Thrombolysis of lower extremity embolic occlusions: a study of the results of the STAR Registry

Pulsed high-intensity-focused US and tissue plasminogen activator (TPA) versus TPA alone for thrombolysis of occluded bypass graft in swine

PURPOSE

Prosthetic arteriovenous or arterial-arterial bypass grafts can thrombose and be resistant to revascularization. A thrombosed bypass graft model was created to evaluate the potential therapeutic enhancement and safety profile of pulsed high-intensity-focused ultrasound (pHIFU) on pharmaceutical thrombolysis.

MATERIALS AND METHODS

In swine, a right carotid-carotid expanded polytetrafluoroethylene bypass graft was surgically constructed, containing a 40% stenosis at its distal end to induce graft thrombosis. The revascularization procedure was performed 7 days after surgery. After model development and dose response experiments (n = 11), two cohorts were studied: pHIFU with tissue plasminogen activator (TPA; n = 4) and sham pHIFU with TPA (n = 3). The experiments were identical in both groups except no energy was delivered in the sham pHIFU group. Serial angiograms were obtained in all cases. The area of graft opacified by contrast medium on angiograms was quantified with digital image processing software. A blinded reviewer calculated the change in the graft area opacified by contrast medium and expressed it as a percentage, representing percentage of thrombolysis.

RESULTS

Combining pHIFU with 0.5 mg of TPA resulted in a 52% ± 4% increase in thrombolysis on angiograms obtained at 30 minutes, compared with a 9% ± 14% increase with sham pHIFU and 0.5 mg TPA (P = .003). Histopathologic examination demonstrated no differences between the groups.

CONCLUSIONS

Thrombolysis of occluded bypass grafts was significantly increased when combining pHIFU and TPA versus sham pHIFU and TPA. These results suggest that application of pHIFU may augment thrombolysis with a reduced time and dose.

Stent-assisted recanalisation of acute occlusive arteries in patients with acute limb ischaemia

OBJECTIVE

To assess the efficacy of stent-assisted recanalisation for acute limb ischaemia in patients considered unfit for thrombolysis or in patients with failed surgical recanalisation.

MATERIALS AND METHODS

Fifteen patients with acute limb ischaemia, treated with stent implantation, were analysed retrospectively. The reasons for acute limb ischaemia were a cardiogenic embolism (n=3), a traumatic injury (n=3), acute in situ thrombosis with atherosclerosis (n=6), immediate graft thrombosis (n=2), or a delayed thrombotic occlusion after a thrombin injection in the pseudoaneurysm (n=1). This study examined the technical and clinical outcomes of the procedures, including complications during the procedural and follow-up periods.

RESULTS

Stent-assisted recanalisation was technically successful and provided immediate recanalisation in all patients (15/15 patients, 100%) and reduced or eliminated the clinical symptoms in 12 patients (12/15 patients, 80%). Two patients died of multi-organ failure related to reperfusion injury, and one patient with a crash injury underwent a below-the-knee amputation as a result of wound necrosis despite recanalisation of the occluded bypass graft.

CONCLUSIONS

Stent-assisted recanalisation has a high technical success rate with good clinical results as a bailout procedure for the management of acute limb ischaemia in patients, considered unfit for thrombolysis or in patients with failed surgical recanalisation.

Popliteal artery disease: diagnosis and treatment

The popliteal artery is a relatively short vascular segment but is affected by a unique set of pathologic conditions. These conditions, which may be common throughout the arterial system or exclusive to the popliteal artery, include atherosclerosis, popliteal artery aneurysm, arterial embolus, trauma, popliteal artery entrapment syndrome, and cystic adventitial disease. The clinical manifestations, imaging appearances, and treatment options associated with these pathologic conditions differ significantly. Consequently, the radiologist should be familiar with these conditions to direct imaging for accurate diagnosis and treatment and to prevent loss of limb.

Catheter-directed Thrombolytic Therapy for Limb Ischemia: Current Status and Controversies

Absence of urokinase from the United States market for the past 4 years has resulted in increasing experience with other plasminogen activators in catheter-directed thrombolytic therapy. The differences in the pharmacologic properties and biologic behavior of these agents may translate into clinical outcomes that are distinct. Some of these manifestations can be predicted based on the existing large clinical trials in the acute myocardial infarction literature. However, because of the fundamental differences in techniques and thrombolytic regimens, extrapolation of the coronary data may not always predict the performance of these agents in peripheral catheter-directed fibrinolysis. In this article, the current status of the available lytic agents in the treatment of limb ischemia is reviewed.

Catheter-directed Thrombolytic Therapy for Limb Ischemia: Current Status and Controversies

Absence of urokinase from the United States market for the past 4 years has resulted in increasing experience with other plasminogen activators in catheter-directed thrombolytic therapy. The differences in the pharmacologic properties and biologic behavior of these agents may translate into clinical outcomes that are distinct. Some of these manifestations can be predicted based on the existing large clinical trials in the acute myocardial infarction literature. However, because of the fundamental differences in techniques and thrombolytic regimens, extrapolation of the coronary data may not always predict the performance of these agents in peripheral catheter-directed fibrinolysis. In this article, the current status of the available lytic agents in the treatment of limb ischemia is reviewed.

Primary stenting of embolic occlusions in iliac arteries

PURPOSE

To present our experience with the use of primary stenting to treat embolic iliac artery occlusions.

METHODS AND RESULTS

Six patients (5 men; mean age 50.6+/-14.1 years range 37-72) underwent primary stenting for embolic occlusions lodged in the common iliac and/or external iliac arteries and were retrospectively evaluated. The probable reason for the embolism was atrial fibrillation in 4 patients and acute myocardial infarction in 2. In 5 patients, an additional embolus was demonstrated in the renal, mesenteric, popliteal, and middle cerebral arteries. Iliac emboli were treated with primary implantation of self-expanding stents followed by very low-pressure balloon dilation. In all cases, primary stenting was technically successful and provided immediate recanalization with elimination or reduction of symptoms. There was no procedure-related complication. During the mean 11-month follow-up (range 1-18), all stented iliac arteries remained patient. One patient died due to cerebral embolism at 21 months.

CONCLUSIONS

Although this experience is limited, excellent midterm results suggest that primary stenting may be a valuable alternative in the treatment of embolic occlusions of the iliac arteries in selected cases.

Pharmacomechanical thrombolysis with use of the brush catheter in canine thrombosed femoropopliteal arterial PTFE bypass grafts

PURPOSE

To assess the efficacy, acute endothelial changes, and distal arterial emboli after use of the Cragg thrombolytic brush catheter in mature thrombosed polytetrafluoroethylene (PTFE) femoropopliteal arterial grafts in canines.

MATERIALS AND METHODS

PTFE femoropopliteal arterial grafts were implanted in 10 canines and were allowed to mature for approximately 4 weeks. The grafts were thrombosed by mechanical means and allowed to remain thrombosed for 24-72 hours. Through a left carotid cut-down, standard Seldinger arterial puncture was performed, followed by catheterization of the thrombosed graft. A soft, low-speed, brush (6 mm in diameter) aided by preprocedure pulse-spray urokinase infusion was utilized for thrombolysis. The native vessels, just proximal and distal to the anastomosis, were evaluated microscopically for endothelial damage. Arteriography was used for assessment of distal embolus.

RESULTS

All grafts were successfully thrombosed before thrombolysis. One graft could not be traversed with a wire and catheter and was, therefore, not treated. Immediate preprocedure pulse-spray urokinase infusion in the remaining nine grafts did not reconstitute antegrade flow in any instance and left significant amounts of residual thrombus in all treated grafts. Mechanical brush thrombolysis reconstituted antegrade flow in all nine treated grafts and complete graft thrombolysis was obtained in most. This was accomplished in a mean time of less than 4 minutes. Emboli were noted angiographically in 67% of cases. Histologic studies showed vessel wall damage limited to the intima or media in 67% of anastomoses.

CONCLUSION

This method offers a simple and rapid means of recanalizing thrombosed PTFE femoropopliteal arterial grafts in the studied model. This technique provides a means of rapidly "debulking" most intragraft thrombi. This may result in a shorter course of thrombolytic infusion. Potential benefits may include shortening the total treatment time and decreasing morbidity and cost associated with percutaneous thrombolysis. The occurrence of distal emboli in a majority of cases is a concerning limitation of this technique.

Initial results of reteplase in the treatment of acute lower extremity arterial occlusions

PURPOSE

To assess the feasibility and efficacy of reteplase in transcatheter arterial thrombolysis for lower extremity occlusive disease.

MATERIALS AND METHODS

Fifteen consecutive patients with acute lower extremity ischemia due to occlusive disease were treated by means of catheter-directed thrombolysis with reteplase. Following diagnostic angiography, thrombolysis was started either from an antegrade puncture site in cases of femoropopliteal occlusions, or from the contralateral groin in cases of thrombosis of the iliac artery, common femoral artery, or infrainguinal bypass grafts. Reteplase was infused at a rate of either 0.5 U/h (six patients) or 1.0 U/h (nine patients).

RESULTS

Complete thrombolysis was achieved in all of the nine (100%) patients in the 1.0 U/h group and in four of six (66%) patients in the 0.5 U/h group for a combined success rate of 13 of 15 (87%). Clinical success was achieved in 11 of 15 patients overall (73%). Major bleeding complications occurred in none of the 9 patients in the 1.0 U/h group and in one (16%) of the six patients in the 0.5 U/h group for an overall rate of 6%.

CONCLUSIONS

Reteplase shows promise as an alternative to urokinase in the treatment of lower extremity ischemia due to arterial occlusive disease.

Quantitative evaluation of selective thrombolysis techniques: influence of catheter characteristics and delivery parameters

Here, we evaluate in vitro the site-specific delivery ability of thrombolysis catheters and compare continuous infusion (CI) and periodic injection (PI) protocols with reference to this parameter. Thrombotic occlusion was simulated by placing a porcine blood clot proximal to an eccentric stenosis in a flow phantom. Iodinated contrast agent was used as the marker. Part I-Evaluation of thrombolysis catheters: four CI and three PI catheters were tested. The marker was delivered as an infusion at 1 ml/min for 1 min (CI), or as two 0.25 ml boluses 30 sec apart (PI). Iodine content of the clot was then estimated with x-ray fluorescence spectrometry. This value as a ratio of the delivered dose was defined as the targeting efficiency. Part II-Evaluation of thrombolysis protocols: CI and PI were compared. The marker was delivered for 3 or 5 min using one of seven protocols. The iodine content of both clot and effluent were estimated. Among PI catheters, the Jet-Lysis catheter proved to be the best (P = 0.02). The EDM catheter had the lowest targeting efficiency in the CI group (P = 0.01). With CI, median iodine recovery dropped from 0.21 (95% confidence interval: 0.08, 0.25) for 1 min to 0.13 (0.05, 0.16) for 3 min and 0.07 (0.03, 0.10) for 5 min; for PI the values remained unchanged. The fraction lost in the effluent increased with the duration of regimen with both CI (P = 0.014) and PI (P = 0.004). Reducing the rate of infusion or the bolus frequency resulted in major improvements with respect to this parameter (P = 0.005). For CI, the targeting efficiency increased as well (P = 0.03). We conclude that currently used thrombolysis protocols do not fully exploit the delivery advantage offered by CI or PI. Fortunately, simple modifications offer the possibility of overcoming these drawbacks.