We have consistently observed that the ascending aorta in patients with bicuspid aortic valve (BAV) seems to be of inferior quality compared to those with tricuspid aortic valve (TAV). Microscopically, BAV patients exhibit more advanced degenerative changes (disruption of elastic laminae, enhanced metalloproteinase activity, cystic medial degeneration), yet it remains unclear whether this is due to a genetic predisposition or hemodynamic stress. The lack of a well-defined genetic profile for aortopathy likely suggests a complex polygenic background, beyond the simple autosomal dominant/recessive or X-linked inheritance, with contributions from environmental factors and hemodynamic stress further complicating its clinical presentation.

Building on this premise, the survival of a patient post-repair of an aortic dissection raises the question of whether the distal aorta will exhibit behavior distinct from that of the proximal, now replaced by a prosthetic graft. This study, from a Michigan-based group, addresses this question by analyzing data from the STS registry for 655 TAV and 60 BAV patients who underwent type A dissection repair at their institution between 1996 and 2021.

Preoperative differences between groups were minimal, with BAV patients being younger (54 vs. 61 years; p < .001) and a higher rate of hypertension in the TAV group (67% vs. 78%; p = .05). BAV patients underwent aortic root replacement more frequently (70% vs. 26%; p < .001) and had more aortic valve replacements, often associated with Bentall-De Bono procedures, while valve-sparing root replacements were more common in the TAV group (20% vs. 65%; p < .001). Distal extension typically involved hemiarch replacement (67% vs. 60%, p = .26), with minimal full or partial arch replacements without differences between groups. Only 6.7% and 4.7% of BAV and TAV patients, respectively, had isolated ascending aorta replacement. Surgical times were comparable to typical practice (circulatory arrest 29-33 minutes, cross-clamp 141-184 minutes, and cardiopulmonary bypass 214-233 minutes). Cerebral protection varied, with deep hypothermia to 17-18°C as standard; isolated antegrade perfusion was used in only 40-46% of cases, while retrograde, combined, or no perfusion accounted for the remainder (4-6%). The group achieved satisfactory outcomes, with an operative mortality of 6.7-8.2% and in-hospital mortality of 5-7.9%. Stroke rates were 6.7-6.9%, with other complications aligning with expectations for a pathology of this severity.

During follow-up, the primary objective of this study, initial mean diameters of the residual aortic arch showed no differences between groups (34-35 mm; p = .12), although differences were noted in the thoracic descending aorta (BAV 32.2 mm vs. TAV 37 mm; p = .003) and abdominal aorta (BAV 27.9 mm vs. TAV 31 mm; p = .01). Arch growth rates over time were not significantly different within the BAV group (mean 0.23 mm/year; p = .13) but were within the TAV group (mean 0.39 mm/year; p < .001). When comparing BAV to TAV, no statistically significant difference was observed. However, BAV patients maintained a mean offset of -1.08 mm, consistently presenting with smaller residual arch diameters (p = .21). For the thoracic descending aorta, growth rates were 0.61 mm/year for BAV and 0.79 mm/year for TAV, both showing significant intragroup differences. Intergroup comparison was not statistically significant, though BAV patients maintained a -4.07 mm mean diameter difference relative to TAV patients (p < .004). In the abdominal aorta, intragroup differences remained significant, with mean growth rates of 0.51 mm/year for BAV and 0.68 mm/year for TAV. Intergroup mean growth rate differences were statistically significant (p = .03), with the BAV group showing a -2.94 mm smaller diameter than the TAV group (p = .005).

Only 12% of patients required interventions over the follow-up period due to progression of residual aortopathy. Among BAV patients, 8.3% required intervention on the descending aorta, and 5% on the thoracoabdominal aorta. In TAV patients, only 0.8% needed intervention on the aortic arch, 9.7% on the descending aorta (5.2% with TEVAR and 4.3% with surgery), and 1.8% required thoracoabdominal surgery. At the 10-year mark, no differences in reintervention rates were noted between BAV and TAV groups (BAV 9.7% vs. TAV 16%; p = .77). Cox regression analysis did not identify independent risk predictors for reoperation during follow-up, aside from female gender, excluding a statistically relevant role for BAV or TAV presence.

The authors conclude that BAV patients, in the absence of known collagenopathies, may be managed similarly to TAV patients regarding the evolution of the residual aorta following type A dissection repair.

COMMENTARY:

This study answers our original question: in terms of degeneration, the residual aorta after type A dissection repair does not have a worse prognosis in BAV patients compared to TAV. In fact, BAV patients show a more favorable evolution with lower growth rates at all levels and smaller mean diameters at the time of ascending aorta and/or aortic root repair. Another key contribution is data on mean growth rates, providing insights into residual aortic degeneration and highlighting the low rates of reintervention necessary for this patient cohort, which constitutes a significant portion of outpatient activity in our specialty.

Additionally, this work offers insights into the importance of acquired and hemodynamic factors in the varied presentations of aortic pathology. While every pathological manifestation has a complex genetic backdrop influencing susceptibility, it is external factors that shape the presentation and explain the wide clinical spectrum. Thus, excluding genetic collagenopathies, hemodynamic factors primarily drive ascending aorta dilation in BAV (which does not occur in the arch or descending aorta) and likely contribute to descending aorta pathology in TAV patients with a higher age and hypertension rates.

Despite its originality, this study should not be interpreted as a typical comparative study due to significant group size disparities and the absence of matching. Preprocedural characteristics were relatively similar, making this more of a descriptive study of two independent groups, with intragroup comparisons more informative than intergroup ones. In fact, these comparisons suggest that the TAV group, given the larger sample size and greater significant differences, is more heterogeneous. Follow-up was exemplary in survivors (100%), reflecting data quality from both the institution and the STS database. Lastly, like all studies examining disease progression by intervention rates, this study has an inherent bias as it omits patients who declined intervention or were deemed too high-risk, thus systematically underestimating progression rates.

Ultimately, this study debunks the myth of poor aortic prognosis associated with BAV, at least for the arch and ascending aorta, even in the challenging context of post-aortic dissection. Such studies allow us to shift focus and achieve a 21st-century understanding, far removed from the initial impressions. This approach supports continuous learning, placing science at the service of curiosity, originality, rigor, and clinical care.

REFERENCE:

Titsworth M, Graham NJ, Orelaru F, Ahmad RA, Wu X, Kim KM, Fukuhara S, Patel H, Deeb GM, Yang B. Distal aortic progression following acute type A aortic dissection repair among patients with bicuspid and tricuspid aortic valves. J Thorac Cardiovasc Surg. 2024 Aug;168(2):453-462. doi: 10.1016/j.jtcvs.2022.12.009.