Complete versus partial distal embolic protection during renal stenting—As good or as worse?

Kanjwal et al. [1] report the results of a secondary analysis of the RESIST trial [2], a four arm study comparing protected (distal protection device, EPD, Angioguard) with unprotected renal stenting. Moreover, both groups were randomly assigned to receive either peri-interventional administration of abciximab or placebo. The use of EPD was not associated with a significant improvement of estimated glomerular filtration rate (eGFR), however, the combined use of EPD and abciximab. In the present trial, the investigators compared the outcome of complete versus incomplete renal protection of the study cohort. Background of this subgroup analysis including 44 patients is the anatomical variation of the renal artery trunk with frequent early off take of branches that can not be protected with current EPD’s. So far, no dedicated EPD for renal use is available. Interestingly, the complete protection group did worse by trend than the partial protection group with a slight decrease in eGFR compared with a mild increase in eGFR in the partial protection group (24 6 25 vs. 3 6 30 ml/min). This result was true despite a significantly higher amount of captured atheromatous debris in the complete protection group. Why is this true? Even if the concept of catching embolic debris with EPD is appealing from a mechanical point of view, so far there is little proof from randomized controlled trials (RCT) that distal protection is beneficial in other vascular beds: the use of EPD during treatment of acute myocardial infarction failed [3], for their use during carotid interventions (CAS) no RCT exists; in a large scale German registry [pro-CAS; 4] no difference in major stroke was found protected and unprotected CAS and a subgroup analysis of the randomized controlled SPACE trial comparing CAS with surgery [5] also found no difference between protected and unprotected carotid stenting. What are the reasons why EPD use failed to significantly improve renal function in the RESIST trial? Most obviously, the study was statistically underpowered. It seems that current filter devices lead to overwhelming platelet activation resulting in a negative microvascular circulation response eliminating the potential beneficial effect of debris capturing. This hypothesis is supported by the result of the RESIST trial with improved renal function following the combined use of EPD and abciximab potentially suppressing the overwhelming platelet activation. Moreover, the key step during stenting of atherosclerotic RAS is the placement of the guiding catheter or the cannulation process of the renal artery origin with a diagnostic catheter. During this manoeuvre, a lot of debris can be scraped from the aortic wall with the tip of the guiding catheter. With the first selective contrast agent injection into the renal artery, all this captured debris is already dislodged into the kidney before any distal protection device works. To avoid embolism during this crucial step of the intervention, the ‘‘no-touch’’ technique [6] should be used or at least before the first dye injection, the catheter should be cleaned from debris by aspirating blood through a Y-connector [7]. The last important aspect questioning about the use of EPD’s is that every additional interventional step increases the risk of embolic complications which is potentially also true for the use of EPD’s. On the one hand, the crossing profile of all available devices is larger than for every 0.014 inch guidewire, on the other hand, the application of the retrieval catheter might become challenging in terms of crossing the stent, especially, if this stent is slightly protruding into the aortic lumen. More or less all current devices have a mismatch of the diameter of the filter containing wire and the width of the tip of the retrieval catheter leading to a significant gap between wire and retrieval catheter tip potentially capturing stent struts when crossing the stent. This means more guiding catheter