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Shockingly shiny shoes – inappropriate discharge from a subcutaneous defibrillator.

Open AccessPublished:November 23, 2022DOI:https://doi.org/10.1016/j.hrcr.2022.11.009

      Keywords

      Introduction

      Inappropriate shocks from subcutaneous implantable cardiac defibrillators (S-ICD) have been a common problem, but their incidence has decreased with contemporary devices, programming, and algorithms. We report an unusual cause for an inappropriate S-ICD shock.

      Case Presentation

      A 41-year-old male endurance athlete experienced a syncopal episode whilst participating in a cycling race. An automated external defibrillator detected a shockable rhythm and successfully defibrillated the patient. His initial ECG showed inferior Q-waves with anterolateral ST depression, however his serum troponin remained within the normal range. Transthoracic echocardiography showed a left ventricular ejection fraction (LVEF) of 30% with inferior regional wall motion abnormalities. Coronary angiography demonstrated a well-collateralized chronic total occlusion of the right coronary artery and a moderate stenosis of the left anterior descending coronary artery. Coronary artery bypass grafting was performed with grafts to the left anterior descending, 1st diagonal, and posterolateral and posterior descending branches of the right coronary artery. Subsequent MRI scanning showed recovery of LV systolic function (LVEF 50%) with late gadolinium enhancement involving the inferoseptal and inferior walls of <50% mural extent.
      A decision was made to implant a secondary prevention defibrillator in view of his cardiac arrest without evidence of an acute coronary occlusion or reversible precipitant with significant residual myocardial scar. As he was young and had no indication for pacing, an S-ICD was implanted with right parasternal lead placement using a three-incision technique (Generator: Boston Scientific Emblem A209, Lead: Boston Scientific 3401 (Figure 1). At implant the device sensing was excellent from the primary and secondary vectors but poor from the alternate vector. Defibrillation threshold testing could not be performed due to non-inducibility of VF. The device was programmed according to manufacturer’s recommendations with a shock zone of 240 beats per min, and a conditional shock zone 220 beats per min. Sensing was programmed via the secondary vector with SmartPass filtering enabled.
      Figure thumbnail gr1
      Figure 1Chest X-ray taken following implant of subcutaneous ICD demonstrating right parasternal lead placement.
      Four years following device implant, the patient abruptly experienced a single unheralded shock from his ICD while polishing his shoes. Shoe-polishing was an uncommon activity for him. There had been no recent changes to device programming or body habitus prior to this event. Figure 2 shows the electrograms recorded at this time downloaded via remote monitor. During the episode repetitive myopotential noise is observed. During a temporary pause in physical activity the myopotentials resolve before resuming with re-initiation of upper extremity motion. While the myopotentials were initially under-detected, the subsequent sensed potentials were detected in the therapy zone triggering an ICD shock.
      Figure thumbnail gr2
      Figure 2Electrograms demonstrating myopotentials leading to oversensensing and inappropriate therapy from S-ICD
      On review in the cardiac device clinic the electrical noise from pectoral muscle activity was reproducible during shoulder movement (Figure 3). Oversensing of myopotentials was present in both the secondary and alternate vectors but not the primary vector. No noise, oversensing, or device malfunction had been identified on previous device downloads.
      Figure thumbnail gr3
      Figure 3Electrograms recorded in clinic during shoulder movement from primary vector (A), secondary vector (B) and alternate vector (C).
      The device was reprogrammed to sense via the primary vector. No further inappropriate shocks have occurred during follow up.

      Discussion

      The subcutaneous implantable cardioverter-defibrillator (S-ICD) is an alternative to transvenous implantable cardioverter-defibrillators. Despite their demonstrated effectiveness in the treatment and prevention of arrhythmic death, conventional transvenous ICD systems are associated with considerable morbidity due to endovascular lead failure. In response, the S-ICD has been specifically developed to address the risk of lead failure, a major limitation of transvenous ICDs. In contrast to the endovascular leads, the S-ICD lead lacks a central lumen, providing increased tensile strength. Moreover, extrathoracic placement of the S-ICD lead exposes the lead to less environmental stress. While these features have been associated with lower lead failure rates, extrathoracic lead placement has been associated with higher rates of inappropriate shocks (10% to 26%, or 2-5x the rate of traditional transvenous ICDs).
      • Weiss R.
      • Knight B.P.
      • Gold M.R.
      • Leon A.R.
      • Herre J.M.
      • Hood M.
      • Rashtian M.
      • Kremers M.
      • Crozier I.
      • Lee K.L.
      • Smith W.
      • Burke M.C.
      Safety and efficacy of a totally subcutaneous implantable-cardioverter defibrillator.
      • Gold M.R.
      • Weiss R.
      • Theuns D.A.
      • Smith W.
      • Leon A.
      • Knight B.P.
      • Carter N.
      • Husby M.
      • Burke M.C.
      Use of a discrimination algorithm to reduce inappropriate shocks with a subcutaneous implantable cardioverter-defibrillator.
      • Moss A.J.
      • Schuger C.
      • Beck C.A.
      • et al.
      Reduction in inappropriate therapy and mortality through ICD programming.
      In contrast to traditional transvenous ICDs, which detect local intracardiac myopotentials, the S-ICD system detects changes in the ventricular rate using subsurface electrocardiography, rendering the system susceptible to arrhythmia misdiagnosis due to errors in discrimination or oversensing.
      Inappropriate ICD shocks can occur due to lack of discrimination (e.g., supraventricular or sinus tachycardia), oversensing of intrinsic cardiac activity (e.g., oversensing of T-waves and P-waves), or oversensing of extrinsic physiologic (e.g., myopotentials) and non-physiologic noise (e.g., electrical noise from the device header or lead, external interference). T-wave oversensing is the most common cause for inappropriate shocks in S-ICD recipients
      • Olde Nordkamp L.R.
      • Brouwer T.F.
      • Barr C.
      • Theuns D.A.
      • Boersma L.V.
      • Johansen J.B.
      • Neuzil P.
      • Wilde A.A.
      • Carter N.
      • Husby M.
      • Lambiase P.D.
      • Knops R.E.
      Inappropriate shocks in the subcutaneous ICD: Incidence, predictors and management.
      .
      Strategies to minimize inappropriate shocks with the S-ICD include: 1) Rigorous pre-implant electrocardiographic screening with optimization of vectors to achieve the best signal-to-noise ratio, which has significantly reduced the incidence of inappropriate shocks due to T-wave oversensing at the expense of rendering ∼10% of patients ineligible to receive an S-ICD
      • Groh C.A.
      • Sharma S.
      • Pelchovitz D.J.
      • Bhave P.D.
      • Rhyner J.
      • Verma N.
      • Arora R.
      • Chicos A.B.
      • Kim S.S.
      • Lin A.C.
      • Passman R.S.
      • Knight B.P.
      Use of an electrocardiographic screening tool to determine candidacy for a subcutaneous implantable cardioverter-defibrillator.
      ; 2) Meticulous surgical technique including lead anchoring (e.g. suture sleeve to prevent post-implant lead movement

      Olde Nordkamp LR, Dabiri Abkenari L, Boersma LV, Maass AH, de Groot JR, van Oostrom AJ, Theuns DA, Jordaens LJ, Wilde AA, Knops RE. The entirely subcutaneous implantable cardioverter-defibrillator: initial clinical experience in a large Dutch cohort. J Am Coll Cardiol Nov 6 2012;60:1933-1939.

      ) and complete expulsion of subcutaneous air
      • Ali H.
      • Lupo P.
      • Foresti S.
      • De Ambroggi G.
      • De Lucia C.
      • Penela D.
      • Turturiello D.
      • Paganini E.M.
      • Cappato R.
      Air entrapment as a potential cause of early subcutaneous implantable cardioverter defibrillator malfunction: a systematic review of the literature.
      ; 3) The use of high ventricular rate cut-offs (rates >220 beats per min) to avoid therapies for sinus and supraventricular tachycardia
      • Jarman J.W.
      • Todd D.M.
      United Kingdom national experience of entirely subcutaneous implantable cardioverter-defibrillator technology: important lessons to learn.
      ; 4) The use of dual-zone programming, with application of the S-ICD discrimination algorithm in the conditional zone. This algorithm, which includes 3 double-detection algorithms, and an analysis of beat-to-beat QRS width and QRS morphology changes, as compared to stored sinus rhythm template, has demonstrated a 98% specificity for appropriately withholding therapy for SVT
      • Gold M.R.
      • Theuns D.A.
      • Knight B.P.
      • Sturdivant J.L.
      • Sanghera R.
      • Ellenbogen K.A.
      • Wood M.A.
      • Burke M.C.
      Head-to-head comparison of arrhythmia discrimination performance of subcutaneous and transvenous ICD arrhythmia detection algorithms: the START study.
      ; 5) the use of a morphology-based algorithm and a 9 Hz high-pass filter (SMART pass), which has significantly reduced the incidence of inappropriate shocks due to T-wave oversensing
      • Theuns D.
      • Brouwer T.F.
      • Jones P.W.
      • Allavatam V.
      • Donnelley S.
      • Auricchio A.
      • Knops R.E.
      • Burke M.C.
      Prospective blinded evaluation of a novel sensing methodology designed to reduce inappropriate shocks by the subcutaneous implantable cardioverter-defibrillator.
      ; and 6) acquisition of a template during exercise stress testing to optimize sensing vector to minimize T-wave oversensing
      • Kooiman K.M.
      • Knops R.E.
      • Olde Nordkamp L.
      • Wilde A.A.
      • de Groot J.R.
      Inappropriate subcutaneous implantable cardioverter-defibrillator shocks due to T-wave oversensing can be prevented: implications for management.
      .
      These approaches have markedly decreased the S-ICD inappropriate shock rates, falling from 13.1%-25% in the early IDE trials, to 7% in the EFFORTLESS registry (dual zone programming and high rate cut-offs), and 3.1-4.8% in the PRAETORIAN trial (2020) and UNTOUCHED study (2021)
      • Weiss R.
      • Knight B.P.
      • Gold M.R.
      • Leon A.R.
      • Herre J.M.
      • Hood M.
      • Rashtian M.
      • Kremers M.
      • Crozier I.
      • Lee K.L.
      • Smith W.
      • Burke M.C.
      Safety and efficacy of a totally subcutaneous implantable-cardioverter defibrillator.
      ,
      • Knops R.E.
      • Olde Nordkamp L.R.A.
      • Delnoy P.H.M.
      • et al.
      Subcutaneous or Transvenous Defibrillator Therapy.
      ,
      • Gold M.R.
      • Lambiase P.D.
      • El-Chami M.F.
      • et al.
      Primary Results From the Understanding Outcomes With the S-ICD in Primary Prevention Patients With Low Ejection Fraction (UNTOUCHED) Trial.
      . However, while the annual inappropriate shock rate has decreased, it is important to realize that the cumulative incidence of inappropriate therapies remains substantial, with nearly 1 in 10 patients in PRAETORIAN receiving an inappropriate shock by 48 months
      • Knops R.E.
      • Olde Nordkamp L.R.A.
      • Delnoy P.H.M.
      • et al.
      Subcutaneous or Transvenous Defibrillator Therapy.
      .
      In addition, while the screening and filtering algorithms (e.g., SMART Pass) have dramatically reduced the incidence of inappropriate shocks due to T wave oversensing, myopotential interference is now the commonest cause of inappropriate ICD discharges with the S-ICD

      Tsutsui K, Kato R, Asano S, Ikeda Y, Mori H, Tawara M, Tanaka S, Hasegawa S, Nakano S, Iwanaga S, Muramatsu T, Matsumoto K. Myopotential Oversensing Is a Major Cause of Inappropriate Shock in Subcutaneous Implantable Defibrillator in Japan. Int Heart J Sep 29 2020;61:913-921.

      . This is a clinically relevant concern given S-ICD implantation is generally favored in young physically active patients, a group most at risk of myopotential interference. In most cases these repetitive low-amplitude high-frequency myopotentials result in undersensing of intrinsic QRS complexes (32% overall), although myopotential-induced oversensing continues to occur in a significant proportion of cases (8%)
      • van den Bruck J.H.
      • Sultan A.
      • Plenge T.
      • Seuthe K.
      • Mödder T.
      • Iliadis C.
      • Stern D.
      • Blankenheim T.
      • Steven D.
      • Lüker J.
      Incidence of myopotential induction in subcutaneous implantable cardioverter-defibrillator patients: Is the oversensing issue really solved?.
      .
      While nearly all S-ICD patients (93%) have clinically relevant myopotentials identified during physical exercise
      • van den Bruck J.H.
      • Sultan A.
      • Plenge T.
      • Seuthe K.
      • Mödder T.
      • Iliadis C.
      • Stern D.
      • Blankenheim T.
      • Steven D.
      • Lüker J.
      Incidence of myopotential induction in subcutaneous implantable cardioverter-defibrillator patients: Is the oversensing issue really solved?.
      , the presence of significant myopotential noise cannot be predicted by preoperative screening. As such, it has been suggested that provocative testing should be performed following S-ICD implant
      • van den Bruck J.H.
      • Sultan A.
      • Plenge T.
      • Seuthe K.
      • Mödder T.
      • Iliadis C.
      • Stern D.
      • Blankenheim T.
      • Steven D.
      • Lüker J.
      Incidence of myopotential induction in subcutaneous implantable cardioverter-defibrillator patients: Is the oversensing issue really solved?.
      . During a temporary period of therapy inhibition, trunk muscular contraction (abdominal crunch), isometric upper limb exercise (isometric chest press, side plank, and lateral arm raise), and strong forward movement against resistance can be used to determine the vectors affected by myopotential noise. These motions are chosen to engage the pectoral muscle, Latissimus dorsi, serratus anterior, and abdominals, as these are the common source of myopotentials for S-ICD implants. Of note, prominent myopotential interference may be observed with different exercises and vectors (e.g., primary vector is more susceptible with side plank, but secondary and alternate vector are more affected with isometric chest press)
      • van den Bruck J.H.
      • Sultan A.
      • Plenge T.
      • Seuthe K.
      • Mödder T.
      • Iliadis C.
      • Stern D.
      • Blankenheim T.
      • Steven D.
      • Lüker J.
      Incidence of myopotential induction in subcutaneous implantable cardioverter-defibrillator patients: Is the oversensing issue really solved?.
      . In this case, the shoe-shining motion mimicked a chest-fly exercise with activation of the pectoral muscles. Prominent myopotential interference during this “stress test” enables preventive programming to avoid the affected vector(s). In extreme cases the lead and/or generator may need to be repositioned.
      Despite the high incidence of myopotentials seen during provocative testing
      • van den Bruck J.H.
      • Sultan A.
      • Plenge T.
      • Seuthe K.
      • Mödder T.
      • Iliadis C.
      • Stern D.
      • Blankenheim T.
      • Steven D.
      • Lüker J.
      Incidence of myopotential induction in subcutaneous implantable cardioverter-defibrillator patients: Is the oversensing issue really solved?.
      , these lead to inappropriate shocks in only a small minority of patients. The SMART Pass algorithm significantly reduces the all-cause incidence of inappropriate shocks, including those due to myopotentials
      • Theuns D.
      • Brouwer T.F.
      • Jones P.W.
      • Allavatam V.
      • Donnelley S.
      • Auricchio A.
      • Knops R.E.
      • Burke M.C.
      Prospective blinded evaluation of a novel sensing methodology designed to reduce inappropriate shocks by the subcutaneous implantable cardioverter-defibrillator.
      . In a study of 1984 patients, the incidence of inappropriate shocks due to extracardiac oversensing was 0.5% in those patients with SmartPass activated and 2.3% in those without SmartPass
      • Theuns D.
      • Brouwer T.F.
      • Jones P.W.
      • Allavatam V.
      • Donnelley S.
      • Auricchio A.
      • Knops R.E.
      • Burke M.C.
      Prospective blinded evaluation of a novel sensing methodology designed to reduce inappropriate shocks by the subcutaneous implantable cardioverter-defibrillator.
      .
      Right sided lead positioning, as was present in this case, has previously been associated with a higher incidence of inappropriate shocks in some

      Tsutsui K, Kato R, Asano S, Ikeda Y, Mori H, Tawara M, Tanaka S, Hasegawa S, Nakano S, Iwanaga S, Muramatsu T, Matsumoto K. Myopotential Oversensing Is a Major Cause of Inappropriate Shock in Subcutaneous Implantable Defibrillator in Japan. Int Heart J Sep 29 2020;61:913-921.

      but not all studies
      • van den Bruck J.H.
      • Sultan A.
      • Plenge T.
      • Seuthe K.
      • Mödder T.
      • Iliadis C.
      • Stern D.
      • Blankenheim T.
      • Steven D.
      • Lüker J.
      Incidence of myopotential induction in subcutaneous implantable cardioverter-defibrillator patients: Is the oversensing issue really solved?.
      . The mechanisms underlying this remain uncertain. Given the induction of myopotential with isometric chest press, we programmed him in the primary vector, which had less noise on provocative testing. It might be supposed that remote monitoring may offer the opportunity to identify short lived myopotentials prior to delivery of an inappropriate shock. However, in this case, a shock occurred without preceding evidence of myopotentials.

      Conclusion

      Clinicians who implant and follow up S-ICDs should be aware of strategies to minimize the risk of inappropriate shocks. A thorough history should be taken regarding the circumstances surrounding an ICD discharge to detect unusual and avoidable causes.

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        Safety and efficacy of a totally subcutaneous implantable-cardioverter defibrillator.
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        Air entrapment as a potential cause of early subcutaneous implantable cardioverter defibrillator malfunction: a systematic review of the literature.
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        United Kingdom national experience of entirely subcutaneous implantable cardioverter-defibrillator technology: important lessons to learn.
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        Prospective blinded evaluation of a novel sensing methodology designed to reduce inappropriate shocks by the subcutaneous implantable cardioverter-defibrillator.
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