Dying Suddenly - Sudden Cardiac Death

Although heart disease is common in the U.S., many of the people who suffer SCD are not recognized to have heart disease prior to their death. Among those who have heart disease, a large proportion will not die suddenly. Identifying those people who are at risk for SCD before an episode of serious arrhythmia is a major challenge for the cardiologist and the cardiac electrophysiologist. Careful screening, evaluation, risk factor modification, and therapy can decrease the likelihood of SCD in people at risk. Unfortunately, no method is perfect.

Ambulatory rhythm monitoring devices have been used for many years to screen patients for the presence of dangerous arrhythmias. Although sustained VT (which is clearly associated with an increased risk of SCD in patients with heart disease) is recorded occasionally, PVC and nonsustained VT are seen quite frequently on such monitors. Unfortunately, the true significance of PVC and nonsustained VT is unclear. While they do carry some degree of increased risk for SCD, it has been shown that treatment of them does not benefit and may actually harm the patient. Further risk stratification involves the performance of an electrophysiology study.

Electrophysiology studies have been used for many years to evaluate the risk of sustained ventricular arrhythmias in individuals with coronary artery disease, prior myocardial infarction, congestive heart failure, and cardiomyopathies. If ventricular tachycardia or fibrillation is not inducible during the study, the risk of SCD appears to be significantly decreased such that ICD implantation may not be necessary, especially for individuals with stable coronary artery disease. Individuals referred for EP studies include those with PVC, nonsustained VT, and syncope without recorded arrhythmias. If sustained VT is induced, ICD implantation is usually recommended.

Although antiarrhythmic drugs have had little impact on the prevention of SCD, two classes of drugs not used to treat arrhythmias have been shown to reduce the risk of SCD in patients with heart disease. Beta-adrenergic blocker drugs have been demonstrated to decrease the risk of SCD in patients with all categories of heart disease. Although beta-blockers are usually regarded as drugs for treating hypertension, they have been shown in several large studies to decrease the risk of SCD by 30-50%. Several possible mechanisms by which the beta-blockers work, including decreasing the workload on the heart and reducing the ability of catecholamines to influence the heart, have been suggested. Beta-blockers were previously thought to be contraindicated in patients with congestive heart failure but have recently been shown to be especially beneficial in decreasing the risk of SCD in these high-risk patients. Angiotensin-converting enzyme (ACE) inhibitors are also commonly used in the treatment of hypertension but have been shown to decrease the risk of SCD in patients with congestive heart failure by approximately 20%. The mechanism(s) by which they exert their effects are also unknown but they also result in a decrease in the cardiac workload and in the level of catecholamines in the blood. When used together, beta-blockers and ACE inhibitors seem to have an additive effect on decreasing SCD risk.

Improvements in technology have made ICD smaller and easier to implant in a relatively short period of time. Current investigations are ongoing to determine whether implanting ICD in patients with heart failure who have not suffered episodes of syncope or serious arrhythmias will save the lives of more high-risk individuals. Since effective technology exists to deal with SCD, the Texas Arrhythmia Institute is dedicated to making it available to as many patients in need as possible. The greatest challenge now is discovering who is "in need" and meeting that need before sudden cardiac death strikes.