Longitudinal Myocardial Contribution to Peak Systolic Flow and Stroke Volume in the Neonatal Heart

Abstract

Systolic longitudinal myocardial function is important for cardiac ejection. Data describing hemodynamic determinants and the time course of myocardial longitudinal contraction as measured by tissue Doppler are lacking. Ten newborn pigs were used for invasive hemodynamic investigation. Tissue Doppler assessment of the lateral part of the mitral valve annulus during systole was performed during pharmacological modulation of inotropy, cardiac pacing, and modulations of loading conditions. The strongest association was found between peak systolic velocity (SЈ) and peak systolic flow (PSF) and end-systolic pressure (ESP), respectively (␤ ϭ 0.09 cm/mL, p Ͻ 0.001 and ␤ ϭ Ϫ0.07 cm/mL, p ϭ 0.003). Displacement (D) was mostly influenced by stroke volume (SV) (␤ ϭ 0.05 cm/mL, p Ͻ 0.001). Ejection time, SV, ESP, maximum first derivative of pressure (dP/dt max ), and PSF were all associated with SЈ and D under different states of hemodynamic modulation; however, the ratio between PSF and SЈ, SV, and D were stable during hemodynamic modulations. Normalized cross correlations indicate that SЈ and D follow the same trajectory as flow and SV, respectively. In conclusion, this study provides validity of accounting systolic D in the long axis as the longitudinal contribution to SV and peak systolic tissue velocity as the longitudinal contribution to PSF. S ystolic excursion and motion of the mitral valve annulus has been evaluated for myocardial function in both children and adults (1,2). It is easily obtainable in most patients and has the potential of being a routine parameter for assessment of myocardial function (3). Most available data are generated on the basis of studies in adults or experimental data from mature animal studies. In children, data are being published, but validated data explaining changes that occur within and between individuals at all age groups are lacking (4).This study was designed to possibly understand the nature of longitudinal peak systolic velocity (SЈ) and systolic displacement (D) when acting under the influence of hemodynamic changes in small individuals. Neonatal pigs were chosen because of the similarity to human neonates with regards to heart size and heart rate (HR). METHODSPopulation. Ten pigs (age 3-6 d, weight 2520 -6080 g) were studied under general anesthesia. A total of 185 echocardiographic assessments were performed. Twenty (11%) assessments were excluded mainly due to no capture during right atrial pacing, missing data file, or atrial contraction before mitral valve opening during pacing. All animals were in good health without overt clinical signs of disease. The experimental protocol was approved by the Norwegian Animal Research Authority. The animals were cared for and handled in accordance with the European Guidelines for Use of Experimental Animals.Experimental model. The piglets were anesthetized with sevoflurane for i.v. cannulation and maintained on midazolam, fentanyl, and penthobarbital. The animals were mechanically normoventilated (fraction of inhaled oxygen [...