ICD's- Your Questions Answered

Medical Terms 04 May 2021

The history of the Implantable Cardioverter Defibrillator

The ICD was developed by pioneering Polish cardiologist Dr Michel Mirowski and his team in the early 1960s. Since then, millions of patients worldwide have received an ICD and uncounted lives have been saved.

Initially, ICD therapy was not widely accepted and many physicians actually considered this potentially life-saving device unethical. Implantation was difficult and required electrodes to be placed directly on the surface of the heart. They were also so bulky that the device had to be placed in the wall of the upper abdomen as it was too large to be placed in the chest.

By the early 1990s, ICDs no longer required wiring directly on the heart, with leads that went through the vein to the inside surface of the heart. This made the implant procedure much easier, and recovery much quicker.

Over time, technology evolved rapidly and ICDs became smaller, allowing them to be placed in the upper chest - like a pacemaker - rather than in the abdomen. Current devices are relatively small, can be implanted subcutaneously in the majority of cases and are channelled under the skin and laid alongside the breastbone (sternum).

Subcutaneous ICDs (S-ICD)  are larger than traditional ICDs as they need a larger battery, owing to the wire being outside of the heart. Some ICDs have a single lead where there is just one wire from the generator and others have a dual lead (one into the ventricle and one into the upper chamber – the atrium). Your cardiologist will make the decision on which ICD is best suited to your condition.

Key facts

An ICD is a small, battery-powered device with a generator, small computer, electrode (lead or wire) and a battery, which lasts five to 10 years.

An ICD is usually fitted under the skin, just below the left collarbone. Fitting can be done under a local or general anaesthetic, depending on the patient and usually takes about an hour.  Patients are given antibiotics because of a small risk of infection. Follow-up checks for your ICD are needed every three to 12 months. 

What ICDs do

ICDs are really implantable computers - programmed to keep track of a patient’s heart rhythm and protecting an individual from dangerous heart rhythm changes that could result in cardiac arrest. The heart normally beats in ‘sinus rhythm’, controlled by electrical signals from within the heart.

ICD are able to pace the heart if your heart rate is slow (bradycardia); deliver anti-tachycardia pacing (ATP) if your heart rhythm is too fast and deliver a series of paced heart beats to restore a normal rhythm. If the device senses a dangerous rhythm, such as ventricular fibrillation and where ATP has not been successful, the ICD defibrillates (shocks) the heart to return the heart rhythm to normal. This may feel as if you’re being kicked in the chest and/or knock you off your feet. The pain typically lasts only a second and there should be no discomfort after the shock is over.

ICDs v pacemakers

Both ICDs and pacemakers are medical devices implanted inside the bodies of heart patients. Pacemakers are designed to correct bradycardia or assist in the treatment of heart failure, by providing an electrical impulse to cause the heart to beat. ICDs are safeguards against sudden life-threatening arrhythmias, (a general term for any abnormal heart rhythm, where the heart is not beating in sinus rhythm). 

Cardiac resynchronisation therapy gets you heart in sync

If your heart is not beating efficiently and you meet the criteria, you may be eligible for a cardiac resynchronisation therapy (CRT) heart device, which improves the heart’s efficiency and in effect, “resynchronises” the heart so both sides beat in sync and thus helps the heart to pump more efficiently.

What is cardiac resynchronisation therapy and how can it help your heart?

CRT is used to help improve the heart’s rhythm and symptoms associated with arrhythmia In heart failure patients. The procedure involves implanting a pacemaker, (about the size of a pocket watch and weighing about 3oz)  just below the collarbone. The device has three leads, (one more than an ICD). The additional lead is attached to the left ventricle to monitor the heart rate to detect heart rate irregularities and emit tiny pulses of electricity to correct them.

Who is a candidate for cardiac resynchronisation therapy?

In general, CRT is for heart failure patients with moderate to severe symptoms and whose left and right heart ventricles are not beating in unison. However, CRT is not effective for everyone and not advised for patients with mild heart failure symptoms, diastolic heart failure, or who do not have issues with the ventricles not beating together.  It is also only suitable for patients, once they have fully explored medication therapies and is often combined with other treatments to achieve the best results.

Benefits of cardiac resynchronisation therapy

Patients have reported alleviations of some heart failure symptoms - such as shortness of breath and studies also suggest CRT reduces the need for patients to be treated in hospital.

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