Heart valve disease module 1: epidemiology

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Table 4. Causes of aortic stenosis
Table 4. Causes of aortic stenosis

Aetiology by valve position

Aortic stenosis and regurgitation

In industrially underdeveloped regions, rheumatic disease remains the most common cause. In the industrially-developed regions and in the elderly throughout the world, aortic valve disease is predominantly a result of calcific disease (see tables 4 and 5), which will be further explored in module 2. Aortic valve sclerosis is defined by valve thickening with a peak transaortic velocity on echocardiography of <2.5 m/s. Around 16% of patients with sclerosis progress to stenosis within seven years.

Figure 7. Numbers of cusps by decade of age in patients having aortic valve surgery for aortic stenosis
Figure 9
Figure 8. Normal vs abnormal (biscupid) aortic valve

The most common congenital anomaly is bicuspid aortic valve and this is found in 0.5–0.8% of large population studies12 although it is reported in up to two thirds all valves excised during valve replacement for aortic stenosis (see figures 7 and 8)13 and up to 2.0% of the population based on autopsy series.

The risk of a bicuspid valve or aortopathy is about 10% in first-degree relatives of probands. The ratio of male to female is approximately 2:1.

The valve is ‘anatomically’ or truly bicuspid in a third of cases or ‘functionally’ bicuspid in two thirds as a result of incomplete separation of two cusps in utero. The most common pattern, in 80% of cases, is failure of right-left separation which is more likely to be associated with aortic dilatation. Failure of separation of right and non-coronary cusps is more likely to be associated with mitral prolapse.

Table 5. Causes of aortic regurgitation
Table 5. Causes of aortic regurgitation

During a 20 year follow-up, 24% of patients with a bicuspid aortic valve developed severe stenosis or regurgitation requiring surgery.14 Events are far more common in those with even mild valve thickening at baseline, with surgical rates of 75% at 12 years in the presence of thickening compared with only 8% without thickening.

The frequency of aortic regurgitation increases with age (figure 9).15 Aortic regurgitation of any degree occurred in 29% and severe regurgitation in 13% in the Helsinki Ageing Study.11 Functional aortic regurgitation results from dilatation of the aortic root usually as a result of arteriosclerosis or medial necrosis. There may often be associated organic regurgitation as a result of a bicuspid aortic valve or arteriosclerosis.

The risk factors for aortic dilatation are:

  • age,
  • weakness of the aortic wall,
  • the arteriosclerotic risk factors: hypertension; dyslipidaemia; smoking; and diabetes.

Weakness of the aortic wall as a result of medial necrosis occurs in Marfan Syndrome (see figure 10) and Ehlers-Danlos Syndrome Type IV.

Bicuspid aortic valve should be regarded as a general thoracic aortopathy and is associated with significant dilatation of the aorta (>40 mm) in about 20% of cases.14 Approximately one half affects the root, and the rest the ascending aorta.

Figure 9. Effect of age on prevalence of aortic regurgitation
Figure 11. Marfan syndrome, as well as affecting connective tissue, typically results in arachnodactyly of the fingers. Wellcome Photo Library
Figure 10. Marfan syndrome, as well as affecting connective tissue, typically results in arachnodactyly of the fingers