Relying on more than 50 years of data on acute MI with reperfusion therapy, the society has identified the following four stages of progressively worsening myocardial tissue injury:
- Aborted MI (no or minimal myocardial necrosis).
- MI with significant cardiomyocyte necrosis but without microvascular injury.
- Cardiomyocyte necrosis and microvascular dysfunction leading to microvascular obstruction (that is, “no reflow”).
- Cardiomyocyte and microvascular necrosis leading to reperfusion hemorrhage.
The classification is described in an expert consensus statement that was published in the Canadian Journal of Cardiology.
The new classification will allow for better risk stratification and more appropriate treatment and provide refined endpoints for clinical trials and translational research, according to the authors.
Currently, all patients with acute MI receive the same treatment, even though they may have different levels of tissue injury severity, statement author Andreas Kumar, MD, chair of the writing group and associate professor of medicine at Northern Ontario School of Medicine University, Sudbury, said in an interview.
“In some cases, treatment for a mild stage 1 acute MI may be deadly for someone with stage 4 hemorrhagic MI,” said Dr. Kumar.
The classification is based on decades of data. “The initial data were obtained with pathology studies in the 1970s. When cardiac MRI came around, around the year 2000, suddenly there was a noninvasive imaging method where we could investigate patients in vivo,” said Dr. Kumar. “We learned a lot about tissue changes in acute MI. And especially in the last 2 to 5 years, we have learned a lot about hemorrhagic MI. So, this then gave us enough knowledge to come up with this new classification.”
The idea of classifying acute MI came to Dr. Kumar and senior author Rohan Dharmakumar, PhD, executive director of the Krannert Cardiovascular Research Center at Indiana University, Indianapolis, when both were at the University of Toronto.
“This work has been years in the making,” Dr. Dharmakumar said in an interview. “We’ve been thinking about this for a long time, but we needed to get substantial layers of evidence to support the classification. We had a feeling about these stages for a long time, but that feeling needed to be substantiated.”
In 2022, Dr. Dharmakumar and Dr. Kumar observed that damage to the heart from MI was not only a result of ischemia caused by a blocked artery, but also a result of bleeding in the myocardium after the artery had been opened. Their findings were published in the Journal of the American College of Cardiology.
The author of an accompanying editorial lauded the investigators “for providing new, mechanistic insights into a difficult clinical problem that has an unmet therapeutic need.”
“Hemorrhagic MI is a very dangerous injury because hemorrhage itself causes a lot of problems,” said Dr. Kumar. “We reported that there is infarct expansion after reperfusion, so once you open up the vessel, the heart attack actually gets larger. We also showed that the remodeling of these hearts is worse. These patients take a second hit with hemorrhage occurring in the myocardium.”