Operative Techniques and Intraoperative Management

Historical note

The first left ventricular assist device (LVAD) was implanted in 1963 by Dr. DeBakey in a patient with postcardiotomy shock. As the incidence of heart failure rose to epidemic proportions, the LVAD emerged as a new solution to this devastating disease, and superiority over medical treatment was demonstrated in the Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure (REMATCH) trial. The first-generation devices were pulsatile, in an attempt to replicate native cardiac physiology. When compared to medical management alone, therapy with these devices showed improved survival. However, their large size limited patient selection to mainly male patients, required large pneumatic drivers, and demonstrated limited durability.

Thus, second- and third-generation devices were developed using continuous-flow pumps. These devices were smaller, allowing implantation in a broader population including women and children. The improved technology allowed for lengthened battery life, longer support times, and overall better quality of life for patients with advanced heart failure. Continuous-flow devices have continued to dominate the market since their introduction and are implanted in over 90% of patients with advanced heart failure.

Principles of device selection

Chronic support of the left ventricle (LV) requires long-term reliability and durability, portability, and adequate cardiac flow for active patients. Three devices currently on the market are widely used: the HeartMate II (HMII) LVAS (Abbott, Lake Bluff, IL, USA), the Heartware HVAD (Medtronic, Minneapolis, MN, USA), and the newly approved HeartMate 3 (HM3) LVAS (Abbott, Lake Bluff, IL, USA). All three pumps have inflow cannulas that are placed in the LV apex. The inflow cannula is connected to a pump body, which then is attached to an outflow cannula and graft that is subsequently sewn onto the ascending aorta. An electrical driveline from the pump exits the patient via a subcutaneous tunnel in the upper abdomen.

These pumps differ in several significant ways. The HMII, a second-generation device, uses an axial flow pump and, in general, requires a preperitoneal pocket for placement. Both the HVAD and HM3, third-generation devices, utilize centrifugal flow in a smaller configuration allowing for intrapericardial implantation. While the survival outcomes are similar for the HMII and HVAD, complication rates differ. The HVAD has a higher stroke rate, while the HMII has a higher rate of driveline infection and hemolysis/thrombosis, all with significant clinical impact (see also Chapter 13 ). The smaller size of the HVAD is more conducive to a minimally invasive approach via thoracotomy, either at the initial operation or if a redo operation is required. Additionally, biventricular configuration of the HVAD has been reported, which is not feasible with the HMII. Early results with the HM3 are promising, as this device appears to have a lower rate of hemolysis/thrombosis. However, survival and disabling stroke rates are similar when compared to the HMII. Ultimately, it appears that device selection must be individualized for each patient, underscoring the importance of patient selection.

Preoperative assessment and preparation

Indication for LVAD placement varies by individual patient and continues to evolve. Historically, LVAD implantation has been indicated for patients with New York Heart Association Class IV heart failure refractory to medical treatment and may include those patients with intractable arrhythmias and/or angina, end-organ dysfunction attributed to heart failure, or postcardiotomy shock. Patients are classified by therapy goals into bridge to transplantation, destination, bridge to recovery, and bridge to decision therapy.

The Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) scoring system is useful to identify appropriate patients and timing of LVAD support. Optimal patient selection is crucial for the success of chronic LVAD implantation and is achieved through an array of diagnostic studies.

Assessment is divided into cardiac and noncardiac considerations. Cardiac considerations include right ventricular (RV) function, valvular function and structure, intracardiac shunting, apical thrombus, and arrhythmias. Transesophageal echocardiography (TEE) is an essential part of the preoperative evaluation. Irreversible, advanced right heart failure is a contraindication to the placement of an isolated LVAD, and these patients may be considered for biventricular ventricular assist devices (VADs), total artificial heart placement, or heart transplantation. Noncardiac considerations include end-organ function (particularly pulmonary, renal, and hepatic), nutrition, body habitus, and social and psychiatric issues. End-organ function must be optimized through the use of inotropes and potentially intra-aortic balloon pump and/or extracorporeal membrane oxygenation if shock is present.

Implant operation

Hemodynamic monitoring is performed using a pulmonary artery catheter, arterial line, and TEE. After induction and skin preparation, a midline sternotomy incision is performed. A preperitoneal pocket is made using sharp and blunt dissection in the case of HMII implantation. As VAD placements are frequently repeat sternotomies, accurate dissection of the LV from surrounding scar tissue is required. Following this dissection, the patient is systemically heparinized.

Aortic cannulation should be placed as high as possible, close to the arch. Single two-stage venous cannulation will suffice in the majority of cases. If more dissection of the LV is required, it is performed during cardiopulmonary bypass (CPB) with the heart beating but decompressed. The driveline is tunneled percutaneously under the rectus muscle to exit usually over the left upper quadrant of the abdomen and can be done prior to heparinization.

The heart is elevated, bringing the LV to the midline of the wound. Pledgeted braided polyester sutures are placed from the myocardium through the sewing ring around a chosen spot for the inflow cannula ( Fig. 11.1 ), which must point toward the mitral valve and parallel to the septum ( Fig. 11.2 ). The sutures are then placed through the sewing ring, which is then seated and tied down. In the case of HMII implantation, coring can be performed prior to placement of the sewing ring.

The patient is placed in the Trendelenburg position in preparation for coring. Strong suction is maintained on an aortic needle vent to capture any air that may be ejected from the ventricle. The heart is emptied and a cruciate incision is made at the apex. The coring tool is used to perform the left ventriculotomy ( Fig. 11.3 ), removing a core of LV muscle. The ventricle is inspected for crossing fibers, thrombus, or obstructing muscle, which, if identified, is removed or resected. Once clear, the heart is deaired, and the inflow cannula of the pump is inserted ( Fig. 11.4 ). Continuous surveillance for air in the ascending aorta is maintained by the echocardiographer or anesthesiologist during this portion of the operation. The pump is secured after proper orientation is confirmed, and the heart is then placed back in normal anatomic position in the chest.

Further deairing is then performed through the outflow graft. The bend relief and outflow graft can be placed inside a 20-mm woven Dacron graft for further protection during subsequent explant for transplantation. The graft is then measured, clamped, and cut. A partial occluding clamp is placed on the greater curvature of the ascending aorta. After aortotomy, the outflow graft is anastomosed to the ascending aorta with continuous polypropylene suture ( Fig. 11.5 ).

Normal ventilation is resumed, and inhaled nitric oxide or prostaglandin and inotropes are initiated. The driveline is passed off the field and connected to the system controller. Following rewarming to normothermia, thorough deairing of the heart and pump is again performed, and CPB is weaned while increasing the LVAD pump speed to achieve adequate flow.

After weaning from CPB, the right heart should be assessed before reversing heparin. Pulmonary hypertension by itself is not an indication for RV support unless accompanied by RV failure. Destabilizing bleeding, with ongoing transfusion requirement, will often lead to RV failure and should be corrected before weaning from bypass. Protamine infusion is administered, and the patient is decannulated. Left pleural, mediastinal, and right pleural drains are inserted. Once adequate hemostasis is achieved, the chest is closed.

Intraoperative considerations