Doppler Assessment of Physiological Stenosis at the Bifurcation of the Main Pulmonary Artery: A Cause of Functional Murmur in Neonates

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A systolic heart murmur is not infrequently recognized in healthy newborn infants, especially those with a low birth weight. This study aimed at assessing the hemodynamics at the bifurcation of the main pulmonary artery using Doppler echocardiography and to correlate the results with this murmur. The peak velocities of main pulmonary artery (MPAV) and right pulmonary artery (RPAV) were studied in 25 low-birth-weight infants who had recovered from acute stage and presented with a systolic murmur, and the ratio of RPAV/MPAV was calculated. Another compatible 25 healthy low-birth-weight infants without a murmur were enrolled as the control group. The initial MPAV values were 79.8 +/- 20.7 (range 51-152) cm/s and 80.7 +/- 14.2 (range 60-111) cm/s in the heart murmur group and in the control group, respectively (p > 0.05). The initial RPAV values were 193.4 +/- 60.2 (range 118-388) cm/s and 99.8 +/- 15.5 (range 76-132) cm/s in the heart murmur group and in the control group, respectively (p < 0.0001). The initial RPAV/MPAV ratios were 2.46 +/- 0.61 (1.59-3.92) and 1.25 +/- 0.14 (0.94-1.47) in the heart murmur group and in the control group respectively (p < 0.0001). When the murmur disappeared after a period of 2-5 months, no significant differences in the last RPAV and RPAV/MPAV ratios between both groups could be found. The RPAV in the heart murmur group faded significantly to 118.7 +/- 16.9 cm/s, and so did the RPAV/MPAV ratio to 1.24 +/- 0.12 (p < 0.0001). A transient functional murmur recognized in healthy premature infants at about 1 month of age is caused by the pressure gradient that implies a physiological stenosis at the bifurcation of the main pulmonary artery. The RPAV is higher than the MPAV, and the RPAV/MPAV ratio is usually over 1.5. The RPAV became slower, and the RPAV/MPAV ratio fell as the murmur faded with age.

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