HealthDay News — Heavy smokers who undergo coronary artery bypass grafting (CABG) with saphenous veins are more likely to have signs of graft failure, even if they quit smoking more than a year earlier, study results suggest.
Patients who smoked at least a pack of cigarettes a day for 20 years prior to surgery experienced imbalances in proteins involved in vascular remodeling after coronary procedures, Wang Chunsheng, MD, of Fudan University in Shanghai, China, and colleagues reported in the Annals of Thoracic Surgery.
These imbalances were associated with worse saphenous vein graft patency at one and two years after CABG, even among patients who had quit smoking one year prior to surgery.
“Although recovery after cessation of smoking appears somewhat disappointing, it illustrates exactly the importance of prompt smoking cessation for patients who will receive coronary artery bypass grafting,” the researchers wrote.
To better understand how smoking affects the proteins involved in revascularization after CABG, Chunsheng and colleagues examined mRNA and protein levels of matrix metalloproteinase (MMP) subtypes MMP-2 and MMP-9 and tissue inhibitors of metalloproteinase (TIMP) 1 and 2.
The study involved 208 patients with various smoking histories undergoing elective CABG, who were divided into six groups according to smoking status:
- Nonsmokers (17%)
- Current heavy smokers, who smoked at least 20 cigarettes a day for at least 20 years before the operation (22%)
- Heavy smokers who had quit less than 3 months before CABG (16%)
- Heavy smokers who had quit 3 to 6 months before CABG (13%)
- Heavy smokers who had quit 6 to 12 months before CABG (18%)
- Heavy smokers who had quit at least 12 months before CABG (14%)
Mean patient age ranged from 60 to 64 years, and 94% to 98% of patients in each group were men. mRNA and protein levels of MMP-2, MMP-9, TIMP-1, and TIMP-2 were measured in samples of the saphenous veins taken at the time of CABG.
Compared with nonsmokers, expression of MMP-2 and MMP-9 was significantly higher, and expression of TIMP-1 and TIMP-2 was significantly lower in all five smoking groups (P<0.05 for all). These disparities were greatest among current heavy smokers and declined as more time passed since smoking cessation.
Increased expression of MMP2 and MMP9 was associated with poor saphenous vein graft patency. “Breakdown of the basement membrane by MMP-2 and MMP-9 allows smooth muscle cell migration, leading to the formation of foam cells and atherosclerotic plaques, which contribute to late vein graft failure,” the researchers wrote.
At 1 year, grafts were patent in 92.7% of the nonsmokers and 85.3% to 89.6% of the rest of the patients. At 2 years, graft patency was present in 89.2% of the nonsmokers and 83.1% to 86.3% of the rest of the patients.
“These data provide preliminary evidence that the balance of MMPs and TIMPs in saphenous vein grafts is altered by smoking and could have a role in early pathologic vein graft remodeling leading to graft failure,” Shahab Akhter, MD, of the University of Chicago, wrote in an accompanying editorial.
Study limitations include the almost exclusively male patient population, and the assessment of gene and protein expression in saphenous veins prior to CABG, which itself can affect graft integrity. The researchers called for additional prospective clinical trials with larger cohorts and long-term follow-up.