Mechanical thrombectomy of major and massive pulmonary embolism with use of the Amplatz thrombectomy device

Percutaneous thrombectomy in patients with intermediate- and high-risk pulmonary embolism and contraindications to thrombolytics: a systematic review and meta-analysis

Catheter-directed interventions have slowly been gaining ground in the treatment of pulmonary embolism (PE), especially in patients with increased risk of bleeding. The goal of this study is to summarize the evidence for the efficacy and safety of percutaneous thrombectomy (PT) in patients with contraindications to systemic and local thrombolysis. We performed a systematic review and meta-analysis using MEDLINE, Cochrane, Scopus and the Web of Science databases for studies from inception to March 2022. We included patients with intermediate- and high-risk PE with contraindications to thrombolysis; patients who received systematic or local thrombolysis were excluded. Primary endpoint was in-hospital and 30-day mortality, with secondary outcomes based on hemodynamic and radiographic changes. Major bleeding events were assessed as a safety endpoint. Seventeen studies enrolled 455 patients, with a mean age of 58.6 years and encompassing 50.4% females. In-hospital and 30-day mortality rates were 4% (95% CI 3-6%) and 5% (95% CI 3-9%) for all-comers, respectively. We found a post-procedural reduction in systolic and mean pulmonary arterial pressures by 15.4 mmHg (95% CI 7-23.7) and 10.3 mmHg (95% CI 3.1-17.5) respectively. The RV/LV ratio and Miller Index were reduced by 0.42 (95% CI 0.38-46) and 7.8 (95% CI 5.2-10.5). Major bleeding events occurred in 4% (95% CI 3-6%). This is the first meta-analysis to report pooled outcomes on PT in intermediate- and high-risk PE patients without the use of systemic or local thrombolytics. The overall mortality rate is comparable to other contemporary treatments, and is an important modality particularly in those with contraindications for adjunctive thrombolytic therapy. Further studies are needed to understand the interplay of anticoagulation with PT and catheter-directed thrombolysis.

Percutaneous Management of High-Risk Pulmonary Embolism

Acute pulmonary embolism (PE) leads to an abrupt increase in pulmonary vascular resistance and right ventricular afterload, and when significant enough, can result in hemodynamic instability. High-risk PE is a dire cardiovascular emergency and portends a poor prognosis. Traditional therapeutic options to rapidly reduce thrombus burden like systemic thrombolysis and surgical pulmonary endarterectomy have limitations, both with regards to appropriate candidates and efficacy, and have limited data demonstrating their benefit in high-risk PE. There are growing percutaneous treatment options for acute PE that include both localized thrombolysis and mechanical embolectomy. Data for such therapies with high-risk PE are currently limited. However, given the limitations, there is an opportunity to improve outcomes, with percutaneous treatments options offering new mechanisms for clot reduction with a possible improved safety profile compared with systemic thrombolysis. Additionally, mechanical circulatory support options allow for complementary treatment for patients with persistent instability, allowing for a bridge to more definitive treatment options. As more data develop, a shift toward a percutaneous approach with mechanical circulatory support may become a preferred option for the management of high-risk PE at tertiary care centers.

Comparison of Aspiration Catheters with Modified Standard Catheters for Treatment of Large Pulmonary Embolism Using an In-vitro Patho-Physiological Model

PURPOSE

The presented in-vitro study provides a comparison of various catheters for mechanical treatment of large-burden pulmonary embolism (PE) under standardized conditions, using a new test rig. Dedicated aspiration catheters (JETi®, Penumbra Indigo®, Aspirex®) were compared with standard catheters (Pigtail, Multi-Purpose, Balloon Catheter) applied for embolus fragmentation.

MATERIALS AND METHODS

Emboli prepared from porcine blood were washed into the test rig which consists of anatomical models of the pulmonary artery (PA) and of the right heart in combination with a pulsatile drive system. For all catheters, the duration of the recanalization procedure and the weight percentage (wt%) of the remaining, removed and washed-down clot fractions were evaluated. For aspiration catheters, the aspirated volume was measured.

RESULTS

All catheters achieved full or partial recanalization. The aspiration catheters showed a significantly (p < 0.05) lower procedure time (3:15 min ± 4:26 min) than the standard fragmentation catheters (7:19 min ± 4:40 min). The amount of thrombus removed by aspiration was significantly (p < 0.001) higher than that by fragmentation, averaging 86.1 wt% ± 15.6 wt% and 31.7 wt% ± 3.8 wt%, respectively. Nonetheless, most of the residue was fragmented into pieces of ≥ 1 mm and washed down. Only in 2 of 36 tests, a residual thrombus of 11.9 wt% ± 5.1 wt% remained in the central PA.

CONCLUSION

Comparison under standardized in-vitro patho-physiological conditions showed that embolus fragmentation with standard catheters is clearly inferior to aspiration with dedicated catheters in the treatment of large-burden PE, but can still achieve considerable success.

LEVEL OF EVIDENCE

No level of evidence, experimental study.

In Vitro Thrombolytic Efficacy of Single- and Five-Cycle Histotripsy Pulses and rt-PA

Although primarily known as an ablative modality, histotripsy can increase the efficacy of lytic therapy in a retracted venous clot model. Bubble cloud oscillations are the primary mechanism of action for histotripsy, and the type of bubble activity is dependent on the pulse duration. A retracted human venous clot model was perfused with and without the thrombolytic recombinant tissue plasminogen activator (rt-PA). The clot was exposed to histotripsy pulses of single- or five-cycle duration and peak negative pressures of 0-30 MPa. Bubble activity within the clot was monitored via passive cavitation imaging. The combination of histotripsy and rt-PA was more efficacious than rt-PA alone for single- and five-cycle pulses with peak negative pressures of 25 and 20 MPa, respectively. For both excitation schemes, the detected acoustic emissions correlated with the degree of thrombolytic efficacy. These results indicate that rt-PA and single- or multicycle histotripsy pulses enhance thrombolytic therapy.

Catheter-directed therapy for acute pulmonary embolism: navigating gaps in the evidence

Systemic thrombolysis for acute pulmonary embolism (PE) reduces the risk of death and cardiovascular collapse but is associated with an increased rate of bleeding. The desire to minimize the risk of bleeding events has driven the development of catheter-based strategies for pulmonary reperfusion in PE. These catheter-based strategies utilize lower-dose fibrinolytic regimens or purely mechanical techniques to expedite removal of the embolus. Several devices providing mechanical or suction embolectomy and catheter-directed thrombolysis, with or without facilitation by ultrasound, have been tested. Data are inconsistent regarding the efficacy and safety of mechanical and suction embolectomy. The most comprehensive data on catheter-based techniques stem from trials of ultrasound-facilitated catheter fibrinolysis. Ultrasound-facilitated catheter fibrinolysis relieves right ventricular pressure overload with a lower risk of major bleeding and intracranial haemorrhage than historical rates with systemic fibrinolysis. However, further research is required to determine the optimal application of ultrasound-facilitated catheter fibrinolysis and other catheter-based therapies in patients with acute PE.

[New aspects of thrombolysis and thrombectomy in pulmonary embolism]

Pulmonary embolism is a potentially life-threatening disease, which can present with varying severity. Based on an emergency risk stratification, the initial treatment strategy should be chosen without delay. While patients with a low mortality risk can be treated in an outpatient setting, patients at high risk should proceed to immediate recanalization by thrombolysis or thrombectomy. Systemic thrombolysis is the first line therapy in the absence of contraindications. The dosing (low versus full dose) and application (systemic versus local via a catheter) of alteplase, the most frequently used agent, is the subject of a number of current studies with the goal to reduce the risk of bleeding. In the case of contraindications for systemic thrombolysis surgical or alternatively, interventional thrombectomy should be performed. This article discusses these procedures in the light of the currently available literature.

Catheter-based therapies in acute pulmonary embolism

AIMS

To provide a systematic review of catheter-based therapies of acute pulmonary embolism.

METHODS AND RESULTS

Studies published in peer-reviewed journals before February 2017 were included and categorized according to the mechanism of thrombus removal: fragmentation, rheolytic therapy, aspiration or catheter-directed thrombolysis. Strengths, challenges and the level of evidence of each device were evaluated. We found 16 different catheter-based therapies for acute PE; all but one being used off-label. The majority of procedures involve catheter-directed thrombolysis. Aspiration therapy shows promise, but limited data are available. Rheolytic therapy should be used with caution, if at all, due to the high number of associated complications.

CONCLUSIONS

Catheter-based therapies show promise as a treatment for acute PE, though evidence is lacking. Further research into the efficacy and safety of devices is needed.

Integrated Histotripsy and Bubble Coalescence Transducer for Thrombolysis

After the collapse of a cavitation bubble cloud, residual microbubbles can persist for up to seconds and function as weak cavitation nuclei for subsequent pulses in a phenomenon known as cavitation memory effect. In histotripsy, the cavitation memory effect can cause bubble clouds to repeatedly form at the same discrete set of sites. This effect limits the efficacy of histotripsy-based tissue fractionation. Our previous studies have indicated that low-amplitude bubble-coalescing (BC) ultrasound sequences interleaved with high-amplitude histotripsy pulses can coalesce the residual bubbles into one large bubble quickly. This reduces the cavitation memory effect and may increase treatment efficacy. Histotripsy has been investigated for thrombolysis by breaking up clots into debris smaller than red blood cells. However, this treatment has low efficacy for aged or retracted clots. In this study, we investigate the use of histotripsy with BC to improve the efficacy of treatment of retracted clots. An integrated histotripsy and bubble-coalescing (HBC) transducer system with specialized electronic driving system was built in-house. One high-amplitude (32 MPa), one-cycle histotripsy pulse followed by 36 low-amplitude (2.4 MPa), one-cycle BC pulses formed one HBC sequence. Results indicate that HBC sequences successfully generated a flow channel through the retracted clots at scan speeds of 0.2-0.5 mm/s. The channel size created using the HBC sequence was 128% to 480% larger than that created using histotripsy alone. The clot debris particles generated during HBC treatments were within the tolerable range. These results illustrate the concept that BC improves the treatment efficacy of histotripsy thrombolysis for retracted clots.

Endovascular treatment of pulmonary embolism: Selective review of available techniques

Acute pulmonary embolism (PE) is the third most common cause of death in hospitalized patients. The development of sophisticated diagnostic and therapeutic modalities for PE, including endovascular therapy, affords a certain level of complexity to the treatment of patients with this important clinical entity. Furthermore, the lack of level I evidence for the safety and effectiveness of catheter directed therapy brings controversy to a promising treatment approach. In this review paper, we discuss the pathophysiology and clinical presentation of PE, review the medical and surgical treatment of the condition, and describe in detail the tools that are available for the endovascular therapy of PE, including mechanical thrombectomy, suction thrombectomy, and fibrinolytic therapy. We also review the literature available to date on these methods, and describe the function of the Pulmonary Embolism Response Team.

Effect of pulse repetition frequency of high-intensity focused ultrasound on in vitro thrombolysis

Vascular occlusion by the thrombi is the main reason for ischemic stroke and deep vein thrombosis. High-intensity focused ultrasound (HIFU) and histotripsy or microtripsy pulses can effectively dissolve the blood clot with no use of thrombolytic agent and ultrasound contrast agent (microbubbles). In this study, HIFU bursts at the same duty cycle (2%) but varied pulse repetition frequency (PRF) from 1Hz to 1000Hz were delivered to in vitro porcine blood clot for 30s. Thrombolysis efficiency initially increases slightly with the PRF, 86.4±10.3%, 89.9±11.9, and 92.9±12.8% at the PRF of 1Hz, 10Hz, and 100Hz, respectively, without significant difference (p>0.05), but then drops dramatically to 37.9±6.9% at the PRF of 1000Hz (p<0.05). The particle size in the supernatant of dissolution is 547.1±129.5nm, which suggests the disruption of thrombi into the subcellular level. Thrombi motion during HIFU exposure shows violent motion and significant curling at the low PRF, rotation about its axis with occasional curling at the moderate PRF, and localized vibration at the high PRF due to the generation of acoustic radiation force and streaming. Quantitative analysis of recorded motion shows the axial displacement decreases with the PRF of delivered HIFU bursts, from 3.9±1.5mm at 1Hz to 0.7±0.4mm at 1000Hz. Bubble cavitation during HIFU exposure to the blood clot was also monitored. The increase of PRF led to the increase of inertial cavitation but the decrease of stable cavitation. In summary, the PRF of delivered HIFU bursts at the same output energy has a significant effect on the thrombi motion, bubble cavitation activities, and subsequently thrombolysis efficiencies.

Histotripsy Thrombolysis on Retracted Clots

Retracted blood clots have been previously recognized to be more resistant to drug-based thrombolysis methods, even with ultrasound and microbubble enhancements. Microtripsy, a new histotripsy approach, has been investigated as a non-invasive, drug-free and image-guided method that uses ultrasound to break up clots with improved treatment accuracy and a lower risk of vessel damage compared with the traditional histotripsy thrombolysis approach. Unlike drug-mediated thrombolysis, which is dependent on the permeation of the thrombolytic agents into the clot, microtripsy controls acoustic cavitation to fractionate clots. We hypothesize that microtripsy thrombolysis is effective on retracted clots and that the treatment efficacy can be enhanced using strategies incorporating electronic focal steering. To test our hypothesis, retracted clots were prepared in vitro and the mechanical properties were quantitatively characterized. Microtripsy thrombolysis was applied on the retracted clots in an in vitro flow model using three different strategies: single-focus, electronically-steered multi-focus and dual-pass multi-focus. Results show that microtripsy was used to successfully generate a flow channel through the retracted clot and the flow was restored. The multi-focus and the dual-pass treatments incorporating the electronic focal steering significantly increased the recanalized flow channel size compared to the single-focus treatments. The dual-pass treatments achieved a restored flow rate up to 324 mL/min without cavitation contacting the vessel wall. The clot debris particles generated from microtripsy thrombolysis remained within the safe range. The results of this study show the potential of microtripsy thrombolysis for retracted clot recanalization with the enhancement of electronic focal steering.

Noninvasive thrombolysis using microtripsy: a parameter study

Histotripsy fractionates soft tissue by well-controlled acoustic cavitation using microsecond-long, high-intensity ultrasound pulses. The feasibility of using histotripsy as a noninvasive, drug-free, and image-guided thrombolysis method has been shown previously. A new histotripsy approach, termed microtripsy, has recently been investigated for the thrombolysis application to improve treatment accuracy and avoid potential vessel damage. In this study, we investigated the effects of pulse repetition frequency (PRF) on microtripsy thrombolysis. Microtripsy thrombolysis treatments using different PRFs (5, 50, and 100 Hz) and doses (20, 50, and 100 pulses) were performed on blood clots in an in vitro vessel flow model. To quantitatively evaluate the microtripsy thrombolysis effect, the location of focal cavitation, the incident rate of pre-focal cavitation on the vessel wall, the size and location of the resulting flow channel, and the generated clot debris particles were measured. The results demonstrated that focal cavitation was always well confined in the vessel lumen without contacting the vessel wall for all PRFs. Pre-focal cavitation on the front vessel wall was never observed at 5Hz PRF, but occasionally observed at PRFs of 50 Hz (1.2%) and 100 Hz (5.4%). However, the observed pre-focal cavitation was weak and did not significantly affect the focal cavitation. Results further demonstrated that, although the extent of clot fractionation per pulse was the highest at 5 Hz PRF at the beginning of treatment (<20 pulses), 100 Hz PRF generated the largest flow channels with a much shorter treatment time. Finally, results showed fewer large debris particles were generated at a higher PRF. Overall, the results of this study suggest that a higher PRF (50 or 100 Hz) may be a better choice for microtripsy thrombolysis to use clinically due to the larger resulting flow channel, shorter treatment time, and smaller debris particles.

Thrombolytic therapy in acute pulmonary embolism

PURPOSE OF REVIEW

The goal of this review is to offer an overview of the use of thrombolytic therapy in acute pulmonary embolism. Clinicians including internists, surgeons, pulmonologists, and other specialists continue to face decisions regarding massive and submassive acute pulmonary embolism in their daily routines. Although an evidence base exists, unanswered questions remain regarding the use of thrombolytic agents.

RECENT FINDINGS

Few large, randomized trials exist in this area of medicine and unanswered questions remain. However, guidelines have been modified and new guidelines have been published over the past several years. Recent data indicating that lower doses of tissue plasminogen activator may be effective and safer are discussed. Newer thrombolytic agents may have advantages, but are less well studied.

SUMMARY

Thrombolytic therapy results in the accelerated lysis of acute pulmonary embolism. However, because nonpathologic thrombi are also lysed, these drugs, although potentially lifesaving, can cause significant bleeding complications. Massive acute pulmonary embolism is the clearest indication for the administration of thrombolytic agents, but patients with acute pulmonary embolism and significant compromise in the absence of hypotension may also merit consideration.

Advances in the diagnosis and treatment of acute pulmonary embolism

Over the past two decades, considerable progress in technology and clinical research methods have led to advances in the diagnosis, treatment and prevention of acute venous thromboembolism. Despite this, however, the diagnosis is still often missed and preventive methods are often ignored. Published guidelines are useful, but are limited by the existing evidence base so that controversies remain with regard to topics such as duration of anticoagulation, indications for placement and removal of inferior vena caval filters, and when and how to administer thrombolytic therapy. The morbidity and mortality of this disease remain high, particularly when undiagnosed. While preventive approaches remain crucial, the focus of this review is on the diagnostic and therapeutic approach to acute venous thromboembolism, with an emphasis on acute pulmonary embolism.

Endovascular therapy for acute pulmonary embolism

Acute pulmonary embolism (PE) is the third most common cause of death among hospitalized patients. Treatment escalation beyond anticoagulation therapy is necessary in patients with massive PE (defined by hemodynamic shock) as well as in many patients with submassive PE (defined by right ventricular strain). The best current evidence suggests that modern catheter-directed therapy to achieve rapid central clot debulking should be considered as an early or first-line treatment option for patients with acute massive PE; and emerging evidence suggests a catheter-directed thrombolytic infusion should be considered as adjunctive therapy for many patients with acute submassive PE. This article reviews the current approach to endovascular therapy for acute PE in the context of appropriate diagnosis, risk stratification, and management of acute massive and acute submassive PE.

Treatment of pulmonary embolism: anticoagulation, thrombolytic therapy, and complications of therapy

During the last two decades, considerable progress in technology and clinical research methods have led to advances in the approach to the diagnosis, prevention, and treatment of acute venous thromboembolism (VTE). Despite this, however, the diagnosis is often delayed and preventive methods are often ignored. Thus, the morbidity and mortality associated with VTE remain high. The therapeutic approach to acute VTE is discussed in this article, with a particular focus on the intensive care unit setting.

Interventional therapies for venous thromboembolism: vena caval interruption, surgical embolectomy, and catheter-directed interventions

Therapeutic strategies other than anticoagulation sometimes require consideration in the setting of acute venous thromboembolism. Vena caval filter placement is increasingly common, in part because of the availability of nonpermanent filter devices. Filter placement, surgical embolectomy, and catheter embolectomy have not been subjected to the same prospective, randomized clinical trial scrutiny as anticoagulation but seem appropriate in certain clinical settings. The indications, contraindications, and available data supporting these therapeutic methods are discussed.

Molecular magnetic resonance imaging of deep vein thrombosis using a fibrin-targeted contrast agent: a feasibility study

PURPOSE

To evaluate the value of a fibrin-specific MR contrast agent (EP-2104R; EPIX Pharmaceuticals) for detection of deep vein thrombosis (DVT) and monitoring of percutaneous intervention for treatment.

MATERIALS AND METHODS

In 6 domestic swine, DVT was induced in an iliac/femoral vein using an occlusion-balloon catheter and subsequent injection of thrombin. The occluded vessels were recanalized by mechanical thrombectomy using a Fogarty catheter and an Arrow rotating thrombectomy device. Magnetic resonance imaging of the pelvis and lung was repeated 4 times (before and after DVT induction, after contrast agent administration, and after intervention) using a 1.5-T whole-body XMR system (ACS-NT, Philips Medical Systems, Best, NL). The visualization of the thrombi and contrast-to-noise ratio (CNR) was assessed.

RESULTS

EP-2104R allowed selective visualization of thrombi with accurate determination of the extent of DVT with high contrast (CNR: 65.3 +/- 17.2). After intervention, dislodged thrombus fragments were selectively visualized in the lung (CNR: 27.9 +/- 9.3).

CONCLUSIONS

Molecular magnetic resonance imaging using fibrin-specific MR contrast agent EP-2104R allowed for selective visualization of DVT and monitoring of percutaneous intervention.

Catheter-directed therapy for the treatment of massive pulmonary embolism: systematic review and meta-analysis of modern techniques

PURPOSE

Systemic thrombolysis for the treatment of acute pulmonary embolism (PE) carries an estimated 20% risk of major hemorrhage, including a 3%-5% risk of hemorrhagic stroke. The authors used evidence-based methods to evaluate the safety and effectiveness of modern catheter-directed therapy (CDT) as an alternative treatment for massive PE.

MATERIALS AND METHODS

The systematic review was initiated by electronic literature searches (MEDLINE, EMBASE) for studies published from January 1990 through September 2008. Inclusion criteria were applied to select patients with acute massive PE treated with modern CDT. Modern techniques were defined as the use of low-profile devices (< or =10 F), mechanical fragmentation and/or aspiration of emboli including rheolytic thrombectomy, and intraclot thrombolytic injection if a local drug was infused. Relevant non-English language articles were translated into English. Paired reviewers assessed study quality and abstracted data. Meta-analysis was performed by using random effects models to calculate pooled estimates for complications and clinical success rates across studies. Clinical success was defined as stabilization of hemodynamics, resolution of hypoxia, and survival to hospital discharge.

RESULTS

Five hundred ninety-four patients from 35 studies (six prospective, 29 retrospective) met the criteria for inclusion. The pooled clinical success rate from CDT was 86.5% (95% confidence interval [CI]: 82.1%, 90.2%). Pooled risks of minor and major procedural complications were 7.9% (95% CI: 5.0%, 11.3%) and 2.4% (95% CI: 1.9%, 4.3%), respectively. Data on the use of systemic thrombolysis before CDT were available in 571 patients; 546 of those patients (95%) were treated with CDT as the first adjunct to heparin without previous intravenous thrombolysis.

CONCLUSIONS

Modern CDT is a relatively safe and effective treatment for acute massive PE. At experienced centers, CDT should be considered as a first-line treatment for patients with massive PE.

A critical review of thromboembolic complications associated with central venous catheters

PURPOSE

Central venous catheters (CVC) are commonly used in critical care. While thrombosis is a well-recognized and frequent complication associated with their use, CVC-related thromboembolic complications, including pulmonary embolism (PE) and right heart thromboembolism (RHTE), occur less frequently and often evade diagnosis. Little information exists to guide clinicians in the diagnosis and management of CVC-related thromboembolic complications.

SOURCE

We critically review and synthesize the literature highlighting the incidence of CVC-related thrombosis. We highlight the risk for developing thromboembolic complications and provide approaches to diagnosing and managing RHTE.

PRINCIPLE FINDINGS

The incidence of CVC-related thrombosis varies depending on patient, site, instrument, and infusate-related factors. Central venous catheters-related thrombosis represents an important source of morbidity and mortality for affected patients. Pulmonary embolism occurs in approximately 15% of patients with CVC-related upper extremity deep venous thrombosis (UEDVT). More frequent use of transesophageal echocardiography, in patients with suspected and confirmed PE, has resulted in increased detection of RHTE. While it is recognized that the occurrence of RHTE, in association with PE, increases mortality, the optimal strategy for their management has not been established in a clinical trial.

CONCLUSION

Central venous catheter-related thrombosis occurs frequently and represents an important source of morbidity and mortality for affected patients. Our review supports that surgery and thrombolysis have both been demonstrated to enhance survival in patients with RHTE and PE. However, important patient, clot, and institutional considerations mandate that treatment for patients with RHTE and PE be individualized.

A porcine deep vein thrombosis model for magnetic resonance-guided monitoring of different thrombectomy procedures

PURPOSE

To establish a porcine model of deep iliac vein thrombosis, which allows monitoring of thrombectomy and thrombolytic procedures by magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Deep iliac vein thrombosis was induced in 12 domestic swine using an occlusion-balloon catheter and subsequent injection of thrombin distal to the occluded vessel site. Thrombosis induction was successfully achieved in all animals after 1 hour as verified by MRI. In addition, x-ray fluoroscopy was performed for comparison. Subsequently, thrombectomy was performed using a Fogarty catheter, an Arrow-Trerotola percutaneous thrombolytic device as well as electrical discharge-induced shock waves. The latter procedure was carried out with and without additional administration of Actilyse. MRI and x-ray fluoroscopy were repeated to monitor therapy.

RESULTS

After successful thrombosis induction within the deep iliac veins in all cases, thrombus material could be completely removed using the Fogarty catheter and the Arrow-Trerotola percutaneous thrombolytic device, whereas electrical discharge-induced shock wave failed to recanalize the occluded vessel even if additional Actilyse was administered. The actual burden of thrombotic material could be reliably visualized using MRI.

CONCLUSIONS

A porcine model of deep iliac vein thrombosis model is presented, which permits reliable visualization of thrombotic material. This model might be a useful tool to compare different thrombectomy devices or to evaluate the effectiveness of new thrombolytic approaches.

Catheter Embolectomy for Acute Pulmonary Embolism

Massive pulmonary embolism (PE) is a life-threatening condition with a high early mortality rate due to acute right ventricular failure and cardiogenic shock. As soon as the diagnosis is suspected, an IV bolus of unfractionated heparin should be administered. In addition to anticoagulation, rapid initiation of systemic thrombolysis is potentially life-saving and therefore is standard therapy. Many patients with massive PE cannot receive thrombolysis because of an increased bleeding risk, such as prior surgery, trauma, or cancer. In these patients, catheter or surgical embolectomy are helpful for rapidly reversing right ventricular failure. Catheter thrombectomy appears to be particularly useful if surgical embolectomy is not available or the patient has contraindications to surgery. Although no controlled clinical trials are available, data from cohort studies indicate that the clinical outcomes after surgical and catheter embolectomy may be comparable.

Catheter-tip embolectomy in the management of acute massive pulmonary embolism

Three catheter interventional techniques are currently available for removing or fragmenting pulmonary emboli: aspiration thrombectomy, fragmentation, and rheolytic thrombectomy. The investigators systematically reviewed all available published research related to the use of catheter-tip devices in patients with pulmonary emboli. Pooled data showed that clinical success with the Greenfield catheter occurred in 72 of 89 patients (81%) when used alone and in 19 of 19 patients (100%) when used in combination with thrombolytic agents. Fragmentation with standard catheters used alone (without thrombolytic agents) was reported in only 3 patients. Clinical success with standard angiographic catheters occurred in 15 of 21 patients (71%) when used in combination with systemic thrombolytic agents and in 115 of 121 patients (95%) when used with local infusions of thrombolytic agents. Data for the Amplatz catheter, the rheolytic Angiojet catheter, and the Hydrolyser catheter when used alone were sparse or absent. Clinical success when used in combination with thrombolytic agents occurred in 6 of 6 patients (100%) with the Amplatz catheter, in 20 of 23 patients (87%) with the Angiojet catheter, and in 19 of 20 patients (95%) with the Hydrolyser catheter. Minor bleeding at the insertion site among all patients, with and without thrombolytic agents, occurred in 29 of 348 patients (8%), and major bleeding at the insertion site occurred in 8 of 348 patients (2%). One patient experienced perforation of the right ventricle with the Greenfield catheter. None reported perforation of a pulmonary artery. In conclusion, all the devices analyzed in this study appear to be useful in the management of acute massive pulmonary emboli.

Evaluation of a Newly Developed Percutaneous Thrombectomy Basket Device in Sheep With Central Pulmonary Embolisms

OBJECTIVE

The authors studied the development of a thrombectomy device that is adequately steerable and quickly placeable in case of extensive pulmonary embolism.

MATERIALS AND METHODS

The device consists of a self-expandable nitinol basket mounted at a catheter-tip, which allows suction and extraction of thrombus material. Five in vitro tests were performed followed by tests in 6 sheep. In vivo thrombus material was introduced through a jugular vein to produce pulmonary embolism. After catheter insertion over the right femoral vein, the basket was placed adjacent to the pulmonary embolus and the extraction procedure was performed.

RESULTS

In in vitro tests, the extracted thrombus amount varied between 60% and 95%. In animal experiments, the extracted amount varied between 30% and 95% as determined angiographically. Limiting factors were steerability and optimal positioning of the basket in relation to the embolus.

CONCLUSIONS

Extraction of pulmonary embolism with the self-expanding suction basket is feasible. However, successful recanalization is limited by catheter maneuverability in the pulmonary arterial system.

Treatment of Acute Pulmonary Embolism: Local Effects of Three Hydrodynamic Thrombectomy Devices in an Ex Vivo Porcine Model

PURPOSE

To report an ex vivo study on the local effects of hydrodynamic thrombectomy for the treatment of acute pulmonary embolism (off-label use).

METHODS

Three devices (6-F AngioJet Xpeedior and 6-F and 8-F Oasis) were used for hydrodynamic thrombectomy inside the arteries of 24 inflated and perfused porcine lung explants. Each system was used at multiple positions inside 4 intact and 4 embolized lungs in vessels measuring 2 to 4 mm, 4 to 6 mm, 6 to 8 mm, and 8 to 10 mm. Angiograms prior to, during, and after catheter positioning and system operation were used to detect arterial wall trauma and to measure local clot removal per 30-second cycle. A total of 21 vessel wall samples were subjected to scanning electron microscopy (SEM) to evaluate non-perforating lesions.

RESULTS

All systems were able to remove clot material. The average recanalized vessel length normalized to 30 seconds for vessel diameters of 2 to 4 and 8 to 10 mm, respectively, was 1.17 and 1.75 cm (AngioJet), 0.97 and 0.25 cm (6-F Oasis), and 2.2 and 1.05 cm (8-F Oasis). Perforations occurred during positioning of the 6-F Oasis (4/78 maneuvers) and 8-F Oasis (13/60), but not the AngioJet (0/89); perforations were also seen during system operation (AngioJet: 21/89 activations, 6-F Oasis: 4/78, and 8-F Oasis: 9/60; all lesions inside vessels <6 mm in diameter). SEM showed 35 lesions, 14 with perforation (contrast extravasation) and 21 without perforation (induced by the tip of the guidewire).

CONCLUSION

The AngioJet was most efficient in clot removal, followed by the 8-F Oasis. The 6-F Oasis was least efficient, but had fewest complications. According to these experiments, the tested hydrodynamic thrombectomy devices may cause perforations in vessels <6 mm in diameter. Changes in catheter design to reduce system-specific complication rates or to improve the efficacy of clot removal are warranted.

When should we thrombolyse patients with pulmonary embolism? A systematic review of the literature

The early mortality in pulmonary embolism (PE) is largely predicted by the associated cardiovascular response, with progressive right ventricular failure, hypotension, shock, and circulatory arrest being associated with increasing mortality. Thrombolysis may improve the prognosis of PE associated with these varying degrees of circulatory collapse, but has no place in the treatment of small emboli with no cardiovascular compromise, as it carries a significant risk of haemorrhage. This review sets out to guide the emergency physician in deciding which patients with PE may benefit from thrombolysis.

AngioJet rheolytic thrombectomy versus local intrapulmonary thrombolysis in massive pulmonary embolism: a retrospective data analysis

PURPOSE

To compare the efficacy of full-dose local intrapulmonary thrombolysis (LIT) versus AngioJet rheolytic thrombectomy (ART) in the treatment of massive pulmonary embolism.

METHODS

A retrospective review was conducted of 8 consecutive patients (5 women; mean age 66.0+/-5.9 years, range 56-74) who underwent LIT with high-dose intrapulmonary urokinase (4400 IU/kg over 10 minutes followed by a 2000-IU/kg/h infusion) and a subsequent 6 consecutive patients (4 men; mean age of 59.2+/-17.0 years, range 26-69) who underwent ART plus adjunctive low-dose urokinase infusions (100,000 IU) until hemodynamic recovery was achieved. Pre and postprocedural Miller scores were calculated, and relative Miller score improvement, total urokinase doses, and duration of therapy were compared.

RESULTS

Hemodynamic stability was restored in all 8 LIT patients and in 5 (83%) of the 6 ART patients; 1 (16.7%) patient died during the ART procedure due to recurrent MPE. In the LIT group, the mean Miller score prior to intervention was 17.38+/-2.67, which was reduced to 6.13+/-1.46 after the intervention (p<0.0001) compared to scores of 18.83+/-2.86 and 6.83+/-2.79, respectively, in the ART group (p<0.0001). The mean urokinase dose was 2.07+/-0.44 million IU in the LIT group versus 0.70+/-0.36 million IU in the ART group (p<0.0001). The mean duration of therapy was 11.45+/-2.94 hours in the LIT group versus 3.37+/-1.41 hours in the ART group (p<0.0001). No significant difference in relative Miller score improvement was observed.

CONCLUSION

By accelerating the fragmentation of thrombus, ART plus adjunctive low-dose urokinase seems to be more rapidly effective compared to LIT. ART achieves both rapid cardiovascular relief and reduces the dose of thrombolytic agent necessary in patients with massive pulmonary embolism.

Acute pulmonary embolism: an update on diagnosis and management

Pulmonary embolism (PE) is a common problem. Given the significant overlap of symptoms and signs between the presentation of PE and acute coronary syndromes, it becomes clear that cardiologists must be familiar with the diagnosis and treatment of PE. The critical issue is always to consider PE in the diagnosis of chest pain. It is then important to determine the likelihood of the diagnosis. For patients at moderate-to-high risk, helical CT provides a rapid and noninvasive diagnostic tool. Several other imaging studies are also available including ventilation/perfusion (V/Q) scan, magnetic resonance imaging, and pulmonary arteriography. Echocardiography can also provide valuable prognostic information. Several biomarkers including the d-dimers, troponins, and natriuretic peptides may provide additional information. The cornerstone of treatment includes anticoagulation. For patients with massive or submassive PE, thrombolysis and embolectomy should be considered. Finally, both primary and secondary prevention are critical to the long-term health of the patient.

How thrombus model impacts the in vitro study of interventional thrombectomy procedures

RATIONALE AND OBJECTIVES

Numerous experimental models are used to investigate the effectiveness of thrombectomy devices. We aimed to study the systematic effects of different in vitro thrombus models on the results of experimental thrombectomy and examined how thrombi formed in vitro and ex vivo differ.

METHODS

Three variables involved in human in vitro thrombogenesis were investigated: spontaneous or thrombin-induced clotting, age (1 or 5 days old), and storage temperature (4 degrees C or 21 degrees C). The fibrin content of in vitro and fresh or old ex vivo thrombi was measured by histologic studies. Ten experiments were performed with each of 8 different in vitro thrombus types using (1) ultrasound thrombolysis, (2) Oasis thrombectomy, (3) Amplatz thrombectomy, and (4) Straub-Rotarex catheters. Thrombus weight was measured after standardized treatment.

RESULTS

The fibrin content was markedly lower in all in vitro than in fresh and old ex vivo thrombi. In vitro thrombus type had no impact on the effectiveness of ultrasound thrombolysis and Amplatz thrombectomy. Thrombogenesis type affected Oasis and Straub-Rotarex catheter use. Storage temperature had a systematic impact on the outcome of Oasis thrombectomies.

CONCLUSION

The fibrin content of in vitro thrombi differs substantially from that of fresh and old ex vivo human thrombi. Experimental conditions may systematically impact experimental evaluation of thrombectomy procedures. In vitro thrombi with thrombin-induced thrombogenesis should be favored for use in thrombectomy experiments.

Massive Pulmonary Embolism: Percutaneous Mechanical Thrombectomy during Cardiopulmonary Resuscitation

Seven patients with massive pulmonary embolism (PE) causing cardiac arrest underwent percutaneous mechanical thrombectomy (PMT) with Hydrolyser and Oasis catheters during cardiopulmonary resuscitation (CPR). Three received adjunctive recombinant tissue plasminogen activator. Thrombectomy was successful in restoring pulmonary perfusion in six patients (85.7%). One patient died of cardiac arrest. Systolic pulmonary pressure decreased after thrombectomy from a median of 73 mm Hg (range, 63-90 mm Hg) to 42 mm Hg (range, 32-81 mm Hg; P < .05). There was one groin hematoma that required blood transfusion. In conclusion, massive PE causing cardiac arrest can be treated with PMT simultaneously with CPR maneuvers to rapidly revert circulatory collapse, with restoration of pulmonary circulation. Larger series are needed to validate this method.

Noninvasive Extracorporeal Thrombolysis Using Electrical Discharge-Induced Shock Waves

RATIONALE AND OBJECTIVES

Many thrombectomy approaches have been developed for the treatment of venous thrombosis; however, no reference standard exists at this time. The aim of this study was to evaluate the efficacy of the transcutaneous application of electrical discharge-induced shock waves for thrombolysis in an in vitro model.

METHODS

Shock waves were applied on a thrombus positioned in a plasma-containing silicon tube using 2 different energy flux densities (0.53 and 2.26 mJ/mm). Depending upon the specific experiment, the thrombus was slightly moved to mimic pulsatory motions or/and additional Actilyse was added. Plasma samples were taken to determine the d-dimers before and after the application of shock waves.

RESULTS

Energy of 0.53 mJ/mm was insufficient for thrombolysis whereas the energy of 2.26 mJ/mm yielded a removal rate of up to 76.4% when the thrombus was slightly moved during the procedure. The amount of d-dimers correlated well with the addition of Actilyse. However, this did not affect the removal rate significantly.

CONCLUSION

The results demonstrate the potential of electrical discharge-induced shock waves for thrombolysis.

New Therapeutic Approaches in Pulmonary Embolism

Pulmonary embolism as a part of venous thromboembolic disease has a broad spectrum of clinical presentations from minimal disease to life-threatening right heart failure. Therapy has to be guided by the risk associated with the individual clinical state of the patient. As long as hemodynamics are entirely stable, anticoagulation is given in order to prevent early or late recurrence, thereby allowing for endogeneous thrombolysis and recovery. In hemodynamically instable patients, i.e. patients under cardiopulmonary resuscitation or in shock, there is the need for a rapid reduction of thrombus mass in order to restore right ventricular function. Systemic thrombolysis is the most feasible modality to reduce the thrombus burden of the pulmonary circulation in the short term. For hemodynamically stable patients with right ventricular dysfunction as assessed by echocardiography, there is still some controversy as to whether thrombolysis improves the long-term outcome. At the least, thrombolysis may positively modify the short-term course of acute disease in patients with an extremely low risk of bleeding. When the acute phase has been overcome, secondary prophylaxis with vitamin K antagonists has to be given. The duration of secondary prophylaxis requires an individual assessment of both the risk of recurrence and the risk of bleeding. In the near future, new anticoagulant drugs such as direct thrombin and factor Xa inhibitors will offer new treatment modalities for the acute phase as well as for secondary prophylaxis.

Applications of percutaneous mechanical thrombectomy in pulmonary embolism

Percutaneous mechanical thrombectomy (PMT) has matured into a reliable and valuable therapeutic tool in acute vascular diseases. PMT devices are designed to achieve rapid clearance of acute occlusion in large arteries and veins. This article provides a summary of cumulated experience on pulmonary embolism (PE) treatment with PMT devices. PMT devices are a heterogeneous group of devices that uses different forms of energy. Most of the devices do not totally eliminate thrombus rather fragment in small particles. The rationale of PMT is based on the rapid relief of central pulmonary obstruction. PMT in massive PE provides efficacious and safe debulking of centrally located thrombus in PE, lowering pulmonary artery pressures and improving hemodynamics and blood oxygenation. This results in lowering mortality if compared with natural history of PE, and reduced procedure time if compared with pharmacological thrombolysis. The clinical indications for percutaneous intervention in PE are discussed in the text.

Suspected pulmonary artery disruption after transvenous pulmonary embolectomy using a hydrodynamic thrombectomy device: clinical case and experimental study on porcine lung explants

PURPOSE

To use porcine lung explants for reconstructing possible situations in which a vessel wall disruption might have occurred in a patient suffering fatal hemoptysis after pulmonary embolectomy with a hydrodynamic thrombectomy device.

METHODS

A 76-year-old woman with massive pulmonary embolism underwent transvenous pulmonary embolectomy using a 6-F AngioJet Xpeedior catheter according to manufacturer's instructions. While activating the device in the middle lobe artery (approximately 8 mm diameter), massive and ultimately fatal arterial bleeding occurred through the tracheal tube. Because no autopsy was authorized, an experimental study was designed to examine possible causes for the vessel disruption. Five fresh porcine heart-lung preparations were examined inside a dedicated chest phantom. Access to the pulmonary vessels was provided through catheters inside the right and left ventricular outlets. A low-flow circulation was maintained with an external pump. The 6-F AngioJet thrombectomy device was activated at 42 sites inside vessels from 2 to 10 mm in diameter; in one lung, 8 activations were made after deliberately withdrawing the guidewire.

RESULTS

Vessels >6 mm in diameter remained intact. Vessel wall disruption occurred in 4 of 7 vessels between 4 and 6 mm in diameter and in 13 of 14 segmental arteries <4 mm in diameter (regardless of whether or not a guidewire was used). The signs of vessel wall disruption included extravasation of contrast material, arteriovenous fistula, and laceration of distal airspaces with contrast inside the bronchus.

CONCLUSIONS

The application of this system has to be considered potentially dangerous when activated inside vessels with diameters <6 mm. The use of this device appears to be safe only inside main branches of the lung vessels at this time. Additional experiments will be required to substantiate these initial results.

Comparison of a new recirculation thrombectomy catheter with other devices of the same type: in vitro and in vivo evaluations

RATIONALE AND OBJECTIVES

To compare a new 7 Fr. Helix thrombectomy catheter with Amplatz thrombectomy devices (ATD) with respect to clot fragmentation efficiency, hemolytic potential, and risk for vascular trauma.

MATERIALS AND METHODS

Particle size was evaluated following the maceration of 8-to-10-day-old clots, each weighing 6 +/- 0.01 g. The clots were macerated using devices of various sizes, including the 7-Fr. Helix thrombectomy catheter, the 7-Fr. over-the-wire (OTW), 8-Fr. ATD and the 6-Fr. ATD. The number of particles by weight was quantified. The 7-Fr. Helix and the 8-Fr. ATD were tested in the native iliac vein of six dogs without presence of clots. Blood samples were obtained before, during, and at 1, 3, 6, 24, and 48 hours after the procedure, to monitor the hemolytic effects. The treated iliac veins were examined histologically.

RESULTS

Most of the clot was fragmented into particles <10 microm. The mean percentage by weight of the original clot that remained as particles larger than 10 microm was 1.59% in the 7-Fr. Helix group. This was significantly less than 3.10% with the 6-Fr. ATD, 2.57% with 7-Fr. OTW and 2.44% in the 8-Fr. ATD group (<0.01). In vivo results showed a higher plasma free hemoglobin (PFH) level starting 5 minutes after initiating the ATD activation, reaching its peak after completion of the activation, and declining afterward, with return to the baseline at 24 hours. The haptoglobin level tended to decline slightly at 10 minutes, reaching its lowest level at 24 hours, and starting to recover at 48 hours. A similar pattern of PFH and haptoglobin changes was found in both groups. There were no significant differences regarding hemolytic effect of the two tested devices. No significant changes of creatinine were observed for up to 48 hours after procedures. Focal microthrombosis was seen in two sites of two vessels treated with the 7-Fr. Helix and a focal injury of a venous valve was noted in the 8-Fr. ATD group. The media and internal elastic lamina (IEL) were intact in all cases.

CONCLUSION

The newly designed 7-Fr. Helix is more effective in fragmentation in vitro clots than the 6 Fr. ATD, 7-Fr. OTW and the 8-Fr. ATD. The 7-Fr. Helix and the 8-Fr. ATD produced hemolytic effects, but they appeared to be tolerated by the animals. The in vivo results indicated that the 7-Fr. Helix appears to be as safe as the 8-Fr. ATD.

In vitro effectiveness of mechanical thrombectomy devices for large vessel diameter and low-pressure fluid dynamic applications

PURPOSE

To determine in vitro the efficacy of clot removal of the AngioJet (AJ; new 6-F generation), Hydrolyser (HL; 6-F), and Oasis (OS; 6-F) hydrodynamic thrombectomy devices and the Amplatz Thrombectomy Device fragmentation catheter (ATD; 8-F and new-generation 7-F) in large-diameter vessels and low-pressure fluid dynamic applications (ie, pulmonary embolism).

MATERIALS AND METHODS

Thrombectomy of clots (N = 60; n = 12 for each tested device) created from 5-day-old porcine blood (16 g) was performed with the AJ (with coaxial 0.035-inch guide wire), HL, OS, and ATD in a bench-top model simulating low-pressure fluid dynamics (pulsed flow, 1,250 L/min). Tubes made of silicone (20-mm inner diameter) containing thrombus simulated a large-diameter vessel. The effluent was passed through a three-step filter system (10-1,000 micro m; pressure drop, 15 mm Hg).

RESULTS

Mean thrombectomy time ranged from 83 seconds (7-F ATD) to 185 seconds (OS; P <.0001 compared to all). Remaining thrombus ranged from 5.4 g/32.7% (AJ) to 11.1 g/68.1% (HL; P <.001 compared to all). The AJ's fluid balance was 0.92, whereas the mean ratio of applied saline solution to aspirated fluid for the other devices were significantly different than isovolumetric conditions (HL, 0.64; OS, 0.59; P <.0001 compared to AJ). The AJ (0.36%), HL (0.43%), and OS (0.38%) caused the least overall emboli larger than 10 micro m; the ATD (7-F, 0.82%; 8-F, 0.74%) caused the most (P <.001 for both).

CONCLUSIONS

The tested mechanical thrombectomy devices showed performance differences in thrombectomy time, efficacy of thrombus removal, and peripheral embolization rates. Based on low embolization rates for all devices tested, the experimental data indicate that the 7-F ATD and the 0.035-inch guide-wire-compatible AJ showed feasibility advantages for thrombectomy in large vessel diameter and low-pressure fluid dynamic applications.