Worldwide cases of coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, neared 52 million on November 12, 2020, with over 1.2 million deaths.
Diagnostic and therapeutic challenges are open.[2–9] Alongside various grades of lung damage and acute respiratory distress syndrome with severe alterations of the ratio between arterial blood oxygen tension (PaO2) and the fraction of inspired oxygen (FiO2), abnormal coagulation parameters are extensively reported in COVID-19 patients,[11–16] those with poor prognosis often exhibiting a pro-thrombotic profile with increased D-dimer, prothrombin time, and fibrin degradation products.[11–13,16–19] Intravascular pulmonary thrombosis acts as a trigger to further worsening of clinical conditions,[20,21] with pulmonary thromboembolism widely reported in retrospective studies.[22–27] However, clinical contextualization of these series highlights how the overlap of pulmonary and systemic inflammation—with widespread activation of the coagulation cascade—hampers timely suspicion of pulmonary thromboembolism in COVID-19 patients.[19–21,28] The aim of this study, conducted during the first SARS-CoV-2 pandemic peak in Lombardy, Italy, was therefore to investigate the incidence of pulmonary thromboembolism in all patients from a single ward of a primarily COVID-19-dedicated hospital, all of them receiving from admission at least prophylactic dosage of low-molecular-weight heparin (LMWH).
2 Materials and methods
The Ethics Committee of IRCCS Ospedale San Raffaele approved this retrospective cross-sectional study. We analyzed 45 COVID-19 patients hospitalized from March 1 to April 30, 2020, in a single non-intensive care ward of IRCCS Policlinico San Donato (San Donato Milanese, Italy)—a primarily-dedicated COVID-19 hospital. SARS-CoV-2 infection was confirmed by reverse transcriptase–polymerase chain reaction on nasopharyngeal swabs. While coagulation parameters of 32 of these 45 patients were already analyzed in another report on the occurrence of early stage coagulopathy in COVID-19 patients, we here progress further in the diagnostic pathway of these patients, focusing our attention on computed tomography pulmonary angiography (CTPA) findings. Indeed, CTPA was subsequently prompted in all these 45 patients by clinical suspicion of pulmonary thromboembolism, even though all of them had been receiving LMWH at least at prophylactic dosage from admission.
Main criteria driving the request of CTPA were the presence of lower-limbs deep vein thrombosis at ultrasound Doppler examination, onset or worsening of dyspnea, and worsening or less-than-expected improvement of the PaO2/FiO2 ratio. We subsequently retrieved clinical data including age, sex, weight, height, body mass index, comorbidities, pharmacological treatments during hospitalization, anticoagulant therapy at admission, PaO2, FiO2, and PaO2/FiO2 ratio. Blood tests performed at admission and before CTPA included coagulation parameters, inflammatory markers, and troponin T.
CTPA exams were performed using a 16-slice CT scanner (Somatom Emotion, Siemens Healthineers, Erlangen, Germany), including breath-hold unenhanced and contrast-enhanced scans. Patients received 1 mL/kg of contrast agent (Iopamidol 370 mg/mL, Bracco Imaging, Milan, Italy), intravenously injected at a 5 mL/s rate, plus a 35 mL saline bolus. Bolus triggering in the pulmonary artery, tube voltage 110 kVp, automatic exposure control, and cranio-caudal scanning were used.
A radiologist with 15 years of experience in body and chest CT reviewed images to assess presence and extent of thromboembolism.
Continuous variables were reported as median and interquartile range (IQR). Comparing patients with and without pulmonary thromboembolism, the Fisher exact test was used to assess significant differences for categorical variables, while the Mann–Whitney U test was used for continuous ones. Statistical analysis was performed using IBM SPSS Statistics v.26.0 (IBM SPSS Inc., Chicago, IL). As 19 comparisons were made overall, P-values were adjusted with the Bonferroni correction, therefore considering P-values <.003 as statistically significant.
Of 45 COVID-19 patients included in this study, 34 were men (76%) and 11 women (24%), with a median age of 67 years (IQR 60–76) (Table 1). At least one comorbidity was found in 33 (73%) patients, hypertension being the most common (23 patients, 51%), followed by previous cardiovascular disease (15 patients, 33%) and diabetes mellitus type 2 (11 patients, 24%).
Table 1 -
Demographic and clinical characteristics of the 45 included patients.
||Patients with PTE (27)
||Patients without PTE (18)
||Number of comorbidities (median)
|Laboratory and clinical variables
||Patients administered tocilizumab
||Patients with LLVT
||Days of hospitalization (median)
aPTT = activated partial thromboplastin time; BMI = body mass index; COPD = chronic obstructive pulmonary disease; CRP = C-reactive protein; FiO2 = fraction of inspired oxygen; IL6 = interleukin 6; LLVT = lower-limbs vein thrombosis; PaO2 = arterial blood oxygen tension; PT = prothrombin time; PTE = pulmonary thromboembolism.
aFisher exact test for categorical variables and Mann–Whitney U test for continuous ones.
bMedian of worst values during hospitalization.
cMedian values before computed tomography pulmonary angiography are reported.
dStatistically significant differences.
On admission, 16 patients had fever, cough, and dyspnea (36%), 13 fever and dyspnea (29%), 5 fever and cough (11%), 9 only fever (20%), 2 only dyspnea (4%). Median room air pulse oximetry was 89% (IQR 76%–95%).
All patients received at least prophylactic LMWH from admission (Enoxaparin 4000 UI or 6000 UI s.c. q.d.). Three patients were already taking apixaban due to permanent atrial fibrillation, while one was started on LMWH at anticoagulation dosage on admission for paroxysmal atrial fibrillation. One patient developed retroperitoneal hematoma during hospitalization, and LMWH was stopped. Tocilizumab was administered to 16 patients.
Median elapsed time from admission to CTPA was 18 days (IQR 13–21). Of 45 patients, 27 (60%, 20 men, 74%) exhibited signs of pulmonary thromboembolism at CTPA, 17 of them (63%) bilaterally. No main branch thromboembolism was found. Examples are presented in Figs. 1 and 2.
In 12/45 patients (27%) with high clinical suspicion of pulmonary thromboembolism CTPA was directly performed without previous lower-limbs ultrasound Doppler examination, 6 of them (50%) being subsequently diagnosed with pulmonary thromboembolism. In the remaining 33/45 patients (73%) lower-limbs ultrasound Doppler examination was performed before CTPA, 3 (9%) patients having superficial vein thrombosis and only 1 patient (3%) having deep vein thrombosis. Of note, only the latter subsequently showed CTPA signs of pulmonary thromboembolism. Overall, among these 33 patients, pulmonary thromboembolism was diagnosed by CTPA in 21 patients (64%).
Before CTPA, 5 patients (11%) had high D-dimer levels (11.21 μg/mL, IQR 9.10–13.02), 19 (42%) had high fibrinogen levels (550 mg/dL, IQR 476–590), 1 (2%) had an altered prothrombin time (64%, INR 1.36), and 7 (16%) an altered partial thromboplastin time (39.6 seconds, 38.4–40.6). Eleven patients (24%) had high C-reactive protein levels (9.60 mg/dL, IQR 6.75–10.65) and 26 (58%) high interleukin-6 levels (79 pg/mL, IQR 31–282). Sixteen patients (36%) had high ferritin values (932 mU/mL, 502–1192) and 41 (91%) high lactate dehydrogenase values (458 μg/L, IQR 376–635). High troponin T values were found in 10 patients (22%, 26.5 ng/L, IQR 18.0–32.5).
After CTPA diagnosis of pulmonary thromboembolism, only 2 out of 45 patients (4.5%) needed intensive care, while 8 out of 16 patients (50%) which were previously administered tocilizumab were found to have pulmonary thromboembolism. One female patient with thromboembolism had autoimmune thrombocytopenia. Prevalence of pulmonary thromboembolism in subgroups of patients with altered clinical parameters was: 1 out of 4 (25%) patients with lower-limbs vein thrombosis; 5 out of 5 patients with high D-dimer levels; 14 out of 19 (74%) patients with high fibrinogen levels; 1/1 patients with altered prothrombin time; 6 out of 7 (86%) patients with altered partial thromboplastin time; 10 out of 11 (91%) patients with high C-reactive protein level; 17 out of 26 (65%) patients with high interleukin-6 levels; 10 out of 16 (63%) patients with high ferritin values; 26 out of 41 (63%) patients with high lactate dehydrogenase values; 10 out of 10 patients with high troponin values. Table 1 shows statistical comparisons between different variables in patients without and with pulmonary thromboembolism.
As of May 4, a median follow-up of 27 days (IQR 26–28) was available, with 3 patients having died during hospitalization, 2 because of complications of pulmonary thromboembolism, and 1 for retroperitoneal bleeding.
SARS-CoV-2 infection—while mainly affecting the respiratory system—also presents systemic inflammatory damage and activation of the coagulation cascade.[11–17] Clinical suspicion of pulmonary thromboembolism is not straightforward, hypoxia being already caused in most patients by acute pneumonia: patients are also frequently paucisymptomatic during oxygen supplementation, despite low PaO2/FiO2 values.
Our results show how coagulation abnormalities in COVID-19 patients represent a considerable threat, even if first-line prophylactic measures are implemented. In our cohort, we observed a 60% prevalence of CTPA-detected thromboembolism: this figure could be even higher, since all our patients were receiving at least prophylactic LMWH. Of note, among 18 compared variables between patients with and without CTPA-confirmed pulmonary thromboembolism, only C-reactive protein values and the median duration of hospitalization significantly differed between the 2 groups. Such differences could be associated with prompt anticoagulation therapy for PTE and its beneficial effect on COVID-19 patients, or with rapid worsening of patients’ conditions. Of note, patients with pulmonary thromboembolism developed clinical signs suspicious for this condition and were referred for CTPA a median 8 days earlier than patients with negative CTPA findings, also having significantly higher C-reactive protein levels. Such findings are in line with the hypothesis which sees pulmonary thromboembolism in COVID-19 patients as a prevalently local byproduct of SARS-CoV-2 induced inflammation.[20,21,30–32] Lung microthrombosis triggered by autoimmune or direct viral endothelial damage is known to be associated with coronavirus infection since the SARS-CoV-1 pandemic in the early 2000s.[19,32,33] The repercussions of such pathogenetic mechanisms on diagnostic[19,21,34] and treatment[19,20,28,30,35,36] pathways of COVID-19 patients are hotly debated, with LMWH administration at prophylactic dosage increasingly deemed to be probably unable in adequately preventing severe coagulopathy.[28,29,35,36] Our study has some limitations, other than its monocentric and retrospective design with a limited sample size. First, since this study was conducted during the first pandemic peak in our area, the generalizability of our findings may be hindered by potential changes in disease spectrum and broader prophylactic measures that have since entered routine clinical use. Second, its focus on patients receiving LMWH at prophylactic dosage could have engendered a selection bias. However, our study hints that even when considering only patients under prophylactic treatment, COVID-19 is still associated with a high prevalence of pulmonary thromboembolism. This plays in favor of extending anticoagulant therapy to all hospitalized COVID-19 patients after considering their bleeding risk, even when D-dimer is not markedly elevated, sepsis-induced coagulopathy criteria are not met, or in absence of acute respiratory distress syndrome, then proceeding to rule out pulmonary thromboembolism in patients with markedly increased D-dimer or other inflammatory markers, deep vein thrombosis, or less than-expected clinical improvement despite optimal oxygen and medical therapy. Further large-scale studies are needed to precisely assess thromboembolism incidence in COVID-19 patients and its true pathophysiological nature, in order to optimize treatment and potentially lower mortality rate.
Conceptualization: Simone Schiaffino, Francesca Giacomazzi, Andrea Cozzi, Pietro Spagnolo, Francesco Sardanelli.
Data curation: Simone Schiaffino, Anastassia Esseridou, Andrea Cozzi, Serena Carriero, Daniela Palmira Mazzaccaro, Giovanni Di Leo.
Formal analysis: Simone Schiaffino, Andrea Cozzi, Giovanni Di Leo.
Funding acquisition: Giovanni Nano, Francesco Sardanelli.
Investigation: Simone Schiaffino, Francesca Giacomazzi, Anastassia Esseridou, Serena Carriero, Daniela Palmira Mazzaccaro, Giovanni Nano, Pietro Spagnolo.
Methodology: Simone Schiaffino, Francesca Giacomazzi, Andrea Cozzi, Giovanni Di Leo, Francesco Sardanelli.
Project administration: Simone Schiaffino, Francesca Giacomazzi, Andrea Cozzi, Giovanni Di Leo, Francesco Sardanelli.
Resources: Francesca Giacomazzi, Giovanni Nano.
Software: Giovanni Di Leo.
Supervision: Simone Schiaffino, Francesca Giacomazzi, Francesco Sardanelli.
Validation: Anastassia Esseridou, Giovanni Nano.
Visualization: Andrea Cozzi.
Writing – original draft: Simone Schiaffino, Francesca Giacomazzi, Anastassia Esseridou, Andrea Cozzi, Serena Carriero, Daniela Palmira Mazzaccaro, Giovanni Nano, Giovanni Di Leo, Pietro Spagnolo, Francesco Sardanelli.
Writing – review & editing: Simone Schiaffino, Francesca Giacomazzi, Anastassia Esseridou, Andrea Cozzi, Serena Carriero, Daniela Palmira Mazzaccaro, Giovanni Nano, Giovanni Di Leo, Pietro Spagnolo, Francesco Sardanelli.
. World Health Organization. WHO Coronavirus Disease (COVID-19) Dashboard. Geneva, Switzerland; 2020. Available at: https://covid19.who.int/
. Accessed November 12, 2020.
. Nair A, Rodrigues JCL, Hare S, et al. A British Society of Thoracic Imaging statement: considerations in designing local imaging diagnostic algorithms for the COVID-19 pandemic. Clin Radiol 2020;75:329–34.
. Xiang KY, Zu ZY, Lu GM, et al. Coronavirus disease 2019 (COVID-19). J Thorac Imaging 2020;35:234–8.
. Sverzellati N, Milanese G, Milone F, et al. Integrated radiologic algorithm for COVID-19 pandemic. J Thorac Imaging 2020;35:228–33.
. Wan Y-L, Schoepf UJ, Wu CC, et al. Preparedness and best practice in Radiology Department for COVID-19 and other future pandemics of severe acute respiratory infection. J Thorac Imaging 2020;35:239–45.
. Rubin GD, Ryerson CJ, Haramati LB, et al. The role of chest imaging in patient management during the COVID-19 pandemic: a multinational consensus statement from the Fleischner Society. Radiology 2020;296:172–80.
. Sun Z, Zhang N, Li Y, et al. A systematic review of chest imaging findings in COVID-19. Quant Imaging Med Surg 2020;10:1058–79.
. Lescure F-X, Bouadma L, Nguyen D, et al. Clinical and virological data of the first cases of COVID-19 in Europe: a case series. Lancet Infect Dis 2020;20:697–706.
. Helmy YA, Fawzy M, Elaswad A, et al. The COVID-19 pandemic: a comprehensive review of taxonomy, genetics, epidemiology, diagnosis, treatment, and control. J Clin Med 2020;9:1225.
. Zhang Y, Gao Y, Qiao L, et al. Inflammatory response cells during acute respiratory distress syndrome in patients with coronavirus disease 2019 (COVID-19). Ann Intern Med 2020;173:402–4.
. Klok FA, Kruip MJHA, van der Meer NJM, et al. Confirmation of the high cumulative incidence of thrombotic complications in critically ill ICU patients with COVID-19: an updated analysis. Thromb Res 2020;191:148–50.
. Ranucci M, Ballotta A, Di Dedda U, et al. The procoagulant pattern of patients with COVID-19 acute respiratory distress syndrome. J Thromb Haemost 2020;18:1747–51.
. Tang N, Li D, Wang X, et al. Abnormal coagulation parameters are associated with poor prognosis in patients with novel coronavirus pneumonia. J Thromb Haemost 2020;18:844–7.
. Han H, Yang L, Liu R, et al. Prominent changes in blood coagulation of patients with SARS-CoV-2 infection. Clin Chem Lab Med 2020;58:1116–20.
. Xiong M, Liang X, Wei Y. Changes in blood coagulation in patients with severe coronavirus disease 2019 (COVID-19): a meta-analysis. Br J Haematol 2020;189:1050–2.
. Klok FA, Kruip MJHA, van der Meer NJM, et al. Incidence of thrombotic complications in critically ill ICU patients with COVID-19. Thromb Res 2020;191:145–7.
. Di Micco P, Russo V, Carannante N, et al. Clotting factors in COVID-19: epidemiological association and prognostic values in different clinical presentations in an Italian Cohort. J Clin Med 2020;9:1371.
. Lippi G, Favaloro EJ. D-dimer is associated with severity of Coronavirus Disease 2019: a pooled analysis. Thromb Haemost 2020;120:876–8.
. Teuwen L-A, Geldhof V, Pasut A, et al. COVID-19: the vasculature unleashed. Nat Rev Immunol 2020;20:389–91.
. Marongiu F, Grandone E, Barcellona D. Pulmonary thrombosis in 2019-nCoV pneumonia? J Thromb Haemost 2020;18:1511–3.
. Saba L, Sverzellati N. Is COVID evolution due to occurrence of pulmonary vascular thrombosis? J Thorac Imaging 2020;35:344–5.
. Léonard-Lorant I, Delabranche X, Séverac F, et al. Acute pulmonary embolism
in patients with COVID-19 at CT angiography and relationship to d-Dimer levels. Radiology 2020;296:E189–91.
. Grillet F, Behr J, Calame P, et al. Acute pulmonary embolism
associated with COVID-19 pneumonia detected with pulmonary CT angiography. Radiology 2020;296:E186–8.
. Monfardini L, Morassi M, Botti P, et al. Pulmonary thromboembolism in hospitalised COVID-19 patients at moderate to high risk by Wells score: a report from Lombardy, Italy. Br J Radiol 2020;93:20200407.
. Lax SF, Skok K, Zechner P, et al. Pulmonary arterial thrombosis in COVID-19 with fatal outcome. Ann Intern Med 2020;173:350–61.
. Carsana L, Sonzogni A, Nasr A, et al. Pulmonary post-mortem findings in a series of COVID-19 cases from northern Italy: a two-centre descriptive study. Lancet Infect Dis 2020;20:1135–40.
. Wichmann D, Sperhake J-P, Lütgehetmann M, et al. Autopsy findings and venous thromboembolism in patients with COVID-19. Ann Intern Med 2020;173:268–77.
. Cattaneo M, Bertinato EM, Birocchi S, et al. Pulmonary embolism
or pulmonary thrombosis in COVID-19? Is the recommendation to use high-dose heparin for thromboprophylaxis justified? Thromb Haemost 2020;120:1230–2.
. Mazzaccaro D, Giacomazzi F, Giannetta M, et al. Non-overt coagulopathy in non-ICU patients with mild to moderate COVID-19 pneumonia. J Clin Med 2020;9:1781.
. Violi F, Pastori D, Cangemi R, et al. Hypercoagulation and antithrombotic treatment in Coronavirus 2019: a new challenge. Thromb Haemost 2020;120:949–56.
. Levi M, Thachil J, Iba T, et al. Coagulation abnormalities and thrombosis in patients with COVID-19. Lancet Haematol 2020;7:e438–40.
. Varga Z, Flammer AJ, Steiger P, et al. Endothelial cell infection and endotheliitis in COVID-19. Lancet 2020;395:1417–8.
. Yang Y-H, Huang Y-H, Chuang Y-H, et al. Autoantibodies against human epithelial cells and endothelial cells after severe acute respiratory syndrome (SARS)-associated coronavirus infection. J Med Virol 2005;77:1–7.
. Spagnolo P, Cozzi A, Foà RA, et al. CT-derived pulmonary vascular metrics and clinical outcome in COVID-19 patients. Quant Imaging Med Surg 2020;10:1325–33.
. Porfidia A, Pola R. Venous thromboembolism and heparin use in COVID-19 patients: juggling between pragmatic choices, suggestions of medical societies and the lack of guidelines. J Thromb Thrombolysis 2020;50:68–71.
. Thachil J. The versatile heparin in COVID-19. J Thromb Haemost 2020;18:1020–2.