Pulmonary hypertension is a cause of significant morbidity and mortality in newborn
infants. Right ventricular function, or dysfunction, is an important consequence of
pulmonary hypertension and may be an important determinant of disease severity.
This work aimed to improve the assessment and management of infants with
pulmonary hypertension by:
1. identifying non-invasive measures of right ventricular function in infants
2. determining the mechanisms of right ventricular dysfunction
3. demonstrating the variability of the relationship between RV function and
PAP
Five echocardiographic measures were selected to assess RV function; tricuspid
valve Doppler inflow, right ventricular output (RVO), RV myocardial performance
index (RVMpi), pulse wave tissue Doppler imaging (PWTDI) and colour tissue
Doppler imaging (CTDI). Using a case-control design each measure was performed
in a control group of infants with normal cardiovascular function, and a PHT group
of infants with elevated pulmonary artery pressure. This design allowed assessment
of each measure, and provided normative data for those measures (RVmpi, PWTDI
and CWTDI) which had not previously been performed in infants.
All measures were found to be technically feasible, and to provide some
quantification of haemodynamic performance. However, the load-dependence of TV
Doppler and the global nature of RVmpi and RVO meant that these measures could
not be considered pure measures of RV myocardial function alone. By contrast,
Tissue Doppler imaging measures allowed separate assessment of systolic and
diastolic function. This study was an important first demonstration of the feasibility
and application of TD1 in an infant disease state. Future studies are indicated to
assess the load-dependence of TDI measures in infants, the repeatability of the
technique and use of TDI in other infant diseases with myocardial dysfunction.
The mechanisms of RV dysfunction in infants with PHT were investigated by
comparison of RV function data between control and PHT groups. Accepting the
limitations of the measures used, the results indicated the presence of impaired
systolic and early diastolic function in infants with PHT. This finding highlighted
the importance of diastolic dysfunction in the failing infant heart, and the usefulness
of measures such as TDI which allow assessment of both systolic and diastolic
dysfunction. There are also potential therapeutic implications, and the theoretical
benefit of drugs with both inotropic and lusitropic actions in this setting was an
important area identified for future research.
Finally, no linear relationship was identified between RV function measures and
PAP in the PHT group. It was concluded that pulmonary artery pressure should not
be used as a proxy measure of RV function in infants and thus emphasised the
importance of directly assessing RV function in infants with pulmonary
hypertension.