Overview of Implantable Defibrillator
When medical professionals talk about sudden cardiac arrest (SCA) and sudden cardiac death, they mean two different things, even though the terms might sound similar. Sudden cardiac arrest refers to a sudden stop in heart function, which makes a person unresponsive and they stop breathing normally or show signs of blood flow. If it’s not treated immediately, it leads to sudden cardiac death.
Sudden cardiac death, on the other hand, is a sudden natural death from heart-related causes, typically accompanied by a sudden loss of consciousness. When this happens outside a hospital setting, it’s called out-of-hospital cardiac arrest. In most cases, emergency medical service personnel are called to deal with it. In the United States, approximately 356,500 occurrences of out-of-hospital cardiac arrests are reported every year.
Anatomy and Physiology of Implantable Defibrillator
Several studies have demonstrated that a device called an implantable cardioverter-defibrillator (ICD) can greatly reduce the risk of sudden heart-related death. These trials are widely recognized in the medical community and include the Antiarrhythmics versus Implantable Defibrillators (AVID) study, the Cardiac Arrest Study Hamburg (CASH), and the Canadian Implantable Defibrillator Study (CIDS).
ICDs are especially effective in patients who experience specific types of irregular heartbeats, called ventricular tachyarrhythmias, due to heart conditions like prior heart attack or a disease that affects the heart’s structure. The device’s effectiveness isn’t affected by other treatments like beta-blockers or surgical procedures, and it is equally beneficial for patients with heart disease and those with non-heart-related conditions.
Tests show that ICDs are beneficial even before a fatal irregular heartbeat occurs. These devices can be particularly beneficial for patients with heart dysfunction and a type of irregular heartbeat known as non-sustained ventricular tachycardia (VT). These patients are the focus of other critical studies.
One such trial, the Multicenter Automatic Defibrillator Trial (MADIT), compared the performance of ICDs to standard therapy and found a positive outcome with ICDs. Moreover, the Multicenter Unsustained Tachycardia Trial (MUSTT) compared ICD or drug therapy to not using such therapies and found a beneficial effect of the treatments. Finally, the Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT) reaffirmed the benefits of ICDs in patients with heart-related conditions.
Besides these applications, ICDs can also assist in preventing sudden heart-related death in high-risk patients with other heart conditions such as Brugada syndrome, long QT syndrome (LQTS), and RV dysplasia. Even though specific, random trials are unlikely to be conducted on these rare heart conditions, there is evidence showing positive outcomes from ICD use in these patients.
Why do People Need Implantable Defibrillator
The American College of Cardiology/American Heart Rhythm Society (ACC/AHRS) suggests implanting an implantable cardioverter-defibrillator (ICD) under certain circumstances. An ICD is a device that is placed in the chest to regulate the heart rhythm.
First, they advise that ICDs should be used for patients who have survived a heart attack due to hemodynamically unstable sustained ventricular tachycardia (VT) or ventricular fibrillation. Hemodynamically unstable means that the VT episode causes symptoms or signs showing that there isn’t enough blood flow to your body’s organs. This device is also advised for patients who have structural heart disease and experience spontaneous sustained VT.
Additionally, individuals who faint without explanation and have induced dangerous heart rhythms during a heart exploration test (also known as an electrophysiology study or EPS) may need an ICD. Those with ischemic cardiomyopathy (sickness caused when the heart muscle is weak due to inadequate blood supply) whose left ventricles pump out less than 35% of their total capacity, face a high risk of cardiac problems. An ICD is advised, especially if they experienced a myocardial infarction, a fancy term for a heart attack, at least 40 days ago and are classified as New York Heart Association functional class II or III.
Also, people diagnosed with non-ischemic dilated cardiomyopathy (a condition where the heart becomes larger and cannot pump blood effectively) and left-ventricular ejection fraction 35% or less are also recommended to use a device if they are in NYHA functional class II or III.
The second suggestion from the ACC/AHRS includes people who inexplicably faint with significant left ventricle damage, patients suffering from Hypertrophic cardiomyopathy, a disease that thickens the heart muscles, making it harder for the heart to pump blood and specifically those who have a high risk of a sudden cardiac arrest.
There are also certain genetic or inherited disorders that cause dangerous abnormal heart rhythms, requiring an ICD. For instance, those with arrhythmogenic right ventricular dysplasia (a rare type of cardiomyopathy), Brugada syndrome patients, or individuals with Long QT syndrome, especially if they’ve had a fainting spell or ventricular tachycardia.
In some cases, ICD may be considered in patients who have non-ischemic heart disease with low left ventricle function, those with Long-QT syndrome and risk factors for sudden cardiac death, or patients with advanced structural heart disease who’ve experienced a close call with sudden cardiac death. This may also be an option for those with a familial cardiomyopathy associated with sudden death or those with left ventricular noncompaction.
When a Person Should Avoid Implantable Defibrillator
There are certain situations where ICD therapy, which is a type of therapy using a device (called an Implantable Cardioverter Defibrillator) to regulate abnormal heart rhythms, is not recommended. These include:
1. If a person is not expected to have an acceptable quality of life and is not expected to live at least one more year, even if they meet all the other criteria for ICD therapy, it may not be indicated.
2. If a patient experiences constant episodes of specific types of dangerous heart rhythms, known as ventricular tachycardia (VT) or ventricular fibrillation (VF), they should not receive ICD therapy.
3. If a person has significant mental health conditions that could get worse upon the implantation of the device, or that may prevent them from attending necessary follow-up appointments, ICD therapy should be avoided.
4. For patients suffering from severe (NYHA Class IV) drug-resistant congestive heart failure, which leads to a buildup of fluid around the heart causing it to pump less efficiently, ICD therapy is not recommended unless they are suitable candidates for heart transplantation or another type of therapy called CRT-D.
Additionally, ICD therapy is not suggested for patients who faint due to an unknown cause and who don’t have certain heart conditions, namely, heart structural abnormalities and inducible ventricular tachyarrhythmias (fast heart rhythms coming from the lower chambers of the heart). It’s also inadvisable when the irregular heart rhythm can be controlled by surgical or catheter ablation (a procedure that destroys the part of the heart causing erratic rhythms), such as in some types of arrhythmias associated with Wolff-Parkinson-White syndrome (a syndrome where an extra electrical pathway in the heart causes a rapid heartbeat), and types of VT occurring due to issues with specific parts of the heart in the absence of structural heart disease. If someone has dangerous heart rhythms as a result of a completely reversible issue, such as drug use, an electrolyte imbalance, or physical injury, and also doesn’t have underlying heart disease, ICD therapy is not recommended.
Equipment used for Implantable Defibrillator
The implantable cardioverter-defibrillator (ICD) is a small device placed in the chest to monitor and manage the heart’s rhythm. It works much like a tiny computer with a battery. The ICD is made up of different parts or components, each performing specific functions.
The main part, called the ICD generator, manages all of the device’s functions. Its battery life can last for about 4 to 7 years, depending on how much it has to regularize your heartbeat or deliver shocks. The generator’s electronic circuitry, its “brains”, is programmed to analyze your heartbeat and decide when to send therapeutic shocks. It also houses a component called the capacitor, which stores energy to provide those shocks if necessary.
The ICD generator communicates with the heart through special wires called leads, attached to the generator in a part known as the header. This area holds and secures the leads in place. The ICD generator is also sealed inside a protective metal case, called the “can,” similar to the casing used in pacemakers. It protects the ICD’s electronic parts from body fluids and external electrical sources.
The leads used in ICD are like special transmission wires. They’re encased in a protective material and have separated metallic cores. Not only do they carry the signals back and forth between the heart and the generator, but they also help deliver shocks when needed. Each lead has a coiled structure and can have one or two such coils. These leads would have a separate pin for each function – one for sensing and regulating your heartbeat and one or two more for delivering shocks, depending on their design. One end of the lead is inserted close to your heart whereas the other end is connected to the ICD generator.
In other words, this sophisticated device keeps a check on your heart rhythm, initiates corrections if it detects anything abnormal, and even communicates this information back to your doctor! Isn’t it amazing what modern medicine can achieve?
Possible Complications of Implantable Defibrillator
Getting an implantable cardioverter defibrillator (ICD), a device placed under the skin to help control irregular heartbeats, is generally safe. However, like all procedures, there can be some complications, although they are not common. Here are the main ones:
* Infection at the site where the ICD is placed under the skin. This can range from a mild issue, like a fluid-filled lump, up to a more severe infection that makes pus and requires removal of the ICD wires.
* Allergic reaction to medications given during the procedure.
* Bleeding or bruising on your body where they put in the ICD.
* Injury to the vein where the leads (wires) of your ICD are inserted.
* In rare cases, there might be a major blood clot in the upper arms, known as deep vein thrombosis (DVT).
* In very rare cases, there might be life-threatening bleeding around the heart, which may include a buildup of fluid around the heart. If this happens, doctors will have to perform procedures to remove the fluid and may even need surgery.
* Finally, there can be a chance of pneumothorax, a condition where air gets trapped in the space between the lung and chest wall during the ICD placement, which can cause the lung to collapse.
What Else Should I Know About Implantable Defibrillator?
Implantable cardioverter defibrillators (ICDs) are devices that doctors use to help control irregular heart rhythms. There are many functions of an ICD to help it detect and respond to these heart problems.
Sensing in an ICD refers to the device’s ability to recognize and interpret signals from your heart. The goal is for the ICD to respond in the right way to these signals. For example, the device should pick up on a particular type of rapid heartbeat (ventricular fibrillation or VF), but it shouldn’t mistake other types of signals for this condition. This process is mostly achieved through a complex digital algorithm.
Arrhythmia detection is another function of an ICD. When an ICD detects abnormal heart rhythms, it might have different responses:
- Anti-tachycardia pacing (ATP), which uses electrical pulses to restore a normal heart rhythm.
- Cardioversion, which uses low-energy shocks to correct the rhythm.
- Defibrillation, which uses high-energy shocks to reset the heart’s rhythm.
There are different configurations of how ICDs can be set up to detect and respond to these heart rhythms. These configurations often depend on the speed of the abnormal rhythm detected.
SVT/VT discrimination is a way that an ICD differentiates between supraventricular tachycardia (SVT), which originates in the upper chambers of your heart, and ventricular tachycardia (VT), which originates in the lower chambers of your heart. Different algorithms are used to help the ICD make this differentiation, relying on measurements like heart rate variability and the suddenness of heart rate changes to deliver the right treatment.
As for the therapy administered by the ICD, it can vary depending on the specific heart rhythm detected. For example, high-energy shocks could be used to correct a rhythm like ventricular fibrillation. Shocks might be given up to eight times per episode of this rapid heartbeat in some cases. Alternatively, ATP can be used for rhythms like ventricular tachycardia, where the ICD uses pacing to try to stop the rhythm.
Finally, ICDs also have bradycardia pacing capabilities, meaning they can detect and respond to heart rates that are too slow. This function is similar to that of traditional pacemakers and is important for patients on certain medications which can cause slow heart rhythms.