Impella CP Heart Pump Fails to Reduce Infarct Size in Major STEMI Trial
Key Insights
The STEMI (search)-Door to Unload trial found that using the Impella CP (search) microaxial flow pump before cardiac stenting did not significantly reduce heart damage in severe heart attack patients without cardiogenic shock (search).
The study analyzed 527 patients across 55 emergency rooms in five countries, showing infarct size was similar between Impella and immediate PCI groups (30.8% vs 31.9% of left ventricular mass).
Bleeding and vascular complications occurred more frequently in the Impella group (30.8%), exceeding the safety performance goal of 26.5%.
The first major clinical trial testing whether a microaxial heart pump can reduce heart damage in severe heart attack patients has failed to meet its primary endpoint, according to results presented at the American College of Cardiology Scientific Sessions and published simultaneously in the Journal of the American College of Cardiology.
The STEMI (search)-Door to Unload (DTU) trial, led by Dr. Gregg W. Stone from the Icahn School of Medicine (search) at Mount Sinai (search), investigated whether using the Impella CP (search) device before and during cardiac stenting procedures could reduce infarct size in patients with ST-segment elevation myocardial infarction (search) (STEMI) who did not have cardiogenic shock (search).
Study Design and Patient Population
The randomized controlled trial enrolled 527 patients with confirmed anterior STEMI (search) across 55 emergency rooms in five countries between December 2019 and September 2024. All patients arrived within five hours of heart attack onset and had blocked arteries involving the front wall of the heart, a location that typically causes large heart attacks.
Patients were randomized to either receive the Impella CP (search) device with delayed percutaneous coronary intervention (PCI) or immediate PCI without the device. The Impella CP, manufactured by Abiomed, is an FDA-approved catheter-based percutaneous microaxial heart pump that ejects blood from the heart's pumping chamber to the body.
Primary Endpoint Results
The trial's primary effectiveness endpoint was reduction in infarct size measured by cardiac MRI three to five days after the procedure. Infarct size expressed as a percentage of total left ventricular mass was 30.8% ± 16.2% in the Impella group compared to 31.9% ± 16.9% in the immediate PCI group. This difference did not reach statistical significance.
"Unfortunately, infarct size, the primary endpoint of the study, was not reduced, and as expected, there were bleeding complications from the device," Dr. Stone explained. "Thus, while the microaxial flow pump is life-saving in patients with cardiogenic shock (search), at the present time we do not recommend its routine use in patients with evolving heart attack without shock."
Safety Concerns
The primary safety endpoint examined rates of major bleeding and major vascular complications. Bleeding and vascular complications occurred in 30.8% of patients in the Impella CP (search) group, exceeding the predetermined performance goal of 26.5%. Differences in cardiovascular mortality between treatment and control groups were not statistically significant.
Clinical Context and Rationale
STEMI (search) represents the most severe, life-threatening type of heart attack, caused by sudden blockage of a major coronary artery (search) that stops blood flow to a large portion of heart muscle. These patients require urgent PCI to restore blood flow and prevent or limit heart muscle damage.
"In medical school we learned that 'time is muscle'—and during a heart attack, every minute that the artery is not open matters," Dr. Stone noted. "Interventional cardiologists are great at unblocking arteries with stents during this medical emergency, a procedure that saves lives, but we are far less effective at reducing the size of infarct for a variety of reasons. Because of this, many patients have large heart attacks and either don't survive or develop heart failure (search)."
For decades, experimental studies suggested that flow pumps could rest the heart, improve blood flow to heart muscle, and reduce heart damage through complex mechanisms. However, the DTU trial represents the first pivotal trial in 30 years to test this hypothesis in a randomized controlled setting.
Potential Benefits Despite Negative Primary Endpoint
Despite failing to meet its primary endpoint, researchers identified potentially important findings. Notably, infarct size among Impella patients did not increase despite an approximately 47-minute delay in treatment caused by device insertion.
"While infarct size with the Impella was not significantly decreased, it is important to note that neither was it increased, despite an increase in total ischemic time of approximately 47 minutes," Dr. Stone observed. "This suggests that the device did have beneficial effects on myocardial recovery."
Future Research Directions
The researchers suggest that combining the Impella approach with pharmacologic therapies may prove synergistic in high-risk patients. Dr. Stone noted that intravenous medications such as nitroglycerin or beta blockers (search) may decrease blood pressure while the heart pump is in place, potentially improving its efficiency.
"This approach coupled with pharmacologic or other therapies may be synergistic and improve outcomes in high-risk non-shock patients with heart attacks," Dr. Stone said. "That is the future direction for new studies."
The study was funded by Abiomed, the manufacturer of the Impella CP (search) device. Only one therapy—supersaturated oxygen (search)—has previously been shown to reduce infarct size in STEMI (search) patients, according to the researchers.