Acute mechanical cardiac support/RVAD: Abiomed Impella (RP, RD)
Michael H. Yamashita, MDCM, MPH; Anson Cheung, MD
Division of Cardiovascular Surgery, St. Paul’s Hospital, Vancouver, British Columbia, Canada
Right heart failure is a highly fatal condition and can be more difficult to treat than left heart failure. The Impella RP and RD (Abiomed Inc., Danvers, MA, USA) are temporary right ventricular assist devices (RVADs) that can mechanically support the right heart. The Impella RP (Figure 1) is a 22 Fr microaxial pump mounted on an 11 Fr catheter which is inserted peripherally via the femoral vein and provide flow from the inferior vena cava into the pulmonary artery up to 4.4L/min. The Impella RD (Figure 2) is a 17g, paracardiac pump, inserted via sternotomy providing up to 5.5L/min of flow from the right atrium to the pulmonary artery.
The indication for the Impella RP and RD devices is right ventricular pump failure refractory to medical therapy. Contraindications include biventricular failure or respiratory failure where patients are likely to be better served with extracorporeal membrane oxygenation.
Special imaging requirements include transesophageal echocardiography (TEE) and fluoroscopy which are required for placement of the Impella RP pump. Cardiopulmonary bypass should also be available in case emergency cardiopulmonary support is required to deal with an intraoperative complication or hemodynamic instability of the patient.
Specific Intraoperative Details
A general anesthetic with endotracheal intubation is recommended. A cardiac anesthesiologist is crucial because all of these patients are critically ill and can be very difficult to manage.
Central venous access, an invasive interarterial pressure line and pulmonary artery catheter with oximetry are useful in patient management.
Transesophageal echocardiography is necessary to assess cardiac function, aid in intraoperative management and for final positioning of the Impella device.
Prophylactic cefazolin 2g IV prior to the procedure is recommended. Vancomycin 1g IV can be given to patients with a documented penicillin allergy.
The patient should be prepped and draped in a sterile manner so that access to both groins and the chest is available.
The patient is placed supine on the OR table.
Insertion of the Impella RP
The Impella RP is inserted percutaneously and no cutdown is required.
Intravenous heparin is given to achieve an activated clotting time of 250 seconds.
The femoral vein is punctured with an angiocath needle and a soft J-wire is inserted. A 7 Fr sheath is then inserted into the femoral vein using the Seldinger technique. The J-wire is then exchanged with an 0.035 inch Amplatz Extra Stiff (Cook Medical, Bloomington, IN, USA) wire followed by the insertion of a 24 Fr peel-away sheath into the iliac vein. A balloon-tip catheter (e.g. Swan-Ganz, Edwards Lifesciences Corp., Irvine, CA, USA) is then placed into the sheath. Using fluoroscopy, the catheter is advanced towards the right atrium, floated through the tricuspid valve and into the right pulmonary artery. The Impella guidewire is inserted into the catheter and advanced until the tip is visible in the right pulmonary artery. The catheter is removed and the guidewire is left in the right pulmonary artery. The Impella device is then prepared and back loaded onto the sheath. The Impella is then advanced along the guidewire using TEE and fluoroscopy until it reaches its optimal position with the proximal inlet situated within the inferior vena cava and the distal outlet placed in the main pulmonary artery (Figure 3). The device should be positioned with the outlet 3 cm distal to the pulmonary valve. This is confirmed with TEE. The introducer sheath is peeled away and removed. Hemostasis is achieved by applying gentle pressure to the femoral vein.
When the device is ready for removal, it can be done at the bedside with the application of finger pressure to obtain hemostasis.
Insertion of the Impella RD
Median sternotomy is used to implant the Impella RD. Pericardial retraction sutures are placed to aid in exposure of the right atrium and pulmonary artery.
A dose of intravenous heparin is given to obtain a target activated clotting time of at least 250 seconds.
A purse-string suture with 4-0 prolene is placed on the anterolateral mid right atrium, large enough to accommodate the inflow of the Impella RD. Another purse-string suture with 4-0 prolene is placed on the pulmonary artery, about 2-3 cm distal to the pulmonary valve. This purse-string should be large enough for the outflow to the device. An 11 blade is then used to make a cut in the middle of the right atrial purse string. The cut is further dilated if needed and the inflow of the device is inserted. The purse-string is snug. An 11 blade is then used to make a cut in the pulmonary artery in the middle of the purse-string. The outflow of the device is inserted and the purse-string is controlled. Correct positioning is confirmed by TEE. The device is tuned onto Performance level 2 and support is gradually increased to Performance level 8 or 9 to ensure it is functioning properly. The driveline is secured so that it is exiting the chest at the inferior portion of the incision. The chest is then closed in the usual fashion.
Removal of the Impella RD is preferably done in the OR. The sternum is reopened and the pericardium retracted. Each side of the device is then removed individually and the purse-strings are tied. Hemostasis is obtained and the chest is closed again in the standard manner.
When the correct positioning of the Impella RD or RP is confirmed, it is turned on and gradually the target output is increased to about 5 L/min (Figure 4). Overflowing from the RVAD may result in pulmonary edema in patients with marginal LV function. Final position confirmation should be made with TEE. The patient is then transferred to the medical unit. Anticoagulation with a target partial prothrombin time (PTT) of 45 to 60 seconds should be maintained throughout the duration of Impella support. As well, a pulmonary artery (PA) catheter should be maintained as the PA saturation can be followed to ensure adequate circulatory support. Echocardiograms every 48 hours should be performed to assess cardiac recovery, as well as additional exams in the case of suspected device malfunction or migration. Weaning trials of the Impella can be attempted when the patient’s heart function has recovered. These trials are performed by decreasing the Performance level and monitoring the cardiac indices. If these trials are successful and the patient is stable without support, the Impella can be removed at the bedside or in the OR.