Initial Experience With the Extravascular Implantable Cardioverter-Defibrillator: Procedure Workflow and Patient Selection

© 2024 HMP Global. All Rights Reserved.

Any views and opinions expressed are those of the author(s) and/or participants and do not necessarily reflect the views, policy, or position of EP Lab Digest or HMP Global, their employees, and affiliates.

EP LAB DIGEST. 2024;24(11):22-23.

Chinmaya Mareddy, MD, MBA, FACC¹; Brooke Hayes, PA Fellow¹; Jose Silva, MD¹; Matthew Sackett, MD¹; Anish Amin, MD^2
1Centra Heart and Vascular Institute, Lynchburg, Virginia; ²Ohio Health, Columbus, Ohio

Sudden cardiac death is the leading cause of mortality accounting for 4-5 million deaths worldwide each year. Since the 1990s, implantable cardioverter-defibrillators (ICD) have significantly reduced cardiac mortality among patients at risk for ventricular arrhythmias.^1-3 Transvenous ICDs (TV-ICDs) have been the mainstay treatment for these patients. However, complications of TV-ICD implant may include infectious compromise, direct cardiac injury, vascular injury or occlusion, and mechanical failure of the leads. 

The subcutaneous ICD (S-ICD) was developed to overcome complications associated with the TV-ICD. The S-ICD is implanted with a midaxillary generator and suprasternal lead, resulting in fewer vascular access and lead-related complications.⁴ Serial evaluations have demonstrated the safety and efficacy of the S-ICD. Despite the obvious advantages of a subcutaneous generator and lead for indicated patients, the fundamental design with a suprasternal lead position limits some of the therapy options. The device is unable to provide anti-tachycardia pacing (ATP) affording the ability to terminate sustained ventricular arrhythmias without painful and often avoidable shock. Similarly, the lead position limits the ability to provide pause prevention pacing. 

The Aurora EV-ICD System (Medtronic) was approved in October 2023 following the EV-ICD Pivotal Clinical study.⁵ With its substernal lead placement, this device allows for fewer intravascular and lead-related complications while incorporating features of ATP, pause prevention pacing, multiple therapy zones for ventricular arrhythmias, and max 40 J defibrillation output.^6,7 The lead position allows for reduced shunting of the defibrillation vector through skeletal muscle, and therefore, a smaller generator with battery longevity (11.7 year) comparable to TV-ICD. Approximating the lead closer to the heart allows for efficient delivery of ATP with termination of episodes in up to 70% of ventricular tachycardia (VT) episodes; generalized estimating equation (GEE) adjusted termination rate was 59%.5 We hereby share our experience of 2 EV-ICD cases from our center. 

Case Presentations

Case #1
The patient is a 68-year-old woman with past medical history of nonischemic cardiomyopathy status post primary prevention single-chamber TV-ICD implantation in 2019. In September 2023, she presented to our office after noticing a beeping noise coming from her device. Remote transmission was concerned for right ventricular (RV) lead fracture with RV lead impedance greater than 3000 ohms. This was confirmed with a chest x-ray (CXR), which showed a fracture of the lead at the entry site of the axillary vein (Figure 1). After shared decision-making, she opted to proceed with extraction of the TV-ICD and implantation of an EV-ICD. 

She underwent successful transvenous laser lead extraction of the VVI DF4 single coil fractured ICD lead and removal of the ICD pulse generator followed by implantation of an EV-ICD system. Prior to the procedure, the anatomical landmarks for the EV-ICD placement were marked: xiphisternum, right and left costal margin, intercostal rib spaces, sternal angle, midline of the sternum, and right and left sternal margin (Figure 2). To begin the implantation, an approximate 3-cm incision was made between the inferior point of the xiphoid and left costal margin to access the retrosternal space. Blunt dissection was then performed beyond the rectus fascia and through the diaphragmatic attachments. Entering retrosternal space is confirmed with a cardiothoracic surgeon in the room and appreciation of the beating heart with the nail bed of the finger. The Epsila EV sternal tunneling tool (Medtronic) was placed within a SafeSheath peel-away introducer sheath (Pressure Products) using lateral fluoroscopy to ensure the tip of the tunneling tool was in direct contact with the posterior surface of the sternum to avoid cardiac injury. The tunneling tool is advanced a few centimeters at a time. Alternating in anteroposterior (AP) and lateral views under fluoroscopy is a crucial step of the procedure. The tunneling path was then extended to the upper border of the cardiac silhouette (Video 1) and between the midline and left sternal margin. Once the tunneling tool was removed, the EV-ICD lead was inserted into the substernal space via the peel-away introducer sheath. After the lead was deployed, acute sensing measurements were collected with the requirement of R wave amplitudes >1 mV and P-wave <0.2 mV. The lead was then anchored to the fascia in the subxiphoid incision using nonabsorbable sutures and a constrictor knot was deployed to fix the anchoring sleeve. Next, an incision the length of the ICD pulse generator was made in the midaxillary region anterior to the intended ICD pulse generator site. The proximal portion of the lead was then tunneled using the Epsila EV transverse tunneling tool to the left lateral device pocket. The device was placed against the fascia in the subcutaneous tissue and sutured within the pocket (Video 2 shows fluoroscopy of the lead/device in lateral view). Defibrillation threshold testing was then performed. Ventricular fibrillation was induced via burst pacing at 50 Hertz and sensing was appropriate with minimal dropout. Defibrillation testing was unsuccessful at 25J, but successful on 2 consecutive occasions at 30J, which gives an extra 10J safety margin for programmed output. The patient remained hemodynamically stable following testing. 

Device parameters at the time of implant were ring 1-ring 2 (608 ohms), ring 1-coil 2 (304 ohms), high voltage (HV) 75 ohms, and R-wave sensing 1.6 mV. Postoperative CXR (Figure 3) showed appropriate lead positioning. The patient remained stable with no complications throughout hospital admission and was discharged home the following day. During 3-month follow-up, her device interrogation showed stable lead parameters with R-wave sensing of 2.6 mV and few runs of nonsustained VT (1-4 seconds duration) due to oversensing. 

Case #2 
This patient is a 21-year-old woman with history of catecholaminergic polymorphic VT with a secondary prevention S-ICD implanted in 2015 who underwent generator change in early 2024. She has been on nadolol 20 mg daily, maximum tolerated dose. Her course was complicated by pocket infection after her recent generator change, which subsequently required extraction of her S-ICD. She was discharged home with antibiotics and a ZOLL LifeVest Wearable Defibrillator (ZOLL Medical) as a bridge to reimplantation. Consideration for reimplant with an EV-ICD was made secondary to her young age and extended battery longevity. 

Ultimately, she underwent EV-ICD implantation without any complications. The implant procedure was performed in the same manner as noted above. Defibrillation threshold testing was successfully performed. Device parameters at the time of implant were ring 1-ring 2 (285 ohms), ring 1-coil 2 (190 ohms), HV 82 ohms, and R-wave sensing 2.6 mV. The patient remained hemodynamically stable following testing. She was discharged home on the same day (Figure 4). During 3-month follow-up, her device interrogation showed stable lead parameters with R-wave sensing of 5.9 mV without any ventricular arrhythmias.

Discussion 

The EV-ICD is a good option for patients who qualify for a de novo primary prevention ICD, have no pacing requirements, and are without any prior history of atrial arrhythmias. It is also a good option for patients who are at high risk of infections, such as patients on dialysis, with central lines, or those who are immunocompromised. It can also be considered in patients with occluded vessels or anatomical anomalies, or in patients who are physically active with their upper body, which may cause subclavian crush or lead fractures at the entry site. 

The Epsila EV defibrillation lead design’s 2 defibrillation coils positioned toward the patient’s right side offers wider defibrillation vector between the coils and device. Pacing/sensing ring electrodes are positioned toward the patient’s left side to be closer to the heart. The lead curvature is intended to help stabilize the lead in the mediastinal tissue. Four electrodes, consisting of 2 coils and 2 rings, support 3 different pacing vector options and 3 sensing vector options. 

Conclusion 

The EV-ICD overcomes multiple limitations of the S-ICD. The EV-ICD allows patients who may not be ideal candidates for transvenous devices, such as those with occluded vessels, anatomical anomalies, prior device infections, or an increased risk for lead complications to receive a device that does not require invasion into the vasculature without losing any of the features of a transvenous device. The EV-ICD also offers therapies similar to a transvenous system and may be a suitable alternative for a single-chamber ICD in patients who do not require bradycardic pacing. Our initial experience has demonstrated success for high-risk patients who have suffered complications from traditional transvenous devices.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. Drs Mareddy, Silva, and Sackett report no conflicts of interest regarding the content herein. Dr Amin reports consulting fees from Medtronic. 

References 

1. Moss AJ, Zareba W, Hall WJ, et al. Prophylactic implantation of a defibrillator in patients with myocardial infarction and reduced ejection fraction. N Engl J Med. 2002;346(12):877-883. doi:10.1056/NEJMoa013474

2. Bardy GH, Lee KL, Mark DB, et al. Amiodarone or an implantable cardioverter-defibrillator for congestive heart failure. N Engl J Med. 2005;352(3):225-237. doi:10.1056/NEJMoa043399.

3. Kadish A, Dyer A, Daubert JP, et al. Prophylactic defibrillator implantation in patients with nonischemic dilated cardiomyopathy. N Engl J Med. 2004;350(21):2151-2158. doi:10.1056/NEJMoa033088

4. Fong KY, Ng CJR, Wang Y, Yeo C, Tan VH. Subcutaneous versus transvenous implantable defibrillator therapy: a systematic review and meta-analysis of randomized trials and propensity score-matched studies. J Am Heart Assoc. 2022;11(11):e024756. doi:10.1161/JAHA.121.024756

5. Friedman P, Murgatroyd F, Boersma LVA, et al. Efficacy and safety of an extravascular implantable cardioverter- defibrillator. N Engl J Med. 2022;387(14):1292-1302. doi:10.1056/NEJMoa2206485

6. Thompson AE, Atwater B, Boersma L, et al. The development of the extravascular defibrillator with substernal lead placement: a new frontier for device-based treatment of sudden cardiac arrest. J Cardiovasc Electrophysiol. 2022;33(6):1085-1095. doi:10.1111/jce.15511

7. Aurora EV-ICD™ MRI SureScan™ DVEA3E4 device manual. Medtronic. Accessed August 30, 2024. aurora-ev-icd-brochure-en.pdf