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Surgery
Protocol
Value of retrograde pulmonary vein perfusion combined with pulmonary artery thrombectomy in acute pulmonary embolism: a protocol for a systematic review and meta-analysis
  1. Jun Xiang1,
  2. Ling He2,
  3. Tailuan Peng1,
  4. Weiwei Liang1,
  5. Shuliang Wei1
  1. 1Department of Cardiovascular Surgery, Affiliated Hospital of North Sichuan Medical College, Nanchong, Sichuan, China
  2. 2Department of Paediatrics, Affiliated Hospital of North Sichuan Medical College, Nanchong, Sichuan, China
  1. Correspondence to Dr Shuliang Wei; shuliang_wei{at}163.com

Abstract

Introduction Acute pulmonary embolism is a serious cardiovascular disease with high mortality. Surgery is an important therapeutic means. The traditional surgical method is pulmonary artery embolectomy with cardiopulmonary bypass, but there is a certain recurrence rate after surgery. Some scholars use retrograde pulmonary vein perfusion as an adjunct to conventional pulmonary artery embolectomy. However, whether this method can be used safely for acute pulmonary embolism and its long-term effects remains unclear. Therefore, we plan to conduct a systematic review and meta-analysis to investigate whether retrograde pulmonary vein perfusion combined with pulmonary artery thrombectomy can be safely used in acute pulmonary embolism.

Methods and analysis We will search key databases (Ovid MEDLINE, PubMed, Web of Science, Cochrane Library, China Science and Technology Journals and Wanfang) for studies on acute pulmonary embolism treated with retrograde pulmonary vein perfusion from January 2002 to December 2022. The useful information will be consolidated into a piloting spreadsheet. The Cochrane Risk of Bias Tool will be used to assess the bias. Data will be synthesised and heterogeneity will be evaluated. The dichotomous variables will be determined by using risk ratio with 95% CI, and weighted mean differences (with 95% CI) or standardised mean differences (95% CI) will be used for continuous variables. Χ2 test and I2 test will be used to assess the statistical heterogeneity. Meta-analysis will be conducted when strong homogeneous data are accessible.

Ethics and dissemination Approval of the ethics committee is not needed for this review. While results will be disseminated electronically, effective dissemination will be done through presentations and peer-reviewed publication.

PROSPERO registration number CRD42022345812; pre-results.

  • Thoracic surgery
  • Vascular surgery
  • Cardiac surgery
  • Cardiology
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This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

https://doi.org/10.1136/bmjopen-2022-069685

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    Strengths and limitations of this study

    • To the best of our knowledge, this will be the first meta-analysis to compare retrograde pulmonary vein perfusion combined with pulmonary artery thrombectomy and conventional pulmonary artery embolectomy in acute pulmonary embolism.

    • All possible forms of these keywords about ‘pulmonary artery thrombectomy’ and ‘acute pulmonary embolism’ will be used to ensure the comprehensiveness of the search, and all the literature will be screened by two authors independently.

    • All the included literatures are in full text, both the quality of the literatures and the final outcomes will be evaluated carefully.

    • Potential study limitations of the study may be the heterogeneity in the results due to languages and countries.

    Introduction

    Acute pulmonary embolism is a serious cardiovascular disease associated with high morbidity and mortality.1 2 It is reported that acute pulmonary embolism is globally the third most frequent acute cardiovascular syndrome behind myocardial infarction and stroke in epidemiological studies, with an annual incidence rate of 39~115/100 000 population and a mortality rate of 34%~59%.3 4 The main causes of pulmonary embolism include trauma, surgery, genetics, antiphospholipid antibody positivity and COVID-19.5 6Acute right ventricular failure due to acute pulmonary arterial pressure was the leading cause of death.7 Therefore, early diagnosis and timely treatment play an important role in reducing mortality and improving prognosis. Although the diagnosis and treatment of acute pulmonary embolism have made considerable progress in recent years, the prognosis of some patients are still poor, especially those with massive pulmonary embolism.8 Therefore, it is necessary to restore pulmonary blood perfusion and stabilise haemodynamic state quickly.9 At present, the treatment of acute pulmonary embolism mainly includes anticoagulation, systemic thrombolysis, percutaneous catheter-directed treatment and surgical embolectomy.1 10–12 Although studies have shown that there was no difference between the thrombolytic therapy and surgical embolectomy of reperfusion treatment regarding 30 days mortality (15% and 13%, respectively), but thrombolysis was associated with a higher risk of stroke and reintervention at 30 days, and thrombolytic therapy was associated with a higher rate of recurrent pulmonary embolism requiring readmission compared with surgical embolectomy (7.9% vs 2.8%).13 According to the European Society of Cardiology and European Respiratory Society guidelines, surgical embolectomy was recommended for those high-risk patients with acute pulmonary embolism who are contraindicated or ineffective with thrombolytic therapy, massive pulmonary embolism and haemodynamic instability.1 14 With the improvement of surgical techniques and cardiopulmonary bypass techniques, the mortality of pulmonary artery thrombectomy has decreased significantly.15 16 Recent studies have shown that the mortality rate of pulmonary embolectomy is about 5%.17 Some studies have shown that surgical embolectomy is also effective for submassive pulmonary embolism.17 18 Therefore, more and more scholars support the surgical treatment of submassive acute pulmonary embolism.

    The conventional surgical embolectomy was mainly performed under cardiopulmonary bypass through the median sternal incision. Some scholars believe that the main causes of death for those who underwent pulmonary artery thrombectomy have been attributed to right heart failure secondary to persistent pulmonary hypertension.19 20 And thrombosis recurrence due to the incomplete removal of thrombotic material lodged in the distal pulmonary arterial tree and mechanical injury to the pulmonary arterial wall were the important factors in persistent pulmonary hypertension.20 Therefore, the removal of thrombus as thoroughly as possible is of great prognostic value. Gahagan, et al21 reported three cases of acute pulmonary embolism using retrograde pulmonary vein perfusion in 1966, and all the three patients had good results in 1-year follow-up. And from then on, retrograde pulmonary vein perfusion has been successfully used as an aid to treat acute pulmonary embolism in a few isolated cases.22 23 The benefits of retrograde pulmonary vein perfusion combined with pulmonary artery thrombectomy appears to not only help to flush out residual thrombotic material lodged in the distal pulmonary arterial branches, but also prevents the air embolism in the pulmonary artery.24 In recent years, Zarrabi et al25 reported the short-term results of retrograde pulmonary embolectomy in massive and submassive pulmonary embolism in 30 patients, the result showed that the in-hospital mortality was 6.6% (2/30). Spagnolo, et al26 reported 19 cases of patients with massive pulmonary embolism who underwent retrograde pulmonary embolectomy combined with pulmonary artery thrombectomy, there were neither in-hospital deaths, nor major postoperative complications in their research and all the patients were discharged from the hospital on anticoagulant medication by the 10th postoperative day. These studies indicate that retrograde pulmonary embolectomy combined with pulmonary artery thrombectomy is safe and feasible for the treatment of acute pulmonary embolism. Unfortunately, these studies are controlled studies or empirical reports with small samples, and there is a lack of research results with large samples. Also, the value of retrograde pulmonary vein perfusion combined with pulmonary artery thrombectomy in acute pulmonary embolism has not been addressed with a systematic review or meta-analysis until now despite the increasing evidence. At the same time, the effect of this method on the long-term prognosis of patients with acute pulmonary embolism has not been reported. Therefore, we aim to evaluate the effectiveness and safety of retrograde pulmonary vein perfusion combined with pulmonary artery thrombectomy in acute pulmonary embolism. We hope that our study can guide future surgery treatments for patients with acute pulmonary embolism.

    Methods and analysis

    We will carry out the meta-analysis and systematic review on the basis of the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P),27 checklist and detailed explanation of scoping reviews, and the Cochrane DTA reviews (Cochrane Handbook). This protocol follows the format recommended by the PRIMA-P guidelines. According to the guidelines, our study has been registered on the website of the International Prospective Register of Systematic Reviews.28 The reporting flow chart is presented in figure 1.

    Figure 1
    Figure 1

    The flow diagram of specific literature screening process.

    Inclusion criteria

    Studies included in this review should satisfy all of the following standards recommended for reviews of diagnostic test accuracy.

    Population

    All patients with acute pulmonary embolism confirmed by preoperative imaging and laboratory inspection who underwent conventional pulmonary artery embolectomy or retrograde pulmonary vein perfusion combined with pulmonary artery thrombectomy are the target population of our study, regardless of age or gender.

    Patient and public involvement

    Since this study is a secondary study based on other studies, there will be no direct patient or public involvement in this study.

    Intervention

    We excluded studies with non-human studies and studies with data that cannot be extracted, as well as non-original studies (reviews, author responses, comments) or secondary research (systematic review, meta-analysis). In this meta-analysis, the selection of surgical procedure was based on the principle of randomised controlled trials (RCTs), exclusion criteria include chronic thrombotic pulmonary hypertension; patients diagnosed with acute pulmonary embolism who were treated surgically but not by cardiopulmonary bypass; patients with malignant tumours. And the control group used the conventional surgical embolectomy and the experimental group used the retrograde pulmonary vein perfusion combined with pulmonary artery thrombectomy. The procedures of conventional surgical embolectomy include the following aspects. First, establish that the extracorporeal circulation, superior vena cava and inferior vena cava were intubated separately. Second, open the pulmonary artery and remove the thrombus. Finally, close the incision and evacuate the extracorporeal circulation. The procedures of retrograde pulmonary vein perfusion combined with pulmonary artery thrombectomy mainly include four aspects. First, establish the extracorporeal circulation, superior vena cava and inferior vena cava were intubated separately. Second, open the pulmonary artery and remove the thrombus. Third, retrograde perfusion of myocardial protective fluid (with a temperature of 25°~28°, flow 10~15 mL/kg/min) was performed at each pulmonary vein outlet via urethral catheter, so that the embolism in small branches of the pulmonary artery can flow out with the retrograde blood flow, thus achieving the purpose of completely removing the embolism as far as possible. Finally, close the incision and evacuate the extracorporeal circulation. Slight adjustments during the procedure to suit the actual situation are considered acceptable.

    Comparison

    Conventional pulmonary artery embolectomy.

    Study design

    We will include all the RCTs. The cross-sectional studies, case series and case reports will be excluded. There will be no limitations on language and publication status.

    Outcomes

    The outcomes assessed in this systematic review and meta-analysis included perioperative outcomes (include operative time, cardiopulmonary bypass time, aortic cross-clamp time, intraoperative blood loss, pulmonary artery pressure), postoperative outcomes (intensive care unit stay time, hospital stay time, 30-day mortality, postoperative complications, pulmonary artery pressure, tricuspid regurgitation) and long-term follow-up results(CT, cardiac function grade, 6-minute walk test, pulmonary artery pressure, tricuspid regurgitation, all-cause mortality).

    Information sources

    Two independent reviewers will search key databases (Ovid MEDLINE, PubMed, Web of Science, Cochrane Library, China Science and Technology Journals and Wanfang) for studies on acute pulmonary embolism treated with retrograde pulmonary vein perfusion from January 2002 to December 2022. There will be no restrictions on countries and languages.

    Search strategy

    Searches were carried out using Medical Subject Headings and free-text words in combination with the search strategy. We used the following keywords: ‘acute pulmonary embolism’, ‘surgery’, ‘pulmonary artery thrombectomy’, ‘retrograde pulmonary vein perfusion’. All possible forms of these keywords will be used to ensure the comprehensiveness of the search. Table 1 shows the search process for PubMed. The search procedure will be revised according to other databases.

    View this table:
    Table 1

    Search procedures for PubMed

    Study selection

    Literature search results will be imported into EndNote 20. Two authors (JX and LH) will review the literature independently. There will be no restrictions to the protocol of the value of retrograde pulmonary vein perfusion combined with pulmonary artery embolectomy in acute pulmonary embolism. The full texts which meet the eligibility criteria of this review will be acquired and will be reviewed by two authors (JX and LH) independently. The full text can be downloaded from the database, obtained by sending an email from the author or corresponding author. Dissimilarities will be solved by discussion with a third author (SW) and discussed until the dispute is resolved. The specific literature screening process will be summarised in a flow diagram (figure 1).

    Collection of data

    The useful information such as study details (first author, journal, year of publication, study design, follow-up period, type of outcome), patient demographics (age, sex, population size, scope of lesions, etc) and the outcomes of perioperative indicators and complications will be consolidated into a piloting spreadsheet. If there were multiple representations of the data, we preferred to use the data after adjusting for confounding factors. To reduce bias and reduce errors in data extraction, the same two authors (JX and LH) independently extracted data from the included literature, cross-checked after extraction. If there is disagreement regarding the data collection, we can reach a consensus through discussion with the third reviewer (SW).

    Risk of bias assessment

    To facilitate the assessment of the possible risk of bias in each study, we will use the Cochrane Risk of Bias Tool to assess bias.29 Which covers: randomisation, incomplete outcome data (eg, dropouts or withdrawals), sequence generation, allocation concealment, blinding, selective reporting and other biases. The methodological quality (including patient selection, comparability of cohorts, assessment of outcome, etc) of potential studies will be assessed by using the Newcastle–Ottawa scale (NOS) for assessing the quality of non-RCTs. The studies will be awarded a maximum of nine stars related to the selection and comparability of the study groups, and the ascertainment of interest outcome when using the NOS. And all the studies will be classified as low quality (0~5 stars) or high quality (6~9 stars) according to the selection and comparability of the studies. RevMan V.5.1 (Review Manager V.5.1) will be used for this process. This process will be accomplished by two authors (JX and LH) independently. And a third senior author (SW) will act as an arbitrator when there is disagreement.

    Statistical analysis

    The dichotomous variables (mortality; recurrent of pulmonary embolism, heart failure, adverse events or major adverse cardiac effects) will be determined by using risk ratio (RR) with 95% CI. Studies have shown that RR is more intuitive than OR, and OR is often interpreted as RR by clinicians, which leads to an overestimation of this effect. The median value cannot combine with the mean value statistically, and only data expressed as the mean and standardised can be used for meta-analysis. So, in our study, we will use weighted mean differences (with 95% CI) or standardised mean differences (95% CI) for the analysis of continuous variables. In order to analyse the long-term results and survival, we will extract the related data of survival analysis from the included studies and then calculate the pooled HR.30 HR and 95% CI will be extracted directly from the article, but for the article that had not reported the HR and 95% CI, we will using a special software named Engauge Digitizer to obtain the required data from Kaplan-Meier curves, following the method provided by Parmar et al.31 Finally, the obtained data will be integrated into the spreadsheet designed to calculate the HR and 95% CI.32 For the studies with non-standard design, such as cluster randomised trials, cross-over trials and studies with multiple treatment groups, we will extract an interclass correlation coefficient to modify the results according to the methods described in the Cochrane Handbook for Systematic Reviews of Interventions. When meeting missing data, we will contact the first author or corresponding author of the study to obtain the missing data, an imputation method will be used if the missing data is not available. All data will be evaluated carefully.

    Χ2 test (significance level: 0.1) and I2 test (0% to 40%: represent not be important; 30% to 60%: represent moderate heterogeneity; 50% to 90%: represent substantial heterogeneity; 75% to 100%: considerable heterogeneity) were used to assess the statistical heterogeneity among the studies.33 We will try to explore the potential causes of heterogeneity by conducting subgroup analysis or sensitivity analysis when heterogeneity exceeds 50%, and qualitative analysis will be performed if the heterogeneity is too high. We will compare the fixed effect estimate against the random effects model to assess the possible presence of small sample bias in the published literature. In the presence of small sample bias, the random effects estimate of the intervention is more beneficial than the fixed effect estimate. A funnel plot will be used to explore the potential reporting bias if ≥10 studies are available. A systematic narrative synthesis will be provided to summarise and explain the characteristics and findings, and if the extracted data are not suitable for pooling. RevMan V.5.1 software and Stata software will be used for statistical processing.34 A p<0.05 was considered statistically significant.

    Discussion

    At present, with the ageing of the population, the incidence of acute pulmonary embolism is increasing annually, COVID-19, in particular, has significantly increased the incidence of acute pulmonary embolism.5 Although the diagnosis and treatment of acute pulmonary embolism have made considerable progress in recent years, the prognosis of some patients are still poor, especially those with massive pulmonary embolism.10 Numerous studies have shown that thrombolytic therapy significantly increases the thrombosis recurrence and readmission rate for patients with massive acute pulmonary embolism, so surgical embolectomy is recommended for massive and submassive acute pulmonary embolism.16 The conventional surgical embolectomy was mainly performed under cardiopulmonary bypass through the median sternal incision, opening the pulmonary artery and removing the thrombus. But the thrombus cannot be cleared for the small distal branch artery. The procedure of retrograde pulmonary vein perfusion is to open the right atrium and atrial septum on the basis of conventional surgical embolectomy, and to retrograde perfusion myocardial protective fluid through the pulmonary vein, so that the embolism in small branches of the pulmonary artery can flow out with the retrograde blood flow, thus achieving the purpose of completely removing the embolism as far as possible.26 Recently, Spagnolo, et al26 reported 19 cases of patients with massive pulmonary embolism who underwent retrograde pulmonary embolectomy combined with pulmonary artery thrombectomy, there were neither in-hospital deaths, nor major postoperative complications in their research and all the patients were discharged from the hospital on anticoagulant medication by the 10th postoperative day, which proves the technique of retrograde pulmonary vein perfusion combined with pulmonary artery thrombectomy is safe and effective method in the treatment of acute pulmonary embolism. Although retrograde pulmonary vein perfusion combined with pulmonary artery thrombectomy can reduce the mortalities and complication rates in patients with acute pulmonary embolism, as a matter of fact, retrograde pulmonary vein perfusion has not been considered an alternative in the guidelines for acute pulmonary embolism. Therefore, more clinical evidence is needed to support it. We think that favourable clinical outcomes are likely to be achieved when retrograde pulmonary vein perfusion is used to treat acute pulmonary embolism extensively. The goal of the present study is to provide a procedure for meta-analysis and systematic review, and ascertain the safety and long-term effects of retrograde pulmonary vein perfusion for acute pulmonary embolism, and provide more clinical evidence for the application of retrograde pulmonary vein perfusion for acute pulmonary embolism.

    However, this study may have several limitations. First, due to the choice of surgical indications and surgical methods in different countries and regions are not the same, the heterogeneity between studies may be high. Second, few RCTs are currently available, which increases the difficulty in conducting a high-quality comprehensive evaluation.

    Ethics and dissemination

    This review and meta-analysis involves secondary data and does not require ethics approval. The outcomes of this study will be presented internationally. These results will be reported in a peer-reviewed scientific journal. The full review will be distributed in printed form, electronically and on appropriate social media sites.

    Ethics statements

    Patient consent for publication

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    Footnotes

    • JX and LH contributed equally.

    • Contributors JX and LH conceived the idea of this study, and will screen the titles, abstracts and full text to identify studies for inclusion or exclusion, extract data and input data and assess risk of bias. TP and WL provided statistical advice and revision of the final text. SW provided feedback on disagreements between the two authors and reviewed the protocol. All authors read and approved the publication of the protocol.

    • Funding This research was supported by university-level scientific research project of North Sichuan Medical College (CBY21-QA22, CBY21-QA30) and Cooperative scientific research project of Science and Technology Bureau of Nanchong, Sichuan Province (22SXQT0007).

    • Competing interests None declared.

    • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

    • Provenance and peer review Not commissioned; externally peer reviewed.