How is the LV pressure-volume loop affected in aortic stenosis?
- As the valve area narrows it poses significant obstruction to blood flow from the left ventricle:
- Normal valve area is 2.6– 3.5 cm2 in adults
- Haemodynamically significant obstruction occurs as the valve area approaches 1.0 cm2
- A greater systolic pressure must be generated by the left ventricle to maintain blood flow across the valve:
- The left ventricle compensates with hypertrophy of the muscle
- Maintains the pressure gradient without decreased cardiac output
- As hypertrophy increases it becomes detrimental:
- Increasingly stiff with reduced lusitropy leading to diastolic dysfunction:
- Ventricular filling becomes dependent upon atrial contraction (contributes 40% rather than usual 20%) –
- Results in atrial hypertrophy to maintain filling –
- Maintenance of sinus rhythm becomes important to maintain cardiac output
- Worsening oxygen demand / delivery mismatch:
- Increased muscle mass requires greater oxygen supply
- Exacerbated by relatively low aortic pressures and increased ventricular wall pressures
- Results in subendocardial hypoperfusion and angina