Preventing Sudden Cardiac Arrest and Sudden Cardiac Death - Indications for Implantable Defibrillators

Sudden cardiac arrest (SCA) is the leading cause of death in the United States and is fatal in 95 percent of cases. Even in the best emergency medicine services/early defibrillation programs, it is difficult to achieve high survival rates, often because SCA events are not witnessed and responders are unable to reach victims in time for successful resuscitation. Improving survival among patients who experience SCA is an important effort, but focusing on preventing SCA in high-risk patients could have a greater impact on overall survivorship.

Sudden Cardiac Death Risk Factors

Although SCA is the first presentation of cardiac disease in 20 percent to 25 percent of patients, most cases occur in patients with clinically recognized heart disease.

According to the American Heart Association, the risk of SCA among patients after myocardial infarction (MI) is four to six times greater than that of the general population. Reduced left ventricular ejection fraction (LVEF) remains the single most important risk factor for overall mortality and sudden cardiac death.

Implantable cardioverter-defibrillator

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Primary vs. Secondary Prevention ICDs

Since their introduction to clinical use in 1980, implantable cardioverter-defibrillators (ICDs) have been indicated for cardiac arrest survivors. In this secondary prevention role, ICDs shock or pace the heart out of ventricular arrhythmias, abort recurrent SCA, and reduce all-cause mortality by about one-third. Extending the use of ICDs from secondary to primary prevention of arrhythmic death has been the subject of several trials in recent years.

Mayo Clinic's SCA Prevention Initiative

Despite the abundance of clinical evidence supporting ICD therapy for both primary and secondary prevention of SCA, published literature shows a low utilization of ICDs in patients who might benefit from this therapy. To address this challenge, Mayo Clinic cardiologists have developed a new system to identify patients at risk for SCA and to provide them with information about risk stratification and treatment options.

Mayo Clinic's Sudden Cardiac Arrest Prevention Initiative identifies and screens patients with LVEF of 35 percent. The patient information reviewed includes:

• Date of prior MI
• Date of initial diagnosis of nonischemic cardiomyopathy
• Date of prior percutaneous coronary intervention or coronary bypass surgery
• Whether an ICD has been placed
• Whether SCA risk has been discussed with the patient
• Other clinical parameters

After this process is completed, if a patient appears at risk for SCA, Mayo cardiologists send a letter to the patient's primary physician, detailing the issue at hand and the mechanism by which consultation for ICD consideration can be arranged.

ICD Trials

Multicenter Automatic Defibrillator Implantation Trial II (MADIT II)

• Showed that ICDs yield better survival rates than conventional therapy in patients with ischemic heart disease and reduced LVEF of 30 percent or less.
• Suggested that ICD benefit increases over time.
• Showed relative mortality reduction (31 percent) and absolute mortality reduction (5.6 percent) among patients who received ICD therapy.

Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT)

• Focused on patients with class II or III congestive heart failure symptoms, no history of cardiac arrest, and ejection fraction of 35 percent or less, including patients with both nonischemic and ischemic cardiomyopathy.
• Showed that amiodarone has no favorable effect on survival and that ICD therapy reduces the relative risk of overall mortality by 23 percent and the absolute risk by 6 percent to 7 percent.