Effect of low-molecular-weight heparin on recombinant tissue plasminogen activator-induced thrombolysis in canine pulmonary embolism

2022 Update of the Consensus on the Rational Use of Antithrombotics and Thrombolytics in Veterinary Critical Care (CURATIVE) Domain 6: Defining rational use of thrombolytics

OBJECTIVES

To systematically review available evidence and establish guidelines related to the use of thrombolytics for the management of small animals with suspected or confirmed thrombosis.

DESIGN

PICO (Population, Intervention, Control, and Outcome) questions were formulated, and worksheets completed as part of a standardized and systematic literature evaluation. The population of interest included dogs and cats (considered separately) and arterial and venous thrombosis. The interventions assessed were the use of thrombolytics, compared to no thrombolytics, with or without anticoagulants or antiplatelet agents. Specific protocols for recombinant tissue plasminogen activator were also evaluated. Outcomes assessed included efficacy and safety. Relevant articles were categorized according to level of evidence, quality, and as to whether they supported, were neutral to, or opposed the PICO questions. Conclusions from the PICO worksheets were used to draft guidelines, which were subsequently refined via Delphi surveys undertaken by the Consensus on the Rational Use of Antithrombotics and Thrombolytics in Veterinary Critical Care (CURATIVE) working group.

RESULTS

Fourteen PICO questions were developed, generating 14 guidelines. The majority of the literature addressing the PICO questions in dogs is experimental studies (level of evidence 3), thus providing insufficient evidence to determine if thrombolysis improves patient-centered outcomes. In cats, literature was more limited and often neutral to the PICO questions, precluding strong evidence-based recommendations for thrombolytic use. Rather, for both species, suggestions are made regarding considerations for when thrombolytic drugs may be considered, the combination of thrombolytics with anticoagulant or antiplatelet drugs, and the choice of thrombolytic agent.

CONCLUSIONS

Substantial additional research is needed to address the role of thrombolytics for the treatment of arterial and venous thrombosis in dogs and cats. Clinical trials with patient-centered outcomes will be most valuable for addressing knowledge gaps in the field.

Effect of recombinant single-chain urokinase-type plasminogen activator on experimental pulmonary embolism

To compare experimental canine pulmonary thromboembolism (PTE) treatment effects among domestic recombinant single-chain urokinase-type plasminogen activator (scu-PA), recombinant tissue plasminogen activator (rt-PA), and heparin, we injected autologous blood clots into 19 dogs. Those dogs were divided into 3 groups randomly: (1) scu-PA group (n = 6), (2) rt-PA group (n = 6), and (3) heparin group (n = 7). The measurement of hemodynamics and pulmonary angiography was, respectively, carried out at the time spots of preemboli and postemboli, 2 hours and 3 hours after treatment.

RESULTS

(1) An obvious increase in mean pulmonary arterial pressure (mPAP) from preemboli (P < .01) and a decrease in cardiac output (CO; P < .01) after blood clot injection. (2) Intergroup comparisons 2 and 3 hours after treatment: mPAP in scu-PA and rt-PA groups were remarkably lower than those of heparin group (P < .05). (3) Intragroup comparisons after thrombolysis, mPAP declined obviously (P < .01), heparin group saw a further decrease in CO. (4) Pulmonary angiography scoring: decrease in the 2 thrombolytic groups was higher than that of the heparin group.

CONCLUSIONS

The effects of domestic recombinant scu-PA in experimental PTE resemble that of rt-PA in terms of the improvements of hemodynamics and angiography, better than heparin.

Efficacy of thrombolytic therapy in pulmonary embolism determined by MION-enhanced MRA: an experimental study in rabbits

RATIONALE AND OBJECTIVES

This study determined whether contrast-enhanced magnetic resonance angiography could be used as a noninvasive imaging technique to determine the therapeutic effect and endpoint in thrombolysis of acute pulmonary embolism in an animal model.

METHODS

New Zealand white rabbits (n = 18) were anesthetized and mechanically ventilated. Single (n = 12 emboli) or dual (n = 12 emboli in 6 animals) pulmonary emboli were created by injecting autologous thrombi through a right internal jugular venous approach. Three-dimensional time of flight (TOF) magnetic resonance angiograms were obtained after intravenous administration of 2 mg Fe of a long circulating monocrystalline iron oxide. Animals then received 5000 IU heparin and 1.3 mg recombinant tissue plasminogen activator/kg intravenously, and magnetic resonance angiography was repeated 30 minutes and 60 minutes after initiation of thrombolytic therapy.

RESULTS

MION-enhanced magnetic resonance angiography accurately detected pulmonary emboli in all rabbits. Thrombolysis during the observation period was successful in 8 of the 18 animals. In animals with a single embolus, the revascularization rate was 50% (6 of 12 emboli). The rate was 33% (4 of 12 emboli) in animals with multiple emboli. Magnetic resonance angiography allowed determination of thrombus resolution or thrombus persistence.

CONCLUSIONS

It was feasible to diagnose pulmonary embolism accurately in this experimental study and to monitor thrombolysis of pulmonary emboli by MION-enhanced magnetic resonance angiography.

Alpha 2-antiplasmin causes thrombi to resist fibrinolysis induced by tissue plasminogen activator in experimental pulmonary embolism

BACKGROUND

In patients with pulmonary embolism, thrombi resist fibrinolysis induced by plasminogen activators. Because the molecular basis of this thrombus resistance is poorly understood, we used a potent inhibitor to examine the potential role of alpha 2-antiplasmin (alpha 2AP) in experimental pulmonary embolism.

METHODS AND RESULTS

Lysis of experimental pulmonary emboli was measured 4 hours after embolization in anesthetized ferrets. All animals received heparin (100 U/kg). Five experimental groups were studied: (1) no recombinant tissue plasminogen activator (rTPA); (2) rTPA at 1 mg/kg; (3) rTPA at 2 mg/kg; (4) rTPA at 1 mg/kg plus a control monoclonal antibody (MAb); and (5) rTPA at 1 mg/kg plus an alpha 2AP inhibitor (MAb 77A3). In comparison with ferrets receiving no rTPA (15.6 +/- 10.5% lysis, mean +/- SD), rTPA-treated groups showed significantly greater lysis (P < .01). Animals treated with rTPA and alpha 2AP inhibitor (56.2 +/- 4.7% lysis) showed significantly greater lysis than all other treatment groups, including ferrets treated with the same dose of rTPA alone (38.5 +/- 6.3%, P < .01), with twice the rTPA dose alone (45.0 +/- 6.5%, P < .05), or with a control MAb (35.2 +/- 4.6%, P < .01). The combination of rTPA treatment and alpha 2AP inhibition caused no consumption of fibrinogen.

CONCLUSIONS

Inhibition of alpha 2AP significantly amplified the lysis of experimental pulmonary emboli by rTPA without increasing fibrinogen consumption. These results suggest that alpha 2AP may play an important role in thrombus resistance in patients with venous thromboembolism.

Coronary thrombolysis. Comparative effects of intracoronary administration of recombinant tissue plasminogen activator and urokinase

We employed a canine model of coronary thrombosis, induced by injection of radioactive blood clot, via a catheter placed in the left anterior descending coronary artery, to compare effects of intracoronary administration of recombinant tissue plasminogen activator (rtPA) and urokinase (UK) on rate and extent of coronary thrombolysis. Two doses of UK, 15,000 U/kg (UK15) and 30,000 U/kg (UK30) and two doses of rtPA, 0.25 mg/kg (rtPA.25) and 0.75 mg/kg (rtPA.75) were given. Drugs were infused over 45 min. Compared with the other regimens, rate and extent of coronary thrombolysis were significantly increased with rtPA.75. Also, despite a much higher dose of UK, coronary thrombolysis was similar with UK30 and rtPA.25. Compared with UK15, rate and extent of coronary thrombolysis were increased with rtPA.25. These results indicate that intracoronary administration of rtPA is superior to intracoronary UK in inducing thrombolysis.