Ventricular assist device

Definition

A ventricular assist device (VAD) is a battery-operated mechanical system consisting of a blood pump and a control unit used for temporary support of blood circulation. The VAD decreases the workload of the heart while maintaining adequate blood flow and blood pressure.

Purpose

A VAD is a temporary life-sustaining device. VADs can replace the left ventricle (LVAD), the right ventricle (RVAD), or both ventricles (BIVAD). They are used when the heart muscle is damaged and needs to rest in order to heal, or when blood flow from the heart is inadequate. In November 2002, the Food and Drug Administration (FDA) approved the use of one type of LVAD as a form of permanent treatment for patients who are ineligible for a heart transplant. VADs can also be used as a bridge in patients awaiting heart transplantation or in patients whose bodies have rejected a transplanted heart.

Examples of patients who might be candidates for a VAD are those who:

• have suffered a massive heart attack
• cannot be weaned from heart-lung bypass after treatment with intravenous fluids, medications, and insertion of a balloon pump in the aorta
• have an infection in the heart wall that does not respond to conventional treatment
• are awaiting a heart transplant and are unresponsive to drug therapy and intravenous fluids
• are undergoing high-risk procedures to clear blockages in a coronary artery

Although one in five people suffer left-side ventricular failure, only a minority are candidates for VADs. To be considered for a VAD, patients must meet specific criteria with regard to blood flow, blood pressure, and general health.

Demographics

About 40,000 people in the United States need a heart from a compatible donor, but only 2,200 donor hearts become available each year; hence there is a great need for mechanical devices that can keep patients alive during the wait for transplantation.

VADs are available to all patients in cardiovascular crisis, but their use is contraindicated in patients with:

• irreversible renal failure
• severe peripheral vascular disease
• irreversible brain damage
• cancer that has spread (metastasized)
• severe liver disease
• blood clotting disorders
• severe lung disease
• infections that do not respond to antibiotics
• advanced age

Description

A VAD is selected based on specific patient criteria, including the patient's size; the length of time that support will be needed; the amount of support (total or partial) required; and the type of flow desired (pulsatile or continuous). Different heart problems require different types of flow.

A VAD is implanted under general anesthesia in a hospital operating room . After the patient has been anesthetized, the surgeon makes an incision in the chest. He or she then inserts a catheter into the jugular vein in the neck. The catheter is threaded through the pulmonary artery, which carries blood from the right ventricle of the heart to the lungs. The catheter is used to measure the oxygen levels in the blood and to administer medications. A urinary catheter is also inserted and used to measure the output of urine. The surgeon sutures the catheters in place, then attaches tubing to connect the catheters to the VAD's pump. Once the pump is turned on, blood flows out of the diseased ventricle and into the pump. The blood is then returned to the proper artery; an LVAD is connected to the aorta, which leaves the heart from the left ventricle, whereas an RVAD is connected to the pulmonary artery. After the VAD has been implanted, the surgeon closes the incisions in the heart and the chest wall. The complete operation may take several hours.

Preparation

VADs are used in patients who have not benefited from other forms of treatment for heart disease. In order to evaluate a patient's eligibility for a VAD, the doctor will use cardiac catheterization to demonstrate poor cardiac function and make pressure measurements of the chambers in the patient's heart. Blood samples are drawn in order to measure the levels of blood cells and electrolytes in the patient's circulation. Monitoring of the heart includes an electrocardiogram (EKG) as well as measurements of arterial and venous blood pressures.

Aftercare

After a VAD implant, the patient is monitored in an intensive care unit (ICU) with follow-up laboratory studies. He or she will remain in the hospital for at least five to seven days. A breathing tube may be left in place until the patient is awake and able to breathe comfortably. Anticoagulant (blood thinning) medications are given to prevent the formation of blood clots, and antibiotics are given to prevent infections.

Patients are slowly and gradually weaned from the VAD, except for those patients awaiting a heart transplant or approved for long-term use of the VAD. As the patient improves, he or she will begin a regular exercise program. Some VADs require drive lines connected to the control console that penetrate the chest or abdominal cavity. These connections must be cleansed and bandaged to prevent infection of the device. With appropriate training, the patient can continue treatment at home, returning to the hospital only when necessary.

Fully implanted VADs do not require the patient to remain connected to a bedside control console and power unit. He or she will need to carry battery packs in a waistband or shoulder harness, however. In addition, some fully implanted VADs require the patient to plug a cord attached to their body into an electrical outlet at night.

Risks

VAD insertion carries risks of severe complications. Bleeding from the surgery is common; it occurs in as many as 30–50% of patients. Other complications include the development of blood clots; partial paralysis of the diaphragm; respiratory failure; kidney failure; failure of the VAD; damage to the coronary blood vessels; stroke; and infection.

An additional risk is physical dependency on the device. If VADs are inserted in both ventricles, the heart may become so dependent that the patient cannot be weaned from ventricular support.

In addition to physical complications, many patients find that their emotions and cognitive functions are affected by the implantation procedure. Depression, mood swings, and memory loss are not unusual in patients with VADs.

Normal results

Because VADs are used in the treatment of critically ill patients, outcomes vary widely according to the state of the patient's health before treatment. The signs of a successful implant include normal cardiac output with normal blood pressure and systemic and pulmonary vascular resistance.

If the patient is a candidate for a heart transplant, a successful VAD transplant may allow him or her to continue treatment at home. The goal of this extended support is to survive the wait for a donor organ. As many as 5% of patients with implanted VADs may recover an adequate level of heart muscle function, however, and avoid the need for a heart transplant.

Resources

books

hensley, frederick a., et al., eds. a practical approach to cardiac anesthesia, 3rd ed. philadelphia, pa: lippincott williams & wilkins, 2003.

"ventricular assist device." in the patient's guide to medical tests, ed. barry l. zaret et al. boston, ma: houghton mifflin, 1997.

periodicals

rose, eric a., annetine c. gelijns, alan j. moskowitz, et al. "long-term use of a left-ventricular assist device for end-stage heart failure." new england journal of medicine 345 (november 15, 2001): 1435-1443.

organizations

american association for thoracic surgery (aats). 900 cummings center, suite 221-u, beverly, ma 01915. (978) 927-8330. <www.aats.org>.

american heart association (aha), national center. 7272 greenville avenue, dallas, tx 75231. (800) 242-8721. <www.americanheart.org>.

united states food and drug administration (fda). 5600 fishers lane, rockville, md 20857-0001. (888) info-fda. <www.fda.gov>.

other

department of biological and agricultural engineering, new york state university. ventricular assist devices. <www.bae.ncsu.edu>

Tish Davidson, A.M. Allison J Spiwak, MSBME

WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?

A VAD is implanted by a cardiothoracic surgeon. A cardiothoracic surgeon is a physician who has completed medical school followed by an internship and residency program for specialized training in cardiac and thoracic surgery .

VADs are implanted in hospitals that are equipped to handle cardiopulmonary bypass procedures, with surgeons that have been trained in the specific techniques required by a given type of VAD. The cost of supplies and the special training required limit the type and number of devices that can be implanted in a specific hospital. Patients are transported to specialized transplant centers for continued support and treatment if their heart function is not expected to return to normal.

QUESTIONS TO ASK THE DOCTOR

• What types of VAD are available for implant at your institution?
• Which of these devices have you been trained to implant?
• What is the success rate for VAD patients at your hospital?
• What institutions are available for transport for patients waiting for a heart transplant?