Ventricular Assist Devices
Joseph C. Cleveland Jr.
Francis D. Pagani
Indications/ContraindicationsReasons for placement of a left ventricular assist device (LVAD) can generally be grouped into four broad categories. An LVAD can be placed as (1) bridge-to-cardiac transplantation (BTT); (2) destination (or permanent) therapy (DT); (3) recovery of ventricular function; and (4) bridge-to-decision (BTD). The latter two categories (recovery and BTD) essentially share the indications for either BTT or DT patients and are mentioned for completeness.
The specific indications for BTT and DT originated from clinical trials conducted for each indication. Common features for either BTT or DT placement include a patient with advanced heart failure with NYHA Class IV heart failure, an ejection fraction (EF) of <25%, optimal medical management for 45 days, dependence upon intravenous inotropes, or intra-aortic balloon counterpulsation. Objective measures include a measured peak maximal oxygen uptake (VO2 Max) of less than 14 mL/kg/min. Lastly, given the strong association of hospitalizations for heart failure with decreased survival, one or more hospital admissions for heart failure is a frequent metric cited for LVAD placement.
A patient should undergo evaluation for heart transplantation to determine whether the patient undergoes LVAD placement as a BTT or as permanent (DT) therapy. In general, clinical reasons which would deem a patient ineligible for transplant and therefore a DT patient include advanced age (transplant center specific, but usually >65 to 70 years of age), severe lung disease, pulmonary vascular resistance (PVR) >6 Woods units (center-specific criteria also exist), recent malignancy, severe peripheral vascular disease, or other comorbid conditions which might result in suboptimal transplant outcomes. Many of these reasons for deeming a patient ineligible for transplantation are center specific and in the original trials which were conducted for DT, age >65 was the most common reason to select a patient for DT.
The strongest contraindication to receiving an LVAD is severe, irreversible RV failure, as RV failure that complicates LVAD placement is a strong risk factor predicting poor outcomes. While biventricular support is an option, the evaluation of RV function is important and will be covered in preoperative planning. Other contraindications to LVAD placement include other medical conditions which are likely to result in death within 2 years (e.g., concurrent malignancy), patients on ESRD, and patients who are in the
throes of an acute and severe deterioration of clinical status which results in cardiogenic shock (requiring mechanical ventilation or associated with cardiac arrest or postcardiotomy failure to wean from cardiopulmonary bypass) are best served by temporary devices or extracorporeal membrane oxygenation (ECMO). Lastly, concerns with compliance/medication adherence/care of the device serve as strong contraindications to proceeding with device placement until they can be addressed and resolved. This last contraindication is relative and ultimately bespeaks to the need for a thorough multidisciplinary evaluation (including social services) and a selection process for DT that mirrors the process for cardiac transplantation.
throes of an acute and severe deterioration of clinical status which results in cardiogenic shock (requiring mechanical ventilation or associated with cardiac arrest or postcardiotomy failure to wean from cardiopulmonary bypass) are best served by temporary devices or extracorporeal membrane oxygenation (ECMO). Lastly, concerns with compliance/medication adherence/care of the device serve as strong contraindications to proceeding with device placement until they can be addressed and resolved. This last contraindication is relative and ultimately bespeaks to the need for a thorough multidisciplinary evaluation (including social services) and a selection process for DT that mirrors the process for cardiac transplantation.
Preoperative PlanningPatients with advanced heart failure undergoing implantation of an LVAD are typically maintained on inotrope infusions or occasionally mechanical circulatory support (MCS) with an intra-aortic balloon pump or temporary extracorporeal MCS to optimize organ function. It is generally recommended that a pulmonary artery catheter be used to assess hemodynamics prior to LVAD implantation to assist with perioperative decisions regarding therapies to optimize hemodynamics including pulmonary vasodilator therapy with nitric oxide as well as inotropic and vasoconstrictor support. Additionally, an echocardiogram is necessary to assess heart valve function, right ventricular (RV) function, exclude the presence of atrial or ventricular thrombus, and to identify intra-atrial shunts such as a patent foramen ovale. Routine laboratory tests are obtained to assess the degree of renal and hepatic dysfunction and to assess coagulation parameters. Additional testing such as pulmonary function tests, carotid duplex examination, abdominal ultrasound and lower extremity Doppler studies may be necessary to assess the degree of other comorbidities that are present.
SurgeryIntraoperative Preparations
Routine broad-spectrum antibiotics are administered intravenously. In addition to the pulmonary artery catheter, an arterial line and a Foley catheter are inserted. A transesophageal echocardiogram (TEE) is placed for intraoperative assessment of the heart and importantly, to optimize pump speed settings when weaning from cardiopulmonary bypass following LVAD implantation.
Patient Positioning
The general preparation is similar to other cardiac surgical procedures with the patient prepared and draped in the standard sterile fashion. It is essential that consideration be given to preparation of the skin at the planned exit site of the driveline for the LVAD. The patient is typically placed in a supine position.
Technique
A standard median sternotomy is performed and the pericardium is incised and the pericardial incision is carried to the left, along the pericardial reflection to the apex of the LV. Prior to the administration of heparin for cardiopulmonary bypass, the driveline or percutaneous lead of the LVAD is typically tunneled to exit along the anterior axillary line, approximately 2 cm below the costal margin on the right side. Using the tunneling device, the driveline is tunneled through the rectus muscle. The woven polyester portion of the driveline should be completely housed in the subcutaneous tissue 1 to 2 cm from the skin exit site. The pump and driveline are temporarily wrapped in an antibiotic-soaked laparotomy pad. The patient is systemically heparinized.
Cannulation for cardiopulmonary bypass is accomplished with an arterial cannula in the distal ascending aorta or proximal aortic arch. It is important to leave enough length on the aorta for a de-airing cannula and positioning of the outflow graft of the LVAD. A two-stage venous return cannula is used for venous return. Bicaval cannulation is alternatively used if closure of a patent foramen ovale or tricuspid valve repair or replacement is performed concomitant with LVAD implant. The procedure is typically performed on full cardiopulmonary bypass on the beating heart. The heart is elevated and supported with moist laparotomy pads to expose the left ventricle (LV) and apex. Correct positioning of the inflow cannula is essential. It should be parallel to the interventricular septum and directed toward the mitral valve. Depending on the type of LVAD, a cuff or ring is sewn to the LV apex to provide a mechanism to secure the inflow cannula of the LVAD within the LV cavity. A core of LV muscle at the apex is removed to facilitate introduction of the inflow cannula of the LVAD into the LV cavity. CO2 may be infused into the LV cavity to facilitate de-airing of the LV. Passively filling the heart and pump and elevating the apex and gently shaking the ventricle accomplish additional de-airing. The outflow graft of the LVAD is then distended, clamped, and trimmed to proper length. It is crucial to determine the appropriate length of the outflow graft as excess length may lead to kinking of the graft. Conversely, a short graft may cause added tension to the anastomosis and lead to bleeding or obstruction. The outflow graft should lie along the right atrium. The anastomosis is performed along the proximal anterolateral ascending aorta. A partial-occlusion clamp is placed without dissecting the plane between the aorta and PA. The aorta is incised and the anastomosis is sewn with a 4-0 polypropylene suture. The anastomosis is de-aired and the partial-occlusion clamp is then removed to assess hemostasis. A vascular clamp should remain on the outflow graft while the device is off to avoid retrograde flow into the aorta. A de-airing cannula is placed in the ascending aorta between the outflow graft and aortic cannula. It is important to place the graft as proximal as possible to allow for future cannulation and aortic anastomosis at the time of heart transplantation.
Cannulation for cardiopulmonary bypass is accomplished with an arterial cannula in the distal ascending aorta or proximal aortic arch. It is important to leave enough length on the aorta for a de-airing cannula and positioning of the outflow graft of the LVAD. A two-stage venous return cannula is used for venous return. Bicaval cannulation is alternatively used if closure of a patent foramen ovale or tricuspid valve repair or replacement is performed concomitant with LVAD implant. The procedure is typically performed on full cardiopulmonary bypass on the beating heart. The heart is elevated and supported with moist laparotomy pads to expose the left ventricle (LV) and apex. Correct positioning of the inflow cannula is essential. It should be parallel to the interventricular septum and directed toward the mitral valve. Depending on the type of LVAD, a cuff or ring is sewn to the LV apex to provide a mechanism to secure the inflow cannula of the LVAD within the LV cavity. A core of LV muscle at the apex is removed to facilitate introduction of the inflow cannula of the LVAD into the LV cavity. CO2 may be infused into the LV cavity to facilitate de-airing of the LV. Passively filling the heart and pump and elevating the apex and gently shaking the ventricle accomplish additional de-airing. The outflow graft of the LVAD is then distended, clamped, and trimmed to proper length. It is crucial to determine the appropriate length of the outflow graft as excess length may lead to kinking of the graft. Conversely, a short graft may cause added tension to the anastomosis and lead to bleeding or obstruction. The outflow graft should lie along the right atrium. The anastomosis is performed along the proximal anterolateral ascending aorta. A partial-occlusion clamp is placed without dissecting the plane between the aorta and PA. The aorta is incised and the anastomosis is sewn with a 4-0 polypropylene suture. The anastomosis is de-aired and the partial-occlusion clamp is then removed to assess hemostasis. A vascular clamp should remain on the outflow graft while the device is off to avoid retrograde flow into the aorta. A de-airing cannula is placed in the ascending aorta between the outflow graft and aortic cannula. It is important to place the graft as proximal as possible to allow for future cannulation and aortic anastomosis at the time of heart transplantation.
In addition to the de-airing cannula in the ascending aorta, the patient is placed in the Trendelenburg position and ventilation is resumed. The device driveline is connected to the controller. At this point, administration of nitric oxide is started as well as a combination of vasopressor and inotropic support to assist the right heart. The patient is then gradually weaned from cardiopulmonary bypass. Once cardiopulmonary bypass flow is less than 2 L/min, the vascular clamp on the outflow graft is removed and the LVAD can be turned on at low speeds and gradually increased to provide more support as cardiopulmonary bypass flows are simultaneously slowly decreased. To optimize and set pump speed, the TEE is used to visualize the position of the interventricular septum, size of the LV, and opening of the aortic valve. Once de-airing is confirmed by TEE, the vent cannula in the ascending aorta is removed and the patient can be weaned from cardiopulmonary bypass. Final adjustments to pump speeds with TEE can be performed following weaning from cardiopulmonary bypass. When the hemodynamics are appropriate, protamine is administered and the cannulae are removed. Mediastinal chest tubes are inserted and the chest is closed in the standard fashion.
Following weaning from cardiopulmonary bypass, poor RV function may impair LV filling and LVAD performance. Insertion of an RV assist device (RVAD) may be necessary to achieve optimal left ventricular filling and LVAD flows. There are several options for mechanical support of the RV including devices that can be inserted percutaneously or devices that require surgical implantation. The majority of devices for RV support are limited to temporary support and longer-term options are limited. For patients experiencing acute RV failure in the operating room following LVAD implantation, devices for surgical implantation typically use the right atrium for venous return to the RVAD and the main pulmonary artery for arterial outflow. Concentric purse strings with pledgets are typically placed around the right atrial appendage and at the main pulmonary artery to secure the atrial and arterial cannulae. Following insertion, cannulae are deaired and tunneled under the abdominal fascia and exit the upper abdominal wall. Exteriorization of the cannulae in this
fashion permits sternal closure and mobilization of the patient. Following recovery of RV function, the patient must be returned to the operating room for RVAD explant. For RV failure occurring in the early postoperative period, devices placed percutaneously may be utilized.
fashion permits sternal closure and mobilization of the patient. Following recovery of RV function, the patient must be returned to the operating room for RVAD explant. For RV failure occurring in the early postoperative period, devices placed percutaneously may be utilized.
Postoperative Management
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