Endovascular mechanical thrombectomy procedures

While thrombolysis in case of an ALI for less than 14 days has proven safety and efficacy, new percutaneous thrombectomy procedures has recently emerged in the endovascular field as an attractive complementary modality of the lytic therapy.

The aim of all of these procedures and techniques is to accelerate the revascularization process, which by adopting the thromobolysis alone may take several hours (e.g., over-night

thrombolysis). The fact that by this way an early initial reperfusion of the threatened limb is obtained in most of the cases, allow to gain the necessary time to adequately perform the thrombolytic regimen, in a patient that is already partially reperfused, thus not anymore in an emergency (i.e., <6 hours) situation. Accordingly, once the acute occlusion is recanalized and there is an initial distal perfusion leading to an immediate symptoms regression, the thombolytic catheter may be safely introduced directly inside the partially recanalizaed occlusion and left at least 12 hours. During this time period the patient should be closely monitored for symptoms and complications, because while compartment syndrome rarely occurs, puncture site bleedings are quite frequently observed.

The next day the patient should undergo again an arteriography though the lytic catheter and the undelying problem has to be fixed by standard endovascular means. Of interest, in case of an acute in-situ occlusion (e.g., by an underlying PAD) there is virtually always a stenosis that is

responsible for the acute occlusion (e.g., plaque rupture [Figure 62] or tight stenosis [Figure 63]), while in case of an arterial embolus, the underlying native vessels are disease free and there is generally no need to further perform an endovascular procedure, because the lytic regimen has “cleaned” all the thrombotic material (Figure 64).

The following Figures describe different clinical scenarios of ALI (e.g., in-situ thrombosis, arterial embolization, etc), all treated with different types of thrombectomy procedures ± in-situ thrombolysis.

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Figure 62 showing a distal SFA acute occlusion (left panel), which was recanalized by a mechanical thrombectomy procedure (central panel: 6Fr Rotarex device™), finally showing the

underlying unstable plaque which has caused the acute occlusion (right panel).

Figure 63 showing an acute prosthetic bypass occlusion from the proximal (CFA) to the distal (ATA) anastomosis.

After a mechanical recanalization (8Fr Rotarex device™), angiography shows the underlying proximal bypass stenosis which has caused the acute occlusion and the persistence of important thrombi.

After having stented the proximal stenosis and after 12 hours of in-situ thrombolysis, there are no more residual thrombi in the bypass.

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Figure 64 shows disease-free femoral arteries (left panel) with an acute embolic occlusion of the distal popliteal artery at the level of the tibial vessels trifurcation (central panel). The right

panel shows a normal flow of the disease-free three tibial vessels after the successful aspiration thrombectomy.

Figure 65 showing an acute common femoral stent occlusion (left panel) treated in a “one-session intervention” by an 8Fr Rotarex Device (central panel) without the need of ballon

angioplasty or other endovascular manipulations

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There are different ways to perform mechanical thrombectomy procedures. Table 9 summarizes the most adopted devices and techniques by performing a mechanical thrombectomy procedure in the peripheral vascular tree in case of ALI.

TECHNIQUE and DEVICES MECHANISM OF ACTION PROS and CONTRAS

Aspiration Thrombectomy (AT)

By simply positioning the aspiration catheter in front of the thrombus and aspirate it.

There are dedicated rapid-exchange (Rx) system and more general over-the-wire (OTW) system

By using a high-speed saline jet, the thrombus is fragmentated. Finally thanks to the Bernoulli/Venturi effect

the macerated thrombus is immediately aspirated. With some devices a low-dose lytic therapy may be directly

injected in the thrombus, in order to facilitate the fragmentation process (= power-pulse spray technique)

The catheters contain a steel spiral powered by an electric motor and rotating at 40.000-95.000 rpm. The rotating spiral

produces a continuous vacuum and the thromboembolic material "drilled" by the tip is drawn into the catheter, where

it is fragmented and transported to the collecting bag.

This Infusion Catheter System is to enhance catheter-directed thrombolysis by accelerating the fibrinolytic process

with the application of ultrasound

In case of large thrombus burden seferal passages are needed. Only the Rx systems allow to leave the wire in place, while by using the OTW systems one needs to regain every time the initial position. In case of very distal embolization the usual shaft length may be too short and the standard catheter may be too bulky to reach the distal

thrombus. In this case a inner lumen of standard OTW balloon may be used

Rheolytic thrombectomy devices are less aggressive than other thrombectomy devices (especially the FT devices).

However, they may produce significant hemolysis leading to bradycardia and hypotension, especially if used in the

coronary-pulmonary circulation

These devices are very useful in case of the thrombus begin to be organized (i.e., >14 days), because thanks to

their rotational head or internal spiral the thrombus is efficaciously fragmentated. Being more “aggressive” in the

native vessels (Rotarex > Aspirex), they may cause dissection or vessel rupture especially if used in small

caliber vessels.

This system is very efficacious in facilitating the lytic therapy to dissolve clots, however it needs several hours to

reestablished sufficient blood flow, thus being too slow for emergency limb-saving interventions

Table 9: different thrombectomy devices, their mode of action and several pros and contras

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These pictures (Figure 66) represent the most used thrombectomy devices for PAD interventions [all the following pictures are reproduced from the respective companies’ websites]:

Angiojet Rheolytic catheter™(Medrad/Possis)

Tips of the 6Fr-8Fr Rotarex Device™ (Straub Medical) Tips of the 8Fr-10Fr Aspirex Device™ (Straub Medical)

Thromcat XT™ (Kensey Nash Corp.)

EKOS Endowave system™ (EKOS Corp.) 10Fr Pronto Catheter™

(Vascular Solutions)

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Of interest, despite these mechanical thrombectomy procedures are performed in order to allow a following regular lytic therapy, it seems that frequently (≈ 50%) these procedures may immediately remove most of the thrombotic material, thus unmasking the underlying problem, finally allowing to complete the revascularization in a one-session procedure. This is of particular interest, because with these one-session procedures, there will be no increased bleeding risks associated with thrombolysis and both, patient’s comfort and catheterization laboratory’s logisitic, were significantly improved (Figure 65).

So far, no randomized controlled trial has established the superiority of these mechanical thrombectomy devices compared to surgery or in-situ thrombolysis and only several retrospective registry or case series are reported in the literature (323-332) . Furthermore, very few direct comparisons between the different thrombectomy devices are available in human trials, thus challenging the decision of which device may be superior to the others (333-335).

Accordingly, as suggested by many operators, one should learn and use as few as possible devices, in order to well recognize their device-related pitfalls or complications, as well as being able to anticipate the aspiration capabilities of the specific used device.

In general, more “aggressive”, thus more powerful devices, such as the fragmentational

devices, are preferred in case of large thrombus burden or in diseased vessel (e.g., prosthetic bypass, atherosclerotic SFA), while more “physiological” devices, such the rheolytic devices, should be

preferrend in small caliber and diseased free vessels (e.g., vein bypass, embolic infra-popliteal occlusions). Finally aspiration catheters may be reserved by very distal embolization, where no other thrombectomy device may arrive, or in case other devices are contraindicated or not available.

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