EDITORIAL COMMENT
Implantable Cardioverter-Defibrillator ShocksA Double-Edged Sword?*
Merritt H. Raitt, MD, FACC*
Division of Cardiology, Portland VA Medical Center, Portland, Oregon.
* Reprint requests and correspondence: Dr. Merritt H. Raitt, 3710 SW U.S. Veterans Road, Portland, Oregon 97239. (Email: merritt.raitt{at}va.gov).
In this issue of the Journal, Daubert et al. (1) report on the details of inappropriate implantable cardioverter-defibrillator (ICD) shocks in the MADIT II (Multicenter Automatic Defibrillator Trial II). The MADIT II study (2) was a primary prevention ICD trial in which patients with ischemic cardiomyopathy and an ejection fraction  0.30 were randomly assigned to ICD implantation or optimal medical therapy. Patients assigned to the ICD arm had significantly improved survival. The results of MADIT II along with the results of the SCD-HeFT (Sudden Cardiac Death in Heart Failure Trial) (3) have led to the recommendation that ICDs be implanted as primary prevention for sudden death in most patients with cardiomyopathy and ejection fraction 0.30 to 0.40 (4). The reduced mortality seen in patients with ICDs compared with standard medical therapy is presumed to be on the basis of ICD shocks terminating ventricular arrhythmias. During a mean follow-up of 20 months, 128 of 719 patients with ICDs in MADIT II had 393 appropriate shock episodes and 83 patients had 184 inappropriate shock episodes. The most common cause of inappropriate ICD shocks was atrial fibrillation (AF), which accounted for 81 episodes (44%), followed by other supraventricular tachycardias, including sinus tachycardia leading to 67 episodes (36%), and abnormal sensing, which was the cause of 36 episodes (20%). If appropriate ICD shocks save lives, it may seem that a few inappropriate shocks is a small price to pay.
What is the down side of inappropriate shocks? There is a growing medical literature on the adverse psychological consequences of ICD shocks, whether appropriate or not. The ICD shocks are perceived as very painful, and in one study were graded 4.0 on a 0 to 5 scale (5). After an ICD shock, patients can be immobilized, fearing that any movement or activity might trigger another shock. Multiple shocks are the most frightening for patients, causing them to wonder if the device is really working or if it might even kill them (5–7). Those individuals who experience an ICD shock relate greater levels of psychological distress, anxiety, anger, and depression than those who do not (5–7). The ICD shocks lead to greater psychological distress for family members as well (7,8). Anxiety after ICD shocks remains elevated for an unknown amount of time, and then begins to return to normal levels as long as no further shocks occur (9). Electrical storms, defined as having more than 3 shocks in a 24-h period, occurs in 10% to 20% (10,11) of patients during the first 2 years after ICD implantation. Electrical storm sets up an adverse conditioned response that includes avoidance of activities that may have been associated with shocks, leading to heightened self-monitoring of bodily functions, increased anxiety, uncertainty, and increased dependence. In some ICD patients this leads to a reactive depression, helplessness, and post-traumatic stress disorder.
The MADIT II data raise the concern that inappropriate ICD shocks may not only have adverse psychological consequences but may also have adverse medical consequences. Daubert et al. (1) observed that patients in MADIT II who received inappropriate shocks had a higher mortality than patients who did not, with a hazard ratio of 2.29 (p = 0.025). Similarly, patients with appropriate shocks also had an increased overall mortality with a hazard ratio between 3 and 4, with the higher hazard in patients who had both appropriate and inappropriate shocks. Of course this is only an association and in no way proves a causal link between ICD shocks and an increased risk of death. It is very reasonable to postulate that patients with progressive heart failure and therefore increased mortality might be more likely to develop AF and to have inappropriate ICD shocks. These same patients may also be more likely to have ventricular tachycardia or ventricular fibrillation develop as a result of progressive congestive heart failure and to have appropriate ICD shocks before dying of congestive heart failure. Similarly, patients not on beta-blocker therapy might be more likely to have ICD shocks for sinus tachycardia, AF, or ventricular arrhythmias with overall higher mortality related to the consequences of not taking beta-blockers as apposed to being a result of ICD shocks. However, close inspection of the MADIT II data creates reason for concern. Depending on the ventricular rate and ICD programming, AF and sinus tachycardia can lead to antitachycardia pacing (ATP) instead of ICD shocks. If rapid AF and sinus tachycardia are markers for increased mortality, then one would expect inappropriate ATP to be associated with increased mortality as well. In contrast to this expectation, in the MADIT II population, although both appropriate and inappropriate shocks were associated with an increased total mortality, appropriate and inappropriate ATP were not. In fact, having only ATP episodes and no shocks was associated with a trend toward lower mortality.
How could ICD shocks contribute to increased total mortality? The primary concern is that ICD shocks might damage the myocardium. An acute elevation of serum troponin is a sensitive and specific marker of myocardial damage. Although elevated troponin levels are not infrequently seen after ICD shocks, it is impossible to determine whether the elevation is caused by myocardial ischemia and injury related to the tachycardia that led to the shock or by the shock itself. At the time of implantation, the ICD is usually tested by inducing brief (10- to 15-s) episodes of ventricular fibrillation, which are then terminated by ICD shocks. A few small studies have reported on troponin levels before and after uncomplicated ICD testing and report that troponin elevation is not infrequently seen after testing, suggesting the ICD shocks are capable of some level of myocardial injury (12–14). This myocardial injury, although mild, might be significant in patients who already have poor ventricular function and congestive heart failure. More research needs to be done, including direct studies of left ventricular function and neurohumoral activity before and after ICD shocks, to give us better idea of what exactly the adverse effects of ICD shocks might be.
It is also possible that there are adverse effects of ICD shocks that could lead to increased mortality that are not the result of direct damage of the myocardium. I have already outlined the adverse psychological effects of ICD shocks. These adverse effects include anxiety and depression. Both anxiety and depression are known to be associated with a worse prognosis in patients with congestive heart failure (15–17). Could the adverse psychological effects of ICD shocks lead to anxiety and depression and a cascade of events that culminates in an increased risk of death in patients with congestive heart failure?
Whether or not there is a causal relationship between ICD shocks and the associated increase in mortality, the psychological effects of shocks alone are reason to do everything possible to reduce the incidence of appropriate and inappropriate shocks. The ICD programming is the first line of defense. In the MADIT II trial AF was the most common cause of inappropriate shocks, and patients who had the stability detection algorithm programmed on in their ICDs, which is designed to prevent shocks for AF, were less likely to have inappropriate shocks (1). There are other detection algorithms available on many ICDs that evaluate the morphology of tachycardias or the timing and frequency of atrial and ventricular activation to prevent inappropriate shocks for supraventricular rhythms such as AF and sinus tachycardia. These algorithms help to prevent inappropriate shocks.
The next step in reducing ICD shocks is programming to use ATP instead of shocks whenever possible. Currently many electrophysiologists do not routinely program ATP in patients with ICDs. By protocol ATP was not turned on in the SCD-HeFT (3). Arguing in favor of the utility and efficacy of ATP is the Pain Free II study, which showed that aggressive use of ATP even for very fast episodes of ventricular tachycardia was effective and reduced the risk of shocks (18). Some physicians are worried that, if ineffective, ATP will delay tachycardia termination. In response, one ICD manufacturer has introduced a feature in which ATP is used to try to terminate ventricular arrhythmias while the capacitor is charging in preparation for an ICD shock. If the ATP works, the shock is aborted; if not, the shock is not delayed. Given the adverse psychological effects of ICD shocks and the possibility that shocks may increase mortality, these programming features should probably be used whenever possible. It is less clear whether medical therapy can reduce the risk of ICD shocks. If, in fact, exacerbations of congestive heart failure lead to ICD shocks, then perhaps more aggressive treatment of congestive heart failure in patients with ICDs and use of congestive heart failure monitoring protocols built into some ICDs might prevent some appropriate and inappropriate shocks. It is less clear whether empiric antiarrhythmic therapy will prevent ICD shocks, and such therapy cannot be recommended at this time because of the risk of proarrhythmia and the cardiac and noncardiac side effects of antiarrhythmic medications. The final question is whether shocks related to ICD testing might have a detrimental effect on patients and whether defibrillation testing should be done only in a limited subset of patients or at all (19). Some have suggested given the efficacy of modern ICDs that testing is not needed. Others have proposed alternative methods of testing ICD efficacy that require no or fewer ICD shocks. The potential benefits of these strategies deserve further study.
The ICD shocks may well be a double-edged sword. They have been shown to prolog life as primary and secondary prevention of sudden death in patients with severe cardiomyopathy (3,4) and in patients with a history of life-threatening ventricular arrhythmias (20). However, the shocks have important detrimental psychological effects, and the results of the analysis of inappropriate shocks in the MADIT II study reported in this issue of the Journal (1) show that inappropriate shocks are common and suggest that the same shocks that save lives by terminating ventricular arrhythmias may paradoxically increase the risk of death. Additional research needs to be done to explore the potential adverse effects of ICD shocks. In the meantime, ICD programming options currently available should be used to reduce the risk of inappropriate shocks, and ATP should be used instead of shocks whenever possible to terminate ventricular arrhythmias.
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Footnotes
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* Editorials published in the Journal of the American College of Cardiology reflect the views of the authors and do not necessarily represent the views of JACC or the American College of Cardiology. 
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References
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1. Daubert JP, Zareba W, Cannom DS, et al. MADIT II Investigators Inappropriate implantable cardioverter-defibrillators shocks in the MADIT II study: frequency, mechanisms, predictors, and survival impact J Am Coll Cardiol 2008;51:1357-1365.[Abstract/Free Full Text]2. Moss AJ, Zareba W, Hall WJ, et al. Multicenter Automatic Defibrillator Implantation Trial II Investigators Prophylactic implantation of a defibrillator in patients with myocardial infarction and reduced ejection fraction N Engl J Med 2002;346:877-883.[Abstract/Free Full Text] 3. Bardy GH, Lee KL, Mark DB, et al. Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT) Investigators Amiodarone or an implantable cardioverter-defibrillator for congestive heart failure N Engl J Med 2005;352:225-237.[Abstract/Free Full Text] 4. Zipes DP, Camm AJ, Borggrefe M, et al. ACC/AHA/ESC 2006 guidelines for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death: a report of the American College of Cardiology/American Heart Association Task Force and the European Society of Cardiology Committee for Practice Guidelines (Writing Committee to Develop Guidelines for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death) J Am Coll Cardiol 2006;48:e247-e346.[Free Full Text] 5. Ahmad M, Bloomstein L, Roelke M, Bernstein AD, Parsonnet V. Patients’ attitudes toward implanted defibrillator shocks Pacing Clin Electrophysiol 2000;23:934-938.[CrossRef][Medline] 6. Dunbar SB, Warner CD, Purcell JA. Internal cardioverter defibrillator device discharge: experiences of patients and family members Heart Lung 1993;22:494-501.[Web of Science][Medline] 7. Dougherty CM, Shaver JF. Psychophysiological responses after sudden cardiac arrest during hospitalization Appl Nurs Res 1995;8:160-168.[CrossRef][Web of Science][Medline] 8. Luderitz B, Jung W, Deister A, Manz M. Patient acceptance of implantable cardioverter defibrillator devices: changing attitudes Am Heart J 1994;127:1179-1184.[CrossRef][Web of Science][Medline] 9. Fricchione GL, Olson LC, Vlay SC. Psychiatric syndromes in patients with the automatic internal cardioverter defibrillator: anxiety, psychological dependence, abuse, and withdrawal Am Heart J 1989;117:1411-1414.[CrossRef][Web of Science][Medline] 10. Exner DV, Pinski SL, Wyse DG, et al. Electrical storm presages nonsudden death: the Antiarrhythmics Versus Implantable Defibrillators (AVID) trial Circulation 2001;103:2066-2071.[Abstract/Free Full Text] 11. Dunbar SB, Kimble LP, Jenkins LS, et al. Association of mood disturbance and arrhythmia events in patients after cardioverter defibrillator implantation Depress Anxiety 1999;9:163-168.[CrossRef][Medline] 12. Allan JJ, Feld RD, Russell AA, et al. Cardiac troponin I levels are normal or minimally elevated after transthoracic cardioversion J Am Coll Cardiol 1997;30:1052-1056.[Abstract] 13. Hurst TM, Hinrichs M, Breidenbach C, Katz N, Waldecker B. Detection of myocardial injury during transvenous implantation of automatic cardioverter-defibrillators J Am Coll Cardiol 1999;34:402-408.[Abstract/Free Full Text] 14. Schluter T, Baum H, Plewan A, Neumeier D. Effects of implantable cardioverter defibrillator implantation and shock application on biochemical markers of myocardial damage Clin Chem 2001;47:459-463.[Abstract/Free Full Text] 15. Jiang W, Kuchibhatla M, Cuffe MS, et al. Prognostic value of anxiety and depression in patients with chronic heart failure Circulation 2004;110:3452-3456.[Abstract/Free Full Text] 16. Sherwood A, Blumenthal JA, Trivedi R, et al. Relationship of depression to death or hospitalization in patients with heart failure Arch Intern Med 2007;167:367-373.[Abstract/Free Full Text] 17. Jiang W, Kuchibhatla M, Clary GL, et al. Relationship between depressive symptoms and long-term mortality in patients with heart failure Am Heart J 2007;154:102-108.[CrossRef][Web of Science][Medline] 18. Wathen MS, DeGroot PJ, Sweeney MO, et al. PainFREE Rx II Investigators Prospective randomized multicenter trial of empirical antitachycardia pacing versus shocks for spontaneous rapid ventricular tachycardia in patients with implantable cardioverter-defibrillators. Pacing Fast Ventricular Tachycardia Reduces Shock Therapies (PainFREE Rx II) trial results. Circulation 2004;110:2591-2596.[Abstract/Free Full Text] 19. Swerdlow CD, Russo AM, Degroot PJ. The dilemma of ICD implant testing Pacing Clin Electrophysiol 2007;30:675-700.[CrossRef][Medline] 20. The Antiarrhythmics versus Implantable Defibrillators (AVID) Investigators A comparison of antiarrhythmic drug therapy with implantable defibrillators in patients resuscitated from near-fatal ventricular arrhythmias N Engl J Med 1997;337:1621-1623.[Free Full Text]
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