Congenital heart defects with left-right shunt

Leonardo Da Vinci made the first drawing of a cadaver with an atrial septal defect and Carl Freiherr von Rokitansky (1804 - 1878) gave the first complete pathological anatomical description. However, it was not until the early 1940s that the atrial septal defect was diagnosed. The first open heart surgery with the heart-lung machine became possible in 1953 (Schmaltz 1998).

A shunt is defined as an imbalance in blood flow between the pulmonary and systemic circulatory systems due to a transition from one circulation to the other. A shunt can be intracardiac or take place at the level of the large arteries or veins. In a left-to-right shunt, arterial blood enters the pulmonary circulation, characterized by Qp > Qs (Blum 2016).

Congenital left-right shunts belong to the group of acyanotic heart defects. These include, for example:

- Atrial se ptal defect (occurs in approx. 7 % [Menche 2020])

- Ventricular septal defect (occurs in approx. 31% [Menche 2020])

- Atrioventricular septal defect

- Partial pulmonary vein malformation

- Persistent ductus arteriosus botalli (occurs in approx. 7 % [Menche 2020])

- Aortopulmonary window (Herold 2023)

- Ruptured aortic sinus (Valsalvae), aortoventricular tunnel

- Partial pulmonary vein malformation

- Anomalies of the coronary arteries (Hombach 2001)

The strength of the left-right shunt is measured in Qp / QS. If the value is > 1, it is a left-to-right shunt (DGfK 2022).

In heart defects with a left-to-right shunt, incomplete septation dominates in the area of the atria, ventricles, truncus or a persistent botallic duct. The result is an increase in lung perfusion with a reactive increase in pulmonary vascular resistance and pulmonary hypertension (Hombach 2001).

The left-right shunt initially leads to a volume overload of all cardiac cavities and to their dilatation. The increased backflow of blood from the lungs leads to left heart failure. The dilatation of the atria can in turn lead to cardiac arrhythmia (Blum 2016).

In the pulmonary circulation, the excessive blood flow causes a dilation disorder of the lungs with a ventilation disorder of the lungs. This causes increased production of mucus in the bronchial area with increased susceptibility to infection. In the pulmonary arteries, the high pressure causes an increase in the muscular layer of the arteries, narrowing the lumen itself and resulting in pulmonary hypertension. In this case, the right ventricle must then constantly pump against increased resistance (Blum 2016).

In the final stage, the so-called Eisenmenger reaction occurs, i.e. an irreversible narrowing of the pulmonary vessels. The patient dies in the final stage due to failure of the right ventricle (Blum 2016).

The clinical picture is very variable, depending on the particular defect. There may be:

- failure to thrive in children

- Reduced performance

- Increased bronchial infections

- Signs of heart failure (Menche 2020)

Postnatal diagnostics include auscultation, ECG, chest X-ray and measurement of oxygen saturation as well as non-invasive imaging such as echocardiography, cardiac MRI and angio-CT. Invasive diagnostics include cardiac catheterization (Blum 2016).

Shunts can be assessed well by echocardiography, otherwise shunts and most congenital heart diseases can be optimally assessed by CMR (Kasper 2015).

The following complications can occur if a left-to-right shunt has been in place for a long time:

- Increasing vascular resistance and the associated increase in pressure in the pulmonary circulation (Menche 2020)

- Pulmonary sclerosis with fixed pulmonary hypertension

- In extreme cases, shunt reversal with central cyanosis and right heart failure, the so-called Eisenmenger reaction (Hombach 2001)

In patients with a congenital left-to-right shunt, all shunt connections that lead to a high pulmonary arterial pressure should be corrected around the 6th month of life, as the resistance begins to become fixed from the 12th month of life (Griese 2013).

As soon as a shunt reversal - the so-called Eisenmenger reaction - occurs, surgical correction of the heart defect is no longer possible (Menche 2020). Clinically, the Eisenmenger reaction is indicated by the loss of splitting of the 2nd heart sound, in the ECG by an increasing right heart strain. The only therapeutic option is then lung transplantation or combined heart-lung transplantation (Koletzko 2004).

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2. German Society for Cardiotechnology e. V. (DGfK) (2022) Formulary
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