Dallas, TX - Poor kidney function is increasingly recognized as a cardiovascular risk factor, but how independently powerful is it as a predictor of poor outcomes? A couple of recent reports add to the growing literature suggesting that chronic kidney disease (CKD) is in the same league as diabetes as a predictor of cardiac mortality and other CV end points and suggest that measuring renal function can add substantially to the risk stratification of patients with suspected CAD [1,2].

In an analysis from the longitudinal Cardiovascular Health Study (CHS), which followed >5000 persons at least 65 years old in four US communities, CKD, diabetes, and a history of MI at baseline were independently and about equally predictive of cardiovascular mortality over a follow-up of more than eight years. The study from Dr Arash Rashidi (Metro Health Medical Center, Cleveland, OH) and colleagues appears in the December 15, 2008 issue of the American Journal of Cardiology.

In a separate study, CKD and ischemia at stress SPECT myocardial perfusion imaging were similarly predictive of all-cause mortality in a referral population with suspected CAD followed for about two years. Furthermore, observed principal author Dr Su Min Chang (Methodist DeBakey Heart and Vascular Center, Houston, TX) for heartwire, their prognostic contributions were additive.

"Most clinicians and patients would think that if you have a normal stress test, your risk is not high. But if you have CKD, your risk is not low, either," according to Chang. Renal function isn't traditionally figured into the risk stratification of patients with suspected CAD, he observed, yet CKD is similar to diabetes as a risk equivalent for poor CV outcomes.

SPECT perfusion imaging also was strongly prognostic for cardiac death and MI regardless of the degree of renal dysfunction in the study published in the December 9, 2008 issue of Circulation, with first author Dr Abdul Hakeem (University of Cincinnati College of Medicine, OH).

Of the 1652 patients referred for rest-stress SPECT perfusion imaging, 36% had CKD as defined by an estimated glomerular filtration rate (eGFR) <60 mL/min per 1.73 m². The rate of cardiac death was 2.7% for patients with normal perfusion scans and CKD, compared with 0.8% for those with normal scans and no CKD.

Over a mean follow-up of 2.15 years, the cardiac-death hazard ratios for ischemia at perfusion SPECT and CKD in a multivariate analysis were similar. Perfusion defects were also significantly predictive of all-cause mortality and nonfatal MI.

Patients with CKD and normal perfusion scans, the group writes, "should be considered a high-risk group, and aggressive medical management, including optimal lipid goals, tight regulation of hemoglobin A_1C, and blood-pressure control, should be pursued."

Their study suggests that "all patients undergoing [myocardial perfusion SPECT] should have eGFR assessed as part of their evaluation. Moreover, eGFR should be integrated into clinical risk-prediction models for morbidity and mortality."

The study from Rashidi et al, which defined CKD according to the same eGFR criteria, followed three cohorts of people from the community, all of whom had CKD, diabetes, or a baseline history of MI without either of the other two risk factors.

In multivariate analyses, the risk of cardiovascular death was similar for the groups with diabetes only and CKD only, compared with the cohort with a baseline history of MI but neither diabetes nor CKD. The risk of fatal and nonfatal CV events was similar in the MI and diabetes groups; those with CKD had a reduced risk compared with those with MI.

CKD was associated with a reduced risk of fatal or nonfatal CV events, suggesting that "the case fatality rate for cardiovascular events may be higher in patients with CKD than in those with either diabetes or history of MI," according to the authors.

Chang observed that physicians aren't generally used to considering renal function in the risk stratification of patients with suspected CAD, but it should probably be a routine part of the evaluation. There are no trial data to support the strategy, he said, but if a patient has "average risk factors and a normal stress test" and is found to have CKD, "you might want to treat them even more aggressively to improve their risk profile."