Pathophysiologically the following congenital heart diseases are leakages of the aortic ‘Windkessel’ (Deeg 1989):

The most frequent leakage of the aortic ‘Windkessel’ is a patent ductus arteriosus Botalli (Table 15.3).

A persistent ductus arteriosus Botalli (PDA) is a frequent problem in the neonatal period, especially in preterm-born babies. A large PDA can be seen through 2D echocardiography in the parasternal short axis view through the right ventricular outflow tract and the pulmonary artery (Fig. 15.1). The best modality for the diagnosis of a PDA with left to right shunt is colour-coded Doppler sonography of the blood flow in the main trunk of the pulmonary artery (Fig. 15.2a–d). It shows a red inflow in the region of the pulmonary bifurcation which is directed towards the anterior wall of the pulmonary artery (Fig. 15.2a–d). If the pulmonary resistance is high, blood flow in the open duct is directed away from the pulmonary artery to the descending aorta. In these cases, the open duct is displayed blue (Fig. 15.2e). A small PDA causes only a tiny flare (Fig. 15.2c, d), whereas a large PDA has a greater width and reaches the pulmonary valve (Fig. 15.2a, b).

PW and CW Doppler show diastolic inflow into the pulmonary artery which is displayed above the baseline, whereas the normal pulmonary flow is displayed below the baseline (Fig. 15.3a–c). As long as the pulmonary resistance is high, pulsed Doppler shows only diastolic inflow into the pulmonary artery with low peak systolic flow velocities (Fig. 15.3a, b). When the resistance of the pulmonary artery has fallen to normal values, systolic-diastolic inflow with high flow velocities can be found (Fig. 15.4a, b). If the pulmonary vascular resistance has fallen to normal values and the PDA remains open, more and more blood is shunted away from the aorta to the pulmonary artery.

In prematurely born infants of 23–28 weeks of gestation, the PDA is the main cause of respiratory deterioration at the end of the first week of life. Immediately after birth, the pulmonary arterial resistance is high. Although the PDA is open, there is no significant leakage of the aortic ‘Windkessel’: Only a small amount of blood is shunted away from the aorta to the pulmonary arterial bed (Fig. 15.2d). Blood flow in the body arteries with low peripheral resistance (brain, abdomen) is therefore normal. If the pulmonary arterial resistance falls at the end of the first week of life and the PDA stays open, the leakage of the aortic Windkessel increases and blood is shunted away to a greater extend from the aorta to the pulmonary vascular bed. This may lead to hyperperfusion of the lungs and cause pulmonary deterioration due to pulmonary oedema. The shunted blood volume is ‘stolen’ from the descending aorta. This may cause hypoperfusion of important body organs such as the brain, liver, kidneys and intestine (Bejar et al. 1982; Dykes et al. 1980; Maier 2005; Kittermann 1975; Sonntag 2005).

Flow measurements in low-resistance peripheral arteries show a reduction of the diastolic amplitude and a decrease of the end-systolic and end-diastolic flow velocities (Figs. 15.5, 15.6 and 15.7) (Perlman et al. 1981; Martin et al. 1982; Deeg et al. 1986a, b). These flow alterations can be found in all low-resistance arteries of the body such as the brain arteries, the coeliac trunk, the renal arteries and their branches (Figs. 15.5, 15.6 and 15.7) (Perlman et al. 1981; Martin et al. 1982; Deeg et al. 1986a, b).

A common arterial trunk is a congenital cardiac malformation where only one single artery originates from the heart that gives rise to the coronary arteries, the pulmonary arteries and the brachiocephalic arteries (Fig. 15.11).

Echocardiographic diagnosis in TAC shows a malalignment ventricular septum defect with an overriding systemic vessel (Fig. 15.11b, c). In contrast to Fallot tetralogy, no pulmonary artery originates from the right ventricle. Careful examination of the ascending aorta and the aortic arch reveals one or two pulmonary arteries which arise from the ascending aorta (Fig. 15.11a–d).

Pathophysiologically TAC is also a large leakage of the aortal ‘Windkessel’. Immediately after birth, the pulmonary vascular resistance is high. Flow measurements in peripheral arteries in the first days of life may show normal flow profiles and flow velocities (Deeg 1989). Thus far the pulmonary vascular resistance falls, the leakage of the aortic ‘Windkessel’ increases, and blood is shunted away from the systemic circulation to the pulmonary vascular bed (Fig. 15.11e). Flow measurements in the aortic arch and the descending aorta show diastolic backflow which is displayed red with colour Doppler (Fig. 15.11e). This causes a marked decrease of diastolic flow in all arteries of the body (Figs. 15.12 and 15.13) (Table 15.7) (Deeg 1989). Typically a diastolic backflow can be found in all low-resistance arteries (Fig. 15.13a, b). The leakage of the aortic ‘Windkessel’ may be aggravated if regurgitation of a malformed truncus valve is associated.

If surgery cannot be performed in the neonatal period, pulmonary hypertension will rapidly develop. Repeated Doppler sonographic controls in low-resistance arteries show an increase of the diastolic flow amplitude and flow velocities and apparently a ‘normalisation’ of the flow profile and flow velocities (Fig. 15.14) (Deeg 1989). This is however a bad sign, as irreversible alterations of the pulmonary vascular bed (Eisenmenger reaction) may soon develop.

To distinguish fixed pulmonary hypertension from flow-dependent pulmonary hypertension, flow measurements should be performed with 21 % oxygen and 100 % oxygen (Deeg 1989). Flow-dependent pulmonary hypertension causes a decrease of the diastolic amplitude in peripheral arteries if 100 % oxygen is inhaled (Fig. 15.15); 100 % oxygen reduces pulmonary resistance and increases blood flow through the pulmonary vascular bed. This increases the leakage of the aortic ‘Windkessel’.