Changes in Myocardial Contractility and Electromechanical Interval During the First Month of Life in Healthy Neonates

This study aims at documenting the changes in ventricular tissue velocities, longitudinal strain and electromechanical coupling during the first month of life. During the neonatal period, when the ventricular myocardium is not yet fully maturated, the heart is subjected to significant hemodynamic changes. We studied the ventricular performance of 16 healthy neonates at three time points over the first month of life: on days 2 (IQR [2;2]), 13 [12;14] and 27 [25;29]. We found that systolic and diastolic tissue velocities increased significantly in both left and right ventricle (by 1.2-1.7 times, p < 0.001). Congruently, we found that peak systolic longitudinal strain of the right and left ventricles increased significantly. However, no significant changes in longitudinal strain rate were observed. Finally, QS-intervals shortened during the neonatal period: being measured at 12 points throughout the left ventricle, time to peak systolic velocity decreased on average to 89 % in the second and to 80 % in the fourth week of life (22.3 ± 0.2 vs. 19.8 ± 0.3 vs. 17.8 ± 0.5 ms, r = -0.564, p < 0.001). When comparing opposing walls of the left ventricle, no dyssynchrony in left ventricular contraction was found. In addition to increasing systolic and diastolic tissue velocities during the first month of life, the time to peak systolic contraction shortens in the neonatal heart, which may reflect an increasing efficiency of the excitation-contraction coupling in the maturing myocardium. While there appears to be no dyssynchrony in ventricular contraction, these findings may extend our appreciation of the immature neonatal heart and certain disease states.