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Defibrillator Implant

A 'defibrillator' refers to an electronic device used for delivering therapeutic electrical pulses to the heart, in order to terminate disruptions in heart rhythms. The current article describes implantable defibrillators that constantly monitor heart rhythms, and deliver appropriate electrical pulses in the event of life-threatening arrhythmia.
Ningthoujam Sandhyarani
Last Updated: Apr 14, 2018
Did You Know?
For each minute that passes without defibrillation, the chances of survival decrease by about 14%.
- British Heart Foundation
The heart is considered the most vital organ since it is responsible for the supply of blood, and hence oxygen and vital nutrients, to every cell of the body. It comprises four chambers: two upper chambers called atria  and two lower chambers called ventricles. The electrical system of the heart causes the atria and ventricles to contract and relax in an alternate and rhythmic manner, giving rise to a heartbeat which in turn leads to the pumping of blood to the organs.
Implantable cardioverter defibrillator
Implantable cardioverter defibrillator
A disruption in the normal electrical activity and rhythms of the heart is termed cardiac arrhythmia. These include bradycardia (decreased heart rate) or tachycardia (increased heart rate). Tachycardia may eventually progress to 'fibrillation', that involves unsynchronized and irregular quivering of cardiac muscles, comprising the upper chambers (atrial fibrillation) or the lower chambers (ventricular fibrillation).
Defibrillation
Sudden Cardiac Arrest (SCA)
The heart stops pumping blood as a result of a sudden disturbance in normal rhythms of the heart.
➥ Fault in the electrical system
Heart Attack
Heart attack
Blood flow to the heart muscles is blocked due to narrowing or clogging of arteries.
➥ Fault in the plumbing system
Although many types of arrhythmia are harmless, certain types may lead to a sudden cardiac arrest or even death, and hence requires immediate medical treatment. Ventricular tachycardia (increased heart rate that originates from the ventricles) and ventricular fibrillation, are two such severe forms of arrhythmia.

In the event of a cardiac arrest, the heart stops pumping blood, and the person loses consciousness within a few seconds. Cessation of blood flow to the brain for more than seven minutes causes irreversible damage, and even death. Hence the need for immediate medical attention and therapeutic intervention, is crucial.

The treatment involves a therapeutic technique called defibrillation, wherein electrical shocks are delivered to the heart with the help of specialized devices called defibrillators. Such high-energy shocks help to depolarize the myocardial cells, and restore their organized electrical activity.
Implantable Cardioverter-defibrillator (ICD)
The need for urgent therapeutic intervention gave birth to the development of publicly accessible defibrillators called Automated External Defibrillators (AED), and implantable defibrillators called implantable cardioverter-defibrillators (ICD). AED is a portable defibrillator that can be placed in public places like airports, train stations etc., where a layperson can provide defibrillator therapy to the affected individual. AED can analyze the electrical activity of the heart, and deliver impulses only if arrhythmia has occurred.

On the other hand, an ICD is a small, matchbox-sized defibrillator that can be implanted in the body (in the chest or abdomen). It can constantly monitor heart rhythms, and deliver the necessary electrical impulse before the disrupted rhythms translate to a cardiac arrest. It is useful for individuals with a high risk of suffering from a life-threatening arrhythmia, as earlier mentioned.
Defibrillator implant
Components
Leading ICD Manufacturers
  • Biotronik
  • Medtronic, Inc.
  • St. Jude Medical, Inc.
  • Guidant LLC (Boston Scientific Corporation)
An ICD consists of a set of wires called 'leads' and a unit called a 'pulse generator', both of which are made from tissue compatible, inert materials.
» Leads are electrode-tipped wires that are placed into the chamber(s) of the heart, and are able to sense the electrical activity of the cardiac muscles, as well as deliver an electric impulse and shock.

» Pulse generator houses the battery, capacitor, a central processing unit, or minicomputer as well, as part of other circuit components.

» Battery serves as the powerhouse of the device. However, it cannot provide the high-energy shock required for defibrillation. Hence the need for a capacitor arises.

» Capacitor is charged through a charging circuit and battery. This capacitor can provide a high-energy shock by releasing all stored energy, instantly.

» Processing unit serves as the control center as well as the data storage center. It can maintain logs of electrical activity as well as the details of arrhythmia episodes and the shocks delivered.
Workflow
Implantable cardioverter defibrillator working
  1. Leads detect the electrical activity in heart muscles, and constantly communicate with the processing unit through a sensing circuit.
  2. The processing unit is programmed to detect the type of arrhythmia, and decide the corresponding treatment that needs to be delivered. In the event of a disturbance in the rhythms, it directs the output control center to deliver electrical impulses through the capacitor.
  3. Antitachycardia pacing (ATP) : The first treatment option, in the event of ventricular tachycardia, is the firing of electrical impulses in rapid succession to the ventricle.
    Sensation: None
  4. Cardioversion : If normal rhythms are not attained through ATP, low-energy shock is delivered in sync with the heartbeat, to prevent it from progressing into ventricular fibrillation.
    Sensation: Mild flutter in the chest
  5. Defibrillation : If cardioversion fails and ventricular fibrillation occurs leading to a very high heart rate, a high-energy shock is delivered to restore a normal rhythm.
    Sensation: Sudden thump or kick in the chest 
  6. Antibradycardia pacing : In case the above therapies lead to heart rhythms lower than what's normal, electrical impulses are delivered to pace the heart and restore normal heartbeats. This serves as a backup treatment for therapy-induced bradycardia, and is also known as antibradycardia backup pacing. It is also useful to treat ventricular bradycardias other than those arising due to the ICD therapy itself.
    Sensation: None 
  7. Once the treatment is delivered and the heart rhythms return to normal, a memory of the episode is maintained in the processing unit. This data can be retrieved by the physician, using a wireless data transfer unit.
Types
Depending on the number of leads, their placement into the cardiac chambers, as well as the therapy offered, there are three types of ICDs available:

» Single chamber: These have a single lead that is placed in the right ventricle, that provide antibradycardia and antitachycardia therapies.

» Dual chamber: They have two leads that are placed in the right atrium and right ventricle. These ICDs can provide antibradycardia pacing through the right atrium and ventricle, as well as provide antitachycardia therapies, cardioversion, and defibrillation through the right ventricle only.

» Biventricular: These ICDs have three leads, of which, one is placed in the right atrium, and the remaining two are placed in the left and right ventricles each. In addition to the functions provided by a dual chamber ICD, these ICDs are also capable of synchronized pacing to the left and right ventricles which is useful for individuals at risk of heart failure.
Who needs an ICD?
An ICD is generally recommended for individuals who are at high risk for ventricular tachycardia and fibrillation. These include individuals who:

» Have experienced at least one episode of ventricular tachycardia, ventricular fibrillation, or sudden cardiac arrest.
» Show symptoms that indicate a potential for ventricular tachycardia.
» Are suffering from diseases that lead to weakening of the heart and reduction in its pumping ability. For example: Dilated cardiomyopathy (enlarged heart) and coronary heart disease (narrowing of coronary arteries).
» Are suffering from genetic diseases that may lead to cardiac arrhythmia. For example: Hypertrophic cardiomyopathy (thickening of heart muscles), Brugada syndrome (genetic mutation that alters the electrical activity of the heart), etc.

However, there is no standard criterion for determining whether a person really needs the device or not. The concerned physician is the most reliable person for determining the need of an ICD.
Defibrillator Implantation
Defibrillator implantation involves a minor surgical procedure that is performed under the use of a local anesthetic or under conscious sedation. The ICD is generally placed to the left side of the chest, under the left collarbone, just beneath the skin. It may also be placed under the right collarbone, and rarely in the lower abdomen. The precise location depends on the age, heart size, chest size, and other medical conditions of the patient.
Surgical Procedure
An incision is made under the left collarbone and a pocket is created under the skin to place the generator. The subclavian vein is located, and a tiny incision is made in this vein. The lead is inserted through this incision and threaded to the left ventricle of the heart, under fluoroscopic or X-ray guidance. The tip of the lead is then attached to the heart muscle. In case of a dual chamber ICD, another lead is inserted and placed in the left atrium in a similar manner. The lead wires may be stitched to the surrounding tissues in order to fix their position to avoid complications that may arise due to their dislocation.

Other ends of the leads are connected to the generator, and it is placed in the pocket. The device is then tested by inducing arrhythmia and evaluating the ICD response. The wound is then stitched close. The vital signs, namely heartbeats, blood pressure, respiration rate, and blood oxygen levels are constantly monitored throughout the procedure.
Post-surgery Checks
The procedure usually lasts for 2-4 hours and is followed by imaging tests to confirm the position of the generator and leads. The patient is kept under observation for about 48 hours to examine any unusual side effects, if any.

» Followed by the implantation procedure and recovery from the surgery, the device is programmed and customized according to the precise medical condition of the individual. This is achieved through a programming unit and wireless data transfer unit.
» Regular follow-up and routine checks are advised in order to ensure efficient functioning of the device, as well as to assess complications (if any). The first checkup is most likely to be scheduled within 3-6 weeks after surgery.
» During one of the follow-ups, the individual may even be asked to exercise, so as to record the increase in heart rate during exercise, and program the device to avoid the delivery of shocks during such normal instances of higher heart rate.
» Battery replacement is generally advised after a period of 5-7 years, whereas the time period for lead replacement varies with each individual case.
» Generally, the patient is given an ID card or medical identification bracelet indicating the presence of an implanted device, as well as the device's details and contact details during an emergency. The patients are advised to carry this card at all times.
Post-implantation Lifestyle
An ICD implant necessitates certain lifestyle modifications and precautionary measures to avoid complications. Some of these have been enlisted below:

» Avoid lifting heavy objects and extending the involved arm for at least 6-8 weeks after the implant.
» Do not indulge in contact sports and activities that might put physical pressure on the region where the device is located, or on the respective arm.
» Exercise regularly but avoid repetitive and rapid movements of the upper body.
» Avoid close and prolonged contact with devices like stereo speakers, audio headsets, metal detectors, as well as powerful magnets. These may interrupt electrical impulse conduction, which may lead to the delivery of untimely shocks.
» Avoid the use of tight clothing, belts, and heating pads around the area of the implant.
» Although the use of cell phones is considered safe, avoid placing them directly above the device. In addition, use the ear on the side opposite to that of the implant location while communicating through a cell phone.
» Consult the concerned cardiologist and physician, before undergoing medical procedures and tests that include the use of magnetic and electric impulses. Examples include magnetic resonance imaging (MRI), radiation therapy, electrocautery, etc.
Risks
Like any other medical technology, defibrillator implants are associated with certain negative outcomes and risks as well. Some of these are described below:

» Complications related to the surgery are reported in about 1-2% of patients. Some of the reported cases include infections and bleeding at the incision site, mild chest pain, and shortness of breath. In rare cases, an individual may succumb to faint spells. It is essential that the symptoms be communicated to the concerned doctor immediately to avoid worsening the condition.

» Internal infections on the generator or leads as a result of normal skin microflora as well as nosocomial infections due to methicillin-resistant Staphylococcus aureus (MRSA), have also been observed.

» The psychological effects of defibrillation shocks is yet to be understood completely. It has been observed that although the longevity of individuals has increased, the quality of life gets affected due to the fear of shock treatment, especially in individuals who have experienced an episode of shock treatment from the ICD.

» Rare instances of lead fractures and lead failures lead to heart rhythms being misread, and unnecessary shock delivery.

» It has also been observed that individuals with ICDs have an increased risk for heart failure. However, it has not been evaluated whether such an association exists solely due to the use of ICD or because heart failure is common in conditions that demand the use of an ICD.
Implantable defibrillators have saved the lives of many heart patients, and decreased the mortality rate due to sudden cardiac arrests. With the advent of technology, newer and more sophisticated devices that involve subcutaneous leads and even wireless electrodes, are available. However, this technology also presents a set of risks and complications. It is essential to discuss and weigh the pros and cons with the concerned expert and then decide whether to opt for such a therapy or not.
Disclaimer: This HealthHearty article is for informative purposes only, and should not be used as a substitute for professional medical advice.
Automated External Defibrillator