December 2006: A standard tool for predicting cardiovascular disease (CVD) risk greatly underestimates the true rate of heart disease among patients receiving dialysis for end-stage renal disease (ESRD), reports a paper being presented at the American Society of Nephrology's 39th Annual Meeting and Scientific Exposition in San Diego.
"We demonstrate that the commonly used Framingham Risk Equation highly underestimates the risk of developing heart disease in patients on dialysis," comment Drs. Darshan S. Dalal and Rulan S. Parekh of Johns Hopkins University. "This may lead to inadequate or delayed initiation of treatments to prevent CVD in a group of patients for whom heart disease is the main cause of death."
Drs. Dalal, Parekh, and their colleagues compared predicted and actual rates of heart disease in 4,229 patients with ESRD who were receiving dialysis to replace lost kidney function. At the beginning of the study, none of the patients had any evidence of CVD. Their one- and four-year risks of CVD events�for example, myocardial infarction (heart attack) or stroke�were calculated using the Framingham Risk Equation. "Based on traditional cardiovascular risk factors such as blood pressure, cholesterol levels, smoking, and diabetes, the Framingham Risk Equation is widely used to predict CVD risk, particularly for patients seen by general internists and cardiologists," Dr. Parekh explains. "However, this tool has not been validated in ESRD patients, a group at high risk for serious heart disease."
The equation greatly underestimated the patients' true risks. For men with ESRD between age 30 and 75 years, the median predicted CVD risk over their follow up was 2.2%. In reality however, 35 percent of the men in the study experienced some type of CVD event over an average of two years' follow-up. The Framingham Risk Equation also underestimated CVD risk among women with ESRD in the same age range. Median predicted risk was 2.0%, compared with an actual CVD event rate of 37 percent.
End stage renal disease is a major public health problem in the United States, with over 104,000 new cases and 84,000 deaths each year. About half of these deaths result from CVD�the leading cause of mortality among ESRD patients. "Over 40 percent of ESRD patients already have atherosclerotic heart disease at the time they start dialysis," according to Dr. Parekh.
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Previous studies have suggested that conventional risk factor analysis may also underestimate CVD risk in patients who have chronic kidney disease: gradual, irreversible loss of kidney function that can lead to ESRD. Up to 20 million Americans may have chronic kidney disease�appropriate early screening and treatment can reduce their risk of CVD, as well as ESRD.
The new results suggest that, for the 60 percent of ESRD patients who are initially free of heart disease, CVD risk is substantially higher than suggested by the Framingham Risk Equation. The reasons for this low predictive ability are unclear�traditional risk factors may have different effects, or additional risk factors may be present in patients with ESRD. "Newer and more comprehensive risk equations are needed to assess and predict cardiovascular risk in ESRD patients," Drs. Dalal and Parekh conclude.
Source: American Society of Nephrology (ASN) / Newswise
