The heart becomes the complex organ we are familiar with from a fairly simple starting point in the developing embryo. As myocardial development continues the heart begins to loop taking on an ‘S’ shape. The septa partition the atria and ventricles from each other and develop simultaneously in the normal heart. Some of the key stages of development can be seen in Fig. 9.1.

As the heart develops one can acquire various congenital defects that vary in incidence and severity. Some of the most common are described here (Table 9.1).

The function of fossa ovalis has been discussed in Chap. 1. To recap: The fossa ovalis is the remains of what was once a hole (foramen) that existed between the left atrium and the right atrium, located in the atrial septum (Fig. 9.2). This hole allows blood to bypass the lungs in a developing fetus when fetal oxygen supply is provided via the placenta, as the fetal lungs are undeveloped. In some cases the fossa ovalis fails to close and can allow blood to pass from the right to left atrium, this can be due to increased intrathoracic pressure, resulting from coughing, sneezing or trying to pass stool. This condition is referred to as a Patent Foramen Ovale or PFO. A PFO can lead to a stroke or heart attack if a clot passes from the right to left atrium.

The ductus arteriosus connects the aorta and pulmonary artery (Fig. 9.3). Pressure forces blood from the aorta to the pulmonary artery as aortic pressure is higher than pulmonary pressure. This in turn increases blood flow through the left side of the heart. This can cause left atrial abnormality and/or left ventricular hypertrophy. An increase in PR interval can also sometimes be seen on the ECG, although rarely seen with adults. Large PDA’s can manifest as biventricular hypertrophy on the ECG. In contrast if the PDA is small the ECG could be completely normal.

Is a rare congenital condition that encompasses several cardiac defects, including: narrowing of the pulmonary trunk, pulmonary valve stenosis, ventricular septal defect and the aorta being positioned directly over the ventricular septal defect, often termed an overriding aorta. The principal problems associated with tetralogy of Fallot arise due to the pulmonary stenosis and ventricular septal defect (see Fig. 9.4).

Most cases are picked up when a baby is born. Low blood oxygen levels can cause the newborn to appear cyanosed, an echocardiogram usually confirms the condition. Surgery in the form of a major repair operation is often used to correct this condition with a good statistical outcome. As the child grows following surgery there will be a degree of pulmonary regurgitation as blood passes back into the right ventricle, due to the abnormal pulmonary valve that doesn’t close properly. Over time this can lead to right ventricular hypertrophy. Tetralogy of Fallot can also be associated with Down’s syndrome and a syndrome called 22q11 deletion. The ECG findings of tetralogy of Fallot can include right axis deviation, voltage criteria for right ventricular hypertrophy and dominant R waves in the precordial leads.

Is a congenital defect in the interatrial septum separating the left and right atrium. This defect allows blood to flow between the two chambers. The mixing of oxygenated and deoxygenated blood can lower the oxygen levels in arterial blood. There are different subcategories of ASD, including, PFO, Ostium primum and ostium secundum atrial septal defects (Fig. 9.5); ostium secundum is the most common type of ASD and may show right axis deviation, whereas an ostium primum shows a left axis deviation. A complete or incomplete right bundle branch block is usually seen with ASD’s.