Microthrombi and use of tPA

SARS was known to be associated with a hypercoagulable state and thrombotic complications.[11] There is now a growing body of literature that suggests coagulation dysfunction and thrombosis are common complications of critically ill COVID-19 patients as well, affecting up to a third of ICU patients in a Dutch study.[1] Coagulation dysfunction in COVID-19 patients is thought to be due to a combination of 1) damaged endothelial cells generating excess thrombin and reducing fibrinolysis and 2) hypoxia increasing blood viscosity and activating transcription factor-dependent signaling pathways.[7] Some studies have shown a reduction in 28-day mortality for those with significantly elevated D-dimer or signs of DIC who were treated with heparin.[7][8] Heparin has also been suggested as a good option for anticoagulation due to its additional anti-inflammatory properties.[4][9]

Coagulation dysfunction is also a predictor of poorer outcome and higher risk of progressing to ARDS.[4][12] A comparison of lab values from hospitalized COVID-19 survivors and non-survivors from the Tang et al paper can be seen in Table 1 below. Swiss and Italian guidelines recommend regular monitoring of PT, D-dimer, fibrinogen, platelet count, LDH, creatinine and ALT, with Italians additionally recommending DVT ultrasound screening.[10][13] Both societies also recommend pharmacological thromboprophylaxis but do not discuss treatment with tPA.

The use of tPA in COVID-19 patients is only documented in a handful of cases.[3][5] However coagulation is thought to be an important part of the ARDS pathogenesis, and fibrinolytics have previously been used for treatment in non-COVID-19 ARDS with some success.[4][6] In reports from a news article, two of the five treated patients died after seeing initial improvement, while three saw improvement in their oxygenation but remained on ventilators at the time of publication.[3] In a case series looking at 3 ventilated patients receiving tPA infusions, one saw initial improvement in P/F ratio before declining to pre-tPA levels and expiring, one saw modest improvement in P/F ratios that allowed a return from prone to supine positioning, and one saw initial improvement before returning to pre-tPA P/F levels.[5] None of the patients were taken off of ventilators by the time of publication. The pattern of initial improvement in oxygenation after administration of tPA supports the theory that thrombi play a role in the disease process. However, more data is needed to determine if tPA produces any long term benefits or reduction in mortality. A team at Harvard Medical School and Beth Israel Deaconess Medical Center is enrolling patients in a clinical trial to evaluate tPA as a treatment for ARDS in COVID-19 patients.[14]

(NPC - Novel coronavirus pneumonia)
Table 1: Tang, N, Li, D, Wang, X, Sun, Z. Abnormal coagulation parameters are associated with poor prognosis in patients with novel coronavirus pneumonia. J Thromb Haemost. 2020; 18: 844– 847. https://doi.org/10.1111/jth.14768

Gaps in knowledge

The utility of tPA in COVID-19 patients has yet to be determined. More data is needed on the use of tPA in COVID-19 patients, and the dosage and length of treatment have yet to be defined. A team at Harvard Medical School and Beth Israel Deaconess Medical Center is enrolling patients in a clinical trial to evaluate tPA as a treatment for ARDS in COVID-19 patients.[14]