ventricular assist device

Ventricular Assist Device 

Definition

A ventricular assist device (VAD) is a mechanical pump used for temporary blood circulation support. It decreases the workload of the heart while maintaining adequate 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. VADs can also be used as a bridge in patients awaiting heart transplantation or in patients who 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 the 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 concerning blood flow, blood pressure, and general health.

Precautions

Poor candidates for a VAD include those with:

• irreversible renal failure
• severe disease of the vascular system of the brain
• cancer that has spread (metastasized)
• severe liver disease
• blood clotting disorders
• severe lung disease
• infections that do not respond to antibiotics
• extreme youth or age

Description

There are four types of VADs, each appropriate for a different condition. Surgery to install a VAD is performed under general anesthesia in a hospital operating room. An incision is made in the chest, then catheters are inserted into the heart and the correct artery. The surgeon sutures the catheters in place, then attaches tubing to connect the catheters to the pump. The pump stays outside the body. Once it is turned on, blood flows out of the diseased ventricle and into the pump, then is returned to the correct blood vessel leaving the heart.

Preparation

Before the operation the patient meets with an anesthesiologist to determine any special conditions that will affect the administration of anesthesia. Standard preoperative blood and urine studies are performed, and the heart is monitored both before and during the operation with an electrocardiograph.

Aftercare

The patient is monitored in intensive care, with follow-up blood, urine, and neurological studies. Blood thinning medications are given to prevent blood clotting.

Except for those patients awaiting a heart transplant, patients are slowly and gradually weaned from the VAD. Even when patients no longer need the VAD, they will require supportive drug therapy and/or a balloon pump inserted in the aorta.

Risks

VAD insertion carries risks of severe complications. Bleeding from surgery is common and 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.

Sometimes when the left ventricle is supported, the right ventricle begins to need assistance. If VADs are inserted in both ventricles, the heart may become so dependent on their support that they cannot be removed.

Normal results

Because conditions for which VADs are used vary widely and because of the high risks associated with VAD insertion, the outcome of surgery cannot be predicted.

Resources

Books

Zaret, Barry L., et al., editors. "Ventricular Assist Device." In The Patient's Guide to Medical Tests. Boston: Houghton Mifflin, 1997.

Other

"Ventricular Assist Devices." Department of Biological and Agricultural Engineering. New York State University. http://www.bae.ncsu.edu.

Key terms

Coronary blood vessels — The arteries and veins that supply blood to the heart muscle.

Diaphragm — The muscle that separates the chest cavity from the abdominal cavity.

Ventricle — The heart has four chambers. The right and left ventricles are at the bottom of the heart and act as the body's main pumps.

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device /de·vice/ (dĭvīs´) something contrived for a specific purpose.

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biventricular assist device  (BVAD) a ventricular assist device with the combined functions of both left and right ventricular assist devices.

contraceptive device  one used to prevent conception, such as a barrier contraceptive, an intrauterine device, or a means of preventing ovulation (e.g., birth control pill).

intrauterine device  (IUD) a plastic or metallic device inserted in the uterus to prevent pregnancy.

ventricular assist device  (VAD) a circulatory support device that augments the function of the left ventricle, the right ventricle, or both, by providing mechanically assisted pulsatile blood flow.

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ventricular assist device (VAD),

a circulatory support device that augments function of the left ventricle, the right ventricle, or both. It consists of one or two implanted or extracorporeal pumps with afferent and efferent conduits attached to provide mechanically assisted pulsatile blood flow. See also artificial heart.

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ventricular

pertaining to a ventricle.

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ventricular assist device

a circulatory support device consisting of a pump with afferent and efferent conduits attached to the left ventricular apex and the ascending aorta, respectively, each conduit containing a porcine valve to ensure unidirectional blood flow; the pump rests on the external chest wall and is connected to an external pneumatic power source and control circuit.

ventricular asystole

see asystole.

ventricular bands

folds of mucosa, parallel and craniolateral to the vocal cords. Called also false vocal cords, vestibular folds.

double right ventricular outlet

a cardiac anomaly rarely seen in animals in which both the aorta and pulmonary artery arise from the right ventricle and there is a defect in the ventricular septum.

excessive ventricular moderator bands

a rare syndrome of cardiomyopathy in cats caused by an excessive number of moderator bands in the left ventricle, extending from the papillary muscles to the ventricular septum.

ventricular extrasystoles

see ventricular extrasystole.

ventricular fibrillation

see ventricular fibrillation.

ventricular function curve

see starling curves.

ventricular hypertrophy

see ventricular hypertrophy.

ventricular outflow obstruction

flow of blood from the ventricles is impaired by lesions or congenital abnormalities in the outflow tract. This is usually associated with hypertrophy of the ventricle and can be demonstrated with echocardiography or contract radiography. Left outflow obstruction occurs with stenosis and other anomalies of the aorta; right outflow obstruction occurs with pulmonic stenosis, pulmonic insufficiency, tetralogy of Fallot, and double-chambered right ventricle.

ventricular premature contraction (VPC)

see premature heartbeats.

ventricular rupture

due to focal weakness causes sudden death due to cardiac tamponade.

ventricular septal defect

a congenital heart defect in which there is persistent patency of the ventricular septum in either the muscular or fibrous portion most often due to failure of the bulbar septum to completely close the interventricular foramen. The defect permits flow of blood directly from one ventricle to the other, bypassing the pulmonary circulation and producing varying degrees of cyanosis because of oxygen deficiency. Its clinical characteristics also include a systolic murmur and a palpable thrill on both sides of the chest, dyspnea and poor exercise tolerance. The occurrence is sporadic except that it is inherited in goats and dogs.

ventricular septum

the muscular wall between the ventricles. A small section, between the aortic vestibule and the right atrium, is membranous. Failure of the septum to close completely during fetal growth causes a septal or subaortic defect.

ventricular shortening fraction

in echocardiography, the percentage change in diameter from diastole to systole. Calculated from the internal systolic and diastolic dimensions. It is a measure of mycocardial function.

ventricular slice method

a method for examination of fixed heart by cutting it into 0.5 inch thick slices, perpendicular to the plane of the ventricular septum, from apex to base. Useful in examination of myocardial lesions and cardiomyopathy.

ventricular tachycardia

is manifested by a high heart rate with or without arrhythmia. In both cases there is severe cardiac disease and often acute heart failure.

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ventricular assist device

Heart surgery A portable, battery-powered device that assists the flow of blood while a Pt is awaiting heart transplant; the VAD is connected at the apex of the left ventricle and pumps the blood past an effete ventricle and aortic valve directly into the aortic arch. Cf Artificial heart, Jarvik-7.