Fetal Cardiac Care

by Dr Mridul Agarwal

Estimation of Combined Ventricle Output in Fetus

1–2 minutes

In the post-natal life, the circulation is in series where pulmonary and systemic circulation is connected in series. Thus the cardiac output volume is expressed in terms of stroke volume and cardiac output, which is the blood ejected by each ventricle. Whereas in the fetus, most of the cardiac output from either ventricle reaches aorta except less than the half of right ventricle output goes to pulmonary circulation.

Schematic Diagram showing approximate distribution of Combined Ventricular Output (CVO) in human fetuses near term. Values in red are percentage of CVO.

Furthermore, similar happened to venous return where most of the venous return reaches RA but shunted to the left side before reaching pulmonary circulation. Thus the fetal circulation is significantly parallel mixing type of circulation. Thus the output from either ventricle does not signify the cardiac output. So the term Combined Cardiac Output (CVO) used in fetal circulation. The LV contributes around 45% of CVO and RV about 55%. The distribution to the various organ is represented as percentage of CVO.

%CVOmL/min/kg
Combined ventricular output100450
Left ventricular output45202
Aortic isthmus836
Brain24107
Upper trunk, forelimbs1359
Right ventricular output55248
Ductus arteriosus32145
Pulmonary circulation23103
Descending aorta38171
Umbilical–placental circulation26112
Hepatic circulation1468
Ductus venosus1144
Lower body organs, hindlimbs1260
Superior vena cava35157
Inferior vena cava + umbilical flow40180
Foramen ovale2090

Table. Showing Combined Cardiac Output in Fetal Circulation near term with distribution and approximate volume

As depicted in the table, the left ventricle (LV) produces 45% of CVO, but the systemic circulation receives 75% of CVO. The Umbilical–placental circulation receives 26% of CVO through systemic circulation, and Umbilical–placental circulation is an oxygenation organ in a fetus similar to the lung in post-natal life. So systemic circulation eventually receive only approximately 50% of CVO.

Echocardiographic Estimation of CVO

Stroke Volume = Annulus Area X Velocity Time Integral

Cardiac Output = Annulus Area X VTI X Fetal Heart Rate

LV Output= 3.14 (Aortic annulus diameter/2)2 X Aortic VTI X Fetal Heart Rate

RV Output= 3.14 (Pulmonary annulus diameter/2)2 X Pulmonary VTI X Fetal Heart Rate

Combined Ventricular output= LV Output + RV Output