Case Review: What’s an Impella?
Recently I transported a patient in cardiogenic shock who had an Impella device in situ. A week later I did it again. Since I always thought an Impella was a type of antelope (actually, that’s an impala; it belongs to the ungulate family), I was caught off guard and more than a little nervous as I arrived in the cardiac ICU. I thought it might be helpful to dig into these futuristic devices, as word on the street is that we will be moving more and more LVAD patients as IABP falls out of favor and ECMO becomes increasingly popular.
What is an Impella LVAD?
A percutaneous left ventricular assist device, the Impella is a medical device that supports left ventricular function. Let’s break it down:
Percutaneous—The device is placed in a cath lab with echo-confirmation via an arterial cutdown of the femoral artery.
The catheter—It is a catheter powered by an external machine that “impels” blood from the left ventricle into the proximal aorta.
The impeller—An impeller is basically a propeller. The difference between the two isn’t really important unless you engineer LVADs. Functioning like a swimming pool pump, it has an inlet (in the LV) and an outlet (in the proximal aorta) and is capable of pumping five liters of blood a minute through the left ventricular outflow tract. It is continuous flow, and unlike an IABP doesn’t cycle or require synchronization with the heart.
LVAD—Used in patients with very low (less than 20%) left ventricular ejection fractions, these devices assist cardiac output in a ventricle that is too sick to provide adequate stroke volume. While some LV function is required, the Impella can nearly entirely compensate for a failed left ventricle in a resting patient.
Why Not IABP?
IABPs decrease systolic aortic pressures, which facilitates improved stroke volume. They also improve coronary and cerebral perfusion. What they don’t do is rest the left ventricle by offloading work. LVADs actually reduce the need for stroke volume by doing the work of the LV themselves, rather than just improving conditions for LV function.
Who Gets an Impella?
The Impella is a bridge therapy. It is installed to address hemodynamics until a more permanent solution can be found. The manufacturer, Abiomed, mentions that Impellas should be used only for six hours, though many intensivists use them for days at a time.
The bridge starts at heart failure and ends at either ECMO, implantable LVAD or heart transplant. ECMO circulates and oxygenates blood so a sick heart can rest and recover, while transplant is the only option when recovery is not anticipated.
Patients may have suffered a massive LV myocardial infarction, recently undergone open cardiac surgery or be diagnosed with myocarditis, dilated cardiomyopathies or rare conditions like sarcoidosis. Myocardial contusions could also recover while being bridged.
Who Doesn’t get an Impella?
Patients who are not suitable candidates for ECMO or transplant should not receive Impella devices. Patients with severe aortic valve disease, like aortic stenosis, are not candidates. Patients must be anticoagulated, so those who have bleeding would be relatively contraindicated.
Transport Considerations
A shared care model is essential to safe transport of patients with Impella devices. On both recent transports, an RN with extensive experience working in the cardiac ICU and knowledge of the Impella device and operating unit accompanied the patient. The role of the RN was to monitor the Impella unit for proper function. This role cannot be replaced by Ornge currently, though potentially select paramedics could be trained in Impella use as they are IABP use. Both patients had in-situ Swan-Ganz catheters, which require constant pressure transducing and monitoring by the RN, as this is no longer in CCP scope.
A physician also accompanied the patient in both circumstances. The physician on the first transport was a third-year resident in anesthesia undergoing training in the cardiac ICU. The physician on the second transport was a first-year resident in cardiovascular surgery. The function of the resident was to reposition the Impella blindly should it be displaced during transport. This is done by comparing the measurement of the catheter at the skin incision before transport and either pulling back or sliding forward the catheter to its original position. Ideally this would be confirmed with ultrasonography, but this capability is currently unavailable in our system. It might be possible for this role to be assigned to other team members.
Flight paramedics monitored the infusions, titrated as needed and managed mechanical ventilation. Infusions included dobutamine, norepinephrine, vasopressin, fentanyl, midazolam, heparin and amiodarone. Bolus doses of sedatives and weaning of medication infusions were required to achieve optimal sedation and mean arterial pressure.
In the United States specially trained transport crews have moved patients with Impella devices in situ without physician escort. Given the limited space and seating on some vehicles, careful consideration and advanced planning and collaboration are required to determine necessary escorts.
Assessment and plan—Extremity pulses were not present, as there was virtually no systolic function. A hum was heard on heart auscultation. Blood pressure was approximately 85/70 on both transports. Narrow pulse pressure is expected. A MAP of 65–80 is desired.
Equipment—Three infusion pumps were in use (eight channels), and a fourth was available in case of failure. An LTV 1200 ventilator was used. We also used the Impella device control unit, which is tethered to the patient. The Impella device was secured to its stand for travel from sending unit to ambulance and by wheelchair from ambulance to receiving unit. The bracket on the Impella is not suitable for attachment to the cot. Two invasive pressure channels are required to transduce an arterial line and a Swan-Ganz catheter.
Transportation—Both transports involved a Crestline wide-body truck with center-mount power cot and outfitted with two jump seats, one right-sided bench seat and one flip-down seat. The RN occupied the side-facing jump seat and monitored the Impella device, which was secured in a makeshift fashion to the IABP bracket using a strap. The physician occupied the right bench seat. The paramedic occupied the aft-facing jump seat. The Impella has 60 minutes of battery time and requires a three-pronged 120-volt outlet.
Adverse events—No adverse events occurred on these two transports. A literature search revealed a paucity of reports but no adverse events reported.
Catastrophe—If the Impella control unit migrates away from the patient, tension will be applied to the tethered catheter and could potentially displace the Impella catheter from the heart. If this happens, the Impella flow should be stopped. Medications and, if necessary, CPR should be used to support cardiac output. Great care was taken to ensure the Impella control unit did not migrate from the patient. This is done similarly with the IABP.
After a decade working as a helicopter paramedic, Blair Bigham, MD, MSC, ACPF, completed medical school in Ontario, Canada, where he is now a resident physician in the emergency department. After completing his Master of Science at the University of Toronto, Blair worked as an associate scientist at St Michael’s Hospital in the fields of resuscitation science, knowledge translation and patient safety. He has authored over 30 scientific articles, led major national projects to advance prehospital research and participated in multiple collaboratives, including the Resuscitation Outcomes Consortium. He has taught and mentored clinical and academic paramedics and loves his new role teaching medical students. He serves as a volunteer on the board of directors for the MedicAlert Foundation of Canada and is a task force member for the International Liaison Committee on Resuscitation. Blair has signed his organ donor card; have you? E-mail him at blair.bigham@medportal.ca; follow on Twitter @BlairBigham.
