Satisfactory Implantable Cardioverter-Defibrillator Programming for Shock Reduction

– No Pain, No Gain –

Implantable cardioverter-defibrillator (ICD) therapy is proven to reduce mortality.^1–4 However, ICD shocks are painful and cause acute adverse physiological effects. The mortality benefit comes at the cost of some morbidity, including the pain and adverse effects caused by defibrillating shocks, both appropriate and inappropriate. Although antitachycardia therapy (ATP) may be proarrhythmic, it has many advantages over shocks. Shocks reduce the quality of life⁵ and cause myocardial injury,⁶ but ATP does not. Frequent delivered or aborted shocks deplete the ICD’s battery, but ATP does not. Responses to ATP that does not terminate the tachycardia can be used to differentiate ventricular tachycardia (VT) from sinus or atrial tachycardia with 1:1 atrioventricular (AV) conduction and thus optimize ICD programming.⁷ Unnecessary shock therapies, appropriate or inappropriate, should be reduced. Most ventricular arrhythmias treated in the ventricular fibrillation (VF) zone are in fact monomorphic VT and can be terminated by ATP. Therefore, many newer ICDs permit 1 sequence of ATP before or during charging in the VF zone.

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Antitachycardia Pacing

The PainFREE RX II (Pacing Fast VT REduces Shock ThErapies) and EMPIRIC (Comparison of Empiric to Physician-Tailored Programming of Implantable Cardioverter Defibrillators) trials demonstrated that specific VT and VF detection and therapy programming strategies reduced the frequency of shock episodes.^8,9 Both trials assessed the ICD detection and therapy strategies to safely reduce the morbidity associated with ICD shocks in a patient population that included primary and secondary prevention patients with no indication for a biventricular (Bi-V) ICD device. The purpose of the PREPARE (Primary Prevention Parameters Evaluation) study was to adapt these strategies specifically to primary prevention patients both with and without Bi-V ICD indications.¹⁰ Strategically chosen tachycardia detection and therapy options targeting primary prevention patients can safely reduce the morbidity related to ICD therapy. By moderately extending the detection duration, using fast rate cutoffs, ATP in faster rate zones, and existing supraventricular tachycardia (SVT) discrimination algorithms, the PREPARE study programming can be safely used to reduce the combined morbidity of spontaneous shock episodes, arrhythmic syncope, and untreated sustained symptomatic VT/VF events in primary prevention patients.

In this issue of the Journal, Watanabe et al¹¹ report the primary result of the SATISFACTION study, which aimed to provide a more precise estimate of the efficacy of ATP therapy in the Japanese ICD population. The authors should be congratulated for the effort they put into the thorough analysis of populations with and without an ischemic etiology. They demonstrate that ATP success was similar for patients in both groups. Although the primary prevention ratio was similar in both studies (48% in PainFREE and 42% in SATISFACTION), non-ischemic etiology was more prevalent in the SATISFACTION (59%) than in the PainFREE (17%) study.^8,11

Self-Terminating Tachycardias

Although the narrower term “inappropriate therapy” means delivered therapies during a rhythm other than VT/VF, the broader term “unnecessary therapy” also includes therapies for VT/VF that would have terminated if the therapy had been delayed. Strategic programming should reduce any unnecessary therapies.^10,12 Two prospective randomized trials in primary prevention patients reported fewer shocks using a duration of 30 beats for fast VT/VF (up to 10 s) without a significant increase in syncope or death.^10,13 It seems likely that the duration of up to 30 beats studied for fast VT is safe and preferable for slower VTs. Overtreatment of self-terminating VT is more common with ATP than with shocks because ATP is delivered immediately after detection, whereas shocks are delayed 6–15 s. Early studies were performed with short detection durations of 12–16 beats, and evidence suggests that many of these VTs would have terminated spontaneously if the duration had been longer, particularly in primary prevention patients. In the PREPARE study, the duration for detection of fast VT was 30/40 beats. The adjusted success rate for ATP was only 49%, and at least 85% of fast VTs lasting at least 12 beats terminated spontaneously.¹⁰ In the RELEVANT study, 90% of fast VTs lasting at least 12 beats terminated spontaneously.¹³ In the PainFREE and SATISFACTORY studies the detection in the VF zone was similarly short (18 of 24 intervals).^8,11 ATP during charging has the same battery cost as a shock and increases the likelihood that shocks will be delivered for self-terminating VT because the confirmation process after charging (reconfirmation) is less specific than the usual redetection process after ATP.

Programming Detection and Therapies

Programming to minimize unnecessary therapies is a major focus of managing ICD recipients.¹² Because there is no significant difference in the efficacy of ATP between a ischemic and nonischemic etiology, as the SATISFACTION study demonstrated, the strategic programming of ICDs can be done separately for primary or secondary prevention, and in patients with VT/VF or VF only, regardless of etiology. Figure shows the strategic ICD programming that I recommend for shock reduction. Primary prevention patients have fewer VT episodes with faster ventricular rates than secondary prevention patients with monomorphic VT.¹⁴ Informed by this observation, strategic programming reduces unnecessary shocks based on the following principles: (1) longer detection time (up to 30–40 beats or 10 s) to reduce the detection of self-terminating VT or SVT that only crosses the rate boundary transiently;^12,13 (2) sinus-VT/VF boundary in the range of 330–300 ms (180–200 beats/min) usually rejects SVTs in adults on β-blockers, yet rarely withholds therapy from hemodynamically significant VTs; (3) systematic programming of SVT-VT discriminators in patients capable of rapid AV conduction; and (4) programming of ATP in all detection zones.⁹ For primary prevention, 1- or 2-zone programming is recommended.

Figure.

Strategic ICD programming for shock reduction in (A) primary prevention patients, (B) secondary prevention patients and (C) patients with VF/polymorphic VT only. See the text for details. *¹The boundary between 2 VT zones should be based on the cycle length at which different durations for detection or different ATP is preferred. *²Especially in CPVT, short detection intervals and exceptionally long detection times (delay) are recommended. ATP, antitachycardia pacing; BrS, Brugada syndrome; bpm, beats per minute; CL, cycle length; CPVT, catecholaminergic polymorphic ventricular tachycardia; cVT, clinically documented ventricular tachycardia; LQT, long QT syndrome; SVT, supraventricular tachycardia; VF, ventricular fibrillation; VT, ventricular tachycardia.

In secondary prevention patients with clinical monomorphic VT, the VT interval should be set at least 40 ms longer (20 beats/min slower) than the slowest VT. In the VT zone, therapy is programmed to 2–4 bursts of ATP, followed by maximum output shocks. There is controversy about the output of ICD shocks because higher output shocks might cause severer myocardial injury.⁶ However, I prefer programming using maximum output shocks to maximize the likelihood of terminating atrial fibrillation and minimize the risk of inducing VF by shocks weaker than the upper boundary of the defibrillation threshold. The boundary between the 2 VT zones should be based on the cycle length at which different durations for detection or different ATP is preferred. For patients whose only arrhythmia is polymorphic VT/VF (eg, long QT syndrome, Brugada syndrome, catecholaminergic polymorphic VT), single-zone programming with a sinus-VF boundary in the range of 300–240 ms may be considered. Especially in CPVT, short detection intervals and exceptionally long detection times (delay) are recommended. Because electrical storm can be initiated by appropriate or inappropriate shocks and subsequent catecholaminergic release.

Recently, a subanalysis of the MADIT-RIT study demonstrated the importance of ICD reprogramming for mortality reduction.¹² Conventional ICD programming was associated with an increased risk of all-cause mortality as compared with ICD programming with a cut-off >200 beats/min, even when taking into account ICD therapies delivered. Tailored ICD programming is sometimes difficult, but should be done.

Disclosures

Akihiko Nogami has received honoraria from St. Jude Medical and Boston Scientific; and an endowment from Medtronic and Johnson & Johnson.

References

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