An Impella is a tiny heart pump that sits inside the heart and helps move blood when the heart is too weak to do the job on its own. About the size of a pencil tip at its working end, it’s threaded through a blood vessel and positioned so it can continuously pull blood out of the heart’s main pumping chamber (the left ventricle) and push it into the aorta, the body’s largest artery. It’s used as a temporary support device, typically for a few days, while the heart recovers from a crisis like a massive heart attack or while doctors perform a high-risk procedure.
How the Pump Works
The Impella’s design traces back to a surprisingly old idea: the Archimedes screw, a rotating helical device invented over 2,000 years ago to raise water. Modern engineers miniaturized that concept into a tiny spinning impeller attached to a motor small enough to ride on the tip of a catheter. Once the device is activated, the impeller spins at high speed, drawing blood in through an inlet port that sits inside the left ventricle and expelling it through an outlet port that sits in the aorta.
This does two things at once. It delivers oxygenated blood to the rest of the body, and it “unloads” the left ventricle, meaning the heart doesn’t have to work as hard to push blood out. That reduced workload gives damaged heart muscle a chance to rest and potentially recover.
Different Models for Different Situations
Impella devices come in several sizes, and the main difference between them is how much blood they can move per minute:
- Impella 2.5: Delivers up to 2.5 liters per minute. The smallest model, designed mainly for use during high-risk heart procedures.
- Impella CP: Delivers up to 3.3 liters per minute. A step up in support, used for both procedures and cardiogenic shock.
- Impella 5.0 and LD: Deliver up to 5.0 liters per minute. These provide near-full cardiac output and are reserved for more severe heart failure.
- Impella RP: Supports the right side of the heart rather than the left, for patients whose right ventricle is failing.
For context, a healthy heart pumps about 5 liters of blood per minute at rest. So the larger Impella models can essentially take over most of the heart’s pumping work, while the smaller ones provide partial support.
When Doctors Use It
The Impella is FDA-approved for two main scenarios. The first is during high-risk percutaneous coronary interventions (stent procedures done through a catheter). When a patient has severe coronary artery disease and a weakened heart, opening a blocked artery can temporarily destabilize blood flow. The Impella 2.5 keeps blood circulating during these procedures, acting as a safety net. It’s approved for up to 6 hours of support in this setting.
The second, more urgent scenario is cardiogenic shock, a life-threatening condition where the heart suddenly can’t pump enough blood to sustain the body’s organs. This most commonly happens right after a major heart attack or open heart surgery. The Impella 2.5 and CP are approved for up to 4 days of support in cardiogenic shock, while the 5.0 and LD models can run for up to 6 days. The goal is to buy time: stabilize circulation, let the heart recover, and give doctors a window to assess how much heart function remains.
The DanGer Shock trial, one of the largest randomized studies of the device, found that adding Impella support to standard treatment reduced the risk of death at 180 days in patients experiencing cardiogenic shock after a major heart attack. That said, cardiogenic shock remains extremely dangerous. Registry data from Japan involving over 1,700 patients showed in-hospital mortality rates around 44%, reflecting just how sick these patients are when they receive the device.
How It’s Placed
Placing an Impella doesn’t require open surgery. The smaller models (2.5 and CP) are inserted through a large artery, most commonly the femoral artery in the groin, using a sheath that’s about 13 to 14 French in diameter (roughly 4 to 5 millimeters). The catheter is then guided up through the aorta, across the aortic valve, and into the left ventricle. Doctors use imaging, typically fluoroscopy (a live X-ray), to confirm the device is positioned correctly.
For larger models like the 5.0, the femoral artery may be too small to accommodate the catheter. In these cases, doctors can access the axillary artery near the shoulder instead. This approach can be done percutaneously (through a needle puncture rather than a surgical cut) using either a transpectoral approach through the chest wall or an infrapectoral approach through the armpit. The transpectoral route, similar in location to where a pacemaker would be placed, has become the more widely adopted technique.
Risks and Complications
Because the Impella involves threading a mechanical pump through blood vessels and across a heart valve, it carries real risks. The most commonly reported complications include:
- Major bleeding: Reported in 0% to 12.5% of patients across studies, with the wide range reflecting differences in patient populations and how “major” bleeding is defined. The large arterial access site is a primary source of bleeding risk.
- Hemolysis: The spinning impeller can physically damage red blood cells as they pass through. This occurs in roughly 0.2% to 3.7% of patients.
- Limb ischemia: The catheter sitting in the femoral artery can reduce blood flow to the leg, potentially requiring intervention in about 3% of cases.
These risks are managed through continuous monitoring in an intensive care unit. Medical teams track blood markers for red blood cell damage, check pulses in the legs, and watch the access site for signs of bleeding throughout the duration of support.
Coming Off the Device
Weaning a patient off the Impella is a careful, stepwise process rather than a sudden removal. Before doctors consider turning it down, the patient needs to be stable without medications that stimulate the heart (called inotropes), and any acute organ damage from the initial crisis should be resolving. Blocked arteries and valve problems need to be addressed first, while the Impella is still providing circulatory support.
Doctors gradually reduce the pump speed, essentially asking the heart to take on more of the workload, and monitor how well it responds. One challenge during this process is that the Impella itself changes how blood flows through the heart, which can mask underlying problems. For example, a leaky mitral valve may not show up on imaging while the pump is running at full speed. Reducing the pump to a lower setting during a “weaning trial” can reveal these hidden issues before the device is fully removed.
If the heart doesn’t recover enough to sustain circulation on its own, the medical team reassesses. Options at that point may include a more durable mechanical heart pump or evaluation for heart transplant. The Impella is always intended as a bridge, not a permanent solution.