New AKI Risk Score for PCI Patients Passes Validation

A pair of updated scoring models for estimating a patient's risk for contrast-associated acute kidney injury during and immediately after percutaneous coronary intervention (PCI) worked better than a widely used prior version in initial validation testing using data collected at a single US tertiary-care hospital.

While the two new risk scores looked promising, they need further, external validation with additional, diverse patient cohorts, Roxana Mehran, MD, cautioned at the American Heart Association (AHA) Scientific Sessions 2021.

"Don't change anything until we externally validate this," urged Mehran, professor and director of the Center for Interventional Cardiovascular Research and Clinical Trials at Icahn School of Medicine at Mount Sinai in New York City. External validation of the two new risk scores is in progress with planned reporting of the results in 2022, she said in an interview.

One of the two new algorithms, which both predict a patient's risk for developing acute kidney injury (AKI) as a result of receiving iodinated contrast media within 48 hours of a PCI, relies on eight easily available variables taken from a patient's medical record just prior to undergoing PCI: age, type of coronary disease (ranging from asymptomatic or stable angina to ST-segment elevation MI), estimated glomerular filtration rate, left ventricular ejection fraction, diabetes, hemoglobin, basal glucose, and heart failure.

This risk score accounted for 72% (a C-statistic of 0.72) of the observed AKI episodes during the derivation phase, which used data from 14,616 consecutive Mount Sinai patients who underwent PCI during January 2012–December 2017.

Internal validation using data from 5606 consecutive Mount Sinai patients who underwent PCI during January 2018–December 2020 showed that the eight-item formula accounted for 84% of all incident AKI events occurring during or within 48 hours of a PCI procedure.

Accounting for Periprocedural Variables

A second risk score included the eight preprocedural variables plus four additional periprocedural variables: complex PCI anatomy, contrast volume during the procedure, development of a periprocedural bleed, and having slow or no reflow into affected coronaries (less than TIMI grade 3 flow) immediately after the procedure. The second model produced a C-statistic of 0.74 during derivation and accounted for 86% of incident AKI events in the validation analysis.

The data Mehran reported appeared in The Lancet.

She and her coauthors designed these two new algorithms to replace a "widely used" and externally validated risk score that Mehran and associates introduced in 2004. Despite its merits, the 17-year-old scoring formula has limitations including "low discrimination" with a C-statistic of 0.67, derivation from data that's now 20 years old, and exclusion of patients with ST-elevation MIs, the authors said in the new report.

Mehran encouraged interventional cardiologists to use both new risk scores (once externally validated) when possible.

The eight-item preprocedural model "gives clinicians an idea about a patient's risk [for incident AKI] before they go into the catheterization laboratory," and then they can further refine the risk assessment during the procedure based on the four periprocedural risk factors, she explained. The goal is to target "tailored preventive strategies" to patients identified by the scoring algorithms as being at high risk for AKI.

A Role for Preventive Measures

Preventive strategies to consider for higher-risk patients include limiting the administered volume of iodinated contrast media, increasing hydration, and avoiding nephrotoxic agents, Mehran said. The two new risk-assessment tools will "allow for better evaluation of PCI patients" when testing "innovative strategies and treatments" designed to help avoid contrast-associated AKI.

"The focus to date has been on measures to protect renal function from contrast media, based on indirect data," Estelle C. Nijssen, MSc, and Joachim E. Wildberger, MD, wrote in an editorial that accompanied the published report. "The effect of prophylactic measures on longer-term averse outcomes is still unclear," they noted. "Perhaps our focus should shift from contrast and renal function to the heart, the role of which has probably been undervalued in this setting," wrote Nijssen, a researcher at Maastricht (The Netherlands) University, and Wildberger, professor and chairman of the department of radiology at Maastricht University.

The editorial's authors noted that the two new risk scores have the advantage of relying on variables that are "readily available in clinical practice." But they also noted several limitations, such as the model's development from largely low-risk patients who had a low, roughly 30% prevalence of chronic kidney disease. During 9 full years studied, 2012-2020, the annual incidence of AKI showed a downward trend, with an incidence of just over 3% in 2020.

Mehran attributed this decline in AKI to "great work identifying high-risk patients" and using the prophylactic measures she cited. But even when occurring at relatively low incidence, "AKI is still an important complication that is associated with mortality post PCI," she stressed.

Establishing a Safe Contrast Dose

"The study is great, and helps reinforce the risk factors that are most important to consider when risk stratifying patients prior to PCI," said Neal Yuan, MD, a cardiologist at the University of California, San Francisco, who has studied contrast-associated AKI in patients who undergo PCI. The report from Mehran also "confirms in a large cohort the association between contrast-associated AKI and death," and describes "an easy method for calculating risk," he said in an interview.

Yuan agreed on the need for external validation, and once adequately validated he called for incorporation of the risk score into EHRs. Another important issue for future study is "how much [AKI] risk is too much risk," he said.

The risk factors identified in Mehran's report "are some of the same ones identified in previous studies. Even though this was a more contemporary dataset, there is not a ton of new [findings]; it mainly strengthens findings from prior studies."

Results published by Yuan and his associates in 2020 used data from more than 20,000 US patients who underwent PCI to try to identify a generally safe upper limit for the dose of iodinated contrast.

The main purpose for performing AKI risk stratification on PCI patients is to "identify high-risk patients and use preventive strategies when treating these patients." Current AKI preventive strategies "mainly fall into intravascular volume expansion, and reduced contrast." What's less clear is "how to operationalize reduced contrast," he said.

The report by Yuan showed that "about 10% of PCI patients were at very high risk" for contrast-associated AKI "no matter what is done." In contrast, about two-thirds of PCI patients "could receive lots of contrast and still be very unlikely to develop AKI," Yuan said.

He voiced some skepticism about the willingness of many clinicians to routinely use a formal risk score to assess their patients scheduled for PCI.

Most operators "approximate AKI risk based on variables such as age and creatinine level, but few take time to put the variables into a calculator to get an exact risk number." In a "small survey" he ran, he found that these rough approximations often ignore important risk factors like hemoglobin level. This inertia by clinicians against routinely using a risk score could be addressed, at least in part, by integrating the risk score into an EHR for automatic calculation, Yuan suggested.

Mehran noted that the risk score that she introduced in 2004 is used "in many EHRs to identify high-risk patients."

The current study received no commercial or external funding. Mehran has been a consultant to Boston Scientific, Cine-Med Research, CIRM, and Janssen, and she holds equity in Applied Therapeutics, Elixir Medical, and STEL. Wildberger had no relevant disclosures. Nijssen and Yuan had no disclosures.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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