Clinical implications of the biomechanics of bicuspid aortic valve and bicuspid aortopathy

Calcification of the aortic valve is the third leading cause of heart disease in adults. The incidence increases with age, and it is often associated with a bicuspid aortic valve present in 1-2% of the population. Despite the frequency, neither the mechanisms of valve calcification nor the developmental origin of a two, rather than three, leaflet aortic valve is known. Here, we show that mutations in the signalling and transcriptional regulator NOTCH1 cause a spectrum of developmental aortic valve anomalies and severe valve calcification in non-syndromic autosomal-dominant human pedigrees. Consistent with the valve calcification phenotype, Notch1 transcripts were most abundant in the developing aortic valve of mice, and Notch1 repressed the activity of Runx2, a central transcriptional regulator of osteoblast cell fate. The hairy-related family of transcriptional repressors (Hrt), which are activated by Notch1 signalling, physically interacted with Runx2 and repressed Runx2 transcriptional activity independent of histone deacetylase activity. These results suggest that NOTCH1 mutations cause an early developmental defect in the aortic valve and a later de-repression of calcium deposition that causes progressive aortic valve disease.

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. 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. 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). 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.

Bicuspid aortic valve (BAV), the most common congenital heart defect, has been thought to cause frequent and severe aortic complications; however, long-term, population-based data are lacking. To determine the incidence of aortic complications in patients with BAV in a community cohort and in the general population. In this retrospective cohort study, we conducted comprehensive assessment of aortic complications of patients with BAV living in a population-based setting in Olmsted County, Minnesota. We analyzed long-term follow-up of a cohort of all Olmsted County residents diagnosed with definite BAV by echocardiography from 1980 to 1999 and searched for aortic complications of patients whose bicuspid valves had gone undiagnosed. The last year of follow-up was 2008-2009. Thoracic aortic dissection, ascending aortic aneurysm, and aortic surgery. The cohort included 416 consecutive patients with definite BAV diagnosed by echocardiography, mean (SD) follow-up of 16 (7) years (6530 patient-years). Aortic dissection occurred in 2 of 416 patients; incidence of 3.1 (95% CI, 0.5-9.5) cases per 10,000 patient-years, age-adjusted relative-risk 8.4 (95% CI, 2.1-33.5; P = .003) compared with the county's general population. Aortic dissection incidences for patients 50 years or older at baseline and bearers of aortic aneurysms at baseline were 17.4 (95% CI, 2.9-53.6) and 44.9 (95% CI, 7.5-138.5) cases per 10,000 patient-years, respectively. Comprehensive search for aortic dissections in undiagnosed bicuspid valves revealed 2 additional patients, allowing estimation of aortic dissection incidence in bicuspid valve patients irrespective of diagnosis status (1.5; 95% CI, 0.4-3.8 cases per 10,000 patient-years), which was similar to the diagnosed cohort. Of 384 patients without baseline aneurysms, 49 developed aneurysms at follow-up, incidence of 84.9 (95% CI, 63.3-110.9) cases per 10,000 patient-years and an age-adjusted relative risk 86.2 (95% CI, 65.1-114; P <.001 compared with the general population). The 25-year rate of aortic surgery was 25% (95% CI, 17.2%-32.8%). In the population of patients with BAV, the incidence of aortic dissection over a mean of 16 years of follow-up was low but significantly higher than in the general population.