Highs and Lows: Contrast Volume in PCI Varies Greatly Among US Physicians

Both the amount of contrast used during PCI and the rate of acute kidney injury (AKI) that develops afterward show wide variation across the United States, researchers have found. Moreover, operators don’t seem to be taking PCI patients’ baseline risk into account when deciding how much contrast is needed.

These patterns “suggest an important opportunity to reduce AKI by reducing the variation in contrast volumes across physicians and lowering its use in higher-risk patients,” say Amit P. Amin, MD, MSc (Washington University School of Medicine, St. Louis, MO), and colleagues.

The National Cardiovascular Data Registry CathPCI Registry findings, derived from more than 1.3 million patients and nearly 6,000 physicians over a 3-year period, were published online last week in JAMA Cardiology.

Commenting on the study, Somjot S. Brar, MD, MPH (Kaiser Permanente, Los Angeles, CA), told TCTMD it valuably provides a big picture of what’s going on across the United States. At the moment, he said, “we don’t really break down contrast volumes by operators, to see if people are outliers.” Better understanding of physicians on the lower-use end of the spectrum could help identify any best practices that could be adopted on a wider scale, Brar suggested.

However, “one of the challenges is that even within the cath lab environment, you may not have systematic reporting of contrast volume on a monthly or quarterly basis by a given operator.” Without this sort of feedback, and knowing how you compare with your peers, “it would be hard to improve,” he said. “You’re always just working in your own little universe to some extent.”

PCI Complexity Can’t Explain Everything

For their analysis, Amin et al looked at 1,349,612 million patients (mean age 64.9 years; 67.3% men) who underwent PCI performed by 5,973 physicians at 1,338 hospitals between June 1, 2009, and June 30, 2012.

Acute kidney injury, defined as an absolute increase of ≥ 0.3 mg/dL or a relative increase of ≥ 50% from preprocedural to peak creatinine, developed in 7% of patients. Across physicians, the unadjusted AKI rates ranged from 0 to 30%. Further calculations showed that a mean 43% excess in AKI risk could still be seen for identical patients treated by two random operators.

Mean contrast volume also varied significantly among physicians, ranging from 79 to 487 mL. Even after adjustment for patient and physician characteristics, 23% of the variation in volume could still be traced to the operators themselves. Physicians who used more contrast tended to have more patients develop AKI (adjusted OR 1.42 per 75-mL increase; 95% CI 1.40-1.43). Yet only a “minimal association” was seen between patients’ baseline risk of developing AKI and the amount of contrast their operators used, the researchers report.

Importantly, Amin and colleague stress, the variation in AKI appears to be related to physician practices rather than to PCI complexity. “We can surmise that variation in contrast volumes is perhaps associated with frequent injections, ventriculograms, larger-bore guides, trainees’ involvement, multivessel PCI without staging the second or third vessel, and variation in interventional techniques of wiring lesions and balloon and stent placement, which all consume contrast. A qualitative study is needed on such interventional practices and the potential unintended consequences of efforts to reduce contrast.”

Awareness and Accountability

To TCTMD, Brar said that higher volumes may stem from a combination of factors, including poor awareness and lack of accountability. “People may just get set in their ways, and if you don’t know if someone else is doing the same thing with 20, 30, 40 percent less contrast, you don’t have a point of reference to necessarily change.”

While “there are risk calculators to help us understand how much contrast may be safe for a given procedure,” these aren’t easy to use, Brar noted. “They’re not ones that you can basically do in your head, so you have to make a conscious effort to input the information into an online calculator or something.”

People may just get set in their ways, and if you don’t know if someone else is doing the same thing with 20, 30, 40 percent less contrast, you don’t have a point of reference to necessarily change. Somjot S. Brar

It may also come down to the case mix. “Some physicians specialize in doing much more complicated cases that other interventionalists may not want to tackle,” he observed. “And in that context you’re going to have more difficult anatomies and longer, more difficult procedures.”

One issue with this paper, Brar said, is that it included not only patients thought to be at risk of contrast-induced AKI—by virtue of having glomerular filtration rates (GFRs) of less than 60%—but those with normal kidney function at baseline. Patients with a GFR > 60%, which represented 71% of the cohort, “may develop acute kidney injury for other reasons, but the contrast is going to be low probability in terms of the mechanisms of injury,” he explained. “So there’s a lot of extra AKI cases in this study that may be very difficult to attribute to contrast.”

Also, there were no serial measurements of serum creatinine, which would be needed to make sure that AKI cases that occurred after discharge weren’t missed, Brar pointed out.

Curbing contrast use may prove difficult for some operators, especially those doing challenging cases, he said. But for interventionalists trying to take easy steps, Brar highlighted the subgroup of patients with GFR values below 60% as the ones who would benefit most from hydration and minimized contrast volume.