OP08.15: Fetal myocardium: Compressible or noncompressible?

Abstract

Background: Controversy exists regarding whether myocardium compresses during contraction. Some studies have shown that during systole the muscle compresses when fluid and blood exit from the muscle during contraction. This theory has not been tested in the fetal heart. Objectives: To examine whether fetal myocardium during systole is of lesser or equal volume to that of diastole, and to compare these measures in newborn myocardium, employing 4D-STIC and inversion mode. Methods: STIC volumes were acquired and analyzed with VOCAL and inversion mode. Right and left heart end-diastolic and endsystolic myocardial (MV) and ventricular volumes were determined. Proportional change between end-diastolic and end-systolic MV was calculated, as were stroke volume (SV) and ejection fraction (EF) for the right and left ventricles. For comparison, echocardiography was performed on 10 normal term newborns and children using 4D-STIC, but limiting acquisition and analysis to the left ventricle. Results: 30 fetuses at GA 20–37 wks were examined. The Total Volume Change (ventricle+myocardium) between end-diastole and end-systole ranged from 0.5–5.38 cm3 in the left ventricle and 0.25–4.89 cm3 in the right, while the SV ranged from 0.13–2.64 cm3 in left ventricle and 0.15–2.16 cm3 in the right at these GAs. SV values therefore are smaller than the total volume change in systole, i.e. SV does not account for all volume change following cardiac contraction. This difference is the compression of the myocardium. MV compressed between end-diastole and endsystole by 8–19% in the right ventricle and 5–25% in the left. In newborns and children left heart MV compression between enddiastole and end-systole was 0–8%. EF was relatively constant at ∼60%. Conclusions: Fetal myocardial volume in the second half of gestation compresses by approximately 20% during systole. To the best of our knowledge this is the first study to demonstrate the compressibility of fetal myocardium.