The frozen elephant trunk: seeking a more definitive treatment for acute type A aortic dissection.

OBJECTIVES: Conventional treatment for type A aortic dissection includes replacement of the ascending aorta with an open distal anastomosis in the hemiarch position. The frozen elephant trunk (FET) is a hybrid technique that extends the repair to the descending thoracic aorta. The goal is to improve resolution of malperfusion syndrome and to induce positive aortic remodelling and reduce the need for reintervention on the downstream aorta. We aim to summarize the data on the short and long-term outcomes of this technique. METHODS: A thorough search of the literature was conducted isolating all articles dealing with aortic remodelling after the use of FET in case of type A acute aortic dissection. Keywords 'aortic dissection', 'frozen elephant trunk', 'aortic remodelling' and 'false lumen thrombosis' were used. Data for type B and chronic aortic dissections were excluded. RESULTS: FET use favourably influences aortic remodelling. The main advantages lie in the exclusion of distal entry tears in either the aortic arch or descending aorta thus restoring antegrade blood flow in the true lumen and inducing false lumen thrombosis. False lumen thrombosis is not only induced at the level of the stent deployment but also lower in the distal descending aorta. Moreover, it offers an adequate landing zone in the mid-descending aorta for second-stage endovascular or open surgical aortic repair, if needed. CONCLUSIONS: FET can be advantageous in the treatment of acute type A aortic dissection dealing with extended aortic pathology.

Trends in sex-specific differences following aortic arch repair: results from the Canadian Thoracic Aortic Collaborative.

Background: Previous data have shown that sex-related differences exist in aortic arch surgery, with female patients experiencing worse outcomes. Over time, as surgical techniques and strategies have improved, these improvements have benefitted female patients. Using a multicenter national aortic registry from the Canadian Thoracic Aortic Collaborative (CTAC), we aimed to determine the relationship between sex and outcomes following aortic arch repair and to examine how these have changed over time. Methods: The multicenter prospective CTAC database of all aortic procedures performed under circulatory arrest from participating centers across Canada (n=9) was used. Patients were included who underwent elective or urgent/emergency arch reconstruction under circulatory arrest from 2002 to 2021. The primary composite endpoint was defined as the occurrence of one of the following endpoints: in-hospital mortality, stroke, dialysis-dependent renal failure, deep sternal wound infection, reoperation, or prolonged ventilation of >40 hours. Secondary endpoints included in-hospital mortality, in-hospital stroke, and a modified version of the Society of Thoracic Surgeons-defined composite endpoint for mortality and major morbidity (MMOM). Results: A total of 2,592 patients who underwent aortic arch repair between 2002 and 2021 (31.4% female and 68.6% male patients). Operative mortality decreased through the study period for female patients. No change in operative mortality was observed in male patients or following elective repair. The composite endpoint improved for female patients over time in both elective and urgent surgery, while for male patients, rates improved for elective surgery and remained stable for urgent. Ultimately, female sex was not an independent predictor of adverse outcomes following aortic arch repair. Conclusions: Our results are congruent with existing data and are highly encouraging. It shows that multilevel improvements in our approach to aortic arch surgery have helped to serve female patients who were previously disadvantaged.

Sex differences in long-term outcomes following surgery for acute type A aortic dissection: a systematic review and meta-analysis.

Background: Recent reports on sex differences in long-term outcomes after surgery for acute type A aortic dissection (ATAAD) are conflicting. We aimed to aggregate updated data on long-term survival and reoperation stratified by sex. Methods: A literature search was conducted using Medline, Embase, and Cochrane Central. Studies reporting sex-stratified long-term survival and/or reoperation following surgery for ATAAD between January 1, 2000, to March 15, 2023 were included. Preoperative characteristics, intraoperative variables, and early perioperative outcomes were meta-analyzed using a random effects model and pooled risk ratio (RR) with men as the reference group. Individual patient-level data for long-term outcomes was reconstructed to generate sex-specific pooled Kaplan-Meier curves to assess long-term survival and freedom from reoperation. Results: A total of 15 studies with 7,608 male and 3,989 female patients were included in this analysis. Female patients were older, had higher rates of hypertension, and had less previous cardiac surgery. Intraoperatively, women received less extensive repairs with lower rates of aortic valve replacement and total arch replacement, and higher rates of hemiarch replacement. There were no sex differences for in-hospital/30-day mortality [risk ratio (RR), 1.18; 95% confidence interval (CI): 0.96, 1.45; P=0.12], stroke (RR, 1.07; 95% CI: 0.90, 1.28; P=0.46), and early reoperation (RR, 0.90; 95% CI: 0.75, 1.09; P=0.28). Female patients had lower long-term survival overall (P<0.001) and amongst survivors at 1-year (P=0.014). Overall survival at 5-year was 82.4% in men and 78.1% in women, and at 10-year was 68.1% for men and 63.4% in women. Male patients had higher rates of long-term reoperation (P<0.001). Freedom for reoperation at 5-year was 88.4% in men vs. 93.1% in women. Conclusions: Though perioperative early outcomes have equalized between the sexes following surgery for ATAAD, differences remain in long-term survival and reoperation.

Pathology and pathophysiology of the aortic root.

Pathologies of the aortic root amenable to repair with valve preservation include aneurysm formation, development of aortic insufficiency (AI) and aortic dissection. In the normal aortic root, the walls are constructed of 50-70 layers of concentric lamellar units. These units consist of sheets of elastin sandwiching smooth muscle cells interspersed with collagen and glycosaminoglycans. Medial degeneration results in disruption of the extracellular matrix (ECM), loss of smooth muscle cells and pooling of proteoglycans/glycosaminoglycans. These structural changes are associated with aneurysm formation. Aortic root aneurysms are commonly linked to hereditary thoracic aortic diseases including Marfan syndrome and Loeys-Dietz syndrome. One important pathway for hereditary thoracic aortic diseases is the transforming growth factor-ß (TGF-ß) cell-signalling pathway. Pathogenic gene mutations affecting various levels of this pathway have been implicated in aortic root aneurysm formation. Secondary effects of aneurysm formation include AI. Severe chronic AI leads to a pressure and volume load on the heart. Once symptoms develop or significant left ventricular remodelling and dysfunction occurs, the patient's prognosis is poor without surgery. Another consequence of aneurysm formation and medial degeneration is the risk of aortic dissection. Aortic root surgery is performed in 34-41% of surgeries for type A aortic dissection. Predicting those who will experience aortic dissections remains a challenge. Finite element analysis, study of fluid-structure interactions and aortic wall biomechanics are important areas of ongoing research.

Ascending aortic aneurysm haemodynamics are associated with aortic wall biomechanical properties.

OBJECTIVES: The effect of aortic haemodynamics on arterial wall properties in ascending thoracic aortic aneurysms (ATAAs) is not well understood. We aim to delineate the relationship between shear forces along the aortic wall and loco-regional biomechanical properties associated with the risk of aortic dissection. METHODS: Five patients with ATAA underwent preoperative magnetic resonance angiogram and four-dimensional magnetic resonance imaging. From these scans, haemodynamic models were constructed to estimate maximum wall shear stress (WSS), maximum time-averaged WSS, average oscillating shear index and average relative residence time. Fourteen resected aortic samples from these patients underwent bi-axial tensile testing to determine energy loss (ΔUL) and elastic modulus (E10) in the longitudinal (ΔULlong, E10long) and circumferential (ΔULcirc, E10circ) directions and the anisotropic index (AI) for each parameter. Nine resected aortic samples underwent peel testing to determine the delamination strength (Sd). Haemodynamic indices were then correlated to the biomechanical properties. RESULTS: A positive correlation was found between maximum WSS and ΔULlong rs=0.75, P = 0.002 and AIΔUL (rs=0.68, P=0.01). Increasing maximum time-averaged WSS was found to be associated with increasing ΔULlong (rs=0.73, P = 0.003) and AIΔUL (rs=0.62, P=0.02). Average oscillating shear index positively correlated with Sd (rs=0.73,P=0.04). No significant relationship was found between any haemodynamic index and E10, or between relative residence time and any biomechanical property. CONCLUSIONS: Shear forces at the wall of ATAAs are associated with local degradation of arterial wall viscoelastic hysteresis (ΔUL) and delamination strength, a surrogate for aortic dissection. Haemodynamic indices may provide insights into aortic wall integrity, ultimately leading to novel metrics for assessing risks associated with ATAAs.