returns, thus terminating the tachycardia. ATP, or overdrive pacing, refers to the delivery of short bursts (eg, eight beats) of rapid ventricular pacing to terminate VT. Although a variety of algorithms exist, ATP is usually programmed to be delivered at a rate that is slightly faster (eg, commencing at a cycle length 10 to 15 percent shorter) than the rate of the detected tachycardia [36-39]. In several studies, as many as 95 percent of episodes of spontaneous VT were successfully terminated with ATP [36,38-41]. Utilization of ATP therapy has evolved from tailored therapy used only if shown to be effective in the electrophysiology (EP) lab to empiric programming as routine therapy. Delivery of ATP has been shown to reduce inappropriate shocks and appropriate shocks and improve quality of life [8-11,42-46]. This programming may improve survival [10]. Indeed, several studies have shown that ATP is effective at terminating slow and fast VT with very low rates of adverse events [41,47- 52]. In the PainFREE Rx II trial, 634 patients with ICDs were randomly assigned to empiric ATP or shock for initial therapy of spontaneous rapid VT (188 to 250 beats per minute) [47]. After a mean follow-up of 11 months, 431 episodes of rapid VT occurred in 98 patients. Pacing was successful in terminating 229 of 284 such episodes in the ATP arm (81 percent). The incidence of VT acceleration, syncope, and sudden death was the same in the ATP and shock arms (seven versus five episodes). The use of ATP during ICD capacitor charging has been clinically validated as safe and effective [51]. It is important to recognize that inappropriate therapies, including inappropriate ATP, delivered primarily in the setting of supraventricular arrhythmias have been associated with increased mortality in the MADIT-RIT and MADIT-CRT trials [33,53]. However, the overall safety of ATP and its value in preventing avoidable ICD shocks are well established. One concern with ATP is that rapid pacing can cause VT to degenerate into VF. For this reason, all ICDs also have high-energy defibrillation, which can be used after ATP as a backup therapy if necessary. However, this theoretical problem associated with ATP appears to be uncommon [23,37,47,48,54,55]. ATP programming Although the ideal number of ATP attempts (ie, bursts) has not been definitively determined, we advocate for two or more attempts, recognizing that a law of https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-optimal-programming/print 12/29 7/6/23, 3:08 PM Implantable cardioverter-defibrillators: Optimal programming - UpToDate diminishing returns applies as the number of attempts increase, and that as ATP becomes more aggressive, proarrhythmia is more likely. The most effective ATP duration is likewise uncertain; however, most clinicians program eight-pulse bursts of ATP. While one study reported that up to five ATP attempts was safe [56], most data support the use of up to two ATP attempts, as additional attempts yield very little additional efficacy [41,47-52,56,57]. The 2015 HRS/EHRA/APHRS/SOLAECE Expert Consensus Statement on Optimal Implantable Cardioverter-Defibrillator Programming and Testing advocates for "at least one ATP attempt" [3]. In the ADVANCE-D Trial, a prospective randomized clinical trial of 925 patients, eight-pulse ATP was as effective and safe as fifteen-pulse ATP [58]. In the PITAGORA ICD clinical trial, which randomized 206 patients with an ICD to two ATP strategies (interval burst versus interval ramp), burst pacing was more effective for terminating fast VT episodes (between cycle lengths of 240 and 320 milliseconds), although ramp ATP appears more proarrhythmic than burst ATP [59]. In primary prevention ICD patients, the VT cycle length is unknown, so empiric programming is necessary. For secondary prevention patients with recorded VT, the programming can be tailored to the rate of the VT and other clinical features, such as hemodynamic tolerability. Slow monomorphic VT that is well tolerated favors an approach using ATP termination with at least two to three sequences of eight pulses or more. The use of a second burst of ATP has also been shown to increase effectiveness from 64 to 83 percent even in the fast VT range of 188 to 250 beats per minute [57]. Although a second burst has clear value, value beyond two bursts is limited to uncommon clinical situations [42]. However, recent data have shown programming up to six-burst ATP therapies for VTs 150 to 200 beats per minute can avoid ICD shocks in most (88 percent) patients. There is incremental benefit for up to six ATP attempts with a risk of accelerating the VT in nearly 7 percent. Ramp ATP after three failed bursts were shown to be similarly effective [60]. Cardioversion A shock that is synchronized to be delivered at the peak of the R wave is referred to as cardioversion. Because VT is an organized electrical rhythm, the delivery of an electrical shock during the vulnerable period of repolarization can cause VT to degenerate into VF. Synchronized cardioversion prevents shock delivery during the vulnerable period. (See "Basic principles and technique of external electrical cardioversion and defibrillation".) Although ICDs can be programmed to deliver synchronized shocks at a range of energies up to the maximum output of the device (usually 30 to 40 joules), synchronized cardioversion can https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-optimal-programming/print 13/29 7/6/23, 3:08 PM Implantable cardioverter-defibrillators: Optimal programming - UpToDate often terminate VT with relatively low energy (eg, 10 joules or less). However, low-energy shocks have been shown to be less effective and more arrhythmogenic compared with high-energy shocks [60]. Defibrillation An unsynchronized shock (ie, a shock delivered randomly during the cardiac cycle) is referred to as defibrillation. Because VF is not an organized rhythm, synchronized cardioversion is neither possible nor necessary. Defibrillation can be delivered across a range of energies. Initial shocks are sometimes programmed for lower energies to reduce capacitor charge time and save battery (although all shocks should be at least 10 joules above the defibrillation threshold). Subsequent shocks are usually delivered at higher energies, often at the maximum output of the ICD (eg, 30 to 40 joules), to optimize efficacy. If the defibrillation threshold is determined, the first shock should be 10 joules above this value. In the absence of defibrillation testing, maximum output shocks are programmed. Defibrillation threshold testing was once a routine part of ICD implantation, with the aim of confirming the correct connection of high voltage components and the ability of the system to detect and terminate VF. However, with stepwise technological innovation (eg, biphasic shocks, high-output devices), failure to defibrillate is increasingly rare. Risks of defibrillation testing include hypoperfusion from the VT/VF, failure to defibrillate, the consequences of the shock, and the sedation required to render the patient amnestic of the shock. Therefore, the risk to benefit ratio of routine defibrillation testing is seen by many to be unfavorable. When the defibrillation threshold is not established, defibrillation is programmed to maximum energy from the first shock. The advantages and disadvantages of defibrillation threshold testing are discussed separately. (See "Implantable cardioverter-defibrillators: Overview of indications, components, and functions", section on 'Defibrillation threshold testing'.) BRADYCARDIA PROGRAMMING While ICDs are implanted primarily for the treatment of tachyarrhythmias, some patients require pacing for bradycardia at the time of implantation, while others will develop a need for bradycardia support at a later time. In addition, the pacemaker settings of an ICD may influence patient outcome even when an indication for bradycardia pacing does not exist [6]. In general, single- and dual-chamber ICDs should be programmed to avoid ventricular pacing, whenever feasible; cardiac resynchronization therapy-defibrillator (CRT-D) devices should be programmed to encourage biventricular pacing. (See "Permanent cardiac pacing: Overview of devices and indications" and "Overview of pacemakers in heart failure".) https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-optimal-programming/print 14/29 7/6/23, 3:08 PM Implantable cardioverter-defibrillators: Optimal programming - UpToDate Our approach to bradycardia programming Our recommendations for bradycardia programming in patients with an ICD are generally in agreement with the 2015 HRS/EHRA/APHRS/SOLAECE Expert Consensus Statement on Optimal Implantable Cardioverter- Defibrillator Programming and Testing and the 2019 focused update discussing manufacturer- specific programming [3,4]. For patients who also have sinus node disease and guideline-supported indications for a pacemaker, we provide dual-chamber (right atrial [RA] and right ventricular [RV]) pacing along with the ICD, rather than RV pacing alone, to reduce the risk of atrial fibrillation (AF) and stroke, to avoid pacemaker syndrome, and to improve quality of life. For patients with a single- or dual-chamber ICD without guideline-supported indications for a pacemaker, we adjust the pacing parameters to minimize ventricular stimulation in an effort to improve survival and reduce heart failure (HF) hospitalization. For patients who are in sinus rhythm, with no or only mild left ventricular (LV) dysfunction, and AV block where ventricular pacing is expected, we provide dual-chamber (RA and RV) pacing rather than RV pacing alone, in order to avoid pacemaker syndrome and to improve quality of life. For patients with sinus rhythm, mild to moderate LV dysfunction, and AV block where frequent RV pacing is expected (>50 percent), we suggest biventricular pacing (ie, cardiac resynchronization therapy [CRT]) rather than dual-chamber (RA and RV) pacing in order to improve the combination of HF hospitalization, LV enlargement, and death. For patients who have chronotropic incompetence, we program the ICD to provide sensor augmented physiological rate-responsive pacing, especially if the patient is young and physically active. For patients with a dual-chamber ICD and native PR intervals of 230 milliseconds or less, the mode, automatic mode change, and rate response should be set so that the patient s native AV conduction is favored and minimizes RV pacing. For patients with biventricular pacing, the device should be programmed to produce the highest achievable percentage of ventricular pacing, preferably above 98 percent, in order to improve survival and reduce HF hospitalization. Additionally, the algorithms providing automatic adjustment of AV delay and/or LV-RV offset should be activated, in order to obtain a high percentage of LV synchronized pacing and to reduce the incidence of clinical events. https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-optimal-programming/print 15/29 7/6/23, 3:08 PM Implantable cardioverter-defibrillators: Optimal programming - UpToDate Pacing modes and rates for bradycardia in ICD patients The knowledge concerning the most suitable pacing modes and rates for patients with bradycardia is mostly gained from trials involving patients with a pacemaker. Although similar, there are some distinct differences among patients with an ICD that influence best programming practice for bradycardia. In patients with a pacemaker but no ICD, dual-chamber (ie, AV) pacing has been associated with lower rates of atrial fibrillation (AF) and stroke [61]; however, no difference in mortality has been shown between dual-chamber AV pacing and ventricular-only pacing modes. Among ICD recipients in the DAVID trial, patients without symptomatic bradycardia fared worse with DDDR pacing than with back-up VVI pacing, most likely due to unnecessary RV pacing associated with DDDR mode [7]. In patients with persistent sinus bradycardia, atrial pacing (AAI) with back-up ventricular pacing (eg, AAI-DDD) is the mode of choice. This is particularly true for patients with sinus node disease where the greatest benefits in AF reduction and stroke have been seen. In AV node disease, large randomized trials have failed to show superiority of dual- chamber pacing modes for clinical end points [62]. Therefore, the benefit of dual-chamber pacing modes is largely confined to improved exercise capacity and the avoidance of pacemaker syndrome, which occurs when single-chamber ventricular pacing conducts retrogradely to the atria resulting in atrial contraction against closed AV valves. This can cause symptoms such as dyspnea, dizziness, palpitations, and chest pain. (See "Modes of cardiac pacing: Nomenclature and selection", section on 'Pacemaker syndrome'.) Evidence supporting the superiority of dual-chamber pacing modes in exercise capacity and the avoidance of pacemaker syndrome is tempered by the lack of improvement demonstrated in hard clinical end points. Taken together with the increased complication risk and expense of dual-chamber ICDs, patients for whom no indication for bradycardia pacing exists generally undergo implantation of single-chamber ICDs over dual-chamber ICDs. In these patients, care should be taken to avoid ventricular pacing if possible. Further information on algorithms designed to minimize ventricular pacing is presented separately. (See "Overview of pacemakers in heart failure", section on 'Pacing modes to limit RV pacing'.) THE SUBCUTANEOUS ICD The novel subcutaneous ICD (S-ICD) follows many of the same principles as intravascular ICDs but is considered here separately for duration criteria, rate criteria, and discrimination https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-optimal-programming/print 16/29 7/6/23, 3:08 PM Implantable cardioverter-defibrillators: Optimal programming - UpToDate algorithms. A full discussion of the S-ICD is presented separately. (See "Subcutaneous implantable cardioverter defibrillators".) Programming is simpler with the S-ICD compared with transvenous ICDs. The programming choices in S-ICDs are limited to detection rate, one- or two-zone detection, post-shock pacing, and therapies on or off. Some automatic features may be manually overridden. As the S-ICD does not act as a pacemaker, bradycardia programming recommendations do not apply. Candidates for the S-ICD must initially be screened with a modified trichannel surface ECG that mimics the sensing vectors of the S-ICD system. This test is designed to assess the R wave to T wave ratio for appropriate signal characteristics and relationships. If the screening is not satisfactory for at least one of the three vectors both supine and standing, an S-ICD should not be implanted. Some patients (those with hypertrophic cardiomyopathy in particular) may benefit from additional screening during exercise [63]. At implant, the S-ICD automatically analyzes and selects the optimal sensing vector. Detection of ventricular tachycardia (VT) or ventricular fibrillation (VF) by the S-ICD is programmable utilizing a single or dual zone. In the single-zone configuration, shocks are delivered for detected heart rates above the programmed rate threshold: the "shock zone" [64]. In the dual-zone configuration, arrhythmia discrimination algorithms are active from the lower rate: the "conditional shock zone." In this latter zone, a unique discrimination algorithm is used to classify rhythms as either shockable or nonshockable. If they are classified as supraventricular arrhythmias or nonarrhythmic oversensing, therapy is withheld. The system utilizes an initial 18 of 24 duration criteria (nonprogrammable) prior to capacitor charging commencement; however, this duration is automatically extended following nonsustained ventricular tachyarrhythmia events. A confirmation algorithm is also utilized at the end of capacitor charging to ensure persistence of the ventricular arrhythmia prior to shock delivery. Shocks for spontaneous (noninduced) episodes are delivered at a nonprogrammable 80 joules regardless of the therapy zone of origination. The S-ICD VT detection algorithm, when programmed to include a conditional shock zone, has been demonstrated to be as effective as transvenous ICD system detection algorithms for the prevention of detection of induced supraventricular arrhythmias [65]. Furthermore, in the clinical evaluation of the conditional shock zone, it was strongly associated with a reduction in inappropriate shocks and did not result in prolongation of detection times or increased syncope [66]. The Praetorian trial showed the S-ICD to be noninferior to transvenous ICDs for patients without a pacing indication for the composite endpoint of inappropriate shocks and device-related https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-optimal-programming/print 17/29 7/6/23, 3:08 PM Implantable cardioverter-defibrillators: Optimal programming - UpToDate complications [67]. However, this trial has come under some criticism for event adjudication and for combining outcomes trending in opposite directions (which favors noninferiority) in the composite endpoint [68]. PRACTICAL PROGRAMMING GUIDANCE With the number of device companies and models available, together with the complexity of programming permutations, attempts have been made to give practical programming guidance. With the publication of the 2015 HRS/EHRA/APHRS/SOLAECE Expert Consensus Statement on Optimal Implantable Cardioverter-Defibrillator Programming and Testing and the 2019 focused update, manufacturer-specific programming recommendations were published online with the aim of providing a practical framework within which to optimally program ICDs as per the recommendations of that document [3,4]. The "Manufacturer-Specific Programming Guidelines" are hosted on the Heart Rhythm Society website. It is hoped that this will keep pace with new technology as it is released so as to become a living document of ICD programming best practice. 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: 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." th th The Basics patient education pieces are written in plain language, at the 5 to 6 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 th th sophisticated, and more detailed. These articles are written at the 10 to 12 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 https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-optimal-programming/print 18/29 7/6/23, 3:08 PM Implantable cardioverter-defibrillators: Optimal programming - UpToDate 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 Background Implantable cardioverter-defibrillator (ICD) implantation is usually the preferred option for the secondary prevention of sudden cardiac death (SCD) and for primary prevention in certain populations at high risk of SCD due to ventricular tachycardia/fibrillation (VT/VF). (See 'Introduction' above.) General approach Our approach to optimal ICD programming seeks to emphasize that much of the risk/benefit ratio of these devices is determined by the way they are programmed. When recommending ICD programming settings, we are often guided in our general approach by randomized trials. However, specific patient circumstances may mandate a different approach from that of generic programming recommendations. (See 'General approach to programming' above.) Tachycardia detection Modern ICD programming utilizes higher arrythmia detection rates, longer detection durations, algorithms that discriminate supraventricular tachycardia (SVT) from VT, and specific electrocardiographic (ECG) features to minimize the sensing of noise. All these strategies combined provide the patient with the security of ICD therapy when needed with the aim of eliminating inappropriate and avoidable therapies. (See 'Tachycardia detection' above and 'Our approach to tachycardia detection' above.) For patients with any ICD (primary or secondary prevention), we recommend that tachyarrhythmia detection duration criteria be programmed to require the tachycardia to continue for at least 6 to 12 seconds (or for 30 intervals), rather than a shorter duration, before completing detection (Grade 1B). For patients with a primary prevention ICD (and for secondary prevention patients in whom the VT rate is not known), we recommend that the slowest tachycardia therapy zone limit should be programmed between 185 and 200 beats per minute (Grade 1B). For secondary prevention ICD patients for whom the clinical VT rate is known, we program the slowest tachycardia therapy zone at least 10 beats per minute below the https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-optimal-programming/print 19/29 7/6/23, 3:08 PM Implantable cardioverter-defibrillators: Optimal programming - UpToDate documented tachycardia rate but not faster than 200 beats per minute. Tachycardia therapies Modern ICD programming for the treatment of arrhythmias utilizes ATP as the initial therapy for many patients with VT, given the high rates of successful VT termination following ATP. If ATP is unsuccessful, or if the presenting rhythm is VF, ICDs can deliver one or more defibrillatory shocks in an effort to terminate VT/VF. (See 'Tachycardia therapies' above and 'Our approach to tachycardia therapies' above.) Bradycardia programming While ICDs are implanted primarily for the treatment of tachyarrhythmias, some patients require pacing for bradycardia at the time of implantation or at a later time. In general, single- and dual-chamber ICDs should be programmed to avoid ventricular pacing, whenever feasible; cardiac resynchronization therapy-defibrillator (CRT-D) devices should be programmed to encourage biventricular pacing. (See 'Bradycardia programming' above and 'Our approach to bradycardia programming' above.) Subcutaneous ICD Programming is simpler with the subcutaneous ICD (S-ICD). The programming choices in S-ICDs are limited to detection rate, one- or two-zone detection, post-shock pacing, and therapies on or off. Some automatic features may be manually overridden. As the S-ICD does not act as a pacemaker, bradycardia programming recommendations do not apply. (See 'The subcutaneous ICD' above.) Adjunctive therapies These include antiarrhythmic medication and/or catheter ablation and are important in the management of patients treated with an ICD, particularly as an effort to prevent recurrent ICD shocks in patients who have received multiple ICD shocks. Additionally, many other therapies such as those indicated for heart failure or in specific conditions (eg, cervical sympathectomy for long QT syndrome) are complementary to ICD therapy. Thus, a multidisciplinary approach is warranted for the management of ICD patients. (See "Secondary prevention of sudden cardiac death in heart failure and cardiomyopathy", section on 'Other treatment options' and "Overview of the management of heart failure with reduced ejection fraction in adults".) Use of UpToDate is subject to the Terms of Use. REFERENCES 1. 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Toff WD, Camm AJ, Skehan JD, United Kingdom Pacing and Cardiovascular Events Trial