But a new study concludes that those limits are wildly off the mark.
The 30-day risk of death doesn't go up until troponin levels hit 218 times the reference limit, according to an assessment of 8,239 patients who had coronary-artery-bypass grafting or either aortic-valve replacement or repair.
For 5,623 patients who underwent other cardiac surgery, troponin levels had to hit 499 times the reference limit before the risk of death was elevated.
Chief author Dr. P.J. Devereaux of McMaster University in Hamilton, Canada, told Reuters Health in a telephone interview that because virtually every heart-surgery patient exceeds that 10-fold limit and their doctors have learned from experience that their patients are not experiencing a horrible outcome, that "has led to a lot of cardiac surgeons ignoring troponin because they think it doesn't matter. And they're right."
The results of the study, known as VISION and reported in the New England Journal of Medicine, may make post-surgical troponin measurements relevant.
"These findings suggest that high-sensitivity cardiac troponin thresholds used to diagnose perioperative myocardial infarction and injury may need to be considerably higher than those currently recommended," Drs. James de Lemos and Michael Jessen of the University of Texas Southwestern Medical Center, in Dallas, write in a linked editorial.
"For many cardiac surgeons and clinical cardiologists, this study will confirm the impression that large troponin elevations are expected after routine cardiac surgery, correlate poorly with clinically evident complications, and remain difficult to interpret and use in determining patient care," they write.
The findings may also have consequences for studies comparing the relative safety of various cardiac interventions, such as angioplasty versus bypass surgery.
If the researchers "are using the wrong threshold, it may make cardiac surgery look a lot worse than it is," said Dr. Devereaux, a cardiologist and director of perioperative care at McMaster. "I think this will have a substantial impact on clinical trials going forward."
The study was done using one particular troponin test - Abbott Laboratories' Architect Stat.
However, Dr. Devereaux joked that he would bet his house that the same problem applies to other troponin tests.
"A lot of people will say that we clearly need to revise the guidelines. These are not credible," he said.
Different groups have proposed different levels of troponin as a warning sign for when prognostically important myocardial damage has occurred, all with little hard evidence to back up their recommendations, even though about 2 million adults undergo heart surgery worldwide each year.
The data in the VISION study came from 24 hospitals in a dozen countries. Levels of the heart-muscle protein were measured before surgery, three to 12 hours after each operation and on days two and three.
Within 24 hours of surgery, 97.5% of patients had a peak troponin level in excess of 260 ng/L, which is more than 10 times the upper reference limit for the Abbott test; 89.4% had a level of at least 910 ng/L and 74.7% had a reading of at least 1,820 ng/L, which is at least 70 times greater.
But only 2.1% of the patients had died at 30 days and only 2.9% had experienced a major vascular complication such as a heart attack, stroke or life-threatening blood clot.
The odds of death within 30 days didn't increase until the troponin level hit 5,670 ng/L among patients with isolated bypass grafting or valve repair, as measured within a day after surgery. On day two or three, the threshold for an increased risk of death was 1,522 ng/L, which is 59 times the reference limit.
For the other types of cardiac surgery, the thresholds were 12,981 ng/L and 2,503 ng/L, respectively.
"There really is a big distinction between what happens in the first 24 hours and there's another threshold on days two and three after surgery," said Dr. Devereaux. "Even on day three, the thresholds are not back to normal. So the timing is important. It's not just the first 24 hours. It also extends at least out to 72 hours."
The risk of a major vascular complication within 30 days of surgery didn't increase until troponin levels hit 4,184 ng/L on day one for those undergoing bypass or valve replacement, and 9,654 ng/L for patients who had undergone other cardiac surgeries.
SOURCE: https://bit.ly/3HtnjuK and https://bit.ly/3IqVMeV The New England Journal of Medicine, online March 2, 2022.
By Gene Emery
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