Aortic regurgitation

Causes and pathogenesis

Aortic regurgitation (AR) develops either due to intrinsic valve leaflet pathology or as a result of aortic wall disease.

• Leaflet pathology: observed in congenital bicuspid aortic valve, infective endocarditis, and rheumatic heart disease. In rheumatic fever, the free edges of the leaflets slowly destroy, and the commissures fuse. A bicuspid valve suffers due to inadequate structural support.
• Aortic wall pathology: characteristic of Marfan syndrome, Ehlers-Danlos syndrome, Takayasu arteritis, rheumatoid arthritis, and aortic dissection. Ascending aortic aneurysms stretch the fibrous annulus, preventing the leaflets from closing properly.

Depending on the rate of onset, the condition is classified into acute (trauma, bacterial endocarditis, dissection) and chronic.

Hemodynamic consequences

Pathological changes directly depend on the rate of lesion progression:

1. Chronic form: the left ventricle (LV) slowly adapts to the continuous volume overload. Its compliance increases, and the chamber dilates significantly. End-diastolic pressure remains normal for a long time, and the patient experiences no symptoms until clinically significant heart failure develops.
2. Acute form: the LV does not have time to dilate (not dilated). A sudden influx of an additional volume of blood causes a rapid spike in intraventricular pressure, frequently resulting in pulmonary edema.

Evaluation using echocardiography and radiography

Chest radiography in chronic disease demonstrates cardiomegaly of the left ventricle, the degree of which correlates with disease severity. In acute regurgitation, heart size remains within normal limits.

Echocardiography is the primary routine diagnostic method. The optimal timing for valve replacement is determined precisely by the progression of regurgitation and the decline in LV function. Key Doppler parameters:

• Color Doppler: it is important to remember that the maximum length of the jet does not reflect the severity of the lesion. The jet cross-sectional area and the width of the narrowest portion (vena contracta) must be evaluated. A vena contracta $\ge$ 6 mm indicates severe regurgitation, whereas < 3 mm indicates mild regurgitation.
• Continuous-wave Doppler: evaluates the rate of pressure decline during diastole. A steep pressure drop (pressure half-time < 200–250 ms) indicates severe regurgitation, while values > 400 ms indicate mild regurgitation.

Role of cardiac MRI and CT

Magnetic resonance imaging (MRI) is considered the most accurate method for quantitative assessment.

• Cine-MRI reveals a signal void (signal void) from the jet: narrow at the base indicates mild grade, wide indicates severe grade.
• Velocity-encoded cine-MRI (Velocity-encoded cine-MRI) in an oblique axial plane above the valve accurately calculates the regurgitant volume and regurgitant fraction (RF). An RF value > 33% is an indication for surgery.

Computed tomography (CT) is not used for primary diagnosis, but is indispensable for preoperative planning (assessment of the coronary bed, valve morphology, and aortic root). CT can measure the regurgitant orifice area using direct planimetry on end-diastolic scans (appearing as a central zone of incomplete closure). However, mild regurgitation can easily be missed on CT if the valve is bicuspid or heavily calcified.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Aortic root pathology in Marfan and Ehlers-Danlos syndromes
• Assessment of leaflet calcification and Agatston score prior to surgery
• Differential diagnosis with aortic stenosis
• Breath-hold-free blood flow velocity MR mapping technique
• Bicuspid aortic valve: associated defects and prognosis

Other topics in the «Chest Radiology» section

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