Version July 2025
INTRODUCTION —
Sudden cardiac death (SCD) resulting from cardiac arrhythmia is the world's leading cause of cardiovascular mortality, accounting for over 50 percent of cardiovascular deaths worldwide. Implantable cardioverter-defibrillators (ICDs) have been shown in numerous large clinical trials to reduce mortality from SCD in selected populations.
Traditionally, ICD systems consist of a pulse generator, typically placed in the pectoral region, and one or more leads that extend from the pulse generator to the myocardium via a transvenous route. However, conventional transvenous ICD (TV-ICD) systems have drawbacks, which include risks associated with insertion (eg, cardiac perforation, pneumothorax, pericardial effusion) and persistence in the intravascular space (eg, endocarditis, venous stenosis, tricuspid regurgitation, and lead fracture).
The subcutaneous ICD (S-ICD) and extravascular ICD (EV-ICD) were developed in an attempt to address some of the limitations of TV-ICD systems by avoiding endovascular access (figure 1 and image 1). Thus, clinicians and patients must choose between the available options for ICD therapy. This topic presents an approach for choosing an ICD system and describes S-ICD and EV-ICD systems.
Notably, while S-ICDs and EV-ICDs are both extravascular ICDs that have a subcutaneous component, the term "S-ICD" is used throughout this topic to describe ICDs with a submuscular or subcutaneous generator and a lead positioned anterior to the sternum in the subcutaneous space. ICDs with a similar generator position and a lead that is positioned posterior to the sternum (ie, retrosternal space) are referred to as "extravascular" ICDs.
TV-ICD systems, including their potential complications, are discussed separately. (See "Implantable cardioverter-defibrillators: Overview of indications, components, and functions".)
The approach to the prevention of SCD is discussed separately. (See "Primary prevention of sudden cardiac death in patients with cardiomyopathy and heart failure with reduced LVEF" and "Secondary prevention of sudden cardiac death in heart failure and cardiomyopathy".)
DEVICE SELECTION
Individualized approach — For patients who require an ICD, the choice of ICD system is individualized. The main advantage of a TV-ICD is the ability to provide bradycardia and antitachycardia pacing, while the main advantage of an S-ICD or an EV-ICD is extravascular placement (algorithm 1). However, patient characteristics may favor or require one type of device over another, as discussed elsewhere in this topic. (See 'Factors favoring transvenous ICD placement' below and 'Factors favoring subcutaneous ICD placement' below.)
An individualized approach to the choice of ICD is consistent with the recommendation of professional societies [1,2].
The evidence suggests similar efficacy and safety of TV-ICD and S-ICD devices. In the PRAETORIAN trial, 849 patients (81 percent with a primary prevention indication) were randomized to either an S-ICD or TV-ICD [3]. At a median follow-up of 49 months, the rate of mortality was nonsignificantly higher in the S-ICD group (16 versus 13 percent; hazard ratio [HR] 1.2, 95% CI 0.9-1.7), the rate of SCD was similar (4 percent), the rate of lead-related complications in patients with a S-ICD was lower (1.4 versus 6.6 percent; HR 0.24, 95% CI 0.10-0.54), and the rate of inappropriate shocks was nonsignificantly higher (9.7 versus 7.3 percent; HR 1.43, 95% CI 0.9-2.3). With newer approaches to S-ICD programming, the rate of inappropriate shocks likely decreased. For example, in the UNTOUCHED Trial, the one-year rate of inappropriate shocks was 2.4 percent [4].
A study from the National Cardiovascular Data Registry showed that among over 16,063 patients (mean age 73 years, 991 with S-ICD) with an ICD, there were no differences in mortality between patients with S-ICD and TV-ICD (12 versus 9 events per 100 patient-years) or hospital readmission (48 versus 38 events per 100 patient-years) [5]. Rates of complications (eg, device reoperation, device removal for infection) were also similar.
A meta-analysis of five nonrandomized studies compared outcomes in S-ICD versus TV-ICD patients in over 6400 patients. The rate of lead complications was lower in S-ICD patients (odds ratio [OR] 0.13, 95% CI 0.05-0.38). There were no significant differences in the rate of infections (OR 0.75, 95% CI 0.30-1.89), system failures (OR 1.13, 95% CI 0.43-3.02), or inappropriate shocks (OR 0.87, 95% CI 0.51-1.49). Patients with S-ICDs were more likely to have inappropriate shocks due to T-wave oversensing and noise, while in TV-ICD patients, inappropriate shocks were more commonly due to supraventricular tachyarrhythmias, including atrial fibrillation [6].
Factors favoring transvenous ICD placement — A TV-ICD is preferred in the following scenarios:
High risk or requirement for pacing — In patients who have or are likely to require pacing for bradycardia, the best option for ICD therapy is a TV-ICD. The S-ICD can only pace transcutaneously for brief periods of time after an ICD shock. (See 'Components and function' below.)
While EV-ICDs are designed to provide backup pacing and antitachycardia pacing, these functions require much higher energy than transvenous systems, and, as such, this type of pacing may not be well tolerated for long periods of time. (See 'System description' below.)
In highly selected patients, the addition of a leadless pacing device with wireless connection to an S-ICD can provide backup pacing and antitachycardia pacing [7].
High likelihood of sustained monomorphic ventricular tachycardia — In patients with a current or anticipated need for antitachycardia pacing, a TV-ICD is typically the better choice for ICD therapy due to its ability to provide antitachycardia pacing for sustained monomorphic ventricular tachycardia (SMVT) [8]. Except for patients with a history of ventricular tachycardia (VT), it can be difficult to predict which patients will develop a need for antitachycardia pacing. However, patients with primary electrical disorders, such as long QT syndrome or Brugada syndrome, rarely experience SMVT and would not be expected to need antitachycardia pacing.
The data on development of SMVT are limited. In a retrospective single-center cohort study of 1345 patients who underwent ICD implantation for both primary and secondary indications, 463 patients (34 percent) received antitachycardia pacing (27 percent) or developed an indication for either bradycardia pacing (11 percent) or cardiac resynchronization therapy (4 percent) [9]. However, data suggest that ATP does not necessarily reduce the risk of ICD shocks [10]. Patients with known VT at a rate below 170 beats per minute or with recurrent SMVT that could not be managed with medication or ablation therapy were excluded from the PRAETORIAN trial.
Requirement for cardiac resynchronization — S-ICDs are also not indicated in patients who require or are likely to require biventricular pacing for cardiac resynchronization therapy [11,12].
Reliance on unipolar pacing — In patients who require unipolar pacing, which is rare, an S-ICD cannot be placed due to noise generated by unipolar pacing that may lead to inappropriate shocks. A study with relatively small sample size suggested that the S-ICD can be expected to function normally in the presence of a preexisting permanent pacemaker functioning in a bipolar pacing mode [8,13].
Small patients — Smaller patients, and patients with little subcutaneous tissue, are less likely to tolerate the large generator size of the S-ICD and are at higher risk for device erosion. However, the S-ICD has been successfully implanted in the pediatric and young adult population by experienced implanting physicians [14].
Factors favoring subcutaneous ICD placement — Compared with TV-ICDs, S-ICDs have advantages in the following groups of patients:
Younger patients — Younger patients (eg, age less than 45 years) with anticipated need for ICD therapy spanning decades (likely requiring multiple ICD systems over time) may have fewer complications with an S-ICD owing to the durability of the S-ICD lead and the absence of intravascular complications associated with TV-ICDs (eg, endocarditis, tricuspid regurgitation) [14,15]. Younger patients may have a higher risk of lead failure. However, the battery longevity with TV-ICDs substantially exceeds that of S-ICDs. As examples, an S-ICD system may be appropriate in patients with hypertrophic cardiomyopathy, congenital cardiomyopathies, or inherited channelopathies who are more likely to require ICD placement at a younger age.
Risk factors for bacteremia — Patients at high risk for bacteremia, such as patients on hemodialysis or with chronic indwelling endovascular catheters, may be less likely to develop a device infection or systemic infection with an S-ICD. The S-ICD's position outside of the intravascular space is less likely to become contaminated with repeated exposures to transient bacteremia. S‐ICD infections have rarely been complicated by systemic infection [16].
Difficult or prohibitive vascular access — In patients with challenging vascular access or prior complications with TV-ICDs, an S-ICD may be an option for ICD therapy [11,12]. Examples include patients with congenital heart disease without straightforward access to the ventricle.
Cosmetic considerations — Some patients perceive the location of the generator in the posterolateral chest as an advantage of the S-ICD. However, the S-ICD generator is larger than a TV-ICD (picture 1).
TRANSVENOUS DEFIBRILLATORS —
Information on the components and implantation of TV-ICDs is presented separately. (See "Implantable cardioverter-defibrillators: Overview of indications, components, and functions".)
SUBCUTANEOUS DEFIBRILLATORS
Devices with a subcutaneous lead
Components and function — Similar to a standard TV-ICD, the S-ICD is composed of a pulse generator and a lead (figure 1 and image 1 and picture 1) [17]. In contrast to a standard TV-ICD, the pulse generator and lead have different characteristics and are placed in different positions. Both the pulse generator and the lead are larger than traditional TV-ICD systems. These characteristics of the S-ICD lead to differences in how it senses and treats ventricular tachycardia:
●Sensing and rhythm detection – The cardiac rhythm is detected via a wide bipole between the two sensing electrodes or between one of the sensing electrodes and the pulse generator [18]. The electrograms generated from these vectors are similar to the those produced by a surface the electrocardiogram (ECG). Because these electrograms are smaller and quite different than those recorded from within the heart, the sensing and discrimination algorithms for S-ICDs vary substantially from the algorithms used by TV-ICDs [19]. In general, arrhythmia detection takes longer than with a TV-ICD, and T-wave oversensing is more common.
●Delivery of shocks – The S-ICD device delivers an 80 joule shock for defibrillation of ventricular tachyarrhythmias. Relative to TV-ICDs, this energy is much higher, and, accordingly, the S-ICD takes longer to charge. If VT or ventricular fibrillation persists after the initial shock, the device will reverse polarity between the electrodes and deliver subsequent shocks. The S-ICD will deliver a maximum of five shocks for a single episode of a ventricular arrhythmia. If more than 3.5 seconds of asystole occurs following a shock, the S-ICD can deliver 30 seconds of demand pacing at a rate of 50 beats per minute. During an event, the S-ICD will store the ECG tracing for subsequent review [18].
Evidence suggests that shocks delivered by an S-ICD are effective in terminating ventricular arrhythmias. In a prospective registry involving 86 centers in the United States, among 1637 patients who received the S-ICD, 1394 patients (99 percent) had successful termination of induced VT at the time of device insertion, with a 30-day complication-free rate of 96 percent [20]. In the START (Subcutaneous versus Transvenous Arrhythmia Recognition Testing) trial, which compared simulated sensing performance of the S-ICD with that of standard TV-ICDs in 64 patients, both S-ICD and TV-ICD devices were successful in detecting 100 percent of ventricular arrhythmias [21]. In this trial, the S-ICD also had greater success in discriminating supraventricular tachycardias from VTs (98 percent S-ICD versus 76.7 percent for single-chamber TV-ICD versus 68 percent for dual-chamber TV-ICD).
Preimplantation screening — A preimplantation surface ECG screening tool was developed to minimize the number of patients at risk for inappropriate shock due to T-wave oversensing errors [17,22,23]. The tool identifies patients who have large and or late T-waves relative to the QRS using three vectors that mimic the device sensing vectors of an S-ICD. Studies suggest that between 7 to 8 percent of patients are ineligible for an S-ICD due to susceptibility to T-wave oversensing and, thus, high risk of inappropriate shocks [22,23].
Implantation procedure — The S-ICD pulse generator (figure 1) is implanted in a subcutaneous or intramuscular pocket in the lower left lateral or posterolateral thoracic position, and the lead is tunneled in the subcutaneous tissue from the pulse generator to a position along the left parasternal margin (picture 2). A more posterior generator placement improves the shocking vector. The generator is typically placed between the serratus anterior and latissimus dorsi muscles (ie, intermuscular), but can be placed in a submuscular position. Advantages of the submuscular position include a lower shock impedance, higher likelihood of defibrillation success, and, in lean patients, a better cosmetic outcome. The implant procedure requires either three incisions (pocket, xiphoid, and upper sternal incisions) or two incisions with omission of the upper sternal incision [24,25]. A two incision implant technique with intermuscular placement (between anterior surface of serratus anterior and the posterior surface of latissimus dorsi) of the S-ICD generator may promote optimal posterior placement of the device, ideal cosmesis, and patient comfort [24].
Optimal positioning for defibrillation — The efficacy of S-ICD defibrillation can be maximized by optimal position of the device at the time of implantation [26,27]. Higher amounts of fat between the coil and the sternum, higher amounts of fat between the generator and the rib cage, and more anterior generator position are associated with higher risk of failure to successfully defibrillate [26].
Defibrillation threshold testing — In patients who undergo S-ICD implantation, we suggest defibrillation threshold testing (DFT) rather than no such testing. The options for DFT testing include:
●Full DFT testing – In full DFT testing, a ventricular arrhythmia is induced and high-energy defibrillation from the S-ICD is used to terminate the rhythm. This mode of testing may not be required in all patients receiving the S-ICD [28].
●High-voltage impedance testing – In high-voltage impedance (HVI) testing, the patient is shocked with a 10 joule shock synchronized to the QRS interval, and impedance is measured. An HVI <90 ohms is predictive of defibrillation success in >95 percent of patients [27].
●Low-voltage impedance measurement – Measurement of impendence between the generator and defibrillation lead can also be used to predict the success of defibrillation [29]. (See "Implantable cardioverter-defibrillators: Overview of indications, components, and functions", section on 'Defibrillation threshold testing'.)
Because of the higher energy required for defibrillation and lower experience with S-ICDs relative to TV-ICDs, DFT testing provides additional evidence that the device is likely to function appropriately. Despite the theoretical benefit of testing, not all patients with S-ICDs undergo testing [30].
Programming — Programming of S-ICDs is different from programming of TV-ICDs due to differences in sensing and charging.
●Detection zones – The programming of an arrhythmia discrimination zone can reduce the frequency of inappropriate S-ICD shocks due to supraventricular arrhythmias [31,32]. In the S-ICD, this is called a conditional zone, in which discriminants are applied to prevent shocks due to rate only; in the faster zone, only rate is used for diagnosis. Conditional zone programming reduced the incidence of inappropriate shocks caused by supraventricular arrhythmias by 70 percent (relative risk reduction) and those caused by T-wave oversensing by 56 percent [31]. In another study, which compared 226 patients with dual-zone programming and 88 patients with single-zone programming, the two-year rates of freedom from inappropriate shocks were 89.7 and 73.6 percent, respectively [32].
●Sensing algorithms – Algorithms that minimize T-wave oversensing are effective at reducing the inappropriate shocks. In a simulation using recorded T-wave oversensing episodes, as well as ventricular and supraventricular arrhythmias, an enhanced sensing algorithm reduced inappropriate detection and device charging by 39.8 percent without a significant reduction in appropriate ventricular arrhythmia detections or specificity for supraventricular arrhythmias [33].
Use of specific settings and filtering may reduce the risk of inappropriate shocks due to T-wave oversensing. In a study of 1984 patients, a filter reduced the rate of first inappropriate shocks by 50 percent and all inappropriate shocks by 68 percent. There was no significant difference in rate of appropriate shocks or in time from arrhythmia onset to appropriate shock [34]. In the UNTOUCHED study that included patients with a primary prevention ICD indication and contemporary S-ICD devices with standardized programming (eg, a conditional zone between 200 and 250 beats per minute and a shock zone at >250 beats per minute) that included contemporary discrimination algorithms (eg, filtering in 60 percent), the 18-month incidence of inappropriate shocks was 4.1 percent [4]. Patients with third-generation devices had a 53 percent reduction in inappropriate shock rates.
Complications — Common complications with the S-ICD system include inappropriate shocks, pocket infection, and lead dislodgement or migration [6].
●Inappropriate shocks – In general, the rate of inappropriate shocks with S-ICDs is nonsignificantly higher compared with TV-ICDs. Patients with a S-ICD are at higher risk of inappropriate shocks due to T-wave oversensing and noise, while patients with a TV-ICD are at higher risk of inappropriate shocks due to supraventricular tachyarrhythmias, including atrial fibrillation [6]. Additional data on inappropriate shocks are discussed elsewhere. (See 'Individualized approach' above and 'Programming' above.)
●Pocket hematoma – The development of a pocket hematoma requiring evacuation, transfusion, or extended hospital stay following S-ICD implantation is relatively low (reported rates of 1 to 5 percent) and similar to rates seen with TV-ICDs [35-37].
●Pocket infections – While generally less concerning than infections involving TV-ICD systems, in which the indwelling venous leads pose a higher risk of systemic infection, pocket infections remain a concern with the S-ICD. Pocket infections have been noted in 1 to 10 percent of S-ICD recipients [18,31,35,38-41]. In a 2017 systematic review of 5380 patients from 16 studies, the pooled rate of pocket infection was 2.7 percent [41]. Complicated infections requiring device explantation are less frequent (1 to 4 percent of patients) [31,36,39]. Unlike the recommended course of therapy for an infected TV-ICD, S-ICD infections can be treated conservatively with a course of antibiotics and without removal of the S-ICD. Because the S-ICD device does not contain any endovascular leads, the risk of infection causing bacteremia/endocarditis is reduced, and, in the event an S-ICD does require extraction, this procedure has less associated risk than transvenous lead extraction. S-ICD infections have rarely been complicated by systemic infection [16].
●Lead movement – Lead dislodgement or migration had been noted to occur in 3 to 11 percent of patients in various studies [18,38,42]. Typically, lead dislodgement or migration is thought to result from vigorous physical activity occurring without adequate fixation of the parasternal lead and requires reoperation to reposition the lead [18,38]. Initially, the lead was fixed at both the xiphoid and upper sternal locations; this essentially eliminated lead dislodgement and migration [38]. The distal (upper sternal fixation) appears to be superfluous. In most patients, a single suture sleeve is used to anchor the lead near the xiphoid.
●Lead failure and extraction – Lead failures and complicated lead extraction do occur with S-ICD systems:
•Lead failure – While it was anticipated that mechanical lead failure would be extraordinarily rare in S-ICD systems, a medical advisory was issued in December, 2020, describing a small number of lead fractures just distal to the proximal sense ring [43]. Mitigation strategies included reengineering of the lead at the site of failure, reprogramming the sensing vector, and increasing remote transmission frequency in patients with the recalled lead.
•Lead extraction – It was anticipated that extraction of chronically implanted S-ICD leads would be far more straightforward than for transvenous leads, which frequently require specialized extraction equipment due to intravascular scarring and fibrous adhesions (see "Cardiac implantable electronic device lead removal"). Though experience thus far has been limited, in some cases, fibrous encapsulation of the subcutaneous lead has made extraction more difficult than expected [44].
In a French registry describing 32 patients, simple traction was successful in 19 patients, while three required an additional incision, and nine required a mechanical sheath to break up adhesions. In one patient, lead extraction was unsuccessful; the patient had undergone subsequent coronary artery bypass graft surgery, and the lead was inadvertently entrapped in a sternal wire [45].
●Less common complications – Other less common complications that may require reintervention may include skin erosion, premature battery depletion, or explantation due to need for antitachycardia/bradycardia pacing or a new indication for resynchronization therapy [38].
In a cohort of 55 patients with the S-ICD who were followed for a median of 5.8 years, 26 patients (47 percent) underwent device replacement, with 25 of 26 patients requiring replacement for battery depletion [46]. The median time to replacement was five years, with five patients requiring replacement due to premature battery depletion within 18 months after implantation. At five years, 71 percent of devices were still intact.
Devices with a substernal lead
System description — The EV-ICD is a form of S-ICD that differs from traditional S-ICDs in that the lead is placed in a retrosternal position rather than a suprasternal position (image 2). It shares many of the advantages of the S-ICD compared with TV-ICDs, but compared with S-ICDs, it can also provide bradycardia pacing, antitachycardia pacing, and has a smaller generator. Compared with TV-ICDs, the energy required for pacing is higher and is not well tolerated by some patients.
The device is placed with surgical dissection into the substernal space, initially with the assistance of a cardiac surgeon and fluoroscopic placement of a sensing and defibrillation lead along the retrosternal space using a dedicated tunneling tool. The generator is implanted along the patient's left midaxillary line. The lead is attached to the pulse generator, which is capable of delivering shocks of up to 40 joules.
Indications and contraindications — There is limited clinical experience with the EV-ICD; it is a reasonable option for sudden death prevention in patients who may benefit from an S-ICD but who are more likely to require bradycardia or antitachycardia pacing. In addition, the EV-ICD generator is smaller than the S-ICD generator, which may favor its use in small or thin patients. The EV-ICD is contraindicated in patients with a prior sternotomy.
In a study that included patients who had an ICD indication and who underwent implantation of an EV-ICD system, successful termination of an induced ventricular arrhythmia occurred in 99 percent of patients, discharge from the hospital with a working system occurred in 95 percent of patients, and there were no major intraprocedural complications [47]. Antitachycardia pacing was successful in 51 percent of patients, and inappropriate shocks occurred in 9.7 percent of patients. At six months, 25 percent of patients had antitachycardia pacing programmed to "off," 4.6 percent had bradycardia pacing programmed to off, and 1.8 percent had postshock pacing programmed to off. The decision to program to off was related to intolerance of the pacing sensation.
SOCIETY GUIDELINE LINKS —
Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Heart failure in adults" and "Society guideline links: Ventricular arrhythmias" and "Society guideline links: Cardiac implantable electronic devices".)
INFORMATION FOR PATIENTS —
UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topic (see "Patient education: Implantable cardioverter-defibrillators (The Basics)" and "Patient education: Sudden cardiac arrest (The Basics)")
●Beyond the Basics topic (see "Patient education: Implantable cardioverter-defibrillators (Beyond the Basics)")
SUMMARY AND RECOMMENDATIONS
●Individualized approach to device selection – For patients who require an implantable cardioverter-defibrillator (ICD), the choice of ICD system is individualized to the patient's characteristics. (See 'Individualized approach' above.)
In general, patients with an indication for pacing (eg, bradycardia, cardiac resynchronization, sustained monomorphic ventricular tachycardia [SMVT]) require a transvenous ICD (TV-ICD), while patients who do not require pacing and either cannot undergo TV-ICD placement or would benefit from extravascular placement of an ICD (eg, patients who receive dialysis) may receive either a subcutaneous ICD (S-ICD) or an extravascular ICD (EV-ICD) (algorithm 1). (See 'Factors favoring transvenous ICD placement' above and 'Factors favoring subcutaneous ICD placement' above.)
●Transvenous ICD systems – Information on the components and implantation of TV-ICDs is presented separately. (See "Implantable cardioverter-defibrillators: Overview of indications, components, and functions".)
●Subcutaneous defibrillators with a subcutaneous lead – Similar to a standard TV-ICD, the S-ICD is composed of a pulse generator and a lead (figure 1 and image 1 and picture 1). Both the pulse generator and the lead are larger than traditional TV-ICD systems, which may reduce the risk of lead issues. These characteristics of the S-ICD lead to differences in how it senses and treats ventricular tachycardia (VT). A preimplantation surface ECG screening tool was developed to minimize the number of patients at risk for inappropriate shock due to T-wave oversensing errors. (See 'Components and function' above and 'Preimplantation screening' above.)
Common complications with the S-ICD system include inappropriate shocks, pocket infection, and lead dislodgement or migration. (See 'Complications' above.)
●Subcutaneous defibrillators with a substernal lead ("EV-ICD") – The EV-ICD is a form of S-ICD that differs from traditional S-ICDs in that the lead is placed in a retrosternal position rather than a suprasternal position (image 2). It can provide bradycardia pacing, antitachycardia pacing, and has a smaller generator compared with TV-ICDs, but the energy required for pacing is higher and is not well tolerated by some patients.
The device is placed with surgical dissection into the substernal space, often with the assistance of a cardiac surgeon and fluoroscopic placement of a sensing and defibrillation lead along the retrosternal table using a dedicated tunneling tool. The generator is implanted along the patient's left midaxillary line. The device cannot be placed in patients with a prior sternotomy. (See 'Devices with a substernal lead' above.)
ACKNOWLEDGMENT —
The UpToDate editorial staff thank Jeffrey Selan, MD, Arjun Majithia, MD, Jonathan Weinstock, MD, FACC, FHRS, and Leonard Ganz, MD, FHRS, FACC, who contributed to earlier versions of this topic review.
