Abstract
The Ross, or pulmonary autograft, procedure presents a fascinating mechanobiological scenario. Due to the common embryological origin of the aortic and pulmonary root, the conotruncus, several authors have hypothesized that a pulmonary autograft has the innate potential to remodel into an aortic phenotype once exposed to systemic conditions. Most of our understanding of pulmonary autograft mechanobiology stems from the remodeling observed in the arterial wall, rather than the valve, simply because there have been many opportunities to study the walls of dilated autografts explanted at reoperation. While previous histological studies provided important clues on autograft adaptation, a comprehensive understanding of its determinants and underlying mechanisms is needed so that the Ross procedure can become a widely accepted aortic valve substitute in select patients. It is clear that protecting the autograft during the early adaptation phase is crucial to avoid initiating a sequence of pathological remodeling. External support in the freestanding Ross procedure should aim to prevent dilatation while simultaneously promoting remodeling, rather than preventing dilatation at the cost of vascular atrophy. To define the optimal mechanical properties and geometry for external support, the ideal conditions for autograft remodeling and the timeline of mechanical adaptation must be determined. We aimed to rigorously review pulmonary autograft remodeling after the Ross procedure. Starting from the developmental, microstructural and biomechanical differences between the pulmonary artery and aorta, we review autograft mechanobiology in relation to distinct clinical failure mechanisms while aiming to identify unmet clinical needs, gaps in current knowledge and areas for further research. By correlating clinical and experimental observations of autograft remodeling with established principles in cardiovascular mechanobiology, we aim to present an up-to-date overview of all factors involved in extracellular matrix remodeling, their interactions and potential underlying molecular mechanisms.
Highlights
The aortic valve opens and closes continuously, upwards of 100,000 times per day
By correlating clinical and experimental observations of autograft remodeling with established principles in cardiovascular mechanobiology, we aim to present an overview of factors involved in extracellular matrix (ECM) remodeling and their interactions
ECM Damage and Remodeling Insight into the underlying mechanisms can be gained by correlating established principles of arterial mechanobiology with changes observed in the pulmonary autograft
Summary
The aortic valve opens and closes continuously, upwards of 100,000 times per day. Smooth functioning of the valve throughout a lifetime is enabled by its innate remodeling ability [1]. In the Ross procedure, first performed in a patient in 1967, the diseased aortic valve is replaced by the patient’s own pulmonary valve and a pulmonary homograft is implanted in the pulmonary position (Figure 1) [5]. As the so-called pulmonary autograft is a native tissue substitute, it offers an excellent hemodynamic profile and resistance to endocarditis without the need for anticoagulant therapy [6, 7]. This translates into superior exercise capacity and freedom from valve-related complications when compared to mechanical or bioprosthetic valve replacement [8,9,10]. Due to a perceived risk of increased operative mortality and the fear of complex reoperations on two valves, there remains skepticism toward the procedure [14, 15]
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