Implantation of TCI Heartmate Left Ventricular Assist System: Keys to Success
Preparation of the pump
- The pump is assembled and calibrated on the back table by an assistant, as detailed in the instruction manual. This includes:
- Preclotting valved inflow and outflow conduits with the patients non-heparinized blood.
- Baking the outflow graft in albumin or plasma.
- Filling the pump with saline solution.
|The Heartmate™ Pump without the dacron outflow graft
Preperitoneal pocket construction
- A midline incision is made extending from the sternal notch to the umbilicus with division of the linea alba.
- Sternotomy is performed prior to creation of the pocket in order to have quick access to the heart in the event of hemodynamic instability.
- The preperitoneal fat is dissected from the undersurface of the rectus sheath using low power cautery. Superiorly the dissection is carried to the undersurface of the diaphragm until the apex of the heart can be palpated just lateral to the inferior phrenic artery and vein. These vessels should be ligated to avoid injury during transdiaphragmatic placement of the inflow cannula, as bleeding from this site is difficult to visualize after device insertion. If the peritoneum is entered during the dissection, the defect is repaired with prolene sutures to prevent herniation of abdominal contents. If the desired plane is difficult to develop, the rectus sheath can be entered and the posterior sheath left as a patch overlying the peritoneum.
- This dissection must be carried well back into the retroperitoneum (posterior to the spleen) to allow adequate mobilization to fit the device preperitoneally
- A plastic model of the device can be inserted into the pocket to assess whether enough room is available for the device.
- The preperitoneal space to the right of the linea alba is also opened for about 2 to 3 cm to facilitate closure of the linea alba at the completion of the case and allow room for the device outflow valve and graft conduit.
- The muscular attachment of the right hemidiaphragm to the medial edge of the sternum must also be divided to allow room for the graft.
Driveline tunnel creation
- The driveline usually exits in the right lower quadrant, approximately at McBurney's point.
- A small incision is made (approx. 85% of the driveline diameter), and a tunneling device passed subcutaneously inferiorly around the umbilicus, and then into the pocket through the rectus sheath at it's most inferior aspect. This entry point into the pocket should later be examined to make sure there is no bleeding from the rectus muscle or an arterial branch. The tunneler is then screwed onto the end of the driveline, which is then pulled back through the tunnel to the skin.
- The drive line is not sutured or otherwise attached to the skin.
Attaching the apical cuff and transdiaphragmatic passage of the inflow cannula
- A standard dose of Heparin is given and cardiopulmonary bypass instituted using standard aortic and dual stage venous cannulae. The aorta is not crossclamped although it can be.
- The apex of the left ventricle is elevated.
- There are two approaches that can be used at this juncture: 1) the apical cuff sutures are placed first and then the myocardium cored out or 2) the hole is first made with the coring device and then the apical cuff sutures placed.
- An apical vent is passed into the left ventricle. The apical vent will serve as the center of the sight of insertion of the apical cuff. Pledgeted 2-0 ethibond sutures are placed circumferentially partial thickness into the myocardium then passed through the sewing ring of the apical cuff. The coring device is then used to cut a hole in the myocardium and the sutures are secured.
- If necessary the heart can be vented through the right superior pulmonary vein. The coring device is used to make the hole in the apex. This technique is particularly useful if there is ventricular thrombus or the myocardium is friable from recent infarction.
- To core the apical hole the ventricle is distended and the coring knife is aimed towards the lateral wall to avoid entering or positioning the inflow cannula towards the septum. Residual muscle or scar that may impinge on the cannula site is resected. A search for loose mural thrombus is made, adherent thrombus is left in place.
- For either method it is important to ensure that more myocardium is gathered at the perimeter of the sewing circle than at its center. These sutures are deep but not full thickness. If a coronary vessel is lacerated, the next suture should incorporate the bleeding site, as it is very difficult to visualize this area once the device has been attached.
- Once the apical cuff is secure, a cruciate incision in the diaphragm opposite the ventricular apex is made just lateral to the inferior phrenic vessels, and the device inflow cannula is brought into the chest. The inflow cannula is then inserted through the apical cuff until the entire sintered titanium surface is within the cuff. The surgeon should aim the cannula away from the interventricular septum to prevent inflow restriction aspiration of the ventricular septal muscle into the cannula. The dacron tie of the inflow cuff is then secured and an additional plastic band and dacron tie used to reinforce the connection and flatten out the silicone cuff to minimize the risk of aspirating air into the device. Blood is now allowed to passively fill the device and exit via the outflow valve, serving as a vent and de-airing the device.
Anastamosis of the outflow graft to the ascending aorta
- A partial occluding clamp is placed on the right lateral aspect of the ascending aorta and a longitudinal aortotomy performed. The periaortic adventitia is left in place, and a strip of bovine or native pericardium incorporated into the anastomosis.
- The outflow graft is usually cut to a length of 12 to 15 cm. If too long the graft will kink as the chest is closed. Finally the connector from the outflow graft is inspected for thrombus and cleaned.
- If the outflow graft is not attached to the housing of the pump already, make sure the nut to secure it has been placed on the graft prior to anastamosis to the aorta.
- The anastamosis is created with 4-0 Prolene suture. The apex and heel of the anastamosis are reinforced with interrupted 4-0 prolene pledgeted horizontal mattress stitches. These are common sites of postoperative bleeding.
- The outflow graft connector should be clean and free of thrombus. Thrombus can interfere with the creation of a water-tight seal and lead to significant hemorrhage. Bleeding from this connector can be treated by wrapping the entire connector circumferentially with a strip of bovine pericardium, and securing it at multiple sites with heavy silk ties to tamponade the leak.
De-airing the pump
- Large pockets of air are retained in the pump during implant and must be removed prior to initiating complete support.
- Components of the de-airing process include:
- Placing the patient in steep Trendelenburg position
- Volume loading, ventilation and the reduction of CPB flow to move air from the lungs and pump to site of egress.
- Sights for air to escape include
- a purposely loose outflow graft connection
- an 18 gauge needle placed in the outflow graft at its highest point
- a 14 gauge ascending aortic root cannula placed to suction
- A vascular clamp remains on the outflow graft distally. The pump is hand cranked. The housing of the pump is shaken repeatedly to release air. de-airing is continued until no air is seen by TEE and no air exits through the de-airing sites on the outflow graft.
- The outflow connector is tightly screwed together and secured with the heavy ethibond suture supplied with the Heartmate. The 18 gauge needle is removed from the graft and its insertion site closed with a 4-0 prolene.
Starting the pump and weaning from cardiopulmonary bypass
- The field is flooded with saline to prevent aspiration of air through the inflow valved conduit and connector in the case of inadequate pump filling.
- Inotropic support is started before separating from bypass and activating the LVAD. Dobutamine and milrinone are useful inotropes particularly in the presence of pulmonary hypertension, norepinephrine and vasopressing are added to maintain a mean blood pressure greater than 65 mmHg.
- Bypass flow is decreased to 2 L/min, the heart filled with volume and the device started in the fixed mode at 20 cycles per minute. If filling is adequate the rate is increased as cardiopulmonary bypass flow is reduced. The device switched to automatic mode after the cessation of cardiopulmonary bypass.
- Transesophageal echocardiography is used to ensure adequate ventricular decompression with bowing of the septum away from the right ventricle. A bubble study is also performed to rule out a patent foramen ovale, which can result in severe hypoxemia due to a right to left shunt.
- A thermodilution cardiac output is performed and compared to the output from the LVAD. A difference of greater 20% between the right heart output and the measured device output signifies significant aortic regurgitation, which will need to be addressed, by either sewing the noncoronary and right coronary valve leaflets together or oversewing the valve completely.
- Protamine is given and clotting factors used as needed. In the presence of severe coagulopathy the chest may need to be packed open.
- Heartmate LVAS (Left Ventricular Assist System)
- Heartmate VE LVAS (Vented, Electrically powered Left Ventricular Assist System)
Thermocardiosystems Inc.470 Wildwood St.Woburn, MA 01888, 1-781-932-8668
- Bovine pericardium
- Standard Cardiac Instrument Tray
- Other necessary instruments are included with the device
- Ethibond 2-0 with pledgets
- Prolene 4-0 with and without pledgets
Tips & Pitfalls
- The requirement for adequate abdominal domain precludes placement of HeartmateTM LVAS into patients with a body surface area less than approximately 1.5 meter2. In borderline patients where linea alba cannot be closed without excessive tension a 2-mm thick prosthetic PTFE membrane is used to bridge the mid-line defect and facilitate abdominal fascial closure. This may allow for placement of devices into smaller recipients.
- We currently favor preperitoneal placement of the LVAD. Significant morbidity including colonic perforation, small bowel obstruction, diaphragmatic hernia, and wound dehiscence were encountered during the initial experience with an intra-abdominally placed LVAD.
- To decrease the incidence of driveline infections, the driveline tunnel is made as long as possible.
- Transesophageal echocardiography is a useful adjunct during insertion. It can be used to determine the source of hemodynamic problems after insertion (e.g. the presence of a PFO, obstruction of the inflow cannula by the septum).
- Aprotinin is used routinely for both the implant and the explant/tranplant operation. If the patient has previously been exposed to aprotinin it is not infused until the patient is prepared for the the initiation of cardiopulmonary bypass, should an allergic reaction and subsequent cardiovascular collapse occur.
Publication Date: 9-Sep-2005
Last Modified: 7-Oct-2009