Defibrillator System Research Articles

The Innominate Vein as Alternative Venous Access for Complicated Implantable Cardioverter Defibrillator Revisions

Venous complications of implantable cardioverter defibrillator (ICD) systems may cause significant problems when the need for system revision or upgrades arises. Such revisions require venous access close to the site of the previous ICD implantation. The internal and external jugular vein have disadvantages due to a long subcutaneous course crossing the clavicle and problems with lead extraction if infection occurs. In seven patients with ICD revisions due to lead dysfunction (n = 4) and upgrade to a biventricular device (n = 2) and status after system removal due to infection with new device implantation (n = 1) conventional venous access could not be obtained. Intraoperative contrast venography demonstrated an occluded left subclavian and/or left innominate vein in all patients. In all patients, we gained venous access through puncture of the right innominate vein and tunneled the new lead subcutaneously to the ICD pocket on the left. No intraoperative complications were observed. All patients are followed in our ICD clinic. Mean follow-up is 16 +/- 4 months now. So far, no clinical or lead complications with this access have been observed. We have demonstrated that ICD lead placement through puncture of the right innominate vein is feasible. We propose the innominate vein as an alternative route for establishing venous access in patients requiring ICD revisions or upgrades who suffer from venous obstruction. ICD implanting physicians should acquaint themselves with the technique of right innominate vein puncture to use this vein as a bail-out strategy in patients with complicated venous access.

Cardiac Tamponade as Complication of Active‐Fixation Atrial Lead Perforations: Proposed Mechanism and Management Algorithm

Cardiac tamponade is a rare complication after implantation of dual chamber pacemaker or defibrillator systems. Its pathophysiology and optimal management are not currently well established. Three cases of cardiac tamponade following successful implantation of transvenous dual chamber pacemakers with active-fixation atrial leads were identified. All three patients with post-implant cardiac tamponade were suspected to have the same etiology of bleeding into the pericardial space. This was due to protrusion of the helix of the active-fixation atrial pacing lead through the atrial wall with subsequent abrasion of visceral pericardial layer and bleeding from the atrium through the perforation. In two patients, the perforation sites were visualized and repaired during open thoracotomy in the operating room. The third patient underwent lead repositioning under fluoroscopic guidance in the electrophysiology laboratory. Based on the reviewed cases, we describe the pathophysiology of, and recommend a safe conservative algorithm for, the management of cardiac tamponade after successful transvenous lead implantation. Percutaneous pericardiocentesis with placement of the pericardial drain followed by lead repositioning under fluoroscopic guidance with surgical backup appears to be safe and effective.

The impact of manual defibrillation technique on no-flow time during simulated cardiopulmonary resuscitation

Rapid defibrillation is the most effective strategy for establishing return of spontaneous circulation following cardiac arrest due to ventricular fibrillation. The aim of this study is to measure the delay due to of charging the defibrillator during chest compression in an attempt to reduce the duration of the pre-shock pause in between cessation of chest compressions and shock delivery as advocated by the American Heart Association (AHA) guidelines compared to charging the defibrillator immediately following rhythm analysis without resuming chest compressions as recommended by the European Resuscitation Council (ERC). This was a randomised controlled cross over trial comparing pre-shock pause times when defibrillation was performed on a manikin according to the AHA and ERC guidelines using paddles and hands free defibrillation systems. The pre-shock pause between cessation of chest compression and shock delivery was significantly different between techniques (Friedman test, P<0.0001). ERC paddles technique had the greatest pre-shock pause (7.4 s [6.7-11.2]) followed by ERC hands free (7.0 s [6.5-8.5]) and AHA paddles (1.6 s [1.1-2.3]). AHA hands free took the least amount of time (1.5 s [0.8-1.5]). Extrapolating these data to older defibrillators with longer charge times saw pre-shock pause intervals of 9 s (Codemaster XL) and 12 s (Lifepak 20) with the ERC approach. This study demonstrated clinically significant delays to defibrillation by analysing and charging the defibrillator without performing concurrent chest compressions. In a simulated scenario, charging the defibrillator whilst performing chest compressions was perceived as safe and significantly reduced the pre-shock pause between cessation of chest compression and shock delivery.

The innominate vein as alternative access for complicated cardioverter defibrillator revisions

Aims: Venous complications of implantable cardioverter defibrillator (ICD) systems may cause significant problems when the need for system revision or upgrades arises. Such revisions require venous access close to the site of the previous ICD implantation. The internal and external jugular vein have disadvantages due to a long subcutaneous course crossing the clavicle and problems with lead extraction if infection occurs.

Erosion of an Extrapericardial Implantable Cardioverter Defibrillator Patch Through the Gastric Fundus With Fistulous Tract Formation

Until as recently as the mid-1990s, implantable cardioverter defibrillator (ICD) leads were placed through thoracotomy as anterior and/or posterolateral patches. The defibrillator patches have reportedly been associated with a number of relatively common mechanical complications as well as less common complications, including patch migration or erosion into contiguous structures. We report a previously unreported late complication of epicardial defibrillator patch placement in which patch migration and erosion through the gastric fundus resulted in fistulous tract formation from the mediastinum to the lumen of the stomach. Although surgically implanted epicardial patch defibrillator systems are relatively uncommon in current U.S. practice, these devices are still used when specific anatomic or electrophysiological considerations preclude the use of more common endocardial lead systems. Several thousand patients with epicardial patch leads in place are still believed to be alive in the United States. In these patients, continued vigilance for lead-related complications is appropriate. Prompt surgical intervention is usually warranted when patch migration or complications such as the one described occur.

Clinical Utility and Safety of a Protocol for Noncardiac and Cardiac Magnetic Resonance Imaging of Patients With Permanent Pacemakers and Implantable-Cardioverter Defibrillators at 1.5 Tesla

Magnetic resonance imaging (MRI) is an important diagnostic modality currently unavailable for millions of patients because of the presence of implantable cardiac devices. We sought to evaluate the diagnostic utility and safety of noncardiac and cardiac MRI at 1.5T using a protocol that incorporates device selection and programming and limits the estimated specific absorption rate of MRI sequences. Patients with no imaging alternative and with devices shown to be MRI safe by in vitro phantom and in vivo animal testing were enrolled. Of 55 patients who underwent 68 MRI studies, 31 had a pacemaker, and 24 had an implantable defibrillator. Pacing mode was changed to "asynchronous" for pacemaker-dependent patients and to "demand" for others. Magnet response and tachyarrhythmia functions were disabled. Blood pressure, ECG, oximetry, and symptoms were monitored. Efforts were made to limit the system-estimated whole-body average specific absorption rate to 2.0 W/kg (successful in >99% of sequences) while maintaining the diagnostic capability of MRI. No episodes of inappropriate inhibition or activation of pacing were observed. There were no significant differences between baseline and immediate or long-term (median 99 days after MRI) sensing amplitudes, lead impedances, or pacing thresholds. Diagnostic questions were answered in 100% of nonthoracic and 93% of thoracic studies. Clinical findings included diagnosis of vascular abnormalities (9 patients), diagnosis or staging of malignancy (9 patients), and assessment of cardiac viability (13 patients). Given appropriate precautions, noncardiac and cardiac MRI can potentially be safely performed in patients with selected implantable pacemaker and defibrillator systems.

Characteristics of ventricular tachyarrhythmias occurring in ischemic versus nonischemic patients implanted with a biventricular cardioverter-defibrillator for primary or secondary prevention of sudden death

The InSync ICD Registry evaluated patients indicated for cardiac resynchronization therapy with defibrillation. Cardiac resynchronization therapy with defibrillation systems are prescribed for both primary and secondary prevention of sudden cardiac death in patients with heart failure with both ischemic and nonischemic etiology. The characterization of ventricular tachyarrhythmias detected by the ICD is not well known in these subpopulations. We enrolled 421 patients with symptomatic heart failure despite optimized medical treatment, ventricular dyssynchrony, and primary or secondary ICD indications. An electrophysiologist reviewed all spontaneous episodes. Patients were grouped by etiology and ICD indications. The 421 patients included 292 ischemic (159 primary prevention) and 129 nonischemic (68 primary prevention) patients. In 19 +/- 11 months of follow-up, 110 patients (63 ischemic, 30 primary prevention and 47 nonischemic, 21 primary prevention) presented ventricular tachyarrhythmias, occurring in a ventricular tachycardia (VT) or a ventricular fibrillation zone (1382 and 456 events, respectively). The incidence of overall ventricular tachyarrhythmias in nonischemic patients in secondary prevention (35.7% at 1 year) was higher than in ischemic patients implanted for either indication (16.5% and 22.9% at 1 year, respectively). The incidence of self-terminating ventricular tachyarrhythmias was greater in patients with nonischemic heart disease, regardless of indication. Patients with ischemic heart disease in primary prevention had a lower occurrence of VTs, whereas nonischemic patients in primary prevention had faster VTs. Both rate of occurrence and characteristics of detected ventricular tachyarrhythmias vary according to underlying etiology and indication. Therefore, different device programming according to patient's profile is advisable to improve ventricular tachyarrhythmias management.

Monomorphic Ventricular Tachycardia Induced by Cardiac Resynchronization Therapy in Patient with Severe Nonischemic Dilated Cardiomyopathy

We report the case of a patient with severe nonischemic dilated cardiomyopathy in whom cardiac resynchronization therapy (CRT) was the source of incessant, drug-resistant, monomorphic ventricular tachycardia (VT). VT recurrences were only resolutive with inactivation of CRT and reactivation of CRT reproduced VT occurrence. The possible pathophysiology of the VT and the potential ventricular proarrhythmic risk related to CRT are discussed. This report points out clearly that CRT can induce ventricular arrhythmias and suggests the need for CRT systematically associated with a defibrillation system.

Internal defibrillation with minimal skeletal muscle activation: A new paradigm toward painless defibrillation

Shock-induced pain produces substantial morbidity in recipients of implantable cardioverter-defibrillators (ICDs). This pain likely derives from activation of skeletal muscle and associated nerves in the chest and abdomen. In an effort to develop a painless defibrillation system, we designed an electrode arrangement that incorporates a conductive sock placed around the heart to confine the electric shock field to cardiac tissue. The purpose of this study was to test whether cardiac defibrillation could be achieved without skeletal muscle activation using a novel electrode system. Eight adult mongrel dogs were studied. Force of skeletal muscle contraction was measured by strain gauges attached to the forelimbs during delivery of internal shocks ranging in energy from 0.1 to 31 J. Biphasic shocks were delivered (1) between a right ventricular coil and a subcutaneous dummy can (standard configuration), and (2) between a left ventricular coil and an epicardial electrode sock. Internal and external defibrillation thresholds (DFTs) were determined for each electrode configuration. Shock-induced muscle contraction force was significantly lower using the sock electrode than with standard ICD electrodes at every shock energy level tested (P < .0001). Internal DFT was similar between electrode configurations (sock electrode: 8.6 +/- 4.2 J; standard: 11.0 +/- 6.3 J, P = .4), but muscle contraction force at DFT was greatly reduced with the new electrode system (1.8 +/- 2.0 kg vs 10.6 +/- 2.1 kg, P < .0001). The sock electrode rendered external defibrillation impossible, however, even at 360 J. Skeletal muscle activation induced by ICD shocks can be greatly reduced using an electrode system that confines the electric shock field to the heart. Refinement of this strategy may allow for delivery of painless shocks by ICDs. Further development is needed to overcome implant complexity and the higher external DFT with this type of electrode system.

Promoting Patient Safety within Implantable Medical Devices: Patient Alert™

Implantable Cardioverter Defibrillator (ICD) systems have been shown to provide lifesaving therapy for patients at risk of sudden cardiac death due to ventricular tachyarrhythmia. In order to assure an ICD system is operating properly, some models of ICDs perform periodic system checks. The Patient Alert™ feature, in Medtronic® ICDs, monitors and alerts patients, via audible tones, to system integrity issues that have the potential to comprise patient safety. The objective of this research was to evaluate: how often patients are being alerted to ICD system issues, and how effective the alerts are at bringing patients into medical clinics for treatment and thus promoting patient safety. An analysis of 14,092 ICDs revealed that the probability of first alert occurrence increased with time since implant, but overall occurrence rates remained low (&lt; 7% per patient year). The average median time from the alert sounding until the patient received medical attention was 4.3 days. Overall, for a life-threatening condition such as ICD therapy delivery being turned off, the majority (76%) of patients with this alert were brought into a clinic within one week to have therapy delivery turned back on. To reach the remaining patients, as well as bring all patients in quicker to seek medial treatment, additional communication modalities are being planned for the next generation of ICD systems.

Comparison of Termination-of-Resuscitation Guidelines for Basic Life Support: Defibrillator Providers in Out-of-Hospital Cardiac Arrest

Termination of resuscitation in the field for out-of-hospital cardiac arrest can reduce unnecessary transport to hospital and associated road hazards and increase availability of emergency medical services (EMS) and emergency department resources for other patients. We compare the performance of 3 termination-of-resuscitation guidelines for basic life support-defibrillator (BLS) providers when applied to cardiac arrest patients in the Ontario Prehospital Advanced Life Support study. This prospective cohort study involved all out-of-hospital cardiac arrest patients attended by BLS defibrillator providers in 21 Ontario urban or suburban communities. The data analyses were conducted secondarily on these prospectively collected data. Three termination-of-resuscitation guidelines (referred to as Marsden, Petrie, and Verbeek rules) were applied and contingency tables calculated to show the relationship between the rule and actual survival. From 1988 to 2003, 13,684 cardiac arrest patients were attended by BLS defibrillator providers. Six hundred thirty-six (4.7%) patients survived to hospital discharge. For the 3 termination-of-resuscitation rules, sensitivity was 99.8% (95% confidence interval [CI] 99.5% to 100.0%) (Petrie rules), 99.5% (95% CI 99.0% to 100.0%) (Verbeek rules), and 99.8% (95% CI 99.5% to 100.0%) (Marsden rules). Specificity was 9.9% (95% CI 9.4% to 10.4%) (Petrie rules), 52.9% (95% CI 52.1% to 53.8%) (Verbeek rules), and 19.4 % (95% CI 18.8% to 20.1%) (Marsden rules). Negative predictive value was 99.9% (95% CI 99.8% to 100.0%) (Petrie rules), 100.0% (95% CI 99.9% to 100.0%) (Verbeek rules), and 100.0% (95% CI 99.9% to 100.0%) (Marsden rules). These rules would have resulted in field termination of resuscitation in 9.4% (Petrie rules), 50.5% (Verbeek rules), and 18.5 % (Marsden rules) of cases. Termination of resuscitation was recommended for 1 patient (Petrie rules), 3 patients (Verbeek rules), and 1 patient (Marsden rules), who survived. We found all 3 termination-of-resuscitation rules to have high sensitivity and negative predictive value. However, the specificity and transport rates varied greatly. The results of this study will be useful for EMS providers considering adoption of termination of resuscitation in BLS defibrillator systems for out-of-hospital cardiac arrest.

Venous Thrombosis and Stenosis After Implantation of Pacemakers and Defibrillators

Venous complications of pacemaker/ implantable cardioverter defibrillator (ICD) system implantation rarely cause immediate clinical problems. The challenge starts when patients come for system revision or upgrade. Numerous reports of venous complications such as stenosis, occlusions, and superior vena cava syndrome have been published. We reviewed current knowledge of these complications, management, and their impact on upgrade/revision procedures. One study has suggested that intravenous lead infection promotes local vein stenosis. Another found that the presence of a temporary wire before implantation is associated with an increased risk of stenosis. Although data for ICD leads is based only on three studies-it suggests that the rate of venous complications is very similar to that of pacing systems, and probably data from pacing leads can be extrapolated to ICD leads. Despite 40 years of experience with transcutaneous implanted intravenous pacing systems and dozens of studies, we were unable to identify clear risk factors (confirmed by independent studies) that lead to venous stenosis. Neither the hardware (lead size, number and material) nor the access site choice (cephalic cut down, subclavian or axillary puncture) appears to affect rate of venous complications. A few factors were proposed as predictors of severe venous stenosis/occlusion: presence of multiple pacemaker leads (compared to a single lead), use of hormone therapy, personal history of venous thrombosis, the presence of temporary wire before implantation, previous presence of a pacemaker (ICD as an upgrade) and the use of dual-coil leads. Anticoagulant therapy (for other reasons than pacemaker lead) seemed to have protective antithrombotic effect.

Implantation of an “extracardiac” internal cardioverter defibrillator in a 6-month-old infant

In infants and small children, ICD implantation is a challenge due to technical limitations and a significant number of complications. This report describes ICD implantation in a 6-month-old infant (body weight 5.5 kg). A completely extracardiac defibrillation system was implanted using a transvenous lead subcutaneously in the back below the left scapula as the defibrillation electrode and an active-can device in the right upper abdomen. Defibrillation threshold of implantation was < or =10 J. During the follow-up of 3 months, 8 adequate ICD discharges were noted. The technique described seems feasible to facilitate ICD implantation in small infants.

Emergency medical services in Japan: An opportunity for the rational development of pre-hospital care and research

Japan is at a crossroads in the development of its Emergency Medical Services (EMS). At present, Japan has an essentially pure scoop-and-run, defibrillation system. However, there is a strong movement toward expanding the scope of paramedic practice to include more complex, Advanced Life Support (ALS) and trauma protocols to its nationally standardized pre-hospital protocols. The implications of introducing complex pre-hospital protocols guided by the use of existing scientific evidence to support such action is discussed in the context of Japan’s unique opportunity to test many fundamental questions in pre-hospital medical care and the public’s understanding and acceptance of these practices. Japan, a technologically advanced country that is not encumbered by entrenched “standards of care,” has the opportunity to develop an efficient and rational EMS system.

Reproducibility of internal atrial defibrillation threshold in paroxysmal and persistent atrial fibrillation.

Several pharmacological or technical factors may affect atrial defibrillation threshold (ADFT) for internal cardioversion (ICV) in the treatment of atrial fibrillation (AF). We evaluated the reproducibility of ADFT in lone paroxysmal (electrically induced AF, 10 pts, 51+/-4 years) or persistent AF (15 pts, 64+/-7 years). The AF pattern (F-F interval) was characterised before each ICV attempt. A first step-up synchronised ICV test (ICV1, biphasic shock waveform 6 ms/6 ms) with increasing energy levels from 0.2 to 20 J was performed by a dual-lead defibrillation system (right atrium-coronary sinus configuration) connected to an external cardioverter defibrillator. After 30 min of stable sinus rhythm, a new sustained AF was induced (>20 min duration) and ICV protocol was repeated (ICV2). The AF cycle length was recorded for 30 s from the lateral wall of right atrium in basal condition and before each cardioversion attempt. The mean values of AF cycle length before a successful shock were similar in both AF populations (paroxysmal AF: pre-ICV1 175+/-21 ms vs pre-ICV2 181+/-20 ms (p=NS); persistent AF pre-ICV1 194+/-25 ms vs pre-ICV2 202+/-15 ms (p=NS)). No significant differences were observed between the two successful ICV tests concerning intensity, energy and impedance levels. The value of ADFT energy was reproducible in paroxysmal AF population (SD differences 1.2, coefficient of variability 9.6%). In persistent AF group only the impedance was reproducible (SD differences 2.6 Omega, coefficient of variability 4.5%), but not the energy requirements (SD differences 9.6, coefficient of variability 44.3%). ADFT is reproducible in paroxysmal AF patients, while a high coefficient of variability is present in persistent AF, possibly related to different patterns of re-entrant circuits in the reinduced AF. This observation is important in order to evaluate factors influencing ICV-ADFT correctly in AF patients.

Incidence of Defibrillator Patch Infection Due to Pulmonary Erosion

Background. Intrathoracic defibrillator patches were used prior to effective transvenous defibrillation systems. Spontaneous erosion through the visceral pleural has been documented but the incidence has not been previously reported. Methods. All patients who underwent insertion of ICD patches at Westmead Hospital were identified from Hospital and device company databases. Medical records were reviewed and further follow-up performed through local doctors and the National Registry of Deaths where appropriate. Results. One hundred and four patients underwent insertion of ICD intrathoracic patches between 1987 and 2000. The patches were positioned adjacent to the pericardium in the pleural cavity. Eight patients died within three months of surgery and two patients developed early ICD infection. Of the other 94 patients, 40 were alive at the time of last review such that there had been 562 patient years of survival with four patients developing spontaneous patch infection. The incidence was 0.7% per patient year. The diagnosis was delayed in all four patients. All underwent removal of the ICD system with one perioperative death. Conclusions. There is a small but significant risk of late spontaneous ICD patch infection. The condition is life-threatening and the diagnosis is usually delayed.

Pacemaker and defibrillator lead extraction.

Continued growth in the elderly population and expanding indications have resulted in a progressive increase in the number of implants of pacemakers and defibrillators. Concomitant with these expanding numbers, more leads require removal, due especially to mechanical dysfunction, the need to upgrade to more complex devices, or local or systemic infection. Further, leads have become more complex, particularly for defibrillator systems, resulting in the development of powered extraction sheaths to expedite their removal. For these reasons, it is important to understand the expanding indications, procedural aspects, and limitations of arrhythmia device extraction. Expanded indications for lead extraction include upgrade to more complex systems, particularly pacemaker to defibrillator or biventricular device, extraction through occluded vasculature to produce a conduit for reimplantation, more frequent removal due to vascular overload with multiple leads, and a finite frequency of infection, occurring particularly with device replacement or revision. Powered sheaths now include laser and electrocautery systems, both improving the ease of lead explantation. Complication rates remain low but constant with extraction of larger numbers of leads using new technologies. Expansion of the use of biventricular systems, with implantation of coronary sinus electrodes, will continue to challenge lead extraction in terms of technology and safety. Design of leads that are easier to remove remains of paramount importance.

Threshold measurements: ten rules for good measuring practice.

The following rules for professionally measuring thresholds are derived and discussed: RULE 1: Thresholds should be expressed as voltage averaged over pulse duration to get reproducible and comparable results! RULE 2: Pacing threshold measurements with exponentially decaying pulses should not be extended beyond 1.4 ms as that portion of the pulse below rheobase does not contribute to the stimulation effect! RULE 3: Threshold measurements are best carried out with fixed pulse duration and variable voltage! RULE 4: If threshold measurements are carried out in discrete steps, the steps should be chosen such that the relative step size is as equal as possible! RULE 5: Accuracy of threshold measurements is highly increased if the arithmetically averaged value of the last effective and the first ineffective pulse is defined as threshold! RULE 6: To determine strength-duration-curves, a linear regression of the quantity versus pulse duration should be calculated which yields simply the numerical values of the chronaxie and rheobase! RULE 7: To reach representative strength-duration-curves, measurements with at least four pairs of values must be carried out! RULE 8: Measuring defibrillation thresholds, the relative voltage step size should be chosen equally to have equal accuracy for all steps. RULE 9: If the result of a defibrillation threshold investigation does not reach significance, a too large voltage step size could be an explanation! RULE 10: Comparing intraindividually the threshold of two different defibrillation systems or parameter settings, the threshold ratios should be formed and averaged! Obeying these rules guaranties professional threshold measurements expressed as "rheobase" and "chronaxie" even with devices with discrete steps in parameter programming.

We have come a long way with device therapy: historical perspectives on antiarrhythmic electrotherapy.

The history of device therapies is long and fascinating. In the beginning, there is not simply the anatomy and physiology of the heart, but also analysis of the pulse, which indicates the activity of the heart. The analysis of the (peripheral) pulse as a mechanical expression of heart activity goes back several millennia. In China, in 280 BC, Wang Shu He wrote 10 books about the pulse. The Greeks called the pulse "sphygmos"; thus, sphygmology deals with a theory of this natural occurrence. In Roman times, Galen interpreted the various types of pulse according to the widespread presumption of the time that each organ in every disease has its own form of pulse. The growing clinical importance of electrical cardiac stimulation was recognized and renewed as Zoll in 1952 described a successful resuscitation in cardiac standstill by external stimulation. Meanwhile, millions of patients with cardiac arrhythmias worldwide have been treated with pacemakers in the last 40 years. The concept of a fully automatic implantable cardioverter defibrillator system for recognition and treatment of ventricular tachyarrhythmias was first suggested in 1970. The first implantation of the device in a human being was performed in February 1980. Further developments involved atrial and atrioventricular defibrillators, radiofrequency ablation, laser therapy, and advanced antiarrhythmic surgery. Since 1990, there has been a growing interest in using cardiac pacing as additional treatment in severe cardiac failure. Recent reports have suggested that intervention with left ventricular or biventricular pacing may be helpful for a subgroup of patients with congestive heart failure. Despite encouraging (preliminary) acute and short-term results, pacing strategies for heart failure still are limited and currently regarded as investigational. Advances in the field of therapeutic application of pharmacologic and electrical tools as well as alternative methods will continue as rapidly as before and provide us further significant aid in taking care of patients.

Recent advances in implantable cardioverter defibrillator systems.

The usefulness of the implantable cardioverter defibrillator (ICD) for the prevention of sudden cardiac death caused by ventricular tachyarrhythmias has been proven by several international randomized multi-center clinical trials. Recent advances in medical technologies, such as size reduction and the functional improvements of the device, have resulted in relatively easy implantation. As a result, the number of ICD recipients has been rapidly increasing and the indications for ICD implantation have been expanding. Dual chamber ICDs offer improved tachyarrhythmia detection algorithms such as discrimination of supraventricular arrhythmias. In Europe and the United States, biventricular ICDs are now available for the treatment of congestive heart failure associated with ventricular tachyarrhythmias. Although the incidence of inappropriate shock by ICDs is decreasing, inappropriate discharges of ICDs and a declining quality of life are still problems.