Myocardial Performance and Baroreceptor Reflexes in Preterm Neonates: An Echocardiographic Evaluation Using the Tilt Table Test Method

Abstract 171 Poster Session III, Monday, 5/3 (poster 124)

Objective: To evaluate myocardial performance and baroreceptor reflexes in stable convalescent preterm infants using 2D, M-mode and Doppler echocardiography at supine, 30° & 60° head up tilt.

Methods: 25 preterm infants with gestational age (GA) (mean ± SD) 31 ± 2.9 wks. (range 25-35.5 wks.), birth weight of 1612 ± 555 g (range 520 - 3260 g) studied. All infants were studied in supine, 30° and 60° head up positions.

Results: A linear increase in stroke volume (SV) and cardiac output (CO) was seen with increasing GA (slope±SE, b=0.021±0.006, p=0.001). The left ventricular ejection time (LVET) increased with GA (slope b=2.5±1.29, p=0.06). End systolic wall stress (ESWS) increased significantly with GA (slope b=3.16±1.02, p=0.004). GA had no effect on velocity of circumferential fiber shortening (VCFS) (p=0.16) and left ventricular filling pattern as seen by early/late atrial doppler flow velocity ratios (E/A) (p=0.72). An inverse relationship was found between VCFS and ESWS (slope b=-0.0197±0.008, p=0.003). GA had a significant effect on HR (p=0.007), SBP (p=0.029), left ventricular (LV) end diastolic dimensions (EDD) (p=0.0002) and end systolic dimensions (ESD) (p=0.001). Head up tilt did not significantly affect HR (p=0.7), SBP (p=0.3), LVET (p=0.3), CO (p=0.8), ESWS (p=0.3), VCFS (p=0.7), and E/A ratios (p=0.8). Ratio of ESWS to VCFS (load independent measure of contractility) did not change significantly with tilt (p=0.4) (Figure).

Fig 1

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Conclusions: Myocardial performance improved with increasing GA. Head up tilt to 30° and 60° did not affect cardiac contractility. Study infants had a well developed baroreceptor response and maintained their myocardial function in the normal range during tilting to 30° and 60°.