ROCHESTER, Minn. — With only a 50% survival rate, the heart attack complication known as cardiogenic shock is one of the direst challenges faced by emergency room and ICU clinicians.

A dangerous sudden worsening in which the left ventricle of the heart becomes too weakened to pump blood, cardiogenic shock can be temporarily assisted during emergency procedures by either medicines or one of two mechanical catheterization methods.

One of these, an intra-aortic balloon that rapidly inflates and deflates to sustain blood pressure and mimic the pumping of the heart, has been around since the mid 1960s. Though it is of uncertain benefit over medicines according to a large so-called meta-analysis from 2015, it has been studied widely.

Both have become superseded of late by the Impella, a sophisticated, $25,000 interventional radiology device manufactured by Abiomed of Massachusetts.

A seemingly ingenuous intravenous blood-flow assistance machine, Impella acts as sort of a miniature airplane propeller built into a catheter inserted through the femoral artery, one capable of sucking blood upward from a weakened lower left chamber, then spraying it into the aorta above.

As most devices are, when Impella first came onto the market for people undergoing complex stent procedures, it was fast-tracked through the FDA's so-called 510k process as comparable to previously tested devices, based on trials showing blood pressure went up while in use. When in 2015 its use was expanded to procedures during cardiogenic shock, the manufacturers obtained this new indication with just two small trials showing it raised blood pressure.

Did critically ill patients treated with Impella survive the procedure more frequently than those receiving the previous technology?

No one knew.

Until this week, that is, when clinicians from Mayo Clinic, Yale University, UCSF and Washington University published findings in the Journal of the American Medical Association showing that among patients undergoing interventional radiology for heart attack followed by cardiogenic shock, those assisted with Impella died 11 percent more often (45% of the time versus 34% of the time), and experienced major bleeding 15% more often (31% of the time versus 16% of the time), than those receiving the older technology.

The findings had originally been announced at the American Heart Association meeting in November, and their implications are great; as of 2017, over 50,000 patients have undergone procedures assisted by the Impella device, as many as a third of those for cardiogenic shock.

"There could be real harm that's going on with this device," says Dr. Nihar Desai of Yale University in an interview with Forum News Service. "Our analysis would indicate that there is a substantial increase in mortality and major bleeding complications."

Dr. Nihar Desai, Submitted photo.
Dr. Nihar Desai, Submitted photo.

Desai believes the device, while effective under the highly controlled conditions found within a manufacturer-sponsored clinical trial, is possibly a bridge too far in the real-world setting of differing clinicians, within differing medical centers, treating all patients severely weakened by cardiogenic shock.

"The bleeding is a big clinical issue," he says. "Patients that suffer major bleeding in the setting of a heart attack and with shock do much worse," he said.

Desai believes the Impella likely causes excess bleeding and death because it is wider in diameter than its predecessor device, not only causing bleeding at the point of insertion but obstructing blood flow to the leg. He says that a spinning propeller within the Impella likely further weakens patients.

"It sits in the left ventricle and has a propeller and you can imagine all the red blood cells that get torn just getting hit by the propeller," he says. "During the procedures you'll see the hemoglobin just go down and down and down. At some point you say 'we have to transfuse them.' That in and of itself is associated with all kinds of downstream consequences. ...You have an individual that's incredibly sick, with a major insult to their heart function. If you add one more adverse event, whether that be bleeding, limb ischemia, stroke, renal failure — any additional thing that happens — puts the patient in an extra precarious position."

Impella manufacturer Abiomed released a letter for physicians on Tuesday Feb. 11, asserting that the JAMA findings are observational data that can only prove an association, not cause and effect, which the authors readily admit. Abiomed added that the patients undergoing the procedures in their study were sicker than is representative. The manufacturer also highlighted clinical trials now underway to address the safety question.

A Mayo Clinic coauthor says Impella may have been widely embraced because heart attack followed by shock has such a dire outcome.

"The idea of doing nothing sometimes may be difficult for clinicians," says Dr. Nilay Shah, associate professor of Health Services Research. Shah believes their findings illustrate the limitations of the research supporting many new treatments now being fast-tracked.

Dr. Nilay Shah. Photo courtesy of Mayo Clinic
Dr. Nilay Shah. Photo courtesy of Mayo Clinic

"Broadly, there's this issue with the quality of evidence sometimes concerning devices," he says. "One of the focuses of the (2016 FDA expediation legislation) 21st Century Cures Act is to use more real world data. ... Sometimes in a trial the sickest are excluded, or the physicians are more experienced. This really does reflect the real-world experience of the device."