Implantable defibrillator therapy: more than defibrillation...

textabstractDuring the past 25 years, the implantable cardioverter-defibrillator (ICD) has evolved from the treatment of last resort to the gold standard for patients at high risk for life­threatening ventricular tachyarrhythmias. Patients at high risk include those who survived life-threatening ventricular tachyarrhythmias, and patients with cardiac diseases who carry an increased risk for these tachyarrhythmias. We performed a clinical assessment during implantation and follow-up of our patients in Rotterdam. Part I Prognosis and follow-up of patients with an ICD In Chapter 1, the clinical benefit of ICD therapy, survival, and adverse events of patients who received an ICD at the Erasmus MC Rotterdam are described. Our data confirm the benefit from ICD implantation, especially for those patients with a poor left ventricular function. In Chapter 2, defibrillation efficacy testing is investigated. The role of a second defibrillation threshold test after implantation appears questionable. With the advances in ICD technology, defibrillation thresholds are low and stable, which changed the mode of death in ICD patients from instantaneous arrhythmic death to heart failure. Our data demonstrate that despite the advanced ICD technology, a subset of patients may require a second defibrillation efficacy test to confirm a poor prognosis. The feasibility of remote monitoring of ICD therapy is discussed in Chapter 3. The expanding indications for ICD therapy and the complexity of current devices have a high impact on follow-up policy. Currently, the quality of medical supervision only depends on scheduled regular follow-up visits, which is time consuming and expensive. Too long follow-up intervals may have the disadvantage of a delay in the awareness of changes of the clinical course of the underlying disease or in the technical status of the device. Transmission of stored ICD data can overcome this problem and thus offers the potential to improve patient care. Finally, a case of Twiddler’s syndrome, which was detected by home monitoring is presented in Chapter 4. Part II Rhythm discrimination by the ICD The primary goal of the ICD is to detect and subsequently terminate ventricular tachyarrhythmias. The secondary goal is to deliver therapy only when necessary. Inappropriate therapy due to atrial tachyarrhythmias is the most common adverse event in ICD patients. In this second part of the thesis, rhythm discrimination by the ICD is investigated. Chapter 5 describes a confusing stored ICD electrogram. This electrogram demonstrates an apparent induction of ventricular tachycardia after appropriate pacing by the ICD. However, accurate analysis demonstrated an artefact representing a ventricular premature beat initiating the ventricular tachycardia. The initial clinical experience with a new dual-chamber algorithm, SMART, is discussed in Chapter 6. This new algorithm is based on comparison of atrial and ventricular rates, which divide tachyarrhythmias into 3 rate branches. Next, applicable single- and dual-chamber arrhythmia discriminators are applied in order to classify the tachyarrhythmia. In our series, the SMART algorithm achieved a sensitivity of 100%, with a positive predictive value of 95.6% for all ventricular arrhythmias. The majority of misclassified episodes appeared to be atrial tachyarrhythmias with stable atrioventricular conduction. In Chapter 7, the evolution of timing-based detection algorithms in ICDs is studied. Over the last 25 years, ICDs base arrhythmia discrimination on timing-based detection criteria in order to avoid inappropriate therapy for atrial tachyarrhythmias. Original single-chamber detection criteria have been implemented as such in dual­chamber devices. Atrial signals can be reliably recognized with atrial leads and improved arrhythmia discrimination algorithms based on atrial signals were developed. However, this did not reduce the incidence of inappropriate therapy over time with the development of algorithms as was proven with comparative studies. Chapter 8 evaluated whether clinical characteristics can predict inappropriate therapy due to atrial tachyarrhythmias. We identified a history of atrial tachyarrhythmias and recurrent slow ventricular tachycardias, rate < 170 bpm, as independent predictors of inappropriate therapy. Whether device selection should depend on the knowledge of a history of atrial tachyarrhythmias still is open for debate, as inappropriate therapy equally occurs in patients with single- and dual­chamber devices. The results of our prospective, randomized study comparing the performance of tachyarrhythmia detection algorithms in single- and dual-chamber devices are presented in Chapter 9. During a mean follow-up of 12 months, the investigators classified 653 tachyarrhythmia episodes with stored electrograms: 391 episodes were ventricular tachyarrhythmias and 262 epsiodes were atrial tachyarrhythmias. Overall, no significant difference in tachyarrhythmia detection, atrial or ventricular, between single- and dual-chamber devices was observed. Not sinus tachycardia or atrial fibrillation were a problem, but atrial tachyarrhythmias with stable N:1 atrioventricular conduction remain a problem for both devices. In Chapter 10, a systematic approach for the analysis of stored electrograms is proposed. Stored electrograms in ICDs have not only improved our patient management, but also contributed to our understanding of tachyarrhythmias. Stored electrograms are usually visually analyzed, but the analysis can also be performed in a methodological way by application of blocks containing physiologic information. Part III Single-chamber, dual-chamber or biventricular devices In Chapter 11, we studied factors influencing appropriate therapy and survival in ICD patients with single- and dual-chamber devices, in an era that dual chamber devices were only implanted for patients with bradycardia indication. Survival analysis demonstrated no significant difference between patients with single- and dual­chamber devices for mortality and for event-free rate of appropriate therapy. A tendency to less inappropriate interventions was observed in a small series of dual chamber devices. In addition, it was observed that a history of atrial fibrillation contributed to appropriate therapy. Resynchronization therapy by means of biventricular pacing is a novel therapy for patients with heart failure and severely diminished left ventricular function associated with intracardiac conduction delay. In Chapter 12, we present a brief review of early trials evaluating the therapeutic effect of biventricular pacing. Furthermore, we propose a method to select the optimal right and left ventricular pacing sites together with a technique of left ventricular lead positioning. The incidence of ventricular tachyarrhythmias in ICD patients with resynchronization therapy is presented in Chapter 13. Event-free survival was analyzed for patients with either a primary or a secondary prevention indication for ICD therapy. Ventricular tachyarrhythmias are very common for congestive heart failure patients with a secondary prevention indication. Patients with primary prophylaxis have an annual event rate of 10%, even when they tend to have a worse heart failure class. The decision-making process to implant an ICD in heart failure patients for primary prophylaxis of sudden cardiac death has presently become a clinical decision, based on low left ventricular ejection fraction plus heart failure