Implantable cardioverter defibrillator

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Implantable cardioverter defibrillator
Usually the conventional ICD-device is implanted on the left prepectoral (i.e. in front of the large pectoral muscle ). The electrode leads through veins into the right ventricle .
implanted cardioverter defibrillator
Conventional ICD in the X-ray image, the shock electrode was inserted through the left subclavian vein . It is a dual-coil electrode. The first shock coil is located at the level of the superior vena cava , the second in the right main chamber.
Subcutaneous ICD Boston Scientific / Cameron Health Model 1010 (side view, left the electrode next to the sternum)

An implantable cardioverter / defibrillator (ICD) (formerly AICD from automatic implantable cardioverter-defibrillator) is a miniaturized automatic electrical device that is used by surgery to patients at high risk for life-threatening cardiac arrhythmias .

The electrodes of the ICD are located in the heart chamber and therefore have direct contact with the heart muscle. In the case of ventricular flutter or fibrillation , an electrical impulse is automatically triggered. This current surge normalizes cardiac muscle activity and thus the organ's vital pumping capacity. The device is implanted like a pacemaker . A further development of the ICD is the subcutaneously implantable defibrillator (S-ICD) .


Doctors Michel Mirowski and Morton Mower began developing the ICD in July 1969 at Sinai Hospital in Baltimore . A first prototype was built from the broken paddle of an external defibrillator and tested on a dog. The successful attempt was noted with interest by experts. However, the project of Mirowski and Mowers to develop an internal battery-powered system for defibrillation and cardioversion for humans was viewed with skepticism by the experts at the time. This led to the previous sponsor Medtronic distancing itself from the inventors' further plans and no longer supporting them.

In 1972 Mirowski and Mower came into contact with Stephen Heilman , the founder of the still small medical technology company Medrad. Heilman was convinced of the ICD project and made his company's engineers available to the doctors, including Alois Langer . When a defibrillator was completely implanted in a dog in 1975, cardiology research again took notice of the innovation. The goal now was to produce a device that could be used by humans.

This goal was achieved on February 4, 1980; At the Johns Hopkins Hospital in Baltimore , the heart surgeon Levi Watkins successfully implanted an ICD on a 57-year-old woman who had previously suffered from severe cardiac arrhythmias that could not be controlled by medication. For the procedure, however, the chest had to be opened in order to place the electrodes. In addition, the device was still relatively heavy (225 g) and was not yet able to initiate actions other than ending ventricular fibrillation.

In the years that followed, Mirowski and Mower's team refined the system, which received approval from the Food and Drug Administration (FDA) in 1985 . Since the late 1980s, an ICD has been able to be implanted without a thoracotomy and has other functions such as synchronized cardioversion .

The classification of the (A) ICD systems was followed by the NBD-code (see FIG. NBG Code ), wherein the first point indicative of the shock chamber, the second the anti-tachycardia stimulation chamber, the third type of tachycardia and the fourth point, the antibradycardia stimulation chamber .

Systems, components and functionality

Conventional ICD

An ICD basically consists of two components. On the one hand the ICD device, which consists of the control unit, a battery and an electrode, and a venous electrode that is anchored in the right ventricle of the heart. The ICD is implanted under the skin in front of or in the left pectoral muscle. The diagnostic part recognizes faults requiring treatment by means of permanent EKG recording, the stimulation part then triggers the current surge. An electric field is built up during shock. In modern devices, this can either be set up between the venous electrode and the housing of the ICD device or, when using so-called dual-coil electrodes (as in the X-ray image shown), between two separate coils of a venous electrode. Depending on the individual anatomy, the electric field can be optimized with the aim of capturing as much heart muscle tissue as possible in the electric field.

The housing of an ICD is made of tissue-compatible titanium . It encapsulates a microcomputer with electronic circuitry and a long-life battery. On the top there are connections for the probes (electrodes) that are inserted into the right heart. The heart signals are continuously relayed to the ICD's microcomputer by sensors located at the ends of the probes. If the incoming signals are identified as ventricular flutter or fibrillation by the computer program, an integrated defibrillation electrode sends shock-like impulses into the heart chamber until the heart rhythm has stabilized at the programmed normal values.

Subcutaneous ICD

While with the conventional ICD the tip of the intravenous electrode has to be pushed directly into the heart chamber, which requires fluoroscopy , this is not necessary when inserting a subcutaneous ICD . Its electrodes are placed under the skin in a region next to the breastbone. This makes implantation easier and possible without exposure to radiation. A reduced risk of infection and the lack of complications from broken electrodes speak in favor of this variant.

Compared to a conventional ICD, stronger and more frequent electrical impulses are required to end the arrhythmia of the heart and to prevent impending cardiac arrest. Nevertheless, the long-term studies showed the positive effects of this new ICD variant.

The device has been on the market in Europe since 2009. In the USA, the FDA approval hurdles are higher; the pacemaker was not approved until 2012.

Diagnostic part

The diagnostic part of the device is able to recognize threatening rhythm disturbances (detection) and to record them for the supervising doctor. A large number of algorithms exist for this , for example suddenness ( onset ), stability ( stability ), QRS morphology ( wavelet or rhythm ID ), AV synchrony (V> A). All modern systems have EKG memories for recording the episodes. The detection algorithms recognize almost 100% of all ventricular tachycardias , the specificity is slightly lower at 80–90%. In some cases, the device therefore incorrectly detects ventricular fibrillation even though there is no rhythm disturbance and delivers what is known as an inadequate shock. Such a shock can also be triggered by a technical defect. An inadequate shock is particularly uncomfortable for the patient, as he is usually fully conscious.

Therapy part

There are currently three functions to be distinguished:

  • Shock delivery (DC shock) when ventricular fibrillation or ineffective overstimulation is detected.
  • Overstimulation (ATP = antitachycardia pacing ) to end stable ventricular tachycardias caused by circulating excitations ( reentry ).
  • Normal (anti-bradycardia) pacemaker stimulation, also as resynchronization therapy for severe heart failure with left bundle branch block . (Three-chamber ICD)

Programming and monitoring of the ICD

The programming is carried out by a specialist in cardiology via telemetry . For this purpose, a programming head is placed on the implantation site, which in turn is connected to the programming device by a cable. The programming includes, among other things, the activation of a signal tone, which indicates possible faults in the device. During the review, stored data is retrieved and evaluated. The ICD may then be reprogrammed. During follow-up examinations, among other things, the charge status of the battery is checked, which depends on the frequency and strength of the impulses.


Strong permanent magnets made of materials such as neodymium-iron-boron , which are found in headphones, for example, can affect pacemakers or ICDs. In addition, strong electromagnetic alternating fields, which can be generated at close range by powerful three-phase motors , for example , can have an impact on the input filters of the ICD and lead to so-called oversensing .

Inappropriate shock delivery

Inappropriate shock deliveries are shock deliveries due to incorrect assumptions by the ICD system about the presence of ventricular tachycardia or ventricular fibrillation . This can occur, for example, due to external electrical interference (see above). If the ventricular perception of the ICD system is too sensitive, the misinterpretation of the T-wave as an R -wave can lead to so-called T-wave oversensing, which results in a double counting of a heart action and thus an alleged double count high perceived heart rate.

Psychological and ethical problems

Some patients describe an almost unbearable, painful sensation of the therapy delivery (“ like reaching into the socket ”). If several electric shocks are triggered close together, the psychological stress can be enormous; in some cases the patients need intensive care by psychologists .

The device can not prevent death from heart failure or other non-cardiac diseases. Many patients experience cardiac arrest at the end of their life , so the ICD is not triggered. However, since electrolyte shifts and thus tachycardia cardiac arrhythmias can occur in the dying phase, up to two thirds of ICD patients and their relatives or nursing staff experience undesirable and stressful shock events during the final phase of death . A possible palliative treatment approach is thereby considerably impaired. In order to avoid this, a conversation with the patient must be sought in good time in order to carry out appropriate programming with their consent or to deactivate the device, in an emergency by placing a strong magnet on the corresponding implantation site.


Major manufacturers of implanted defibrillators are:

Market shares in Germany

According to the German Pacemaker Register, of the 30,002 implantations registered in Germany in 2015, the defibrillators (ICD units) came from the following manufacturers:

Number of ICD Market shares in% Manufacturer
10,054 33.5% IrelandIreland Medtronic with NayaMed
8,586 28.6% United StatesUnited States St. Jude Medical (with Abbott Laboratories since 2017 )
6,962 23.2% GermanyGermany Biotronics
4.018 13.4% United StatesUnited States Boston Scientific with CPI (Cardiac Pacemakers Inc.) / Guidant and Intermedics
346 1.2% United KingdomUnited Kingdom LivaNova (formerly Sorin Biomedica / ELA Medical)
36 0.1% Others

Individual evidence

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