15.8
二尖瓣狭窄 I: 介绍
二尖瓣狭窄（MVS）是一种心脏病，指二尖瓣狭窄，阻碍血液从左心房流向左心室。该病的病因和病理生理复杂多样，会导致一系列心血管并发症。
二尖瓣狭窄的原因
- 风湿性心脏病：这是二尖瓣狭窄的主要原因，尤其是在发展中国家。此病源于风湿热，这是一种由于链球菌感染（如咽炎或猩红热），未获充分治疗或未经治疗而引起的…
二尖瓣狭窄是一种医学病症，其中二尖瓣变得狭窄，限制了血液从左心房流向左心室，最常见原因为风湿性心内膜炎。
较少见的原因包括先天性畸形、自身免疫性疾病、放射治疗以及严重的二尖瓣环钙化。
其病理生理学机制涉及风湿性心内膜炎，可引起炎症和瘢痕形成。
这会导致二尖瓣瓣叶和腱索增厚、钙化并融合，使瓣膜开口狭窄，阻碍舒张期血液从左心房流向左心室。
因此，左心房内的残余血量增加，长期可导致左心房肥厚和扩张。
左心房持续高压可导致肺部充血和水肿，并使心房易于发生心房颤动等心律失常，从而降低心脏功能效率。
还可能导致肺动脉高压和右心室负荷增加，进而引发右心室肥厚和心力衰竭。
View the full transcript and gain access to JoVE Core videos
Q1: What causes mitral stenosis?
Mitral stenosis is most commonly caused by rheumatic endocarditis, which results from inadequately treated streptococcal infections. Less common causes include congenital malformations, autoimmune disorders like rheumatoid arthritis, radiation therapy to the chest, and severe mitral annular calcification in older adults.
Q2: How does rheumatic endocarditis damage the mitral valve?
Rheumatic endocarditis causes inflammation and scarring of the mitral valve leaflets and chordae tendineae. This leads to thickening, calcification, and fusion of valve structures, creating a characteristic fish-mouth appearance. These deformities narrow the valve orifice and obstruct blood flow from the left atrium to the left ventricle during diastole.
Q3: What happens to the left atrium when the mitral valve narrows?
When the mitral valve narrows, blood backs up in the left atrium, increasing residual blood volume. Over time, this elevated pressure causes left atrial hypertrophy and dilation. The enlarged atrium becomes prone to arrhythmias like atrial fibrillation, which decreases cardiac efficiency and further compromises blood circulation.
Q4: How does mitral stenosis affect the pulmonary circulation?
Mitral stenosis causes blood to back up into the pulmonary veins, leading to pulmonary congestion and edema. The increased pressure in the pulmonary circulation can cause pulmonary hypertension and place excessive strain on the right ventricle, potentially leading to right ventricular hypertrophy and eventual heart failure.
Q5: Why does increased heart rate worsen mitral stenosis symptoms?
An increased heart rate shortens the diastolic phase, reducing the time available for blood to flow from the left atrium into the left ventricle. This causes more blood to back up into the pulmonary veins, further reducing cardiac output and increasing pulmonary pressures, exacerbating the condition's hemodynamic effects.
Q6: What is the relationship between mitral stenosis and cardiac output?
Mitral stenosis reduces cardiac output through two mechanisms: decreased ventricular filling due to the narrowed valve orifice, and reduced forward blood flow into the left ventricle. This decreased cardiac output compromises the heart's ability to deliver oxygen-rich blood to body tissues, affecting overall cardiovascular function.
Q7: How do structural changes in mitral stenosis create a pressure gradient?
The thickened, fused, and calcified mitral valve leaflets create an obstruction that prevents normal blood flow during diastole. This obstruction generates a significant pressure differential between the left atrium and left ventricle, forcing the atrium to work harder to push blood through the narrowed valve opening.