Proximal before distal and techniques for one level do not necessarily apply to another. I am reminded of these principles in the article reporting the decision by Medtronic to withdraw the drug-eluting balloon developed for use below-the-knee. The financial losses to the company must be vast in terms of money that they will not receive after years of development of their below-the-knee drug-eluting balloon. Quite simply, they have put the patients’ interests first. This has to be regarded as a most venerable decision and it will be a great ordeal for the company that after years of research the drug-eluting balloon is not effective and could even be associated with less good results than the balloon without drug elution.
One reflects of the changes which have occurred over recent decades—in the past, every reconstruction was an open surgical one and then there was a gentle and gradual introduction of balloon angioplasty followed by many intra-arterial ways of reconstruction. Before this period the surgeons had learnt some lessons from years of surgery to the aortoiliac and the femoropopliteal and femorotibial segments. The adage has always been to correct proximal disease before distal. For example, a distal bypass from the femoropopliteal level would have less chance of survival and be less effective if the bypass was performed below an iliac segment with a significant stenosis in it than if the perfusion from the aortic system was 100% normal. Consequently and after many years of disappointment, surgeons learnt to take great note of proximal lesions and have a two-dimensional view of these and to correct proximal lesions initially by arterial reconstruction such as endarterectomy or bypass and these techniques have carried into the endovascular era.
With the application of coronary artery techniques to the arteries below the knee there is a danger that the proximal vessels have been ignored too much. Of course it was novel that the balloons developed for the coronary artery could then be used effectively to improve the tibial arteries. This is why the interventional cardiologists who applied these techniques in the first place became interested in the ischaemic limb and showed outstanding results after a balloon angioplasty to the below-the-knee vessels. It appeared that we were in a new era. Then it became plain that it is difficult to follow a patient’s series of below-the-knee arterial disease for very long and results appeared at six months, one year and very seldom two years, fairly definitely never beyond that point. There are many reasons for this, not least that the patient is very sick and life expectancy is poor in patients with severe below-the-knee arterial disease. Reinterventions were common and long-term results have been difficult to achieve. In recent years, though, we have been struggling to understand the appropriate treatment to use in the superficial femoral artery; for example, whether one should use a stent with or without drug elution, or a plain old balloon angioplasty, or a balloon with drug elution. Atherectomy has also been a serious player in this. Surgeons were used to reconstructing the aortoiliac segment and delivering high volume blood into the profunda femoris before turning to the femoropopliteal segment or below. It is not clear that the importance of the proximal vessels is as strong these days as it was some years ago, certainly the rule to attend to proximal vessels before distal is one not to forget.
Consider a motorway coming to an end and traffic going into an A-road and then into a B-road and then into a country lane and into a small one-way street. If all of the small one-way streets at the end of the journey are blocked then it will be impossible for the traffic to flow. But even if the small lanes are freed and there is a block in the motorway or the A-road the traffic flow will still be inadequate. The practice, therefore, is to give precedence to the aorta over the internal iliac, over the external iliac, over the common femoral, profunda femoris, superficial femoral, etc down the leg. Many vascular surgeons have experienced that blood can get to the foot through vessels that are not entirely obvious to the operator. The higher pressure blood reaches a more distal position in the leg and blood gets through to the toes somehow and the leg warms up. Subintimal angioplasty produces similar results—that the blood travels down within the wall of the vessel and gets to branches way below the knee and blood can find its way frequently to the foot and relieve severely ischaemic tissue.
Surgeons have also learnt that the technique in one situation does not necessarily work so well in another. Take the most frequently performed aorto-bifemoral Dacron bypass. This could expect results of approximately 90% patency over five years. On the other hand, a Dacron tube used in the femoropopliteal segment would have an extremely poor patency at five years compared with the aortoiliac segment. The same would apply to endarterectomy. Endarterectomy in the aortoiliac segment would do extremely well. Some would say at least as well as bypass and even better in some cases, 90–95% patency, whereas endarterectomy in the superficial femoral artery would have a poor result. Many legs were saved by re-establishing higher pressure blood into the unblocked profunda femoris artery without paying much attention to the superficial femoral artery, the blood got to the foot very well indeed. These adages are as important now as they ever were.
Now in the era where drug-eluting stents and balloons are used we are not at liberty to assume that what works in a proximal vessel will necessarily work in a distal vessel. The reverse is also true. Therefore, poor results of drug-eluting balloon used below the knee in small very seriously diseased vessels will not necessarily predict the outcome of the use of a drug-eluting balloon in the superficial femoral artery. We know from histological studies that when a balloon is used the artery wall tends to crack and the drug elution can penetrate the wall and if a crack occurs then healing follows. It is understood that drug elution could also cause some changes in the vessel wall and the healing process involves a deposition of platelets. In a small vessel with low blood flow it is so very easy for that to occlude. However, in vessels such as the iliac or even the superficial femoral artery, an endovascular reconstruction would be accompanied by a huge flow and swoosh through the lumen of the vessel and the circumstances of velocity of blood flow are quite different after the use of a drug-eluting balloon in the superficial femoral artery from below the knee. It should be no surprise that results in the below-the-knee vessels cannot predict results in the superficial femoral artery segment.
These principles do not just underline lessons that we may have forgotten but they also endorse the view stated in the article about the recent results of drug-eluting balloon below the knee. This tells us nothing about what would be expected when the results are analysed for the use of drug-eluting balloons at 12 months in the superficial femoral artery. It will be exciting to see these results. In the meantime BASIL 2 is underway, a randomised controlled trial of endovascular therapy against open-surgical bypass to below-the-knee vessels. So after all these years of development with drug-eluting stents, plain metal stents, drug-eluting-balloons, and plain old balloon angioplasty, are we about to see a resurgence of surgical reconstruction? It is of interest that surgical results are reported on a five-year basis, endovascular seldom beyond two years. It seems that there is some mileage to go with this subject and it is a space to be watched carefully.
Roger Greenhalgh is head of the Imperial College Vascular Research Group, London, UK, and editor-in-chief of Vascular News