Clinical usefulness of psoas muscle thickness for the prognosis of acute type A aortic dissection patients undergoing total arch replacement

Introduction

Sarcopenia is characterized by the decline of skeletal muscle mass, muscle strength, and physical activity (1). It has been suggested to be associated not only with aging process (2), but also an impaired physical capability (3,4). Moreover, the relationship between sarcopenia and mortality, comorbidities of patients with cardiac surgery, is reported by several studies (5-7). Noteworthy, there is still no consensus measurement on quantifying and diagnosing sarcopenia. The skeletal muscle index (SMI), defined as the cross-sectional area of several muscles on computed tomography (CT) at the L3 vertebral level, is one of the most commonly used assessment in research area (8). However, the delineation of different groups of muscles surfaces is relatively complex, takes time, and requires specific software, restricting its clinical applicability. Durand et al. tried to used psoas muscle thickness/height (PMTH) measured on CT to diagnose sarcopenia and was determined to be associated with mortality in patients with cirrhosis (9). The diameter of the psoas muscle perpendicular to the longest axial diameter of the muscle at the umbilical level could be measured directly and the value was normalized by body height. All the acute type A aortic dissection (AAAD) patients underwent thoraco-abdominal aorta computed tomography angiography (CTA) scans before operation to assess the aorta. In this study, we aimed to assess whether preoperative computed tomography-measured psoas muscle thickness per height can be used to predict the prognosis after emergency surgery in AAAD patients. We present this article in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-196/rc).

Methods

Study participants and study design

This was a retrospective, single-center observational study with a sample of patients with emergency surgery for AAAD selected from Fujian Medical University Union Hospital between January 2020 and December 2020. All the patients underwent thoracic and abdominal CTA before aortic repair operation. Individuals of missing data on the key variables were excluded. For this retrospective study, the requirement for informed consent was waived by the ethics committee of Fujian Medical University Union Hospital because patient data were anonymized. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). This study was approved by the Medical Ethics Committee of Fujian Medical University Union Hospital (No. 2021KY0127).

We divided the included patients into two groups according to PMTH cut off value. Subsequently, baseline characteristics, in-hospital outcomes, and long-term survival were compared among the patients. Patients were followed up until June 2023. Follow-up data were obtained via outpatient clinic visits or by telephone.

Measurement of PMTH

The PMT was determined using abdominal CT that was performed before the operation using a 64-slice multidetector CT scanner (Discovery CT750 HD; GE Healthcare, Waukesha, WI, USA), yielding 0.6-mm-thick slices, in accordance with what was done in previous studies (9-12) (Figure 1). A cross-sectional CT image at the level of L3 was selected, and the maximum transverse thickness of the right psoas muscle was measured using STARTPACS (Start Group Co., Ltd., Fuzhou, China). PMT was standardized by height to control for differences: PMTH (mm/m) =PMT (mm)/height (m). The cut-off point of PMTH was set at 16.8 mm/m, according to existing literature (11).

Figure 1 Measurement of psoas muscle thickness on preoperative computed tomography. The red line represents the measured thickness of the psoas muscle at the level of the third lumbar vertebra (L3).

Statistical analysis

SPSS version 27.0 (IBM Corp., Armonk, NY, USA) was used for all statistical analyses. Data were presented as mean ± standard deviation, median (interquartile range), or number (%). The unpaired student’s t-test or Mann-Whitney test was performed to compare the continuous variables between groups, and the Chi-squared test or Fisher test was used for categorical variables. Patients were classified into two groups based on PMTH cut off value. Propensity score matching (PSM) was calculated based on a logistic regression model, with a caliper 0.05, matching ratio =1:1 to balance potential bias. The mirror histogram of propensity scores is listed to show the matching details (13). Long-term survival was estimated via the Kaplan-Meier method, and comparisons between the two groups were performed with the log-rank test. To find out independent risk factors, variables with P<0.20 on univariate analysis were entered into Cox proportional hazards regression analysis. And the heterogeneous effect of PMTH on long-term survival was assessed by creating interaction terms between PMTH and age. Statistical significance was set at P<0.05.

Results

Patient selection and baseline characteristics

The patient selection chart and PSM details are shown in Figure 2. After grouping by the cut-off point of PMTH, analyses revealed statistical differences in age, gender, body mass index (BMI), hemoglobin and albumin. Not surprisingly, psoas muscle mass decreased with increasing age and the worse trophic status. To solve this issue, a 1:1 PSM was conducted to reduce the potential bias. Finally, 68 pairs were successfully matched. The baseline characteristics before and after PSM in each group are summarized in Table 1. After PSM, the clinical and demographic characteristics were well-balanced between the two groups, including age, gender, BMI, preoperative comorbidities, laboratory indicators, echocardiography data, aortic root procedure, operative times.

Figure 2 The study design. (A) Patient selection flowchart; (B) mirror histogram of propensity scores for patients. AAAD, acute type A aortic dissection; PMTH, psoas muscle thickness/height; PSM, propensity score matching.

Clinical outcomes

In the entire cohort, in-hospital death occurred in 16 patients (13 in low PMTH group and 3 in high group) and the mortality rate was 5.7% for all patients. After PSM, the number of deaths in the two groups was 10 and 2 (P=0.02) (Table 2). Patients with the low PMTH values had a generally poor short-term outcomes, which had a markedly higher odds for in-hospital mortality (P=0.02) and renal failure (P=0.001) (Figure 3). Receiver operating characteristic (ROC) analysis was performed to verify whether PMTH could predict in-hospital mortality. The area under ROC curve (AUC) was 0.81 (95% CI: 0.64–0.97), which reflects a good predictive performance of the PMTH. The cut-offs for in-hospital mortality were PMTH at 15.68 mm/m (sensitivity: 97.6%, specificity: 66.7%).

Figure 3 ROC curve for evaluating PMTH predicting performance. The AUC was 0.81 and indicate a good discrimination and differentiation. PMTH, psoas muscle thickness/height; AUC, the area under curve; ROC, receiver operating characteristic curve.

Among the 124 survivors, late death occurred in 24 patients (19.4%) [cardiovascular and cerebrovascular events, n=15 (62.5%); infection, n=5 (20.8%); cancer, n=2 (8.3%); and others, n=2 (8.3%)]. Kaplan-Meier survival estimates according to PMTH for AAAD patients is shown in Figure 4. The cumulative survival rates in low PMTH group and high PMTH group patients were 61.9%±9.5% and 82.0%±6.9%, respectively [log-rank P=0.02; HR 2.53 (95% CI: 1.13–5.66)]. The mean follow-up period was 37 months, and the follow-up rate was 100%.

Figure 4 Kaplan-Meier curves of overall survival with 95% confidence intervals. PMTH, psoas muscle thickness/height.

Predictors of long-term survival

To assess the impact of sarcopenia on the long-term survival, Cox proportional hazards model was performed. On univariate analysis, the PMTH value was significantly associated with higher mortality [HR 2.86 (95% CI: 1.12–8.99)], and remained as an independent predictor of survival after adjusting for multivariable analysis [HR 2.73 (95% CI: 1.15–8.78)]. Other predictors identified included age [HR 1.03 (95% CI: 1.01–1.05)], preoperative malperfusion [HR 2.35 (95% CI: 1.57–9.22)], cardiopulmonary bypass (CPB) time [HR 1.01 (95% CI: 1.00–1.02)] (Table 3). Subgroup analysis was conducted to determine the association between PMTH and age, as well as its impact on prognosis outcomes (Table 4). There was no significant difference in the relationship between PMTH and long-term survival among age (interaction P=0.59).

Discussion

The principal finding of this study was that preoperative sarcopenia was independently associated with the greater risk of mortality in patients after AAAD surgery. Computed tomography-measured psoas muscle thickness is a simple, objective, and readily available method to assess skeletal muscle mass. In comparison with other methods for identifying the sarcopenia, e.g., questionnaires and the assessment of certain physical activities (14), PMTH is convenience in actual clinical practice. Considering the fact that the PMTH value has been reported to be tightly correlated with sex and BMI (15,16), the propensity-matched analysis was adopted to make the baseline characteristics comparably.

AAAD is a lethal disease with poor prognosis. The in-hospital mortality is reportedly 9.4–22% (17,18). Technological advances in cardiac surgery have led to personalized treatment options for each condition. As such, preoperative and fast identification of patients at high risk for mortality and morbidity has become more essential to provide optimal treatment to each patient. The occurrence of aortic dissection is associated with connective tissue abnormalities of the arterial wall influenced by enzymatic activity (19). Matrix metalloproteinases, which are implicated in this process, have also been shown to affect muscle development (20). It is commonly accepted that muscle wasting may be explained by the malnourished state of negative protein balance, characterized by the chronic loss of body protein and fuel reserves (21). There have been previous studies on the relationship between the sarcopenia and the prognosis of patients with chronic wasting diseases, like cirrhosis, end-stage kidney disease and valvular heart disease (15,22,23). However, less is known about the impact of sarcopenia on the outcomes of AAAD patients, such an acute onset, rapid progressive condition. Ganapathi et al. used a 6-component index which included total psoas volume to define frailty and proved that it can serve as an independent predictor of early and late mortality risk in patients undergoing proximal aortic surgery (24). Regrettably, with more than 50% CT data missing, the trustworthiness of the findings remain doubtful. The mechanism by which sarcopenia leads to a decreased survival in AAAD patients still needs further investigation. The resistance in muscle homeostasis and anabolic metabolism, as well as inflammation and mitochondrial dysfunction and could be the main reasons for poor prognosis (25). The catabolic state after surgery accelerates muscle loss, further leading to reduced physical activity and decreased physical function, resulting in significant functional limitations (26). This suggests a bidirectional association between sarcopenia and survival after surgery. At the same time, in patients undergoing aortic surgery with deep hypothermic circulatory arrest (DHCA), the incidence of neurological complications is relatively high and significantly impacts the prognosis. Neuromuscular system integrity impairment plays a crucial role in the decline of muscle strength, leading to muscle weakness (dynapenia) (27,28). This muscle weakness may further exacerbate functional impairments and decreased quality of life during the recovery period. With the accelerated aging of the population, the number of patients suffering from frailty is increasing. There has been an increasing interest in the use of sarcopenia as a tool to define frailty and to further be used for preoperative risk assessment. Conventional risk models in cardiac surgery, like the European System for Cardiac Operative Risk Evaluation II (EuroSCORE II) (29) and the German Registry for Acute Aortic Dissection Type A (GERAADA) score (30), traditionally focus only on characteristics of the disorders and specific medical comorbidities. Ignoring nutritional deficiency status and age-related systemic vulnerability is considered to have negative impacts on the prediction results. CT-based psoas muscle area has been used to determine the quantity and quality of muscle and impact of sarcopenia (31). However, volumetric measurement requires particular software and can be time-consuming. In this study, two cardiovascular surgeons read the CTA assessing the true lumen, intimal tears and extent of the dissection. At the same time, the PMTH could be rapidly measured without preoperative complex scoring process.

Sarcopenia was also found to be a prognostic factor for the postoperative severe complications in this study, especially renal failure, characterized by the loss of body protein (muscle) and fuel reserves (fat) due to catabolic inflammation (22), seriously affecting the quality of life and long-term survival of patients. At the same time, sarcopenia may also be related to patients’ baseline renal function. Wilkinson et al. found that the prevalence of sarcopenia among participants with declining renal function (defined as eGFR <60 mL/min/1.73 m²) may be 9.7%, which is approximately twice that of non-CKD patients (32). Different from other conditions, patients who are diagnosed AAAD have to receive surgery as soon as possible. The regimen for frail can be applied only during the rehabilitation phase. Available evidence suggests that nutritional treatment in addition to resistance training may improve the skeletal muscle mass and thus the ability to perform activities of daily living (33). In elderly perioperative patients with a diagnosis of sarcopenia, a simplify surgical step and a more aggressive nutritional intervention will profit more. The most important of all, determinating the cause of loss of muscle mass and appropriate management is necessary.

Limitation

Several limitations of this study should be noted. On top of all of these, the retrospective nature of this study introduces inherent biases, causality cannot be determined. Currently, there is a lot of research on sarcopenia in cardiovascular disease patients, studies using standardized psoas muscle thickness for diagnosis are relatively limited. Therefore, there is controversy over the cut-off value used for grouping. In this study, we adopted the commonly reported cut-off value of 16.8 mm/m. In terms of measurement, we acknowledge that there is a degree of subjectivity involved in this method. In patients with an anomaly of the vertebrae, an exact psoas muscle level cannot be easily determined. Furthermore, in elderly patients, compression fractures of the vertebrae are relatively common. In the meantime, the cut-off values for sarcopenia potentially differ among races, sexes, and age groups. And it is difficult to identify a definition that could be applied to all populations. Systemic inflammation has a close relationship with sarcopenia/muscle wasting (34). In this study, the number of AAAD patients with Marfan syndrome, Behcets disease and syphilitic aortitis included was limited.

Conclusions

Sarcopenia defined from the PMTH was associated with short- and long-term survival after AAAD surgery. Preoperative CT measurement of the psoas muscle thickness can be a useful tool for quick identification of patients at high risk.

Acknowledgments

Funding: This work was funded by the Fujian Provincial Special Reserve Talents (Grant No. 2021-25).

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-196/rc

Data Sharing Statement: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-196/dss

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-196/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-196/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). This study was approved by the Medical Ethics Committee of Fujian Medical University Union Hospital (No. 2021KY0127), and individual consent for this retrospective analysis was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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