Right anterior mini-thoracotomy as first-line strategy for isolated aortic valve replacement: a retrospective study

Introduction

Background

Minimally invasive cardiac surgery (MICS) procedures are increasingly used to minimize surgical trauma and achieve early patient recovery (1,2). Recently, the standard of care for aortic valve disease has changed from surgical aortic valve replacement (AVR) via median sternotomy (MS) to minimally invasive AVR (MIAVR) and transcatheter aortic valve implantation (TAVI). The two approaches for MIAVR comprise right anterior mini-thoracotomy (RAMT) or partial upper sternotomy [J-sternotomy (JS)] (3-5). Patient outcomes using both approaches are favorable, including decreased blood loss and ventilator care (6-8).

AVR via MS has been the gold standard approach. The relatively similar field of view and shorter running curve of the JS approach have been considered to minimize anatomical limitations in relation to AVR, compared with the RAMT approach (9,10). However, as the process of splitting the sternum is similar to that used in MS, intraoperative chest wall instability and bleeding offset the advantages of MICS in relation to the JS approach (11). The RAMT approach avoids sternotomy, with single-center studies reporting favorable short-term outcomes, including shorter time to first mobilization and length of stay (LOS) (6). Although the RAMT approach has become increasingly adopted, issues remain concerning the effects of longer cardiopulmonary bypass (CPB) time and cardiac ischemic time (CIT) owing to the limited operation field (12,13).

Rationale and knowledge gap

Since MICS was first introduced at Pusan National University Yangsan Hospital (PNUYH), utilization of the RAMT approach has markedly increased. The growing experience obtained using this approach has led to reduced CPB time and CIT and has also allowed for expansion of the range of patients eligible for RAMT. Currently, RAMT is considered the primary surgical approach for isolated AVR unless there are specific contraindications.

Although several studies have compared early outcomes between RAMT and JS approaches, research focusing on mid-term outcomes is scarce.

Objective

We aimed to compare short- and mid-term surgical outcomes between the RAMT and JS approaches conducted at PNUYH, with RAMT being the primary approach. This manuscript is written in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-928/rc).

Methods

Study details

In this retrospective study, we used data from our institutional database. Between February 2009 and June 2022, a total of 832 consecutive patients underwent AVR via RAMT, partial upper sternotomy, or sternotomy. Exclusion criteria comprised concomitant aortic or root surgery, concomitant coronary artery bypass, aortic valve valvuloplasty, concomitant repair of congenital anomaly, or infective endocarditis (Figure 1). To compare between the two MIAVR approaches, 168 patients with MS were also excluded. After applying the exclusion criteria, data from 407 patients with isolated MIAVR were used for statistical analyses. Of these, 315 (77.4%) had undergone AVR via RAMT and 92 (22.6%) had undergone AVR via JS. After propensity score matching (PSM), 90 matched patients from the RAMT group and 90 from the JS group were included for analysis.

Figure 1 Patient selection. A retrospective review was conducted on a prospectively collected database of patients who underwent aortic valve replacement via right anterior mini-thoracotomy, partial upper sternotomy, or sternotomy. CABG, coronary artery bypass grafting; JS, J-sternotomy; RAMT, right anterior mini-thoracotomy.

Selection of the surgical approach

In February 2009 (the start point for data collection), sternotomy was the standard surgical access for isolated AVR surgery in PNUYH. However, since March 2018, RAMT has become the dominant approach for isolated AVR (Figure 2). During the study period, preoperative computed tomography (CT) of the aorta was performed for all patients who required an isolated AVR to determine the suitability of patients for the RAMT approach and femoral cannulation. The size, position, and distance from the sternum of the ascending aorta and anatomy of the femoral artery from preoperative CT scans were considered to determine the optimal surgical approach. Most isolated AVR surgeries prioritize a minimally invasive approach via RAMT. If CT scan findings indicated that the aorta was centrally located and directly behind the sternum, the JS approach was selected; otherwise, RAMT was performed, provided peripheral cannulation was feasible (Figure 3).

Figure 2 Trends in aortic valve replacement surgery. Initially, isolated aortic valve surgeries, which were predominantly conducted via median sternotomy, gradually shifted toward minimally invasive approaches. While both J-sternotomy and RAMT have been introduced, RAMT has dominantly been performed since 2018. The y-axis represents the number of surgeries. MS, median sternotomy; JS, J-sternotomy; RAMT, right anterior mini-thoracotomy.

Figure 3 Selection of surgical approach. The surgical approach is determined based on the location of the great vessels identified through computed tomography and the condition of the peripheral vessels for cannulation. AVR, aortic valve replacement; JS, J-sternotomy; RAMT, right anterior mini-thoracotomy.

Figure 4 illustrates the preferred surgical approach based on the position of the ascending aorta. During the initial adoption of the RAMT approach, it was predominantly performed for patients with an ascending aorta position similar to those in Figure 4D,4E. However, with increased surgical team proficiency, application of the RAMT approach was expanded to include patients with an ascending aorta position similar to that in Figure 4B,4C, which then led to an increase in the number of RAMTs undertaken. However, when the ascending aorta was positioned exactly in the center and closely attached beneath the sternum, as shown in Figure 4A, JS was performed.

Figure 4 Surgical approach determination based on ascending aorta position. Surgical approach based on the position of the ascending aorta confirmed according to the preoperative computed tomography. In case A, where the aorta is directly behind the sternum, RAMT is most challenging. In case B, although the distance between the sternum and the ascending aorta is short, making the surgery challenging, RAMT is not impossible. As we move toward C, D, and E, it becomes easier to establish surgical visualization during RAMT. Initially, RAMT was performed only on patients with position of the ascending aorta similar to those in categories D and E. However, recently, RAMT is being performed on most patients excluding those in category A. The red line shown in the figure indicates the distance measured between the sternum and the aorta. JS, J-sternotomy; RAMT, right anterior mini-thoracotomy.

Ethical considerations

The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). This study was approved by the Pusan National University Yangsan Hospital Institutional Review Board (March 29, 2024; No. 55-2024-033). Informed consent was waived owing to our study’s retrospective design.

Surgical procedure

All patients had been intubated with a single-lumen endotracheal tube, and all patients had undergone transesophageal echocardiography. Patients in the RAMT group underwent one-lung ventilation during surgery through inserting an endo-bronchial blocker (EZ-Blocker^TM; Teleflex Medical OEM, North Carolina, USA) into the endotracheal tube.

In the RAMT group, surgical access was achieved via a horizontal 6-cm skin incision, with lower rib cutting performed at the second or third right intercostal space. Conversely, in the JS group, surgery began with a vertical 6-cm skin incision, followed by a J-shaped upper mini-sternotomy at the fourth intercostal space.

Cannulation for CPB was achieved via the common femoral artery in 436 (98.7%) patients and via the common femoral vein in all patients in the unmatched cohort. Femoral cannulation was performed primarily through a surgical approach with a skin incision measuring 2 cm below the inguinal ligament. Since September 2017, percutaneous femoral cannulation for CPB via ultrasound-guided sonography has been performed in combination with a vascular closure device (Perclose ProGlide^TM; Abbott Vascular, CA, USA) for femoral artery cannulation. During peripheral cannulation, transesophageal echocardiography was used to confirm real-time guidewire positioning: at mid-thoracic level of the descending thoracic aorta for arterial cannulation and via the superior vena cava for venous cannulation. If grade 3 or 4 atherosclerosis of the aorta was identified on preoperative CT scans, perfusion was directed through the ascending aorta or axillary artery, instead of through the femoral artery. Supplementary venous cannulation of the superior vena cava was conducted, either directly or through the right internal jugular vein, as detailed in MICS protocols (14). All cardiac procedures were performed under mild hypothermia (29–34 ℃).

On-table extubation after MIAVR

On-table extubation after heart surgery was introduced in 2009 in PNUYH and has become increasingly common, reaching 75.7% per year in patients undergoing MICS at PNUYH. For on-table extubation, anesthesia was induced with propofol, rocuronium, and remifentanil and maintained with remifentanil and sevoflurane. When the aortic cross-clamp was released, rocuronium administration was discontinued. On-table extubation was considered following consultation between the surgeon and anesthesiologist. Ventilatory status was evaluated according to standard protocols, ensuring adequate oxygenation (O₂ saturation >92% or PaO₂ >60 mmHg) and absence of acidosis (pH >7.25) through arterial blood gas analysis. Sugammadex (Bridion, MERCK Connect, New Jersey, USA), a neuromuscular blocking reversal agent, was promptly administered after skin closure. Extubation was performed following confirmation of complete reversal of the neuromuscular blockade, hemodynamic stability, and the absence of surgical site bleeding.

Study endpoints

The outcome variables were in-hospital surgery-related morbidity and survival. An analysis of risk factors influencing long-term survival was also conducted. Postoperative morbidity was defined using standard Society of Thoracic Surgeons data element definitions (15).

Early mortality was defined as death within 30 days of surgery. Survival and date of death were confirmed using National Health Insurance data. In cases of death, medical records were reviewed if the patient had died at PNUYH. If not, the cause of death was recorded following a phone conversation with the deceased patient’s family.

To analyze the effect of surgical incision on the early clinical outcome, both early death and postoperative comorbidities were compared between the two groups, as was mid-term survival.

Follow-up

After discharge, patients underwent direct assessments in PNUYH at the 3-month mark and annually thereafter. Alternatively, for those unable to visit the clinic, telephone interviews were conducted during a 3-month late closing interval, concluding in April 2021, achieving a completion rate of 98%. Telephone contact was used to evaluate each patient’s current physical condition, and inquiries were made regarding the need for additional cardiovascular interventions and check-ups. Referring cardiologists and family doctors were also contacted for supplementary information when necessary.

Statistical analysis

Categorical variables were compared using Chi-squared and Fisher’s exact tests and presented as frequencies and percentages. Continuous variables were compared using independent t-test or a Mann-Whitney U tests and expressed as mean ± standard deviation or as the median with interquartile range (IQR). We employed the inverse probability of treatment weighting (IPTW) method to retain the sample size. IPTW values were calculated using the formula: [1/propensity score (PS)] for the RAMT group and [1/(1 − PS)] for the JS group. After IPTW, we examined the prognosis of patients in both groups using linear and logistic regression analyses using the IPTW values of the two groups. We applied Firth’s penalized maximum likelihood bias reduction method for logistic regression, which has been shown to adequately address monotone likelihood (nonconvergence of likelihood function) (16). As both groups in our study population were not randomly assigned, potential confounding and selection biases were accounted for through applying PSM, calculated using a multivariable logistic regression model, with age, sex, body surface area, hypertension, diabetes mellitus, New York Heart Association (NYHA) class, EuroSCORE II, presence of aortic valve stenosis, chronic kidney disease (CKD), and previous cardiac surgery as independent variables. For 1:1 matched data, we compared group differences using a paired t-test or a Wilcoxon’s signed rank test for numeric variables and a McNemar test for categorical variables. The Kaplan-Meier method with a log-rank test and Cox proportional hazard regression analysis were used to investigate the prognostic factors influencing mid-term survival. Variables showing a univariate association with outcome (P<0.10) were included in stepwise backward multivariate Cox proportional hazard regression to adjust for confounders. We used Firth’s penalized maximum likelihood bias reduction method for Cox proportional hazard regression, which has been shown to address monotone likelihood (nonconvergence of likelihood function) (16).

All statistical analyses were conducted using the following software: SPSS 26.0 (released 2019, version 26.0., IBM SPSS Statistics for Windows, IBM Corp., Armonk, NY, USA), MedCalc^® Statistical Software version 20.009 (MedCalc Software Ltd., Ostend, Belgium; https://www.medcalc.org; 2021), and R statistical software (version 4.2.1; R Foundation, Vienna, Austria, http://www.r-project.org/). A P value <0.05 was considered statistically significant.

Results

Considerable differences were observed in terms of baseline characteristics in the unmatched cohort (Table 1). In the crude analysis, the JS group had a higher EuroSCORE II (4.4±8.2 vs. 2.5±3.4, respectively; P<0.001) and a higher NYHA class than the RAMT group did. Moreover, there were more patients with diabetes mellitus and CKD treated with hemodialysis in the JS group than in the RAMT group. PSM for 16 covariates yielded 90 pairs of well-matched patients with almost all standardized mean differences of <0.25 for matched covariates (Figure S1). Qualitatively, the distribution of PSs after matching appeared similar (Figure S2).

Intraoperative data

The JS group exhibited a higher utilization of tissue valves, compared with the RAMT group; however, the frequency of sutureless and rapid deployment (SURD) aortic valve usage did not differ between the two groups. Despite the recognized technical challenges of RAMT, no significant difference between the two groups was observed in terms of CPB time (P=0.42) or CIT (P=0.79) (Table 2). Two patients from the JS group and four from the RAMT group required intraoperative sternotomy conversion because of bleeding (JS vs. RAMT, 2.2% vs. 1.3%, respectively; P=0.62). Significantly more bioprostheses were implanted in the JS group than in the RAMT group (JS vs. RAMT, 65.2% vs. 49.2%, respectively; P=0.007).

After PSM, no significant difference between the two groups was observed in terms of CPB time (P=0.77) or CIT (P=0.64) (Table 2). The median cross-clamping time was relatively shorter in the RAMT group (63.0 min; range, 52.8–81.3 min) than in the JS group (68.0 min; range, 56.0–82.5 min). In both groups, no significant difference was observed between the utilization of tissue valves and SURD aortic valves. Intraoperative data for the entire cohort and matched cohort are detailed in Table 2.

Early outcomes

The postoperative outcomes of the unmatched cohort are summarized in Table 3. Thirty-day mortality was similar between the RAMT and JS groups (1.1% vs. 0.3%, respectively; P=0.40). The rates of postoperative acute kidney injury and new occurrence of an atrioventricular block were also similar between the two groups. The frequency of on-table extubation was significantly higher in the RAMT group than in the JS group (69.8% vs. 30.4%, respectively; P<0.001). The rate of blood transfusion was lower (27.9% vs. 57.8%; P<0.001) and median LOS [5.0 days (IQR, 4.0–7.0 days) vs. 6.0 days (IQR, 5.0–7.0 days); P<0.001] was shorter in the RAMT group than in the JS group.

In the matched cohort, early mortality was similar between the groups. Even after PSM, the frequency of on-table extubation remained significantly higher (67.8% vs. 31.1%, respectively; P<0.001) and the rate of blood transfusion was lower (28.9% vs. 57.8%, respectively; P<0.001) in the RAMT group than in the JS group (Table 3). When IPTW was performed using the same variables used for matching, the RAMT group showed similar results (Table S1).

Late outcomes

The median and maximum follow-ups were 38.3 months (IQR, 34.7–41.9 months) and 140.8 months, respectively, in the overall cohort. In the overall cohort, the rate of late survival was significantly higher in the RAMT group than in the JS group at the 5-year follow-up (RAMT, 92.9%; JS, 86.0%; P=0.02; Figure 5).

Figure 5 Kaplan-Meier curve for all patients after aortic valve replacement. The rates of mid-term mortality are higher in the J-sternotomy group versus the right anterior mini-thoracotomy group. JS, J-sternotomy; RAMT, right anterior mini-thoracotomy; SD, standard deviation.

The mid-term survival of all patients was similar to those in the matched cohort (Figure 6). For 1:1 matched patient, Cox proportional hazard regression was applied to investigate the prognostic factors influencing mid-term survival (Table 4). The RAMT group was significantly associated with higher late survival [hazard ratio (HR) =0.21, 95% confidence interval (CI): 0.06–0.79; P=0.02]. Age, ejection fraction, and creatinine clearance were independent prognostic factors for late survival.

Figure 6 Kaplan-Meier curve for matched patients after aortic valve replacement. The rates of mid-term mortality are higher in the J-sternotomy group versus the right anterior mini-thoracotomy group. JS, J-sternotomy; RAMT, right anterior mini-thoracotomy; SD, standard deviation.

Even after performing IPTW to analyze mid-term survival, the RAMT group had higher survival rates, compared with the JS group, which was similar to results obtained from the previous PSM analysis (Figure S3).

Discussion

In this PSM cohort retrospective study, we compared the AVR outcomes between the RAMT and JS approaches in patients who were followed up for 5 years. The key findings for the matched cohort were as follows: (I) perioperative morbidity and mortality were similar between the two groups; (II) the rate of postoperative blood transfusions and LOS were significantly lower in the RAMT group vs. the JS group; and (III) overall survival was higher in the RAMT group vs. the JS group at the 5-year postoperative follow-up.

Previous studies have no reported differences in mid- and long-term mortality between patients undergoing AVR via JS or RAMT (3). Bakhtiary et al. conducted a PSM analysis including 202 patient pairs undergoing AVR via RAMT or JS. They reported no difference in 30-day mortality between the groups (JS, 1.5% vs. RAMT, 1.5%; P>0.99) and similar 1-year mortality (JS, 2.0% vs. RAMT, 3.5%; P=0.54) (3). In a meta-analysis comparing the JS and RAMT approaches across nine studies that included 2,926 patients in total, no difference in in-hospital mortality was observed; however, the RAMT approach was associated with a shorter hospital stay and shorter duration of use of mechanical ventilation (17). Short-term recovery with RAMT appeared superior to that observed with JS; however, this difference was not significant. However, these studies did not report long-term survival rates.

Consistent with meta-analysis findings, we observed that the RAMT approach was associated with fewer blood product transfusions and a shorter LOS than the JS approach was. Many patients who underwent AVR using the RAMT approach required on-table extubation immediately postoperatively. This outcome was not unexpected. Overall, these findings suggest that the less invasive RAMT approach reduced upfront morbidity and mortality, leading to improved late survival.

Patients who undergo on-table extubation experience prompt initiation of oral intake without the need for additional mechanical ventilation in the intensive care unit, leading to rapid patient recovery (18). Reducing the duration of additional mechanical ventilation correlates with decreased postoperative pneumonia rates and a decrease in the use of anesthetic agents typically employed during sedation for mechanical ventilation (19). Furthermore, a decrease in the use of narcotic analgesics has been linked to a lower occurrence of delirium (19). These processes are referred to as the Enhanced Recovery After Surgery (ERAS) protocols. The ERAS protocols, involving multiple healthcare professionals, are comprehensive strategies used in perioperative care (20,21). In recent years, considerable endeavors have been directed toward the integration of ERAS protocols into cardiac surgery (22). Specifically, surgical trauma reduction through MICS facilitates a more effective application of ERAS protocols in cardiac surgery (23,24).

A restrictive red-cell transfusion strategy has been reported to be non-inferior to a liberal strategy in patients undergoing cardiac surgery at moderate-to-high risk of death (18). However, patients undergoing cardiac surgery often have marginal cardiovascular reserve and may experience intraoperative hemodilution, leading to a decrease in hemoglobin concentration. This situation can potentially increase the risk of anemia-induced tissue hypoxia (19). Therefore, both indiscriminate restriction and excessive use of transfusions can be detrimental to patients. Excessive blood transfusion can increase complications, such as pulmonary complications or acute kidney injury (25). In this study, despite applying the same transfusion criteria, fewer transfusions were performed in the RAMT group vs. the JS group. In contrast, the amount of blood drained via chest tubes over 24 h was similar between the groups. This suggests that there was likely less intraoperative blood loss with the RAMT approach vs. the JS approach.

MICS using the JS or RAMT approaches has been considered potentially harmful to patients owing to prolonged extracorporeal circulation time and cardiac arrest time compared with conventional MS (4,11). However, our study findings indicted similar CPB times and CITs between the two groups in both the matched and unmatched cohorts. Furthermore, several studies have reported that, with increasing surgical experience, the duration of surgery using the RAMT approach progressively decreases (3,6,26,27).

Cardiac surgery using CPB through femoral arterial cannulation increases the risk of postoperative stroke (28,29). However, the rate of stroke was not significantly higher in the RAMT group, which included most cases of femoral cannulation, when compared with the JS group. The rate of postoperative stroke was significantly lower in our study than in previous studies (28,29). This finding may be because, in most patients, a decision to cannulate or to use a surgical approach for cannulation of the femoral artery is determined preoperatively, according to the vascular condition of the aorta on CT. Furthermore, no difference in CPB times and CITs was observed between the RAMT and JS groups, despite these times being generally known to be longer with the RAMT approach.

Patient selection remains pivotal in the choice of surgical approach, and specific anatomic and patient characteristics may determine the preferred approach. In patients with atherosclerotic burden, JS was performed owing to the difficulty of femoral cannulation. These patients may be inherently vulnerable in relation to mid-term survival, compared with those who are relatively healthy. Such unavoidable selection bias, which is difficult to overcome even with the use of statistical methods, may have contributed to the differences in survival curves between the two groups.

Many patients prefer to undergo TAVI to treat aortic stenosis without the need for surgery (30). The number of patients eligible for the TAVI procedure, which was previously limited to older adult patients with many comorbidities, is gradually expanding (31,32). This trend reflects the preference among patients for less invasive treatment and strategies associated with faster recovery. RAMT could be the first-choice approach for AVR in experienced centers, as it is minimally invasive and associated with good mid-term results without the disadvantages of increased CPB time or CIT.

This study has some limitations. The study’s retrospective observational design raises concerns regarding potential confounding, namely, treatment allocation bias. Despite the use of PSM to adjust for known confounders, the presence of unmeasured confounders, particularly factors, such as smoking or peripheral vessel disease, that may bias the outcome cannot be excluded. Furthermore, it may be difficult to generalize the positive effect of the RAMT approach in all centers. The majority of isolate AVRs have been undertaken using the RAMT approach at PNUYH; however, it may be difficult to accommodate the findings of this study in centers that do not routinely practice MICS or have low rates of undertaking MICS. Moreover, the relatively small sample size reduced the statistical power of comparisons between the groups showing significant differences. These limitations highlight the need for a comprehensive prospective study to compare RAMT with JS.

Conclusions

This study examined differences in outcomes between the RAMT and JS approaches in patients who underwent isolated AVR. Although no difference in early mortality or major morbidity was observed between the two groups, the blood transfusion rate was lower and the on-table extubation rate was higher in the RAMT group vs. the JS group. Furthermore, the RAMT approach was associated with better mid-term survival, compared with the JS approach. These findings support the RAMT approach as the first-line strategy for performing isolated AVR in carefully selected patients.

Acknowledgments

Funding: This study was supported by a 2024 research grant from Pusan National University Yangsan Hospital.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-928/rc

Data Sharing Statement: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-928/dss

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-928/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-928/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). The study was approved by the Pusan National University Yangsan Hospital Institutional Review Board (approved March 29, 2024, No. 55-2024-033) 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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