The mitral valve orifice method for noninvasive two-dimensional echo Doppler determinations of cardiac output

We developed and validated a mitral valve orifice method for Doppler cardiac output determination. In 15 open-chest dogs, cardiac output was controlled and measured by a roller pump interposed between the right atrium and pulmonary artery as a right-heart bypass. Left heart flows were measured in the open-chest dog model by Doppler measurements at the mitral valve orifice and compared not only to volume flow measured by the roller pump, but to electromagnetic flow meters as well. The maximum mitral valve orifice area was measured off short-axis two-dimensional echocardiographic views by planimetry. The maximal orifice was then adjusted for its diastolic variation in size by calculating a ratio of mean-to-maximal mitral valve separation on a derived M-mode echocardiogram. Flow was sampled parallel to mitral valve inflow in a four-chamber plane. The multiplication of mean flow throughout the cardiac cycle by the mean mitral valve area after correction for diastolic size variation yielded a cardiac output determination that could be compared to the roller pump measurement. Fifty-two cardiac output determinations over roller pump values of 1-5 l/min yielded a high correlation between roller pump flows and Doppler (r = 0.97 +/- 0.23 l/min). Our study shows that the mitral valve orifice provides an accurate site for Doppler cardiac output measurements.     

Calculating cardiac output from transmitral volume flow using Doppler and M-mode echocardiography

To simplify transmitral volume flow determination by Doppler echocardiography, a formula for calculating mean mitral valve orifice area using M-mode echocardiography without any 2-dimensional measurements was developed and evaluated in this study. The maximal mitral orifice area was assumed to be circular and its diameter was calculated from the maximal M-mode mitral leaflet separation. The maximal area was multiplied by the mean to maximal anterior mitral leaflet excursion ratio to correct for phasic changes in flow orifice area during ventricular filling. This measurement had a high correlation (r = 0.97, standard error of the estimate + 0.26 cm2) with mean mitral valve orifice area calculated from frame-by-frame analysis of short-axis 2-dimensional echoes in a select group of 10 normal volunteers and 10 patients with cardiomyopathy who had very high quality images of the mitral valve leaflet tips. Cardiac output calculated using the new method for orifice area estimation combined with apex view mitral valve Doppler velocities was then validated in 48 consecutive patients undergoing thermodilution cardiac output determinations with a close correlation between Doppler and thermodilution cardiac output (2.3 to 6.1 liter/min, r = 0.93, standard error of the estimate = 362 ml). The correlation improved when 12 patients with mild mitral insufficiency were excluded (r = 0.95). The M-mode echocardiogram-derived mitral valve orifice method combined with Doppler mitral valve velocities is accurate, easy to perform, has a high success rate and should increase the applicability of Doppler echocardiography for estimation of cardiac output.     

Comparison of Doppler echocardiographic methods of determining cardiac minute volume

In 40 patients without valvular disease, cardiac output was determined by pulsed Doppler echocardiography and thermodilution simultaneously. The sample volume was located in the center of the mitral valve ring, at the tips of the mitral leaflets and in the left ventricular outflow tract, directly proximal to the aortic valve leaflets. Circular cross-sectional areas of the mitral valve ring, aortic ring and bulbus of the aorta were calculated from the M-mode and two dimensional echocardiographic diameters. The mitral orifice was assumed to be an ellipse with varying short axes, determined as the mean diastolic leaflet separation in the M-mode and a constant long axis, derived from the maximal mitral orifice area or mitral ring diameter. Cardiac output was calculated by multiplying time-velocity integrals with different areas and heart rate. Cardiac output, measured by the thermodilution technique, ranged from 4.0 l/min to 10.2 l/min. Cardiac output determined by the different Doppler methods correlated significantly with the thermodilution measurements. Cardiac output measurements in the left ventricular outflow tract provided the best correlation coefficient (0.93) and a standard error of the estimate of 0.589 l/min, when the circular flow area was derived from the M-mode echo of the aortic ring.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mitral valve aneurysm: M-mode and two-dimensional echocardiographic features

The following report presents M-mode and two-dimensional echocardiographic findings in a case of mitral valve aneurysm. M-mode echocardiography showed abnormal intravalvular echoes during diastole and a linear echo in the left atrium, with a motion pattern similar to that of the anterior mitral valve leaflet. By allowing visualization of the aneurysmal sac, two-dimensional echocardiography proved to be a more specific diagnostic method.     

Flail aortic valve leaflets: M-mode and two-dimensional echocardiographic manifestations

Four patients with documented flail aortic valve leaflets were studied using M-mode and two-dimensional echocardiography (2-D echo). Two had aortic valve endocarditis, one had endocarditis involving a congenital heart defect, and one had a myxomatous aortic valve. Mitral valve flutter and early mitral valve closure led to the diagnosis of severe aortic insufficiency in three patients. Diastolic aortic valve flutter, considered to be specific for a flail aortic leaflet, was present in three patients. In the fourth patient left ventricular outflow tract (LVOT) echoes were present, but did not distinguish between a flail aortic leaflet and an aortic vegetation. Two-D echo confirmed LVOT echoes in all patients. Discrimination between a flail leaflet and a vegetation(s) without leaflet disruption was accomplished by noting the hinge point of the LVOT diastolic echoes, which was the aortic wall in patients with a flail leaflet.The combination of these M-mode and 2-D echocardiographic findings permitted the diagnosis of a flail aortic leaflet to be made accurately and noninvasively. In two patients surgery was performed without prior cardiac catheterization.     

Echocardlographic evaluation of patients with mitral stenosis

Since the introduction of ultrasound technics to study the heart, echocardiographic evaluation of the mitral valve has become the most sensitive and specific noninvasive method for diagnosing mitral stenosis. Identification of the anterior mitral leaflet and the reduction of its velocity of motion was the first clinical application of M-mode echocardiography. Although simultaneous visualization of both mitral leaflets aids in the diagnosis of mitral stenosis, quantitation was not achieved until real-time imaging systems were developed to produce cross-sectional images of the mitral orifice. Currently, M-mode echocardiography remains the technic of choice for routinely diagnosing mitral stenosis. It is also useful in confirming mitral stenosis when associated abnormalities, such as aortic regurgitation, are present. Mitral orifice area is best determined with cross-sectional (two-dimensional) imaging systems. This method correlates well with hemodynamic parameters. Both methods offer the clinician serial evaluation before and after operative intervention.     

Echocardiographic analysis of intracardiac anatomy in endocardial cushion defect.

A standard echocardiographic technique was proposed for an analysis of the intracardiac anatomy of endocardial cushion defect (ECD). It consisted of two beam directions, mitral and tricuspid, and two M-mode scans, between the mitral and tricuspid valves and between the mitral and aortic valves. Using this technique, echocardiographic studies were performed on 13 patients with ECD, including 10 patients with the incomplete form and three patients with the free-floating form. In patients with the incomplete form, an M-mode scan between the mitral and tricuspid valves showed the specific features of the interaction between the mitral valve, the interventricular septum, and the tricuspid valve, termed the "mitral-interventricular septal-tricuspid (MVT) connection." The systolic multiple echoes and the diastolic echoes of the so-called posterior leaflet of the mitral valve were constant findings in the mitral direction. The tricuspid valve, although less continuous, was recorded simultaneously with the mitral valve in the same direction. Ateriorly displacement of the anterior mitral leaflet was shown on an M-mode scan between the mitral and aortic valves, giving an echocardiographic representation of the angiocardiographic "goose-neck" sign. Evidence showing the presence of right ventricular volume overload was also found. In patients with the free-floating form, an anterior common A-V valve with a large excursion was recorded on an M-mode scan between the mitral and tricuspid valves. The valve was located posterior to the interventricular septum in the mitral direction and anterior to the septum in the tricuspid direction. There was no finding to show the interaction between the valve and the septum. The posterior common A-V valve was registered only in the mitral direction. Our technique made it possible to diagnose ECD, using a noninvasive echocardiographic method, and discriminate the free-floating form from other forms of ECD.     

Mitral valve closure index. Echocardiographic index of severity of mitral stenosis.

A new echocardiographic index of mitral valve diastolic closure, based on the rate of diastolic apposition of the anterior and posterior mitral leaflet echoes, was measured in 40 patients with mitral stenosis. This mitral valve closure index correlated highly significantly with the mitral valve orifice area (calculated from the Gorlin formula) (r = 0-87). Correlation between the diastolic closure rate (based) on the EF slope) and the calculated valve area was poor (r = 0-37). It is proposed that the mitral valve closure index excludes movement extraneous to the mitral apparatus and expresses the actual rate of valve closure, thus avoiding some of the factors known to contribute to the poor specificity of the diastolic closure rate. The better correlation of the mitral valve closure index with the calculated valve orifice area makes it possible to assess the severity of mitral stenosis by echocardiogram with greater accuracy and confidence.     

Comparison of M mode echocardiography and pathologic findings in the hypoplastic left heart syndrome

The M mode echocardiograms and pathologic specimens from 18 infants with the hypoplastic left heart syndrome were compared to determine the accuracy with which the echocardiogram reflects the state of the mitral valve, left ventricle and aortic valve, and its limitations in establishing this diagnosis. Mitral valve echoes were recorded in 7 of the 11 cases with an anatomic mitral valve orifice diameter greater than 3 mm. Ventricular septal echoes were found only in the seven cases in which the mitral valve was recorded. Differences between echocardiographic and anatomic left ventricular internal dimensions were not statistically significant in this small group. When aortic valve echoes were recorded, this valve was always patent in the anatomic specimen. The aortic valve was atretic in 9 of the 11 cases in which no aortic valve echoes were present. The echocardiographic and anatomic aortic root dimensions had a statistically significant correlation (p < 0.05), but there was considerable scatter in the data.None of the 18 infants met all of the previously proposed criteria for the echocardiographic diagnosis of hypoplastic left heart syndrome. An echocardiographic left ventricular dimension of 10 mm or greater was present in five cases (28 percent), and an aortic root dimension of 10 mm or greater in six (33 percent). The most reliable echocardiographic finding was excursion of 5 mm or less of the anterior leaflet of the mitral valve or inability to detect the mitral valve. Noninvasive findings are not always sufficient to establish the diagnosis of hypoplastic left heart syndrome, and further studies may be necessary in some patients.     

Assessment of valvular heart disease by Doppler echocardiography

Doppler echocardiography provides direct hemodynamic data that are often complementary to those demonstrated by M-mode and two-dimensional echocardiographic imaging. This relatively new noninvasive technique has a number of important uses in patients with valvular heart disease. In both adults and children, Doppler measures of peak flow velocity through a stenotic valve allow accurate prediction of the pressure gradient across the valve, and the technique has particular promise for screening patients with suspected aortic or pulmonic stenosis. In patients with mitral stenosis but parasternal short-axis images of limited quality, Doppler velocity measures can provide novel data about the pressure gradient and mitral orifice area. Doppler techniques can also provide direct evidence for or against the presence of valvular regurgitation, and several approaches allow clinically useful estimation of the extent of aortic, mitral, or tricuspid regurgitation. In patients with known disease of one cardiac valve, Doppler is accurate for evaluating the integrity of a second valve. Finally, Doppler techniques have great promise for defining the nature, and perhaps the severity, of suspected prosthetic valve malfunction. Hence, we believe that Doppler echocardiography should become a routine part of the noninvasive evaluation of patients with known or suspected valvular heart disease.     

Influence of sampling site and flow area on cardiac output measurements by Doppler echocardiography

In 40 patients cardiac output was simultaneously determined by pulsed Doppler echocardiography and thermodilution (range 4.0 to 10.2 liters/min). The sample volume was located in the center of the mitral anulus, at the tips of the mitral leaflets and in the center of the aortic anulus. Circular cross-sectional areas of the mitral anulus, aortic anulus and aortic bulbus were calculated from M-mode and two-dimensional echocardiographic diameters. The varying short axis of the elliptical mitral opening area was obtained from the diastolic leaflet separation in the M-mode, and the long axis was derived from the maximal mitral orifice area or mitral anulus diameter. Cardiac output was calculated by multiplying time-velocity integrals with the different areas and heart rate. Doppler flow measurements correlated significantly with the thermodilution method (r = 0.79 to 0.93). Flow measurements at the aortic anulus were most accurate (r = 0.93, SEE = 0.589 liter/min) if the annular area was derived from the M-mode tracing. Measurement of the anulus in the apical five chamber view yielded a significant underestimation and the area of the aortic bulbus provided an overestimation of cardiac output. Left ventricular inflow was underestimated at the mitral leaflet tips and overestimated at the mitral anulus. The accuracy of pulsed Doppler cardiac output measurements strongly depends on the assumed flow area and sampling site. Both should be determined at the same level in the inflow or outflow tract of the left ventricle. Measurement of cardiac output in the center of the aortic anulus provided the highest accuracy.     

Analysis of interobserver and intraobserver variation of interpretation of the echocardiographic and Doppler flow determination of cardiac output by the mitral orifice method.

The variability of the interpretation by two individuals of a combined echocardiographic and Doppler method of calculating output was studied in 30 normal adults. In each subject three separate cardiac cycles were recorded to calculate maximal mitral valve orifice, the ratio of mean to maximal mitral valve leaflet separation, and the mean flow velocity through the mitral valve. The recordings were digitised twice by two independent observers. Estimates of cardiac output ranged from 3.2 to 8.11 1/min. Analysis of variance showed that interobserver and intraobserver variability for these measurements was 5.8% and 6.1% respectively. It is concluded that the reproducibility for interpreting this non-invasive method is adequate for clinical use in adults with cardiac outputs within the normal range.     

Doppler echocardiographic measurement of mitral flow volume: validation of a new method in adult patients

Instantaneous intracardiac flow volumes can be calculated as the product of instantaneous flow velocity and instantaneous orifice area. This was accounted for in a new method of measuring stroke volume and cardiac output in the mitral orifice by pulsed Doppler echocardiography. This method was compared with simultaneous thermodilution in 30 adult patients in sinus rhythm without substantial atrioventricular or pulmonary valve abnormalities. The mitral orifice was assimilated to a conduit with 1) an ellipse-shaped inlet and outlet, 2) the same (and constant) long axis for the inlet and outlet ellipses (that is, the mediolateral anulus diameter measured on apical four chamber views), and 3) a varying outlet short axis (that is, the mitral anteroposterior leaflet separation derived from left parasternal M-mode recordings). This method design avoided the need for a short-axis view of the whole circumference of the mitral outlet orifice, which is difficult to obtain in many adult patients. The mitral flow velocity was recorded from the apex under two-dimensional guidance, within the mitral canal, close to the outlet section. Integration of instantaneous mitral leaflet separation multiplied by instantaneous flow velocity was performed using Simpson's rule. In addition to the proposed "instantaneous orifice area" method (method A), a "mean orifice area" method (method B) was also compared with thermodilution. In this simplified method, mitral flow was the product of mean orifice area and the diastolic mitral velocity integral, both derived from the same recordings as for method A.(ABSTRACT TRUNCATED AT 250 WORDS)     

Analysis of interobserver and intraobserver variation of interpretation of the echocardiographic and Doppler flow determination of cardiac output by the mitral orifice method

The variability of the interpretation by two individuals of a combined echocardiographic and Doppler method of calculating output was studied in 30 normal adults. In each subject three separate cardiac cycles were recorded to calculate maximal mitral valve orifice, the ratio of mean to maximal mitral valve leaflet separation, and the mean flow velocity through the mitral valve. The recordings were digitised twice by two independent observers. Estimates of cardiac output ranged from 3.2 to 8.11 1/min. Analysis of variance showed that interobserver and intraobserver variability for these measurements was 5.8% and 6.1% respectively. It is concluded that the reproducibility for interpreting this non-invasive method is adequate for clinical use in adults with cardiac outputs within the normal range.     

Method for computation of cardiac output in mitral stenosis independent of left ventricular dimensions and kinetic state: correlation with cardiac catheterization via the Fick method

An hydraulic orifice formula offering the possibility of quantifying cardiac output in conditions of mitral stenosis is tested using potentially noninvasive portions of catheterization data from patients evaluated for obstructive mitral valve disease. The equation studied is V = (1/21) R A T2, where V is the cardiac output (ml/min), R is the heart frequency, A is the mitral valve area (cm2), and T is the diastolic filling interval (sec/min). The mitral valve area was determined by the Gorlin formula, and R and T were measured from the pressure tracings recorded at cardiac catheterization. The degree of correspondence between the equation tested and the measured cardiac output as determined by the Fick principle technique is characterized by r = 0.87, SE = 450 ml/min, N = 10. The results suggest that the new formulation may offer a noninvasive method for estimating the cardiac output status of patients with mitral valve disease once mitral valve area is measured either at catheterization or by two-dimensional echocardiography.     

Assessment of valvular lesions with M-mode, two-dimensional and Doppler echocardiography

M-mode, two-dimensional and Doppler echocardiography enable evaluation of morphologic changes in valvular structures, detection of secondary changes in cardiac chambers and left ventricular function and quantification of blood flow patterns. In mitral stenosis, with M-mode echocardiography the diagnosis can be established on the basis of defined criteria, two-dimensional echocardiography enables planimetric calculation of the orifice area and Doppler echocardiography allows determination of the transvalvular pressure gradient and estimation of orifice area as well as detection of concomitant lesions. In mitral regurgitation, M-mode and two-dimensional echocardiography are less sensitive in its detection but they may be useful in delineating the etiology and whether the disease is of acute onset or chronic; the severity can only be judged indirectly on the basis of chamber dimensions. Doppler techniques render extremely sensitive and specific detection of mitral regurgitation as well as a means of quantifying severity. In this lesion, echocardiographic parameters have proven useful in the timing of valve replacement through early detection of myocardial dysfunction. In aortic regurgitation, M-mode and two-dimensional echocardiography may be useful in establishing the diagnosis, etiology, duration and, through assessment of dimensions and motion, estimating the severity as well. Doppler echocardiography is extremely sensitive and specific in the detection of aortic regurgitation and, additionally, provides a quantitative means for evaluation of severity. In aortic stenosis, both M-mode and two-dimensional echocardiography are sensitive in detection of changes in valve structure and motion but these methods are not capable of rendering reliable quantification of severity. Doppler techniques readily identify aortic stenosis and render, in addition, a close estimation of the transvalvular pressure gradient.     

Echocardiography in patients with acute cerebral events

The question of the clinical and economic feasibility of echocardiographic screening for cardiac disease in patients with symptoms of acute cerebral events was assessed by recording M-mode and two-dimensional (2D) echocardiograms in 170 patients. Patients with transient ischemic attacks or cerebral infarctions were included. Of the patients with satisfactory echocardiograms, 96 (56%) had normal diagnostic findings; 74 (43%) had cardiac disorders possibly related to the acute cerebral event. There were 4 patients who fulfilled the standard criteria for mitral valve prolapse and 7 patients who were identified as having probable cardiac thrombosis or vegetation, or both. Thus, M-mode and two-dimensional echocardiography was of limited value in patients referred for these studies for screening to exclude mitral valve prolapse and cardiac thrombosis or vegetation. Although a diverse range of cardiac disorders was demonstrated that may be associated with cerebral ischemia, the overall low yield does not support such screening and should be reserved for selected patients.     

Morphometric investigations in mitral stenosis using two dimensional echocardiography.

A method is proposed for comparing the orifice size and the morphology of stenotic mitral valves, removed intact at the time of replacement, with the preoperative two dimensional echocardiographic cross-sections. The excised mitral valve apparatus is suspended on a specially constructed mounting. To avoid shrinkage the orifice is stabilised with an airfilled balloon. A radiography is taken directing the x-ray beam perpendicular to the valve orifice. In 40 of 51 patients this method provided the means of relating the echocardiographic cross-sections to the morphology of the valve. Planimetry of the valve area compared favourably with the postoperatively determined orifice size. Agreement was found in 34 of 40 patients in orifice shape between preoperative echocardiograms and x-rays of th excised valve. The relation between intraoperative estimation of size of the valve, using dilators with known diameters, and the postoperative results was less favourable. Areas of calcification were identified on echocardiography as dense conglomerate echoes. In 30 patients (75%) the localisation of calcium deposits and in 67% the degree of calcification was in agreement with the x-rays of the valve taken after operation. In addition to determination of the area, two dimensional echocardiography allows detailed studies of the stenotic valves, and is of particular importance for planning operative treatment.     

Determination of mitral valve area by cross-sectional echocardiography

Cross-sectional echocardiograms of the mitral valve orifice were recorded in 37 patients with mitral stenosis. Twenty-seven had pure mitral stenosis, and 10 had associated mitral regurgitation. Mitral valve area in patients with pure mitral stenosis measured from cross-sectional echocardiography was highly correlated (r = 0.89) with that calculated with the Gorlin formula using the pressure gradient and Fick cardiac output. With mitral regurgitation, mitral valve area by cross-sectional echocardiography correlated well (r = 0.90) with that calculated from the pressure gradient and cineangiographic stroke output. In two cases, direct pathologic measurements of mitral valve area agreed exactly with the cross-sectional echocardiographic measurement. Correlation between the mitral E-F slope and mitral valve area by cross-sectional echocardiography (r = 0.56) and catheterization (r = 0.49) was less reliable. Cross-sectional echocardiographic measurement of the mitral valve area correlates well with catheterization in patients with pure mitral stenosis and those with associated regurgitation.     

Instrumental methods in the study of vascular disease

M-mode and two-dimensional echocardiographic features are reported in a patient who developed severe stenosis of a porcine xenograph valve implanted in the aortic position. The presence of increased cusp echoes along with reduced cusp opening was the most consistent echocardiographic finding in this patient. The clinical and the echocardiographic findings were subsequently confirmed by cardiac catheterization and surgery.