
diameter (≤ 20 mm) with subnormal collapse (≤ 50%) or
above normal diameter with normal collapse constitutes
intermediate group where RAP range is 5 to 10 mmHg.
Guidelines recommend midrange values (i.e. 3 for
normal and 8 for intermediate group).
3
Some studies
have evaluated the validity of the IVC parameters for the
accuracy of the estimation of RAP.
16-18
Most, but not all,
studies have demonstrated good correlations between
the IVC collapsibility index ([IVC max-IVC min] / IVC
max) and RAP (0.57 < r ≤ 0.76).
19,20
In this study, this
default value (10 mmHg) of RAP was replaced with RHC
derived RAP and then adjusted RVSP calculated.
Hence, adjusted RVSP is calculated by both DE and
RHC findings and cannot be attributed to DE alone. The
objective was not to discourage the estimation of RAP,
but to assess the impact of RAP on correlation between
RVSP and sPAP. Only minimal improvement was found
(Table I). This suggests that had RAP be estimated with
100% accuracy on DE, even then DE would have
remained inaccurate in estimating sPAP.
Greiner
et al. conducted a retrospective study on large
sample of unselected patients. Their results validate the
reliability of DE in estimating sPAP. They have
highlighted the causes of over- and under-estimation of
DE derived RVSP. Over-estimation was mainly due to
maximum TR velocity boundary artifacts. They
suggested that maximum velocity should be measured
at the best spectral-wave boundary, avoiding Doppler
artifacts (fringes). Incomplete spectral-wave envelope
was second common reason. They suggested that only
signals extended for at least half of the systole should be
measured, and incomplete or absent TR may be
avoided by increasing blood pool volume with a
strategy as simple as drinking a cup of water before
examination.
7
Fisher et al. conducted a prospective
study where time interval between DE and RHC was just
one hour. Their results are in line with our results, apart
from the fact that under-estimation was as common as
over-estimation.
8
This study has few limitations which should be kept in
mind while interpreting its results. It was a retrospective
collected data and images of DE recordings were not
available so the authors could not really look into the
causes of over- or under-estimation. Maximum time
interval between DE and RHC was set at 30 days.
Pulmonary pressures in patients with PH are known to
fluctuate significantly over the course of several hours.
21
Mean time interval in this study was 8.57 ±8.21 days.
The study population consisted of selected patients with
suspicion of PH on DE. Hence, evaluation of diagnostic
accuracy may be questioned. Sample size was small.
CONCLUSION
Doppler echocardiography is not very accurate in
estimating pulmonary artery pressures. Over-estimation
was more common than under-estimation. Correct
estimation of right atrial pressures may improve the
correlation between DE derived RVSP, and RHC derived
sPAP. However, this contribution is only minimal.
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