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* From The Heart Institute, Beth Israel Medical Center, New York, NY.
Correspondence to: Marvin Berger, MD, FCCP, Beth Israel Medical Center, First Avenue at 16th Street, New York, NY 10003
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Abstract |
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Background: Doppler echocardiography has been used to estimate right ventricular systolic pressure noninvasively. Because right ventricular and pulmonary artery diastolic pressure are equal at the time of pulmonary valve opening, Doppler echocardiographic estimation of right ventricular pressure at this point might provide an estimate of pulmonary artery diastolic pressure.
Methods: We studied 31 patients who underwent right heart catheterization and had tricuspid regurgitation. Pulmonary flow velocity was recorded by pulsed wave Doppler echocardiography, and tricuspid regurgitant velocity was recorded by continuous wave Doppler echocardiography. The time of pulmonary valve opening was determined as the onset of systolic flow in the pulmonary artery. Tricuspid velocity at the time of pulmonary valve opening was measured by superimposing the interval between the onset of the QRS complex on the ECG and the onset of pulmonary flow on the tricuspid regurgitant envelope. The tricuspid gradient at this instant was calculated from the measured tricuspid velocity using the Bernoulli equation. This gradient was compared to the pulmonary artery diastolic pressure obtained by right heart catheterization.
Measurements and results: The pressure gradient between the right atrium and right ventricle obtained at the time of pulmonary valve opening ranged from 9 to 31 mm Hg (mean, 19 ± 5) and correlated closely with invasively measured pulmonary artery diastolic pressure (range, 9 to 36 mm Hg; mean, 21 ± 7 mm Hg; r = 0.92; SEE, 1.9 mm Hg).
Conclusion: Doppler echocardiographic measurement of right ventricular pressure at the time of pulmonary valve opening is a reliable noninvasive method for estimating pulmonary diastolic pressure.
Key Words: Doppler echocardiography • pulmonary artery diastolic pressure • tricuspid regurgitation
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Introduction |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionReferences |
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Recently, Reynolds et al8 demonstrated that pulmonary artery diastolic pressure can be estimated by measuring right ventricular pressure at the time of pulmonary valve opening, since right ventricular and pulmonary artery pressure equilibrate at this point in the cardiac cycle. In patients with tricuspid regurgitation, continuous wave Doppler echocardiography can be used to derive the right ventricular systolic pressure from the gradient between the right ventricle and right atrium.9 10 11 12 Therefore, calculating the gradient between the right ventricle and right atrium at the time of pulmonary valve opening and adding it to the right atrial pressure should allow an estimation of pulmonary artery diastolic pressure. Previous work in our laboratory10 13 has shown the feasibility of calculating right ventricular systolic pressure from the Doppler echocardiographic gradient, without an estimate of right atrial pressure, by using a regression equation.
We therefore undertook this study with the following objectives: (1) to ascertain whether Doppler echocardiographic estimation of right ventricular pressure at the time of pulmonary valve opening could accurately predict pulmonary artery diastolic pressure in patients undergoing bedside hemodynamic monitoring; and (2) to determine whether this could be accomplished without estimating right atrial pressure.
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Materials and Methods |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionReferences |
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Echocardiography
Echocardiographic studies (Sonos 500 or Sonos 1000;
Hewlett-Packard; Palo Alto, CA) were performed using a 2.5-MHz
phased-array transducer for color flow and pulsed wave Doppler
echocardiographic studies and a 2-MHz nonimaging transducer for
continuous wave Doppler echocardiographic studies. Pulsed wave and
continuous wave Doppler echocardiographic velocity tracings were
recorded on a strip chart recorder (model 77501A;
Hewlett-Packard) at a paper speed of 100 mm/s.
The maximal velocity of the tricuspid regurgitant jet was assessed by continuous wave Doppler echocardiography from the parasternal or apical position. Tricuspid velocities and pulmonary artery pressures were recorded simultaneously. Immediately after recording the velocity of the tricuspid regurgitant jet, pulmonary flow velocity was recorded by pulsed wave Doppler echocardiography from the parasternal short-axis view, with the sample volume located in the pulmonary artery at the level of the pulmonary valve. The time of pulmonary valve opening was determined as the onset of systolic flow in the pulmonary artery (Fig 1 , top).
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Right Heart Catheterization
Pulmonary artery diastolic pressure was measured at
end-expiration by an independent observer with the patient supine and
the reference level for zero pressure at midchest.
Statistics
Data are expressed as mean ± SD. Linear regression analysis
was used to compare the pressure gradient between the right ventricle
and the right atrium at the time of pulmonary valve opening, with the
pulmonary artery diastolic pressure measured invasively. Interobserver
and intraobserver variability were expressed as a percent for each
measurement, and they were determined as the difference between the two
observations divided by their mean value.
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Results |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionReferences |
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Doppler Echocardiographic Findings
The interval from the onset of the QRS complex to the onset of
flow in the pulmonary artery ranged from 40 to 140 ms (mean, 91 ± 26
ms). The velocity of the tricuspid regurgitant jet at the onset of flow
in the pulmonary artery ranged from 1.5 to 2.8 m/s (mean, 2.2 ± 0.3
m/s). The pressure gradient between the right ventricle and the right
atrium at the time of pulmonary valve opening as calculated using the
Bernoulli equation ranged from 9 to 31 mm Hg (mean, 19 ± 5 mm Hg).
Doppler Echocardiographic vs Catheterization Findings
The mean difference between the pulmonary artery diastolic
pressure and the gradient between the right ventricle and right atrium
at the time of pulmonary valve opening was 2.5 ± 2 mm Hg. A close
correlation was found between the right ventricular to right atrial
pressure gradient at the time of pulmonary valve opening and the
invasively measured pulmonary artery diastolic pressure (r = 0.92;
SEE, 1.9 mm Hg; Fig 2
). Interobserver and intraobserver variabilities for this method were
8.4% and 6.2%, respectively.
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Discussion |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionReferences |
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Technical Considerations
The success of our method is dependent on two factors: obtaining
an accurate gradient between the right ventricle and right atrium, and
determining the time when the pulmonary valve opens. Previous studies
have established that continuous wave Doppler echocardiography can
measure the instantaneous gradient between two chambers of the heart at
virtually any point in the cardiac cycle.14
In an
experimental model of aortic outflow obstruction, it was shown that
instantaneous Doppler echocardiographic gradients and catheterization
gradients correlated closely throughout systole over a wide range of
pressure differences.15
Similar findings have also been
observed in patients with prosthetic valves and with left and right
ventricular outflow obstructive lesions.16
17
Thus, there
is ample evidence confirming the ability of continuous wave Doppler
echocardiography to obtain accurate instantaneous gradients.
Determining the time of pulmonary valve opening is important, because at this point in the cardiac cycle, right ventricular and pulmonary artery diastolic pressure are equal. In the present study, pulmonary flow velocity was recorded by pulsed wave Doppler echocardiography, and the onset of flow in the pulmonary artery was used to approximate the time of pulmonary valve opening. This point was then located on the tricuspid velocity tracing, and the gradient between the right ventricle and right atrium was calculated.
Estimation of Right Atrial Pressure
Obtaining an accurate estimate of right atrial pressure at the
time of pulmonary valve opening may be difficult. In part, this relates
to the fact that pulmonary valve opening occurs towards the end of
right atrial relaxation, when right atrial pressure may be relatively
low. The mean difference of 2.5 ± 2 mm Hg between the tricuspid
gradient and invasively measured pulmonary artery diastolic pressure
found in our patients is in accord with this observation. Traditional
methods for the estimation of right atrial pressure include an
examination of the jugular venous pulse, using a constant mean right
atrial pressure of 10 to 14 mm Hg for all patients, or measuring the
degree of inspiratory collapse of the inferior vena
cava.11
12
18
19
These methods may result in an
overestimation of pulmonary artery diastolic pressure, because they
provide an assessment of mean right atrial pressure rather than right
atrial pressure at the time of pulmonary valve opening.
An alternative method involves using only the tricuspid gradient and substituting this value into a regression equation.10 13 This avoids the need to estimate right atrial pressure, and it is supported by our findings. We observed a close correlation between the Doppler echocardiographic-derived tricuspid gradient at the time of pulmonary valve opening and invasively derived pulmonary artery diastolic pressure, with a small but consistent underestimation of pulmonary artery diastolic pressure by the tricuspid gradient. In addition, previous work20 21 has shown a linear relation between pulmonary artery pressure and mean right atrial pressure. Thus, as pulmonary artery diastolic pressure rises, there is a proportionate increase in right atrial pressure.
Limitations
The slope of the initial portion of the tricuspid regurgitant jet
is relatively steep at the time of pulmonary valve opening. Therefore,
extreme care must be taken in localizing this point on the tricuspid
velocity tracing, because small errors can significantly alter the
estimated gradient between the right ventricle and right atrium.
However, the relatively low interobserver and intraobserver variability
and the close correlation between Doppler echocardiography and invasive
measurements suggest that with careful technique this problem can be
minimized. The fact that tricuspid and pulmonary velocities were not
recorded simultaneously may also have affected our results. Another
potential source of error involves the measurement of right atrial
pressure at the time of pulmonary valve opening. Our findings suggest
that linear regression can be used to incorporate an estimate of right
atrial pressure into the calculation of pulmonary artery diastolic
pressure. However, in cases where right atrial pressure is very high,
the gradient between the right ventricle and right atrium may be low,
and the use of a regression equation might result in significant
underestimation of pulmonary artery diastolic pressure. To minimize
this problem, patients with severe tricuspid regurgitation were
excluded, because in this group right atrial pressure may be high. A
similar situation may be encountered in patients with severe
right-sided congestive heart failure and markedly elevated jugular
venous pressure. Patients who were receiving mechanical ventilation
were excluded because obtaining accurate invasive measurements can
sometimes be difficult in this group. Therefore, our findings may not
be applicable to patients receiving mechanical ventilation. The absence
of tricuspid regurgitation or a clear, well-defined tricuspid velocity
envelope in 15% of patients is an important limitation, because in
these patients pulmonary artery diastolic pressure could not be
estimated.
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Conclusion |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionReferences |
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Footnotes |
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Received for publication July 17, 1998. Accepted for publication February 10, 1999.
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This article has been cited by other articles:
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  J. W. Christman, R. T. Sadikot, and T. S. Blackwell The Role of Nuclear Factor-{kappa} B in Pulmonary Diseases Chest, May 1, 2000; 117(5): 1482 - 1487. [Abstract] [Full Text] [PDF]
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