When a person goes into a state of cardiac arrest, the Implantable Cardioverter-Defibrillators (ICDs) detect the abnormal heart rate and send signals through the electrodes to the ICD which sends electric shock automatically and internally to the heart to start pumping normally again.

Implantable Cardioverter-Defibrillators (ICDs) is implanted under the collarbone of the patient and consists of the following:

• A pulse generator, which is almost the size of a big pocket watch. It contains electrical circuits and batteries. This electrical circuit helps in reading the electrical signals of the patient's heart.
• Electrodes or leads, which go through the veins and connect the heart to the Implantable Cardioverter-Defibrillators (ICDs). This may contain 1, 2 or 3 leads.
• Many ICDs consists of an in-built pacemaker. This is important as it identifies the heartbeat either too fast or too slow and even after the electrical shock received from the ICD, to pace up the heart rate to normal.
• There is a special ICD known as subcutaneous ICD, which has an electrode in the tissue to the left side of the breastbone. Such an ICD does not have a pacemaker.

According to the issues in the heart rate, an ICD can be set up for the following therapies as well:

• Low-energy pacing therapy – When the ICD detects and responds to the mild interruptions in the heart, either the patient feels nothing or a slight painless fluttering sensation.
• Cardioversion therapy – A patient might have a thumping sensation felt in the heart when the heartbeat gets dangerously abnormal and in order to bring back the normal heartbeat, an ICD may give a strong electrical shock of high energy.
• Defibrillation therapy – This is delivered in order to prevent a risk of cardiac arrest. In this therapy, the heartbeat gets highly irregular and in order to get it back to normal, the ICD delivers very high energy shock to the heart to start pumping normally again. A patient might feel pain but only during the delivery of the shock, which lasts for only a second.

ICDS are usually advised to the people with the following problems:

• Weakened heart muscles
• Personal or family history of coronary artery disease.
• Cardiomyopathy i.e. abnormally enlarged heart.
• Hypertrophic cardiomyopathy i.e. thickening of the heart muscles.
• Tachycardia or ventricular arrhythmia.
• Congenital heart disorder.
• Long QT syndrome which causes ventricular fibrillation and then death, without showing any signs or symptoms.
• Arrhythmogenic right ventricular dysplasia
• Brugada syndrome
• One or more episodes of abnormal heart rate.
• The inefficiency of the heart to pump oxygen and blood to the rest of the body.

General risks related to any surgery are as follows:

• Infections
• Formation of blood clots which may lead to the lungs
• Allergic reactions to the medicines, used during the surgery e.g. redness, rashes, itching, etc.
• Post-anesthesia problems e.g. nausea, vomiting, headaches, discomfort, confusion, difficulty in breathing normally.
• Heart attack or stroke

Risks associated with ICDs are as follows:

• Bruising, bleeding or swelling on the site of implantation of the ICDs.
• Infections at the surgical site
• Bleeding around the heart which can be fatal
• Damage to the veins which had ICD wires
• Leakage of blood from the heart valves due to the placement of the ICD.
• Injury caused in the lungs or the heart

The doctor discusses the details of the procedure, including the risks and the benefits, with the patient. The doctor may advise some of the following tests to the patient before the surgery:

• ECG or Electrocardiography
• Echocardiography
• Holter monitoring
• Event recorder
• Electrophysiology study

The following are the steps for the preparation before the surgery:

• The doctor takes a complete medical history and physical examination test before performing the surgical procedure. The patient may be asked about the age and weight of the patient, any past surgeries, allergies to any medicines, previous personal history and family history of heart attacks. In the physical examination, the doctor examines the patient very carefully for any other concerning signs and symptoms.
• If a patient is diabetic, the patient is advised to ask the doctor if he/she should continue taking insulin before the procedure or not. The patient is also asked to inform the doctor about any past allergies or surgeries, if any.
• The patient is advised to quit smoking, avoid alcohol, avoid drinking or eating anything after midnight or one night before the bypass surgery.
• The patient is advised to empty the urinary bladder and bowel, before the test.
• The patient has to remove or avoid any jewelry, eyeglasses, hairpins, electronic gadgets or any metal objects and is asked to change into a hospital gown, during the procedure.

During the procedure:

Usually, the surgery is done under local anesthesia and the patient is given some sedative medicines to calm down and relax. One or more electrodes are attached under the collarbone and are guided to the patient’s heart with various X-ray images. An electric shock generator (ICD) is placed under the collarbone of the patient from one end and to the lower chambers of the heart (ventricles) from the other.

After the procedure:

After the procedure of implanting ICD, the doctor gives general anesthesia to the patient to make him/her unconscious. This is done, in order to check the proper functioning of the heart by giving shock waves to the patient’s heart.

The surgery takes around 2 to 3 hours to complete. The hospitalization of the patient is usually for one to two days. Before getting discharged, the doctors again check the working of the ICD to ensure its proper working. Patients can return to normal activities very soon after the surgery, after approximately 4 to 6 weeks to have a full recovery.

The doctor may advise some of the following points after the ICD implantation:

• Avoid strenuous physical activity or exercise
• Avoid lifting heavy objects for at least a month
• Avoid playing contact sports
• Avoid vigorous shoulder movements e.g. while swimming, tennis, golf, bowling or bicycling.
• Avoid smoking

The doctor may also suggest taking some painkillers, e.g. ibuprofen or Ultracet (a combination of paracetamol and tramadol), to relieve pain from the surgical site. 

After the ICD implanting procedure, frequent doctor visits are required in order to monitor the working of ICD. Some of the activities tracked during these visits include

• Sensing the heart rate properly.
• Total electric shocks delivered.
• Battery-life of the ICD. Usually, the battery life is approximately 7 years. But frequent visits to the doctor are necessary to check if the battery needs to be changed or not.

ICD is a very useful and effective device which helps in controlling and correcting the abnormal heartbeats in the patient. It is programmed to perform many functions which are as mentioned:

• Treating a very slow heart rate- This condition is known as bradycardia. ICD helps in sensing the slow heartbeat and start functioning like a pacemaker. This stimulates the heart to pump and beat normally.
• Treating a very fast heartbeat- This condition is known as tachycardia. ICD helps in sensing a fast heartbeat and start functioning like a pacemaker. This stimulates the heart to pump and beat normally. This prevents the need for defibrillation and cardioversion.
• Recording heart activity – An ICD helps in recording the heart rate and electrical activity, which assists the doctor in detecting abnormal heartbeats.
• Biventricular pacing – There is a special ICD combined with a biventricular pacemaker, which helps in normal pumping of the blood from both the lower chambers of the heart. This is advised for the patients with heart failure wherein, the electrical system of the heart does not function normally.

There are some special long-term precautions advised by the doctor to the patient, related to electronic equipments. Rarely, electrical appliances interfere with the working of an ICD. However, the patient should keep the following points in check:

• Cellphones – The patient is advised not to keep the cellphone near or over the surgical site. This is because the ICD can take wrong signals from the cellphones considering them as heart rate and cause sudden tiredness to the patient.
• Security systems – In case of metal detectors or hand metal detectors, patient must ask the security staff to avoid holding the device close to the site where an ICD is placed and to be on a safer side the patient should carry an ID or doctor's prescription stating the implantation of an ICD.
• Medical equipment – It is always important to inform the doctor about an ICD installation before going for any other medical procedure like MRI, shock wave lithotripsy and therapeutic radiations for treatment of cancer, which use electromagnetic energy. Electrocautery procedure may also cause interference in the working of the ICD.
• Power generating machines – The patient is advised to stay away at least 2 feet, from power generating devices like motor generator, transformers or welding machines. If the patient is working in such an environment then the doctor might want to check if the working of the ICD is affected or not.
• Driving – The patient with an ICD implanted, should avoid driving. If the heartbeat goes abnormal while driving, the ICD will start delivering shock waves to the heart, which may be very dangerous while driving.