Adjusting Therapy in Pulmonary Arterial Hypertension – Novel Echocardiographic Techniques
diastolic heart failure, it would be essential to document the accuracy of abnormal findings against invasively determined diastolic dysfunction, or to show that observed changes were predictive of an adverse prognosis.
Assessing Loading Conditions
From the early 1980s, it has been possible to echocardiographically estimate pulmonary artery pressure using Doppler assessment of tricuspid velocity.36
Initial studies suggested that this was a highly accurate measure of pulmonary systolic pressure; however, these were unblinded studies.37,38
Attempts to define filling pressures using
the jugular venous pressure or inferior vena cava collapse do not reliably improve the accuracy of estimation.
Subsequent studies have shown that in practice echocardiographic estimation correlates poorly with pulmonary pressures.39,40
Performing
echocardiography within one hour of catheterisation, Fisher et al.40 found that the 95% confidence interval for patients with a mean systolic pressure of 62mmHg was ±38mmHg, and that a significant portion of this inaccuracy was due to attempts to estimate RA pressure using the IVC diameter variation. Intriguingly, they observed that pressures were generally overestimated where tracing quality was scored as good, and underestimated when the envelope was poorly defined.
In one study, as a result of the use of contrast echocardiography, an additional 15 of 38 patients were designated as having elevated pulmonary artery systolic pressure during stress echocardiography.41 However, while some of these results were assessed against invasive evaluation, it is evident from Fisher et al. that increased signal quality is not always associated with increased accuracy.40
The result is that
while very abnormal velocity readings (>3.4m/second) have a high predictive value for pulmonary hypertension, the reproducibility is poor and velocity alone cannot be used to identify those who have responded to therapy even where this includes a significant reduction in pressures versus those whose pressures remain very elevated.42
Therefore, the problem in essence is that echocardiography can provide data on so many aspects of ventricular function and the haemodynamic loading to which the ventricle is exposed; however, clarifying which of these adds incremental information both at baseline and during therapy is difficult. Small studies with inadequate patient follow-up cannot inform the debate. As with pharmaceutical studies, it is time to move to adequately ‘blinded’ and powered studies of pre- defined parameters with survival as the agreed end-point.
Conclusion
No other technique has the capacity of echocardiography to measure as many of the relevant parameters required to describe the RV–pulmonary artery interaction. Nevertheless, even if all possible
EUROPEAN CARDIOLOGY
Pulmonary regurgitant flow is used to estimate diastolic and mean PAP. Estimation of PAP diastolic pressure with TR flow has been described.43 Estimation of mean PAP with RVOT flow acceleration time has also been described and is dependent on CO, and is valid when HR is between 60 and 100bpm and when there are no intracardiac shunts. Full haemodynamic assessment always includes CO and cardiac index calculations. In a similar way to invasive assessment, the average of five measurements must be obtained. Unfortunately, as with estimates of pulmonary systolic pressure, there are few data to suggest that echocardiographic estimates of CO are currently sufficiently reproducible to meet clinical need in the management of patients with PAH.40
Figure 2: Speckle Tracking Imaging of a Dilated Right Ventricle
Right ventricular (RV) walls are colour-coded pink, showing low strain values compared with red-coded walls for normal values. The mid-lateral free RV wall is blue-coded, suggesting unco-ordinated segment motion. However, interpretation should be cautious as this abnormal motion could be related to the moderator band insertion.
Figure 3: Vector Velocity Imaging in Early Systole of the Left Ventricle
Individual arrows represent the velocity and direction of contraction of individual regions of the myocardium.
measures were accurate and reproducible, together they would not fully describe this interaction.
The real strengths of echocardiography lie in providing ongoing monitoring of RV structural and functional responses to the loads faced. Since the RV tolerance of the afterload demand is the main determinant of outcome in PAH, if we can define a limited number of parameters that change reliably with changing prognosis, therapy of PAH can be adjusted using echocardiography and clinical assessment. n
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