Pathophysiology
Summary
Left-to-right shunts such as ventricular septal defect (VSD), atrial septal defect (ASD), and patent ductus arteriosus (PDA) allow oxygen-rich blood to mix with deoxygenated blood. This mixing culminates in increased O2 saturation in the right chambers of the heart. Over time, these shunts can give rise to pulmonary artery hypertension (PAH), an escalating condition that may evolve into Eisenmenger syndrome. In this syndrome, the original left-to-right shunt inverts to a right-to-left orientation, ushering in late-onset cyanosis.
Clinical presentation of VSDs depends on their size. While a small VSD typically manifests as a systolic ejection murmur or a holosystolic murmur, remaining largely asymptomatic, a sizable VSD paints a graver picture. It can trigger heart failure, impede growth leading to failure to thrive, and cause excessive sweating during feeding.
The etiology of ASD is bound to the development of the cardiac septum. The condition emerges from the incomplete formation of the septum secundum, or when the septum secundum fails to fully overlay the ostium secundum in the septum primum. Clinically, ASD can be recognized by certain characteristic signs: a systolic murmur, a distinct wide fixed splitting of the S2 heart sound, and a diastolic rumble due to increased flow across the tricuspid valve.
Additionally, an intriguing clinical phenomenon related to ASD and the patent foramen ovale (PFO)—resulting from the incomplete fusion of the septum primum with the septum secundum—is the ability for blood flow to reverse under specific conditions. This reversal, especially when augmented by actions like Valsalva, can shepherd a paradoxical embolism into the systemic circulation, causing a cryptogenic stroke. Cardiac echo in PFO reveals a positive bubble study.
Patent ductus arteriosus (PDA) may be kept open by placental prostaglandin E2 and manifests with a continuous ‘machine-like' murmur. It can be closed using indomethacin, an NSAID that blocks prostaglandin production. Endocarditis can occur due to PDA and other left-to-right shunts, although it is uncommon in the case of ASD.
Coarctation of the aorta causes a narrowing of the descending aorta and is associated with Turner syndrome and bicuspid aortic valves. Severe coarctation can result in cyanosis in the lower extremities, and ultimately heart failure. It can also lead to hypertension increases the risk of aortic dissection and hemorrhagic stroke. Clinically, it may present with a blood pressure discrepancy between the upper and lower extremities, lower extremity claudication, and inferior ‘rib notching’ on chest X-ray.
Lesson Outline
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FAQs
Left-to-right shunts such as ventricular septal defect (VSD), atrial septal defect (ASD), and patent ductus arteriosus (PDA) elevate oxygen saturation levels in the right chambers of the heart. This occurs due to the diversion of oxygenated blood from the left side to the right side, thus enriching the right heart's oxygen content.
Untreated left-to-right shunts may lead to pulmonary artery hypertension (PAH). Over time, chronic PAH can induce remodeling of the pulmonary vasculature, elevating resistance. Eventually, this increased resistance can reverse the shunt flow from left-to-right to right-to-left, resulting in systemic circulation of deoxygenated blood, a condition known as Eisenmenger syndrome.
A small VSD often remains asymptomatic but may manifest through audible cardiac sounds. Specifically, a systolic ejection murmur or a holosystolic murmur can be detected during cardiovascular examination.
Reversal of flow in an atrial septal defect (ASD) or patent foramen ovale (PFO) can lead to severe complications, such as paradoxical embolism. This condition allows venous clots or particles to enter the systemic circulation, posing a risk for cryptogenic stroke.
Coarctation of the aorta can result in hypertension, heart failure, and blood pressure discrepancy between the upper and lower extremities. Additional signs may include delayed lower extremity pulses and lower extremity claudication. Severe cases can cause cyanosis in the lower extremities and may display inferior "rib notching" on a chest X-ray due to collateral circulation. Aortic coarctation can associated with a bicuspid aortic valve.
