|
Sudden Cardiac Death » Clinical Information
Sudden Cardiac Death ("SCD") occurs when the electrical system in the heart malfunctions and beating suddenly becomes irregular, causing the heart to cease to effectively pump blood. SCD is a major health problem accounting for over 600,000 deaths annually in the U.S. and EU. Of the total number of deaths, about 80% of SCD victims die without being hospitalized or admitted to an emergency room, since the timing and manner of death are unexpected. Only 5-6% of victims survive their initial arrhythmic event if they are not treated within minutes of the event.
Recent advances in medical technologies have resulted in a decrease in the mortality rate from cardiovascular disease, and therefore, cardiovascular patients are now living longer. As a result, there has been a significant increase in the number of individuals living at a higher risk of SCD. Currently, there are over 20 million people living with elevated risk of SCD in the world. Common risk factors for SCD include:
- The most common risk factors of heart disease: high blood pressure, diabetes, high cholesterol, inactivity, overweight, smoking and poor diet;
- Previous heart attacks (75% of people who died of SCD show signs of a previous heart attack);
- History of heart disease or heart rhythm disorders (80% of SCD victims have signs of coronary artery disease);
- Poor heart pumping (ejection fraction, or "EF") indicator of 35% or less; and
- Family history of cardiac arrest or other heart diseases.
Implantable cardiac defibrillators ("ICD") have been proven to be a reliable therapy for effectively treating SCD. Over the past several years, there have been a number of landmark trials (SCD-HeFT, MADIT II, etc.) that have shown that when ICDs are implanted in patients with no history of arrhythmias, mortality of cardiac arrest is significantly reduced, contributing to a significant growth (> 25%) in ICD implantation. Based on the results from these trials, the U.S. ICD implant guideline recommendations were expanded to include patients with symptomatic heart failure and reduced heart function, which included individuals with EF < 35%.
However, EF is a mechanical measurement of heart function, and SCD is the result of an electrical problem in the heart. Because of this, EF is often a poor predictor of patient susceptibility to life-threatening arrhythmias. Although significant effort has been made to improve SCD risk stratification, other methods lack broad clinical evidence and predictive accuracy, which has led to poor physician confidence in existing risk stratification methods.
Consequently, only a minority of patients currently indicated for ICD implantation actually receives an ICD, as physicians want to avoid the acute and chronic risks of implanting patients who have a low probability of benefiting from the therapy. In addition, a significant number of patients at risk of SCD are not indicated for ICD therapy, since even the expanded ICD guidelines still only cover a minority of patients who are at risk. Meanwhile, the majority of patients who do receive expensive ICD implants never experience a life-threatening arrhythmia and are sometimes subjected to unnecessary, excruciatingly painful shocks. According to an April 2008 article in the Wall Street Journal, ICD implantations are declining, with only 30% of eligible patients receiving an implant. The article cites proper patient identification and the lack of effective risk stratification tests as the primary driver behind this drop, as well as the high number (10-20) of implants required to save one life.
Robert Califf, a Duke University cardiologist, summed up the attitude toward current arrhythmia diagnostic tests at the American College of Cardiology conference in March, 2008, where he was quoted in the April 2008 Wall Street Journal article as saying "None of the tests are any good."
There is a tremendous need for a way of identifying patients in this EF>35% group that are at risk of SCD, and in better identifying those patients with an EF<35% who are truly at risk.
|
