Implantable Cardioverter Defibrillator

An implantable cardioverter defibrillator (Engl. implantable cardioverter defibrillator, ICD; earlier designation AICD from automatic implantable cardioverter-defibrillator) is an implantable defibrillator system that detects cardiac arrhythmias such as ventricular tachycardia (VT; cardiac arrhythmias that originate in the heart chambers (ventricles); heart rate > 120/min) and their extreme form, ventricular fibrillation (life-threatening condition), are automatically detected and can be converted to sinus rhythm (normofrequency, regular heartbeat) by targeted electrical pulses (defibrillation; overstimulation). In many cases of life-threatening cardiac arrhythmias, defibrillator therapy is the only method that can save the life of the affected person. The ICD is usually used for secondary prophylaxis (secondary prevention), i.e., after the occurrence of a cardiac arrhythmia to prevent the progression of the disease.

Indications (areas of application)

To reduce the risk of sudden cardiac death (PHT; Sudden cardiac arrest, SCA), an ICD is recommended for patients with:

  • Ventricular arrhythmias (cardiac arrhythmias originating in the ventricle) leading to hemodynamic instability (condition in which the circulation is impaired to a clinically relevant degree) [ACCF 2009]
  • Symptomatic heart failure (cardiac insufficiency).
    • Symptomatic heart failure* (NYHA II-III), an ejection fraction (ejection fraction of the heart) ≤ 35% (despite optimal drug therapy), ischemic etiology (“oxygen deprivation of the heart muscle”) due to and > 40 days after acute myocardial infarction (heart attack) [ACCF 2013].
    • Symptomatic heart failure* (NYHA II-III), an ejection fraction ≤ 35% (despite at least 3 months of optimal drug therapy), and nonischemic cardiomyopathy (diagnosed for at least 9 months) [ACCF 2013]
    • NYHA I* : with nonischemic cardiomyopathy and an ejection fraction ≤ 30% (despite optimal drug therapy) [ACCF 2009].
    • Heart failure after AHA stage B* : with asymptomatic ischemic cardiomyopathy (myocardial disease associated with oxygen depletion), an ejection fraction ≤ 30% (despite optimal drug therapy), and > 40 days after acute myocardial infarction (heart attack) [ACCF 2009]
    • Patients with chronic heart failure should be recommended for implantation of a defibrillator (ICD) if they have a life expectancy of more than one year and meet one of the following conditions [see S3 guideline below]:
      • Survived sudden cardiac death (PHT).
      • Sustained, hemodynamically effective ventricular tachycardia (that did not occur from preventable causes).
  • Defibrillator (ICD) implantation should be recommended to patients with ischemic cardiomyopathy who meet the following requirements:
    • NYHA II-III
    • LVEF ≤ 35% despite ≥ 3 months of optimal drug therapy.
    • Life expectancy > 1 year
    • Good functional status

    Implantation should be performed no earlier than 41 days after past myocardial infarction (heart attack).

* Patients should be informed prior to planned ICD implantation that an ICD is for the prevention of sudden cardiac death (PHT) and not for the prevention of progression (progression) of heart failure (heart failure). Legend

  • ACCF: American College of Cardiology Foundation
  • AHA: American Heart Association
  • NYHA: New York Heart Association

The procedure

The implantable cardioverter defibrillator (ICD) is a miniaturized automatic defibrillator. The electrodes of the ICD are located in the right atrium (atrium) as well as in the right ventricle (ventricle; dual-chamber system) and thus have direct contact with the myocardium (heart muscle). In the event of ventricular flutter or fibrillation, for example, an electrical impulse is automatically triggered. This electrical impulse normalizes the activity of the heart muscle. This restores the heart’s pumping capacity. Depending on the type of arrhythmia, antitachycardia pacing, cardioversion or defibrillation therapy is performed.ICD implantation is similar to that of a pacemaker. A further development of the cardioverter defibrillator is the subcutaneously implantable defibrillator (S-ICD).

Electromagnetic interference sources

Interference with implants occurs in approximately 0.3-0.7 cases per year. The following are notes on electrical devices

  • Cellular phones* (only still possible if the cellular phone is placed directly on the skin site above the implant).
  • Anti-theft devices (in the entrance area of department stores): a safety distance is required for radio-frequency systems (so-called RFID scanners):
    • Pacemaker 60 cm
    • Defibrillator 40 cm
  • Induction stoves: safety distance of at least 25 cm.

* A study has found that the risk of electromagnetic interference of the iPhone 6 and Apple Watch with implantable electronic devices is low. there was only one incident of interference in a patient with persistent atrial fibrillation and a dual-chamber pacemaker. Tested 148 subjects; 1,352 tests were performed. However, the authors advise against using electronic mobile devices immediately adjacent to the implant during device interrogation.

Benefits of defibrillator therapy

In secondary prevention,* defibrillator therapy is superior to pharmacotherapy (AVID, CASH, and CIDS trials).In primary prevention of coronary artery disease (CAD), prospective trials demonstrate an improvement in all-cause mortality (all-cause mortality rate) with defibrillator therapy.In non-CRC-related heart failure, implantable cardioverter/defibrillators (ICDs) disappoint. Younger patients aged less than 55 years benefit from a significant 52% relative reduction in mortality (death rate) (8.2% versus 17.4%). However, the survival benefit appeared to diminish with increasing age. Among patients aged 65 to 74, the risk reduction was still 33% (22.9% versus 33.5%). * Measures taken (here, defibrillator therapy) after the onset of a condition (here, cardiovascular arrest due to ventricular tachycardia) to prevent recurrence (e.g., loss of consciousness). Further notes

  • In a study of cardiac patients with an implantable cardioverter-defibrillator who were concomitantly treated with digitalis, they had significantly higher mortality (death) than ICD patients without digitalis.
  • Competitive sports are usually safe for patients with implantable cardioverter defibrillators (ICDs). Only patients with arrhythmogenic right ventricular cardiomyopathy (ARVC), a rare inherited disease, experienced more ventricular arrhythmias during exercise (versus the rest of the study participants), which had to be compensated for by one or more shocks from the ICD. In 120 of 440 participants, the ICD became active during the 4-year observation period: 7% of patients received a shock during exercise, 5% during other physical activities, and 6% during rest.
  • Cardioverter-defibrillator vest (WCD) after myocardial infarction versus optimal drug therapy: primary end point (combination of sudden cardiac death and death from ventricular tachyarrhythmias at 90 days): occurred in 1.6% of patients randomized to WCD and in 2.4% of patients treated with optimal drug therapy alone (difference was not significant; p = 0.18).
  • In patients with ischemic or nonischemic cardiomyopathy (myocardial disease), prophylactic implantation of an ICD resulted in a reduction in mortality/stroke rate (43% reduction in mortality in the ICD group compared with the control group). A novel marker of sympathetic activity-associated repolarization instability was used to select patients to identify those at electrical risk who would benefit from prophylactic implantation of an ICD by reducing mortality.
  • EU-CERT-ICD study (2247 patients; follow-up period mean 2.4 years): patients benefited from primary prophylactic ICD implantation when indicated according to guidelines: this resulted in a significant 27 percent reduction in mortality (death rate) (hazard ratio, HR: 0.731); number of sudden cardiac deaths (PHT) was significantly lower in the ICD group than in the control group (19 versus 32 events, unadjusted HR: 0.158). Furthermore, ICD implantation was found to be associated with significantly lower mortality in men (adjusted HR: 0.691) but not in women (adjusted HR: 1.063).
  • CD-HeFT trial: primary prophylactic ICD therapy was still associated with a survival benefit in patients with heart failure in a long-term study after a median follow-up of 11 years: All-cause mortality (all-cause mortality rate) 52.5% (ICD arm), 52.7% (amiodarone arm), and 57.2% (placebo arm); the benefit was greatest in the first 6 years, with a significant 25% relative decrease in all-cause mortality. Of importance to the long-term benefit of ICD therapy was the etiology (cause) of heart failure: ischemic heart disease (disease in which there is a reduced oxygen supply to the heart muscle due to narrowing of the coronary arteries) showed a 19% lower all-cause mortality; in the group with a non-ischemic etiology, no mortality benefit was seen over the long-term.