45. Embryopathies. Cardiovascular system malformations.

Embryopathies. Cardiovascular system malformations

Embryopathies occur within the period of 16-75 days following fertilisation. Congenital heart diseases account for 20-30% of all birth defect.

Most diseases arise from faulty embryogenesis during weeks 3-8 when most cardiovascular structures develop. Causes are often environmental, teratogens and genetic factors. The formation of the cardiovascular system is a complex series of steps with multiple genes involved, including Wnt factor, vascular endothelial growth factor, bone morphogenetic protein, transforming growth factor beta, fibroblast growth factor and notch pathways. The miscoding of any of these factors will cause CVS errors.

Malformations are divided into three categories based on their properties:

1. 1. Malformations causing left to right shunt
2. 2. Malformations causing right to left shunt
3. 3. Malformations causing obstruction

Left to right shunt

• Results in increased pulmonary blood flow. Such exposure of the low-pressure, low-resistance pulmonary circulation to the increased pressures and volumes of the left to right shunt causes lung vasculature to increase resistance in an attempt to protect itself, which in turn resulting in right ventricular hypertrophy and eventually failure
• These are the most common type of malformation and include
• Atrial septal defects (a defect in the atrial septum, most often of the secundum type)
• Ventricular septal defects
• Patent ductus arteriosus

Right to left shunt

• Causes cyanosis as a result of decreased pulmonary circulation
• This decreased pulmonary circulation causes decreased blood oxygen levels

Tetralogy of Fallot, the most common cyanotic (right-to-left) defect: pulmonary stenosis, VSD, overriding aorta, right ventricular hypertrophy.

Image: “Tetralogy of Fallot” by Mariana Ruiz LadyofHats, Public domain, via Wikimedia Commons.

Mnemonic: the right-to-left (cyanotic) defects are the 5 Ts: Tetralogy of Fallot, Transposition of the great arteries, Truncus arteriosus, Tricuspid atresia, Total anomalous pulmonary venous return. A long-standing left-to-right shunt can also reverse once pulmonary resistance exceeds systemic, giving late cyanosis (Eisenmenger syndrome).

Obstruct vascular flow

• Narrowing of the chambers, valves or major blood vessels
• Generally increases pressure proximal to the obstruction and depending on the extent of obstruction can cause ischemia

Example: coarctation of the aorta, a narrowing usually near the ductus arteriosus, gives high blood pressure in the arms with weak, delayed femoral pulses and low pressure in the legs. Other obstructive defects: pulmonary stenosis and aortic valve stenosis or atresia.