Optimal Programming of Implantable Cardiac-Defibrillators
The following are 10 points to remember about optimal programming of implantable cardioverter-defibrillators (ICDs):
1. Patients with ICDs receive unnecessary shocks, which have been associated with proarrhythmia, anxiety, depression, poor quality of life, and possibly increased mortality. This article discusses tachycardia detection algorithms and programming selections aiming to reduce unnecessary or inappropriate shocks.
2. The PREPARE, RELEVANT, and MADIT-RIT trials have evaluated the strategy of prolonged detection time in primary prevention patients to reduce inappropriate therapy. The rates of syncope in patients with prolonged detection time and the conventional programming (rapid detection) were not different. Additionally, the MADIT-RIT trial showed dramatic reduction in mortality in patients with programmed prolonged detection times. Similar trials with prolonged detection times in the secondary prevention population are lacking.
3. Single-chamber ICD algorithms for superventricular tachycardia-ventricular tachycardia (SVT-VT) discrimination include onset, stability, and intracardiac electrogram morphology. Dual-chamber algorithms add atrial rate information to standard ventricular rate–only algorithms, and compare the relative timing of atrial and ventricular events during arrhythmia, or mix interval and morphology algorithms, incorporating atrial information.
4. There is conflicting evidence about the advantages of dual-chamber ICD algorithms over single-chamber algorithms at discriminating SVT from VT. Because secondary prevention patients tend to have slower VT rates, which overlap with supraventricular arrhythmias, dual-chamber ICD algorithms appear to be advantageous in this population. Atrial undersensing and far field R-wave oversensing are significant causes of arrhythmia misclassification in the dual-chamber ICD algorithms.
5. ICD discriminator timeout can override inhibition of therapy for an SVT if the tachycardia persists longer than a programmed time period; however, this can lead to inappropriate shocks for sustained SVTs. In the PREPARE study, programming timeouts off was not associated with inappropriate inhibition of therapy.
6. Antitachycardia pacing (ATP) terminates up to 90% of VT episodes with the acceleration risk of 1-5%. In the PainFREE II trial, the rates of syncope and mortality were unaffected by ATP use, but the quality of life was significantly better in the ATP arm.
7. Novel subcutaneous ICD uses three sensing vectors recorded from three subcutaneous electrodes to construct far field electrograms. A shock zone and a conditional shock zone can be programmed. Rate alone is used to determine therapy in the shock zone; morphology discriminators are applied in the conditional shock zone.
8. Additional features in conventional ICDs, which aim to reduce inappropriate shocks, are T-wave oversensing prevention, noise detection, and lead fracture surveillance.
9. The Boston Scientific Dynamic Noise Algorithm is useful to prevent myopotential detection. Medtronic Lead-Integrity Alert algorithm has been shown to be effective in detecting most Sprint Fidelis lead fractures, and reduces the incidence of inappropriate shocks related to lead fracture. St. Jude’s SecureSense right ventricular lead noise discriminations detect noise caused by lead fracture or a loose set screw.
10. Short-long-short sequences may be implicated in the initiation of up to 15% of VT/ventricular fibrillation episodes in ICD patients. Ventricular pacing avoidance modes, lower-rate programming, and capture management algorithms can lead to short-long-short sequences. Although pause-prevention algorithms such as rate smoothing may reduce VT burden in selected patients, the randomized, controlled VAST (Ventricular Arrhythmia Suppression Trial) study failed to show efficacy in the general ICD population.
Keywords: Tachycardia, Supraventricular, Boston, Heart Conduction System, Ventricular Fibrillation, Syncope, Pacemaker, Artificial, Electrophysiologic Techniques, Cardiac, Death, Sudden, Cardiac, Defibrillators, Implantable, Primary Prevention
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