Discussion RAS is increasingly diagnosed in patients suffering from hypertension and renal insufficiency and in multivascular diseased patients. PTRA is now the first treatment to be proposed with a high technical success rate, a low complications rate, a low restenosis rate, and good long-term anatomical results. A large percentage of patients seem to benefit from the procedure concerning hypertension and renal insufficiency, with stabilization or improvement in RF, and in selected patients, RAS could slow the progression of renovascular renal failure and may delay the need for renal replacement therapy.27–31,41–60 However, as we have noticed in many published series, a deterioration RF may be detected in at least 20–30% of the patients, not only in patients with renal insufficiency, but also in patients with normal RF at baseline and even after successful initial technical results and good long-term patency.32–34,41–45,50 Many factors may account for this functional deterioration. But atheroembolism during the procedure could play an important role. As we have mentioned its diagnosis is difficult and it is crucial to prevent it. The risk can be reduced with a good selection of patients and some technical points, but the use of protection devices seems the best technique to overcome this problem. For this reason, we have applied the concept of protected renal angioplasty and stenting to circumvent atheroembolism. The rationale for distal embolic protection is similar to that of brain protection during carotid angioplasty and stenting of the carotid arteries. These techniques are now mandatory in this field and represent the standard of care.79 We have postulated that the same technique could be of value in the management of RAS in mitigating the risk of atheroembolism. Our results show only one acute deterioration of RF probably due to contrast nephropathy in a multivascular patient in poor condition and renal insufficiency at baseline. At 6-month follow-up, 98% of the patients were stabilized or improved and only two instances of deterioration (7%) appeared. Of the patients, 93% remained improved or stabilized. These results seem to be favorable when compared with available published data and may well be attributed to the use of a protection device during the procedure. It is noteworthy that visible atherosclerotic debris was extracted in all cases with balloon occlusion techniques and in 80% of cases with current filters. But with the new filter FiberNet®, visible debris was removed in all cases and at least five times more than with other filters. Four filters were totally or almost totally blocked by debris, thereby highlighting the role of protection devices. Similar results were also recently published by Holden et al80 and Edwards et al.84 Both authors insist on the role of protection devices to reduce atheroembolism and the risk of RF deterioration. However, this technique has some limitations as we have already mentioned. • Distal protection devices do not prevent emboli from reaching the kidney during initial catheter manipulation or angiography or while crossing the lesion. We discussed some technical points to reduce the risk of atheroembolism. • The use of distal embolic protection devices may be limited by the renal anatomy and the lack of devices currently available on the market and dedicated for this application. • In the case of large vessels, we have to carefully select the device and choose a device with a diameter at least equal to the diameter of the renal artery. • In case of an early renal artery bifurcation, it is not possible to protect all arteries. The protection device could be placed in the main branch (Figure 2). We could use two protection devices, one protection device is placed in each branch, but this technique could be limited by technical, anatomical problems and by the cost. In fact, in daily practice, 90% of the renal arteries can be protected with current protection devices. • To place the protection device we need a landing zone of at least 1.5 to 2 mm, which may be a problem with long stenosis or non-ostial stenosis. Current protection devices are not dedicated to renal arteries and have to be modified and improved. The new Fibernet device does not require a long landing zone. • The occlusion balloon has its own limitations and disadvantages: - It may deflate or may be non occlusive during the procedure; - Some particles may be too large for suction (very rare); - Below the balloon there is a shadow zone where some particles may remain blocked and are difficult or impossible to aspirate with the aspiration catheter. These particles may migrate to the kidney when the balloon is deflated; - The occlusion balloon could lead to transient nephron ischemia. In our series the mean occlusion time was short 6.46 mm. We do not think that this transient ischemia could cause any damage to the kidney. This occlusion time is less than that of the campling required during a surgical procedure. Edwards et al84 also used this technique without any complication. • Filters also have limitations and disadvantages: - Bad wall apposition with the possibility of migration of some particles around the filters; - A filter may plug up with suspended particles that will embolize if we retrieve the filter. In this case before retrieving the filter we have to very carefully aspirate the blood below the filter (as we did in some cases); - A filter may thrombose: we need an effective anticoagulation with an ACT > 250 to 300 seconds; - Closure and retrieval of filters can dislodge their content collected during the procedure; - Some difficulties in retrieving a filter may be encountered. The filter could get caught on the struts of the stent during retrieval; - But the major limitation of the filters is the pore size, which in general is greater than 100 microns. This is larger than the size of microcholesterol crystals85 and allows small particles going to the kidney. Atheroemboli typically occlude the medium-sized arterioles (150 to 200 microns in diameter) and glomerular capillaries. The pathogenesis of renal failure may be due entirely to occlusion of these vessels. But reactive inflammation surrounding the cholesterol crystals may play a significant role in causing the luminal occlusion and subsequent renal failure.86 As we have mentioned, the new generation of filters like FiberNet® should reduce the risk of atheroembolism and of RF deterioration. Particles of 30–40 microns can be removed with this device and the possibility of suction with the retrieval catheter is an important improvement. Although no device-related complications occurred in this small series of patients, adding another instrument to the procedure while trying to prevent complications could create new problems. The potential for renal artery thrombosis during protection is extremely small, even with occlusion balloons, because the patients are on heparin and antiplatelet therapy. Moreover, the duration of occlusion is usually short, less than the time required to perform the distal anastomosis of a conventional aortorenal bypass. The risk of dissection with a protection device is negligible, but one has to consider the possibility of spasm (2 cases in our series), which is, however, usually treatable medically. The indications for this technique of renal protection are debatable. Is the technique indicated for all patients? The indications for protection in patients with normal renal function need to be considered. The incidence of procedure-related decline in the renal function is considered to be low in this patient group. Many interventionists think that the extra cost of a renal protection system for these patients is not justified. However, I would like to point out the series recently published by Zeller et al50 where the highest proportion (36%) of patients with worsened renal function were found in the subgroup with normal baseline creatinine. In our series, 66 hypertensive patients were treated with protection despite a normal serum creatinine. Only 1 patient experienced a renal function deterioration detected at 2-year follow-up. This technique of including renal protection may therefore become the standard of care in the future. At the present time, selective indications should at least be pointed out: • Patients with renal insufficiency and a creatinine level of more than 1.4 mg/dl, or possibly better, and a GFR of less than 50 ml/min; • Elderly patients; • Patients with ischemic nephropathy; • Bilateral RAS; • Solitary or single functioning kidney; • Patients with diseased aorta and renal ostia; • Possibly diabetes. As has been mentioned by Sos et al,85 physicians performing renal artery interventions must understand the non-linear relationship of renal function reserve (RFR) and serum creatinine (SCr) and its implication for the margin of safety (Figure 3). Severe iatrogenic renal parenchymal damage due to interventional or diagnostic procedures can be masked in patients with normal pre-intervention global SCr values. Thus, 50% of total renal mass can be destroyed without any change in renal function. Patients with elevated SCr whose renal function is at the “knee” of this curve have very diminished renal reserve and are at much greater risk. An additional 10% loss of renal parenchyma can put such a patient on dialysis. There can be extensive damage to the kidneys that, in many patients with normal preintervention renal function, may not be apparent during or after renal intervention. It is difficult to know exactly which patient needs protection. For example, a patient with 60% renal function reserve (normal SCr) before the procedure could have renal insufficiency after the procedure if cholesterol embolism destroyed 20% of the nephrons. A good evaluation of the GFR is necessary before the procedure and particularly in patients with limited renal function, elderly patients and patients with extensive atheromatous disease. The choice of which protection device to use merits discussion. We have seen no difference between balloon occlusion and filter use in carotid angioplasty, but our series is limited. For Sos et al,85 balloon occlusion protection devices seem more applicable, because the filters have a pore size of 100 microns or more, allowing small particles and cholesterol crystals into the kidney. For Holden et al, filters are the ideal renal protection system.80 New protection devices have to be developed and dedicated to the renal system. The new Fibernet device seems promising, allowing capture of smaller particles, with a good wall opposition and because only a short landing zone is required, it should enlarge the possibilities of renal protection. Conclusion Renal artery angioplasty and stenting is largely performed with very good technical success, good anatomical results, and a low complication rate and with a good long-term patency rate. The effects on blood pressure are encouraging. However, the deterioration of renal function after the procedure, which may occur in 20–40% of cases may limit the immediate benefits of this technique. Atheroembolism seems to play an important role. Physicians dedicated to this field should be aware of the risks of atheroembolism and deterioration of renal function after renal interventional procedures.