Atlas of Mitral Valve Repair, 1st Edition

4

Assessing the Functional Substrate of Mitral Regurgitation with Echocardiography

Echocardiography, in particular transesophageal echocardiography (TEE) has emerged as the preferred method for the assessment and quantification of the nature and degree of mitral regurgitation. Complete assessment of the mitral valve is possible with details of structure and function easily observed. The results of this assessment will guide the surgeon and the referring physician. Points of assessment include the degree of regurgitation; the valvular abnormality, indicating the likelihood for repair; the degree of ventricular dysfunction; pulmonary pressure; and the status of other valves.

A good transthoracic echocardiogram (TTE) is often adequate for assessment; however, any remaining questions should be clarified by transesophageal echocardiogram (TEE). In one series of 118 patients comparing TTE to TEE, 25% had mitral regurgitation detected by transesophageal echocardiography that was not noted by transthoracic echocardiography; of these 14% had significant (2 to 3+) mitral regurgitation (1). TEE also can demonstrate specific abnormalities, such as a ruptured chordae, which may not be detected with TTE.

TEE is uniquely useful for intraoperative assessment of the mitral valve. It should be used for a final assessment before surgery begins and after the completion of the repair. Multiple views of the valve from different angles provide systematic assessment of the mitral valve. These views are detailed in Figure 4.1.

Functional analysis is provided by pulsed, continuous, and color flow Doppler. Pulsedwave Doppler measures velocity at a specific point but has a limited velocity range; it is useful for measuring pulmonary venous flow. Continuous Doppler is limited by spatial ambiguity but has a greater velocity range; it is useful for measuring high velocity flow through a stenotic valve. Color-flow mapping is used to assess patterns of blood flow (2). In color-flow Doppler, flow towards the transducer is red and flow away from the transducer is blue. Higher velocities are represented by brighter hues.

Doppler color-flow imaging is used to assess the degree of mitral regurgitation. The size of the jet indexed to the size of the atrium provides a consistent accurate assessment, though there are exceptions. Peripheral jets or jets next to the wall will recruit less blood, therefore, they may be judged as smaller unless appropriately corrected. With moderate-to-severe regurgitation flow reversal can be noted in the pulmonary veins (3). Effective regurgitant

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orifice area calculated on the basis of the proximal isovelocity surface area method has been advocated as an accurate, consistent method of assessment (4). Central jets imply annular dilatation with resultant poor leaflet coaptation, eccentric jets imply leaflet pathology with the jet directed away from the affected leaflet.

 

Figure 4.1 Views obtained by transesophageal echocardiography. (From Lambert AS, Miller JP, Merrick SH, et al. Improved evaluation of the location and mechanism of mitral valve regurgitation with a systematic transesophageal echocardiography examination. Anesth Analg. 1999; 88:1205-1212.)

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The severity of regurgitation is judged by the proportion of the maximal area of the jet relative to the left atrium; 1%-15%, (1+); 16%-35%, (2+); 36%-55%, (3+); and greater than 55%, (4+). The severity of regurgitation is also assessed by the direction of flow in the pulmonary veins; blunted or reversed flow implies greater degrees of regurgitation. These terms are relative; though one laboratory may report 1+ as mild, 2+ as moderate, 3+ as moderately severe, and 4+ as severe, semantics vary and should be clarified before making management decisions (5). Assessment can be quite subjective and is operator dependent, many of the settings on the machine (e.g., gain) can make the degree of regurgitation seem greater or less than it really is. Likewise the size of the atrium will have an impact on the relative assessment of regurgitant jets and pulmonary venous flow.

The other factor that impacts greatly on the degree of regurgitation is peripheral vascular resistance; this is specifically reflected by the systolic blood pressure. At lower blood pressures, particularly after the induction of anesthesia, the degree of regurgitation may be underestimated. At higher blood pressures, particularly in patients who presents with poorly controlled hypertension, the degree of regurgitation may be overestimated. Thus knowledge of the blood pressure at the time of assessment is useful. Intraoperatively, the blood pressure needs to be artificially raised to completely assess the competency of the valve. This can be done with an infusion of phenylephrine to raise the systolic BP to 150 mmHg.

As three-dimensional echocardiography improves, the pictures showing the dynamic valvular pathology will help in planning reparative procedures (Figs. 5.2,5.3,5.4,5.5,5.6).

 

Figure 4.2 Preoperative echocardiogram of a myxomatous valve with a flail posterior leaflet and anteriorly directed jet. (Clip 1, Case 1) 

 

Figure 4.3 Preoperative echocardiogram of a rheumatic valve demonstrating mobile leaflets with reduced excursion, tethering and thickening, and a dilated annulus. (Clip 1, Case 3) 

 

Figure 4.4 Preoperative echocardiogram of a myxomatous valve with anterior leaflet prolapse and a posteriorly directed jet. (Clip 1, Case 4) 

 

Figure 4.5 Preoperative echocardiogram of mitral regurgitation secondary to a dilated cardiomyopathy (Clip 1, Case 5) 

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Figure 4.6 Preoperative echocardiogram of mitral regurgitation secondary to chronic ischemia demonstrating a dilated annulus, tethered chords, and poor coaptation (Clip 2, Case 2) 

REFERENCES

  1. Castello R, Fagan L Jr, Lenzen P, Pearson AC, Labovitz AJ. Comparison of transthoracic and transesophageal echocardiography for assessment of left-sided valvular regurgitation. Am J Cardiol.1991; 68:1677-1680.
  2. Kodavatiganti R: Intraoperative assessment of the mitral valve by transesophageal echocardiography: an overview. Ann Cardiac Anaesthesia.2002; 5:127-134.
  3. Enriquez-Sarano M, Dujardin KS, Tribouilloy CM, et al. Determinants of pulmonary venous flow reversal in mitral regurgitation and its usefulness in determining the severity of regurgitation. Am J Cardiol.1999; 83:535-541.
  4. Enriquez-Sarano M, Miller FA Jr, Hayes SN, et al. Effective mitral regurgitant orifice area: clinical use and pitfalls of the proximal isovelocity surface area method. J Am Coll Cardiol.1995; 25:703-709.
  5. Muehrcke DD, Cosgrove DM. Mitral valvuloplasty. In Edmunds, LH Jr., ed. Cardiac Surgery in the Adult.New York: McGraw-Hill, 1997:998.