Critical Care Medicine-Neurologic Disorders>>>>>Valvular Heart Disease
Question 7#

A 34-year-old female with a history of rheumatic heart disease presents for mitral valve replacement. Preoperative echocardiography demonstrates a transmitral gradient of 14 mm Hg, a mitral valve area of 0.9 cm2 , and an underfilled left ventricle with normal function. Electrocardiogram shows atrial fibrillation.

What is the most likely finding on postoperative transesophageal echocardiography following mitral valve replacement in this patient?

A. Decreased right ventricular function
B. Increased transpulmonary pressure gradient
C. Decreased left ventricular systolic function
D. Worsened tricuspid regurgitation

Correct Answer is C

Comment:

Correct Answer: C

Left ventricular preload (left ventricular end diastolic volume) is decreased in chronic mitral stenosis leading to deconditioning of left ventricle with time. Following mitral valve replacement, the abrupt increase in preload frequently unmasks left ventricular dysfunction requiring temporary postoperative inotropic support. The transpulmonary gradient is the difference between the mean pulmonary artery pressure and the left atrial pressure. Following mitral valve replacement, both values drop (mean pulmonary artery pressure decreases more than the left atrial pressure), thus the transpulmonary gradient decreases. Right ventricular function will typically improve because of the decreased transpulmonary gradient. This may reduce the degree of tricuspid regurgitation (typically due to right ventricular dilation). In the presence of a prosthetic mitral valve, the transmitral gradient is typically less than 6 mm Hg. A higher gradient is concerning patient prosthesis mismatch (the prosthetic valve is too small for the size of the patient). 

Mitral stenosis is typically secondary to rheumatic heart disease. In approximately 40% of patients, mitral stenosis occurs with mitral regurgitation. The second most common valve affected is the aortic valve followed by the tricuspid valve. The time course between rheumatic fever and obstructive mitral valve disease can vary from a couple years to more than 20 years. Rheumatic heart disease causes characteristic changes in the mitral valve including leaflet-edge thickening, chordal shortening and fusion, and commissural fusion. The normal mitral valve area is 4 to 6 cm2 . Mild mitral stenosis occurs as the mitral valve area drops below 2 cm2 , and stenosis is severe with a mitral valve area of less than 1 cm2 . Mitral stenosis leads to increased left atrial pressures, left atrial dilation, and increased pulmonary venous, capillary, and ultimately arterial pressures. Anything that increases blood flow across the stenotic mitral valve (tachycardia due to exercise, anemia, infection) will increase the pressure gradient (modified Bernoulli equation: pressure gradient = 4*velocity 2 ) and worsen pulmonary congestion. Atrial fibrillation reduces cardiac output by eliminating the atrial contribution to diastolic filling leading to increased left atrial pressure and worsened pulmonary congestion. Atrial fibrillation in patients with mitral stenosis begins intermittently and progresses to persistent atrial fibrillation overtime as the left atrium continues to dilate.

References:

  1. Chandrashekhar Y, Westaby S, Narula J. Mitral stenosis. Lancet. 2009;374:1271-1283.
  2. Kaul TK, Bain WH, Jones JV, et al. Mitral valve replacement in the presence of severe pulmonary hypertension. Thorax. 1976;31:332-336.