We studied how periodic and complex heart rate dynamic changes as pulmonary artery pressure increases in 32 infants with ventricular septal defet. In addition, we tested the possibility that the dynamical changes can be used to noninvasively predict the pulmonary artery pressure.

During cardiac catherterization, mean pulmonary artery pressure was measured and, at the same time, 5minute segments of continous electrocardiographic recording was stored. High-(>0.15 hertz) and low-(0.03-0.15 hertz) frequency components of heart rate variability were computed using spectral analysis. Yhe overall complexity of heart rate time series was quantified by its approximate entropy.

Pulmonary hypertensive infants(mean pulmonary artery pressure>20mmHg, n=17) had significantly lower low-(p<0.05)and high-(p<0.05) frequency power and lower approximate entropy(p<0.0001) than pulmonary normotensive infants(mean pulmonary artery pressure20mmHg, n=15). The mean pulmonary artery pressure was significantly correlated not with the spectral powers but with approximate entropy(=-0.51, P=0.0001).

It can be concluded that, in infants, pulmonary hypertension induced by left-to-right shunt lesions suppress both periodic and complex heart rate oscillation and that mean pulmonary artety pressure can be predicted by calculating approximate entropy of heart trate variability.