Valvular Stenosis

Stenosis of either atrioventricular valves (tricuspid, mitral) or outflow tract valves (pulmonic, aortic) leads to a pressure gradient across the valve during the time blood is flowing through the valve opening. This increased pressure gradient is expressed as an increase in the pressure proximal to the valve and a small fall in pressure distal to the valve. The magnitude of the pressure gradient depends on the severity of the stenosis and the flow rate across the valve.

Mitral valve stenosis results from a narrowing of the mitral valve orifice when the valve is open. The high resistance across the stenotic mitral valve causes blood to back up into the left atrium thereby increasing LA pressure. This results in the left atrial (LA) pressure being much greater than left ventricular (LV) pressure during diastolic filling (shaded gray in figure). The gradient is highest during early diastole when the the flow across the valve is highest. Normally, the pressure gradient across the valve is very small (a few mmHg); however, the pressure gradient can become quite high during severe stenosis (10-30 mmHg). Despite this elevated LA pressure, filling (end-diastolic volume) of the left ventricle may be significantly reduced. (The effects of mitral stenosis on ventricular filling can be appreciated better by examining the changes in the LV pressure-volume loop).  The reduced ventricular filling (decreased preload) decreases ventricular stroke volume by the Frank-Starling mechanism.  If stroke volume falls significantly, the reduced cardiac output may result in a reduction in aortic pressure.  The increase in LA pressure can cause pulmonary congestion and edema because of increased pulmonary capillary hydrostatic pressure.  Mitral valve stenosis is associated with a diastolic murmur because of turbulence that occurs as blood flows across the stenotic valve.

Tricuspid valve stenosis is similar to mitral valve stenosis except that the pressure and volume changes occur on the right side of the heart.

Aortic valve stenosis is characterized by the left ventricular pressure being much greater than aortic pressure during left ventricular ejection (shaded gray in figure). LV pressure is greatly elevated and the aortic pressure is slightly reduced in this example. Normally, the pressure gradient across the aortic valve is very small (a few mmHg); however, the pressure gradient can become quite high during severe stenosis (>100 mmHg). The pressure gradient across the stenotic lesion results from both increased resistance (related to narrowing of the valve opening) and turbulence distal to the valve. The magnitude of the pressure gradient is determined by the severity of the stenosis and the flow rate across the valve. Severe aortic stenosis results in 1) reduced ventricular stroke volume due to increased afterload (which decreases ejection velocity), 2) increased end-systolic volume, and 3) a compensatory increase in end-diastolic volume and pressure.  (These changes in ventricular pressures and volumes are best depicted using pressure-volume loops).   Long-term consequences include left ventricular hypertrophy and heart failure.  Aortic valve stenosis is associated with a mid-systolic systolic murmur because of turbulence that occurs as blood flows across the stenotic valve.

Pulmonic valve stenosis is analogous to aortic valve stenosis except that the changes in pressure are on the right side of the heart.  A pressure gradient occurs across the pulmonic valve during right ventricular ejection.  Compensatory increases in right ventricular end-diastolic pressure as well as right atrial pressure and volume occur.  

RK Revised 04/05/07