ICD (cardioverter-defibrillator): what it is, who needs it, what to do after a shock

According to the patient website of the European Heart Rhythm Association (EHRA), an ICD consists of a box (the electrical circuits and the power source) and leads, that is, wires. According to EHRA and NHLBI, it works against two dangerous rhythms. In ventricular tachycardia, the heart beats very fast. In ventricular fibrillation, the ventricles quiver instead of pumping blood. These are the rhythms that most often lead to cardiac arrest.

An ICD is not the same as an automated external defibrillator (AED) in public places or a defibrillator vest, which is usually worn for a short time. EHRA lists four types:

• Single-chamber ICD: one lead.
• Dual-chamber ICD: two leads.
• CRT-D: three leads; it combines resynchronization and defibrillation.
• Subcutaneous ICD (S-ICD): the box is placed in the armpit area and the lead under the skin. It only delivers shocks and does not pace, and the incision is larger.

EHRA distinguishes two groups. Secondary prevention: the person has already had a life-threatening ventricular arrhythmia, confirmed or suspected. Primary prevention: there has been no such arrhythmia, but the risk is high because of a diagnosed heart disease or, sometimes, a disease or genetic defect found in the family.

LVEF shows how much blood the left ventricle pumps out with one beat: the lower the number, the weaker the heart pumps. The NYHA class shows how much heart failure limits everyday activity: the higher the number, the greater the limitation.

According to the 2022 ESC guideline (as summarized by ACC and Healio), in coronary artery disease, despite at least 3 months of properly chosen drug treatment:

• with NYHA class II–III and an LVEF of 35% or lower, an ICD is recommended;
• with NYHA class I and an LVEF of 30% or lower, an ICD should be considered.

In coronary disease, an ICD is considered if the LVEF is 40% or lower, there is ventricular tachycardia that stops on its own, and the tachycardia can be triggered during an electrophysiology study (EP study, a test of the heart's electrical signals from inside the heart). In dilated and hypokinetic non-dilated cardiomyopathy (diseases of the heart muscle), the LVEF threshold of 35% is not the only thing looked at; other risk factors are also taken into account (ACC: an LVEF below 50% and at least two risk factors). In other heart muscle diseases, the specialist makes the decision using separate criteria.

The times on the EHRA pages differ: the ICD page says about one hour, and the pacemaker page says usually 1–2 hours and that it may take longer for an ICD. Usually local anesthesia and a sedative are used, sometimes general anesthesia. A 5–10 cm incision is made below the collarbone, usually on the left side, and the procedure is done under X-ray guidance. After a few hours of observation and a check of the device, you are usually allowed to go home the same day or the next day.

Complications listed by EHRA: swelling, bruising, bleeding or infection at the incision site, and displacement of the lead. According to the summary of the 2021 ESC guideline, infection is more common with an ICD than with an ordinary pacemaker. According to patient guides, tell your doctor right away if your temperature rises above 38.5 °C, if there is redness or swelling over the device, fluid leaking from the incision or increasing pain.

Sources differ on arm movement (EHRA: no restriction is needed; the NHS in Britain: do not raise the elbow above the shoulder for 4–6 weeks after a pacemaker), so follow your doctor's instructions.

According to NHLBI, low-energy pulses are usually painless and feel like a fluttering sensation. A strong shock is brief but may be painful. This is a serious event. A shock may be a response to a dangerous rhythm, but according to NHLBI it can also happen when the heart is working normally, so tell your doctor about every shock.

The steps below are based on EHRA and NHLBI recommendations and adapted to the 103 number:

1. One shock and you feel well: check that you have not been injured and rest for a few hours.
2. The same day or the next day, let your doctor or the center where the device was implanted know, and follow their instructions.
3. More than one shock within 24 hours: contact your doctor or the center very quickly. If a second shock comes a few hours after the first, go to a facility that can help ICD patients.
4. Several shocks in a short time, chest pain, shortness of breath, fainting, or a head injury while taking a blood thinner (anticoagulant): call 103.

EHRA calls more than three shocks within 24 hours an electrical storm. This requires a hospital, often intravenous medication or general anesthesia.

Sources differ, so follow the schedule your doctor gives you. EHRA: the first check at 2–12 weeks, then usually once a year. NHLBI: at least once every 6 months.

Battery life also varies: EHRA says 7–10 years on average, NHLBI 5–7 years. Replacement is simpler than the first implantation, and the leads are replaced only if they are not working well. However, according to the ACC summary of the 2021 ESC/EHRA guideline, the risk of infection is higher at replacement.

According to NHLBI, people living with an ICD may have anxiety, stress, depression and post-traumatic stress disorder, especially after cardiac arrest or shocks. Tell your doctor about this without feeling ashamed.

If the illness reaches a very severe stage and the end of life is being discussed, this question can be calmly talked over with your doctor. According to NHLBI, in an ICD or CRT-D implanted through a vein, the shock function can be turned off without surgery, while pacing continues.