Microbubbles Are Saving Hearts And Lives
06/22/06 Portland, Ore.
OHSU is the first hospital on the West Coast to implement a revolutionary technology for rapid detection of heart attacks; the result has been a total transformation in its treatment of unexplained chest pain
Elton Cain's chest pain was unrelenting. It was unlike anything the 81-year-old retired civil servant and World War II combat veteran had ever experienced. But the electrocardiogram and blood enzyme readings doctors commonly rely on to determine whether someone is having a heart attack weren't showing any signs of one-and wouldn't for almost seven hours after Cain's ordeal started.
Speed and accuracy are critical in diagnosing heart attacks because, as Oregon Health & Science University cardiologist Kevin Wei, M.D., puts it, "time is muscle." Wei determined it was a heart attack within an hour after emergency medical technicians wheeled Cain into OHSU's Chest Pain Center. The swift diagnosis occurred because of state-of-the-art microbubble echocardiograph technology. The OHSU Chest Pain Center is the first on the West Coast - and one of only a handful in the nation - to implement the technique.
Microbubble technology has led to a sea change in the way OHSU manages patients arriving on its doorstep complaining of chest pain. Elton Cain's story is emblematic of that change. Wei's speedy diagnosis saved precious time in administering blood thinners and other appropriate therapeutics to forestall further heart muscle damage.
"If there is a blockage, heart muscle will begin to die in 30 minutes," said Wei, an associate professor of cardiology in the OHSU School of Medicine and director of the Adult Echocardiography Laboratory. "If left untreated the damage will be complete in six hours. The quicker the intervention, the more hearts and lives will be saved."
Cain is one of 350 OHSU patients who have had microbubble, or more precisely, myocardial contrast echocardiography (MCE) performed for diagnostic purposes in the period from Jan. 1 through the end of May. The technique was first implemented last November. Now every patient who enters OHSU Hospital with undiagnosed chest pain receives an MCE. Some 50 a month are being performed.
Unlike standard methods for detecting a heart attack, MCE enables specially trained cardiologists to look directly at the heart and instantaneously interpret whether damage has occurred. Electrocardiograms can be inaccurate and must be repeated. Blood enzyme tests, while conclusive, take time to process. In Cain's case, the first biochemical marker of heart cell damage did not show up until 9 p.m., nearly seven hours after he first felt the pressure in his chest. That's when the blood test results came back showing a slightly elevated level of troponin, a protein released into the bloodstream as heart muscle cells die.
"The precision of myocardial contrast echocardiography will revolutionize how heart attacks are diagnosed and treated," said Wei, "Heart attacks are difficult to diagnose and symptoms vary widely from patient to patient, especially among women. Until now, there was no noninvasive tool sensitive or specific enough to make a definitive diagnosis at the time of patient presentation. Additionally, echocardiography can be used to swiftly rule out those patients with nonserious chest pain."
"Sorting out who does and doesn't have heart disease is tough," says OHSU emergency medicine and Chest Pain Center physician Robert L. Norton, M.D. "The only definitive test has been the angiogram, but it's expensive and invasive and not everyone can have it. The standard protocol for heart attack patients is an examination, an oral history of previous heart problems and other maladies and their medications, an electrocardiogram followed by a blood enzyme test. The problem with this process is that a patient can have a normal blood test and a normal EKG and still have a heart attack or heart disease. All of this must be repeated to rule out a heart attack and that takes time, time we don't have in these cases."
Myocardial contrast echocardiography was first developed by Sanjiv Kaul, M.D., OHSU chairman of cardiovascular medicine. Kaul, with six of his colleagues, joined OHSU in September 2005 after 21 years at the University of Virginia where he and his team built what became one of the most respected cardiovascular imaging programs in the world. Few chest pain centers in the nation have used this technology, which requires specially trained cardiologists to administer and read.
In MCE, microscopic gas-filled bubbles containing a fluorocarbon gas have been agitated to make the bubbles vibrate. The bubbles are injected into the body and travel through the bloodstream to the heart muscle. The vibrating bubbles dramatically improve the physician's ability to assess heart muscle function, and illuminate any damage or blockage, even in the tiniest vessels.
Although Cain first felt chest discomfort at around 2:30 in the afternoon on an outing at the Oregon coast with a senior citizens group, he didn't call 911 until late in the afternoon after he'd returned to his home in Gresham. His pain-which he described as "deep pressure behind the chest bone that wouldn't move over and wouldn't go away"- could have been symptomatic of a myriad of things, including indigestion. He'd just enjoyed a big buffet lunch. "I kept thinking maybe by the time I got home that whatever it was, gas or something, would shake out," he recalls.
The majority of patients who come to the emergency department with chest pain do not have a serious underlying cause, according to Wei. The challenge, he said, is to weed through those in the process of having a heart attack and those who are suffering from gastric reflux, for example, and can safely be sent home. Studies by Wei and Kaul have proven that MCE is more efficient and more accurate in identifying heart attack patients than standard EKGs.
At most hospitals, patients with unexplained chest pain either are admitted for overnight evaluation or sent home, said Norton, professor and vice chair of the OHSU Department of Emergency Medicine. At OHSU's Chest Pain Center, physicians and nurse practitioners with training in cardiovascular medicine staff a 10-bed, dedicated observation unit. There patients with nonacute chest pain are closely monitored for several hours while further tests are administered. Very often the tests rule out any serious problem, obviating the need for a costly overnight stay.
How, in the end, did Elton Cain fare? OHSU doctors found one of the main arteries of his heart had a 95 percent blockage, another 80 percent. Matthew Slater, M.D., OHSU assistant professor and section chief of adult cardiac surgery, performed bypass surgery. And now Cain is on a treadmill three times a week and feels almost chipper enough, he says, to come out of retirement. Not surprising for a man who was one of only eight members of a 42-man infantry platoon who survived the Battle of Okinawa and one of only two who came away without a scratch.
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