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Letters to the Editor |
Department of Cardiovascular Radiology, Clinique St-Gatien, Place de la Cathédrale, Tours 37000, France* e-mail: luc.turmel@wanadoo.fr
Pierre Bourquelot, MD,
Department
of Surgery, Clinique Jouvenet, Paris, France
Josette Pengloan, MD,
Department of Nephrology-Hemodialysis, Centre Hospitalier Universitaire, Tours, France
Editor:
In the October 2002 issue of Radiology, Dr Robbin and colleagues published their findings of ultrasonographic (US) evaluation of immature dialysis fistulas and concluded that "US measurements of AVF [arteriovenous fistulas] at 2–4 months ... are highly predictive of fistula maturation and adequacy for dialysis" (1). Unfortunately, these US results were not correlated with angiography findings, and this purely diagnostic approach is not in agreement with the view of a multidisciplinary team who reported their experience in articles published too recently to have been referenced by the authors (2,3).
First, it is not clearly stated in the article that a patient with an immature fistula is referred for US or angiography only when nephrologists or nurses feel that a vein is either difficult to cannulate or offers insufficient inflow. Imaging should be able to demonstrate the cause in all cases. Our experience is that there are only two possible answers: deep location of the vein or presence of stenosis.
Deep location of the arterialized vein is adequately diagnosed with US and must lead to surgical transposition of the vein into a more superficial location.
Stenosis must be demonstrated in all other cases, and these stenoses can be either dilated or treated with conventional surgery. Unfortunately, the word "stenosis" is hardly mentioned in the article, and this key point is never emphasized. The authors measure diameters but forget that an area of smaller diameter is called a stenosis, and we know today that a low flow rate is predictive of significant stenosis in dialysis accesses (4).
In a series of 69 immature forearm fistulas, we identified an underlying stenosis in all cases by using angiography with puncture of the brachial artery at the elbow (2). We know that these findings are in contrast with the results in another publication (5), but that article was written by a nephrologist, not by a team that includes an interventional radiologist, and the brachial artery approach was not used. These stenoses were dilated to at least 4 mm when they were located in the feeding artery and 5 mm when located in the vein, with a 97% initial success rate, 41% primary patency rate, and 75% secondary patency rate at 1 year. Among the 25% of failures, new anastomoses were achieved surgically because of early recurrence of anastomotic stenoses after dilation, but the fistulas were eventually functional.
The other point of concern in the article is that the authors measure fistula flow in the vein but not in the brachial artery. This obviously leads to underestimation of flow when the authors describe "multiple draining venous branches close to the anastomosis" (1). This description emphasizes the technical difficulties of US in the diagnosis of certain stenoses, since the interventional radiologist knows that there is no opacification of collateral vessels in correctly performed side-to-end fistulas without significant stenosis of the main draining vein. The consequence is that the treatment of collateral vessels is not embolization or ligation but sufficient dilation of the stenosis of the main outflow vein.
The last comment is about the best timing for imaging an immature fistula, but this is in the hands of nephrologists and surgeons who care for the patients. However, delayed maturation can be obvious as early as 1 month after fistula creation, and waiting 3 or 4 months is obviously inappropriate, since the fistula that might have been saved at 6 weeks can thrombose at 2 months and become impossible to reopen, even by experienced hands.
In conclusion, the opinion of our multidisciplinary team is that US examination of fistulas with delayed maturation is extremely helpful. It must be performed as early as 1 month after fistula creation and almost always indicates the need for surgery or angiography. Surgery is necessary whenever US shows evidence of a deep venous location or an anastomotic stenosis that would be best treated with the creation of a new anastomosis. Angiography with concomitant dilation, with use of diluted iodine when dialysis has not already been initiated (6), is indicated in all other cases, since angiography can demonstrate stenoses that are underestimated in the US examination.
REFERENCES
Department of Radiology* and Division of Nephrology, University of Alabama Hospital, 619 19th Street South, JTN350, Birmingham, AL 35249-6830. e-mail: mrobbin@uabmc.edu
We appreciate the interest Dr Turmel-Rodrigues and colleagues have shown in our recent article (1). Our work is based on the collaboration of a multidisciplinary team that includes nephrologists, radiologists, and surgeons, who have been prospectively acquiring patient data since 1996.
Our study was a less biased sample than that reported by Dr Turmel-Rodrigues and colleagues (2), in that we attempted to study all patients with an arteriovenous fistula (AVF), not just those patients referred to the interventional radiology department with an immature AVF (3). Although all patients with an AVF were supposed to be referred for US evaluation, there was a modest referral bias toward referring patients in whom fistula maturation was questionable, as stated clearly in our discussion (1). Furthermore, the standard of clinical adequacy for hemodialysis is a more rigorous and clinically important standard of reference than that of angiography.
Although Dr Turmel-Rodrigues and colleagues state in their letter that AVF evaluation should be performed as early as 1 month after placement, in fact, the average maturity of the AVF in his recent series is 2
months (10 weeks), which is in our evaluation window of 2–4 months (2).
In some fistulas, it was obvious at US that there was a focal stenosis in the draining vein or at the anastomosis. In others, however, there was a slightly narrowed venous area that did not definitively limit flow. In other AVFs, only a small vein was seen without a definite cause for low blood flow. Some AVFs had multiple large proximal branches that were obviously sumping blood flow out of the main draining vein, without a definite more distal stenosis. Patients with deep veins or anastomotic stenosis were referred for superficialization or revision, respectively. Patients with immature AVFs were otherwise referred for interventional radiologic evaluation of stenosis.
In a subsequent study, we reported an analysis of 189 known fistula outcomes reported at our institution (4). Among those patients with AVF who were not lost to technical failure or early thrombosis, 31% underwent one or more interventions because the AVF failed to mature.
With regard to the statement that the brachial artery approach is necessary for AVF evaluation, Beathard et al (5) performed fistulography in 63 AVFs by means of a draining vein approach, and ligation of branches or stenosis angioplasty (or both) was performed. The AVF access was salvaged in 82.5% of cases, an excellent success rate.
As for the matter of blood flow measurement in the draining vein, it is important to realize that the calculation of blood flow is heavily dependent on an accurately measured vessel diameter. The smaller the overall vessel measured, the higher the potential that small errors in diameter measurement will cause substantial error in blood flow calculation. We chose the larger draining vein rather than the smaller inflow artery with full realization that this is an undermeasurement of blood flow in some fistulas with large distal branches. Occasionally, we were able to measure blood flow distal to the draining branches if there was a straight section of nonturbulent venous flow. Our experience differed from that of Dr Turmel-Rodrigues and colleagues in that a more central draining vein stenosis was not always found in a patient with large distal branches.
In summary, we are in agreement that early evaluation of immature fistulas should be performed with US. The patients can then be referred for either surgery or further investigation with interventional radiology, which will hopefully lead to a mature AVF.
REFERENCES
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