Friday, July 28, 2006

Use of Internal Mammary Artery (IMA) Grafts Produces Better Long-term Outcomes
By Julie McKeel

Patients who have already undergone coronary artery bypass graft (CABG) surgery and then have catheterization (percutaneous coronary intervention or PCI) of internal mammary artery (IMA) grafts have better results and longer survival rates than those who undergo PCI of saphenous vein grafts (SVG).

Dr.

[In addition to Mehta, DCRI study authors included the Emily Honeycutt, MBI; Eric Peterson, MD; Chris Granger, MD; Abdul Halabi, MD; Linda Shaw, MS; Peter Smith, MD; Rob Califf, MD; Bob Harrington, MD; and Michael Sketch, MD.]

Mehta's team used the Duke Cardiovascular Disease Databank to select patients with previous CABG who underwent cardiac catheterization who had at least 1 SVG placed during the previous CABG. After their initial catheterization, patients were contacted by telephone or mailed questionnaire at 6 months and annually thereafter to determine if adverse events or death had occurred.

The 2119 patients who met the study criteria were categorized into 4 groups:

• group I, SVG intervention and parent IMA
• group II, no SVG intervention and patent IMA
• group III, SVG intervention without patent IMA
• group IV, no SVG intervention without patent IMA

During follow-up, information was collected on death/cause of death, nonfatal heart attack, and date of last known follow-up. The adjusted patient survival rates after 4.8 years in groups I, II, III, and IV were 72.8%, 72.3%, 64.5%, and 58.9%, respectively.

In contrast, the adjusted event-free rates for nonfatal heart attack were lower in the SVG intervention groups (groups I and III) than in the non-SVG intervention groups (groups II and IV), with the presence of a patent IMA providing little benefit.

The findings suggest that the presence of an open (unobstructed) internal mammary artery (IMA) graft improves the survival rate for patients undergoing saphenous vein graft (SVG) surgery; however, it does not improve the rate of heart attacks.

On the other hand, the SVG procedure itself does not improve survival, and is also associated with an increased risk of heart attacks.

The data imply that the presence of IMA graft produces a positive outcome for patients undergoing SVG angioplasty, similar to that seen for patients undergoing CABG. This isn’t surprising given that IMA grafts remain open over 5 years at greater than 90% as compared to 50% for vein grafts, and this improved graft openness has been associated with better long-term survival. In addition, PCI of coronary arteries or vein grafts does improve patient symptoms even though it has not been shown to improve long-term survival rates.

Earlier studies show that survival after vein graft intervention and among patients with prior CABG in general has improved significantly in recent years compared with the 1980s and early 1990s. While technological advances in coronary interventions have helped to improve outcomes, the authors point out that the use of IMA is an important quality of care indicator for patients undergoing CABG. They note that a large percentage of the improved survival rates after SVG treatment seen in recent years could be the result of increasing IMA use rather than due just to improvements in PCI technology.

In fact, none of the randomized clinical trials evaluating stents and distal protection devices have shown significant survival benefit after treatment of SVG. So it is quite likely that the favorable effect on survival in these prior observational studies may be as the result of other factors including the increasing use of an IMA.

Finally, the authors suggest that to improve the long-term survival rates of patients with CABG, these patients should receive an IMA graft. In addition, clinical best practice efforts need to focus on reducing the SVG disease by carefully selecting and harvesting SVG, as well as implementing aggressive secondary prevention strategies. This is necessary because once SVG disease occurs, PCI of a diseased vein graft has very little impact on improving the patient’s survival rate.

This study was supported by Duke Clinical Research Institute, Durham, NC.