Use of the Impella CP microaxial flow pump plus a 30-minute delay to coronary angioplasty did not significantly reduce heart damage compared with no left ventricular (LV) support in patients with ST-segment elevation myocardial infarction (STEMI) who are not experiencing cardiogenic shock, according to a new study.

However, results from the STEMI-Door to Unload (STEMI-DTU) trial did establish the feasibility of the intervention and point toward subgroups that could benefit from the protocol in a subsequent trial, said Navin Kapur, MD, an interventional cardiologist at Tufts Medicine in Boston and first author on the study.

“My perspective is that it turned out great because we learned an immense amount. The trial sets us up for even more knowledge,” he said. Kapur last year joined J&J MedTech, maker of the Impella CP, as global chief medical and scientific officer and executive VP in heart recovery.

The study was presented at the American College of Cardiology (ACC) Scientific Session 2026 and simultaneously published in JACC.

Time Is Muscle

The current standard of care for STEMI involves rapidly restoring blood flow to the coronary artery via percutaneous coronary intervention (PCI) to re-establish an oxygen supply. However, even with the best care, for those older than 65 years presenting with their first acute MI, 10% will die in the hospital, 34% will experience in-hospital heart failure, and 76% will have heart failure within 5 years. Two key variables that contribute to worse outcomes are the extent of damaged heart muscle and the duration of ischemia.

While methods for resolving the arterial blockage have advanced over the years, little progress has been made toward preventing tissue death during the procedure.

“We’re good at opening the infarcted artery. We’re not good at salvaging myocardium,” said Gregg Stone, MD, a professor of cardiology and population health sciences at Icahn School of Medicine at Mount Sinai in New York City and a co-author of the trial.

Preclinical studies in animals demonstrated that LV unloading reduces myocardial ischemia and promotes cardioprotective signaling. In pigs, the use of a microaxial flow pump for 30 minutes before reperfusion reduced heart damage by almost 50% compared to immediate reperfusion alone. A pilot study in STEMI patients without cardiogenic shock confirmed safety and feasibility of the approach in humans.

A Neutral Result

In the STEMI-DTU trial, Kapur, Stone, and collaborators randomly assigned 527 patients to either Impella CP with a delay or immediate PCI without mechanical support. To qualify for inclusion, patients must have presented with anterior STEMI as their first MI between 1 and 6 hours after onset of chest pain. Researchers tracked infarct size as a percentage of LV mass as the primary outcome measure.

The mean infarct size differed little between the treatment and control groups in the intent-to-treat population — 30.8% and 31.9%, respectively, at 3-5 days following the procedure. Similarly, in the per-protocol population, infarct size was 31.8% for patients in the treatment group and 33.7% in the control group.

“Our combination of putting in a heart pump and waiting 30 minutes did increase our total ischemic time because it delayed the PCI,” Kapur said. Researchers were concerned about whether this would increase infarct size, and while it did not, they also did not see a significant reduction in infarct size, he added.

Subgroups for Future Study

One factor that may have contributed to the discrepancy in results between STEMI-DTU and the preclinical studies was that many patients in the trial had high blood pressure, Kapur noted.

“Most of the preclinical studies were done under conditions where there was normotensive or hypotensive blood pressure, and hypertension can negatively impact the efficiency of the pump,” Kapur said.

When his team looked closely at subgroups, they found that high cardiac filling pressures, low pulse pressures, beta-blockers, and age over 61 favored the treatment intervention. “All of that informs our ability to develop and execute the next study in the series,” he said.

Manesh Patel, MD, president-elect of the American Heart Association and chief of the Division of Cardiology at Duke University School of Medicine in Durham, North Carolina, said even though the use of Impella with delayed PCI didn’t reduce the infarct size, it also didn’t seem to increase the risk to the patient.

Impella heart pumps have faced a series of recalls and safety alerts, most recently in April when the FDA recalled purge cassettes sold with certain models including the Impella CP.

Studies such as STEMI-DTU and CHIP-BCIS3, which did not show a benefit for use of the Impella CP device in high-risk planned PCI, “will make us carefully think about the patient types we’re putting these support devices in,” said Patel, who was not involved in either trial. “These two studies certainly tell us that acute MIs, without shock, are not clearly a place to use the device.”

Kapur reported being an employee of J&J MedTech. Stone reported receiving grants from Shockwave, Biosense Webster, BioVentrix, Abbott, Abiomed/J&J Medtech Heart Recovery, Cardiovascular Systems Inc, Phillips, Pulnovo, V-Wave, and PCORI. Stone also reported receiving consulting fees from MillenniaBiopharma, Apollo Therapeutics, Cardiac Success, Occlutech, Oxitope, Elixir, Impulse Dynamics, Asceneuron, Myochron, Vesalio, Heartflow, Colibri, BioVentrix, Abbott, Remote Cardiac Enablement, Valfix, ZOLL, Shockwave, Adona Medical, HighLife, Elucid Bio, Aria, Alleviant, FBR Medical, MedHub, Biotyx Medical, and Ablative Solutions. Stone reported receiving payment honoraria from Boehringer Ingelheim and owning stock or stock options in Cardiac Success, Ancora, Cagent, Applied Therapeutics, BioStar family of funds, SpectraWAVE, Orchestra BioMED, Aria, Valfix, Xenter, and Vascentis. Patel reported receiving grants or consulting fees from Bayer Healthcare, Heartflow, Jansen, Johnson and Johnson, Novartis, and PCORI.

Catherine Shaffer is a freelance science and medical writer with a background in molecular biology and pharmaceutical research. Her work has appeared extensively in scientific trade and mainstream publications and on public radio.

Melissa Foster contributed to this report.