What is the cause of aortic regurgitation (AR) in Ankylosing Spondylitis (AS)?

Pathophysiology of Aortic Regurgitation in Ankylosing Spondylitis

Aortic regurgitation in ankylosing spondylitis occurs due to chronic inflammatory aortitis affecting the aortic root, leading to fibrosis, thickening of the aortic valve cusps, and formation of characteristic subaortic fibrous ridges that prevent proper valve coaptation. 1

Primary Inflammatory Mechanism

The underlying pathology is an inflammatory process (aortitis) that primarily targets the aortic root and ascending aorta, eventually progressing to fibrosis. 1 This inflammatory cascade specifically affects:

• The aortic root tissue, where chronic inflammation leads to structural changes that compromise valve function 2
• The aortic valve cusps themselves, which become thickened and fibrotic, losing their normal pliability and ability to close completely 3
• The subvalvular region, where characteristic fibrous ridges or "subaortic bumps" develop below the valve leaflets, mechanically interfering with valve closure 1, 3

Structural Consequences

The inflammatory-fibrotic process creates specific anatomical abnormalities:

• Aortic root dilatation can occur, though this typically develops only after regurgitation is already present, rather than being the primary cause 3
• Discrete areas of increased echogenicity (fibrosis) appear below the left or noncoronary cusps on echocardiography, representing the pathognomonic subaortic bump 3
• Valve cusp thickening and fibrosis prevent normal leaflet coaptation during diastole 3
• Extension of fibrosis into the left atrium can occur in advanced cases, potentially affecting the mitral valve and cardiac conduction system 1

Clinical Progression Pattern

The development of aortic regurgitation in AS follows a predictable pattern:

• Early subclinical changes are detectable on two-dimensional echocardiography before clinical regurgitation develops, showing increased bright echoes suggestive of inflammation or fibrosis 3
• Age and disease severity correlate with progression: older patients and those with more severe AS are more likely to develop these aortic abnormalities 3
• The risk for aortic valve disease increases significantly with age and duration of AS, with surgical intervention eventually required in many cases 2
• Unlike other causes of AR, aortic root dilatation in AS usually does not occur without pre-existing aortic regurgitation, suggesting the valve pathology precedes the root changes 3

Associated Cardiac Complications

The inflammatory process extends beyond just the valve:

• Conduction system involvement is common, with first, second, and third-degree atrioventricular blocks occurring due to extension of fibrosis into the conduction pathways 1
• Mitral valve involvement can occur when the inflammatory-fibrotic process extends into the left atrium, though this is less common than aortic involvement 1, 4
• Periaortitis (inflammation of tissues surrounding the aorta) has been described, representing a more extensive inflammatory process 1

Key Clinical Pitfall

The critical distinction is that AS-related AR is primarily a valve and subvalvular pathology driven by inflammation and fibrosis, not simply aortic root dilatation as seen in conditions like Marfan syndrome. 3 This has important implications for screening, as echocardiographic detection of subaortic bumps and cusp thickening may identify patients at risk before significant regurgitation develops. 3