ICD implantation

In patients who have experienced VT and are at risk for sudden cardiac death, implantation of an implantable cardioverter-defibrillator (ICD) is the treatment of choice.44 An ICD is a device that provides internal electrical cardioversion of VT or defibril -lation of VF the ICD does not prevent the patient from developing the arrhythmia, but it reduces the risk that the patient will die of sudden cardiac death as a result of the arrhythmia. Whereas in the past ICD implantation required a thoracotomy, these devices now may be implanted transvenously, similarly to pacemakers, markedly reducing the complication rate. 

GFR Glomerular filtration rate ICD Implantable cardioverter defibrillator... 

Patients with pulseless VT or VF (with or without associated myocardial ischemia) should be managed according to the American Heart Association s guidelines for cardiopulmonary resuscitation and emergency cardiovascular care (see Chap. 7). After successful resuscitation, antiarrhythmics should be continued until the patient s rhythm and overall status are stable. Long-term antiarrhythmics or ICD implantation may or may not be required. 

Following resuscitation from ventricular fibrillation (VF) or pulseless VT, ICD implantation is a proven strategy for the prevention of recurrent SCD. Three prospective, randomized, controlled trials, the Antiarrhythmics Versus Implantable Defibrillators (AVID) study, the Canadian Implantable Defibrillator Study (CIDS), and the Cardiac Arrest Study Hamburg (CASH), support this strategy [27-29]. 

The Canadian Implantable Defibrillator Study studied ICD therapy versus amiodarone while CASH studied ICD therapy versus a variety of antiarrhythmic medications in patients with resuscitated SCD. Both trials found nonsignificant reductions in mortality with ICD implantation. CIDS showed a relative risk (RR) reduction of 19.7% [p = 0.14] and CASH showed a RR reduction of 23% in mortality [p = 0.08]. 

A significant mortality benefit of ICD therapy was shown in the largest of the three studies, the AVID study. In this study, over 1,000 patients with ischemic cardiomyopathy and an EF < 40% who were resuscitated from VF or from symptomatic, sustained VT were randomized to antiarrhythmic medications (>90% amiodarone) or ICD implantation. The trial was stopped early because the ICD showed a significant survival benefit with an 11.3% absolute and 31.5% RR reduction for all-cause mortality over 3 years. Persistent benefit with the ICD was seen even after adjustment for age, beta blocker use, and baseline EF. 

A review of these three trials concluded that, compared to antiarrhythmic therapy, ICD implantation for secondary prevention results in significant reductions in all-cause mortality (RR 0.76) and SCD (RR 0.50) [30]. A meta-analysis of secondary prevention trials found an absolute reduction in... 

Since survival rates for out-of-hospital cardiac arrest are quite low, ranging from 2 to 25% in the United States [32], secondary prevention strategies only address a small minority of ischemic cardiomyopathy patients at risk for SCD. A more substantial reduction in SCD will result from primary prevention of SCD with ICD implantation. Evidence for this strategy comes from several recent trials. The findings of primary prevention trials for SCD in ischemic cardiomyopathy are summarized in Table 3.1. 

Because the above trials showed a >50% relative reduction in total mortality with ICD therapy, MADIT II used broader entry criteria for primary prevention of SCD, removing the criteria for NSVT and EPS 1,232 patients with a history of MI > 30 days prior and an EF < 30% were randomized to conventional therapy or ICD implantation [10]. Conventional therapy was comparable in both arms and included a high rate of use of beta blockers, angiotensin-converting enzyme inhibitors, and statins (over two thirds for all medications in both arms). The trial was stopped early at 20 months because the relative reduction in total mortality... 

Studied population in the immediate period following acute MI or surgical revascularization. However, in direct contrast to DINAMIT, a recent substudy of VALIANT (Valsartan in Acute Myocardial Infarction Trial) found that the risk of SCD is highest in the first 30 days after MI among patients with LV dysfunction, heart failure, or both [35], Therefore, the timing of ICD implantation after MI in the setting of LV dysfunction may still be open to debate. 

A meta-analysis performed before SCD-HeFT synthesized the evidence for ICD implantation in primary and secondary prevention [30]. The RR for SCD with ICDs in primary prevention was 37%... 

As a result of the weight of evidence for ICD therapy in prevention of SCD in patients with ischemic cardiomyopathy, the American College of Cardiology, American Heart Association, and the North American Society for Pacing and Electrophysiology (now Heart Rhythm Society) revised guidelines for ICD implantation in October 2002... 

These guidelines, as applicable to heart failure patients, are summarized in Table 3.2. Of significance was the upgrade of recommendation for prophylactic ICD implantation in patients with EF < 30%, >1 month after MI, and >3 months after revascularization, NYHA class I from Class IIA to Class I. Also, ICD therapy in patients with LVEF less than 35% due to prior MI who are at least 40 days post-MI and are in NYHA functional Class II or III remained a Class I indication, although the EF cutoff (<35%) was lower compared to the 2006 guidelines. 

Implantable cardioverter defibrillator implantations have increased dramatically over the last decade [45], with a 24% worldwide annual increase in ICD implantations between 1998 and 2002 [1]. There was an increase in the number of Medicare beneficiaries eligible for ICDs by two- to threefold, to more than 500,000, based on the most recent reimbursement criteria [46]. 

Implantable cardioverter defibrillator implantation is expensive, with an estimated cost of 30,000- 50,000 per implant, not including the cost of follow-up. However, economic analysis of ICD studies has shown that ICD implantation compares favorably with such commonly accepted therapies as dialysis for end-stage renal failure [47]. It is estimated that the cost effectiveness ratio for ICDs is 27,000 per life year saved, comparable to those for other well-... 

ICD implantation is recommended for prevention of sudden cardiac death in patients with ARVC with documented sustained VT or ventricular fibrillation. Drug therapy with amiodarone or stalol can be effective in selected patients with ARVC. 

ESR erythrocyte sedimentation rate ICD implantable automatic cardioverter defibrillation... 

On the other hand, the medical condition where the heart beats too fast is known as tachycardia. If untreated, tliis condition may lead to ventricular fibrillation, that is, a condition in which the heart stops beating and shakes uncontrollably and is usually fatal. In 1980, a special device was developed and implanted in patients. It could sense the condition and provide a shock that would stop the fibrillation and restore the normal sinus rhythm via an electrode sutured onto the heart. The device was first powered by a lithium/vanadium pentoxide system later it was replaced by a system using a cathode material of silver vanadium oxide (SVO or Ag2V40ii). This is the actual system used in modem ICDs (implantable cardioverter/defibrillator). Another material used is the lithium/manganese dioxide system. Also, a new system using a sandwich cathode design with an inner cathode material of carbon monofluoride and an external cathode layer of silver vanadium oxide is in wide use. 

FIGURE 17-16. Example of an approach to the management of survivors of cardiac arrest (resuscitated VT/VF). Reversible causes of cardiac arrest (e.g., electrolyte abnormalities, acute phase of Ml) should be treated with specific therapy. AADs = antiarrhythmic drugs BBs = /i-blockers EPS = invasive electrophysio-logic studies ICD = implantable cardioverter-defibrillator VT/VF = ventricular tachycardia/ventricular fibrillation Ml = myocardial infarction. 

Once the patient is resuscitated successfuUy, antiarrhythmics should be continued until the patient s rhythm and overaU status is stable. If the episode of ventricular flbriUation was associated with acute ischemia, long-term antiarrhythmic drugs probably are uimec-essary, but the patient should be monitored closely for recurrence of ventricular tachycardia and/or ventricular flbriUation. If, on the other hand, ventricular flbriUation was not associated with acute MI (or a known precipitating factor), the patient should undergo invasive elec-trophysiologic studies and (depending on the results) probably ICD implantation (Fig. 17-16). 

ICD implantable cardioverter-defibrillator LADs late after-depolarizations LQTS long-QT syndrome MI myocardial infarction... 

FIGURE 18-4. Treatment algorithm for hypertrophic cardiomyopathy. ACEI = angiotensin-converting enzyme inhibitor NSVT = nonsustained ventricular tachycardia ICD = implantable cardioverter-defibrillator LV = left ventricular SCD = sudden cardiac death. 

The Antiarrhythmics versus Implantable Defibrillators (AVID) trial (7) was the largest secondary prevention trial, and helped define ICD implant indications for patients with a history of ventricular arrhythmias. In AVID, 1013 patients who presented with VF, sustained VT with syncope, or sustained VT with a LVEF of <40% were randomized to either an ICD or antiarrhythmic... 

The results of these primary prevention trials in nonischemic cardiomyopathy patients led to an indication for ICD implantation in patients with a nonischemic cardiomyopathy, LVEF <35%, and class II or III HF (Figure 1.5b) (9). Importantly in SCD-HeFT, patients had to have a diagnosis of HF for at least three months and be on appropriate medical therapy. 

When the primary prevention trials started using LVEF as essentially the sole criterion for ICD implantation (i.e., not requiring inducibility of VT/VF at EPS), the absolute reduction in mortality decreased with a corresponding increase in the number needed to treat to save one life. For instance, in MUSTT the absolute reduction in mortality was 31% and the number needed to treat was three at five years, and in MADIT the absolute reduction in mortality was 19% with a number needed to treat of four at two years. However, in MADIT-II and SCD-HeFT the absolute mortality reduction was 6% and 7% respectively, with a number... 

Better risk-stratifying tools, ideally with both higher sensitivity and specificity, are needed to avoid unnecessary ICD implantation in patients who will never benefit from them, and to identify those patients in traditionally low-risk populations who are actually at high risk. It is important to remember that most patients with an LVEF under the range of 30% to 35% that meet MADIT-II or SCD-HeFT criteria will not experience SCD and are subject to untoward complications of ICDs, including inappropriate shocks and device infections. In MADIT II, the rate of inappropriate shocks was 11.5% of patients (34) while in SCD-HeFT the rate of inappropriate shocks was 37%... 

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