Among all other complications of the pulmonary and systemic infections of the COVID-19 virus, pulmonary thromboembolic (PTE) events are of major significance. The prevalence of PTE in COVID-19 symptomatic patients is reported high at up to 40%. Increased PTE prevalence in COVID-19-infected patients is supported by certain theories concerning the infection of pericytes and changing coagulation status of the infected patients. Pulmonary CT angiography and lung perfusion scans (LPS) are done to exclude PTE. We previously discussed and reported the high accuracy of LPS in our center to diagnose PTE. In the current study, we report the prevalence of abnormal LPS among COVID-19 patients with pulmonary infection and suspected PTE.
We listed patients referred to the Nuclear Medicine Department (NMD) of Imam Khomeini Hospital to perform LPS to exclude PTE from 20 February 2020 to 20 December 2020. Imam Khomeini Hospital has been a referral hospital for the management of COVID-19 patients since the beginning of the COVID-19 pandemic in February 2020. The report of LPS was collected from the reporting system of NMD. The report was based on the PISAPED criteria in a positive/negative method, SPECT acquisition, and a comparison with the available chest CT scans and the chest X-ray (CXR). Macroaggregated albumin (MAA) kits (Pars Isotope, Tehran, Iran) were employed with an injected activity of 1–3mCi with 200k-600k particles. Then, the PACS was searched for the CT scans of the patients for the research. The CT scans were reviewed for the signs of pulmonary infection of COVID-19 including ground-glass opacities and consolidations.
The prevalence of PTE-positive LPS was cross-tabulated against the presence of COVID-19 pulmonary infection. The chi-squared test at a significance level of p<0.05 in SPSS v.19 was used for analyses.
During the study period, 408 LPS were performed including 240 patients who had chest CT scans (n=207) or chest X-ray (n=33) imaging. Patients without chest CT or CXR were not included. The prevalence of abnormal LPS is presented in Table 1. The overall prevalence of acute PTE was 8.8%. The frequencies of LPS-detected PTE were similar between patients with and without COVID-19 pulmonary infection (7.5% vs. 11.9%; p=0.2). The age of patients with and without COVID-19 pulmonary infection was similar (59.9±16.5 vs. 54.8±18.5; p=0.1; Mann–Whitney U test). Also, the age of patients with and without PTE was not statistically different (63±18.3 vs. 57.7±17.7; p=0.1).
Prevalence of acute PTE among patients with and without COVID-19 pulmonary infection.
| COVID-19 pulmonary infection | TotalN=240 | ||
|---|---|---|---|
| Positive | Negative | ||
| Gender | |||
| Male | 81(46.8) | 29(43.3) | 110(45.8) |
| Female | 92(53.2) | 38(56.7) | 130(54.2) |
| Age (years) | 59.5(16.5) | 54.8(18.5) | 58.2(17.2) |
| Perfusion scan | |||
| Positive | 13(7.5) | 8(11.9) | 21(8.8) |
| Negative | 160(92.5) | 59(88.1) | 219(91.3) |
| All | 173(72.1) | 67(27.9) | |
Data are mean and standard deviation in parentheses or frequency (percentage).
The prevalence of acute PTE was 8.8% in all patients. This figure is not higher than the prevalence of PTE positive scans in the study center before COVID-19 infection era which was 14.3%. Among patients with chest imaging based COVID-19 pulmonary infection, 7.5% had PTE similar to the 11.9% prevalence of PTE in patients without pulmonary COVID-19 infection. Compared to our study, Ozturk et al. observed acute PTE at 36.6% among 77 mild to moderate COVID-19 patients and another study reported that 42.6% of 54 patients with COVID-19 suffered from mismatched perfusion defects suggestive of PTE.
The accuracy of LPS is high to detect clinically important acute PTE, 88% at the center of this report and ranging from 90% to 95% elsewhere. The patients were not sent for imaging due to research purposes and the clinicians were suspicious of the presence of clinically important acute PTE hence the real prevalence of PTE should be much lower in all patients including those without pulmonary involvement, as well as symptomatic outpatient or asymptomatic patients.
It is speculated that in COVID-19 infection, the pericytes are damaged which causes microvascular occlusion and consequent thrombus formation. This kind of pulmonary thrombosis presents with elevated D-dimer and possibly low blood oxygen level but is not considered a PTE event. Consequently, although, before the COVID-19 era, LPS negative for PTE has been considered against the need for anticoagulation, in COVID infected patients, further insight should be acquired through practice and future researches.
FundingThis research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Ethical approvalThis study has been approved by the Tehran University of Medical Sciences ethics committee.
Conflict of interestThe authors of this manuscript declare no relationships with any companies, whose products or services may be related to the subject matter of the article.
