Sudden Cardiac Death and Left Ventricular Systolic Dysfunction
Abstract & Commentary
By John P. DiMarco, MD, PhD. Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.
Synopsis: These findings support the aggressive development of alternative screening methods to enhance identification of patients at risk for sudden cardiac death.
Source: Stecker EC, et al. Population-Based Analysis of Sudden Cardiac Death with and without Left Ventricular Systolic Dysfunction: Two-Year Findings from the Oregon Sudden Unexpected Death Study. J Am Coll Cardiol. 2006;47:1161-1166.
Stecker and colleagues report observations from the Oregon Sudden Unexpected Death Study, which is an ongoing epidemiologic investigation of the characteristics of out-of-hospital sudden cardiac death. The study is being conducted in Multnomah County, Oregon (Portland and surrounding area).
In this report, the availability and significance of a pre-arrest assessment of left ventricular function is studied. Patients who experienced sudden cardiac death between Feb. 1, 2002 and Jan. 31, 2004 were evaluated. Resuscitated survivors of out-of hospital cardiac arrest were not included. Records for classifying the sudden death event were obtained from the county emergency medical response system, county medical examiners, and area hospitals. Prior medical records for the sudden cardiac death victims were then obtained from either these sources or from their primary care physicians.
Sudden cardiac death was defined as an unanticipated cardiac death within one hour of symptom onset. The study included unwitnessed sudden deaths in which patients were found dead within 24 hours of having been last seen alive and in a normal state of health. Patients with terminal noncardiac illnesses or identified non-cardiac etiologies for sudden death were excluded. The medical records were reviewed to see if they could contain a quantitative assessment of the patient's left ventricular ejection fraction (LVEF). The left ventricular ejection fractions were then categorized as either normal (greater than 55%), mildly to moderately reduced (36% to 54%), and severely reduced (less than or equal to 35%).
During the 2-year period included in this study, 714 residents of Multnomah County experienced an out-of hospital sudden cardiac death that satisfied study criteria. The mean age was 66 ± 19 years, and 60% were male. Medical records were available for review in 704 of 714 cases. Of these, only 121 cases (17%) had a prior assessment of left ventricular function before the sudden cardiac death event. Of these, in only 74 cases (63%) were the LVEF assessment conducted within 2 years of the cardiac arrest. Among the 121 patients for whom LVEF data were available, 58 patients had a normal LVEF, 27 had a mild to moderately reduced LVEF, and 36 had severely reduced LVEF. There were also 4 patients who had survived a prior cardiac arrest but had a normal LVEF and 2 patients with other cardiac conditions with a high risk for sudden death. Thus, based on current criteria for ICD implant, only 40 of the 121 patients would have been eligible for a primary prevention ICD implant.
Several interesting points about other clinical characteristics were noted. In the normal LVEF group, there were 8 patients (14%) who had a history of a seizure disorder. It could not be determined whether these arrests were precipitated by a seizure, were facilitated by anticonvulsant therapy, or were just an unrelated finding. Diabetes mellitus, hypertension, prior cerebrovascular accidents, and sleep apnea were found in reasonably equal proportions in the 3 LVEF groups. Left ventricular dysfunction was also significantly more prevalent among the 51 (42%) patients older than 75 years of age. Acute myocardial infarction or acute ischemia was a relatively uncommon finding. In only 7 cases was an acute MI recognized, nd 6 cases had pre-arrest ischemic symptoms. Other predisposing syndromes associated with sudden cardiac deaths were found in a few additional patients. Five patients had aortic stenosis, one patient had hypertrophic cardiomyopathy, and one patient had arrhythmogenic right ventricular cardiomyopathy that was diagnosed by other techniques.
Stecker and colleagues conclude that evaluation for left ventricular dysfunction before sudden cardiac death is uncommon. Even among those in whom an assessment of LV function had been obtained, left ventricular dysfunction is not common. Stecker et al encourage a renewed emphasis on identifying alternative sudden cardiac death risk predictors in the general population.
Strategies to prevent sudden cardiac death need to be broadly based. As illustrated in this study, a majority of sudden deaths occur in low-risk individuals. In low-risk individuals, expensive, toxic, or invasive therapies are impractical. The best method to prevent sudden death among low-risk individuals in the general population is to prevent or delay the development of acquired cardiac diseases that can lead to fatal arrhythmias. Despite this fact, individuals at much higher risk can be identified, and it is on such patients that current recommendations for ICD implantation are focused. What remains controversial is what level of baseline risk justifies proceeding to an ICD. Although the oldest and sickest patients are most likely to receive a shock after receiving an ICD, these patients also have higher mortality rates from nonarrhythmic causes, and the incremental gain in longevity may not be great. The data in this study indicate that nonspecific therapies that can be applied broadly may have greater value from a public health perspective than more complex interventions.