Thrombolytic therapy for pulmonary embolism

Targeting Fibrinolytic Inhibition for Venous Thromboembolism Treatment: Overview of an Emerging Therapeutic Approach

Venous thrombosis and pulmonary embolism (venous thromboembolism) are important causes of morbidity and mortality worldwide. In patients with venous thromboembolism, thrombi obstruct blood vessels and resist physiological dissolution (fibrinolysis), which can be life threatening and cause chronic complications. Plasminogen activator therapy, which was developed >50 years ago, is effective in dissolving thrombi but has unacceptable bleeding risks. Safe dissolution of thrombi in patients with venous thromboembolism has been elusive despite multiple innovations in plasminogen activator design and catheter-based therapy. Evidence now suggests that fibrinolysis is rigidly controlled by endogenous fibrinolysis inhibitors, including α2-antiplasmin, plasminogen activator inhibitor-1, and thrombin-activable fibrinolysis inhibitor. Elevated levels of these fibrinolysis inhibitors are associated with an increased risk of venous thromboembolism in humans. New therapeutic paradigms suggest that accelerated and effective fibrinolysis may be achieved safely by therapeutically targeting these fibrinolytic inhibitors in venous thromboembolism. In this article, we discuss the role of fibrinolytic components in venous thromboembolism and the current status of research and development targeting fibrinolysis inhibitors.

[Catheter-assisted local lysis therapy for submassive pulmonary embolism]

BACKGROUND

Pulmonary embolism is the third most common cardiovascular disease. Interventional treatment options as an alternative to systemic lysis therapy of hemodynamically stable, submassive pulmonary embolisms have received an unprecedented boost in innovation in recent years. The treatment options are heterogeneous and can be roughly divided into local thrombolysis and local thrombectomy. For years in our center we have been carrying out catheter-assisted, locoregional lysis therapy with side-hole lysis catheters and a cumulative dose per pulmonary branch of 10 mg alteplase over 15 h for hemodynamically stable, submassive pulmonary emboli.

AIM

The aim of this retrospective study was to review this therapeutic concept and to collect data on clinical endpoints and possible complications.

METHODS

The study included data from 01/2018-03/2023. For this purpose, the patients were selected based on the OPS codes (8.838.60 and 1‑276.0), and the data was collected using the medical records. Biometric data, data on previous illnesses and vital parameters, laboratory chemistry data, CT diagnostic data, echocardiographic data, data on drug treatment and data on complications were collected anonymously.

RESULTS

There was a significant reduction in the strain on the right heart. Peripheral oxygen saturation also improved significantly and heart rate decreased significantly. The complication rate remained low and was almost exclusively limited to access-related problems.

CONCLUSION

Catheter-assisted, locoregional lysis therapy is a safe and effective treatment method for submassive pulmonary embolism.

[Interventional therapy of pulmonary embolism - update]

Several catheter-based systems have been developed for interventional recanalization of pulmonary embolism. These include local ultrasound assisted thrombolysis (EKOS), in-toto-thrombectomy via retriever and aspiration system (FlowTriever) and the Indigo mechanical aspiration system. Safety and efficacy in the removal of thrombus have been demonstrated for all systems. Interventional recanalization strategies for high- and intermediate-high risk pulmonary embolism are potentially more effective in the removal of thrombus and restoration of right heart function than systemic thrombolysis with a lower risk of major bleeding complications. Preliminary data from registries and observational studies are very promising whereas the evidence for systemic thrombolysis treatment in high and intermediate-high risk pulmonary embolism is low. Randomized controlled clinical trials are currently performed comparing catheter based interventional therapies to systemic thrombolysis for the treatment of intermediate-high risk pulmonary embolisms. Primary outcome measurements include mortality, hemodynamic collapse, and major bleedings. Results are expected in 2025. The introduction of interventional therapies for pulmonary embolism was accompanied by an increased awareness of the complexity of pulmonary embolism management. The need for specialized interdisciplinary pulmonary embolism response teams (PERT-teams) and a well-structured approach including a PDCA cycle was recognized.

Evolving paradigm of thrombolysis in pulmonary embolism: Comprehensive review of clinical manifestations, indications, recent advances and guideline

Thrombolytic therapy has been the mainstay for patients with pulmonary embolism (PE). Despite being linked to a higher risk of significant bleeding, clinical trials demonstrate that thrombolytic therapy should be used in patients with moderate to high-risk PE, in addition to hemodynamic instability symptoms. This prevents the progression of right heart failure and impending hemodynamic collapse. Diagnosing PE can be challenging due to the variety of presentations; therefore, guidelines and scoring systems have been established to guide physicians to correctly identify and manage the condition. Traditionally, systemic thrombolysis has been utilized to lyse the emboli in PE. However, newer techniques for thrombolysis have been developed, such as endovascular ultrasound-assisted catheter-directed thrombolysis for massive and intermediate-high submassive risk groups. Additional newer techniques explored are the use of extracorporeal membrane oxygenation, direct aspiration, or fragmentation with aspiration. Because of the constantly changing therapeutic options and the scarcity of randomized controlled trials, choosing the best course of treatment for a given patient may be difficult. To help, the Pulmonary Embolism Reaction Team is a multidisciplinary, rapid response team that has been developed and is used at many institutions. Hence to bridge the knowledge gap, our review highlights various indications of thrombolysis in addition to the recent advances and management guidelines

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.

Acute Pulmonary Embolism: A Review

IMPORTANCE

Pulmonary embolism (PE) is characterized by occlusion of blood flow in a pulmonary artery, typically due to a thrombus that travels from a vein in a lower limb. The incidence of PE is approximately 60 to 120 per 100 000 people per year. Approximately 60 000 to 100 000 patients die from PE each year in the US.

OBSERVATIONS

PE should be considered in patients presenting with acute chest pain, shortness of breath, or syncope. The diagnosis is determined by chest imaging. In patients with a systolic blood pressure of at least 90 mm Hg, the following 3 steps can be used to evaluate a patient with possible PE: assessment of the clinical probability of PE, D-dimer testing if indicated, and chest imaging if indicated. The clinical probability of PE can be assessed using a structured score or using clinical gestalt. In patients with a probability of PE that is less than 15%, the presence of 8 clinical characteristics (age <50 years, heart rate <100/min, an oxygen saturation level of > 94%, no recent surgery or trauma, no prior venous thromboembolism event, no hemoptysis, no unilateral leg swelling, and no estrogen use) identifies patients at very low risk of PE in whom no further testing is needed. In patients with low or intermediate clinical probability, a D-dimer level of less than 500 ng/mL is associated with a posttest probability of PE less than 1.85%. In these patients, PE can be excluded without chest imaging. A further refinement of D-dimer threshold is possible in patients aged 50 years and older, and in patients with a low likelihood of PE. Patients with a high probability of PE (ie, >40% probability) should undergo chest imaging, and D-dimer testing is not necessary. In patients with PE and a systolic blood pressure of 90 mm Hg or higher, compared with heparin combined with a vitamin K antagonist such as warfarin followed by warfarin alone, direct oral anticoagulants such as apixaban, edoxaban, rivaroxaban, or dabigatran, are noninferior for treating PE and have a 0.6% lower rate of bleeding. In patients with PE and systolic blood pressure lower than 90 mm Hg, systemic thrombolysis is recommended and is associated with an 1.6% absolute reduction of mortality (from 3.9% to 2.3%).

CONCLUSIONS AND RELEVANCE

In the US, PE affects approximately 370 000 patients per year and may cause approximately 60 000 to 100 000 deaths per year. First-line therapy consists of direct oral anticoagulants such as apixaban, edoxaban, rivaroxaban, or dabigatran, with thrombolysis reserved for patients with systolic blood pressure lower than 90 mm Hg.

An Update on the Management of Acute High-Risk Pulmonary Embolism

Hemodynamic instability and right ventricular (RV) dysfunction are the key determinants of short-term prognosis in patients with acute pulmonary embolism (PE). High-risk PE encompasses a wide spectrum of clinical situations from sustained hypotension to cardiac arrest. Early recognition and treatment tailored to each individual are crucial. Systemic fibrinolysis is the first-line pulmonary reperfusion therapy to rapidly reverse RV overload and hemodynamic collapse, at the cost of a significant rate of bleeding. Catheter-directed pharmacological and mechanical techniques ensure swift recovery of echocardiographic parameters and may possess a better safety profile than systemic thrombolysis. Further clinical studies are mandatory to clarify which pulmonary reperfusion strategy may improve early clinical outcomes and fill existing gaps in the evidence.

Catheter-directed therapies for the treatment of high risk (massive) and intermediate risk (submassive) acute pulmonary embolism

BACKGROUND

Acute pulmonary embolism (APE) is a major cause of acute morbidity and mortality. APE results in long-term morbidity in up to 50% of survivors, known as post-pulmonary embolism (post-PE) syndrome.  APE can be classified according to the short-term (30-day) risk of mortality, based on a variety of clinical, imaging and laboratory findings. Most mortality and morbidity is concentrated in high-risk (massive) and intermediate-risk (submassive) APE. The first-line treatment for APE is systemic anticoagulation.  High-risk (massive) APE accounts for less than 10% of APE cases and is a life-threatening medical emergency, requiring immediate reperfusion treatment to prevent death. Systemic thrombolysis is the recommended treatment for high-risk (massive) APE. However, only a minority of the people affected receive systemic thrombolysis, due to comorbidities or the 10% risk of major haemorrhagic side effects. Of those who do receive systemic thrombolysis, 8% do not respond in a timely manner. Surgical pulmonary embolectomy is an alternative reperfusion treatment, but is not widely available.  Intermediate-risk (submassive) APE represents 45% to 65% of APE cases, with a short-term mortality rate of around 3%. Systemic thrombolysis is not recommended for this group, as major haemorrhagic complications outweigh the benefit. However, the people at higher risk within this group have a short-term mortality of around 12%, suggesting that anticoagulation alone is not an adequate treatment. Identification and more aggressive treatment of people at intermediate to high risk, who have a more favourable risk profile for reperfusion treatments, could reduce short-term mortality and potentially reduce post-PE syndrome. Catheter-directed treatments (catheter-directed thrombolysis and catheter embolectomy) are minimally invasive reperfusion treatments for high- and intermediate-risk APE. Catheter-directed treatments can be used either as the primary treatment or as salvage treatment after failure of systemic thrombolysis. Catheter-directed thrombolysis administers 10% to 20% of the systemic thrombolysis dose directly into the thrombus in the lungs, potentially reducing the risks of haemorrhagic side effects. Catheter embolectomy mechanically removes the thrombus without the need for thrombolysis, and may be useful for people with contraindications for thrombolysis.  Currently, the benefits of catheter-based APE treatments compared with existing medical and surgical treatment are unclear despite increasing adoption of catheter treatments by PE response teams. This review examines the evidence for the use of catheter-directed treatments in high- and intermediate-risk APE. This evidence could help guide the optimal treatment strategy for people affected by this common and life-threatening condition.

OBJECTIVES

To assess the effects of catheter-directed therapies versus alternative treatments for high-risk (massive) and intermediate-risk (submassive) APE.

SEARCH METHODS

We used standard, extensive Cochrane search methods. The latest search was 15 March 2022.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) of catheter-directed therapies for the treatment of high-risk (massive) and intermediate-risk (submassive) APE. We excluded catheter-directed treatments for non-PE. We applied no restrictions on participant age or on the date, language or publication status of RCTs.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods. The main outcomes were all-cause mortality, treatment-associated major and minor haemorrhage rates based on two established clinical definitions, recurrent APE requiring retreatment or change to a different APE treatment, length of hospital stay, and quality of life. We used GRADE to assess certainty of evidence for each outcome.

MAIN RESULTS

We identified one RCT (59 participants) of (ultrasound-augmented) catheter-directed thrombolysis for intermediate-risk (submassive) APE. We found no trials of any catheter-directed treatments (thrombectomy or thrombolysis) in people with high-risk (massive) APE or of catheter-based embolectomy in people with intermediate-risk (submassive) APE. The included trial compared ultrasound-augmented catheter-directed thrombolysis with alteplase and systemic heparinisation versus systemic heparinisation alone. In the treatment group, each participant received an infusion of alteplase 10 mg or 20 mg over 15 hours. We identified a high risk of selection and performance bias, low risk of detection and reporting bias, and unclear risk of attrition and other bias. Certainty of evidence was very low because of risk of bias and imprecision.  By 90 days, there was no clear difference in all-cause mortality between the treatment group and control group. A single death occurred in the control group at 20 days after randomisation, but it was unrelated to the treatment or to APE (odds ratio (OR) 0.31, 95% confidence interval (CI) 0.01 to 7.96; 59 participants). By 90 days, there were no episodes of treatment-associated major haemorrhage in either the treatment or control group. There was no clear difference in treatment-associated minor haemorrhage between the treatment and control group by 90 days (OR 3.11, 95% CI 0.30 to 31.79; 59 participants). By 90 days, there were no episodes of recurrent APE requiring retreatment or change to a different APE treatment in the treatment or control group. There was no clear difference in the length of mean total hospital stay between the treatment and control groups. Mean stay was 8.9 (standard deviation (SD) 3.4) days in the treatment group versus 8.6 (SD 3.9) days in the control group (mean difference 0.30, 95% CI -1.57 to 2.17; 59 participants). The included trial did not investigate quality of life measures.  AUTHORS' CONCLUSIONS: There is a lack of evidence to support widespread adoption of catheter-based interventional therapies for APE. We identified one small trial showing no clear differences between ultrasound-augmented catheter-directed thrombolysis with alteplase plus systemic heparinisation versus systemic heparinisation alone in all-cause mortality, major and minor haemorrhage rates, recurrent APE and length of hospital stay. Quality of life was not assessed.  Multiple small retrospective case series, prospective patient registries and single-arm studies suggest potential benefits of catheter-based treatments, but they provide insufficient evidence to recommend this approach over other evidence-based treatments. Researchers should consider clinically relevant primary outcomes (e.g. mortality and exercise tolerance), rather than surrogate markers (e.g. right ventricular to left ventricular (RV:LV) ratio or thrombus burden), which have limited clinical utility. Trials must include a control group to determine if the effects are specific to the treatment.

A retrospective analysis of fibrinolytic and adjunctive antithrombotic treatment during cardiopulmonary resuscitation

Synergistic effects of fibrinolytic and additional antithrombotic treatment during cardiopulmonary resuscitation in out-of-hospital cardiac arrest of assumed cardiac origin were evaluated retrospectively. Data were drawn from electronic files of the physician-staffed Emergency Medical Services Tyrol. During a 22-month observation period 53 adult patients were treated with tenecteplase (mean 7641 IU), 19 (32.1%) of whom received additional antithrombotic treatment with heparin (4000-5000 IU) and acetylsalicylic acid (250-500 mg). Lasting return of spontaneous circulation occurred in four of 34 patients who received fibrinolytic treatment only and in seven of 19 patients with additional antithrombotic treatment (p = 0.037). Four of five patients who were discharged from hospital had received additional antithrombotic treatment during CPR and were in appropriate neurological status (CPC 1). Considering the small sample size in this retrospective study, the argument may be still be made that fibrinolytic and adjunctive antithrombotic treatment during cardiopulmonary resuscitation in out-of-hospital cardiac arrest of assumed cardiac origin may increase the chances for survival.