Accepted on 22 Feb 2019
Submitted on 9 Jan 2019
Acute aortic dissection (AAD) is a rare and extremely dangerous cardiovascular surgical disease with an annual incidence of 3–4 per 100,000. About two-thirds of the patients with AAD involve ascending aorta, which is classified as type A according in Stanford classification [1]. Mortality in patients with Stanford type A aortic dissection was significantly correlated with the extent of dissection, the time from onset to diagnosis, and the method of treatment. If only relying on conservative medical treatment, the mortality rate within 24 h of onset is as high as 20%, and up to 50% within 2 weeks. In recent IRAD database published data, the early hospital mortality rate is 59% [2]. Because the main cause of early death is aortic rupture, surgical repair before rupture is currently recognized as the main treatment of type A aortic dissection. According to the extent and progress of dissection, a variety of surgical methods can be selected for aortic repair. However, as a large-scale cardiac surgery requiring deep hypothermic circulatory arrest and selective cerebral perfusion, the hospital mortality rate of type A aortic dissection is higher than that of other types of cardiac surgery. Multicenter data show that the hospital mortality rate within 60 days or in the early stage is about 23% [3]. By establishing risk prediction model, we can not only comprehensively assess the risks of surgery before operation, but also distinguish the severity of patients' disease, stratify the risk levels, and help clinicians choose the best treatment strategies according to the individual characteristics of patients, so as to reduce the mortality and complication rate of surgery.
The primary aim of the study is to establish a risk scoring system for Stanford A aortic dissection patients based on the largest database of aortic dissection in northern China. Validate the scoring system in surgical risk assessment and provide the evidence-based medical basis for clinicians in treatment of acute type A aortic dissection.
The aim will be achieved in following steps:
This study is designed as a cohort study. The establish of model is conducted using retrospective cohort data, the validation of model is performed using prospective data in our center.
Patients with acute type A aortic dissection (less than 2 weeks) over the age of 18, the dissection involves the ascending aorta or the arch of the aorta, receive surgical treatment in our center, informed consent by relatives or later on in during the hospital admission when patients regain mental capacity.
The dissection tear was located lower than the left subclavian artery, patients with chronic aortic dissection.
Primary endpoint events: death during hospitalization, both intraoperatively and postoperatively. Secondary endpoint events: Whether patients was discharged home; if patients was transferred to other hospitals, the reason for transfer need to be collected. Re-operation and hospitalization complications associated with surgery within 30 days of the procedure, such as MODS, sepsis, cardiovascular adverse events, respiratory failure, acute renal failure and nervous system complications (Table 1). The death and complications of the patients after discharge and the detailed time of occurrence were observed by special follow-up personnel through telephone and mail questionnaires.
Table 1
Definition of operation related complication.
| Complication | Definition |
|---|---|
| MODS | The failure of two or more organs 24 h after the onset of the symptom |
| Sepsis | Significant elevation of white blood cell and neutrophil counts, blood culture is positive, or infection that is difficult to control using antibacterial therapy |
| Respiratory failure | Severe impairment of pulmonary ventilation or ventilation due to various causes, resulting in arterial partial oxygen pressure less than 60 mmHg |
| Cardiovascular adverse events | Cardiovascular adverse events were defined as low cardiac output syndrome, malignant arrhythmia, and aortic rupture |
| Nervous system complications | Cerebral hemorrhage, cerebral infarction, paraplegia, hemiplegia and spinal cord ischemia diagnosed by physical examination or brain imaging examination |
| ARF | The estimated GFR decreased by at least 25% in the 48–72 h period after surgery |
| Re-operation | Reason for re-operation is classified into major bleeding, implant infection, tamponade, anastomotic leakage |
MODS = Multiple organ dysfunction syndrome, ARF = acute renal failure.
Only variables with less than 25% missing will be included in the univariate analysis [4], only variables with less than 10% missing will be included in the parsimonious regression model, and the missing values will be estimated by multiple imputation method (see Table 2).
Table 2
Data fields for the study.
| Data field | Option (definition) |
|---|---|
| Section 1–Demographic data | |
| Age | In years |
| Height | In meters |
| Weight | In kilograms |
| Body mass index | In kg/m2 |
| Body surface area | In m2 |
| Time from the onset | In days |
| Smoking status | Current smoker/Quit > 6 weeks/Non-smoker |
| Cardiovascular history | Yes/No |
| COPD history | Yes/No |
| Diabetes | Yes/No |
| Hypertension | Class I/Class II/Class III/Class IV |
| Diabetes | Yes/No |
| Previous Aortic surgery | Yes/No |
| Previous valve surgery | Yes/No |
| Previous coronary bypass surgery | Yes/No |
| Previous history of cerebrovascular disease | Yes/No |
| If yes - | |
| New neurological deficit | Transient syncope/lethargy/coma/limb/sensory/disorder/hemiplegia/paraplegia/limb movement disorder |
| Section 2–Baseline blood test results | |
| White blood cell count | In 1 * 109/L |
| Red blood cell count | In 1 * 109/L |
| Platelet count | In 1 * 109/L |
| Hemoglobin | In mg/L |
| Neutrophil percentage | In % |
| MCHC | In g/L |
| ESR | In cm/min |
| BUN | In mg/dL |
| SCr | In mmol/L |
| TnI | In ng/mL |
| Albumin | In g/L |
| ALT | In U/L |
| AST | In U/L |
| D-Dimer | In mmol/L |
| INR | |
| Fibrinogen | In g/L |
| FDP | In ug/mL |
| Lactate | In mmol/L |
| Section 3–Perioperative characteristics | |
| Time of operation | In hours |
| Bentall procedure | Yes/No |
| Total arch replacement combined with stented elephant trunk implant procedure | Yes/No |
| Combined valve surgery | Yes/No |
| Combined coronary bypass surgery | Yes/No |
| Time of cardiopulmonary bypass | In minutes |
| Time of aorta clamping | In minutes |
| Selective cerebral perfusion performed | Yes/No |
| ASA grade | 1 – Normal healthy individual 2 – Mild systemic disease that does not limit activities 3 – Severe systemic disease that limits activities but is not incapacitating 4 – Incapacitating systemic disease which is constantly life threatening |
| hypothermia circulatory arrest lowest anal temperature | In °C |
| Amount of intraoperative suspended frozen plasma infusion | In mL |
| Amount of intraoperative platelet infusion | In unit |
| Status of operation | Emergency/Urgent/Elective |
| Section 4–Ultrasonic correlation parameters | |
| Aortic sinus diameter | In mm |
| Ascending aorta diameter | In mm |
| Eject fraction | In % Classified into <30%/30–50%/>50% |
| LVEDD | In mm |
| Aortic vale regurgitation | Mild/Moderate/Severe |
| Mitral vale regurgitation | Mild/Moderate/Severe |
| Bicuspid aortic valve | Yes/No |
| Pericardial effusion | Mild/Moderate/Severe |
| Pulmonary hypertension | Mild/Moderate/Severe |
| Section 5–Post-operative outcomes | |
| Re-operation | Yes/No |
| If yes – reason for re-operation | Major bleeding/Implant infection/Tamponade/Anastomotic leakage |
| Discharged home | Yes/No |
| If not – reason for transfer | |
| Neurological complications | Yes/No |
| If yes – details of complications | Cerebral hemorrhage/Cerebral infarction/Diffuse encephalopathy/Spinal cord injury/Limb paralysis |
| Cardiovascular complications | Yes/No |
| If yes – details of complications | Pericardial tamponade/Perioperative myocardial infarction/Low cardiac output syndrome/Arrhythmia/Rupture of aorta |
| Respiratory complications | Yes/No |
| If yes – details of complications | Atelectasis/Pulmonary infection/Pulmonary embolism/Pneumothorax Pleural effusion/Respiratory failure |
| Incision-related complications | Yes/No |
| If yes – details of complications | Incisional infection/Poor healing of sternum |
| Peripheral organ ischemia | Osteofascial compartment symptoms/Limb ischemia symptoms |
| Renal complications | Yes/No |
| If yes – stage of renal complications | ARF − 48–72 h after surgery, eGFR decreased by more than 25% |
| AKI – Stage 1: SCr is 1.5–1.9 times baseline level/Stage 2: SCr is 2.0–2.9 times baseline level/SCr is more than three times the baseline level | |
| Postoperative dialysis | Yes/No |
| MODS | The failure of two or more organs 24 h after the onset of the symptom |
| Sepsis | Significant elevation of white blood cell and neutrophil counts, blood culture is positive, or infection that is difficult to control using antibacterial therapy |
| Section 6 –Aortic computed tomography Angiography data | |
| Aortic arch involvement | Yes/No |
| If yes – involved branch | Brachiocephalic artery/Left common carotid artery/Left subclavian artery |
| Coronary artery involvement | Yes/No |
| If yes – involved branch | Left/Right |
| Branch involvement of abdominal viscera | Yes/No |
| If yes – involved branch | Renal artery/Superior mesenteric artery/Celiac trunk |
MCHC = Mean erythrocyte hemoglobin concentration, ESR = Erythrocyte sedimentation rate, BUN = blood urea nitrogen, SCr = serum creatinine, TnI = cardiac troponin I, ALT = glutamic-pyruvic transaminase, AST = glutamic oxalacetic transaminase, INR = International Normalized Ratio, FDP = fibrin degradation products, LVEDD = left ventricular end diastolic diameter, ASA = American society of Anesthesiology, ARF = acute renal failure, eGFR = estimated glomerular filtration rate, AKI = acute kidney injury.
Data collection will follow Caldicott II principles (http://systems.hscic.gov.uk/infogov/caldicott/). The data of the patients were obtained by inquiring the medical record system by specialized collectors. Study data will be stored and managed using an electronic data capture tools (http://r.empowerstats.cn/dataweb/), including demographic data, co-morbidity, and prior medical history. Echocardiography and aortic computed tomography angiography data was evaluation by experienced ultrasound physicians and imaging specialists in our hospital.
To ensure the realness of data collection, 10% of the patients were randomly selected from the database, and the contents and the original data were checked. Check all patient data entered by the researcher if the error rate of variables entered by the researcher exceeds 5%.
By collecting retrospective cohort data, 890 patients with acute type A aortic dissection who underwent surgical treatment at our hospital from January 2015 to December 2018 were consecutively collected to form a modeling cohort. Through a prospective cohort study, 890 consecutive surgery patients with acute type A aortic dissection in our center from January 2019 to July 2021 were selected to form a model validation cohort.
Data collection and analysis will be conducted following the time line below
The area under ROC curve for predicting mortality risk of patients with acute type A aortic dissection was obtained as the main index and the sample size was estimated. According to previous reports, the early surgery mortality rate of acute type A aortic dissection is 10–30%. As the area under ROC curve predicted by European Score System is 0.79. The area under ROC curve is set 0.8 as the reference standard and 0.7 as the acceptable threshold. PASS 11.0 software was used to estimate the sample size needed to establish a mortality prediction model. The significance level (a) is set as 0.05, the grasp degree (1-beta) is set as 0.9, using the bilateral test, the research needs at least. The results showed that at least 890 acute type A aortic dissection who underwent surgery needed to be enrolled in the study.
Continuous variables are expressed as mean ± standard deviation and categorized variables as percentage. T-test, One-Way ANOVA test, Kruscal Whallis H test and chi-square test (categorical variables) were used to determine any statistical difference between different outcome groups. Univariate analysis was used to evaluate the relationship between variables and outcomes, and stepwise method was used to eliminate variables with P > 0.20. Cox proportional hazard model is applied for multivariate analysis and adjusted for the potential confounding. Final models were selected based upon Akaike Information Criterion (AIC) measures of model quality and performance. Hosmer-Lemeshow method was used to test the goodness of fit, c-statistics was used to test the discriminant ability of the model, and NRI was used to test the classification ability of the model.
Score assignment is conducted by rounding the adjusted odds ratio for each variable and then a clinical risk score is created. The association between the clinical risk score and the probability for mortality was determined.
Because of the particularity, complexity and high perioperative mortality of cardiac surgery, many models for post-operative complications and mortality risk prediction have been designed. For example, the first surgical risk prediction method used in cardiovascular surgery field, the Parsonnet's score in 1989 [14], due to the existence of related items influenced by subjective judgment of physician, the performance of prediction model is not enough. Similarly, the European System for Cardiac Operative Risk Evaluation (EuroSCORE) [5], EuroSCORE II updated in 2012 [6], Ontario Province Risk (OPR) established in 1991, the Society of Thoracic Surgeons score (STS score) [7], and Cleveland model established in 1992 are also widely used scoring systems to predict early and in-hospital mortality in a variety of cardiac surgery, including aortic dissection. However, these scoring systems for patients undergoing conventional cardiac surgery are not suitable for patients with acute type A aortic dissection [8]. On the other hand, the average age of onset of aortic dissection in China is lower than that in western countries for 10–15 years [9], and it takes longer from onset to surgical treatment than in developed countries (average 4.5 h in developed countries and 2–7 days in developing countries likes China). Therefore, a scoring system suitable for patients in developing countries is needed to predict their risk of early death and to guide their choice of further treatment strategies. There have been some risk prediction models for aortic related surgery based on limited sample [10], [11], [12], [13], [14]. However, due to inappropriate selection of variables included in the model: most of the models included only medical history and clinical symptoms while not many blood test variables or imaging characteristics was included, their predictive performance is doubtful.
Under the current condition of improved blood test and image examination methods (consequently, there will be fewer patients lack these variables), we urgently need an early death risk prediction model for patients with acute type A aortic dissection receiving surgical treatment in developing countries, which can predict early death and complication risk accurately enough. Although emergency surgery is still the preferred treatment for acute type A aortic dissection, the subgroup of high-risk population identified by this risk prediction model will remind clinicians to take preventive measures for specific complications.
Our center has the largest single-center sample of aortic dissection in northern China, most of which were transferred from neighbouring provinces. As the immense sample size advantage – to our knowledge most European centers can only achieve one-tenth of the number of operations in our center within the same time frame, the experience gained in this study will be more convincing and applicable to developing countries.
This study was approved by the Ethics Committee of Beijing Anzhen Hospital. For prospective validation cohort patients, patients will be recruited and their clinical data will be collected after being informed of the study protocol and obtained consent. Dissemination of the study protocol will be via the Capital Health Development Project and Results will be published in clinical research journals when the study is finished.
This study was supported by National Key R&D Program of China (2017YFC1308000); Capital Health Development Research Project (NO. 2018-2-2066); National Science Foundation of China (81600362) and the Beijing Lab for Cardiovascular Precision Medicine, Beijing, China. (NO. PXM2017_014226_000037).
Contributions: (I) Conception and design: H Zhang, M Gong; (II) Statistical method design: Z Wu, S Xu; (III) Modification suggestion: X Wang, H Li; (IV) Manuscript writing: All authors.
The authors declare that there is no conflict of interests regarding the publication of this article.
Hongjia Zhang, the corresponding author, accept full responsibility for the work and/or the conduct of the study, had access to the data, and controlled the decision to publish.
This study have not been registered.
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Thanks to J Liu for the guidance of the statistical method in this paper. All the authors agree with the opinions proposed in this paper.