The damage to the heart caused by a myocardial infarction is not just a result of ischemia caused by the blocked artery but is also brought about by bleeding in the myocardium after the artery has been opened, a new study suggests.
This observation is leading to new approaches to limiting infarct size and treating MI.
“In MI treatment, we have always focused on opening up the artery as quickly as possible to limit the myocardial damage caused by ischemia,” the study’s senior author, Rohan Dharmakumar, PhD, Indiana University, Indianapolis, told this news organization.
“We are pursuing a completely new approach focusing on limiting the damage after revascularization,” he said. “We are totally rethinking what a myocardial infarction is – what causes the injury and the time course of the injury – our results suggest that it’s not just ischemic damage and a lot of the harm is caused by hemorrhage after reperfusion.”
It has been known for many years that hemorrhage is often seen in the myocardium in large MIs, but it has not been established before now whether it contributes to the injury or not, Dr. Dharmakumar explained.
“This study was done to look at that – and we found that the hemorrhage drives a second layer of injury on top of the ischemia.”
Dr. Dharmakumar said this hemorrhage is part of the phenomenon known as reperfusion injury. “This has been known to exist for many years, but we haven’t fully understood all the factors contributing to it. Our results suggest that hemorrhage is a major component of reperfusion injury – probably the dominant factor,” he said.
The researchers are now working on therapeutic approaches to try to prevent this hemorrhage and/or to minimize its effect.
“We are studying how hemorrhage drives damage and how to block these biological processes,” Dr. Dharmakumar said. “Our studies suggest that hemorrhage could account for up to half of the damage caused by a myocardial infarction. If we can limit that, we should be able to reduce the size of the infarct and this should translate into better long-term outcomes.
“I’m very excited about these results,” he added. “We are already seeing a remarkable improvement in animal models with some of the potential therapeutic approaches we are working on.”
The current study is published in the January 2022 issue of the Journal of the American College of Cardiology (JACC).
The authors explain that it is now recognized that reperfusion injury can contribute to increasing infarct size, which they refer to as “infarct surge.” Previous studies have also shown that reperfusion injury can contribute to as much as 50% of the final infarct size, but the factors contributing to the observed variability are not known, and previous attempts to limit infarct surge from reperfusion injury have failed.
They noted that after reperfusion, microvessels can remain obstructed, resulting in intramyocardial hemorrhage. They conducted the current study to investigate whether such hemorrhage causes expansion of the infarct.
They studied 70 patients with ST-segment elevation MI who were categorized with cardiovascular MRI to have intramyocardial hemorrhage or not following primary PCI, and for whom serial cardiac troponin measures were used to assess infarct size.
Results showed that while troponin levels were not different before reperfusion, patients with intramyocardial hemorrhage had significantly higher cardiac troponin levels after reperfusion and these levels peaked earlier than in patients without hemorrhage.
In animal models, those with intramyocardial hemorrhage had a more rapid expansion of myocardial necrosis than did those without hemorrhage, and within 72 hours of reperfusion, a fourfold greater loss in salvageable myocardium was evident in hemorrhagic MIs.
“We have shown that damage to the heart continues after revascularization as measured by rapidly increasing troponin levels in the hearts that have had a hemorrhage,” Dr. Dharmakumar said.
“Hemorrhage in the myocardium was associated with larger infarctions, and in infarcts causing the same area of myocardium to be at risk, those with hemorrhage after revascularization lost a lot more of the salvageable myocardium than those without hemorrhage,” he added.
Dr. Dharmakumar estimates that such hemorrhage occurs in about half of MIs after revascularization, with risk factors including male gender, anterior wall MIs, and smoking.
He pointed out that previous attempts to treat or prevent reperfusion injury have not been successful, probably because they have not been addressing the key mechanism. “We have not been looking at hemorrhage in this regard until now. This is because it is only recently that we have had the tools to be able to identify hemorrhage in the heart with the use of cardiac MRI.”