The assessment of right ventricular function in infants with pulmonary hypertension

• Main Author: Patel, Neil
• Published: University of Edinburgh 2010
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.739030

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.