Richard Knorr’s heart is making medical history.
But there’s actually not much that’s unusual about it. Though two of his coronary arteries are partially blocked, the 64-year-old Framingham man has never had a heart attack and he can control his chest pain with medications.
Still, doctors are fascinated by his heart, and those of a handful of other coronary patients at Beth Israel Deaconess Medical Center in Boston, because they’ve found what seems to be a safe, painless, noninvasive way to detect heart blockages.
If the researchers, led by Dr. Warren J. Manning, co-director of the hospital’s Cardiac MRA Center, are right, the imaging technique – called 3-D coronary magnetic resonance angiography – could someday replace standard angiography. In this invasive procedure, doctors thread a catheter through an artery in the groin up to the heart, inject iodine dye through the catheter, and then view X-ray images of the arteries on a monitor, enabling them to see blockages.
Magnetic resonance imaging has actually been in use for about 10 years to scan blood vessels, but it’s mainly used in parts of the body, such as the brain, that don’t move. Imaging the heart and coronary vessels has proved tougher because of the blurring that’s caused by each heartbeat and respiration.
Indeed, imaging coronary vessels is “the holy grail of MR angiography,” says Dr. William Palmer, clinical director of magnetic resonance imaging at Massachusetts General Hospital.
If an international study now underway confirms Manning’s preliminary findings, which were published recently in the journal Circulation, the technique could be available in a couple of years, Manning says, though others think that’s too optimistic.
It’s also possible that the technique will not be able to match the 90 percent accuracy of standard angiography, warns Dr. Robert Herfkens, director of Magnetic Resonance Imaging at Stanford University.
Like 1.7 million other Americans who will have a coronary angiogram this year, Knorr can vouch for the fact that the current tests are no fun. The first time was “very, very intimidating,” says Knorr, who has had it done twice.
Most serious is the risk of heart attack, stroke or death, which occurs less than 1 percent of the time, says Dr. Peter Danias, a Beth Israel cardiologist and co-author on Manning’s paper. But there’s also risk of artery damage and bleeding from the incision where the catheter is inserted. To minimize bleeding, patients must lie still for four to six hours after an angiogram.
On top of that, some patients have allergic reactions to the dye (or “contrast agent”) injected to highlight the image of the arteries. And the radiation from the X-rays needed to “see” the arteries can damage tissue.
No wonder, then, that researchers have been scrambling for safer, noninvasive alternatives.
One hope is improved CT (computerized tomography) scans, though like regular angiograms, CT angiograms involve radiation (taking a series of X-ray slices that a computer stacks into 3-dimensional images) and injections of a contrast agent.
Newer, so-called fast CT scans that take four X-ray slices at once may be particularly useful for cardiac problems because they can be timed to get images of the heart between beats, says Dr. Andre Duerinckx , chief of cardiovascular magnetic resonance imaging at the Greater Los Angeles Health Care System.
Another alternative might be ultrasound, in which sound waves are bounced off the body and reflected back as an image. But sound waves don’t penetrate deeply enough to “see” coronary arteries, so this technique is mainly used to scan superficial vessels like the carotid arteries in the neck or veins in the leg.
In magnetic resonance, or MR, the patient is placed in a strong magnetic field and radio waves are sent into the body. This causes changes in the alignment of protons, or hydrogen atoms, the building blocks of molecules.
When the radio waves are stopped, the protons fall back into alignment with the magnetic field; in doing so, they send out their own radio waves, which are detected and used to create an image. With MR, doctors can track the flow of blood through vessels and the anatomy of the vessels as well, looking for spots where the flow is blocked by clots.
Several years ago, Manning’s team showed that coronary MR angiography could yield images if the patient held his breath repeatedly for 20 seconds or so at a time. Now, partly by tweaking the computer software, Manning’s new research shows it’s possible to get better images, at least in parts of arteries closest to the heart, without patients having to hold their breath.
In a tiny group of patients – Richard Knorr and four others – with known coronary disease, the MR scans corresponded “very well” with results from traditional angiograms, Manning says.
Still, MR imaging of the coronary arteries is “not ready for prime time” and may never be “comparable in quality” to standard angiograms, cautions Palmer of MGH, whose team is also working on the MR techique. In fact, because of the magnetic field, MR is not safe for people with pacemakers and some people with metal clips in their brains to treat aneurysms. MR may be safe for some of those who have metal stents implanted to keep arteries open.
But MR can only diagnose a clogged artery, not treat it. With standard angiography, doctors can not only image arteries but insert stents or use a balloon to compress artery-clogging clots as part of the procedure.
And while standard angiography can detect blockages anywhere in coronary arteries, so far MR works best at spotting problems only near the aorta, the heart’s largest artery.
Although one advantage of MR is that it can be done without a contrast agent, doctors sometimes inject a substance called gadolinium to make blood vessels show up better on scans. A new generation of contrast agents may further improve coronary MR, says Herfkens of Stanford.
But even in its current stage of development, the MR technique already has one enthusiastic fan: Richard Knorr. With each standard angiogram, he had to make two trips to the hospital – one for preliminary blood tests and one for the angiogram itself. With the standard angiogram, he says, “you’re confined all day in an OR,” compared to just an hour or so with magnetic resonance.
And with standard angiograms, he says, “you’re surrounded by three, four, five people getting you ready. . .I don’t want to put them out of a job, but. . ..”