Results from randomised clinical trials of stents versus surgery such as the SOS and SYNTAX favour CABG as superior treatment compared to stenting. CABG appears to be associated with a lower likelihood of repeat revascularisation.
But there is a problem with these trials. Inherent clinician bias usually favours repeating angiograms in patients treated with stents who develop symptoms after the procedure compared to those patients who have received treatment with CABG. Since the clinician and the patients are not blinded to the original treatment this belief that surgery is a more robust and reliable method of revascularisation is likely to increases the rate of repeat angiography which leads to a high rate of repeat revascularisation.
So what is the rate of CABG vein graft occlusion? A recent paper looked at this question in 1829 patients who had a coronary angiogram within 12-18 months after CABG and were then followed for a further 3 years.
Within 18 months after CABG 43% of patients (770/1829) had at least one vein graft occlusion. The identification of this occlusion was associated with a 5-fold increase in repeat revascularisations procedures although it did not lead to a higher number of heart attacks or deaths compared to patients whose grafts were all patent. There rate of revascularization procedures within 14 days of angiography demonstrating a vein graft occlusion shows the power of the occlulostenotic reflex as discussed before in an earlier blog. Since the angiography was protocol, and not symptom, driven the identification of the stenosis on an angiogram was enough to result in a repeat revascularisation procedure with a stent.
What is the reason for the graft occlusion? Surgical technique, quality of the vein graft and target vessels or is it perhaps that the stenosis didn’t need bypassing in the first place. The FAME study using pressure wire showed that 20% of coronary arteries with significant stenosis (70-90%) on an angiogram were not associated with ischemia and in such cases vein graft failure could easily ay occur without clinical consequence or symptoms.
So when answering the question about the longevity of a bypass graft we should say that nearly half of patients will lose at least one graft within 18 months of surgery but the chance that it will cause harm to the patient is low unless someone discovers that it is occluded.