key: cord-0805190-5lhmwf2o authors: De Cobelli, Francesco; Palumbo, Diego; Ciceri, Fabio; Landoni, Giovanni; Ruggeri, Annalisa; Rovere-Querini, Patrizia; D'Angelo, Armando; Steidler, Stephanie; Galli, Laura; Poli, Andrea; Fominskiy, Evgeny; Calabrò, Maria Grazia; Colombo, Sergio; Monti, Giacomo; Nicoletti, Roberto; Esposito, Antonio; Conte, Caterina; Dagna, Lorenzo; Ambrosio, Alberto; Scarpellini, Paolo; Ripa, Marco; Spessot, Marzia; Carlucci, Michele; Montorfano, Matteo; Agricola, Eustachio; Baccellieri, Domenico; Bosi, Emanuele; Tresoldi, Moreno; Castagna, Antonella; Martino, Gianvito; Zangrillo, Alberto title: Pulmonary Vascular Thrombosis in COVID-19 Pneumonia date: 2021-01-13 journal: J Cardiothorac Vasc Anesth DOI: 10.1053/j.jvca.2021.01.011 sha: a8504a9123e6b9e19be1959f26470e6c986127ba doc_id: 805190 cord_uid: 5lhmwf2o OBJECTIVES: During SARS-CoV-2 infection, dramatic endothelial cell damage with pulmonary microvascular thrombosis has been hypothesized to occur. Our aim was to assess whether pulmonary vascular thrombosis is due to recurrent thromboembolism from peripheral deep vein thrombosis or rather to local inflammatory endothelial damage with a superimposed thrombotic late complication. DESIGN: Observational study SETTING: Medical and intensive care unit wards of a teaching hospital PARTICIPANTS: We report a subset of patients included in a prospective institutional study (CovidBiob study) with clinical suspicion of pulmonary vascular thromboembolism. INTERVENTIONS: Computed Tomography Pulmonary Angiography and evaluation of laboratory markers and coagulation profile. MEASUREMENTS AND MAIN RESULTS: Twenty-eight out of 55 (50.9%) patients enrolled showed pulmonary vascular thrombosis, with a median time interval from symptoms onset of 17.5 days. Simultaneous multiple pulmonary vascular thromboses were identified in 22 cases, with bilateral involvement in 16, mostly affecting segmental/subsegmental pulmonary arteries branches (67.8% and 96.4%). Patients with pulmonary vascular thrombosis had significantly higher ground glass opacities areas (31.7% [22.9-41] vs. 17.8% [10.8-22.1] p<0.001) compared to those without pulmonary vascular thrombosis. D-Dimer level at hospital admission was predictive of pulmonary vascular thrombosis. CONCLUSIONS: Our findings identify a specific radiological pattern of COVID-19 pneumonia with a unique spatial distribution of pulmonary vascular thrombosis overlapping areas of ground glass opacities. These findings support the hypothesis of a pathogenetic relationship between COVID-19 lung inflammation and pulmonary vascular thrombosis and challenge the previous definition of pulmonary embolism associated with COVID-19 pneumonia. Observational study Medical and intensive care unit wards of a teaching hospital We report a subset of patients included in a prospective institutional study (CovidBiob study) with clinical suspicion of pulmonary vascular thromboembolism. Computed Tomography Pulmonary Angiography and evaluation of laboratory markers and coagulation profile. Twenty-eight out of 55 (50.9%) patients enrolled showed pulmonary vascular thrombosis, with a median time interval from symptoms onset of 17.5 days. Simultaneous multiple pulmonary vascular thromboses were identified in 22 cases, with bilateral involvement in 16, mostly affecting segmental/subsegmental pulmonary arteries branches (67.8% and 96.4%). Patients with pulmonary vascular thrombosis had significantly higher ground glass opacities areas (31.7% [22.9-41] vs. 17.8% [10.8-22 .1] p<0.001) compared to those without pulmonary vascular thrombosis. D-Dimer level at hospital admission was predictive of pulmonary vascular thrombosis. Our findings identify a specific radiological pattern of COVID-19 pneumonia with a unique spatial distribution of pulmonary vascular thrombosis overlapping areas of ground glass opacities. These findings support the hypothesis of a pathogenetic relationship between COVID-19 lung inflammation and pulmonary vascular thrombosis and challenge the previous definition of pulmonary embolism associated with COVID-19 pneumonia. KEYWORDS: COVID-19; thrombosis; D-Dimer increase; inflammation; critical care; computed tomography. Clinical manifestations of COVID-19 disease include a variety of phenotypes, spanning from asymptomatic disease to severe interstitial pneumonia with acute respiratory distress syndrome (ARDS) and death. The clinical evolution of COVID-19 can be described in three major patterns (1): mild illness with upper respiratory tract clinical symptoms; non lifethreatening pneumonia; and severe pneumonia with ARDS, which begins with mild symptoms for 7-8 days and then rapidly progresses to symptoms requiring advanced life support. In addition to a possible direct cytopathic effect, the virus may elicit a local cytokine dependent inflammatory and potentially detrimental immune reaction. Our group previously hypothesized that this host immune response may cause a massive vascular endothelial and alveolar epithelial cell damage with microvascular thrombosis leading to worsening of ventilation/perfusion imbalances and loss of hypoxic vasoconstrictors reflexes (2) . Progression of this endothelial thrombo-inflammatory syndrome to the microvascular bed of other vital organs may result in multiple organ failure and eventually death. Direct viral infection of the endothelial cells with diffuse endothelial inflammation and apoptosis has been reported in kidney, small bowel and lung tissue specimens from COVID-19 patients (3) . On the other hand, pulmonary embolism has been described as part of the clinical manifestation associated with COVID-19 pneumonia (4-6) as have elevated D-dimers (6) (7) (8) . In this peculiar pathogenic scenario, one could argue whether pulmonary vascular thrombosis is due to recurrent thromboembolism from peripheral deep vein thrombosis (DVT) or rather to local inflammatory endothelial damage with a superimposed thrombotic late complication. A possible hint to such a pathogenetic dilemma could come from imaging. Computed Tomography (CT) Pulmonary Angiography is a non-invasive imaging tool able to identify filling defects in pulmonary artery branches (9) as well as radiological hallmarks of COVID-19 pneumonia: bilateral ground glass opacities (GGOs); crazy paving pattern; and/or consolidations predominantly in subpleural locations in the lower lobes (10, 11) . Furthermore, chest CT (irrespective of contrast medium administration) has been used to quantify disease burden (12, 13) . To address the question whether pulmonary vascular thrombosis reflects recurrent thromboembolism from peripheral DVT or rather local thrombosis secondary to inflammatory endothelial damage, along with inflammatory markers and coagulation profile, spatial distribution of pulmonary vascular thrombosis in SARS-CoV-2 pneumonia was evaluated in a consecutive cohort of COVID-19 patients with clinical suspicion of pulmonary thromboembolism. Specifically, the topographical pattern of distribution of pulmonary vascular thrombosis was investigated using CT pulmonary angiography and then correlated with pneumonia extent. This series is a subset of a larger prospective study at the San Raffaele Scientific Institute, a 1350-bed tertiary care academic hospital in Milan, Italy; the COVID-BioB study is an institutional observational study with the aim to collect and analyse biological samples and clinical outcomes in COVID-19 patients (COVID-BioB, ClinicalTrials.gov NCT04318366). The study was approved by the Institutional Review Board, (protocol number 34/INT/2020). All procedures were conducted in agreement with the Declaration of Helsinki (1964 and further amendments); informed consent was collected from all patients according to the Institutional Review Board guidelines. Between March 29 and April 9, 2020, patients with a positive nasopharyngeal swab result for SARS-CoV-2 who underwent CT pulmonary angiography for clinical suspicion of pulmonary vascular thrombosis were enrolled in our study. Last follow up date was set at July 15th, 2020. Clinical suspicion of pulmonary vascular thrombosis in SARS-CoV 2 patients was defined as ARDS non-responsive to increasing O 2 therapy. Exclusion criteria were defined as i) severe respiratory and/or motion artefacts that did not allow proper evaluation of lung parenchyma and identification of eventual filling defects in pulmonary arteries branches ii) pneumothorax (Figure 1) . CLINICAL DATA COLLECTION -Data were entered into a dedicated electronic case report form specifically developed on site for the COVID-BioB study. Before analysis, data managers and clinicians verified data for accuracy. Details regarding treatments administered to patients other than anticoagulants have been extensively reported previously by our group (14) . Data regarding lower and upper limb compression ultrasonography with Doppler evaluation were also collected to evaluate possible DVT. CT PROTOCOL -CT pulmonary angiography examinations were first performed in a dedicated CT suite (GE CT Light Speed VCT CardiacPro) easily accessible via assigned elevators and paths from the emergency department, SARS-CoV-2 dedicated Intensive Care Units (ICUs) and COVID dedicated wards (15) . Two additional ICUs specifically dedicated to critically ill Covid-19 patients with a total of 24 beds were created with a dedicated novel CT scanner (Philips CT Incisive 128 pro) (15) . CT pulmonary angiography protocol included an unenhanced, breath hold axial scan of the thorax (from lung apex to the lowest hemidiaphragm) followed by an additional scan starting a few seconds after intravenous administration of non-ionic iodinate contrast medium in order to specifically enhance pulmonary arteries and their branches; the automatic bolus tracking technique had the region of interest positioned in the right ventricle with a trigger threshold of 100 Hounsfield Unit (HU). This protocol ensured evaluation of lung parenchyma and eventual filling defects in the branches of the pulmonary arteries, since an enhanced scan alone would not allow proper characterization of pneumonia (16) . IMAGE EVALUATION -All CT pulmonary angiography images were independently reviewed by two radiologists experienced in thoracic imaging (R.N. and D.P., with 28 and 5 years of experience, respectively) both blinded to the patient symptoms and outcome; differences in assessment were resolved with consensus. Pulmonary vascular thrombosis was defined when contrast enhanced CT demonstrated filling defects in the branches of the pulmonary arteries and classified in terms of distribution (number and site of pulmonary lobes affected) and extent (down to subsegmental branches). Irrespective of presence or absence of pulmonary vascular thrombosis, the diameter of perilesional subsegmental vessels was always measured on unenhanced slices; a subsegmental vessel was defined as enlarged when its axial diameter exceeded 3 mm (17) . Imaging post processing was carried out using a commercially available software (Intellispace version 8.0, Philips Medical Systems, Chronic Obstructive Pulmonary Disease tool); after automated identification of pulmonary lobes on unenhanced slices, the software differentiated diverse areas of lung parenchyma based on HU thresholds. In the setting of SARS-CoV-2 pneumonia, the following settings were used: in order to quantify and differentiate between normal and pathological lung parenchyma, a -740 HU threshold was set: areas with higher density values were considered pathological (disease burden). To distinguish between GGO and non-GGO (crazy paving and/or consolidation) areas, we applied a 660 HU threshold. Descriptor definitions are taken from the Fleischner Society: Glossary of Terms for Thoracic Imaging (18) : Ground glass opacity is defined as a hazy increased opacity of lung with preservation of bronchial and vascular margins; consolidation as an opacity of lung with obscuration of bronchial and vascular margins; crazy paving pattern as thickened interlobular septa and intralobular lines superimposed on a background of GGO, resembling irregularly shaped paving stones. Software outputs refer to both lungs and single pulmonary lobes as percentages of the overall lung volume. Finally, in order to accurately assess the precise contribution of GGO and non-GGO patterns to the overall disease burden we calculated the so-called GGO ratio, defined as the percentage of pneumonia made up by GGO. Sixty-seven patients underwent CT pulmonary angiography during the study time period. Following exclusions due to severe respiratory and motion artefacts (n=9) and pneumothorax (n=3) (Figure 1 Table 1 , Online data supplement. Before CT pulmonary angiography, 28 patients were already receiving low-molecular-weight heparin, or direct thrombin inhibitor (12/28 with and 16/27 without pulmonary vascular thrombosis, p= 0.06). After a median follow up of 29.5 (IQR 15-55.7) days following hospital admission, 17 patients died (8 of the patients with and 9 of those without pulmonary vascular thrombosis, p=0.7), 36 were discharged after a median time of 30 (IQR 20-56) days, and 2 patients were still hospitalized (one with indication of bilateral lung transplantation due to severe fibrosis). Univariate and multivariate analysis are reported in Table 2 . Increased level of D-Dimer at baseline (OR 1.09, 95% CI 1-1.18, p=0.02) and absence of anticoagulation before occurrence of pulmonary vascular thrombosis (OR 3.81, 95% CI 1.21-11.9, p=0.04) were independently associated with the increased risk of pulmonary vascular thrombosis. Pneumonia evaluation -CT features of SARS-CoV-2 pneumonia are summarized in Table 3 . (Figure 4 ). Our study shows a unique pattern of distribution of pulmonary vascular thrombosis overlapping areas of active ground glass opacities in patients with severe COVID-19 ARDS. The vast majority of patients with pulmonary vascular thrombosis showed multiple thrombi (78.6%) with frequent bilateral involvement (57.1%) in segmental and subsegmental pulmonary artery branches, in presence of larger subsegmental vessels within GGO areas. Furthermore we confirmed an association between D-Dimers values and the presence of pulmonary vascular thrombosis. The percentage of pneumonia characterized by pure GGO (GGO ratio) was significantly higher in patients who developed pulmonary vascular thrombosis, with a cut-off, estimated with the receiver operating characteristics analysis, of 36.4%. As a consequence, our results provided the opportunity to define a specific pattern of COVID-19 pneumonia, that is GGO predominant, significantly associated with occurrence of pulmonary vascular thrombosis (figure 5, central image). Ground glass opacity is believed to represent the initial, typical response to lung injury, and roughly represents the amount of active inflammation. Furthermore, the observed subsegmental vascular enlargement previously described in SARS-CoV-2 pneumonia (17, 19) has also been associated with SARS-CoV-2 triggered hyperaemia. Our results point out a reliable association between subsegmental vascular enlargements within a GGO prevalent pneumonia and the presence of multiple bilateral pulmonary vascular thromboses in the peripheral branches of each lobe artery. Overall, our findings confirm the ability of CT scan to provide a quantitative assessment of the disease severity and confirm the extension of active inflammation as the major determinant of pulmonary vascular thrombosis (22) . Multiple and bilateral pulmonary thromboembolic events have already been reported in COVID-19 patients (23). However, a systematic topographical analysis of this pattern was lacking and an "embolism" concept was rather proposed: we showed stringent pulmonary vascular thrombosis topographical distribution in overlap with GGO areas. Overall, these features support the concept of an atypical COVID-19 associated ARDS, since the pattern of distribution of pulmonary thromboembolic events in typical ARDS involves areas spared by inflammatory changes (24) . The presence of a high percentage of lung involvement in chest CT has been shown to range between 6 and 13 days from symptom onset (25,26); our median time in pulmonary vascular thrombosis presentation (17.5 days) well fits with the hypothesis of an intermediate stage disease (27) in which lung inflammation is at its highest, resulting in possible progressive endothelial damage. Subsequent activation of the coagulation cascade in the microvascular compartment could lead to a critical functional deterioration of O 2 exchange, ultimately unresponsive to mechanical ventilation. There is increasing evidence supporting the important role of endothelial cells in the initiation of inflammation and in the development of extensive pulmonary intravascular coagulopathy which is common in COVID-19 patients with ARDS (28) (29) (30) . However, it has long been known that not only diffuse alveolar damage but also pulmonary vascular injury is a central pathological feature of ARDS (31, 32) . Dysregulated inflammation and endothelial cell direct injury promote the expression of coagulation initiating factors, like tissue factor, on cell surfaces, thereby causing downstream activation of coagulation. At the same time, natural anticoagulant mechanisms, including antithrombin, tissue factor pathway inhibitor, and the protein C system, are suppressed and this further propagates an uncontrolled cycle of coagulation (33, 34) . Other authors suggest that the disruption of pulmonary circulation causes platelet and fibrinogen depletion, suggesting local thrombosis formation (35) . Histologic post mortem studies revealed diffuse extensive fibrin thrombosis of small and large pulmonary arteries and lung necrosis distal to vascular obstruction in ARDS of diverse aetiology (36) (37) (38) . Furthermore, bedside balloon occlusion pulmonary angiography demonstrated pulmonary artery filling defects in about one half of the patients with ARDS of diverse severity and aetiology (36) . Severity of the respiratory insufficiency, pulmonary artery pressure, pulmonary vascular resistance and mortality were significantly higher in patients with angiographic evidence of vascular obstruction than in those with normal angiography (36) . Other authors used the same angiographic technique and found multiple pulmonary artery filling defects in a relevant fraction of patients with severe ARDS (39) . As a limitation we acknowledge that our study reports a subset cohort of a larger institutional prospective study. Furthermore, the clinical progression of respiratory distress in our cohort was associated with, but not necessarily caused by the increased level of D-dimers. On top of this, all consecutive patients undergoing a CT scan for a clinical suspicion of pulmonary vascular thrombosis were enrolled, therefore the overall prevalence in those not presenting clinical suspicion remains unknown. Importantly, in our hospital, deep vein thrombosis (41) was found only in a relatively small percentage of patients with lung thrombosis, and there were no cases in the iliofemoral venous axis, supporting the hypothesis of a lung disease related complication, due to SARS-CoV2 pathogenicity. The limitation linked to data collected from a single center remains, yet the critical role of the association of disorders in the coagulation pathway, disease severity and death has been reported in independent cohorts in COVID-19 patients (4, 5, 6, 42) . Acute systemic inflammation features have been previously associated with disease severity and mortality (8, 43) . Importantly, D-dimer levels should be considered as an additional predictive tool to stratify patients at risk of adverse outcome and may guide physicians to proceed with CT pulmonary angiography as well as assign Immunomodulation therapies to reduce the risk of cytokine release syndrome induced by SARS-CoV-2 has demonstrated efficacy in single center and multicenter trials (48, 49) . In conclusion, our study supports the hypothesis of a pathological relationship between lung inflammation and pulmonary vascular thrombosis, definitively challenging the previous definition of embolism associated with COVID-19 pneumonia and strongly supporting the rational for an association of anti-inflammatory and anti-coagulant treatments in patients with severe COVID-19 pneumonia. The authors declare no conflict of interest We are indebted to all healthcare personnel who helped during the COVID-19 emergency. ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. 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