Implanted ventricular defibrillators

Demand pacemakers are very low current devices, requiring only 25-50 jiW for sensing and 60-100 pW for stimulation. In contrast, implanted ventricular defibrillators (Fig. 1.3) must be able to deliver short electric pulses of 25-40 J (e.g. 2 A at 2 V for 10 s) which can shock the heart into normal rhythm, and hence require a much higher rate battery. The most common system is a lithium-silver vanadium oxide cell with a liquid-organic based electrolyte. More than 80 000 such units have been implanted. Implanted drug delivery devices also use lithium primary batteries, as do neurostimulators and bone growth stimulators. 

Implantable cardioverter-defibrillator (ICD) A device implanted into the heart transvenously with a generator implanted subcutaneously in the pectoral area that provides internal electrical cardioversion of ventricular tachycardia or defibriUation of ventricular fibrillation. 

Abstract Two thirds of the nearly half a million deaths per year in the United States due to sudden cardiac death (SCD) is attributed to coronary artery disease (CAD) and most commonly results from untreated ventricular tachyarrhythmias. Patients with ischemic cardiomyopathy and left ventricular dysfunction are at highest risk for SCD, but this still defines only a small subset of patients who will suffer SCD. Multiple lines of evidence now support the superiority of implantable cardioverter defibrillator (ICD) therapy over antiarrhythmic therapy for both primary and secondary prevention of SCD in advanced ischemic heart disease. Optimization of ICD therapy in advanced ischemic cardiomyopathy includes preventing right ventricular pacing as well as the use of highly effective anti-tachycardia pacing to reduce the number of shocks. While expensive, ICD therapy has been shown to compare favorably to the accepted standard of hemodialysis in cost effectiveness analyses. 

Implantable cardioverter defibrillators, on the other hand, have demonstrated a remarkable effectiveness in prevention of SCD, with an overall 1-year survival rate of 92% in patients with documented life-threatening ventricular tachyarrhythmias [26]. Three randomized, controlled trials have demonstrated the ICD to be superior to antiarrhythmic medications in the secondary prevention of SCD [27-29]. Recent primary prevention studies have also demonstrated improved... 

As left ventricular dysfunction is a major predictor of sudden arrhythmic death, cardiac death and total mortality, it can be stated that in general sudden cardiac death prevention is achievable with the combination of an implantable cardioverter defibrillator (ICD) and medical therapy. 

The first implantable cardioverter-defibrillator (ICD) was placed in 1982. Since that time, their use has expanded exponentially. Several large clinical trials have demonstrated the superiority of ICDs compared with pharmacological therapy for the secondary prevention of arrhythmic death and possibly as primary therapy for patients at risk for ventricular arrhythmias. 

Low doses (100-200 mg/d) of amiodarone are effective in maintaining normal sinus rhythm in patients with atrial fibrillation. The drug is effective in the prevention of recurrent ventricular tachycardia. It is not associated with an increase in mortality in patients with coronary artery disease or heart failure. In many centers, the implanted cardioverter-defibrillator (ICD) has succeeded drug therapy as the primary treatment modality for ventricular tachycardia, but amiodarone may be used for ventricular tachycardia as adjuvant therapy to decrease the frequency of uncomfortable cardioverter-defibrillator discharges. The drug increases the pacing and defibrillation threshold and these devices require retesting after a maintenance dose has been achieved. 

Some of the beneficial effects of fish oils after acute myocardial infarction have been attributed to an antidysr-hythmic effect on the heart (5). However, the results of a randomized trial in 200 patients with implantable cardioverter defibrillators are at variance with this the rate of cardioversion was higher in those taking fish oils 1.8 g/day than in a control group who took olive oil (6). The lack of benefit and the suggestion that fish oil supplementation may increase the risk of ventricular tachycardia or ventricular fibrillation in some patients with implantable cardioverter defibrillators can reasonably be interpreted as evidence that the routine use of fish oil supplementation in patients with implantable cardioverter defibrillators and recurrent ventricular dysrhythmias should be avoided. 

In a 62-year-old man with dilated cardiomyopathy and an implantable cardioverter defibrillator for ventricular tachycardia, microvolt T wave alternans differed when amiodarone was added (55). The onset heart rate with T wave alternans was lower and the alternans voltage higher with amiodarone than without it. 

In 154 patients with implantable cardioverter-defibrillators randomly assigned to dofetilide or placebo, there were pause-dependent runs of polymorphic ventricular tachycardia in 15 of the 87 patients who received dofetilide and in only five of the 87 who received placebo (57). There were five early events (at less than 3 days of therapy), all torsade de pointes in patients taking dofetilide. There were 15 late events, 10 with dofetilide and five with placebo. The median time to a late event was 22 (range 6-107) days for dofetilide and 99 (34—207) days for placebo. 

Mazur A, Anderson ME, Bonney S, Roden DM. Pause-dependent polymorphic ventricular tachycardia during long-term treatment with dofetilide a placebo-controlled, implantable cardioverter-defibrillator-based evaluation. J Am Coll Cardiol 2001 37(4) 1100-5. 

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. 

Recent studies demonstrate that cardiac resynchronization therapy (CRT) offers a promising approach to selected patients with chronic heart failure. Delayed electrical activation of the left ventricle, characterized on the ECG by a QRS duration that exceeds 120 ms, occurs in approximately one-third of patients with moderate to severe systolic heart failure. Since the left and right ventricles normally activate simultaneously, this delay results in asynchronous contraction of the left and right ventricles, which contributes to the hemodynamic abnormalities of this disorder. Implantation of a speciahzed biventricular pacemaker to restore synchronous activation of the ventricles can improve ventricular contraction and hemodynamics. Recent trials show improvements in exercise capacity, NYHA classification, quality of life, hemodynamic function, and hospitalizations. A device that combined CRT with an implantable cardioverter-defibrillator (ICD) improved survival in addition to functional status. CRT is currently indicated only in NYHA class ni-IV patients receiving optimal medical therapy (ACE inhibitors, diuretics, -blockers, and digoxin) and... 

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. 

Strickberger SA, Hummel JD, Bartlett TG, et al. Amiodarone versus implantable cardioverter-defibrillator randomized trial in patients with nonischemic dilated cardiomyopathy and asymptomatic nonsustained ventricular tachycardia. AMIOVIRT. J Am Coll Cardiol 2003 41 1707-1712. 

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. 

Domanski MJ, Sakseena S, Epstein AF, et al. Relative effectiveness of the implantable cardioverter-defibrillator and antiarrhythmic drugs in patients with varying degrees of left ventricular dysfunction who have survived malignant ventricular arrhythmias. AVID investigators. Antiarrhythmics Versus Implantable Defibrillators. J Am Coll Cardiol 1999 34(4) 1090-5. 

Buxton AE, Sweeney MO, Wathen MS, et al. QRS duration does not predict occurrence of ventricular tachyarrhythmias in patients with implanted cardioverter-defibrillators. PainFREE Rx II Investigators. J Am Coll Cardiol 2005 46(2) 310-6. 

AF atrial fibrillation CHF congestive heart failure ICD implantable cardioverter defibrillator LBBB left bundle branch block LVEDD left ventricular end diastolic dimension LVEF left ventricular ejection fraction 6MHWD 6-minute hall walk distance NSR normal sinus rhythm QoL quality of life TDI tissue Doppler imaging. 

A woman with congenital heart disease and atrial and ventricular arrhythmias managed by an implanted cardioverter defibrillator, epicardial pacing and amiodarone 400 mg daily, experienced deterioration in the control of her condition. She developed palpitations and experienced a shock from the defibrillator. Her amiodarone serum levels were 40% lower than 2 months previously, and her A-desethylamiodarone levels were undetectable. It was noted that 5 weeks earlier rifampicin 600 mg daily had been started to treat an infection of the pacing system. The amiodarone dose was doubled, but the palpitations continued. Amiodarone and A-desethy-lamiodarone levels increased after rifampicin was discontinued. Rifampicin is a potent enzyme inducer and it may have increased the metabolism and clearance of amiodarone. This case suggests that combined use of amiodarone and rifampicin should be well monitored. 

The heart is an electromechanical system, in which mechanical pumping function is initiated and coordinated by automatic rhythmic cardiac electrical activity. Transient electrical disturbances m this activity (cardiac arrhythmias) can immediately cause death. The implantable cardioverter defibrillator (ICD) is a medical device that can be implanted in a human body and will automatically detect and treat cardiac arrhythmias. Mirowski et al. [1] first reported on a demonstration of a functioning ICD in 1970. In his demonstration, he induced a fatal ventricular tachyarrhythmia in a dog. The dog was then successfully and dramatically rescued by the automatic operation of a previously implanted ICD. The first report of successful ICD implantation in humans soon followed [2]. In subsequent decades, advances in ICD technology have reduced ICD size from more than 200 cm, originally, to as httle as 25 cm, while markedly improving functionality, reliability, and longevity. ICDs are now considered as standard of care for patients at risk for ventricular arrhythmia and are implanted in more than 150,000 patients per year in the United States alone [3]. 

Fig 1 41 Section of interventricular septum from a patient who underwent cardiac transplantation 676 days after implantable cardioverter-defibrillator lead implantation and 7 days after last defibrillator shock (a). Right ventricular surface of interventricular septum (R) is at the top and left ventricular surface (L) at bottom. Characteristic fibroelastic tissue encircles the lead curved arrow). Trichrome-stained section of tissue (b) band of fibroelastic tissue curved arrow) encircles lead (L), and beneath, in myocardium, lies fibrous connective tissue F). Area of confluent fibrous connective tissue immediately adjacent to lead also extends into surrounding myocardium, forming radial pattern of interstitial fibrosis arrows), suggesting that shocks have caused lines of electrical injury (courtesy [51])... 

MirowskiM, Reid PR, Mower MM etal( 1980) Termination of malignant ventricular arrhythmias with an implanted automatic defibrillator in human beings. N Engl J Med 303(6) 322-324... 

Fig 5 14 (a-d) Temporal-sequence fluoroscopic images (same patient as in Figure 5.8) after exposure of the atrial lead from the internal jugular vein showing introduction and sheath advancement over the lead, overcoming binding sites to the tip. (e-h) The same maneuver on an implantable cardioverter-defibrillator (ICD) ventricular lead... 

TLR, transvenous lead removal A, atrial RV, right ventricular LV, left ventricular PL, pacing leads ICD, implantable cardioverter defibrillator L, leads... 

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