Science / Medicine : New Pump Curbs Angioplasty Risk for Patients With Blocked Arteries

This year 200,000 Americans with blocked coronary arteries will undergo a procedure called angioplasty in which a balloon is inflated inside one or more of the arteries to reopen the blocked passageways.

This method of restoring blood flow to the oxygen-starved heart muscle downstream from the blockage has been hailed as a major advance in cardiology.

But while angioplasty usually is lifesaving, about 200,000 additional candidates are turned down as being too high risk for the procedure.

Moreover, doctors say that in emergency situations, success depends on performing the procedure within three to four hours after the patient experiences the first warning symptoms.

According to Dr. Eliot Corday and researchers at Cedars-Sinai Medical Center, the time logistics of getting the patient quickly to the special angioplasty facility and through the preliminary diagnostic procedures often leaves insufficient time to perform angioplasty in an optimal manner.

Any delays in completing the procedure within the time limit may result in death of heart tissue or, if the patient survives, damage to the heart muscle that results in the patient becoming an invalid.

Sometimes not even enough time is left to inflate the balloon for 10 minutes--a length of time sufficient to open the blockage adequately.

The research investigators say that too short an inflation period will increase the likelihood of the artery reclogging within the succeeding four months in up to 40% of emergency cases.

After 14 years of animal research, Corday, a clinical professor at UCLA Medical School, and the Cedars team have developed a computerized emergency pump system that makes it possible to get nourishing blood to the oxygen-starved region despite the presence of the artery blockage--thereby extending the time available to perform safer angioplasty without further endangering the patient.

Studies with patients have already proved that the new life-saving technology, called synchronized coronary venous retroperfusion, can maintain the stricken heart for extra hours or even days.

This is accomplished in a novel manner.

It occurred to the Cedars-Sinai investigators to use a large vein that normally drains the heart of “used” blood (the coronary sinus vein) as a conduit to get fresh blood into the area affected by the blockage.

They are able to do this by threading a hollow tube called a catheter into the sinus vein and using it as a channel through which fresh blood is pumped from elsewhere in the body. This emergency pumping system can be set up within two minutes.

Normally the function of arteries is to supply fresh blood to tissues and the function of veins is to carry off the used blood. The researchers have found a way to allow coronary veins to serve both functions.

The computerized pump accomplishes this by synchronizing with each heartbeat the inflation and deflation of a tiny balloon on the tip of the catheter which acts as the gatekeeper to alternately direct the flow of incoming fresh blood from the catheter and the outflow of used blood through the vein.

According to Corday and Drs. Sheila Kar, Kevin Drury, Lars Ryden, George O’Byrne and Bing-Lo Chang, coronary retroperfusion will greatly increase the number of persons who could benefit from angioplasty but who now are rejected because of their risk of dying during the procedure.

Retroperfusion lessens the risk by keeping the damaged heart muscle nourished long enough to complete multiple angioplasties in cases that require considerably more time because there is a blockage in more than one artery.

An additional benefit, they said, is that catheters inserted via coronary veins draining the damaged part of the heart enable doctors to introduce specific life-saving drugs past the obstructed coronary arteries directly into sites where they are needed most.

Studies done at Cedars-Sinai to date show that drugs that control wildly racing heartbeats and clot dissolving compounds can be delivered in this way.

This new method of drug delivery is safer and faster than conventional methods, Corday said.

“Because the pharmacologic agents can be delivered directly into the jeopardized heart tissue by the innovative venous route, it is no longer necessary to flood the whole body with toxic dosages of these agents when only a small dose is really needed for effective retroinfusion therapy,” Corday told a recent medical meeting in Boston.

He said studies indicate that the retroperfusion route requires only about one-tenth to one-fiftieth the standard dosage to dissolve the blood clots that caused the coronary attack.

To date, 69 retroperfusions have been performed at Cedars and seven other centers around the world. The Cedars study has been funded by the National Heart, Lung and Blood Institute.

GAINING TIME IN HEART OPERATIONS

Angioplasty--in which a balloon is inflated inside one or more arteries to reopen blocked passageway--is increasingly hailed as a life-saving procedure. But an important issue is time, particularly in emergencies. Delays may result in damage to the heart and patient. A newly devised computerized pump system makes it possible to get blood to oxygen-starved regions of the heart despite the blockage, extending the time to perform safer angioplasty. Doctors say the system--synchronized coronary venous retroperfusion--can maintain the stricken heart for hours or days.

1. Doctors use a large vein that normally drains the heart (the coronary sinus vein) as a conduit to get fresh blood into the area affected by blockage. A catheter is threaded into the sinus vein from the pump system to carry fresh blood drawn from the femoral artery.

2. Ordinarily it would not be possible to use the same vessel as both a vein and an artery because the bloodflow for each is in the opposite direction. The computerized pump solves the problem, synchronizing with each heartbeat to inflate and deflate the tiny balloon as a gatekeeper to alternately direct the flow of incoming fresh blood from the catheter and the outflow of “used” blood through the vein.