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6. Thrombectomy–Embolectomy
Thrombectomy–Embolectomy
Acute arterial occlusion can be caused by embolization or arterial thrombosis. Extractions of the embolus (embolectomy) or thrombus (thrombectomy) are frequently performed vascular procedures. Because thrombosis is very likely to occur distal to an embolization site, an embolectomy is often referred to as thrombo-embolectomy (TE). Several important considerations need to be addressed when performing these procedures. These include the type of blood vessel incision used to remove the thrombi, and the methods to minimize blood loss and blood vessel trauma during the procedure. Other important issues relate to the various methods used to achieve retrieval of all offending thrombi in addition to assessing the completeness and effectiveness of the clot extraction. Finally, the examination of the extracted thrombi can be very important, as it can provide insight into the etiology of the occlusive process.
Incision Type
Thrombectomy or embolectomy can be performed through a transverse or a longitudinal incision in the vessel. It is important to ensure that the patient is adequately anticoagulated before occluding the vessels. When the occlusion is suspected to be due to embolization, a transverse incision may be most desirable. In this situation, a transverse incision can be closed primarily with relative ease and without causing any significant narrowing of the lumen. Embolization is usually suspected in a patient with arrythmias and intracardiac thrombi who lacks prior history of chronic arterial insufficiency and presents with acute arterial occlusion. In the presence of significant plaque in the artery or when the occlusion is suspected to be caused by thrombosis secondary to a stenotic pathology, a longitudinal arteriotomy will be most appropriate. Thrombosis secondary to a stenotic pathology is usually suspected when a patient presents with acute ischemia and has prior history of chronic arterial insufficiency in the absence of any cardiac arrythmias. A longitudinal arteriotomy will allow for inspection of the diseased area, as well as possible endarterectomy or repair with a patch. In addition, if TE proves to be inadequate, and a distal bypass becomes necessary, the incision can serve as the site of the proximal anastomosis of the bypass. The various methods used for closure of vascular incisions are discussed in Chap. 8.
Minimizing Blood Loss
Blood loss during a TE can be significant. Most of the blood loss tends to occur when performing TE of the proximal segment of the vessel and reestablishing the arterial inflow. Blood loss may occur while passing the TE catheter beyond the thrombus and while retrieving the thrombus. To minimize blood loss, elastic loops are usually used to encircle and double loop the blood vessel. Gentle tension is then applied on the vessel loop when advancing or withdrawing the catheter. When dealing with a prosthetic graft or a large thickened artery, vessel loops may be inadequate to control bleeding around the TE catheter. In this situation, one option is to use “soft-jaw clamps” such as the Fogarty clamps to occlude the blood vessel. The soft jaws may be able to appose the blood vessel walls just enough to prevent bleeding and still allow the TE catheter to be advanced. The jaws are opened as the inflated TE catheter is being withdrawn. Another useful option is to pinch the vessel between the thumb and the index finger of one hand, while the other hand is manipulating the TE catheter.
Avoiding Vessel Trauma
Catheter manipulation during a TE can result in significant injury to the blood vessel [1, 2]. Vessel injury can be induced by the tip or the balloon of the TE catheter. The vascular trauma can occur during insertion, advancement, or withdrawal of the TE catheter. One type of injury occurs when the catheter is inadvertently introduced into a subintimal location. Thus, during insertion, it is very important to be sure that the catheter tip is actually going into the lumen of the vessel. If resistance is met and the catheter cannot be advanced any further with gentle manipulation, forceful advancement should be avoided. Forceful advancement can result in vessel perforation or can drive the catheter into a subintimal plane. The latter will result in intimal dissection. Furthermore, upon withdrawal of the inflated TE catheter, part of the intima may be stripped. It is also important to realize that every time an inflated catheter is withdrawn, intimal damage could occur. In fact, this is one of the techniques used in experimental animal models to harvest endothelial cells or to cause endothelial trauma for the evaluation of neointimal hyperplasia. Vessel injury can occur from excessive shear forces on the wall while retrieving the TE catheter, especially if the balloon is overinflated. Balloon overinflation can also result in vessel rupture.
Several steps can be helpful in avoiding vessel trauma during TE. First, it is important to select the appropriate size of the TE catheter. In general, a size 2 Fogarty catheter will be appropriate for vessels less than 2 mm in diameter, such as the pedal or hand vessels. A size 3 Fogarty catheter is usually most appropriate for vessels with diameters of 2–4 mm, such as the tibial vessels or the infrageniculate popliteal artery. A size 4 Fogarty catheter is usually most appropriate for vessels with diameters of 4–10 mm, such as the above-knee popliteal and superficial femoral arteries, as well as the common femoral artery. A size 4 Fogarty catheter can also be useful for the iliac arteries. A size 5 Fogarty catheter is most appropriate for vessels larger than 10 mm in diameter; it can be useful for TE of some relatively large iliac arteries. Other sizes available include size 6 and 7, which can also be used for thrombectomy of an aortic graft or a saddle aortic embolus. Before inserting the TE catheter, it is imperative to test the balloon and get a visual assessment of its size once fully inflated. It is a good practice to limit the amount of fluid used in the syringe to inflate the balloon to the minimum volume needed for full inflation to avoid overexpansion and rupture of the balloon or the vessel. Another helpful step is to measure the distance from the arteriotomy to the area where the thrombus is expected to be lodged. This will help determine if the catheter has reached far enough to the desired location. In addition, this may help avoid pushing the catheter beyond the desired location unnecessarily, thus limiting the potential injury to the artery. Once the catheter has reached maximal advancement, gentle inflation, while pulling the catheter back, will allow feeling the friction between the balloon and the vessel wall. At that point, the balloon should not be inflated any further. The catheter should just be retrieved with that amount of tension. It is very important that the same individual withdrawing the catheter is also controlling the degree of balloon inflation. Similarly, slight deflation of the catheter may be necessary if the catheter is passing across a stenotic area. As the catheter is being pulled back, additional deflation or inflation may be necessary to accommodate for any change in the caliber of the vessel. With experience, you realize tactile feeling and resistance are important in achieving TE with minimal wall barotrauma.
Achieving a Complete Thrombectomy–Embolectomy
The ability to retrieve all clots and thrombi depends on getting the catheter into all the desired locations as well as the degree of adherence of the thrombi to the vessel wall. If the TE catheter does not reach the desired location, an angiogram can be very useful to delineate the anatomy. One useful approach is to perform the entire TE under fluoroscopic guidance. Half-strength contrast is used to inflate the balloon. The balloon is first tested under fluoroscopy to appreciate its shape when inflated and deflated. The balloon is then inserted and manipulated, based on the prethrombectomy angiogram. This step can be facilitated further if the fluoroscopy machine used has road-mapping capabilities. The fluoroscopy machine will also be used to follow the withdrawal of the catheter. Useful information can be gained from observing the movement of the catheter tip and the inflated balloon under fluoroscopy. First, better insight into the anatomical location of the catheter tip and the vessels that are being catheterized can be obtained. Furthermore, if the inflated catheter is passing across an area of stenosis, the balloon will be seen changing in shape and developing a “waist” at the level of the stenosis.
Thrombectomy–Embolectomy of the Lower Extremity Vessels
During TE of the lower limb vessels, a Fogarty catheter introduced through the superficial femoral artery will tend to repeatedly travel into the peroneal artery. Thus, it is possible to perform a thrombectomy of the peroneal artery alone, leaving behind significant clots in the anterior and posterior tibial arteries. Several techniques can be used to guide the TE catheter selectively into the various tibial arteries. Prior to the use of intraoperative fluoroscopy, one helpful technique is to bend the tip of the TE catheter with the hope that at the level of the popliteal trifurcation, the bent tip will advance into the anterior or posterior tibial artery. Another technique is to perform the procedure using two TE catheters under fluoroscopic guidance. One TE catheter is placed at the origin of the tibioperoneal trunk, and the balloon is then inflated. Another TE catheter with a bent tip is advanced and manipulated under fluoroscopy to proceed into the anterior tibial artery. To catheterize the posterior tibial artery, the balloon of the first TE catheter is inflated at the level of the peroneal artery origin. The second catheter is then advanced after flipping the tip by 180 degrees. Another option is to use special TE catheters that can be introduced over a wire (Fogarty Thru-Lumen Catheter; Baxter Healthcare Corp., Irvine, CA). The wire will be directed first into the desired vessels under fluoroscopic guidance, using an angled tip catheter. The TE catheter is then introduced over the wire, and TE is performed under fluoroscopy. This technique can also be useful when performing aortoiliac thrombectomy. A wire is introduced through each common femoral artery and the thrombo-embolectomy is performed over the wire, while maintaining wire access in case additional endovascular interventions are needed. It is often challenging to withdraw the catheter, while maintaining wire access and adjusting the balloon inflation at the same time, and, often, the wires are pulled out of the artery during the procedure, especially that the tibial TE catheter travels over a 0.018 wire.
An additional valuable technique, especially if the TE over the wire catheter is not available, is to catheterize the artery of interest with a regular 0.034 glide wire, and then introduce a long 6 French 65-cm Ansel sheath into the artery. The obturator is then removed and the 3 French TE catheter is introduced through the Ansel sheath to its desired location. The support provided by the sheath usually will allow the catheter to travel easily as far as it is needed. The inflated TE balloon catheter and the Ansel sheath are then withdrawn together out of the arteriotomy. Along the same principles, special aspiration catheters have been designed to be introduced instead of the traditional TE catheter and then activated, resulting in clot aspiration. These catheters come in various sizes and may allow for a percutaneous approach for retrieval of localized thrombi and small clot burdens. If despite all these maneuvers the desired vessels cannot be canalized, exposure of the popliteal trifurcation will be necessary. The TE catheter can be introduced into the orifice of each individual tibial vessel under direct vision. Occasionally, exposure of the tibial vessels at a more distal level, such as the ankle, may be necessary. This allows direct catheterization and TE of the individual tibial vessels.
One of the difficulties encountered with TE of prosthetic grafts is the excessive adherence of the clot to the graft wall. The usual Fogarty catheter may not be able to retrieve the clot, and other catheters can be used. These catheters have been designed especially for the purpose of recovering adherent thrombi. One of these catheters has a mesh over the balloon of the catheter, which theoretically helps in capturing and retrieving adherent clots (Latis Graft Cleaning Catheter; Applies Medical Resources, Laguana Hills, CA). Other catheters have a curved springy wire at the tip instead of the balloon. The curved wire will serve to strip the adherent thrombus from the vessel wall. (Fogarty Adherent Clot Catheter and Fogarty graft thrombectomy catheter; Baxter Healthcare Corp., Irvine, CA) These special catheters are intended to be used in prosthetic grafts. Their use in native vessels should be avoided.
Evaluating the Completion and Result of the Thrombectomy–Embolectomy
A thorough irrigation of the lumen with heparinized solution is performed. Angiography or angioscopy can be performed to check for residual clots. If the TE appears to be satisfactory, the arteriotomy is closed. One helpful maneuver is to tighten the suture line without tying of the suture and then allow for reperfusion of the limb. Blood flow distally is then assessed, using a Doppler probe or angiography. Should additional thrombectomy become necessary, tension is taken off the sutures, and the suture line is gently loosened and unraveled. The TE catheter insertion and withdrawal are repeated until no additional clots can be retrieved on two consecutive withdrawals. In the presence of a clot that could not be retrieved, an attempt at suction aspiration of the residual clot can be tried, using a 60-cc syringe with negative pressure or an aspiration catheter device. Furthermore, an intraoperative injection of a thrombolytic agent (tPA 0.05 mg/kg) into the arterial bed harboring the clot can be helpful. If there is a spasm, you can inject 100–200 mcg of nitroglycerin or 30–60 mg of papaverine directly into the vessel; wait for a few minutes and repeat the angiogram. Notify anesthesia in case the systemic blood pressure drops. Finally, it is important to check for compartmental hypertension as a possible cause for poor distal Doppler signals despite what appears to be an adequate thrombectomy. The normal compartmental pressure should be less than 35 mmHg.
Examination of Retrieved Thrombi
All retrieved clots and thrombi should be inspected. Inspection of the clots can be helpful in determining the etiology of the occlusion. Clots retrieved when thrombosis develops from low flow secondary to a tight stenosis are similar to coagulated blood. The presence of a grayish granular clot suggests platelet depositions. The presence of a darker or grayish organized clot at the end of the thrombus suggests embolization. An embolus from an atrial myxoma or tumor tends to be gelatinous with a grayish color. In this situation, microscopic examination of the thrombus is essential to delineating the source of the clot and establishing the diagnosis.
Thrombo–Embolectomy
Minimizing Blood Loss
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