Introduction
Prolonged aortic cross-clamp time (XCL) and cardiopulmonary bypass time (CPB), potentially leading to increased morbidity and mortality, are a possible drawback of minimally invasive aortic valve replacement. To date, studies has mainly focused on facilitating the procedure with sutureless prosthetic valves. Although anatomical selection criteria are recommended for some minimally invasive surgical approaches, research on the influence of anatomic circumstances in the thorax on operative times is rare and limited. It is also unknown whether the learning curve of the procedure is prolonged in the presence of unfavourable anatomical circumstances.
The aim of the first part of this study was to identify the anatomical variables that influence XCL and CPB in minimally invasive aortic valve replacement and to determine the extent of the effect. The second part of the study aims to determine the potential prolongation of the procedure learning curve in the presence of unfavourable anatomical circumstances.
Methods
68 patients undergoing minimally invasive aortic valve replacement with sutureless aortic valves and the surgical approaches mini-sternotomy (MS) or mini-thoracotomy (RT) were included in the study. All procedures were standardised and performed by the same surgeon with extensive experience in minimally invasive aortic valve surgery. In the first part, we performed a retrospective study. Patients were allocated into two groups according to the type of minimally invasive surgical approach. Measurements of anatomical variables, namely; aortic dextroposition, aortic depth, aortic inclination, aortic length, skin-to-ascending aorta distance and the thoracic-wall thickness, were performed on preoperative computed tomographic (CT) scans of the thorax. Measurements of the aortic annulus diameter were taken during the surgery. XCL and CPB measurements were obtained from the documentation. In the second part, we performed a retrospective study. Patients with unfavourable anatomical circumstances for minimally invasive aortic valve replacement via the RT approach were identified, chronologically classified and allocated into three groups. XCL and CPB were compared between the groups.
Results
XCL was shorter in those having MS approach than in those having RT approach (41.1 min vs. 52.3 min; p < 0.001). CPB was not significantly different between groups (p = 0.09). In bivariate analysis of the entire cohort, XCL and CBP were prolonged in smaller aortic annulus (r = -0.245, p = 0.046 and r = -0.318, p = 0.009, respectively), XCL was shorter at a shorter skin-to-ascending aorta distance (r = 0.296, p = 0.041), and XCL and CBP were longer at the medial and most lateral positions of the ascending aorta in the coronal plane (r = 0.248, p = 0.042 and r = 0.284, p = 0.019, respectively). A multivariable (including aortic depth, aortic dextroposition, aortic angulation and aortic annulus diameter variables) linear-regression analysis of the RT group (p = 0.018) found aortic dextroposition was a statistically significant predictor of XCL and CPB (p = 0.005 and p = 0.003, respectively). A linear-regression models predicted 90 s longer XCL and 231 s longer CPB for every 1 mm smaller aortic annulus diameter, 12 s longer XCL for every 1 mm longer skin-to-ascending aorta distance. The optimal aortic position for the RT approach was a 9 mm dextroposition to the sternal edge. A 1 mm deviation from that position prolonged XCL for 24 s and CPB for 60 s. In the second part of the study, there was no statistically significant learning curve effect on XCL (p = 0.16) while CBP was statistically significantly different between groups (p = 0.017).
Conclusion
In minimally invasive aortic valve replacement, the aortic annulus diameter and the position of the ascending aorta in the coronary plane influence XCL and CBP. The skin-to-ascending aorta distance influences XCL. A prolonged XCL is unavoidable despite the surgeon's increasing experience with unfavourable anatomical circumstances. Considering these results, preoperative planning and selection of minimally invasive approaches according to the anatomical characteristics of the patients is reasonable.
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