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Implantable Cardioverter-Defibrillator Indications

Implantable Cardioverter-Defibrillator Indications

While prevention of sudden cardiac arrest is challenging, there are available options to help patients deal with this when it occurs. Indications and guidelines for device-based therapy of cardiac arrest help patients who require implantation of ICDs due to cardiac rhythm abnormalities. 

What Is a Cardioverter Defibrillator?

An implantable cardioverter-defibrillator, called an ICD, is a battery-operated system that monitors the heart rate, and a doctor implants it under the skin. An ICD is linked to a patient’s heart by thin wires. If the heart is beating uncontrollably and way too quickly, the ICD can administer an electrical shock to restore a natural heart rhythm if it finds an irregular heartbeat.

Patients who suffer from sustained ventricular tachycardia or ventricular fibrillation (VF) have found that an ICD is very efficient in preventing sudden cardiac death. They may play a role in preventing cardiac arrest in high-risk patients who have not had but face the risk of life-threatening ventricular arrhythmia, according to research.

Before a patient is considered a candidate for an implantable cardioverter-defibrillator (ICD), the American Heart Association advises that the examined arrhythmia must be life-threatening and that physicians have excluded remedial causes of the arrhythmia, including:

  • Acute myocardial infarction (AMI), a form of heart attack that occurs unexpectedly 
  • Ischemia of the heart muscle (insufficient flow of blood to the heart muscle)
  • Drug toxicity and electrolyte imbalances

As various patients are unaware of their underlying heart condition, such as a hereditary predisposition to sudden cardiac death or a high risk of heart failure – and due to the fact that an ICD is often used to avoid sudden cardiac death, they may be unaware of the advantages and drawbacks of implanting one of these devices. If you are one of those patients confused about an ICD, you can find helpful information and advice here.

What Is the Purpose of a Cardioverter-Defibrillator?

In patients with established, sustained VF or ventricular tachycardia (VT), an ICD can help prevent sudden death. Implantable cardioverter-defibrillators have been identified in research to help avoid sudden cardiac arrest in high-risk patients that have not had ventricular arrhythmias but are at risk of experiencing it.

Purpose of a Cardioverter-Defibrillator

Therapy with implantable defibrillators from the latest generation may have a dual purpose, including the ability to act as pacemakers. If the heart rhythm is found to be too slow, the pacemaker function induces the heart to beat at a natural rate. Note that a pacemaker is different from a defibrillator.

How Do Implantable Cardioverter-Defibrillators Operate?

Electric impulses regulate the heart’s rhythm and rate. If this electrical system malfunctions, it can result in a dangerous arrhythmia, and the heart is unable to pump blood in the normal manner.

Doctors may need to use an electrified pad to provide a shock to a patient’s heart if they have gone into cardiac arrest. One of these devices does the same thing as an AED, except it is automatic and located within the patient’s body.

Wires and electrodes attach the ICD to the heart. It tracks the heartbeat and can deliver one of several types of shocks if it senses an abnormal rhythm.

Low-energy pacing is a form of pacing therapy. These are generally for slower VT and are mild. They do not cause pain, but they can feel like a flutter in your body.

Cardioversion is a form of therapy that requires the use of electricity, which can make a patient feel as if someone is kicking their chest.

Defibrillation therapy is a form of defibrillation used to treat severe heart rhythm issues with a powerful shock. You can experience extreme pain if your ICD starts defibrillation therapy.

With only a single shock, the ICD restores a natural heartbeat. In a 24-hour cycle, you could get two or more shocks. If this happens to you, you should seek emergency medical treatment.

Why Do Patients Need Implantable Cardioverter Defibrillators?

Now that you know the specific details of what an ICD is, why would patients need to consider an ICD implant? A healthcare provider may recommend an implantable cardioverter-defibrillator if the patient is at risk of experiencing life-threatening ventricular arrhythmias due to:

  • Previously having ventricular arrhythmias
  • Experiencing a heart attack or heart failure
  • Surviving sudden cardiac arrest
  • A severe heart disease or condition that may result in sudden cardiac arrest. 
  • Long QT syndrome
  • Brugada syndrome

Implantable Cardioverter Defibrillator Criteria

What are the criteria for an ICD implant? The power of the heart to beat continuously for a person’s entire life is a product of muscles and an incredible electric system. However, the heart sometimes goes into an erratic rhythm. Ventricular fibrillation and ventricular tachycardia are two of the most dangerous. An electric shock is one powerful method to interrupt these unstable heart rates and restore a natural heart rhythm.

Due to advanced technology, implantable cardioverter defibrillators are now small enough to fit into a compact area of muscle underneath the collarbone. An implantable cardioverter-defibrillator (ICD) continuously tracks the heartbeat and provides the necessary treatment if it is required. 

Approximately 100,000 American citizens receive an ICD per annum. Determining which patients receive one is still as much an art as it is a science, as the price of these devices is also a factor to consider. According to two reports, 13% of people who get an ICD implant do not require one; this occurs when considering the specific requirements set out in various professional guides. 

What are the criteria for an ICD implant

The criteria for implantable cardioverter-defibrillator therapy include:

  1. Surviving sudden cardiac arrest, which was caused by ventricular fibrillation.
  2. Structural heart diseases, ventricular fibrillation, or ventricular tachycardia that results in fainting.
  3. Surviving a heart attack with an ejection fraction of 35% or lower
  4. Ejection fraction and dilated cardiomyopathy of 35% or less
  5. Previous encounters with ventricular tachycardia
  6. Unexpected fainting dilated cardiomyopathy, and reduced left ventricular fibrillation
  7. One or more high-risk factors associated with sudden cardiac arrest
  8. Hypertrophic cardiomyopathy
  9. Heart rhythm issues
  10. Giant cell myocarditis, Chagas disease, or cardiac sarcoidosis

What about the criteria under which you should not consider ICD implantation?An automatic defibrillator implantation trial shows that ICD therapy in patients has been proven harmful or ineffective when:

  1. They have a life expectancy of one year or less
  2. Continuous experiences of ventricular tachycardia or fibrillation
  3. Psychiatric diseases – the device may interfere with the current medical care
  4. Undetermined causes of fainting
  5. Ventricular arrhythmias that one can cure by catheter ablation or other surgical procedures
  6. Heart conditions that result from a reversible cause such as medication 

Implantable Cardioverter Defibrillator Guidelines

For high-risk patients, cardiac resynchronization therapy (CRT) and implantable cardioverter-defibrillator therapy have become principal factors of clinical cardiology practice, backed by compelling clinical trial results. However, circumstances of clarity are offset by substantial confusion regarding reimbursement and cardiac resynchronization therapy, and implantation conditions. 

Therefore, what are the guidelines regarding ICD therapy in patients and ICD devices?

Guidelines Recommendations Basis

Medical practice recommendations are the product of a joint effort between physicians, patients, and scientists to direct patient treatment using the most up-to-date research. While expert consensus has existed for decades, the current age of clinical recommendations is based on the principle of evidence-based medicine, which was first implemented in the 1980s. Evidence-based medicine, which has its’ origins in the fields of clinical epidemiology and public health, blends the best research with the best clinical practice. The quality of evidence is ranked by class: Class I is the strongest recommendation, Class II needs more physician consideration, and Class III discourages the use of the therapy under consideration. From A, which indicates the highest certainty, to C, which indicates the lowest certainty, a complimentary grading scale considers the relative gain versus risk as a declaration of treatment impact certainty. Recommendations provide a detailed review of the available information for practicing healthcare providers, including areas of disagreement and discrepancies in research protocols and patient divisions. Physician and hospital success measurements would be adrift without such criteria, and patients would lack an objective footprint to determine the fair quality of treatment.

While medical practice guidelines are a valuable tool for doctors making medical decisions, they can be problematic if they are interpreted too strictly. Patients may actually not fit under the guidelines, or they may do so but comorbid risk and patient ideals prevent them from receiving specific treatment. Physicians must rely on available clinical evidence and their best efforts in all cases to provide treatment that is more likely to help than damage. Physicians must also consider whether or not their treatment would be reimbursed. Certain standards do not always align with guidelines, are more stringent in general, and are not revised as often in response to new clinical trial results. Doctors must eventually rely on their best judgment when faced with disputes between guidelines and patients. The healthcare provider should make a final decision on the treatment of a specific patient and should consider all the concerns of the patient. 

ICD Therapy Clinical Considerations

ICD Therapy Secondary Prevention

After the conclusion of the Amiodarone Versus Implantable Defibrillator trial, which was sponsored by the National Institutes of Health, the secondary prevention guidelines for implanting ICDs in patients with hemodynamically relevant VT or survival from sudden cardiac arrest were identified nearly two decades ago. The AVID trial enrolled cardiac arrest survivors, patients with syncopal VT, and patients with symptomatic VT who had a left ventricular ejection fraction of less than 40%. Patients treated with an ICD device had a substantially lower all-cause mortality rate than those treated with an anti-arrhythmic drug, specifically called amiodarone. Two other randomized trials, the Canadian Implantable Defibrillator Study (CIDS) and the Cardiac Arrest Study Hamburg backed up these results. While neither study achieved statistical significance, both showed a strong trend toward ICD-related mortality reduction. For patients who meet the AVID admission requirements and have ruled out reversible causes, the American College of Cardiology or the American Heart Association (ACC or AHA) recommendations encourage a Class I recommendation. 

ICD Therapy Primary Prevention

The Multicenter Automatic Defibrillator Implantation Trial II (MADIT II) study, published in 2002 by Moss and colleagues, was the first significant, randomized primary prevention trial assessing the utility of primary prevention implantable cardioverter-defibrillator therapy. The researchers enrolled 1232 patients who had had a myocardial infarction (MI) at least 30 days prior to enrollment and had an LVEF of less than 30%. ICDs decreased all-cause mortality by 31% after 21 months. As a result, MADIT II patients were given an NYHA Class IIa indication in the updated ACC or American Heart Association or North American Society for Pacing and Electrophysiology 2002 guideline update for the implantation of cardiac pacemakers and anti-arrhythmia devices. The authors of the guideline considered that more risk stratification could refine ICD gain in particular subpopulations, which contributed to the Class IIa recommendation.

The relationship between the ICD gain and QRS width was investigated by CMS in response to the request for extended ICD reimbursement. ICD-related survival with a QRS of less than 120 milliseconds displayed a nonsignificant higher pattern, which was discovered after the fact using a subset study. Based on these statements, the CMS states that the evidence is not currently sufficient to conclude that implantable defibrillator therapy is appropriate and essential for the entire population of patients with previous MI and left ventricular dysfunction who meet the MADIT II eligibility information. 

The SCD-HeFT research, which was sponsored by the National Institutes of Health, enrolled 2521 patients with nonischemic or ischemic NYHA class II or III heart failure and an LVEF of less than 35%. The patients were randomly assigned to receive either amiodarone or a placebo drug or ICD therapy. When compared to the placebo, amiodarone had no impact on all-cause mortality, while ICD therapy substantially decreased all-cause mortality over a 45.5-month median follow-up. The effect of ICD therapy was comparable if the heart failure was nonischemic or ischemic. When the NYHA class was taken into account, a different visual emerged. The ICD significantly reduced mortality in NYHA class II patients, who accounted for 70% of the SCD-HeFT patients enlisted, while there was no clear advantage of ICD therapy in the remaining 30% of NYHA class III patients. This result was both surprising and unexpected, raising concerns about how SCD-HeFT should be interpreted for patients who are sicker. The HR for ICD versus the placebo is better applicable to the entire patient population enrolled, according to the clinical trialist approach. Nonetheless, further investigation into this finding led to a study using the Seattle Heart Failure Model (SHFM), which assesses individual risk based on expected annual mortality and death mode. The SHFM was developed and validated in a broad population of heart failure patients without ICDs, and it uses a variety of routine clinical variables to predict annual mortality, such as NYHA class, LVEF, and drug doses. At estimated annual mortality of 15% to 20%, the risk of death from progressive heart failure starts to outweigh the risk of sudden arrhythmic death, resulting in a lower mortality gain from treatment aimed at preventing sudden arrhythmic death in sicker patients.

Understanding the ICD Registry’s complementary position and limitations helps to avoid overinterpreting registry data analysis, which can lead to implications about physician practice based on assumptions and uncertainty between data elements that represent payment requirements and guideline-based medical practice. The two are not always synonymous. When it comes to primary preventive ICD reimbursement, this is an excellent example. The CMS NCD for primary prevention ICD therapy refuses reimbursement to four patient groups that do not always follow the guidelines. 

The four categories include:

  1. Implanting implantable cardioverter-defibrillators within 40 days of acute MI
  2. The time frame from the initial diagnosis of heart failure
  3. Implantable defibrillators in patients within 90 days of receiving coronary artery bypass surgery
  4. NYHA class IV heart failure

What Are the Indications for Defibrillation?

The clinical use of an electrical activity to depolarize the myocardium so that synchronized contractions can occur is known as defibrillation. Defibrillation is a term used to describe an attempt to stop an abnormal heart rhythm.

VF and pulseless VT are both indications for defibrillation. Defibrillation is not recommended for asystole or pulseless electrical operation, and it is also not recommended for sinus rhythm, a conscious patient with a pulse, or when the operator or for other patients at high risk. Electrical energy can stop an irregular rhythm, but if delivered incorrectly, it can also trigger VF. This can occur if the electrical shock is applied during the cardiac electrical activity’s relative refractory period. 

Check the patient and heart rhythm before defibrillation to ensure that a shock is genuinely required. New defibrillator technology can filter compression or movement artifacts, allowing the underlying rhythm to be seen. 

Indications for Defibrillation


Who Needs an Implantable Cardioverter Defibrillator?

If you have had a history of VT, survived sudden cardiac arrest, or fainted from ventricular arrhythmia, you are a candidate for one of these devices. If you have any of the following conditions, you can benefit from an ICD:

  • Your heart has been compromised by a history of coronary artery disease, heart attack, and heart failure.
  • A cardiac disease is characterized by irregular heart muscles, including thickening or enlargement.
  • Congenital heart defects cause the heart to beat irregularly. Long QT syndrome, for example, can result in fibrillation and death in patients who have no signs or symptoms of heart failure.

Several additional unusual disorders can influence the heart’s rhythm.

When Should an ICD be Implanted?

Arrhythmias are a group of conditions that cause an irregular heartbeat. VT is a form of arrhythmia in which the heart beats too quickly and VF occurs when the heart muscle can’t pump enough blood due to an irregular heartbeat.

An ICD can detect and stop a risky, irregular heartbeat in either case. It accomplishes this by jolting the heart back into a regular rhythm and beat with an electrical shock. Implantable cardioverter-defibrillator therapy helps to reduce the chances of cardiac arrest or a stopped heart, which can be fatal.

ICD Implantation – Getting an Implantable Cardioverter-Defibrillator

An ICD is inserted under the skin and does not require a great deal of surgery. The procedure only takes a few hours to complete. The majority of individuals who receive ICDs are awake during the treatment. In these cases, the surgeon uses a sedative and numbing drug to help you relax. You may be unconscious if you are given general anesthesia.

X-ray scans are used by the doctor to direct wires into the veins and attach them to the heart during the operation. The device located under the skin, usually below the patient’s collarbone, receives the other ends of the wires.

Finally, the defibrillator is programmed for the particular arrhythmia the patient is diagnosed with by the doctor.

After ICD Implantation

You probably have to stay in the hospital for a few days after the device is installed and functioning so the healthcare provider can continue testing until you get discharged. Although you may experience pain around the incision, the doctor may prescribe drug therapy with implantable defibrillator surgery.

You cannot drive for approximately seven days after the treatment, so make sure you have someone to take you home after the surgery. You need a few weeks to heal properly. Your doctor should give you detailed guides, but for at least a month, you have to avoid the gym and sporting events.

How Long Can a Person Live with an Implanted Defibrillator

If you have an implantable cardioverter-defibrillator, you are most probably going to have it for the rest of your life. As a consequence, it is essential to cater routine check-ups and testing every three months to ensure that the device is working properly. You should get back to living a normal life; it does not impact your lifespan in any negative manner. 

Machines or factors that may affect the automatic defibrillator implantation device, such as building screening machines or transcutaneous electrical nerve stimulation (TENS) devices, must be avoided. Powerful magnetic fields may cause the device to not operate properly, which is why you want to steer clear of them. 

Your doctor can give you all the necessary tips regarding what to do and what not to do with the implantation device.


When getting an implantable cardioverter-defibrillator, there are many factors to consider. You want to ensure that you take all the necessary guidelines and implications into consideration before you get an implantable cardioverter-defibrillator, ICD. From the New York Heart Association, AHA, Canadian Implantable Defibrillator Study, American College of Cardiology, and Cardiac Arrest Study Hamburg, there is a wide variety of information and training available on the functions of these medical devices. 

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