Aortic Insufficiency: Etiology, Pathophysiology, and Clinical Presentation

Etiology

• AI occurs due to a failure of the aortic valve leaflets from fully closing (coapting) during diastole. The etiology of AI is broad and can be categorized in the following ways (Figure 1).
  • Type 1: aortic root or aortic annular dilation
  • Type 2: excessive aortic cusp motion
  • Type 3: restricted leaflet motion or poor tissue quality leaflets

• The most common cause of chronic AI is congenital valvular disease (specifically bicuspid valve) and aortic dilation.¹
• Causes of acute AI include endocarditis, aortic dissection, and prosthetic valve complications such as leaflet dysfunction, paravalvular leak, and valve dehiscence.²
• Other causes include age-related senile valvular calcification, age-related aortic dilation, systemic hypertension, myxomatous valve degeneration, aortitis, and aortic root dilation from syphilis or rheumatologic disease.²

Epidemiology

• Trace AI as seen on echocardiography with color Doppler is very common and is seen even in healthy patients.³
• AI prior to age 50 is unusual and when present, typically progresses over time.³ It is estimated to occur in approximately 2% of the population older than 70 years, with men affected more commonly than women.³
• Bicuspid aortic valves are estimated to affect 0.5-3% of the general population, with prevalence being three times higher in males than females.⁴ Of these patients, between 13-30% will develop moderate to severe AI in their lifetimes, and up to 40% of these patients will also develop an aortopathy with enlargement of the sinuses of Valsalva or ascending aorta.⁴

Pathophysiology

• AI produces a predictable hemodynamic response. When the aortic valve leaflets fail to coapt during diastole, a fraction of the left ventricle (LV) stroke volume leaks from the aorta back into the LV. This causes an increase in LV end-diastolic volume and LV wall stress. In response, the LV adapts to the increased volume through eccentric hypertrophy and dilation.
• Initially, the LV increases total stroke volume and maintains forward flow. Through eccentric hypertrophy and LV dilation, which maintains LV compliance, LV end-diastolic pressure initially remains normal despite the increase in LV volume. Low aortic diastolic blood pressures and a widened pulse pressure result from the increasing regurgitant volume back into the LV.
• As the disease progresses, there is an eventual increase in LV wall stress and afterload, which result in progressive LV systolic dysfunction in the setting of dilated cardiomyopathy.
• To compensate for a reduction in cardiac output, there is further peripheral vasoconstriction to maintain blood pressure. This adaptation eventually becomes pathologic, further exacerbating the severity of regurgitation in advanced stages of aortic insufficiency.⁵

Clinical Presentation

• Patients with chronic regurgitation may be asymptomatic for decades, even with evidence of ventricular remodeling.
• Those who develop severe disease have typical signs and symptoms of heart failure, including exertional dyspnea, angina, orthopnea, paroxysmal nocturnal dyspnea, and/or pulmonary edema. Of note, angina in these patients can be due to underlying atherosclerotic disease or poor coronary perfusion because of low diastolic aortic pressure.
• On auscultation, the classic decrescendo early diastolic murmur can be heard at the left upper sternal border.
• The pulse pressure is widened with a high systolic and low diastolic pressures.
• Bounding carotid pulses, head bobbing, retinal, and uvular pulsations are some of the peripheral signs of chronic AI.²
• Chest x-ray shows pulmonary congestion and cardiomegaly.
• Echocardiography is the gold standard in the evaluation of aortic regurgitation, providing valuable diagnostic information regarding severity, etiology, and pathologic maladaptations (Figure 3).

• The American Heart Association (AHA) stages AI based on symptoms, valve anatomy, severity of valve dysfunction, and degree of cardiac maladaptation or hemodynamic effects.⁵
  • Stage A: No or trace AI
  • Stage B: Mild to moderate regurgitation with normal systolic function and only mildly dilated LV volume
  • Stage C: Asymptomatic, severe regurgitation: Stage C1 is characterized by normal LV systolic function with mild to moderately increased LV dilation, while stage C2 is characterized by a decreased LV systolic function as well as markedly increased LV systolic volume.
  • Stage D: Symptomatic, severe aortic regurgitation, along with decreased systolic function and severely increased LV volume
• Acute AI is less common than chronic regurgitation and is poorly tolerated because the LV has not had time to adapt to the increase in LV end-diastolic volume. In these settings, the LV typically fails quickly, rapidly resulting in pulmonary edema and hemodynamic instability unless the underlying cause of insufficiency is addressed.

See Also

Aortic Insufficiency: Hemodynamic Management, Medical and Surgical Management