Implantable cardioverter-defibrillator

An implantable cardioverter / defibrillator (ICD) is a device that is implanted as a cardiac pacemaker. It was originally developed ( Michel Mirowski, 1980) in order to prevent sudden cardiac death due to ventricular fibrillation by a shock with high energy ( 10 to 40 joules). Meanwhile, the principle has been continually refined and adds functionality. A current system basically consists of two components.

Subcutaneous ICD

The conventional ICD was developed in the 80s and needs intravenous electrode, the tip must be advanced directly into the ventricle. In recent years, a subcutaneous ICD ( S-ICD ) was developed in which these intravenous electrode is omitted. Thus, the implantation is possible easily and without radiation exposure. Also, a reduced risk of infection and the lack of complication of lead fracture speak for this variant.

It is more current pulses required to terminate the arrhythmia of the heart and prevent an impending cardiac arrest. Nevertheless, the long-term studies have shown the positive effects of this new ICD- variant.

In Europe, the device is on the market since 2009. In America, the FDA approval hurdles are higher, it was not until 2012 stood until the pacemaker approved.

Diagnostic part

The diagnostic part of the equipment shall be able to record to recognize the threatening arrhythmias ( detection) and for the supervising physician. For this purpose, there exist a variety of algorithms (eg, suddenness ( onset), stability ( stability ), QRS morphology ( wavelet or Rhythm ID ), AV synchrony (V > A)). All modern systems have ECG memory to record the episodes. Current detection algorithms achieve a sensitivity of almost 100% at a specificity of up to 80-90%. That is deadly ventricular fibrillation is always recognized in practice. That the specificity is less than 100 %, but means that occasionally incorrectly ventricular fibrillation is detected, even though no arrhythmia is present. This can lead to so-called inappropriate shocks, which can be very uncomfortable and painful for the patient. On the other hand, inappropriate shocks, however, be accepted as an overlooked and untreated ventricular fibrillation (approx. 5 to max. 10 minutes) leads to death within a short time. However, inadequate treatment charges can even trigger with a frequency of about 5% a life-threatening arrhythmia, which must then be terminated under certain circumstances by a sequence of ICD therapy again.

Therapy part

There are currently three distinguishing features:

  • Shock (DC - shock) for a detected ventricular fibrillation or ineffective over-stimulation.
  • Over-stimulation ( anti-tachycardia pacing = ATP ) for terminating stable ventricular tachycardia caused by circular excitation ( reentry ).
  • Normal ( bradycardia ) pacing, also called resynchronization therapy in severe heart failure with left bundle branch block. ( Three-chamber ICD)

Interference

According to studies, can influence small but extremely strong neodymium-iron- boron magnets, which occur for example in nameplates and headphones, pacemakers or ICDs also. In addition, strong alternating electromagnetic fields that can be generated for example by powerful AC motors or alternators, have an influence on the input filter of the ICD and lead to the so-called oversensing.

Manufacturer (selection)

Defibrillation Cardiac dysrhythmia#Re-entry St. Jude Medical Digital Object Identifier American Heart Association
91462
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