Mitral insufficiency: medical management

The treatment of choice for acute mitral insufficiency is MVR if insufficiency is severe. However, most of these patients need some sort of medical stabilization/treatment. In the acute period, IV vasodilators are the first line of treatment. Specifically, sodium nitroprusside is the most commonly used medication. Nitroprusside will help to vasodilate which will reduce afterload and thus increasing cardiac output, improving mitral incompetence, and diminishing pulmonary congestion. The use of nitroprusside may, in turn, lead to hypotension that is best treated with a positive inotrope (i.e. dobutamine). Long term treatment for mitral insufficiency depends on the degree to which the left ventricle is impaired. If the LV function is preserved, then vasodilator therapy is not indicated. If the pt has impaired LV function and is not a surgical candidate, then vasodilator therapy is indicated (i.e. hydralazine).

In mitral insufficiency (or regurgitation), blood flows from the LV to the LA during systole Physiology differs between acute and chronic MR:

• Chronic MR = Chronic Volume Overload
• Atrial and ventricular chamber enlargement
• Ventricular wall hypertrophy
• Increased ventricular compliance
• Decreased EDP and decreased O₂ consumption
• Decreased contractility
• Normal or near normal EF despite significant ventricular dysfunction
• Acute MR = Acute Volume Overload
• No compensatory ventricular enlargement
• Increased filling pressures
• Increased pulmonary pressures
• Decreased cardiac output
• Pulmonary edema

In both cases, regurgitant volume is related to:

• Size of the regurgitant orifice (depends on ventricular size)
• Time available for regurgitant flow
• Pressure gradient across the valve

Measures that reduce regurgitant flow:

• Preload reduction: reduces ventricular size and size of regurgitant orifice
• Increase heart rate: also reduces ventricular size and size of regurgitant orifice, decreases time for regurgitant flow
• Arteriolar Dilators: reduce ventricular pressure gradient

Therefore, medical management of chronic MR includes:

• Preload: Normal to low normal
• Afterload: Reduce
• Rate: Normal to high normal
• Rhythm: Maintain sinus rhythm
• Contractility: Normal

Management of acute MR includes:

• Afterload reduction with arteriolar dilators
• Use of an inotrope with a vasodilator if the patient is hypotensive
• Use of an intra-aortic balloon pump to stabilize the patient prior to surgery