Echocardiographic and hemodynamic characteristics of reconstructed bicuspid aortic valves at rest and exercise

Heart Valve Biomechanics and Underlying Mechanobiology

Heart valves control unidirectional blood flow within the heart during the cardiac cycle. They have a remarkable ability to withstand the demanding mechanical environment of the heart, achieving lifetime durability by processes involving the ongoing remodeling of the extracellular matrix. The focus of this review is on heart valve functional physiology, with insights into the link between disease-induced alterations in valve geometry, tissue stress, and the subsequent cell mechanobiological responses and tissue remodeling. We begin with an overview of the fundamentals of heart valve physiology and the characteristics and functions of valve interstitial cells (VICs). We then provide an overview of current experimental and computational approaches that connect VIC mechanobiological response to organ- and tissue-level deformations and improve our understanding of the underlying functional physiology of heart valves. We conclude with a summary of future trends and offer an outlook for the future of heart valve mechanobiology, specifically, multiscale modeling approaches, and the potential directions and possible challenges of research development. © 2016 American Physiological Society. Compr Physiol 6:1743-1780, 2016.

Midterm follow-up dynamic echocardiography evaluation after aortic valve repair for aortic valve insufficiency

We prospectively evaluated 46 patients who underwent aortic valve repair (AVR) for AV regurgitation. Rest/stress echocardiography follow-up was performed. Follow-up duration was 30.7 months, age 56 ± 14 years, ejection fraction% 57.5 ± 10.5%. Preoperative bicuspid AV was present in 14 (30.4%), leaflets calcifications in 8 (17.4%), thickening in 17 (37.0%) and prolapse in 22 (47.8%). Surgical technique included commissuroplasty (22, 47.8%), leaflet remodelling (17, 37.0%), decalcification (7, 15.2%) and raphe removal (14, 30.4%). At follow-up, rest/stress echocardiography median AV regurgitation (rest 1.0 vs. stress 1.0) and mean indexed AV area (IAVA) (rest 2.6 ± 0.74 cm(2)/m(2) vs. stress 2.8 ± 0.4 cm(2)/m(2)) were unchanged (P = ns). Mean (rest 4.7 ± 3.9 mmHg vs. stress 9.7 ± 5.8 mmHg) and peak (rest 9.5 ± 7.2 mmHg vs. stress 19.0 ± 10.5 mmHg) transvalvular gradients were significantly increased (P < 0.0001). At linear regression, there was an independent inverse correlation between commissuroplasty and AV gradients during stress (B = -9.9, P = 0.01, confidence interval= -17.7 to -2.1). Although follow-up haemodynamics of repaired AVs are satisfactory, there was a fixed IAVA and significant increase in AV gradients. We were not able to identify any pre-existing anatomical condition independently related to this non-physiological behaviour under stress. Moreover, commissuroplasty seems to prevent abnormal increase of the AV gradients.

The bicuspid aortic valve and related disorders

Bicuspid aortic valve (BAV) is the most common congenital cardiac malformation, affecting 1-2% of the population, with strong male predominance. Individuals may have a normally functioning BAV, and may be unaware of its presence and the potential risk of complications. However, they may easily develop aortic valve disorders: either stenotic or regurgitant, or both. Today, BAV is recognized as a syndrome incorporating aortic valve disorders and aortic wall abnormalities, including aortic dilation, dissection or rupture. Congenital or hereditary diseases such as ventricular septal defect, patent ductus arteriosus, coarctation of the aorta, Turner's syndrome, Marfan's syndrome etc., may frequently be associated with BAV. Infective endocarditis and occasionally thrombus formation may develop during the lives of BAV patients. Elevated cholesterol or C-reactive protein may be seen in laboratory findings of these patients. Beta-blockers and statins are the possibilities for medical treatment, and aortic valve repair/replacement and ascending aorta replacement are indicated for patients with a severely diseased aortic valve and aorta. Rigorous follow-up throughout life is mandatory after BAV has been diagnosed. The aim of the present article was to describe the implications of BAV and its associated disorders, and to discuss diagnostic and treatment strategies.

Heart valve function: a biomechanical perspective

Heart valves (HVs) are cardiac structures whose physiological function is to ensure directed blood flow through the heart over the cardiac cycle. While primarily passive structures that are driven by forces exerted by the surrounding blood and heart, this description does not adequately describe their elegant and complex biomechanical function. Moreover, they must replicate their cyclic function over an entire lifetime, with an estimated total functional demand of least 3x10(9) cycles. As in many physiological systems, one can approach HV biomechanics from a multi-length-scale approach, since mechanical stimuli occur and have biological impact at the organ, tissue and cellular scales. The present review focuses on the functional biomechanics of HVs. Specifically, we refer to the unique aspects of valvular function, and how the mechanical and mechanobiological behaviours of the constituent biological materials (e.g. extracellular matrix proteins and cells) achieve this remarkable feat. While we focus on the work from the authors' respective laboratories, the works of most investigators known to the authors have been included whenever appropriate. We conclude with a summary and underscore important future trends.

A classification system for the bicuspid aortic valve from 304 surgical specimens

OBJECTIVE

In general, classification of a disease has proven to be advantageous for disease management. This may also be valid for the bicuspid aortic valve, because the term "bicuspid aortic valve" stands for a common congenital aortic valve malformation with heterogeneous morphologic phenotypes and function resulting in different treatment strategies. We attempted to establish a classification system based on a 5-year data collection of surgical specimens.

METHODS

Between 1999 and 2003 a precise description of valve pathology was obtained from operative reports of 304 patients with a diseased bicuspid aortic valve. Several different characteristics of bicuspid aortic valves were tested to generate a pithy and easily applicable classification system.

RESULTS

Three characteristics for a systematic classification were found appropriate: (1) number of raphes, (2) spatial position of cusps or raphes, and (3) functional status of the valve. The first characteristic was found to be the most significant and therefore termed "type." Three major types were identified: type 0 (no raphe), type 1 (one raphe), and type 2 (two raphes), followed by two supplementary characteristics, spatial position and function. These characteristics served to classify and codify the bicuspid aortic valves into three categories. Most frequently, a bicuspid aortic valve with one raphe was identified (type 1, n = 269). This raphe was positioned between the left (L) and right (R) coronary sinuses in 216 (type 1, L/R) with a hemodynamic predominant stenosis (S) in 119 (type 1, L/R, S). Only 21 patients had a "purely" bicuspid aortic valve with no raphe (type 0).

CONCLUSIONS

A classification system for the bicuspid aortic valve with one major category ("type") and two supplementary categories is presented. This classification, even if used in the major category (type) alone, might be advantageous to better define bicuspid aortic valve disease, facilitate scientific communication, and improve treatment.