Malfunctioning kidneys may raise risk of sudden death in women

Women whose kidneys are poor at filtering impurities from the blood are at heightened risk of sudden cardiac death, according to a report published in Hypertension: Journal of the American Heart Association.

The study analyzed 2,760 postmenopausal women with a history of some heart disease to determine whether less serious, unrecognized deficiencies in kidney function also raised the risk of sudden cardiac death (SCD). After controlling for several baseline risk factors – including heart failure, age, smoking, heart rate and level of high-density lipoproteins (HDL, “good” cholesterol) – researchers found the risk of SCD in women with advanced kidney dysfunction was 3.16 times higher than in women with normal kidney function.

Sudden cardiac death occurs when the heart abruptly and unexpectedly stops beating, leading to death within minutes of the first symptoms. It causes about 310,000 deaths each year among U.S. adults, according to American Heart Association statistics.

“Sudden cardiac death is an important public health problem, but it is poorly understood and understudied, especially in women,” said lead author Rajat Deo, M.D., the study's lead author and a fellow in cardiac electrophysiology at Johns Hopkins Hospital in Baltimore.

Many people who die of SCD have pre-existing heart disease or heart disease risk factors. People with end-stage kidney disease, who require dialysis to survive, are at particularly high risk: about 22 percent of deaths in these patients are caused by SCD. Chronic kidney disease is also associated with SCD risk in people with advanced heart failure (their heart muscles are weakened and can't pump all the blood the body needs).

Deo and colleagues from the University of California-San Francisco, examined data on postmenopausal women who participated in the Heart and Estrogen/progestin Replacement Study (HERS). The women, average age 67 with none over 79, had been diagnosed with coronary heart disease because of a previous heart attack, coronary artery bypass surgery, angioplasty or tests showing more than 50 percent narrowing in one or more coronary arteries. Some of the women had mild heart failure, but none had severe heart failure or end-stage renal disease.

At the start of HERS, researchers measured blood creatinine, a waste product that healthy kidneys remove from the blood. Creatinine levels were used to estimate the filtering ability of the kidneys (the glomerular filtration rate, or eGFR).

During the 6.8-year follow-up period, 135 of the women experienced SCD:

• 36 (3.5 percent) of those had normal kidney function (eGFR over 60 milliliters per minute [ml/min]);
• 69 (4.6 percent) of those had moderate kidney dysfunction (eGFR 40-60 ml/min);
• 30 (13 percent) of those had advanced kidney dysfunction (eGFR less than 40 ml/min).

Other women at heightened SCD risk during the HERS study were those who had a heart attack or were hospitalized one or more times for heart failure during the follow-up period. However, after controlling for these events, the risk remained 2.27 times as high for women with advanced kidney dysfunction.

“We found a strong, independent association between kidney function and SCD in a group of women with coronary heart disease who were not on dialysis and had less sick hearts than patients in previous studies,” Deo said.

“We already know that patients with kidney disease are at greater risk of heart attack, heart failure and stroke. This study extends that concern to SCD and supports previous recommendations that people with kidney disease be monitored aggressively for cardiac risk factors.”

Whether women had received estrogen/progestin replacement therapy or a placebo as part of the HERS trial had no impact on their chance of SCD, Deo said.

Although the analysis involved only women, the researchers believe it will apply to men, too. They are preparing an analysis of kidney function and SCD risk in elderly men and women.