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J Am Coll Cardiol, 1998; 32:1819-1824 © 1998 by the American College of Cardiology Foundation |
a Cardiovascular Division, Department of Medicine, Brigham and Womens Hospital, Boston, Massachusetts, USA
Manuscript received April 10, 1998; revised manuscript received July 27, 1998, accepted August 20, 1998.
Address for correspondence: Dr. Sharon C. Reimold, Cardiovascular Division, Brigham and Womens Hospital, 75 Francis St., Boston, Massachusetts 02115
screimold{at}bics.bwh.harvard.edu
| Abstract |
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Background. Mitral regurgitation may be dynamic in patients with heart failure and ultimately correlate with outcome in a group of patients.
Methods. Fourteen patients with severe heart failure felt to require hemodynamic monitoring for the optimization of medical therapy were enrolled. Two-dimensional and Doppler echocardiograms were performed before and following invasively guided therapy. Hemodynamics and standard echocardiographic dimensions were determined as well as regurgitant volume and regurgitant orifice area derived from color M-mode and Doppler measurements.
Results. Invasively guided therapy for heart failure was associated with a reduction in weight, filling pressures of the left and right heart, systemic vascular resistance, and echocardiographic left atrial, left ventricular and mitral annular dimensions. The mitral regurgitant volume decreased from 47 ± 27 ml before therapy to 14 ± 14 ml after therapy; p < 0.001. While therapy for heart failure markedly attenuated the volume of regurgitation, the pattern of regurgitant flow across the mitral valve was not significantly altered. In contrast, there was no difference in the velocity time integral of the continuous-wave Doppler spectra of mitral regurgitation with therapy (128 ± 23 cm to 123 ± 25 cm, p = 0.23). In all patients, the regurgitant orifice area decreased with therapy from 0.55 ± 0.38 cm2 to 0.21 ± 0.20 cm2 (p < 0.001).
Conclusions. Pharmacologic reduction in filling pressure and systemic vascular resistance leads to a reduction in the dynamic mitral regurgitation of heart failure through a reduction in the regurgitant orifice area but not through a change in the gradient across the mitral valve. Reduction of the regurgitant orifice area is likely related to decreased left ventricular volumes and decreased annular distention.
A postulated mechanism for the development of mitral regulation in heart failure is dilatation of the mitral valve annulus (10). With mitral annular dilatation, mitral leaflet coaptation becomes ineffective and mitral regurgitation ensues (10). The mitral annulus has cyclical changes in diameter including a reduction in annular dimensions in systole (11). The mechanisms behind the development of mitral regurgitation as well as the factors that determine its response to therapy, however, may be more complex than previously assumed. The degree of mitral regurgitation in cardiomyopathy may be influenced not only by dilatation of the mitral annulus but also the geometry and function of the papillary muscles, chordae tendineae and mitral leaflets themselves (12,13). Reduction of mitral regurgitation in heart failure patients may be related to a decrease in afterload, changes in transmitral pressure gradients, reduction in the regurgitant orifice area or some combination of these mechanisms.
Recently, the echocardiographic proximal flow convergence method has been used to quantify the instantaneous mitral regurgitant flow and instantaneous effective regurgitant orifice area in patients with mitral regurgitation (14,15). Patients who have mitral regurgitation secondary to congestive heart failure have a unique pattern of flow across the mitral valve in systole which consists of early systolic accentuation of mitral regurgitant flow with lesser flow in the latter two-thirds of systole (15). The purpose of this study was to characterize this dynamic regurgitation in patients with severe heart failure and identify components responsible for reduced regurgitant flow during pharmacologic therapy for severe heart failure.
| Methods |
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Pharmacologic therapy included intravenous sodium nitroprusside and intravenous furosemide with subsequent uptitration of angiotensin-converting enzyme inhibitors and nitrates with occasional addition or substitution of hydralazine. Low-dose dobutamine was employed to facilitate initial diuresis in three patients. Doses of these medications were adjusted to approach goals of pulmonary capillary wedge pressure
15 mmHg, right atrial pressure of
8 mmHg and systemic vascular resistance of 1,000 to 1,200 dynes/s/cm5 while maintaining systolic blood pressure
80 mmHg (12,13).
Echocardiographic examination. Echocardiographic studies were performed using a Hewlett Packard Sonos 2000 imaging device with a 2.5 MHz transducer. Imaging was performed at the beginning and conclusion of invasively guided therapy. The average time between imaging studies was 2.8 ± 1.4 days with a median of 2.5 days. Images were recorded within 30 min of obtaining hemodynamic parameters. Parasternal and apical two-dimensional images were recorded. Doppler pulsed-wave tracings of left ventricular inflow and outflow along with continuous-wave Doppler of the mitral regurgitant jet were also obtained from apical views.
Apical color M-mode recordings were obtained at a depth of 16 to 18 cm and a Nyquist limit of 18 to 25 cm/s (15). Color M-mode recordings were guided by the two-dimensional jet appearance in order to orient the interrogation plane through the zenith of the proximal convergence isovelocity area; this minimizes effects of errors due to the angle between the interrogation axis and the main axis of the jet (15). The gain was adjusted to abolish background noise. The zero shift of the color map was also adjusted in order to have a hemispheric shape of the proximal convergence shell, thus avoiding shape changes caused by the constraints of the atrial walls or the orifice size and shape that may impair the calculations using the proximal isovelocity surface area method (15).
Echocardiographic image analysis. All images were acquired in video format and analyzed with a custom-made post-processing program by an observer blinded to the identity and timing of each test. For each measurement and tracing, a minimum of three cardiac cycles were used. M-mode left ventricular chamber dimensions were measured from parasternal long-axis views according to specifications of the American Society of Echocardiography. Mitral annulus diameter was measured from the apical four chamber view at end-diastole and end-systole. Pulsed-wave Doppler measurements of E and A wave maximal velocity as well as E wave deceleration time and velocity time integrals of left ventricular inflow and outflow were performed using the modal velocity. Color M-mode recordings of mitral regurgitation were traced (15). The distance between the aliasing boundary and the mitral valve over time was measured and the aliasing velocity recorded.
Theoretical background.
As flow converges toward an orifice, the theory of conservation of mass predicts that velocity should increase, creating a hemispheric geometry of flow with increasing velocities and decreasing surface areas as blood approaches the orifice. Using the appropriate settings for color Doppler echocardiography, it is possible to visualize and record the hemispheric acceleration zone. Color Doppler M-mode has the temporal and spatial resolution to record the changes in the radius of the shell during the cardiac cycle. Assuming that the blood passing through the hemispheric shell is the same as that passing through the orifice, the flow through the orifice can be calculated from the formula:
In the color Doppler M-mode tracings, the distance from the valve to the first aliasing boundary was digitized over time and used to calculate the instantaneous volumetric flow across the mitral valve during systole (15). The regurgitant volume was calculated by integrating over systole the instantaneous volumetric curve according to the formula:
The effective mitral regurgitant orifice area was calculated as
Instantaneous flow rates and regurgitant orifice area were calculated for each patient and comparisons were made before and after therapy. In addition, the proportion of regurgitant flow occurring in the first third of systole was assessed to determine if aggressive therapy for heart failure altered the temporal pattern of blood flow through the mitral orifice.
Statistics. Paired Students t tests were used to compare hemodynamic parameters and echocardiographic characteristics before and after therapy. A p value of <0.05 was considered to be statistically significant.
| Results |
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| Discussion |
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Several studies performed in the 1970s and 1980s investigated the hemodynamic effects of exercise and various inotropic and vasodilator agents in patients with heart failure and mitral regurgitation (3,79,1620). Keren et al. (3) noted that isometric exercise resulted in a decrease in forward stroke volume and an increase in mitral regurgitant volume in patients with heart failure. Nitroglycerin and dobutamine therapy each led to a reduction in mitral regurgitation and an increase in stroke volume in one study (3). This pharmacologic effect was most apparent in patients with the greatest amounts of mitral regurgitation (3). Other investigators have described divergent responses to nitroprusside and dobutamine therapy (18). Nitroprusside led to increased cardiac output, reduced filling pressure and a decrease in mitral regurgitation while dobutamine led to increased cardiac output with a variable effect on the degree of mitral regurgitation by color Doppler echocardiography (18). Nitroglycerin may result in improved hemodynamics when administered topically as well as intravenously (3,19). Both sodium nitroprusside and hydralazine result in a decrease in mitral regurgitation and an increase in forward cardiac output by decreasing systemic vascular resistance but sodium nitroprusside may result in a greater reduction in left ventricular diastolic volumes (20).
Although prior studies have described a reduction in the color jet area of mitral regurgitation in patients treated for heart failure, our study more precisely quantifies the magnitude of this change and helps to elucidate the mechanism (16). The decrease in regurgitant volume and orifice area, a uniform finding in all study participants, was not associated with any significant changes in the systolic blood pressure to pulmonary capillary wedge pressure difference or in the mitral regurgitant Doppler continuous-wave velocity time integral, suggesting that the mechanism for a reduction in the orifice area is related predominantly to alterations in the mitral apparatus geometry as opposed to altered pressure gradients across the mitral apparatus. These results correspond well with the observation of a decrease in the regurgitant orifice area using nitroglycerin (7). The bulk of mitral regurgitation occurs during aortic ejection (21). The timing of regurgitant flow does not change significantly with therapy, suggesting that the intrinsic mechanisms responsible for producing mitral regurgitation in this heart failure population remain operative following intensive therapy.
It is likely that leaflet coaptation is improved at smaller left ventricular volumes due to a small decrease in mitral annular distention. For instance, a reduction in the mitral annulus diameter from 3.5 cm to 3.3 cm observed in our population would result in a decrease in the effective annular area (assuming a circular annulus) from 9.6 cm2 to 8.6 cm2, a difference that far exceeds the average change in orifice area of 0.34 cm2 in the population. In addition, reduction in left ventricular volumes may improve the relationship between the subvalvar apparatus and valve leaflets and decrease ischemia in those individuals with coronary artery disease. Because the mechanisms underlying mitral regurgitation are complex, it is difficult to determine the relative contributions of changes in the annulus and the subvalvar apparatus to this effect. A decrease in left atrial size and pressure may contribute to reduced stress on the annular apparatus.
Doppler echocardiographic mitral flow velocity patterns have been shown to be useful in estimation of left ventricular filling pressures and predicting the risk of death (22,23). Administration of vasodilators is also associated with a decrease in Doppler echocardiographic mitral valve Doppler E wave velocities and a decrease in the antegrade velocity time integral consistent with a decrease in mitral regurgitation (24,25). Our results are consistent with these prior observations. Mitral inflow deceleration times did not change in our study. This is possibly related to the advanced degree of heart failure in our patients.
Limitations. Calculation of mitral regurgitant transvalvar flow as described in this study makes several assumptions regarding uniformity of flow through the mitral valve and to the technique of the proximal isovelocity surface area as previously described (15,26,27). These limitations were minimized because the study was designed as a comparison of regurgitant flow before and after therapy in individual patients. Regurgitant flow following therapy may be difficult to determine when flow falls below a critical level. The assumption that regurgitant flow is zero in these instances may lead to a slight overestimation of the size of treatment effect, but this small difference would not influence the statistical significance of these findings. Since heart failure treatment was aimed at reaching predetermined treatment goals, therapy was not randomized and it would not be possible to attribute the effects to a specific drug. It should also be recognized that the hemodynamic and mechanistic changes in this study may not apply to patients with other etiologies of mitral regurgitation such as rheumatic valvular disease.
Clinical implications. The use of vasodilators and diuretics leads to a reduction in the dynamic mitral regurgitation of heart failure through a reduction in the regurgitant orifice area. Much of the benefit of therapy for decreasing pulmonary congestion and improving forward output is from the redistribution of mitral regurgitant flow to forward flow. This study suggests that serial measurement of mitral regurgitation may provide important guidance for acute and chronic adjustment of vasodilators and diuretics in heart failure.
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