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Editors

PekkaRaatikainen
JarkkoKarvonen

Implantable Cardioverter-Defibrillator (ICD)

Essentials

  • The indications for implantable cardioverter-defibrillator (ICD) therapy should be known.
  • The principles of ICD function and the impact the treatment has on the patient's everyday life should be understood.
  • Signs and symptoms suggestive of device malfunction should be recognized. If indicated, an extra visit should be arranged at a pacemaker clinic.

Principles of ICD function

  • An ICD system consists of a pulse generator, which is implanted subcutaneously in the chest wall, and one or more leads (electrodes), which are inserted through a vein into the heart.
  • In severe heart failure, an ICD that allows biventricular pacing may be used.
  • An ICD continuously monitors the heart rhythm. Should the heart rate slow down the device will function as a conventional pacemaker Cardiac Pacemakers and Monitoring Their Function. In ventricular arrhythmia the device will return normal heart rhythm either by antitachycardia pacing, cardioversion or defibrillation.
    • During antitachycardia pacing (overdrive pacing), an ICD stops ventricular tachycardia (VT) by delivering a few impulses at a rate higher than the arrhythmia.
    • In cardioversion, an ICD returns normal rhythm by delivering a shock that is timed (synchronised) to the underlying rhythm.
    • Defibrillation, where the shock is delivered unsynchronised, is used to treat ventricular fibrillation (VF).
  • Antitachycardia pacing is painless but both cardioversion and defibrillation cause pain, even though the energy delivered is considerably smaller than during an external cardioversion (5-40 J vs. 100-360 J).
    • The energy needed to deliver the shocks is provided by a small special battery that usually last for 5-10 years.
  • An ICD will record abnormal rhythms that trigger treatment in the device's memory in ECG format.

Investigations before ICD implantation

  • Before an ICD is implanted the patient must undergo thorough investigations at an appropriate hospital in order to ascertain that the device is indicated and no contraindications exist.
  • The most common investigations before ICD implantation are:
    • history (history of events, occurrence of arrhythmias and sudden deaths in close relatives, heart diseases and other diseases in the patient and their effect on the patient's prognosis)
    • physical examination
    • plasma electrolytes, cardiac enzymes
    • echocardiogram
    • continuous ambulatory ECG monitoring
    • clinical exercise testing
    • contrast studies of the heart and coronary arteries
    • invasive electrophysiological studies.
  • In some cases, other specialist cardiac investigations may also be indicated, including MRI of the heart, myocardial biopsy or genetic examinations.

Indications for ICD therapyImplantable Defibrillators Versus Medical Therapy for Cardiac Channelopathies, Implantable Cardiac Defibrillators in Nonischaemic Cardiomyopathy

  • The efficacy of ICD therapy has been demonstrated in several randomised studies in indications presented in table T1. ICD therapy is at least as cost-effective as the pharmacotherapy used in hypertension or hypercholesterolaemia.

Generally accepted indications for ICD therapy

Prophylactic treatment (primary prevention)LVEF ≤ 35% and NYHA class II-III symptoms after myocardial infarction (≥ 40 days)
LVEF ≤ 30% and NYHA class I symptoms after myocardial infarction (≥ 40 days)
Nonsustained VT and LVEF ≤ 40% after myocardial infarction, as well as sustained VT or VF during electrophysiological examination
LVEF ≤ 35% and NYHA class II-III symptoms or syncope in dilated cardiomyopathy
If considered appropriate by a specialist physician in other structural heart diseases (e.g. hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy) and in inherited, potentially life-threatening ion-channel abnormalities (e.g. long QT syndrome, Brugada syndrome, catecholamine-sensitive polymorphic VT)
Treatment post cardiac arrest (secondary prevention)VT or VF induced cardiac arrest not due to a treatable or reversible cause, even if the heart is structurally normal
Sustained VT in a patient with a structural heart disease, irrespective of the left ventricular function
Unexplained syncope, as well as sustained VT or VF triggered during an electrophysiological examination
LVEF = left ventricular ejection fraction; VT = ventricular tachycardia; VF = ventricular fibrillation
Prophylactic treatment, i.e. primary prevention
  • The aim of primary prevention is to prevent cardiac arrest in high risk patients.
  • The risk of life-threatening arrhythmias and sudden death is particularly high after myocardial infarction in patients with markedly reduced contractility of the left ventricle (LVEF ≤ 35%).
    • An ICD will significantly improve the prognosis of these patients, and an ICD is recommended particularly if nonsustained VT has been recorded.
    • The need for an ICD is assessed only when at least 40 days have passed since myocardial infarction.
    • If the duration of the QRS complex is > 130 ms and the patient has a left bundle branch block (LBBB), additional heart failure pacing (cardiac resynchronisation therapy) to synchronize the cardiac contractions is recommended.
  • Prophylactic treatment may also be used in other structural heart diseases if considered appropriate by a cardiac electrophysiologist (e.g. dilating and hypertrophic cardiomyopathy) and in patients who are at high risk of life-threatening arrhythmias due to an inherited illness with the potential of causing ventricular arrhythmias (e.g. long QT syndrome, Brugada syndrome).

Treatment post cardiac arrest, i.e. secondary prevention

  • An ICD was initially developed to prevent sudden death in patients who had been diagnosed with a life-threatening ventricular arrhythmia.
  • VT/VF in the late post myocardial infarction period is the most common indication for an ICD. However, the efficacy of the device in other conditions is indisputable, and implantation should always be considered when cardiac arrest is not due to a treatable or reversible cause.
  • An ICD is indicated in sustained VT, particularly if the arrhythmia causes syncope or the patient has a structural heart disease (LVEF < 40%).
  • In severe heart failure, additional heart failure pacing is recommended if the duration of the QRS complex is > 130 ms, the patient has a LBBB and LVEF is ≤ 35%.

Contraindications to ICD therapy

  • ICD therapy is contraindicated if VT/VF is caused by a reversible or treatable cause, such as
    • acute myocardial infarction or ischaemia
    • trauma
    • myocarditis
    • an electrolyte disturbance
    • drug-induced proarrhythmia
    • WPW syndrome, VT in a healthy heart or other arrhythmia treatable with catheter ablation.
  • Other contraindications for ICD therapy
    • Life expectancy less than 12 months due to coexistent conditions
      • However, an ICD may serve as a bridge to heart transplantation in patients with severe heart failure.
    • Poor treatment compliance, e.g. due to a mental illness
    • Incessant VT or frequently recurring VT/VF (”arrhythmia storm”), unless the situation is stabilised with the aid of pharmacotherapy or other means.
  • When assessing the significance of underlying diseases, the role of the patient's own doctor is crucial. Therefore, he/she should in the initial referral letter take a stand on possible contraindications to invasive investigations and to ICD therapy.

Implantation of an ICD and patient monitoring

Implantation of an ICD

  • The type of the ICD is selected on an individual basis, taking into account each patient's needs.
    • Patients requiring permanent pacing benefit from physiological pacing, and patients with severe heart failure benefit from biventricular pacing.
    • In other cases, a device capable of sole ventricular pacing is recommended.
  • As is the case with an ordinary pacemaker, an ordinary ICD pulse generator is usually implanted subcutaneously below the left clavicle under local anaesthesia. The leads are inserted through a vein into the heart. The early devices were bigger and they needed to be inserted under general anaesthesia either under the pectoral muscle or buried in the abdominal wall.
  • In selected cases, a completely subcutaneous device can be used (so-called subcutaneous ICD), with no leads inserted inside the heart.
    • Such a device may be considered if there is no need for pacing of the heart or if inserting the leads inside the heart is not possible.
  • Earlier, as a part of the implantation procedure, the patient was usually anaesthetized and VF was induced to ensure that the ICD detects and terminates the arrhythmia correctly. Modern devices are so reliable that - apart from the implantation of a subcutaneous ICD - this practice has been almost completely abandoned.
  • Most patients are discharged from the hospital the day after the implantation. Before discharge, the ICD is individually programmed, taking into account the patient's condition, the character of the arrhythmia and the results of the cardiac investigations, to recognize the normal heart rhythm and to automatically treat bradycardia and ventricular arrhythmias.
    • In order to prevent painful “shock therapy”, long detection times and antitachycardia pacing are favoured in the programming as the first line treatment for arrhythmias.

Follow-up at the pacemaker clinic

  • The first follow-up appointment at the pacemaker clinic is usually after 1-3 months followed by appointments approximately every 6-12 months.
    • With the remote monitoring systems, the intervals between visits at the pacemaker clinic can be extended without endangering patient safety. Remote monitoring also allows the recognition of various functional failures of the device more rapidly than earlier.
  • A physician at the pacemaker clinic will check the patient's clinical condition and carry out routine pacemaker measurements Cardiac Pacemakers and Monitoring Their Function. In addition, an external programming unit will be used to read the data stored in the memory of the ICD and to check whether the device has detected and treated any arrhythmias since the last appointment.
  • All episodes stored in the memory are carefully scrutinised, and the efficacy of the ICD in appropriately detecting and treating arrhythmias is evaluated.
  • It is estimated that 10-30% of the activations of the ICD are inappropriate.
    • The most common causes of inappropriate activations are sinus tachycardia and atrial fibrillation.
    • An attempt should be made to prevent the recurrence of inappropriate activation by altering the programming of the ICD. The rate of the arrhythmia is the main criteria used to detect ventricular arrhythmias, but an ICD may also be programmed to detect the suddenness of the arrhythmia onset, the regularity of the rate, the duration of the tachycardia and the morphology of the ventricular complex.
    • In addition to reprogramming, it often is necessary to modify the patient's medication (e.g. by increasing the dose of a beta blocker).
  • An isolated, adequately treated episode usually requires no further action. However, should the ICD therapy events be frequent, either the patient's medication or the programming of the unit usually needs adjustment.

Follow-up in primary care

  • Optimal management of the underlying condition will reduce the risk of ventricular arrhythmias and reduce the incident of ICD-generated shocks.
  • The management of the underlying condition is usually the responsibility of the patient's own doctor, who should verify and optimise the treatment and medication during each follow-up appointment.
  • Antiarrhythmic medication, however, must not be changed before first consulting the pacing clinic physician.
  • When a patient is transferred to terminal care, it is usually advisable to turn off the management of ventricular arrhythmias in order to avoid painful shocks. In an acute situation, this can be done by placing a powerful magnet over the ICD. The pacing of bradycardia is continued normally during palliative care.

Indications for pacemaker clinic consultation

ICD function

  • An ICD does not prevent arrhythmias; it will only arrest an already started VT/VF. A shock delivered by an ICD is always an indication for a check-up at the pacemaker clinic or for remote data transfer.
    • If an isolated shock is delivered, the patient experiences an episode of syncope or has sustained palpitations, the pacing clinic should be contacted the following weekday.
  • Emergency care should be sought if the device delivers several subsequent shocks or the patient's condition worsens after the shock.
    • After first aid has been delivered, the patient should be sent to a hospital where the function of the ICD can be checked.

ICD malfunction

  • Modern ICDs are highly resistant to external interference and the possibility of sustaining permanent damage during every day life is in practice impossible (table T2).
  • However, many hospital investigations and procedures may affect ICD operation, and a prior consultation with a pacemaker clinic physician is always warranted.
    • The shock functions of the ICD must usually be temporarily deactivated during surgery because diathermy may be misinterpreted as VF causing inappropriate firing of a shock.
  • Modern ICD systems incorporate several self-check features to increase patient safety.
    • An ICD may be programmed to check at regular intervals, for example, battery life and the integrity of the leads. The monitoring system notifies the patient by audible tones if certain conditions exist, and the patient then arranges an appointment at the pacing clinic.
    • The remote monitoring system allows the information about possible malfunction to be automatically forwarded so that the physician at the pacemaker clinic is able to check the situation on the remote monitoring website.
  • The battery life of an ICD is usually 5-10 years. At the end of battery life the entire pulse generator must be changed as the battery is an integral part of the system and cannot be recharged.
  • Even when the problem or malfunction suspected is transient Cardiac Pacemakers and Monitoring Their Function, the function of the ICD system must be checked at the pacing clinic or via remote monitoring as soon as possible.

Interference caused by household appliances and other equipment

EquipmentInterference on the ICD function and precautions
Household appliancesNo interference provided that the appliances are in good condition
ComputerNo interference
Mobile phoneNo interference; it is recommended that the phone should not be carried in a breast pocket over the ICD.
Chain sawMay cause interference
Welding equipmentMay cause interference
Strong magnetsMay cause interference: the recommended safety distance is about an arm's length
Electronic article surveillance gateways at retail shopsHardly any interference: however, the patient should walk briskly through the gated area and avoid standing around the gateway
Security check at an airportHardly any interference: however, on presenting a pacemaker identification card, the patient does not have to pass through the metal-detector gate, and the airport officials will carry out a manual safety check.

Treatment of arrhythmias in patients with an ICD

  • Of the patients with an ICD in situ, 40-70% use antiarrhythmic medication.
  • In addition to life-threatening ventricular arrhythmias, medication is needed particularly for the treatment of atrial fibrillation.
    • Effective treatment of atrial arrhythmias reduces the risk of inappropriate ICD therapy.
    • The guidelines for anticoagulant treatment in atrial fibrillation are similar to those given for other patients,
    • It is safest to carry out electrical cardioversion by using the leads of the ICD. If that is not possible the same precautions should be followed as in patients with an implanted pacemaker. After external cardioversion, the operation of the ICD must be verified at the pacemaker clinic or via the remote monitoring system.
  • When antiarrhythmic medication is started, the monitoring of the patient should be intensified. The ICD may also need to be reprogrammed or even retested.
  • If the ICD is frequently activated in spite of intensified medication (so-called arrhythmic storm) catheter ablation may be warranted.

The effect of an ICD on everyday life

  • Modern ICDs are small and lightweight and are therefore fairly inconspicuous, and most patients quickly get used to their presence.
  • After the initial stage, the device hardly affects the patient's work, home life or hobbies.
    • Mild exercise is recommended but sudden, strenuous exertion should be avoided, as such exercise could trigger an arrhythmia.
    • Swimming alone, diving to a depth of more than 5 metres and martial arts are forbidden.
    • There is no reason why the patient should not enjoy a normal sex life or travel.
  • Restrictions regarding driving are dependent on the patient's underlying disease and the symptoms that the arrhythmia causes.
    • After VF, or VT that impairs the level of consciousness for however short a period, driving will be forbidden for 3 months. After this time, driving may be resumed provided that the symptoms have not recurred.
    • Antitachycardia pacing during an arrhythmia that does not affect the level of consciousness is usually not an indication to stop driving.
  • Professional driving is permanently forbidden, and pacemaker clinic personnel should be consulted regarding any other occupational restrictions.
  • The therapies given by the ICD do not affect other people, and in a resuscitation situation, for example, normal practice is followed.