S h o c k Av o i d a n c e a n d t h e Newer Tachycardia Th er ap y Algorithms Kushwin Rajamani, MD, Adam S. Goldberg, MD, Bruce L. Wilkoff, MD* KEYWORDS Inappropriate shocks Avoidable shocks Antitachycardia pacing (ATP) ICD programming
KEY POINTS Patients who receive shock therapy have an associated reduction in the mortality benefit from implantable cardioverter defibrillators (ICDs). Prolonging the time to therapy and restricting therapy to faster tachycardias can significantly reduce shocks overall, with an associated mortality benefit. The decision on single-chamber versus dual-chamber defibrillator implantation needs to be individualized. Remote monitoring facilitates earlier recognition of patient-related and device-related issues, reducing the risk of inappropriate therapy. Medical therapy and catheter ablation are effective adjunctive strategies in patients with ICD shocks to reduce or eliminate future events.
Implantable cardioverter defibrillator (ICD) therapy has been proven in several large-scale clinical trials to reduce mortality in patients with primary and secondary indications.1–4 There is evidence to suggest that receiving shocks may reduce the mortality benefit; however, more recent study has suggested that this maybe due to the arrhythmia or comorbidities rather than the shock itself.5,6 Shock therapy, despite the benefits, is also associated with significant psychological issues, including anxiety, depression, and posttraumatic stress.7–9 Therefore, reducing both appropriate and inappropriate shocks, without compromising
patient safety, is desirable. This can be achieved with a multifaceted approach with medical therapy, improved device-based programming, and ablation strategies. This article discusses these strategies.
BACKGROUND The first ICD was implanted in 1980, and was revolutionary in the approach to cardiac arrhythmias and sudden cardiac death.10 It is now well established that ICD therapy improves mortality and is generally considered to be cost-effective.2,3,11 Over many years, large randomized trials have identified patients with greatest potential benefit
Drs K. Rajamani and A.S. Goldberg have no disclosures. Dr B.L. Wilkoff is on the Medical Advisory Board for Medtronic, St. Jude Medical, and Spectranetics. He has received speaker honoraria from Boston Scientific and royalties from Medtronic. Section of Cardiac Pacing and Electrophysiology, Robert and Suzanne Tomsich Department of Cardiovascular Medicine, Sydell and Arnold Miller Family Heart and Vascular Institute, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA * Corresponding author. E-mail address: [email protected]
Cardiol Clin 32 (2014) 191–200 http://dx.doi.org/10.1016/j.ccl.2014.01.002 0733-8651/14/$ – see front matter Ó 2014 Elsevier Inc. All rights reserved.
Rajamani et al from ICD placement and therapy, and this is reflected in current guidelines.12 ICD implantation has become a cornerstone of therapy for many patient groups, including those with inherited or acquired cardiomyopathies and channelopathies. Although sudden cardiac death (SCD) is a leading cause of death in the United States and Europe, identification of those at higher risk of death than the general population has been critical in reducing mortality in select groups. Although there are inherent risks associated with ICD implantation (infection or lung, vascular, or cardiac injury), in these populations the benefits of prophylaxis outweigh the risks. Despite these benefits, ICD shocks can have a profound effect on patients when a shock is delivered, such as physical and psychological trauma, as well as impairment of their quality of life and general health.7–9,13–15 As a result, reduction in shock exposure is an ideal strategy, and various methods have been developed to avoid both appropriate and inappropriate shocks. In this pursuit, it is important to understand the types of shocks that patients are exposed to (Box 1). It has been reported that among patients with an ICD who have received a shock from the device, about one-third were inappropriate.3 There are conflicting data regarding the effect of ICD shocks on survival. Some studies have indicated that mortality is increased among patients with an ICD who receive shock for any reason compared with receiving no shock.5,16 An analysis of 2135 patients from 4 trials of antitachycardia pacing (ATP) therapy to reduce shock therapy revealed that shocked ventricular arrhythmic events were associated with increased mortality risk compared with ATP-terminated tachycardia.17 This was attributed to the substantially higher ventricular arrhythmia burden among these patients and a poorer survival compared with ATP-only treated patients. A recent study supported this finding
that the increased mortality is due to the underlying arrhythmia, and not the physical effect of the shock itself, as those who receive shock for inappropriate reasons did not have increased mortality compared with those without any shock.6 In the United States, more than 250,000 ICD implantations occurred in 2011, with most (>70%) for primary prevention indications.18 Inevitably, clinicians will be faced with increasingly complex management issues pertaining to shock therapy, both appropriate and inappropriate. Knowledge in strategies to reduce shock therapy is vital, as it is associated with significant beneficial implications to the patient, as well as the health care system (Box 2).
Management Options to Minimize Shock Therapy 1. Medical therapy 2. Catheter ablation 3. Advanced device programming General measures, such as electrolyte replacement and avoidance of aggravating factors like sleep deprivation, caffeine, alcohol, over-the-counter medications, herbal remedies (eg, gingko, ephedra, ginseng, guarana, and yohimbine), and cardiac stimulants (eg, theophylline, cocaine, and amphetamines), should be used. Patients with underlying heart disease should be on optimal medical therapy (eg, aspirin, angiotensin-converting enzyme inhibitor/angiotensin receptor blocker, beta-blockers, aldosterone antagonists, statins). Treatment of other underlying structural or ischemic heart disease should be considered, as these are associated with proarrhythmia.
MEDICAL THERAPY Beta-blocker therapy can be beneficial in reducing shocks of any type, as they can suppress supraventricular tachycardias, as well as ventricular ectopy and arrhythmias. Recently, analysis of the
Box 1 Classifications of shock therapy 1. Appropriate shocks: triggered by lifethreatening ventricular arrhythmias, which can be further classified as follows: a. Necessary shocks: shock delivered due to failure of antitachycardia pacing (ATP) therapy/other means b. Avoidable shocks: as a result of underutilization of other termination methods 2. Inappropriate shocks: shocks triggered from incorrect detection
Box 2 Benefits of shock-avoidance techniques 1. Improved survival 2. Better quality of life 3. Reduced hospitalizations 4. Increased ICD battery life 5. Lower health care expenditure 6. Less need for post-shock care 7. Greater acceptance of ICD therapy
Newer Tachycardia Therapy Algorithms Multicenter Automatic Defibrillator Implantation With Cardiac Resynchronization Therapy (MADITCRT) trial found that there were even intraclass differences in the rates of inappropriate ICD therapy (ATP or shock without the presence of ventricular arrhythmia) among beta-blockers. Carvedilol was associated with a 36% lower rate of inappropriate ICD therapies compared with metoprolol, and a 50% reduction in inappropriate therapies due to atrial fibrillation.19 Amiodarone is a commonly utilized antiarrhythmic but has serious long-term adverse effects. In the Sudden Cardiac Death in Heart Failure (SCD-HeFT) trial, although amiodarone was not associated with increased mortality overall, among patients with New York Heart Association Class III heart failure, increased deaths were observed.3 A recent meta-analysis found that amiodarone was associated with a 29% reduction of sudden cardiac death and 18% reduction of cardiovascular mortality.20 The Optimal Pharmacologic Therapy in Cardioverter Defibrillator Patients (OPTIC) study was a randomized trial that compared amiodarone plus beta-blocker with sotalol alone or beta-blocker alone in 412 patients who had received a dual-chamber ICD for inducible or spontaneous ventricular tachycardia (VT) or ventricular fibrillation (VF) and left ventricular ejection fraction lower than 40% or syncope. During 1 year of follow-up, shocks occurred in 41 patients (38.5%) assigned to beta-blocker alone, in 26 (24.3%) assigned to sotalol alone, and in 12 (10.3%) assigned to amiodarone plus beta-blocker, a difference that was statistically significant.21 Despite the lack of clinical data applicable to current defibrillation systems, it has been noted that chronic amiodarone administration causes a significant increase in defibrillation threshold (DFT). In addition, clinicians need to be aware that antiarrhythmic drugs can influence antitachycardia pacing and tachycardia detection.22,23
CATHETER ABLATION Although medications are often the first line of adjunctive therapy in patients with repeated episodes of shock for ventricular arrhythmia, they are associated with considerable side effects and inherent risks. Further, medical therapy is not universally successful in preventing further ventricular arrhythmia, and in some patients a more invasive approach must be taken with catheter ablation. Determining the effectiveness of catheter ablation in clinical studies has been somewhat challenging as a result of maintenance of antiarrhythmic therapy pre and post ablation.
More recent studies have shown that in patients with recurrent VT and subsequent ICD therapies, catheter ablation significantly decreases the frequency of subsequent VT events. In one trial using THERMOCOOL catheters (Biosense Webster, CA), patients had a median of 11.5 episodes of VT in the 6 months preceding ablation, compared with a median of 0 episodes in the 6 months following, and frequency of VT was reduced by more than 75% in two-thirds of patients.24 VT recurrence after ablation was associated with the presence of increased patient comorbidities, age, and higher number of inducible VTs at time of ablation. Initial attempts at catheter ablation were complicated by the need for hemodynamic stability while in the arrhythmia, allowing mapping to be performed. However, with improved technology, specifically electroanatomic mapping, targets and foci of arrhythmia could be identified and tagged as areas of low voltage or scar.25 This allowed for mapping and successful ablation of targets while in sinus or with pace mapping, rather than the need for induction of ventricular arrhythmia, with an associated reduction in VT recurrence and subsequent need for ICD therapies.25,26 Despite advancements in catheter ablation techniques and technology, it remains an invasive procedure with relatively high procedural mortality. Furthermore, the previously mentioned ablation trials have shown that there is still a high post procedure follow-up mortality, with onethird attributable to arrhythmic death, and another third to heart failure mortality. Perhaps most importantly, few data remain regarding ablation in nonischemic disease, and this substrate differs in that there is diffuse scar, often with more epicardial origin than the endocardial scar seen with prior infarction.27 In electrical storm and in incessant VT presentations, catheter ablation has been shown to improve outcomes by altering the substrate or by targeting triggers of arrhythmia (premature ventricular contractions). Studies have shown the ability to eliminate electrical storm, and to reduce ICD therapies in patients who underwent ablation.28,29 Finally, studies have also evaluated the utility of catheter ablation before ICD implantation. These have shown that ablation significantly decreases the rate of ICD shocks and increases the time to first ventricular arrhythmic event.30,31
DEVICE PROGRAMMING There are many different adjustable parameters in ICDs that allow for the reduction of shocks, both avoidable and inappropriate, and thus improve patient satisfaction and outcomes.
Rajamani et al Lowest Detected Rate Patients who receive defibrillators for primary prevention tend to have spontaneous VT rates that are significantly faster in comparison with patients implanted for secondary prevention indications. Among 829 patients with an ICD in a primary prevention study, 269 patients (33.2%) received a shock, of which 128 patients received only appropriate shocks, based on a slowest detection rate of 188 beats per minute (bpm) (