An end-run around the heart

Surgery: Aortic valve replacements in pregnant women are rare and risky - more so when the mother's heart is stopped and a machine circulates the blood.

Medicine & Science

May 03, 2004|By Erika Niedowski | Erika Niedowski,SUN STAFF

There was just one patient on the operating table, but two lives were at stake.

Doctors had urged Omayma Ahmad to end her pregnancy before undergoing an aortic valve replacement - a complex surgery in which her heart would be stopped and a machine would take over circulation of her blood.

The operation wasn't just risky for her: It was even more dangerous to her unborn child.

"They said, `The chances that the baby will survive are less than 40 percent,'" Ahmad, a native of Sudan, recalled. "I said, `I'm not going to abort it. Let us take our chances. If it is going to survive, OK.'"

Ahmad, 38, gave birth March 4 to a healthy baby boy named Mahmood - six months to the day after doctors at the Johns Hopkins Hospital opened her chest and implanted an inch-wide mechanical valve made of titanium.

"I'm very happy that I survived," the Baltimore resident said. "I'm very happy that my baby survived."

Sisyphean situation

According to a study published last year, heart disease occurs in about 1 percent of pregnant women, making operations such as Ahmad's relatively uncommon. As a result, medical research journals offer cardiac surgeons little guidance on the safest and most effective techniques.

"There are very few of them that have actually done [surgeries on] a pregnant patient," said Dr. Tomas Salerno, an assistant professor of surgery at the University of Miami and chief of cardiothoracic surgery at Jackson Memorial Hospital, who has performed two or three.

Ahmad's surgeon, Dr. David D. Yuh, had never performed such an operation. But he found himself uniquely prepared, thanks to some obscure experiments he had performed on pregnant sheep during his medical residency at Stanford several years ago.

"It was basically the physiology [of pregnancy] that we took away the most information about," said Yuh, director of cardiac surgical research at Hopkins.

Ahmad, who has a congenital heart defect, had undergone an emergency aortic valve repair in San Francisco in 2001. But the valve had become clotted and was stuck open. Blood was leaking back into her heart, forcing the cardiac muscle to work harder to do its job.

"It's like rolling a boulder up a hill and having it slide back," said Yuh.

`Crude' calculation

After opening her chest, the medical team hooked Ahmad to a heart-lung bypass pump, which circulated blood through her body - and to her baby's, by way of the placenta. Just as the lungs do, the machine replenished the blood's oxygen and removed carbon dioxide. Next, surgeons clamped Ahmad's aorta to stop her heart.

Here's where Yuh's work on the pregnant ewes came into use.

Often, cardiac surgeons cool a patient's body 12 or more degrees during the procedure, which helps preserve the function of the heart and other vital organs. But Yuh recalled needing to maintain a higher temperature and keep the pump going at a faster rate to ensure that the fetus got enough blood and oxygen.

In the absence of a heartbeat, blood pumped by the machine flows continuously without a pulse. So the question for Yuh was how fast to run it. Making what he calls a "crude" calculation, he estimated the size of the baby at 12 weeks and ran the machine, in essence, for two.

Racing the clock

The rest of the operation - Yuh delicately teased away scar tissue that had formed after Ahmad's prior surgery, removed the clotted valve and replaced it with a mechanical one - was a race against the clock.

"The longer you're on bypass, the less functional the placenta is," said Yuh. "The [goal] was to get in and done as fast as possible."

All told, Ahmad was on the pump for 99 minutes - and her heart was stopped for a little more than an hour. During some complicated cardiac surgeries, patients remain on the machine for as long as six hours.

Dr. James Gammie, assistant professor of surgery at the University of Maryland Medical Center, said studies have shown the maternal mortality rate during such procedures to be about 5 percent. But it can be much higher - 20 to 30 percent - for the fetus.

Cardiac surgeons operating on women in their first trimester also worry that some of the medications they must use can cause birth defects.

Also, they have to prepare for the possibility that the mother will go into premature labor, or that the baby will die on the operating table.

Because the mother is on anticoagulants to keep her blood from clotting, she could bleed to death.

"The take-home message is, if you can avoid doing it, avoid doing it," Gammie said.

`Really gratifying'

The University of Miami's Salerno says he performs all his cardiac bypass surgeries while the patient's heart is beating. He did one such operation in 2002 on a 23-year-old woman, in her 27th week of pregnancy, who would have died from congestive heart failure without surgery.

Salerno said doing a bypass surgery on a patient with a "warm heart," as he calls it, has multiple benefits.

That approach, he said, means there's no need to administer the electrolyte potassium, which can cause abnormal heart rhythms and potentially harm the baby.

"When the operation ends, it requires powerful drugs to make the heart work [again]," said Salerno. " ... When you finish, that heart has to beat for two people."

Although the operation Yuh performed on Ahmad is relatively rare, by coincidence he soon encountered another case - a pregnant woman in need of an emergency valve repair. Maria Johnson delivered a healthy baby this month.

"It's really gratifying," said Yuh. "It was a very unusual circumstance."

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