QUARTERLY FOCUS ISSUE: HEART RHYTHM DISORDERS: STATE-OF-THE-ART PAPER
Appropriate Evaluation and Treatment of Heart Failure Patients After Implantable Cardioverter-Defibrillator DischargeTime to Go Beyond the Initial Shock
Joseph D. Mishkin, MD*,
Sherry J. Saxonhouse, MD*,
Gregory W. Woo, MD*,
Thomas A. Burkart, MD*,
William M. Miles, MD*,
Jamie B. Conti, MD*,
Richard S. Schofield, MD*,
Samuel F. Sears, PhD and
Juan M. Aranda, Jr, MD*,*
* Division of Cardiovascular Medicine, University of Florida College of Medicine, Gainesville, Florida
Departments of Psychology and Cardiovascular Sciences, East Carolina University, Greenville, North Carolina
Manuscript received May 15, 2009;
revised manuscript received June 25, 2009,
accepted July 12, 2009.
* Reprints requests and correspondence: Dr. Juan M. Aranda, Jr, Division of Cardiovascular Medicine, University of Florida College of Medicine, 1600 SW Archer Road, Room M421, Gainesville, Florida 32610 (Email: arandjm{at}medicine.ufl.edu).
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Abstract
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Multiple clinical trials support the use of implantable cardioverter-defibrillators (ICDs) for prevention of sudden cardiac death in patients with heart failure (HF). Unfortunately, several complicating issues have arisen from the universal use of ICDs in HF patients. An estimated 20% to 35% of HF patients who receive an ICD for primary prevention will experience an appropriate shock within 1 to 3 years of implant, and one-third of patients will experience an inappropriate shock. An ICD shock is associated with a 2- to 5-fold increase in mortality, with the most common cause being progressive HF. The median time from initial ICD shock to death ranges from 168 to 294 days depending on HF etiology and the appropriateness of the ICD therapy. Despite this prognosis, current guidelines do not provide a clear stepwise approach to managing these high-risk patients. An ICD shock increases HF event risk and should trigger a thorough evaluation to determine the etiology of the shock and guide subsequent therapeutic interventions. Several combinations of pharmacologic and device-based interventions such as adding amiodarone to baseline beta-blocker therapy, adjusting ICD sensitivity, and employing antitachycardia pacing may reduce future appropriate and inappropriate shocks. Aggressive HF surveillance and management is required after an ICD shock, as the risk of sudden cardiac death is transformed to an increased HF event risk.
Key Words: implantable cardioverter-defibrillator therapy • heart failure • appropriate shock • inappropriate shock
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Abbreviations and Acronyms
| | ACEI = angiotensin-converting enzyme inhibitor | | AF = atrial fibrillation | | ATP = antitachycardia pacing | | AV = atrioventricular | | HF = heart failure | | ICD = implantable cardioverter-defibrillator | | NYHA = New York Heart Association | | RV = right ventricular | | SVT = supraventricular tachycardia | | VF = ventricular fibrillation | | VT = ventricular tachycardia |
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More than 200,000 patients with heart failure (HF) have received an implantable cardioverter-defibrillator (ICD) to reduce their risk of sudden cardiac death since 2005, when the last of the HF ICD prevention trials was published (1,2). Since the original American College of Cardiology/American Heart Association/North American Society of Pacing and Electrophysiology 2002 guidelines introduced the concept of ICDs as primary prevention therapy for patients with left ventricular dysfunction and myocardial infarction, subsequent updated practice guidelines have expanded ICD indications to include patients with nonischemic cardiomyopathy, an ejection fraction  35%, and New York Heart Association (NYHA) functional class II or III HF (3–5). Current practice guidelines are based on several prospective multicenter clinical trials that support the use of ICD therapy to reduce the risk of sudden death in a wide variety of HF patients (6–10).
Data from  6,000 patients enrolled in clinical trials have revealed several complicating issues arising from the universal use of ICDs in HF patients (Table 1). Twenty percent to 35% of HF patients who receive an ICD for primary prevention will receive an appropriate shock within 1 to 3 years for a life-threatening arrhythmia (11,12). Forty-five percent of HF patients who survive a cardiac arrest and receive an ICD for secondary prevention will receive a shock within 1 year of implant (9). The incidence of inappropriate shock in the HF ICD population is as high as 27%, with an overall annual shock rate of 7.5% (11).
Among HF patients, an ICD shock is associated with a 2- to 5-fold increase in mortality, most commonly due to progressive HF (11). It is not known whether the arrhythmia leading to ICD shock is a marker for worsening HF or whether the shock itself leads to worsening HF. Subgroup analyses from MADIT-II (Multicenter Automatic Defibrillator Implantation Trial II) confirm that ICD shocks increase the risk for first and recurrent HF events (9,13).
Despite the risks associated with an ICD shock, current practice guidelines do not offer a clear stepwise approach to the evaluation and treatment of HF patients who experience their initial ICD shock. This review describes an evidence-based, multidisciplinary strategy for evaluating and managing HF patients who receive an ICD shock, with special emphasis on aggressive monitoring to reduce future shocks and HF events.
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HF Prognosis After ICD Discharge
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Although physicians are commonly relieved that sudden cardiac death was prevented after an ICD shock, current data suggest that the natural history of the disease is now transformed. The MADIT-II investigators first described the issue of worsening prognosis after ICD therapy (6). After an ICD shock for a life-threatening arrhythmia, hospitalizations for HF were more frequent, and mortality was increased 3-fold (13). Within 1 year of an ICD shock for ventricular tachycardia (VT) or ventricular fibrillation (VF), the probability of an HF event was 26% and 31%, respectively, while it was 19% for those not having an ICD (13). Survival rate was 80% 1 year after initial ICD shock for VT or VF. Survival curves were related to the rate of the presenting tachycardia. Increased tachycardia rates were associated with lower survival rates. Other clinical factors associated with increased mortality after appropriate ICD discharge were blood urea nitrogen >25 mg/dl, lack of beta-blockade, greater NYHA functional class, presence of atrial fibrillation (AF), and diabetes mellitus (13,14). Subsequent analysis demonstrated that ICD therapy was associated with a 39% increased risk of a first HF hospitalization and a 58% increase in recurrent admission for HF (13).
Analysis of the SCD-HeFT (Sudden Cardiac Death in Heart Failure Trial) data (11) showed findings similar to those of the MADIT-II study. In the SCD-HeFT study, 33% of HF patients received an ICD shock, and among those patients, the most common cause of death was progressive HF. Patients receiving an appropriate shock had a 5-fold increase in risk of death, whereas patients receiving an inappropriate shock had a 2-fold increase in risk of death. Multiple shocks ( 1) further increased the risk of death. The median time from shock to death was 168 days among patients receiving appropriate shocks and 294 days among patients receiving inappropriate shocks. Similar to MADIT-II patients, SCD-HeFT patients with NYHA functional class III and ischemic cardiomyopathy had a shorter duration between initial shock and death.
There is much debate as to why ICD patients tend to have worsening prognosis and more frequent HF after an ICD shock. Myocardial damage induced by ICD shocks may contribute to decompensated HF (15). In the MADIT-II study, however, inappropriate shocks did not increase the risk of worse outcomes. In the SCD-HeFT study, mortality after an inappropriate shock was 3-fold less than after appropriate therapy, thus downplaying the role of shock-induced myocardial damage contributing to HF risk, and suggesting that arrhythmia may simply be a marker of already-worsening HF. Others report that right ventricular (RV) pacing with a dual-chamber ICD may contribute to increased HF risk after ICD implant (16). In the MADIT-II study, however, the risk of HF events was similar whether patients received a single- or dual-chamber ICD despite differences in RV pacing (92% of patients with single-lead ICDs had no pacing, whereas 66% of patients with dual-chamber ICDs had cumulative RV pacing exceeding 50%) (13). Therefore, the increased risk of HF after ICD implantation cannot be solely due to RV pacing.
Regardless of the individual factors causing greater HF events in current ICD populations, there appear to be multiple triggers that, when combined with high-risk patients (whose lives are saved by appropriate ICD therapy), cause an increased HF risk. Heart failure patients with high-risk features such as NYHA functional class III, AF, and ischemic cardiomyopathy require closer observation and management after ICD shock as sudden death risk is now transformed to an increased HF event risk.
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Evaluation of HF After ICD Discharge
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The initial evaluation of the HF patient who receives an ICD shock begins with interrogation of the device (Fig. 1). The timing of the device interrogation depends on the number of shocks and related symptoms. If an HF patient receives 1 isolated shock without change in clinical status or symptoms, evaluation should generally occur within 1 week (17,18). This evaluation can occur in the form of a clinic visit or review of downloaded home telemetry from the ICD that can provide diagnostic information. There may be potentially reversible causes such as electrolyte abnormalities that should be checked and corrected to prevent possible recurrence that could lead to future shocks. Thyroid function should also be measured, and a thorough review of potentially exacerbating medication should be undertaken. The rate of recurrent inappropriate shocks is as high as 43% (11). ICD shocks accompanied by worsening HF symptoms, syncope, angina, or electrical storm warrant emergency medical attention (17).
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Figure 1 Algorithm for Evaluation and Management of ICD Shock
Evaluation of implantable cardioverter-defibrillator (ICD) shock based on time frame and etiology of shock, with current suggested management strategies. AF = atrial fibrillation; HF = heart failure; IV = intravenous; SVT = supraventricular tachycardia; VF = ventricular fibrillation; VT = ventricular tachycardia.
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Device interrogation will reveal whether the ICD shock was appropriate or inappropriate. The definition of an appropriate shock is controversial. Some argue that with current antitachycardia pacing (ATP) algorithms, a shock for VT may be appropriate but unnecessary. For the purpose of this review, any shock for VT or VF is considered appropriate. This definition is similar to the criteria used in reviews of major ICD trials (2,7,19).
Inappropriate shock.
Inappropriate ICD shocks account for 10% to 24% of ICD discharges (20). Causes of inappropriate shocks include AF, supraventricular tachycardia (SVT), oversensing (i.e., QRS and T-wave double counting), and mechanical problems such as lead fracture, insulation break, and lead dislodgement. Heart failure patients who receive inappropriate shocks tend to be younger and more likely to have AF. They have less coronary artery disease, and their HF is more advanced (17–19,21,22). The most common cause of an inappropriate ICD shock is AF or SVT with rapid ventricular conduction, with an incidence of 15% to 18% (19). Large HF databases suggest that the overall incidence of AF in HF patients is 10% to 50%, making the potential of inappropriate detection a significant problem (23). Because initial device detection of VT or VF is based on the ventricular rate, SVT with rapid ventricular response may fall into a device's programmed VT or VF zone with subsequent delivery of inappropriate therapy (Fig. 2). Various algorithms that address morphology, stability, and onset of tachycardia have been developed to differentiate between VT and SVT (24). The continued problem of VT/VF therapy delivered for SVT may reflect a reluctance to activate detection-enhancement algorithms, which have the potential to underdetect VT or VF and may result in the delay or suppression of appropriate therapy (25). When studied in clinical trials, many of these algorithms have had a limited effect in reducing inappropriate therapies. In some cases, this is due to the "time out" function that overrides SVT discriminators when arrhythmia is persistent.
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Figure 2 Example of Inappropriate Shock for Atrial Fibrillation
A heart failure patient with a dual-chamber implantable cardioverter-defibrillator received multiple shocks. The atrial electrogram demonstrated atrial fibrillation (single arrow). The ventricular electrogram reveals fast and irregular activity. The device recognized the rate in the ventricular fibrillation zone, shown as "F" in the marker channel. An inappropriate shock was delivered (double arrow). AS and S = atrial sensed events; DDI = non-P-synchronous dual chamber pacing and sensing with an inhibited pacing mode (the pacing mode after shock); HV = high voltage; VS = ventricular sensed events.
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Pharmacologic therapy can be used to reduce inappropriate shocks caused by AF and SVT. Despite the abundance of data regarding the benefits of beta-blocker therapy in HF (26–28), beta-blocker therapy alone has not been shown to reduce inappropriate shocks, perhaps because doses used may not have provided adequate control of AF with fast ventricular response (29). Nevertheless, the OPTIC (Optimal Pharmacological Therapy in Cardioverter Defibrillator Patients) study demonstrated that inappropriate shocks (mostly for SVT) were significantly reduced by amiodarone plus beta-blocker therapy (30).
Oversensing can also lead to inappropriate shocks, specifically when the device incorrectly detects more ventricular activity than is actually present. This can occur from both intracardiac and extracardiac sources. Two common intracardiac sensing problems are T-wave oversensing and QRS double counting. The incidence of T-wave oversensing accounting for inappropriate shocks is 3% (31). Oversensing of T waves can be transient and triggered by exercise or electrolyte abnormalities (Fig. 3). This problem can often be corrected with device reprogramming. The sensitivity level of the device can be changed so that only the appropriate ventricular signal is sensed by the device. In addition, adjusting the refractory period (interval after ventricular sensed event in which the device is essentially "blind") may also help prevent abnormal sensing of T waves. When programming changes make a device less sensitive, defibrillation testing is recommended to ensure that the device still detects ventricular arrhythmias. Oversensing of T waves that cannot be overcome with reprogramming may be due to suboptimal lead position, and placement of a new pace-sense lead may be required.
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Figure 3 Example of Inappropriate Shock for T-Wave Oversensing
A patient with a dual-chamber ICD presented with frequent ICD shocks. (A) The interval plot demonstrates atrial and ventricular cycle length over time. The initial interval plot shows a 1:1 atrioventricular ratio (single arrow). Fifteen seconds before detection (double arrows) reveals a classic "train track" pattern of 2 ventricular sensing rates. (B) An intracardiac electrogram shows the device detecting the T waves as ventricular events (see marker channel), interpreting the episode as VF, resulting in an inappropriate shock. The patient was subsequently found to be hyperkalemic. Abbreviations as in Figure 1.
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Extracardiac sensing can arise from skeletal myopotentials, electromagnetic interference, or mechanical lead problems including fracture, dislodgement, and insulation break. A lead fracture (incidence 1% to 4%), should be suspected in the HF patient presenting with multiple shocks in rapid succession (32). Interrogation of the device will demonstrate a change in lead impedance and often a failure to sense or capture appropriately. Software upgrades are available to closely monitor leads that may be susceptible to fracture. Unfortunately, lead failures cannot be resolved with simple device reprogramming. Tachyarrhythmia detection algorithms usually need to be turned off to prevent inappropriate shocks, and the patient needs to be observed in a closely monitored setting until the lead can be revised or replaced.
Appropriate shock.
Twenty-two percent to 35% of patients will receive appropriate ICD therapy for VT or VF within 3 years of implant (11,12), with an annual ICD shock rate of 5%. Whether a patient with VT receives an ICD shock or ATP will depend on device algorithm programming. The SCD-HeFT study was designed to provide ICD therapy that consisted of shock-only, single-lead therapy for rapid, sustained VT or VF. No dual-chamber or ATP therapy was allowed. The incidence of appropriate shock for VT or VF was 22.4%. Sixty-seven percent of patients received no ICD therapy. In the MADIT-II study, dual-chamber devices were used with the capability of ATP or shock therapy. With 59% of patients having ATP activated, 281 episodes of VT were terminated by ATP in 147 patients, and 305 episodes of VT were terminated by ICD shock in 108 patients (12). Three years after ICD implant, 35% of patients had received appropriate therapy for VT or VF.
ATP therapies painlessly interrupt re-entrant ventricular arrhythmias using brief, rapid bursts of pacing. Antitachycardia pacing is routinely used to terminate slower ventricular arrhythmias (<188 beats/min) with efficacy of >90% and a low risk (<5%) of accelerating lower VT rates leading to eventual shock. The PainFREE Rx II (Pacing Fast Ventricular Tachycardia Reduces Shock Therapies II) study evaluated the efficacy of ATP for fast ventricular arrhythmias in 634 patients (33). Compared to shock therapy, ATP for fast arrhythmias was highly effective and safe, with improvement in both physical and emotional well-being as well as in social functioning. In a more recent study of primary prevention patients (34), there was significant reduction in ICD shocks during the first year of follow-up with strategic VT/VF detection programming.
Pharmacologic therapy for appropriate shocks includes institution of standard HF therapy such as angiotensin-converting enzyme inhibitors (ACEIs), statins, and beta-blockers with the addition of antiarrhythmic medications. ACEIs and statins have both been shown to reduce atrial and ventricular arrhythmias (35–37). In an analysis of the MADIT-II study, a significant reduction in ICD therapy for VT and VF was noted in patients taking a higher dose of beta-blocker (29). Up-titration to optimal doses of beta-blockers should include metoprolol succinate (200 mg daily) or carvedilol (25 mg twice daily). The appropriate dose of ACEIs includes lisinopril equivalents between 20 and 40 mg daily (26,27,37). These medications decrease the incidence of both atrial and ventricular arrhythmias (37,38).
Antiarrhythmic therapy is prescribed to 49% to 69% of patients with an ICD (39). Adverse events such as proarrhythmia and serious side effects leading to discontinuation occur in 20% of patients (40). Despite this, the addition of amiodarone to beta-blockers has been shown to reduce the risk of appropriate ICD shocks and is commonly added to standard HF therapy for these patients (41). Sotalol is another option for the prevention of ICD shocks and has been shown to reduce the incidence of appropriate ICD shocks in a small randomized trial (42).
The HF ICD patient presenting with recurrent appropriate shocks while receiving amiodarone therapy remains a difficult challenge. Current treatment strategies include titrating beta-blocker therapy while simultaneously increasing the dose of amiodarone. A second antiarrhythmic agent such as mexiletine can also be used, although there is minimal supporting evidence in recent literature. An ICD should be tested after antiarrhythmic drug changes to assure proper detection and efficacy of therapy.
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Treatment of Refractory Arrhythmias
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If both optimization of pharmacologic therapy and device reprogramming fail to prevent continued appropriate and inappropriate shocks, the more invasive strategy of catheter ablation can be employed. A recent multicenter observational study demonstrated a reduction in VT in ICD patients after myocardial infarction with the use of irrigated radiofrequency catheter ablation (43). In addition, the SMASH-VT (Substrate Mapping and Ablation in Sinus Rhythm to Halt Ventricular Tachycardia) study showed a significant reduction in ICD therapy with prophylactic catheter ablation in post-MI patients who received ICDs for secondary prevention (44). The updated European Heart Rhythm Association/Heart Rhythm Society guidelines support the use of catheter ablation in symptomatic sustained VT that persists despite antiarrhythmic drug therapy as well as control of incessant VT storm that has no reversible cause (45). A large number of supraventricular arrhythmias are also amenable to this therapy. For patients with AF and difficult-to-control ventricular rates that lead to recurrent inappropriate shocks, atrioventricular nodal ablation with biventricular pacing is a viable option (46).
Patients presenting with electrical storm, defined as >3 episodes of hemodynamically destabilizing VTs within 24 h (47), need immediate attention and care. Electrical storm, which can occur in up to 20% of patients, causes a more than 5-fold higher risk of death in the subsequent 3 months (20). Recent data suggest both short- and long-term benefits with catheter ablation in these high-risk patients who are refractory to antiarrhythmic therapy (48). If catheter ablation and antiarrhythmic medications fail, then these patients may benefit from more advanced therapy such as left ventricular assist device or cardiac transplantation.
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HF Surveillance After ICD Shock
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Although a fair amount of evidence suggests that HF patients who receive an ICD shock are at increased risk of HF hospitalization and HF events (12), current guidelines do not address the need for more aggressive HF surveillance and management. Current ICD trials have shown that the time from shock to HF event is 160 to 204 days (11) depending on the number of appropriate or inappropriate shocks and the etiology of HF. About one-third of patients with ischemic cardiomyopathy will have an HF event within 1 year of an appropriate shock.
Chronic management of the HF patient after ICD shock should involve close surveillance throughout the following year for early signs and symptoms of impending decompensated HF. During this time, careful monitoring for recurrent AF (especially in patients who received inappropriate shocks) and titration of beta-blockers to optimal dosage should be undertaken. Although there are no prospective data that suggest these interventions will reduce HF events, the current poor prognosis after ICD shock justifies aggressive surveillance of these patients. This surveillance should include a combination of more frequent clinical encounters, titration of established HF therapy as tolerated, and close attention to volume status. A multidisciplinary approach involving the primary care physician, the HF specialist, and the electrophysiologist should be employed.
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Quality of Life
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The patient and family response to ICD shocks remains an important consideration during appropriate management. ICD patients may vary in their ability to tolerate multiple shocks before reporting detectable decrements in quality of life (49). Regardless, an ICD shock can initiate a set of concerns for ICD patients and families that warrants significant intervention.
The primary patient benefit of an ICD is achieving a sense of security from potentially life-threatening arrhythmias. An ICD shock can affect that sense of security and alter a patient's adjustment to HF and acceptance of the ICD. The SCD-HeFT data indicate that ICD patients had better psychological quality of life at 3 and 12 months after implantation than did amiodarone patients (50). There were no differences between groups at 30 months in patient-reported quality of life. This course of quality of life was different if the ICD patient had received a shock. Shocked ICD patients reported significant decrements in quality of life. ICD shocks create a degree of lifestyle interruption to the patient and family. A suggested plan for managing psychosocial distress related to ICD shock is shown in Table 2
(51–53).
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Conclusions
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ICD therapy is now part of standard medical care to reduce the risk of sudden cardiac death in HF patients. Although >60% of patients who receive an ICD for primary prevention will not receive an ICD shock over the first several years, many will receive appropriate and inappropriate shocks that are associated with an increase in HF event risk. Appropriate evaluation of the HF patient after ICD shock is required to identify the cause and reduce the incidence of future shocks. Heart failure surveillance strategies need to be developed as patients continue to avoid sudden cardiac death while increasing their risk of HF events after an ICD shock.
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Acknowledgments
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The authors thank Lisa A. Hamilton, MA, for editorial assistance and manuscript preparation.
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Footnotes
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Dr. Burkart is a consultant for Medtronic. Dr. Miles is on the Data Safety Monitoring Board for Ablation Frontiers and Medtronic. Dr. Conti has received research grants from Medtronic, Boston Scientific, and St. Jude Medical. Dr. Sears is a consultant to Medtronic, has or has had research grants from Medtronic and St. Jude Medical, and has received speaker's honoraria from Medtronic, Boston Scientific, St. Jude Medical, and Biotronik. Dr. Aranda is a consultant to Medtronic.
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Abstract
HF Prognosis After ICD...