1.1. Indications for AVF treatment
Local complications of femoral arterial catheterization like hematomas, pseudoaneurysm (PSA) and arteriovenous fistula (AVF) are increasing in incidence due to the large number of patients undergoing diagnostic and therapeutic angiographic procedures through this route [1 - 3] (see figure 1). A PSA refers to a confined collection of thrombus and blood associated with tear of one or more layers of an arterial wall . An iatrogenic AVF occurs when an arterial puncture inadvertently extends to involve an adjacent vein leading to a communication between the two. Color flow Doppler ultrasound is the imaging modality of choice for the diagnosis and assessment of a PSA, with a high sensitivity and specificity .
Incidence of post-angiographic femoral PSA and AVF varies between 0.07-9% , . The risk factors include age more than 65 years, low or high femoral arterial puncture, anticoagulation and use of a large arterial sheath size .
2. AFV diagnosis using imaging modalities
In the femoral region, turbulence is seen within either the common femoral or profunda femoral vein with arterialized signals shown on the Doppler spectrum (see Figure 2A). The fistulous communication can be seen on color flow Doppler, although it may be difficult to localize with duplex ultrasound alone (see Figure 2B). The turbulence associated with the fistula can be confused with turbulent signals due to extrinsic compression of the vein by hematoma or PSA, which is also a common complication following catheterization. The characteristic findings of a PSA include a slow swirling flow [Yin -Yang sign] within a hypoechoic lesion which is connected to the parent artery via a neck (see Figure 3 A-D). The latter displays a characteristic “to-and-fro” high velocity flow . Doppler features of an AVF include a region of aliasing interposed between an artery and vein with increased diastolic flow in the artery and turbulent flow within the vein .
Visualization of the communicating channel allows a confident diagnosis of AVF rather than extrinsic venous compression by the surrounding hematoma or PSA. The use of computerized axial tomography (CTA) can resolve the problem (see Figure 4 A-B).
3. Methods of treatment for AVF
Transcutaneous therapy aimed at achieving closure of the fistula has been described using ultrasound monitoring and by applying pressure over the fistula for periods of 20 to 60 minutes success rates are 30% or lower .
Despite ultrasound guided thrombin injection [UGTI ] is an off label use of topical thrombin which is not FDA approved for injection, but it is only the treatment of choice when favorable anatomy is present such as a well defined narrow neck for post catheterization PSA [5 - 7]. Ultrasound guided compression [USGC] without thrombin injection retains a high success rate [6, 7] and it is a useful substitute for inducing thrombosis in the PSA and closure of AVF tract, with good results [10-17]
4. Treatment algorithm for AVF
Any patient who experiences local site pain disproportionate to that expected after an angiographic procedure should be evaluated with duplex ultrasound to rule out the presence of a PSA and/or AVF. Color Doppler ultrasound and spectral analysis has a high sensitivity [94%] and specificity [97%] for detection of a PSA .
Untreated PSA can lead to progressive lesion enlargement, infection, compression neuropathy and rupture . Until the early nineties, surgery was the only treatment available for PSA and AVF closure. Presently it is only rarely employed to treat the post catheterisation PSA, when other treatment options fail or if a complication develops .
In 1991 Fellmeth et al. described a method of ultrasound guided compression (USGC) for closing post catheterization femoral PSA and AVF . Subsequent studies confirmed a high rate of success [varying from 75% to >90%] for closure of PSA by this method [14 - 15]. In patients on anticoagulants, the success rate is reported to be between 30%-73 % [14 - 17]. Success rate for AVF closure is described between 33%-50% [12 - 16].
The mechanical compression is exerted using the ultrasound probe and is positioned directly over the neck of the PSA or the tract in case of the AVF . It is titrated so as to obliterate blood flow within them. At all times an adequate flow is maintained in the concerned artery. The compression is usually continued for cycles of 10 minutes each with intermittent release to assess for closure of the neck. This can be repeated till the neck is closed or else discontinued if the physician/patient develops fatigue .
The only limiting factor in USGC method is the time it takes to induce thrombosis to close the PSA or AVF tract . Patient may experience intra-procedural pain which responds to intravenous analgesia . Complications are rare and include vasovagal reactions, PSA rupture, skin necrosis and DVT .
Successful obliteration o the PSA and the AVF is the main goal of the whole procedure (see Figure 5). This is the major goal every treating physician should achieve for better patient management and treatment.
Ultrasound guided compression of the post-angiographic femoral arterial injuries is a technically simple and relatively safe method.