Cardiology

Implantable cardioverter-defibrillators: Primary and Secondary Prevention of Sudden Cardiac Death

I. Implantable Cardioverter-Defibrillators: What every physician should know.

The implantable cardioverter defibrillator known as ICD is an implantable device similar to a pacemaker that has leads, usually transvenous, that connect to the right ventricle. Often these devices have sophisticated pacemaker capability and have additional leads in other cardiac chambers, such as the right atrium and coronary sinus.

ICDs are offered to individuals with a history of dangerous sustained ventricular arrhythmias known as "secondary prevention" ICDs or with medical conditions that place them at increased risk for such arrhythmias and the associated risk of sudden cardiac arrest (SCA) known as "primary prevention" ICDs. The ICD was inspired by Dr. Michel Mirowski after his mentor died suddenly after having a history of sustained ventricular arrhythmias.

The first human implant was in 1980 and the first approved implantable defibrillator was in 1985. Contemporary ICDs are often implanted in the outpatient setting and involve a subcutaneous pocket for the generator and transvenous placement of the ICD lead in the right ventricle.

II. Diagnostic Confirmation: Are you sure your patient has risk for Sudden Cardiac Arrest?

Does your patient have or need an ICD?

Patients that have or may need an ICD usually have an underlying cardiac diagnosis. Survivors of a sudden cardiac arrest event are usually offered an ICD if the event was not deemed reversible or treatable.

The most common associated comorbidities associated with an ICD are coronary artery disease and systolic heart failure. For those at risk for sudden cardiac arrest with coronary artery disease (CAD) or history of myocardial infarction, their left ventricular systolic ejection fraction is usually less than or equal to 35%.

In those with congestive heart failure (CHF), the ejection fraction is usually 35% or less. Other inherited and acquired cardiac diagnosis that are associated with an increased risk of SCA, making a need for an ICD, include hypertrophic cardiomyopathy, channelopathies such as long Q–T and Brugada, and more rare conditions such as arrhythmogenic right ventricular dysplasia, cardiac sarcoid, and catecholaminergic polymorphic ventricular tachycardia (VT).

A. History Part I: Pattern Recognition:

The typical patient with an ICD has a diagnosis of CHF and/or coronary artery disease. If the patient has survived a cardiac arrest that was not during an acute MI, then ICDs are usually indicated.

Alternatively, patients may also have a very concerning family history with a relative dying suddenly at young ages or a family member with an ICDs. Patients that may be considered for an ICD usually have a history of systolic CHF and/or coronary artery disease. Less commonly, they may have a diagnosis or family history that places them at increased risk for dangerous sustained ventricular arrhythmias and SCA.

B. History Part 2: Prevalence:

The chances of surviving a cardiac arrest in the out-of- hospital setting are very low. Even with the fastest early defibrillation programs, the survival rate is estimated at 4.6% to 8% for an out-of-hospital cardiac arrest.

The rationale behind SCA prevention is to identify individuals at the highest risk for cardiac arrest and offer ICD for sudden death prevention. To benefit from ICD placement, individuals must have an anticipated survival time of 1 year and a reasonable functional capacity.

Historically those at highest risk for SCA are those that have been fortunate enough to survive a cardiac arrest. However, with the data of large randomized controlled trials, we now know that those at highest risk may be identified prior to such an event by assessment of heart function mainly by evaluation of left ventricular ejection fraction (LVEF) and presence of CAD and history of myocardial infarction (MI).

C. History Part 3: Competing diagnoses that can mimic dangerous Ventricular Arrhythmias.

Patients who are at risk for dangerous sustained ventricular arrhythmias are eligible for ICDs. Usually these patients have LV systolic CHF and/or CAD.

If they have a history of sustained ventricular arrhythmias, then they meet the criteria for an ICD as a secondary indication. An exception to this would be the less common diagnosis of benign ventricular tachycardia.

This less common form of ventricular tachycardia usually is hemodynamically stable and occurs in structurally normal hearts without a personal or family history of cardiac arrest. Other exceptions would include documented sustained ventricular arrhythmias that are due to a treatable or reversible cause, such as acute myocardial infarction or torsades de pointes in the presence of Q–T prolonging medication.

In the case of individuals with CHF, if the left ventricular function improves with optimal medical therapy, then they may no longer be at risk for sudden cardiac arrest and may be no longer eligible for an ICD.

D. Physical Examination Findings.

Findings on physical exam may include evidence of chronic heart failure such as jugular venous distention (JVD) and third heart sound. Alternatively these patients may have very compensated heart failure and may have a very normal exam.

Patients with inherited disorders placing them at risk for sudden cardiac arrest may have a completely normal exam. Those with exam findings suggestive of severe chronic CHF with very little functional capacity considered NYHA functional class IV or who have an anticipated survival of 1 year or less will not likely benefit from ICD placement and should not be considered for ICD placement.

E. What diagnostic tests should be performed?

The most important evaluation in assessing risk for sudden cardiac arrest is the left ventricular ejection fraction (LVEF). This evaluation is usually done by a noninvasive method of transthoracic echocardiogram.

Nuclear perfusion imaging and cardiac magnetic resonance imaging (MRI) are alternatives in assessing LVEF noninvasively. Alternatively, LVEF can be assessed invasively by cardiac catheterization and left ventriculography.

The other very important test is the electrocardiogram (ECG). In the case of CHF or CAD, assessment of coronary anatomy is also indicated either by stress test imaging or cardiac catheterization. In some cases or situations, special imaging such as cardiac MRI is indicated to evaluate for less common pathology, such as fat infiltration of the right ventricular myocardium as in the case of arrhythmogenic right ventricular dysplasia.

1. What laboratory studies (if any) should be ordered to help establish the diagnosis? How should the results be interpreted?

Basic laboratory testing should be done to evaluate for comorbidities rather than establishing the primary diagnosis. Recommended laboratory tests include a basic metabolic panel to evaluate for electrolyte abnormalities and renal function; a complete blood count with platelets to evaluate for anemia and bleeding risks for a potential procedure; and prothrombin time (PT)/partial thromboplastin time (PTT) to further exclude bleeding risks for potential procedures.

2. What imaging studies (if any) should be ordered to help establish the diagnosis? How should the results be interpreted?

Patients with a history of cardiac arrest or at risk for cardiac arrest should have an assessment of heart function including valvular function. This is usually done by transthoracic echocardiography.

In the case of CHF, patients should have an evaluation for CAD. The finding of coronary artery disease will help plan treatment, including revascularization.

Assessment for coronary artery disease in this situation is usually done by cardiac catheterization. In individuals where risk of invasive cardiac catheterization is not warranted, then noninvasive stress testing with imaging may be adequate.

III. Management.

There are patients with a history of dangerous sustained ventricular tachyarrhythmias or sudden cardiac arrest who may be considered for an ICD for secondary prevention of sudden cardiac death, and there are patients who are at increased risk for dangerous sustained ventricular tachyarrhythmias or sudden cardiac arrest who may be considered for an ICD for primary prevention of sudden cardiac arrest.

Secondary prevention cases include:

  1. Survivors of sudden cardiac arrest

  2. Individuals with syncope from presumed sustained ventricular arrhythmias

  3. Those with a history of sustained ventricular arrhythmias

ICDs for secondary prevention of SCA have been shown to reduce the risk of death by 20% to 30% in this patient population. These three situations are considered class I indications for ICDs by recent 2008 ACC/AHA/HRS Guidelines for Device Based Therapy of Cardiac Rhythm Abnormalities.

Other indications for secondary prevention ICDs that have less evidence for the recommendations, considered class II by current guidelines, include:

  1. Unexplained syncope with significant LV dysfunction with a nonischemic cardiomyopathy

  2. Syncope or VT while receiving beta-blockers with long Q–T syndrome

  3. Sustained VT with normal or near-normal ventricular function

  4. Syncope or sustained VT with Brugada syndrome

  5. Syncope or sustained VT with catecholaminergic polymorphic VT receiving beta-blockers

  6. Syncope with advanced structural heart disease with investigations failing to find the cause of syncope.

Primary prevention cases include:

  1. Individuals with history of myocardial infarction (MI) and EF of less than 35% on optimal medical therapy (OMT). These patients should be NYHA functional class II or III, be ≥40 days from their last MI and >3 months from revascularization to be considered for an ICD.

  2. Individuals with nonischemic cardiomyopathy with LVEF ≤35% with NYHA functional class II or III have been identified to be at high risk for sudden cardiac death. To be eligible for an ICD, they should be on OMT for at least 3 months.

  3. Individuals with NYHA functional class I and a history of MI ≥40 days from most recent MI and >3 months from revascularization with LVEF <30% have also been identified at high risk for sudden cardiac death.

  4. Individuals with history of MI, with inducible VF or sustained VT at electrophysiologic study are also at increased risk for sudden cardiac death.

These four situations have been identified as class I indications by current guidelines, reducing the risk of death by as much as 30% in 2 years.

There are other primary prevention ICD indications with less evidence and are considered class II indications for ICD by current guidelines. These include:

  1. Hypertrophic cardiomyopathy with one or more major risk factors for sudden cardiac death

  2. Arrhythmogenic right ventricular dysplasia/cardiomyopathy with one or more risk factors for SCD

  3. Nonischemic cardiomyopathy with LVEF ≤35% with NYHA functional class I

  4. Nonhospitalized individuals awaiting heart transplantation

  5. Long Q–T syndrome with risk factors for SCD

  6. Cardiac sarcoid, giant cell myocarditis, Chagas disease

  7. Familial cardiomyopathy associated with sudden death

  8. LV noncompaction

All the patients described above are at increased risk for SCA and would be considered eligible for an ICD for the prevention of sudden cardiac death. To benefit from the ICD, they need to have an anticipated survival (based on other comorbidities) of more than 1 year. Those with NYHA functional class IV have not shown to benefit from ICD placement, with the exception only in those awaiting heart transplantation.

Authors preferred methods: As with all guidelines and indications, this document serves only as a tool to help guide the caregiver in assessing the risk of SCA . In the case of sustained ventricular arrhythmias, the arrhythmias need to be controlled before consideration of ICD placement.

If the arrhythmias are uncontrolled, then frequent shocks from the ICD and a marked decrease in quality of life will be the result. In the case of VT in a normal heart without other risk factors for SCD, the treatment of the VT with medications or ablation may be all that is warranted without ICD placement. In those with structural heart disease, the VT needs to be controlled or suppressed with medication or ablation with ICD placement serving as back-up protection for breakthrough arrhythmias.

A. Immediate management.

Once a patient has been identified as a secondary prevention candidate for an ICD, the ICD is usually implanted prior to discharge from the hospital. In the rare instances where an ICD cannot be implanted at the time of hospitalization, then an external defibrillator vest may be offered as a bridge until placement can be scheduled.

In those identified at risk for primary prevention, placement of ICD is done in an elective manner but offered to be completed in a short time span usually within a month. The benefit of ICDs in survival are dependent on the risk of ICD implantation being relatively low and at a level comparable to those found during the randomized controlled trials.

There are acute and chronic conditions that may increase the procedural risk and this can alter the overall benefit of the device. An example of an acute risk would be an underlying infection, such as pneumonia or osteomyelitis. In the case of infection, this may increase the procedural risk by increasing infection risk. This could lead to infection of the device, a complication that would necessitate removal of entire ICD system. In this case, waiting until infection is definitively treated for ICD placement would be the most appropriate approach. An example of a chronic condition would be end-stage renal disease. Patients on dialysis for end-stage renal disease have been shown to have a 5-fold increase in in-hospital mortality following ICD placement compared to those with an ICD implant who do not require dialysis.

B. Physical Examination Tips to Guide Management.

There are some conditions where ICD implantation may be difficult or not possible. For contemporary ICDs, there needs to be a patent subclavian vein for transvenous placement of an ICD lead.

In some patients, patency to the subclavian veins bilaterally may be interrupted, such as those on or with a history of hemodialysis or with complex congenital heart disease. In this type of situation, the procedural risk, perhaps requiring a thoracotomy, may be greater than anticipated, with the resulting net benefit less than anticipated. There is currently a completely subcutaneous ICD system that is being studied for efficacy and may be an alternative for such situations in the future.

C. Laboratory Tests to Monitor Response To, and Adjustments in, Management.

There are no laboratory tests to follow. However, ICDs require routine follow-up approximately every 3 months to assess appropriate device function, battery status, and lead stability.

D. Long-term management.

The ICD patient will require lifelong follow-up for an ICD and likely for underlying conditions leading to the placement of an ICD. The ICD will be evaluated every 3 months.

Most contemporary ICDs allow for in home remote follow-up using a standard phone line. This decreases the number of office visits for the patient, but still allows for monitoring of the ICD for proper function and in some cases monitoring for arrhythmias. This remote monitoring of ICDs has shown to improve outcomes compared to traditional regularly scheduled office visits.

E. Common Pitfalls and Side-Effects of Management

Pitfalls of the ICD include complications from shocks, placement, infection, abnormal device function, and arrhythmias. The most common issue post implant of an ICD is shocks.

Approximately 20% to 30% of these shocks may be due to "inappropriate" shocks. In this case, the patient is shocked when there was no dangerous arrhythmia.

The most common cause of this is due to atrial fibrillation with rapid ventricular response. Any shock reduces quality of life for the patient especially if there are repeated shocks.

Data also has shown that shocks, both appropriate and inappropriate, are associated with increased mortality. Sometimes reducing shocks can be achieved by altering the programming of the ICD. Other interventions may include ablation of arrhythmia or medical treatment with AV nodal blocking agents or antiarrhythmics.

Because this device is a chronic system residing in the venous system, any infection in the blood stream will risk infection of the ICD system. If the system is suspected of being involved in an infection, the only effective treatment is removing the ICD system (including leads).

In most situations, the ICD generator works appropriately >98% of the time. The lead performance is not as reliable, but still with >96% appropriate performance at 10 years.

Occasionally, there may be problems in how the ICD system functions in a particular patient that can lead to device malfunction such as inappropriate shocks. These devices are also sensitive to electromagnetic fields that usually only transiently effect the ICD system. However, there are reports of permanent damage to ICD systems from strong electromagnetic fields, such as therapeutic radiation.

Because ICDs are sensitive to electromagnetic fields, special caution is required in hospital environments where there may be such an interaction. A common scenario occurs with interference from electrocautery during surgical procedures.

Advice from the heart rhythm specialist team may be required to avoid the consequences of such interactions. Many times the placement of a magnet on the ICD generator, essentially inactivating the ICD portion of the device, while continuously monitoring the patient is all that is required to safely perform such procedures on patients.

IV. Management with Co-Morbidities

Patients with ICDs have an underlying cardiac condition in most if not all cases. The most common comorbidities in ICD patients are CHF and CAD. Both CHF and CAD are progressive disease processes that require lifelong follow-up and require chronic medications for maintenance.

V. Patient Safety and Quality Measures

A. Appropriate Prophylaxis and Other Measures to Prevent Readmission.

Adherence to follow-up guidelines for ICDs may avoid complications. Such evaluations include evaluation and prevention of inappropriate shock, management of recurrent arrhythmias, and regular follow-up for device function and battery status.

The importance of medical compliance for the patients underlying cardiac condition is paramount in reducing hospitalization. In the case of ICDs, education in ICD management for surgical procedures will minimize device interference with other medical procedures.

B. What's the Evidence for specific management and treatment recommendations?

"ACC/AHA/HRS 2008 Guidelines for Device Based Therapy of Cardiac Rhythm Abnormalities". Circulation. vol. 117. 2008. pp. e350-408.

Bardy, GH, Lee, KL. "Amiodarone or an implantable cardioverter-defibrillator for congestive heart failure". N Engl J Med. vol. 352. 2005. pp. 225-37.

Poole, JE, Johnson, GW. "Prognostic importance of defibrillator shocks in patients with heart failure". N Engl J Med. vol. 359. 2008. pp. 1009-17.

Aggarwal, Wang. "Clinical characteristics and in-hospital outcome of patients with end-stage renal disease on dialysis referred for implantable cardioverter-defibrillator implantation". Heart Rhythm. vol. 6. 2009. pp. 1565-71.

Crossley, GH, Poole, JE. "The Heart Rhythm Society (HRS)/American Society of Anesthesiologists (ASA) expert consensus statement on the perioperative management of patients with implantable defibrillators, pacemakers and arrhythmia monitors". Heart Rhythm. vol. 8. 2011. pp. 1114-52.

C. DRG Codes and Expected Length of Stay.

DRG 227: Cardiac defibrillator placement without cardiac catheterization. Anticipated length of stay for ICD placement is less than 24 hours for patients with observational status. In patients with more comorbidity or complexity, inpatient hospitalization may be required for anticoagulation management, heart failure management, or further invasive testing.

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