Cardiac bypass surgery can be a traumatic, even life-changing, experience that gives patients with coronary artery disease - the leading cause of death among adults in the United States - a new lease on life. In the United States, the number of bypass procedures, which restore blood supply to the heart muscle by bypassing a blockage, continues to grow: from 1983 to 1993, coronary artery bypass grafting procedures increased from an estimated 162,000 to 241,000 per year.
But as these patients age, approximately half experience a bypass vein graft that closes down within five years after surgery, prompting a need for diagnostic tests. A cardiac catheterization, in which a tube is passed along a blood vessel into the heart, is often performed to identify precise locations of coronary artery disease or to examine bypass grafts.
To take the guesswork out of later catheterizations, surgeons can attach small wire circles, called saphenous vein graft (SVG) markers, to the aorta during surgery to indicate the precise location of the grafts that bypass blockages. But although these markers have been available for years, they have not been used widely. Even where markers are used, the practice varies greatly from one medical facility to the next.
A new study of 182 patients in St. Louis shows what many interventional cardiologists - doctors who perform cardiac catheterization - have suspected all along: SVG markers benefit patients after bypass surgery by improving the efficiency of later cardiac catheterizations and by reducing exposure to radiation and potentially toxic contrast agents, or dyes, during such procedures.
"Using markers is clearly the best way, I think, to find graft sites," says Linda Peterson, M.D., assistant professor of internal medicine at Washington University School of Medicine in St. Louis. "With an X-ray of the patient's chest, you can see how many markers are there, so the cardiologist knows how many grafts to find and where to aim the catheter to ensure a complete study." Checking out every graft is important because the physician must assess whether there are zones of the heart muscle that are not getting adequate blood supply from either the native vessels or the grafts.
Peterson and her colleagues reported their findings in the December 1999 issue of Annals of Thoracic Surgery.
There when you need them
Medical procedures do not always occur under ideal conditions. An avid traveler, for instance, having fully recovered from bypass surgery, could appear in an emergency room far from home with chest pain. The patient may need a catheterization before hospital staff can get his or her medical records, so the presence of markers could help the diagnostic accuracy under such urgent conditions. Even when a surgical report is available, it could be unclear or incomplete, leaving markers to serve as an effective backup.
"Using markers is one way to help ensure that cardiologists can do catheterizations in the most thorough and efficient manner possible," says Peterson, a cardiologist.
Without a thorough surgical report or the roadmap that markers provide, the procedure is done largely by feel. The cardiologist moves the catheter up, down, and around inside the aorta, hoping it catches on a graft, indicating a bypass. "When markers aren't in place, a catheterization is kind of like a fishing expedition where you're hoping to catch a fish by the tail," Peterson says.
The tricky part comes in knowing when all grafts have been found. If a previous graft is missed, the patient may need to repeat the catheterization, or worse, undergo repeat bypass surgery that was based on the incomplete catheterization, which happened to one patient in the study.
The study included 76 patients with markers and 106 patients without markers. Catheterization procedures took significantly less time for patients with markers, lasting an average of 33.7 minutes compared with 42.4 minutes for patients without markers. In addition, study participants with markers received an average of 172 milliliters of dye-like contrast agents, significantly less than the average 196 milliliters received by patients without markers. Contrast dyes can have harmful side effects.
Peterson and colleagues found that the presence of markers meant both patients and the physicians performing the catheterization procedures were exposed to less radiation from X-ray fluoroscopy. In fact, patients without markers spent on average an extra 3.3 minutes of fluoroscopy time, receiving additional radiation equal to approximately nine chest X-rays. Remarkably, the patient without markers who underwent the longest diagnostic procedure spent an extra 20 minutes of fluoroscopy time and received the equivalent of approximately 50 more chest X-rays than the patient who underwent the longest procedure in the marked group.
Convincing surgeons
If SVG markers have so many plusses, why are they not more widely used? Some cardiothoracic surgeons are concerned that some larger markers, which encircle a graft, could slip and close off the graft. But, Peterson counters, smaller washer-like rings that lie flat on the aorta do not present such risks. Others suggest that inserting markers unnecessarily increases the complexity of bypass surgery, but the study points out that no research supports this idea. Whether the bypass is done with veins or arteries taken from elsewhere in the body, the extra few seconds needed to stitch in the tiny markers during surgery could benefit all but the few patients with rare connective tissue diseases.
Perhaps surgeons will be convinced by an economic incentive: many cardiologists in private practice refer patients only to surgeons who place SVG markers.
"The long list of benefits appears to outweigh any risk or inconvenience of placing these markers at the time of bypass surgery for almost all patients," Peterson says.