In the population of the United States, acute kidney injury (AKI) — previously called acute renal failure — is on the rise.
Although the precise reasons behind this are unclear, it is a concern; AKI has relatively poor long-term outcomes and can be fatal in some cases.
Commonly, AKI will progress to chronic kidney disease (CKD), which increases the risk of heart failure threefold when compared with people without CKD. Whether this cardiovascular risk extends to AKI is not known.
Understanding the potential risk to heart health for people with AKI is important as it may guide treatment and follow-up for those at greatest risk.
A new study, published in the American Journal of Kidney Diseases, set out to look at this question in more detail. Could the researchers find a relationship between AKI and heart failure? They were headed up by Dr. Nisha Bansal, of the Kidney Research Institute at the University of Washington in Seattle.
Link between AKI and heart failure examined
Their investigation included 300,868 U.S. veterans from 116 Veterans Affairs hospitals from 2002 to 2013. Participants — who were aged 62, on average — had no history of heart failure.
Within these data, they matched patients with AKI to those without. They used a range of variables to ensure a close match was achieved, including age, year of admission, demographics, medications being used, and pre-existing conditions.
Over the following 2 years, they collated information on heart failure. They defined incident heart failure as at least one hospitalization or at least two outpatient visits with a heart failure diagnosis.
Overall, heart failure incidence rate was 27.8 per 1,000 person years. In the AKI group, it was 30.8, and in the non-AKI group, it was 24.9.
This equates to a 23 percent increased risk of heart failure for individuals with AKI within a 2-year follow-up window.
Individuals who developed heart failure following AKI were more likely to be white, be older, and have high blood pressure, diabetes, and proteinuria, or excess protein in their urine. The implications of these findings are laid out by the authors:
"It has been estimated that approximately 2 million cases of hospitalized AKI occur annually. Based on the differences observed in our study, this would translate to approximately 16,000 additional cases of incident heart failure per year."
The researchers also analyzed a healthier subgroup of patients: those without diabetes, high blood pressure, vascular disease, or cardiac surgery. Surprisingly, these patients had a 38 percent increased risk of heart failure during the following 2 years.
In other words, patients with fewer existing conditions were more likely to have cardiovascular problems following AKI than individuals with ongoing medical issues. But it is not clear why this might be.
How does AKI impact heart health?
Exactly how AKI impacts heart health is not known, but there are several possible mechanisms. For instance, AKI changes the way that the kidneys handle salt, leading to hypertension, a well-known risk factor for heart disease. AKI also appears to increase levels of inflammation in other parts of the body, including the heart.
And, AKI can produce ongoing oxidative stress, which interferes with the renin-angiotensin axis, a hormone system that helps to regulate fluid balance and blood pressure. These disruptions are known to promote fibrosis of the kidneys and heart muscle.
The authors discuss certain limitations to the study. For instance, only 5 percent of the cohort were women. Also, the veteran population has a higher rate of heart failure than the general population.
However, the analysis was carried out on a large group of patients, and the scientists had access to detailed information about the participants' health status before hospitalization. And, these findings agree with earlier results from similar studies.
Still, further investigations will be needed to firm up the conclusions and tease out the mechanisms behind the relationship. Overall, the authors believe that paying more attention to cardiovascular risk factors may be particularly important for individuals who are recovering from AKI.