Subcutaneous Implantable Cardioverter Defibrillator

36 year old male. Chronic renal failure, on dialysis. Name the device and location • Xray of the Week

Figure 1. Name the device and location.

Figure 2. AP CXR showing S-ICD placement with tripolar lead electrode at sternal border (blue arrow) and pulse generator outside chest cavity (red arrow). Note the tunneled dialysis catheter (green arrow).

Figure 2.

3D-chest CT reconstruction shows S-ICD placement with tripolar lead electrode at sternal border (blue arrow) and pulse generator outside chest cavity (red arrow). Note the tunneled dialysis catheter (green arrow). There are multiple chest wall collateral veins (yellow arrows) due to venous obstruction related to the dialysis catheter.

Discussion:

The subcutaneous implantable cardioverter defibrillator (S-ICD) is a minimally invasive device, approved for use by FDA in 2013 for detection and correction of ventricular tachyarrhythmias. Transvenous ICD (T-ICD) is another type of implantable defibrillator but has been associated with higher complication rates due to the more invasive procedure for placement and high occurrence of lead failures. (1,3) Both S-ICD and T-ICD have similar indications to detect and treat ventricular arrhythmias including ventricular fibrillation (VF) and ventricular tachycardia (VT) which are often the cause of sudden cardiac death. However, the obvious advantage of S-ICD is that it does not require venous access for lead placements and sits outside the chest cavity, decreasing chances of complications such as pneumothorax, hemothorax, and cardiac tamponade during placement (3). S-ICD is approved to treat patients who may not qualify for T-ICD. Indications for S-ICD includes young patients who may require a long-term ICD due to hypertrophic cardiomyopathy or other congenital cardiomyopathies, patients who have limited vascular access, are at higher risk for lead endocarditis, in addition to the current indications for ICD implants (3). In this case, there was no vascular access due to chronic venous obstruction related to the dialysis catheter. Therefore, the traditional transvenous ICD could not be placed.

The S-ICD is composed of the tripolar lead electrode and the pulse generator. The tripolar lead electrode is placed 1-2 cm to the left of, and parallel to the sternal midline. It has proximal and distal sensing electrodes and an 8-cm shocking coiled electrode. The pulse generator is implanted at the sixth rib between the left mid-axillary and anterior axillary line. (3) In the images above, a blue arrow points to the lead electrode as a thickened linear opacity near the sternal border on chest x-ray and the large pulse generator is noted to be positioned outside the chest cavity at the left 6th rib.   

According to a study in 2013, the efficacy of the S-ICD in detecting ventricular arrhythmias is 99.8% and the incidence of incorrect shocks is noted to be between 4-18% compared with TV-ICD incidence to be 20-30%. In the EFFORTLESS study, the complication rate associated with S-ICD is estimated to be approximately 2% at 1-year follow up. The S-ICD is a novel device that provides an alternative to patients who need it, but there is still limited data on correcting life-threatening heart rhythms that will continue to be studied and examined (4).

References:

1. Bardy GH, Smith WM, Hood MA, et al. An Entirely Subcutaneous Implantable Cardioverter–Defibrillator. The New England Journal of Medicine. 2010;363(1):36-44. DOI: 10.1056/NEJMoa0909545

2. Weiss R, Knight BP, Gold MR, et al. Safety and Efficacy of a Totally Subcutaneous Implantable-Cardioverter Defibrillator. Circulation (New York, NY). 2013;128(9):944-953. DOI: 10.1161/CIRCULATIONAHA.113.003042

3. Kaya E, Rassaf T, Wakili R. Subcutaneous ICD: Current standards and future perspective. Int J Cardiol Heart Vasc. 2019 Aug 8;24:100409. PMCID: PMC6700427 DOI: 10.1016/j.ijcha.2019.100409

4. Boersma L, Barr C, Knops R, et al. Implant and Midterm Outcomes of the Subcutaneous Implantable Cardioverter-Defibrillator Registry: The EFFORTLESS Study. Journal of the American College of Cardiology. 2017;70(7):830-841.DOI: 10.1016/j.jacc.2017.06.040

Nirali Dave is a medical student at Medical University of Lublin in Poland, currently doing clinical rotations in New York. Before that she completed her undergraduate education at Rutgers University, and worked as a medical scribe. Nirali was first exposed to basic radiologic imaging while scribing, and was very quickly taken by the field. Her passion for radiology comes from the bridging of anatomy, health technologies, and patient care. In the future, she hopes to complete a diagnostic radiology residency and stay committed to clinical research and patient education.

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Kevin M. Rice, MD is the president of Global Radiology CME

Dr. Rice is a radiologist with Renaissance Imaging Medical Associates and is currently the Vice Chief of Staff at Valley Presbyterian Hospital in Los Angeles, California. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator.

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