Implantation of the Subcutaneous Implantable Cardioverter-Defibrillator

Patient Selection

S-ICD candidates are patients with a class I or IIa ICD indication, who do not require pacing for either bradycardia or tachycardia, because the subcutaneous position of the lead does not allow pacing at low energy values. Patients with monomorphic ventricular tachycardia are likely to benefit from antitachycardia pacing (ATP) and therefore are not suitable for S-ICD therapy. Patients who have been successfully treated for monomorphic ventricular tachycardia with ablation or medication can be considered for S-ICD therapy. Also, patients with progressive cardiac conductivity disease or patients who are likely to develop cardiac conductivity disease that requires bradycardia pacing are not suitable for S-ICD therapy. There are several case reports describing patients with transvenous pacemakers in whom an S-ICD has been added for sudden cardiac death prevention.

The can of the S-ICD is relatively large compared with current transvenous ICDs. Patients with a small body size and little subcutaneous fat may therefore be prone to skin erosion or discomfort. Use of the S-ICD in pediatric patients has been described, but it is limited by body size because the S-ICD lead has to fit at least 14 cm alongside the sternum.

Patient Assessment

The S-ICD relies on a morphology-based sensing algorithm, for which accurate discrimination between QRS complexes and T waves is vital. To ensure adequate sensing of the cardiac rhythm, there is a prerequisite electrocardiogram (ECG) morphology screening test. This ECG differs from a regular 12-lead recording, because the four limb electrodes are positioned on the xiphoid, sternomanubrium junction, V6 and abdomen (ground electrode), simulating the sensing vectors of the S-ICD. A 10- to 20-second ECG (25 mm/s; ECG gain 5, 10, and/or 20 mm/mV) is recorded with the patient in both supine and standing positions. Subsequently, the appropriateness of the QRS complex and the relevant T wave is tested using the dedicated screening tool ( Fig. 28-1A ). A patient is considered eligible for S-ICD therapy when all QRS-complex and T-wave profiles on the screening ECG fit in at least one sensing vector in both supine and standing position ( Fig. 28-1B ).

The ECG morphology analysis screens out approximately 7% to 15% of the potential S-ICD candidates. The screening is important to prevent QRS-complex undersensing or T-wave oversensing, which may result in inappropriate shocks and failure to deliver appropriate shocks.

Personnel and Equipment

The personnel required for S-ICD implantation is similar to transvenous procedures. The creation of the pocket requires adequate surgical skills, because the can is significantly larger than modern transvenous ICDs. Therefore the assistance of a thoracic or general surgeon with initial implants might be useful to reconfirm basic surgical techniques for hemostasis and wound closure. Also, in cases where the can is placed submuscularly, initial surgical assistance is advised to prevent damage to muscle and nerve tissue. In cases where general anesthesiology is to be used, a nurse-anesthetist or an anesthesiologist is needed. A second implanter can be used to reduce procedure time. In our experience, simultaneous preparation and wound closure can cut procedure time by approximately 10 minutes. Box 28-1 presents the preferred members of an S-ICD implantation team. Box 28-2 provides an overview of the supplies and tools used in S-ICD implantation.

Planning of the Procedure

The larger size of the can of the S-ICD necessitates a larger pocket, thus increasing the bleeding risk due to the larger wound bed. However, the lack of vascular access reduces the chance of major bleeding. Ideally, anticoagulation therapy is paused during the procedure to minimize the bleeding risk. If a patient uses anticoagulants, the individual risk for thromboembolic complications needs to be assessed by the implanting physician. Current regimens recommended in guidelines for transvenous ICDs should be followed in high-risk patients.

A chest x-ray should be part of routine preparation to prevent unexpected anatomic variations such as those that have been described in the literature, including cardiomegaly, shifted mediastinum, and situs inversus, because some of these variations mandate a different anatomic position of the S-ICD system.

The implants can be performed in a sterile surgical environment with or without fluoroscopic capability because anatomic landmarks are adequate for implantation. The decision whether to implant in surgical theater or in a catheterization room is often based on availability and local logistics. In general, surgical theaters are often more likely equipped for general anesthesia and the surgeon's needs. Therefore submuscular device implants (discussed later) that require general anesthesia and surgical assistance might be better performed in the surgical theater. Fluoroscopy can be useful, particularly early on ones learning curve to verify correct lead and pulse generator positioning.

Anesthesia

Both local and general anesthesia are used for S-ICD implantations. The choice depends primarily on operator and patient preference. We advise consideration of general anesthesia for patients in the following settings: (1) during the implanters learning curve to get familiar with the procedure; (2) patients who are difficult to instruct or are anxious; (3) obese patients (body mass index >30) in whom it is difficult to get enough volume of local anesthesia to the correct position, as the device and the lead need to be placed deep on the muscular fascia to ensure adequate sensing and a low defibrillation threshold (DFT); and (4) young patients (age <40 years), because use of local anesthesia might be more painful, as their subcutaneous tissue is more difficult to dissect.

Subcutaneous implantation can be done under local anesthesia in combination with intravenous moderate and deep sedation for DFT testing. It requires a significant volume of locally applied anesthetics, as the entire trajectory of the lead and the larger pocket for the pulse generator need to be anesthetized. Injecting the local anesthetic may be painful and cause adrenergic stimulation, thereby reducing the effectiveness of the local anesthetic. The adrenergic stimulation can be anticipated using the intravenous moderate sedation before injection of the local anesthetic under close monitoring of blood pressure and oxygenation. Various drugs (e.g., midazolam, fentanyl, propofol) can be used for intravenous moderate sedation, and the choice should be based on personal experience of the implanting physician. In the authors' institution, a cocktail of midazolam and fentanyl is used. The anesthetic injected over the implant trajectory is lidocaine 1%. Lidocaine may be diluted to 0.5%, to anesthetize a larger area of subcutaneous tissue without overdosing the patient.

Patient Positioning

The patient is placed in supine position on the surgical table with the left arm in 60- to 90-degree abduction on an armrest. The patient's arm should be firmly fixed to the armrest because the 50-Hz, 200-mA pacing burst for ventricular fibrillation induction causes a forceful adduction of the left arm due to capture of the muscles of the chest wall and extremities. Stress on the shoulder cuff should be avoided, because this may cause postprocedural shoulder complaints. The chest hair may be clipped but not shaved for easier marking of incision sites, but there is no supporting evidence that it reduces the risk of surgical site infection.

Incision Marking

The surgical incisions are marked on the chest, using anatomic landmarks to ensure accurate positioning. The lower part of the xiphoid is palpated, and a line of approximately 3 cm is drawn from the xiphoid perpendicular to the midsagittal line, the xiphoid-midaxillary line ( Fig. 28-2 ). The superior parasternal incision mark is placed 14 cm above the xiphoid and 1 cm left parasternal in a craniocaudal direction, because the distance between the proximal and distal electrode on the lead is 14 cm (for which the S-ICD ruler can be used). To avoid oversensing from the pectoral muscles, it is important to make sure that both sensing electrodes are not placed too far from the midline. The incision for the pocket is marked in the inframammary crease. The lower margin of the can should be just above the xiphoid-midaxillary line ( Fig. 28-3 ). The can is centered on the midaxillary line, as lateral as possible so that half of the can is on the anterior side of the thorax and the other half is on the posterior side. Incorrect positioning of the can may result in a higher defibrillation threshold. Pressure from the can on the incision may prohibit healing. This should be avoided by marking the incision site just above the anticipated position of the can. In obese patients, adequate positioning can be challenging. Therefore in obese patients, fluoroscopy can be considered to identify the correct position of the system relative to the cardiac silhouette.

Surgical Site Preparation

The skin can be sterilized with chlorhexidine-alcohol or povidone-iodine. The nonsterile parts of the body are covered with four sterile surgical drapes (instead of a single surgical drape with a self-adhesive hole), because the surgical field is much larger compared to transvenous implantations. It is important to prevent too much skin traction by the drapes, as this may displace the incision sites. Additionally, the surgical work field can be covered with plastic adhesive drapes (Ioban; 3M, St. Paul, MN) or cyanoacrylate technology (INTEGUSEAL; Halyard Health, Alpharetta, GA) to further reduce the chance of surgical site infections, but evidence for its effectiveness is limited.

Creating the Pocket

First, an incision is made along the inframammary crease in the predefined position ( Fig. 28-4 ). The pocket should be deep, either under the muscle or in the fascial plane. In obese patients, care should be taken to ensure the pocket is below all the adipose tissue directly on the muscular fascia. In these patients, the incision should be made directly down to the fascia. From there, the contour of the chest wall is followed. Most of the pocket can be made with blunt dissection, but electrocautery can be used for areas difficult to reach deep in the pocket. The exact anatomic plane of the pocket depends on the size and position of the latissimus dorsi muscle. In most patients, the posterior part of the can will be positioned in the natural anatomic space ( Fig. 28-5 ) between the latissimus dorsi and serratus anterior muscles ( Fig. 28-6 ). This will prevent defibrillation failures that may occur when the can is positioned too far from the chest wall due to either underlying muscle or fatty tissue.

Ideally, the pocket is large enough to allow one's finger to be placed next to the can in the pocket. This is important in our experience, because a pocket that is too tight is prone to pocket erosion and discomfort. The lower part of the can should be positioned on the parallel line from the xiphoid to the midaxillary line. The middle part of the can is ideally placed on the midaxillary line as mentioned earlier. Adequate hemostasis must be ensured.

Lead Tunneling

There are two techniques for tunneling the subcutaneous lead. The three-incision technique as described in the device user's manual and recommended by the manufacturer that requires three incisions. We recommend that implanters new to the procedure start with this technique. The second technique, the two-incision technique, was introduced to improve the cosmetic result, reduce the chance of wound infection, and reduce procedure time. This technique requires only two skin incisions: the pocket incision and the xiphoid incision. Online we provide videos showing the three-incision technique ( Video 28-1 ) and the two-incision technique ( Video 28-2 ).

Three-Incision Implantation Technique

At the xiphoid in the midsagittal line, a 3- to 5-cm horizontal incision (xiphoid incision) is made in the direction of the pocket incision ( Fig. 28-7 ). The subcutaneous tissue should be dissected to the fascia. The distal tip of the electrode insertion tool (EIT), used to create the subcutaneous tunnels in which the electrode is placed, is inserted at the xiphoid incision and tunneled laterally until the distal tip emerges in the device pocket ( Fig. 28-8 ). Conventional suture material is used to tie the anchoring hole of the electrode to the EIT, creating a long loop of at least 15 cm. With the electrode attached, the EIT is pulled back through the tunnel to the xiphoid incision until the proximal sensing electrode emerges ( Fig. 28-9 ). A suture sleeve is placed over the electrode shaft 1 cm below the proximal sensing electrode ( Fig. 28-10 ). The preformed grooves are used to bind the suture sleeve to the electrode shaft with nonabsorbable suture material.

Xiphoid-to-Superior Parasternal Tunneling

Xiphoid-to-manubriosternal junction tunneling can be done using two techniques described below. The three-incision technique as described in the device user's manual requires a left superior parasternal incision. The tip of the electrode is still sutured to the EIT with the loop between the electrode and the EIT. Then the EIT is tunneled from the xiphoid to the superior parasternal incision. After picking up the long suture at the superior incision site, the suture is cut from the EIT. Holding the long suture in position, the EIT is removed. The lead will then be pulled upward from distal to proximal and fixated with nonabsorbable suture material ( Figs. 28-11 and 28-12 ). When tunneling, one must ensure that the final position of the lead is as close as possible to the left lateral margin of the sternum. When the sensing electrodes are not positioned correctly and are positioned over the pectoral muscle, there is a risk for oversensing and inappropriate shocks. For an optimal cosmetic result and to avoid DFT issues, it is important that the lead be tunneled as close to the fascia as possible. To achieve this, the downward direction of the sternum (from xiphoid to manubrium) should be followed by lifting the handle of the EIT away from the body while tunneling. By doing this, the tip of the EIT scrapes over the surface of the sternum while the EIT is steered in a cranioposterior direction.

Two-Incision Implantation Technique

The two-incision technique described below is not in the S-ICD device user's manual but has been published in a journal article written by the authors. In a small cohort of 39 patients who underwent implants using the two-incision technique, no dislocations were observed during 18 months of follow-up. Besides two superficial pocket infections, no complications were seen; therefore it seems that the two-incision technique is a safe and efficacious alternative for S-ICD implantations. Although evidence is currently lacking, the two-incision technique may reduce infection risk, because it omits one incision from the three-incision technique. Experience in a recent, larger cohort (unpublished) confirms our earlier published results.

The two-incision technique consists of only one parasternal incision at the xiphoid position, similar to the one described above, and abandons the superior parasternal incision. The lead is positioned using a standard 11-French peel-away sheath of 14-cm length, which is commonly used in transvenous lead placement (Greatbatch, Clarence, NY). The peel-away sheath is placed over the EIT before tunneling ( Fig. 28-13 ). Tunneling the EIT parasternally is identical to the three-incision technique, emphasizing the importance of positioning the lead directly on the left lateral margin of the sternum ( Fig. 28-14 ). Next, the peel-away sheath is advanced over the EIT until it is fully inserted. The EIT is removed, and the peel-away sheath is left in the subcutaneous position ( Fig. 28-15 ). The electrode is inserted into the subcutaneous sheath until the suture sleeve reaches the opening of the sheath. The lead is now in the desired parasternal position. The sheath is peeled away, leaving the electrode in place ( Fig. 28-16 ). It is possible to confirm manually that the tip of the lead is in the correct superior parasternal position. The suture sleeve is secured to the fascia. The parasternal incision requires at least two suture layers to ensure that enough tissue is pulled over the sometimes superficially positioned subcutaneous lead.