Does aortic stenosis (AS) cause reduced cardiac output, also known as hypoperfusion?

From the Guidelines

Aortic stenosis (AS) indeed causes reduced cardiac output, also known as hypoperfusion, due to the obstruction of blood flow from the left ventricle into the aorta during systole. This condition forces the left ventricle to generate higher pressures to eject blood through the narrowed valve opening, leading to increased afterload and limiting stroke volume 1. As the disease progresses, the heart cannot maintain adequate cardiac output, particularly during exercise when the heart cannot increase output to meet the body's demands.

Key Points

• Aortic stenosis affects approximately 12% of individuals aged >75 years, with no pharmacological treatments available to delay its progression 1.
• The severity of AS is classified into four stages of myocardial damage, with incremental impact on mortality, and heart failure in severe AS is multifactorial, reflecting myocardial damage secondary to valvulo–arterial impedance and myocardial ischemia 1.
• The narrowed valve creates increased afterload, which limits stroke volume, and the hypertrophied ventricle becomes less compliant, impairing diastolic filling, resulting in decreased cardiac output 1.
• Symptoms of reduced cardiac output include fatigue, exercise intolerance, syncope, and in severe cases, heart failure, with the reduction in cardiac output proportional to the severity of the stenosis 1.

Clinical Implications

• The definition of severe aortic stenosis (AS) is consistent among guidelines, with agreement that besides the classic high-gradient AS, AS may also be severe when peak velocity or mean gradient are low [<4 m/s or <40 mm Hg] 1.
• The use of dobutamine stress echocardiography and/or noncontrast computed tomography (CT) aortic valve calcium scoring is recommended in patients with low-gradient AS presenting with reduced left ventricular ejection fraction (LVEF) ≤50% 1.
• The severity of paradoxical low-flow low-gradient AS should be assessed using an integrative approach including echocardiographic, CT aortic valve calcium score, and clinical variables 1.

Management

• Valve replacement is recommended for those patients with severe AS who have symptoms, impaired LV systolic function, or in whom other cardiac surgery is being performed 1.
• Treatment of hypertension is a valid target, with pragmatic goals of a systolic blood pressure of 130–139 mmHg and a diastolic blood pressure of 70–90 mmHg 1.
• The American and European guidelines recommend intervention in the presence of symptoms documented by history or exercise stress test, very severe AS, reduced left ventricular (LV) function, or elevated brain natriuretic peptides 1.

From the Research

Aortic Stenosis and Cardiac Output

• Aortic stenosis (AS) can lead to reduced cardiac output, also known as hypoperfusion, due to the progressive narrowing and stiffening of the aortic valve 2.
• Severe AS causes pressure overload of the left ventricle, resulting in progressive cardiac dysfunction that can extend beyond the left ventricle 3.
• The staging system for AS quantifies the extent of structural and functional cardiac changes, including left ventricle changes, left atrial or mitral changes, pulmonary artery or tricuspid changes, and right ventricle changes 3.

Relationship Between Aortic Stenosis and Cardiac Output

• A significant number of patients with AS have right ventricular dysfunction, likely due to ventricular interdependence, which can lead to reduced cardiac output 4.
• The relationship between right ventricular dysfunction and increased mortality in both symptomatic and asymptomatic patients with severe AS has been demonstrated 4.
• A reduced preoperative cardiac output is significantly related to reduced overall survival rate in patients with AS undergoing aortic valve replacement 5.

Clinical Implications

• Understanding the complex normal anatomy and physiology of the aortic valve can help nurses appreciate the consequences of AS and manage patients with this condition effectively 2.
• A standardized echocardiographic examination of patients with severe AS should provide a detailed analysis of right ventricular function to identify patients at risk of reduced cardiac output 4.
• The risk of aortic valve replacement for AS is acceptable and related to coronary artery disease and mean aortic gradient, and long-term survival is related to coronary disease and cardiac output 5.