C.7. What are the usual TEE findings in a patient with AS or MR? How do you grade the severity of AS by TEE? How do you quantify the severity of MR? What is the impact of AS on the severity of MR?
Answer:
The echocardiographic severity of native valvular AS is usually determined by AV area and transaortic valve pressure gradient (Table 7.1). Severe AS is present when the mean pressure gradient exceeds 40 mm Hg or the valve area is less than 1.0 cm2. Of note, in the setting of low cardiac outputs and low gradients, additional investigation might be necessary. The clinical severity of AS is determined by a combination of echocardiographic and clinical factors. A patient with less than severe AS by echocardiography or catheterization criteria is considered to have severe AS if their daily activities of life are reduced, they experience symptoms, or left ventricular systolic dysfunction is present.
MR is graded by the amount of blood regurgitated into the LA during systole on color Doppler. Common methods for MR quantification include analysis of the area of the regurgitant orifice (effective orifice area), the width of the MR jet (vena contracta), and pulmonary vein flow profiles. It is important to remember that the amount of regurgitant blood flow in the setting of MR is determined by the amount of time spent in systole, the size of the MV defect, and the pressure gradient across the defect. Therefore, MR severity by Doppler color flow is load dependent. Lower systemic pressure or decreased preload (relative hypovolemia) due to the anesthetic state can often mask more severe degrees of MR that are present in the awake state.
Left ventricular pressures increase in the setting of AS. Therefore, the gradient across the MV is increased often leading to more severe MR. Following replacement of the stenotic AV and elimination of the obstruction to systolic flow, left ventricular pressures are markedly reduced. In cases of functional MR without major structural defects in the MV apparatus, MR becomes less severe following replacement of AV.
References
- Baumgartner H, Hung J, Bermejo J, et al. Recommendations on the echocardiographic assessment of aortic valve stenosis: a focused update from the European Association of Cardiovascular Imaging and the American Society of Echocardiography. J Am Soc Echocardiogr. 2017;30:372-392.
- Mahmood F, Matyal R. A quantitative approach to the intraoperative echocardiographic assessment of the mitral valve for repair. Anesth Analg. 2015;121:34-58.
- Zoghbi WA, Adams D, Bonow RO, et al. Recommendations for noninvasive evaluation of native valvular regurgitation: a report from the American Society of Echocardiography developed in collaboration with the Society for Cardiovascular Magnetic Resonance. J Am Soc Echocardiogr. 2017;30:303-371.