Age-related Morphological Changes in Cardiac Valves
Jagdish Butany, MBBS, MS, FRCPC, Departments of Pathology, Toronto General Hospital, University Health Network and University of Toronto, Toronto, ON.
Manmeet S. Ahluwalia, MBBS and Vidhya Nair, MBBS, MD, Departments of Pathology, Toronto General Hospital, Toronto, ON.
Christopher Feindel, MD, FRCPC, Cardiovascular Surgery, Toronto General Hospital, University Health Network and University of Toronto, Toronto, ON.
Valvular heart disease is a common cardiac problem. There are many age-associated changes that can occur in otherwise healthy heart valves. These commonly develop in the aortic valve and, to a lesser extent, in the mitral valve. In both cases there is fibrosis and thickening of the tissues with the deposition of calcium salts in the aortic valve cusps and in the annulus of the mitral valve. These changes can contribute to progressive secondary changes in the heart (left ventricle and left atrium), which can be associated with significant morbidity related to complications of valvular disease, such as congestive heart failure, infective endocarditis and sudden death.
Key words: heart valves, age-related changes, calcified aortic valve, mitral annular calcification.
Introduction
The mandate of quality health care includes improved neonatal survival, better maternal and neonatal health and an improved life expectancy, resulting in an increasingly older population with the largest growth in the 65+ age group. Therefore, there is a growing need for an improved awareness of age-related changes in the body in general and in the heart in particular. In addition to risk factors such as diabetes mellitus, abnormal lipid levels and hypertension,1 increasing age is a major independent risk factor for cardiovascular disease. In a previous issue of Geriatrics & Aging, the age-related changes in the myocardium were highlighted.2 In this paper we review age-related cardiac valvular changes and briefly discuss their sequelae and treatment.
Heart Valves: Structure and Function
Heart valves serve the important function of preventing backflow, or regurgitation, in the healthy heart. It is well known that cardiac valves can and do suffer congenital and acquired disease (Table 1) and that neoplasms are exquisitely rare. Congenital valvular disease manifesting in childhood is usually seen in right-sided valves, while acquired disease is more common in left-sided valves (higher pressure). All four valves have a similar basic structure and are divided morphologically into atrioventricular valves (mitral [MV] and tricuspid [TV]) and the semilunar valves (aortic [AV] and pulmonary [PV]). The valves on the left side (MV, AV) are exposed to higher closing pressures than those on the right side (TV, PV), and they consequently show structural differences such as a thicker zona fibrosa, a thicker spongiosa and a more prominent nodulus Arantius.
The valve function of maintaining unidirectional blood flow requires the integrated movement of all anatomic components of the valve, collectively referred to as the valve apparatus. The atrioventricular valve apparatus is comprised of the annulus, leaflets, chordae tendineae, papillary muscles and the myocardium of the chamber on either side. The semilunar valve apparatus is comprised of the annulus (aortic valve only), cusps, commissures, vessels and the ventricular myocardium. Endothelial cells cover the valve surfaces. While appearing structurally similar throughout the cardiovascular system, endothelial cells likely have different functional effects at different sites, including the heart valves.3
Histologically, all valves have four basic layers: the soft compressible spongiosa; the firm collagen-rich fibrosa; the ventricularis (continuation of the ventricular endocardium) and; the atrialis (continuation of the left and right atrial endocardium, the aorta or the pulmonary arterial intima). The tip of the AV is composed only of fibrosa and spongiosa. The fibrosa, the central layer of the valve composed of collagen and elastic fibres,