Implantable devices/implantation therapy device failure

Brennan TD, Haas GJ. The role of prophylactic implantable cardioverter defibrillators in heart failure recent trials usher in a new era of device therapy. Curr Heart Fail Rep. 2005 2 40-45. 

Medical Device Batteries describes wearable and implantable medical devices powered by batteries. Devices include those that are used for cardiac rhythm management (pacemakers, defibrillators, and heart failure devices), hearing loss, bone growth and fusirm, drug delivery for therapy or pain relief, nerve stimulation for pain management, urinary incompetence and nervous system disorders, vision, diagnostic measurements and monitoring, and mechanical heart pumps. 

There are three implantable devices used today to treat cardiac arrhythmias - the pacemaker, the implantable cardioverter defibrillator (ICD), and the cardiac resynchronization therapy (CRT) devices for heart failure patients. 

Carbon monofluoride (CFx) is one such fluoride compound that today is used as a positive electrode material in Li batteries for a number of different applications. For example, they are used in certain types of heart failure devices - implantable cardiac resynchronization therapy pacemakers (CRT-P). CRT-P devices can pace the right atrium and right ventricle, but they are also capable of pacing the left ventricle. Pacing three chambers requires more power than a cell can deliver, so a different battery type is needed. Li/CFx cells were developed in response to the increased power required by CRT-P devices. Vagal nerve stimulator devices also use a Li/CFx cells. 

The Comparison of Medical Therapy, Pacing, and Defibrillation in Heart Failure (COMPANION) Smdy was the first large scale, randomized CRT trial to suggest that in addition to symptomatic improvement, CRT may confer mortahty benefit (13). COMPANION was started in early 2000 and was eventually published in May 2004. In this trial, 1,520 patients with NYHA class in and IV heart failure and QRS duration >120ms were randomized to optimal medical therapy, implantation of CRT device, or implantation of a CRT device with defibrillator capability. Mean follow-up was over 11 months. 

In those randomized to an ICD, 93% had a nonthoracotomy lead system, 5% had an epicardial system, and 2% had no device implanted. In those randomized to drug therapy, 356 immediately began empiric therapy with amiodarone. These patients were not considered candidates for sotalol becanse of concern about heart failure, a low ejection fraction, or both. Antiarrhythmic drug therapy was assigned to the remaining 153 patients randomized to drug therapy 79 to amiodarone and 74 to sotalol. In 53 of the 74 patients assigned to... 

Bristow, M.R., A.M. Feldman, and L.A. Saxon, Heart failure management using implantable devices for ventricular resynchronization Comparison of Medical Therapy, Pacing, and Defihrillation in Chronic Heart Failure (COMPANION) trial. COMPANION Steering Committee and COMPANION Clinical Investigators. J Card Fail, 2000. 6(3) p. 276-85. 

Management of a Biventricular Device. It has been estimated that up to 38% of patients with moderate to severe congestive heart failure due to left ventricular systolic dysfunction have intraventricular conduction delays with wide QRS complexes and ventricular dyssynchrony (79). Cardiac resynchronization therapy using a biventricular pacemaker is now a Class I indication therapy for systolic heart failure in patients with a QRS complex > 120 ms and left ventricular ejection fraction < 35% (80). Although cardiac resynchronization therapy decreases heart failure hospitalizations (81,82), as the overall number of patients with biventricular pacemakers and ICDs increase, more critical care patients will present with implanted biventricular devices, and familiarity with the management of these devices will become increasingly important. 

As early as the late 1700s, Physicians speculated that electrical current could be used to stimulate the heart. In 1882, von Ziemssen used electrical current to directly stimulate the heart of a woman whose anterior chest wall had been removed after resection of a chest tumor. In 1952, ZoU used transthoracic current to pace the heart, and in 1958 the first implantable pacanaker was placed by Ake Senning and Rune Elmquist. At the same time, Furman and Robinson demonstrated the feasibility of transvenous cardiac pacing. In the late 1960s, Mirowski and colleagues pioneered the concept of an implantable device that could be used to defibrillate the heart. Over the last 50 years, implantable cardiac devices have become the primary treatment for bradyarrhythmias and ventricular tachyarrhythmias and have emerged as an important adjunctive therapy for patients with heart failure. It is currently estimated that almost 400,000 pacemakers and defibrillators are implanted annually in the United States. 

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. 

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... 

CRT reduces symptoms of CHF and improves cardiac performance in patients with moderate-to-severely symptomatic heart failure, severe left ventricular systolic dysfunction, normal sinus rhythm and a wide QRS complex. Resynchronization therapy significantly reduces hospitalizations in these patients and is highly cost-effective. Perhaps most important, resynchronization therapy for heart failure improves survival for these patients, particularly when employed in conjunction with an implantable defibrillator. However, randomized clinical trials show that a substantial minority of patients are clinical nonresponders. Therefore, critical questions remain with respect to identifying appropriate candidates for CRT, optimal device programming, and left ventricular lead placement. 

There are no prospective studies that compare cure rates for antibiotic treatment alone vs antibiotic therapy combined with CIED system removal. However, the high rate of uncontrolled or relapsing bacteremia, even after prolonged medical therapy, makes removal of the entire CIED system optimal. In one recent retrospective case analysis [11] that included patients with an infected pacemaker or ICD, infection relapse was strongly associated with failure to completely remove all hardware. This case series included 123 patients, 119 (97%) of whom had transvenous implanted leads. Only one (0.86%) of 117 patients who underwent removal of their entire system had infection relapse. In contrast, three of six (50%, P = 0.003) without complete hardware removal suffered relapse. The only patient who had hardware removal and still had infection relapse had a new generator implanted in an old pocket site. All other patients had new devices placed at different sites at... 

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