The posterior left atrial echocardiogram of mitral regurgitation

The Mitral Regurgitation Index: an echocardiographic guide to severity

OBJECTIVES

The purpose of this study was to develop a semiquantitative index of mitral regurgitation severity suitable for use in daily clinical practice and research.

BACKGROUND

There is no simple method for quantification of mitral regurgitation (MR). The MR Index is a semiquantitative guide to MR severity. The MR Index is a composite of six echocardiographic variables: color Doppler regurgitant jet penetration and proximal isovelocity surface area, continuous wave Doppler characteristics of the regurgitant jet and tricuspid regurgitant jet-derived pulmonary artery pressure, pulse wave Doppler pulmonary venous flow pattern and two-dimensional echocardiographic estimation of left atrial size.

METHODS

Consecutive patients (n = 103) with varying grades of MR, seen in the Adult Echocardiography Laboratory at UCSF, were analyzed retrospectively. All patients were evaluated for the six variables, each variable being scored on a four point scale from 0 to 3. The reference standards for MR were qualitative echocardiographic evaluation by an expert and quantitation of regurgitant fraction using two-dimensional and Doppler echocardiography. A subgroup of patients with low ejection fraction (EF < 50%) were also analyzed.

RESULTS

The MR Index increased in proportion to MR severity with a significant difference among the three grades in both normal and low EF groups (F = 130 and F = 42, respectively, p < 0.0001). The MR Index correlated with regurgitant fraction (r = 0.76, p < 0.0001). An MR Index > or =2.2 identified 26/29 patients with severe MR (sensitivity = 90%, specificity = 88%, PPV = 79%). No patient with severe MR had an MR Index <1.8 and no patient with mild MR had an MR Index >1.7.

CONCLUSIONS

The MR Index is a simple semiquantitative estimate of MR severity, which seems to be useful in evaluating MR in patients with a low EF.

Echocardiography in mitral valve disease: a review

Echocardiographic evaluation of the mitral valve has attracted much attention and generated much discussion since its beginnings, some thirty years ago. Echocardiography affords the physician a detailed assessment of mitral valve integrity unequalled by any other non-invasive test. Aside from the normal appearance of the valve, a variety of pathological conditions have been studied in detail; mitral stenosis was the first and over the years the state-of-the-art has evolved from simply looking at the EF slope as an indicator of severity to the accurate quantification utilizing planimetry and 'pressure half-time.' Mitral regurgitation, although not as well quantified as mitral stenosis, can be detected and its etiology usually determined. Mitral valve prolapse may easily be overdiagnosed by echocardiography, however together with auscultation, ultrasound remains the best way to evaluate this common condition. Echocardiography is also invaluable in the evaluation of endocarditis and prosthetic mitral valves.

Echocardiographic findings after tricuspid valvectomy

Resection of the tricuspid valve without prosthetic replacement has successfully been performed in patients with tricuspid valvular endocarditis. Using M-mode, two-dimensional, and Doppler echocardiograms, we studied four patients who underwent tricuspid valvectomy. All patients had previous history of intravenous drug abuse and staphylococcal endocarditis with tricuspid valvular involvement. In all patients, M-mode and two-dimensional echocardiograms showed that the tricuspid valve was absent. The right ventricle was dilated, and the interventricular septum had paradoxical motion in each patient. In each patient the right atrium was dilated, and with each ventricular systole, it expanded and its short axis increased by 20 to 33 percent. This caused shift of the interatrial septum toward the left atrium, with compression of its cavity. Doppler echocardiographic studies showed retrograde flow during systole in the right atrium, inferior vena cava, and hepatic vein. Echocardiographic findings in patients with tricuspid valvectomy correlate with the pathophysiologic findings of this condition.

Two-dimensional echocardiographic determination of left atrial emptying volume: a noninvasive index in quantifying the degree of nonrheumatic mitral regurgitation

Several noninvasive techniques, including radionuclide angiography and Doppler echocardiography, have attempted to measure the regurgitant volume in patients with mitral regurgitation; however, none of these techniques are entirely satisfactory. Utilizing a computerized light pen method for tracing the left atrial endocardial border during systole and diastole in two orthogonal planes (apical four and two chamber views), biplane volume determinations were calculated in 12 normal subjects and 30 patients with nonrheumatic mitral regurgitation. Left atrial emptying volume determinations were performed by subtracting the left atrial end-diastolic volume from the left atrial end-systolic volume. The degree of mitral regurgitation was visually assessed as normal (0, trivial, Group I, 12 patients), mild (1+, Group II, 4 patients), moderate (2+, Group III, 8 patients), moderately severe (3+, Group IV, 12 patients) and severe (4+, Group V, 6 patients) by contrast left ventricular angiography and also quantitatively by regurgitant fraction at cardiac catheterization. All 18 patients with moderately severe (Group IV) and severe (Group V) mitral regurgitation had a left atrial emptying volume greater than 40 ml compared with none of the normal subjects and patients with mild (Group II) or moderate (Group III) mitral regurgitation. There was good correlation between left atrial emptying volume and mitral regurgitant fraction (r = 0.85, p less than 0.01). Thus, in patients with nonrheumatic mitral regurgitation, left atrial emptying volume is useful in separating mild from severe mitral regurgitation.

Detection and estimation of rheumatic mitral regurgitation in the presence of mitral stenosis by pulsed Doppler echocardiography

The sensitivity and specificity of pulsed Doppler echocardiography (PDE) in diagnosis and estimation of the severity of mitral regurgitation in the presence of rheumatic mitral stenosis was studied in 34 patients (18 women and 16 men) ranging in age from 33 to 70 years (mean 55). Definitive diagnosis of mitral regurgitation was confirmed in all patients by angiography and in 20 patients also by indicator dilution technique. Mitral regurgitation was detected by PDE in all patients with angiographically proven severe mitral regurgitation and in 7 of 8 patients with moderate mitral regurgitation. In patients with trace to mild mitral regurgitation, PDE was positive in only 7 of 13 patients. When subdivided for mild, moderate and severe mitral regurgitation, PDE sensitivity for diagnosis was 54, 88, and 100%, respectively; overall accuracy was 79% and specificity was 100%. Average systolic dispersion on time-interval histogram was 59% for mild, 89% for moderate, and 100% for severe mitral regurgitation. Groups of patients with mild mitral regurgitation could be differentiated from those with moderate (p less than 0.05) and severe (p less than 0.01) mitral regurgitation. A significant overlap of individual values, however, occurred. In 7 of 11 patients with moderate to severe mitral regurgitation, systolic turbulence also was detected in the left atrium. PDE was sensitive and specific in diagnosing moderate to severe mitral regurgitation in the presence of mitral stenosis. Assessment of precise severity of mitral regurgitation is still a problem in individual patients.

Left atrial volume overload in mitral regurgitation: a two dimensional echocardiographic study

Left atrial volume in patients with mitral valve disease was studied with two dimensional echocardiography. The left atrial dimension was derived by planimetry of the left atrial area and, assuming spherical geometry, left atrial volume was calculated. Patients with severe mitral regurgitation had marked systolic expansion of the left atrium with large phasic changes in left atrial cubic dimension. Conversely, patients with severe mitral stenosis had small changes in the cubic dimension in comparison with the large left atrial size. Left atrial volumetric changes were similar among patients with atrial fibrillation and normal sinus rhythm. Therefore, left atrial volume overload is an additional two dimensional echocardiographic diagnostic feature of severe mitral regurgitation.

Measurement of normal left atrial function with gated radionuclide angiography

A method is described for measuring relative left atrial volume changes with gated radionuclide angiography, using an approximate computer-generated functional image to locate the atrial region of interest. M mode echocardiographic measurements of left atrial and left ventricular distances from the chest wall allowed calculation of a correction factor for the differential attenuation of atrial and ventricular photons. Background-corrected left atrial time-activity curves obtained from normal subjects exhibited excellent temporal resolution and were used to identify and quantitate the reservoir and contractile phases of left atrial volume change. In 20 normal subjects, the mean (+/- standard deviation) value for left atrial fractional emptying was 0.39 +/- 0.07. Expressed as fractions of the left ventricular stroke volume, mean values of the specific phases of atrial volume change were (1) reservoir volume 0.25 +/- 0.09, (2) contractile volume 0.29 +/- 0.10, and (3) conduit volume 0.46 +/- 0.12.

Motion of the interatrial septum in acute mitral regurgitation. Clinical and experimental echocardiographic studies

The interatrial septal echocardiograms from 15 patients with acute mitral regurgitation due to ruptured chordae tendineae were compared with those from 14 normal subjects. On the cross-sectional echocardiogram, the interatrial septal configuration in patients with chordal rupture showed a characteristic pattern in which the interatrial septum (IAS) was flat or slightly convex toward the left atrium at end-diastole and became markedly convex toward the right atrium at end-systole. On the M-mode echocardiogram, the interatrial septal amplitude was greater in patients with chordal rupture (12.4 +/- 1.9 mm) than in normal subjects (9.4 +/- 0.9 mm). Systolic fluttering of the IAS was found in five of 10 patients with rupture of the chordae attached to the posterior mitral leaflet. This finding was thought to be specific for acute mitral regurgitation due to ruptured chordae to the posterior mitral leaflet. After operation, the amplitude of the IAS became normal or diminished and systolic fluttering of the IAS disappeared. Animal experiments performed to clarify the mechanism of these findings showed that increased systolic motion of the IAS resulted from an increased in the systolic left atrial-to-right atrial pressure gradient due to acute mitral regurgitation. The systolic fluttering of the IAS was thought to represent a jet stream against the IAS due to rupture of the chordae tendineae to the lateral half of the posterior mitral leaflet. We conclude that the interatrial septal echocardiogram reflects the hemodynamic changes due to acute mitral regurgitation and direction of the regurgitant jet against the IAS. This finding may prove to be important in diagnosing acute mitral regurgitation secondary to ruptured chordae tendineae.