the sternum. This patient (background of pulmonary atresia) had failed left parasternal screening but passed right parasternal screening. for patients with transvenous pacemakers to lack vascular access. ICD sensing is an important concern in patient with pacemakers. With transvenous systems, separate pacemaker and ICD systems could result in inappropriate shock due to spike over-counting or underdetection of VF due to sensing spikes as QRS complexes. 32 Currently, there is limited experience with S-ICD therapy in patients with pre-existing pacemakers. In both circumstances, S-ICD had been placed, with subsequent appropriate detection and termination of VF by the S-ICD. 29 Therapy delay was absent and no inappropriate shocks delivered. To avoid undersensing of tachycardia and delayed appropriate therapy, avoidance of large unipolar pacing spikes is fundamental and bipolar pacing should be used preferentially for both atrial and ventricular pacing. The decision to consider this management strategy entailing 2 cardiac devices remains highly individualized and nuanced based on the patient s anatomy, mode of pacing, location of the leads and the paced QRS complex. Inverted T Wave in Precordial Lead as Predictor of Screening Failure We found that inverted T wave in any of leads V2 V6 or prolonged QT interval predicts failure of left parasternal screening in patients with CHD. This correlates with previous reports (in patients with hypertrophic cardiomyopathy) in which prolonged QT interval was also an independent predictor for screening failure and also an independent predictor of inappropriate shock (largely due to T-wave oversensing). 8,33 Putatively, the diurnal change of T-wave morphology in patients with hypertrophic cardiomyopathy 34 might explain the inappropriate shock due to T-wave oversensing, which cannot be detected on screening ECG alone. Patients with Brugada syndrome at high risk of VF should also be considered for S-ICD implantation (give their young age), 35 but the clinician should be aware that a positive ST-T segment change in precordial leads during class I blockade has been reported to indicate failure for S-ICD on screening ECG. 36 Careful

7 1334 OKAMURA H et al. monitoring of T-wave oversensing appears to be necessary even after S-ICD implantation in patients with inverted T wave in the precordial leads. Study Limitations Although this is the largest study to date on eligibility for S-ICD in CHD patients, the small number of patients who failed the screening (n=21) was a significant limitation for the univariate and multivariate analysis. ICD indication was not required for study inclusion; thus, it is possible that patients with CHD who require ICD may have different screen failure rates than found in the present study. Another limitation was the paucity of information regarding the impact of right parasternal lead placement on defibrillation threshold (DFT). In the available small experience with right parasternal lead placement, successful defibrillation with 65 J has been reported. 31 A study on defibrillation efficacy of S-ICD using a computer simulation model reported that DFT for the coil lead paced at the right parasternal margin may be lower than that for the coil lead placed at the left parasternal margin. 37 Additionally, a screening ECG test result cannot guarantee the absence of inappropriate shock due to T-wave oversensing after S-ICD implantation. We tested screening ECG in the supine and standing positions only at rest; screening ECG during exercise may be helpful to detect T-wave oversensing. 30 Conclusions This study identified a high eligibility failure rate with standard left-sided screening in adults with CHD. Use of bilateral parasternal ECG screening increases S-ICD eligibility in adult patients in this group, and potentially should be considered in all S-ICD candidates. Interestingly, inverted T wave in precordial leads as well as QT prolongation were strongly associated with screen failure, and may facilitate use of standard 12-lead ECG to identify individuals who are not S-ICD candidates. Acknowledgments We thank Mrs Patricia C. Roth and Mrs Mary L. Silhasek, registered nurses, and Mrs Jennifer L. Dugan, research coordinator in the Department of Cardiovascular Diseases, Mayo Clinic, Rochester, MN, USA, for enrolling the patients in this study. Disclosures Okamura H is a recipient of the Medtronic Japan Fellowship for Young Japanese Investigator from the Japanese Heart Rhythm Society. This publication was supported by Grant Number UL1TR from the National Center for Advancing Translational Sciences (NCATS). The contents of this paper are solely the responsibility of the authors and do not necessarily represent the official views of the NIH. References 1. Goossens E, Fernandes SM, Landzberg MJ, Moons P. Implementation of the American College of Cardiology/American Heart Association 2008 guidelines for the management of adults with congenital heart disease. Am J Cardiol 2015; 116: Warnes CA, Williams RG, Bashore TM, Child JS, Connolly HM, Dearani JA, et al. ACC/AHA 2008 guidelines for the management of adults with congenital heart disease: Executive summary: A report of the American College of Cardiology/American Heart Association task force on practice guidelines. Circulation 2008; 118: Gatzoulis MA, Balaji S, Webber SA, Siu SC, Hokanson JS, Poile C, et al. Risk factors for arrhythmia and sudden cardiac death late after repair of tetralogy of Fallot: A multicentre study. Lancet 2000; 356: Oechslin EN, Harrison DA, Connelly MS, Webb GD, Siu SC. Mode of death in adults with congenital heart disease. Am J Cardiol 2000; 86: Silka MJ, Hardy BG, Menashe VD, Morris CD. A population-based prospective evaluation of risk of sudden cardiac death after operation for common congenital heart defects. J Am Coll Cardiol 1998; 32: Gallego P, Gonzalez AE, Sanchez-Recalde A, Peinado R, Polo L, Gomez-Rubin C, et al. Incidence and predictors of sudden cardiac arrest in adults with congenital heart defects repaired before adult life. Am J Cardiol 2012; 110: Kooiman KM, Knops RE, Olde Nordkamp L, Wilde AA, de Groot JR. Inappropriate subcutaneous implantable cardioverter-defibrillator shocks due to T-wave oversensing can be prevented: Implications for management. Heart Rhythm 2014; 11: Olde Nordkamp LR, Warnaars JL, Kooiman KM, de Groot JR, Rosenmoller BR, Wilde AA, et al. Which patients are not suitable for a subcutaneous ICD: Incidence and predictors of failed QRS-Twave morphology screening. J Cardiovasc Electrophysiol 2014; 25: Olde Nordkamp LR, Brouwer TF, Barr C, Theuns DA, Boersma LV, Johansen JB, et al. Inappropriate shocks in the subcutaneous ICD: Incidence, predictors and management. Int J Cardiol 2015; 195: Randles DA, Hawkins NM, Shaw M, Patwala AY, Pettit SJ, Wright DJ. How many patients fulfil the surface electrocardiogram criteria for subcutaneous implantable cardioverter-defibrillator implantation? Europace 2014; 16: Groh CA, Sharma S, Pelchovitz DJ, Bhave PD, Rhyner J, Verma N, et al. Use of an electrocardiographic screening tool to determine candidacy for a subcutaneous implantable cardioverter-defibrillator. Heart Rhythm 2014; 11: Warnes CA, Liberthson R, Danielson GK, Dore A, Harris L, Hoffman JI, et al. Task force 1: The changing profile of congenital heart disease in adult life. J Am Coll Cardiol 2001; 37: Surawicz B, Childers R, Deal BJ, Gettes LS, Bailey JJ, Gorgels A, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: Part III: Intraventricular conduction disturbances. Circulation 2009; 119: e235 e240, doi: /CIRCULATIONAHA Zeb M, Curzen N, Veldtman G, Yue A, Roberts P, Wilson D, et al. Potential eligibility of congenital heart disease patients for subcutaneous implantable cardioverter-defibrillator based on surface electrocardiogram mapping. Europace 2015; 17: Khairy P, Harris L, Landzberg MJ, Viswanathan S, Barlow A, Gatzoulis MA, et al. Implantable cardioverter-defibrillators in tetralogy of Fallot. Circulation 2008; 117: Janson CM, Patel AR, Bonney WJ, Smoots K, Shah MJ. Implantable cardioverter-defibrillator lead failure in children and young adults: A matter of lead diameter or lead design? J Am Coll Cardiol 2014; 63: Alter P, Waldhans S, Plachta E, Moosdorf R, Grimm W. Complications of implantable cardioverter defibrillator therapy in 440 consecutive patients. Pacing Clin Electrophysiol 2005; 28: Atallah J, Erickson CC, Cecchin F, Dubin AM, Law IH, Cohen MI, et al. Multi-institutional study of implantable defibrillator lead performance in children and young adults: Results of the pediatric lead extractability and survival evaluation (PLEASE) study. Circulation 2013; 127: Wilkoff BL, Love CJ, Byrd CL, Bongiorni MG, Carrillo RG, Crossley GH, et al. Transvenous lead extraction: Heart Rhythm society expert consensus on facilities, training, indications, and patient management. Heart Rhythm 2009; 6: DeSimone CV, Friedman PA, Noheria A, Patel NA, DeSimone DC, Bdeir S, et al. Stroke or transient ischemic attack in patients with transvenous pacemaker or defibrillator and echocardiographically detected patent foramen ovale. Circulation 2013; 128: Phillips SD, Bonnichsen CR, McLeod CJ, Ammash NM, Burkhart HM, Connolly HM. Adults with congenital heart disease and previous intervention. Curr Probl Cardiol 2013; 38: Aydin A, Hartel F, Schluter M, Butter C, Kobe J, Seifert M, et al. Shock efficacy of subcutaneous implantable cardioverter-defibrillator for prevention of sudden cardiac death: Initial multicenter experience. Circ Arrhythm Electrophysiol 2012; 5: Burke MC, Gold MR, Knight BP, Barr CS, Theuns DA, Boersma LV, et al. Safety and efficacy of the totally subcutaneous implantable defibrillator: 2-year results from a pooled analysis of the IDE study and EFFORTLESS registry. J Am Coll Cardiol 2015; 65: Bardy GH, Smith WM, Hood MA, Crozier IG, Melton IC, Jordaens L, et al. An entirely subcutaneous implantable cardioverter-defibrillator. N Engl J Med 2010; 363: Jarman JW, Todd DM. United Kingdom national experience of

8 Eligibility for SICD in CHD 1335 entirely subcutaneous implantable cardioverter-defibrillator technology: Important lessons to learn. Europace 2013; 15: Kobe J, Reinke F, Meyer C, Shin DI, Martens E, Kaab S, et al. Implantation and follow-up of totally subcutaneous versus conventional implantable cardioverter-defibrillators: A multicenter casecontrol study. Heart Rhythm 2013; 10: Lambiase PD, Barr C, Theuns DA, Knops R, Neuzil P, Johansen JB, et al. Worldwide experience with a totally subcutaneous implantable defibrillator: Early results from the EFFORTLESS S-ICD registry. Eur Heart J 2014; 35: Weiss R, Knight BP, Gold MR, Leon AR, Herre JM, Hood M, et al. Safety and efficacy of a totally subcutaneous implantable-cardioverter defibrillator. Circulation 2013; 128: Kuschyk J, Stach K, Tulumen E, Rudic B, Liebe V, Schimpf R, et al. Subcutaneous implantable cardioverter-defibrillator: First singlecenter experience with other cardiac implantable electronic devices. Heart Rhythm 2015; 12: Francia P, Adduci C, Palano F, Semprini L, Serdoz A, Montesanti D, et al. Eligibility for the subcutaneous implantable cardioverterdefibrillator in patients with hypertrophic cardiomyopathy. J Cardiovasc Electrophysiol 2015; 26: Chan NY, Yuen HC, Mok NS. Right parasternal electrode configuration converts a failed electrocardiographic screening to a pass for subcutaneous implantable cardioverter-defibrillator implantation. Heart Lung Circ 2015; 24: e203 e205, doi: /j.hlc Glikson M, Trusty JM, Grice SK, Hayes DL, Hammill SC, Stanton MS. Importance of pacemaker noise reversion as a potential mechanism of pacemaker-icd interactions. Pacing Clin Electrophysiol 1998; 21: Frommeyer G, Dechering DG, Zumhagen S, Loher A, Kobe J, Eckardt L, et al. Long-term follow-up of subcutaneous ICD systems in patients with hypertrophic cardiomyopathy: A single-center experience. Clin Res Cardiol 2016; 105: Iida K, Sugishita Y, Yukisada K, Ito I. Diurnal change of giant negative T wave in patients with hypertrophic cardiomyopathy. Clin Cardiol 1990; 13: Okamura H, Kamakura T, Morita H, Tokioka K, Nakajima I, Wada M, et al. Risk stratification in patients with Brugada syndrome without previous cardiac arrest: Prognostic value of combined risk factors. Circ J 2015; 79: Conte G, Regoli F, Moccetti T, Auricchio A. Subcutaneous implantable cardioverter-defibrillator and drug-induced Brugada syndrome: The importance of repeat morphology analysis during ajmaline challenge. Eur Heart J 2015 November 3, doi: /eurheartj/ehv Noro M, Zhu X, Enomoto Y, Asami M, Ishii R, Toyoda Y, et al. Efficacy and myocardial injury with subcutaneous implantable cardioverter defibrillators: Computer simulation of defibrillation shock conduction. Circ J 2015; 80: