Case Study: The First Subcutaneous ICD Implant in Iowa

Case Study

The patient is an 82-year-old woman who suffered an inferior wall myocardial infarction one year ago. At that time, her left ventricular ejection fraction measured 35%; it remains below 35% despite optimal medical management for her ischemic disease and heart failure. She has chronic obstructive lung disease with emphysematous changes and longstanding New York Heart Association functional class II congestive heart failure; otherwise, she is healthy and functional. She has no evidence for symptomatic bradycardia or atrial fibrillation. She was referred to the EP service at Mercy Hospital in Mason City for consideration of an implantable cardioverter defibrillator (ICD). 

On physical examination the patient was of slight build (at 47 kg and 153 cm tall), had a blood pressure of 120/80 mm Hg, and heart rate of 70 bpm. Her physical examination was normal except for expiratory slowing. Her electrocardiogram showed a narrow QRS complex in sinus rhythm. 

After an involved discussion about the possibility of an ICD, the patient was adamant she did not want leads implanted in her heart (she had also previously stated this to her cardiologist on previous visits); however, she did want protection from an ICD. Therefore, we discussed the option of a subcutaneous ICD (Boston Scientific’s S-ICD^™ System); if she qualified, this would be the first implantation of the S-ICD System in the state of Iowa. 

To determine if she was a candidate, a screening tool was applied to the surface electrocardiographic leads to examine the QRS and T wave amplitude ratios as well as the QRS width and morphology (Figure 1). A small sensed QRS complex or large T wave excludes the patient from an S-ICD implant due to possible double counting and subsequent delivery of inappropriate shocks. She passed the screen based on surface leads II and III. 

The S-ICD was implanted in the EP laboratory under general anesthesia. Prior to draping, anatomical skin markers were placed; fluoroscopy verified proper device placement. The pocket to house the S-ICD generator was created in the lateral chest at the mid-axillary line. An incision was made 1 cm left of the xyphoid process and 14 cm vertically along the left sternal border. The subcutaneous lead was tunneled from the S-ICD pocket to the incision at the inferior portion of the sternum and then tunneled superiorly. Initial placement showed the electrode to be too superior, so repositioning was required. The lead was affixed at both incision sites, checked via fluoroscopy to confirm its position, attached to the ICD header block, and placed in the pocket. An anchoring suture secured the S-ICD generator to the underlying fascia of the serratus anterior muscle.

Defibrillation conversion testing was performed. An Auto Setup algorithm chose the optimal detection vector (Figure 2). Ventricular fibrillation, induced by a 50 Hz electrical burst delivered from the S-ICD through the leads, was converted with a 65 Joule standard polarity shock. The shock impedance was 79 ohms, and the time to therapy was 13.4 seconds. Total fluoroscopy was 0.1 minutes. The entire procedure, exclusive of lead repositioning, took 15 minutes. The entire time in the lab was approximately one hour. 

After wound closure, the patient was transferred to the postoperative recovery area and discharged within a few hours without complications. At follow-up two weeks later, the incision site was well healed. The patient complained of no pain and felt that, despite her small size, the device was cosmetically acceptable as it had been placed away from the breast. The chest x-ray confirmed adequate lead placement (Figure 3).

The device was programmed with a 200 bpm conditional zone and 220 bpm shock zone (Figures 4 and 5). Pre-discharge optimization chose the primary sensing vector. Quarterly follow-up is planned, as remote follow-up is not available for the present generation device.

DISCUSSION

The S-ICD represents a novel approach to protect patients against sudden cardiac death from ventricular arrhythmias. Worldwide, over 3000 S-ICDs have been implanted to date — most outside the U.S. The implant is straightforward and minimal fluoroscopy is needed.

The greatest advantage of this device is the ability to eliminate problems with leads implanted inside the heart. Lead issues remain the “Achilles heel” of the ICD system and cause the greatest amount of complications and risks, especially if lead extraction is required. There is no risk of subclavian vein thrombosis, damage to the tricuspid valve, perforation, pneumothorax, and/or serious systemic infections. Additionally, the device has specific discrimination algorithms that virtually exclude inappropriate therapy delivery for supraventricular tachycardias between 170 and 250 bpm. Furthermore, placement of the S-ICD eliminates the issue of inappropriate right ventricular pacing that may occur with dual chamber devices that are not properly programmed.

The present S-ICD does not have the capability for antibradycardia or antitachycardia pacing. However, 30 seconds of post-shock transthoracic pacing is available. Although unable to directly sense atrial signals, the wide detection vector frequently allows the identification of atrial electrograms. 

Fortunately, many patients only require protection from the risk of sudden death due to ventricular tachycardia or fibrillation. This includes young patients with inherited conditions that can lead to sudden cardiac death and the majority of primary prevention ICD candidates who do not require antibradycardia or antitachycardia pacing. While a small number of these latter patients may require transvenous pacing at some point following ICD implantation, this could be many years, during which time the patient has been spared the risk of a transvenous lead system. 

Identification of appropriate patient candidates for the S-ICD is an evolving challenge. As implant experience with the device grows and follow-up increases, patient selection will become clearer. Guidelines are being considered (and being developed, at least, by insurance companies). However, selection of “ideal” patient candidates are not based on carefully controlled studies, and any recommendations should be viewed as preliminary. Of course, patients with a higher risk for lead complications, such as those who have limited or no venous access or those with indwelling catheters, patients with previously infected ICD systems, younger patients who will have leads in place for many years, patients with a long life expectancy, those with prosthetic valves, and perhaps women who prefer a more lateral chest wall device placement are some of the more obvious patient candidates. Indications and billing issues have also not yet been fully resolved on a national scale. Therefore, before implantation, clearance for the S-ICD should be obtained from insurance companies. 

While patients who require atrial pacing, cardiac resynchronization therapy, and antitachycardia pace termination of recurrent monomorphic ventricular tachycardia are not ideal candidates, the S-ICD should be considered strongly in patients without these needs. Indeed, although not presently available, future iterations of these devices will undoubtedly allow for leadless pacing.

One of the features of the S-ICD is the long detection and charge time. For the S-ICD, the average time to shock delivery of 20 seconds is well within the now-accepted approach to ICD programming. Long detection times have not been shown to be associated with higher syncope rates, but are associated with fewer unnecessary and inappropriate ICD therapies. 

Regarding device-related complications, the S-ICD exceeded the FDA benchmark expectations in the IDE trial. 

Critics of the S-ICD express concerns that the lack of spontaneous events leaves open the true success of the S-ICD. However, the European EFFORTLESS S-ICD Registry indicates first shock defibrillation for spontaneous events is 88%.¹ A U.S. S-ICD system post approval implant registry study has begun with the target to enroll 1500 patients. Data from this registry will allow an assessment of spontaneous events and long-term complications. While a randomized clinical trial could go far to support this new technology, the S-ICD has already been shown to effectively terminate ventricular tachycardia and fibrillation. 

This will not be the last technology change in the evolution of the ICD. If one were to require a controlled clinical trial to demonstrate benefit and effectiveness for every conceivable technological advancement, we would never be able to conclude that any device is really effective and we’d be unable to provide the best care for our patients. 

The role for the S-ICD in clinical practice continues to evolve. While it remains unclear which patients will be the optimal candidate for this device, estimates suggest 10-50% of ICD implants will be S-ICDs. In Mason City, we plan to routinely use this approach when we determine it is the best option.

I’d like to thank Dr. Jeanne Poole for her critical comments, as well as the EP lab staff at Mercy Medical Center in Mason City for their hard work in providing the best patient care in electrophysiology in Northern Iowa.

Disclosure: Outside the submitted work, Dr. Olshansky reports consultancy with Boston Scientific, employment with Executive Health Resources, expert testimony with Thompson Reuters, honoraria with Medtronic, and travel/accommodations expenses covered or reimbursed by BioControl. 

Reference

1. Lambiase PD, Theuns DAMJ, Barr C, et al, on behalf of the EFFORTLESS S-ICD Investigators.  International Experience with a Subcutaneous ICD; Preliminary Results of the EFFORTLESS S-ICD Registry. Heart Rhythm. 2012;9:5(S1-33):AB07-2.