Version May 2024
INTRODUCTION — Ventricular tachyarrhythmia is a common cause of sudden cardiac arrest (SCA) and sudden cardiac death (SCD). Although cardiopulmonary resuscitation, including chest compressions and assisted ventilation, can provide transient circulatory support for the patient with SCA, the only effective approach for terminating pulseless ventricular tachycardia (VT) or ventricular fibrillation (VF) is electrical defibrillation. Success with external defibrillation led to the development of an implantable defibrillator in the mid-1960s. It was not until 1980 that the first automatic internal defibrillator was implanted in humans [1,2]. (See "Pathophysiology and etiology of sudden cardiac arrest".)
Because of its high success rate in terminating VF rapidly, along with the results of multiple clinical trials showing improvement in survival, implantable cardioverter-defibrillator (ICD) implantation is generally considered the first-line treatment option for the secondary prevention of SCD and for primary prevention in certain populations at high risk of SCD due to VT/VF. Alternatives to ICD implantation include antiarrhythmic drugs, ablative surgery, catheter ablation, and, in rare individuals, cardiac transplantation. (See "Sustained monomorphic ventricular tachycardia in patients with structural heart disease: Treatment and prognosis", section on 'Radiofrequency catheter ablation' and "Secondary prevention of sudden cardiac death in heart failure and cardiomyopathy" and "Pharmacologic therapy in survivors of sudden cardiac arrest".)
This topic will review the approach to optimal ICD programming. The general indications for ICD implantation as well as the components and functionalities of the ICD, the clinical trials documenting the efficacy of an ICD in different clinical settings (including both secondary and primary prevention), complications of ICD placement, and follow-up care of patients with ICDs are discussed separately. (See "Secondary prevention of sudden cardiac death in heart failure and cardiomyopathy" and "Primary prevention of sudden cardiac death in patients with cardiomyopathy and heart failure with reduced LVEF" and "Cardiac implantable electronic devices: Long-term complications" and "Cardiac implantable electronic devices: Patient follow-up" and "Cardiac implantable electronic devices: Periprocedural complications".)
OVERVIEW OF ICD PROGRAMMING AND THERAPIES
General approach to programming — Our approach to optimal ICD programming seeks to emphasize that, while the decision to implant the ICD and perioperative management are important factors in patient outcome, 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. In particular, evidence for ICD programming is often gleaned from adult populations, and direct translation to pediatric patients may not always be appropriate; this is particularly pertinent for rate cutoff settings in children, teenagers, and young adults. Thus, programming guidelines are simply that: guidelines. They are not always applicable to every patient, and care must be taken to tailor therapy to the individual. Fortunately, most patients do not have such specific requirements, and an empiric approach to programming is reasonable for the majority.
Readers who wish for a more comprehensive overview on ICD programming are directed to 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].
Types of ICD programming and therapies — As ICD technology has evolved, the number and variety of available programming and therapeutic options have dramatically increased [3]. Contemporary ICDs have a variety of flexible programming and therapeutic options [5]:
●Bradycardia settings – While ICDs are implanted for the treatment of tachyarrhythmias, patients occasionally have a need for bradycardia support also. In addition, the pacemaker settings of an ICD may influence patient outcome even when an indication for bradycardia pacing does not exist [6,7]. A general principle of ICD bradycardia pacing settings is to minimize the percentage of right ventricular pacing. (See "Overview of pacemakers in heart failure".)
●Cardiac resynchronization therapy (CRT) – The indications for ICD implantation and CRT overlap to a degree. A general principle of ICD bradycardia pacing settings in patients with CRT-defibrillators is to maximize the percentage of biventricular pacing. A detailed discussion of CRT devices is presented separately. (See "Cardiac resynchronization therapy in heart failure: Indications and choice of system".)
●Arrhythmia detection – At their most basic, ICDs detect arrhythmias based on duration criteria (an arrhythmia must be of sufficient length to be significant) and rate criteria (an arrhythmia must exceed a programmed rate cutoff to be significant). Therefore, an episode must be both sufficiently long and sufficiently rapid to trigger therapy. Recommendations for rate criteria and duration have evolved over time and are further refined by the addition of supraventricular tachycardia (SVT) discriminators and algorithms to reduce detection of noise (both physiological and nonphysiological sources of noise).
●Arrhythmia discrimination – The ability to distinguish arrhythmias requiring ICD therapy from other heart rhythms is crucial to appropriate ICD function. ICDs can be programmed to assess heart rate, suddenness of onset, atrioventricular (AV) dissociation, interval stability, QRS templates, and other parameters to help identify ventricular tachyarrhythmias requiring therapy.
●Noise discrimination – Algorithms to avoid signal noise being detected as an arrhythmia have evolved over time. These aim to prevent physiological noise (eg, T-wave oversensing) and nonphysiological noise (eg, electromagnetic interference) from being falsely detected as ventricular arrhythmia and triggering inappropriate therapy. (See "Cardiac implantable electronic device interactions with electromagnetic fields in the nonhospital environment".)
●Multiple available therapies – ICDs can treat ventricular tachyarrhythmias with antitachycardia pacing (ATP) and/or shocks. These therapies have parameters that can be varied and adjusted (eg, the number, rate, and duration of ATP cycles and the delivered energy for cardioversion and defibrillation). In each therapy zone, a sequence of therapies (ATP, cardioversion, or defibrillation) can be delivered. After each therapy, the device reevaluates the rhythm, and if the tachyarrhythmia persists, the next therapy is delivered. These therapies are discussed in detail below. (See 'Tachycardia therapies' below.)
●Multiple zones – ICDs can be programmed to provide different therapies to tachyarrhythmias in up to three heart rate zones. The rationale for this approach is that relatively slow ventricular tachyarrhythmias (eg, ventricular tachycardia [VT] with a heart rate <180 beats per minute) may not lead to loss of consciousness or other unstable symptoms for at least several minutes. Additionally, VT can often be terminated with ATP, which can be delivered quickly and with no pain and minimal battery drainage. By contrast, faster VTs (eg, heart rate >250 beats per minute) are more likely to be unstable and poorly tolerated; they can require high-energy defibrillation and can become increasingly difficult to terminate if definitive therapy is delayed. Thus, the most successful approach for such fast VTs is high-energy defibrillation. However, there is some evidence that ATP can be effective even for very fast VTs and that self-termination is not uncommon. This has led to strategies employing longer detection times and attempts to terminate VT with ATP before or during capacitor charging. (See 'Duration criteria for ventricular arrhythmia detection' below.)
●Avoidable therapy – A relatively new concept to ICD programming is to recognize therapy as not just appropriate (delivered for ventricular arrhythmia) or inappropriate (delivered for SVT or noise), but to recognize that any given therapy may be avoidable. It is increasingly accepted that self-terminating arrhythmias are common and that programming to treat slower or short duration arrhythmias tends to overtreat patients, often with negative consequences. Thus, eliminating avoidable therapy is one of the aims of modern ICD programming. (See 'Our approach to tachycardia therapies' below.)
TACHYCARDIA DETECTION — Modern ICD programming for the detection of arrhythmias utilizes higher detection rates, longer detection durations, antitachycardia pacing (ATP), algorithms that discriminate supraventricular tachycardia (SVT) from ventricular tachycardia (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.
ICDs detect arrhythmias based on two primary criteria (both must be satisfied):
●Duration criteria – An arrhythmia must be of sufficient length to be significant
●Rate criteria – An arrhythmia must exceed a programmed rate cutoff
With early generation ICDs in clinical practice, the focus was on rapid detection and treatment of VT/ventricular fibrillation (VF). This was necessary due to the inherent limitations of the devices: long charge times, potential for undersensing, monophasic waveforms, and the knowledge that defibrillation thresholds increased with VF duration. Therefore, early generation ICDs were programmed to detect and treat arrhythmia rapidly.
With subsequent technological improvements in ICDs, resulting in the advent of stored electrograms, improved electrogram sensing, and the move toward primary prevention of sudden cardiac death, there has been a gradual appreciation of the adverse effects of an ICD shock. Initially, the focus was mainly on inappropriate shocks (ie, shocks delivered for nonlife-threatening arrhythmias or because of oversensing). Oversensing is divided into physiological oversensing (eg, T-wave oversensing or double counting of QRS) or nonphysiological oversensing (eg, electromagnetic interference or lead fracture noise). More recently, there has been an appreciation that ventricular arrhythmias may self-terminate without therapy and that slower arrhythmias need not necessarily be treated. Early shock therapies for benign or self-terminating ventricular arrhythmias may appear to be appropriate shocks, but if they were not going to be absolutely necessary, then shocks for these rhythms are avoidable shocks.
Our approach to tachycardia detection — Our recommendations for tachycardia detection 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 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.
●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.
●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 documented tachycardia rate but not faster than 200 beats per minute.
The aim of the above three recommendations is to reduce the total number of ICD therapies. Faster minimum rates for detection may be appropriate in young patients or those in whom SVT-VT discriminators cannot reliably distinguish SVT from VT, provided no clinical VT exists below this rate.
●Programming multiple tachycardia detection zones can be useful to allow effective use of tiered therapy and/or SVT-VT discriminators. This may allow a shorter delay for faster (and potentially unstable) arrhythmias while allowing slower (and potentially stable) arrhythmias a longer time to self-terminate and/or more attempts at ATP.
●Discrimination algorithms to distinguish SVT from VT should be programmed to include rhythms with rates faster than 200 beats per minute and potentially up to 230 beats per minute to reduce inappropriate therapies. Discriminator time-out functions should generally be programmed OFF. T-wave oversensing algorithms should usually be ON.
●Lead-failure alerts should be activated to detect potential lead problems.
Duration criteria for ventricular arrhythmia detection — For the vast majority of patients with modern ICDs, the devices should be programmed to a longer duration interval. This will allow for a greater number of nonsustained arrhythmias to terminate spontaneously, without any ICD therapy, thereby reducing avoidable shocks (table 1).
Early ICDs used short duration "detection" criteria of up to five seconds (variable depending on manufacturer and tachycardia rate) before either ATP or charging to shock. This time period was comprised of detection time plus duration or number of intervals. More recently, awareness of potential harm from avoidable shocks has led to strategies of prolonged detection settings, with data derived from numerous studies, initially from the nonrandomized PREPARE and RELEVANT studies but subsequently from three randomized trials [8-12]:
●MADIT-RIT, a randomized trial of three different ICD programming and therapy strategies, assigned 1500 patients receiving an ICD for primary prevention (both ischemic and nonischemic cardiomyopathy) to one of three programming strategies [10]:
•"Conventional" therapy programming – 2.5-second delay at rates of 170 to 199 beats per minute; 1-second delay at rates of 200 or more beats per minute.
•Delayed therapy programming – 60-second delay at rates of 170 to 199 beats per minute; 12-second delay at rates of 200 to 249 beats per minute; 2.5-second delay at rates of 250 or more beats per minute.
•High-rate therapy programming – No therapy at rates of 170 to 199 beats per minutes; 2.5-second delay at rates of 200 or more beats per minute.
Patients were followed for an average of 1.4 years, with the primary outcome being the time to first delivery of inappropriate therapy and two prespecified secondary outcomes (all-cause mortality and first syncopal episode). While relatively few patients received appropriate ICD therapy (242 patients, or 16 percent, with 70 percent of appropriate therapies being ATP), the primary outcome occurred in 152 patients (11 percent). When compared with conventional programming:
•Inappropriate therapies were lower in both high-rate therapy (hazard ratio [HR] 0.21, 95% CI 0.13-0.34) and the delayed therapy (HR 0.24, 95% CI 0.15-0.40) groups.
•All-cause mortality was lower in the high-rate therapy group (HR 0.45, 95% CI 0.24-0.85), and there was a trend toward lower mortality in the delayed therapy group that was not statistically significant (HR 0.56, 95% CI 0.30-1.02).
●The ADVANCE III trial, a randomized, single blind trial of 1902 patients receiving an ICD for primary (1425 patients, 75 percent) or secondary (477 patients, 25 percent) prevention, assigned patients to "standard" detection (18/24) or long detection (30/40) strategies for ventricular rates >187 beats per minute (cycle length ≤320 milliseconds) [11]. Programming for treatment options of ATP and shocks was the same for all participants. Long detection was associated with a highly significant reduction of overall therapies (appropriate and inappropriate ATP and/or shocks), inappropriate shocks, and all-cause hospitalizations.
●In the PROVIDE trial, which randomized 1670 patients to experimental programming (two VT and one VF zone requiring 25-, 18-, and 12-beat detections, respectively) or conventional programming (12-beat detection in each of two zones), there was a 36 percent reduction in two-year all-cause shock rate and reduction in mortality with a prolonged detection interval (HR 0.7, 95% CI 0.50-0.98) [12].
These studies (PREPARE, RELEVANT, MADIT-RIT, ADVANCE III, and PROVIDE) consistently showed that programming a prolonged detection algorithm benefited the patient without compromising safety. Importantly, ADVANCE III included a subset of secondary prevention patients (published separately) in whom similar findings were reported [13]. Subsequent meta-analyses of these trials have demonstrated a mortality benefit in the combined therapy-reduction arms without an increased risk of syncope [14,15]. However, there are some limitations to be acknowledged, including that not all ICD manufacturers are represented in these trials [16], there are no data from aging devices in which charge times can be long, and there will always be specific situations in which prolonged detection times may be deleterious (eg, ventricular undersensing).
Rate criteria for ventricular arrhythmia detection — Ventricular tachyarrhythmia detection by implantable devices is primarily based on rate. For the vast majority of patients with modern ICDs, the devices should be programmed to a higher rate at which therapies should be provided. This will prevent inappropriate shocks for slower supraventricular tachyarrhythmias and allow for slower nonsustained arrhythmias to terminate spontaneously, thereby reducing avoidable shocks.
Heart rates can be extremely rapid during ventricular tachyarrhythmias, and it is less likely that such rates are achieved during supraventricular tachyarrhythmias, thus making rate a powerful component of arrhythmia discrimination. However, VT can also have slower rates in the range of those of supraventricular tachyarrhythmias or even of sinus tachycardia. Therefore, any rate cutoff will always imply a trade-off between maximizing sensitivity for ventricular tachyarrhythmia detection at the expense of inappropriate detection of fast supraventricular tachyarrhythmias and maximizing specificity at the expense of some slow VTs going undetected [17].
The recognition of a significant number of inappropriate therapies in ICD patients, as well as their potentially deleterious consequences, prompted the development of studies that tested if programming faster rate criteria would reduce avoidable ICD therapies and, particularly, shocks. In the MADIT-RIT trial, the primary end point of first occurrence of inappropriate therapy was observed in 20 percent of the conventional group and in 4 percent of the high-rate group over a mean follow-up of 1.4 years. ICD shocks occurred in 4 and 2 percent in the conventional and high-rate groups, respectively. Importantly, all-cause mortality was approximately double in the conventional group (6.6 percent) than in the high-rate group (3.2 percent). Observational studies have demonstrated that even a rate cutoff of 220 beats per minute has been shown to be safe and reduce avoidable shocks [18]. (See 'Duration criteria for ventricular arrhythmia detection' above.)
Supraventricular tachyarrhythmia discrimination — SVTs are common in patients with ventricular arrhythmias [19-21]. If the ICD interprets an SVT incorrectly as VT, the patient may experience inappropriate shocks, which occur in up to 20 to 25 percent of patients [22-25]. The majority of inappropriate shocks for SVT occur within the range of 181 to 213 beats per minute. Therefore, adjustment of rate criteria and the deployment of SVT discriminators are most likely to be successful at around these rates. Once the duration and rate criteria for VT/VF have been satisfied, SVT discriminators aim to classify the rhythm as SVT (therapies for VT withheld) or VT (therapies delivered).
Examples of algorithms used to distinguish SVT from VT include:
●AV dissociation – Identification of different and distinct rhythms in the atrium and the ventricle, particularly when the ventricular rate exceeds the atrial rate, is consistent with AV dissociation seen with VT.
●Atrial rate exceeds ventricular rate – In dual-chamber devices (and those with an atrial sensing ring on the ventricular lead), information from the atrial electrode may help differentiate VT from atrial tachyarrhythmias [19-21,26]. The primary discriminator is heart rate; if the atrial rate is greater than the ventricular rate, the arrhythmia is almost certainly SVT, usually atrial fibrillation (AF) or atrial flutter. However, care must be taken not to withhold therapy in the case of a "dual tachycardia" (eg, VT with coexisting AF).
●QRS templates – Many devices record templates of the ventricular electrogram during intrinsic rhythm. During a tachyarrhythmia, the device compares the electrograms during the tachycardia with the baseline recording. Deviations in shape, duration, and polarity all increase the likelihood that the device will categorize the tachycardia as VT or VF.
●An interval stability criterion detects irregularity in cycle length and can distinguish AF from VT. Obvious pitfalls with this are regularization of AF (perhaps from antiarrhythmic drugs) and irregular VT [27,28].
●An onset criterion monitors the cycle length for the sudden or abrupt onset of a high ventricular rate (indicative of a VT) rather than a gradually increasing heart rate (as might be seen in exercise-induced sinus tachycardia). As this discriminator is applied "once only," care should be taken not to allow this discriminator to withhold therapy indefinitely (in case of VT/VF occurring after the rate threshold is crossed gradually). Some dual-chamber devices have "chamber of onset" as a discriminator.
Each of these discrimination features is designed to help prevent SVT from being erroneously categorized as VT or VF; therefore, they reduce the likelihood of inappropriate shocks. However, as none of these discriminators are 100 percent specific for SVT, these discriminators can be programmed to "time out" so that the ICD eventually treats the arrhythmia as VT/VF. As discriminator reliability has improved, recommendations have moved away from endorsing the use of the "time out" feature [29].
In addition to discrimination criteria, most contemporary ICDs have a "second look" feature designed to help prevent or limit inappropriate shocks. Once the criteria for delivering a shock are met, the capacitors charge. This takes several seconds (more as the device ages). Following charging, the device reevaluates the heart rhythm to confirm that the tachycardia persists and has not spontaneously terminated. If the tachycardia has resolved, the shock will be diverted.
Dual-chamber ICDs can be programmed for mode switching to prevent inappropriate tracking of atrial arrhythmias. In addition, some devices can deliver therapy for atrial tachyarrhythmias such as pace termination of atrial flutter or AF [20,21]. (See "The role of pacemakers in the prevention of atrial fibrillation".)
Therapeutic alternatives for patients who continue to have frequent inappropriate shocks for atrial tachyarrhythmias include antiarrhythmic drugs and catheter ablation. (See "Pharmacologic therapy in survivors of sudden cardiac arrest", section on 'Treatment of breakthrough arrhythmias'.)
Noise discriminators — Noise detected by an ICD can lead to inappropriate shocks. The source of noise may be physiological or nonphysiological. Although less common than inappropriate shocks due to SVT, noise-related therapies can be repetitive and cause serious harm to a patient.
Physiological noise can be due to T-wave oversensing, double counting of QRS events, or P wave oversensing. Displacement of the ICD lead into the fibrillating atrium is also possible in the immediate post-implant period. The problem of T-wave oversensing has led to several methods to identify this, including high bandpass filters, altering the sensing bipole, reducing sensitivity, and looking for specific repetitive patterns consistent with T-wave oversensing. Additionally, physiological noise due to T-wave oversensing can often be remedied with reprogramming (eg, adjusting sensitivity, etc).
Nonphysiological noise is most commonly related to ICD lead failure. Several high-profile lead recalls have brought this issue to the forefront and led to the development of algorithms designed to alert the clinician early to a potential lead failure and to delay or divert therapy if noise is the likely reason for the episode detected.
Generally, the following features are identified when detecting lead noise:
●Intervals are very short; so short as to be physiologically unlikely
●Such short intervals are transient and repetitive
●If noise is present on the lead distal bipole, it is absent on the wide bipole (shock coil electrogram)
The first two of these are used to provide alerts (vibratory, audible, or via home monitor). The third may be used to withhold shocks. Many of the algorithms are designed for particular lead failure (eg, Lead Integrity Alert on Medtronic Devices are designed to detect Fidelis fractures, SecureSense on St. Jude Medical Devices to detect Riata failures). Accompanying data, such as a change in lead impedance, sensing, or threshold, are frequently available from remote monitoring and may assist in diagnosing lead failure.
TACHYCARDIA THERAPIES — Modern ICD programming for the treatment of arrhythmias utilizes antitachycardia pacing (ATP) as the initial therapy for many patients with ventricular tachycardia (VT), given the high rates of successful VT termination following ATP. If ATP is unsuccessful, or if the presenting rhythm is ventricular fibrillation (VF), ICDs can deliver one or more defibrillatory shocks in an effort to terminate VT/VF.
Although therapies delivered by the ICD aim to abort sudden cardiac death, both appropriate and inappropriate ICD shocks have been associated with a considerable increase in the risk of mortality [30-35]. In the SCD-HeFT trial, the risk of mortality was fivefold higher in patients who received appropriate ICD shocks and twofold higher in patients who received inappropriate shocks [31]. Likewise, in pooled data from four studies of 2135 ICD patients, shocked VT was associated with a 32 percent increase in the risk of mortality, and patients receiving a shock had lower survival rates than patients treated with ATP only [32]. ICD shocks are likely to be a marker of advanced heart disease, but defibrillation therapies have been associated with troponin release and increased left ventricular dysfunction. Additionally, ICD shocks deplete the battery and are painful for the patient.
Our approach to tachycardia therapies — Our recommendations for tachycardia therapy 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 all patients with structural heart disease and ATP-capable devices, ATP therapy should be active for all ventricular tachyarrhythmia detection zones to include arrhythmias up to 230 beats per minute (except when ATP is documented to be ineffective or proarrhythmic). This aims to reduce total shocks.
●ATP therapy should be programmed to deliver at least one ATP attempt with a minimum of eight stimuli and a cycle length 84 to 88 percent of the tachycardia cycle length for ventricular tachyarrhythmias. Burst ATP therapy is preferred to ramp ATP therapy.
●We activate shock therapy in all ventricular tachyarrhythmia therapy zones to improve the termination rate of ventricular tachyarrhythmias, except in rare cases where ATP only might be prescribed for hemodynamically stable monomorphic VT.
●We program the initial shock energy to the maximal available energy in the highest rate detection zone to improve the first shock termination of ventricular arrhythmias, unless specific defibrillation testing demonstrates efficacy at lower energies.
Antitachycardia pacing — VT, particularly reentrant VT associated with scar from a prior myocardial infarction, can often be terminated by pacing the ventricle at a rate slightly faster than the VT. When a paced impulse enters the reentrant circuit during a tachycardia, it can depolarize a segment of the circuit, leaving that segment refractory when the reentrant wave 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 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 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".)
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.
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 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 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." 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
●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 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".)
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