16.13: Rheumatic Heart Disease I: Introduction

Rheumatic heart disease or RHD is a chronic condition that results from rheumatic fever, causing permanent damage to the heart valves.

Etiology and Risk Factors

It primarily arises from rheumatic fever, an inflammatory disease that can develop after untreated or inadequately treated group A streptococcal (GAS) pharyngitis. Streptococcus spreads through direct contact with oral or respiratory secretions. While the bacteria are the causative agents, factors like malnutrition, overcrowding, poor hygiene, and lower socioeconomic status can predispose individuals to rheumatic fever.

Acute rheumatic fever typically develops about 2 to 4 weeks after a group A streptococcal pharyngitis infection episode and can affect the joints, skin, brain, and heart. In the acute stage, rheumatic fever causes pancarditis, involving myocardium, endocardium, and epicardium inflammation. Chronic rheumatic heart disease causes the heart valves to become fibrotic, leading to stenosis and insufficiency. After repeated episodes of rheumatic fever, the heart valves can undergo progressive fibrosis, resulting in rheumatic valvular heart disease.

Pathophysiology

The pathophysiology of RHD involves an autoimmune response in which the body's immune system mistakenly targets cardiac tissues, particularly the heart valves, due to molecular mimicry between streptococcal antigens and cardiac myosin. The immune response induces widespread inflammation, leading to valvulitis and pancarditis.

Rheumatic infective endocarditis (IE) can cause valvulitis, characterized by swelling and erosion of the heart valves, predominantly the mitral and aortic valves. The inflammatory response results in fibrin and blood cells deposition in the eroded areas, forming vegetations. These lesions cause thickening of the valve leaflets, fusion of commissures, and chordae tendineae. Additionally, fibrosis of the papillary muscles occurs. As the disease progresses, valve leaflets may become calcified, resulting in stenosis, which narrows the valve opening and restricts blood flow. Conversely, the stiffened and less mobile valve leaflets may fail to close properly, leading to regurgitation, where blood leaks backward.

A hallmark of Acute Rheumatic Fever (ARF) is the formation of Aschoff bodies. These nodules arise from an inflammatory reaction that causes swelling and destruction of collagen fibers. As Aschoff bodies mature, they become fibrotic, forming scar tissue within the myocardium, the heart muscle. This scarring can impair the myocardium's contractile function, contributing to the overall cardiac dysfunction seen in RHD.

Rheumatic pericarditis, another complication of ARF, affects both layers of the pericardium—the protective sac surrounding the heart. Inflammation causes the pericardial layers to thicken and become covered with fibrinous exudate. It can lead to the development of a serosanguineous pericardial effusion, a fluid accumulation containing both blood and serum. During the healing process, fibrosis and adhesions can form, potentially leading to partial or complete obliteration of the pericardial sac, which restricts heart movement and function.

The damage to the heart begins with the initial attack of rheumatic fever and is exacerbated by recurrent streptococcal infections. Each recurrence triggers further inflammation, leading to progressive structural damage and dysfunction of the heart valves and surrounding cardiac tissues. Over time, this can result in severe cardiac complications, including heart failure, atrial fibrillation, and an increased risk of infective endocarditis.