Differential Diagnosis
- Single most likely diagnosis:
- The patient's symptoms, including a loud, narrowly split S2, a grade 2/6 early to mid-systolic murmur over the lower left sternal border, right ventricular hypertrophy on ECG, and an oxygen saturation of 93%, are most consistent with Atrial Septal Defect (ASD). The increased flow through the pulmonary valve due to the left-to-right shunt in ASD leads to an increase in pulmonary vascular resistance over time, which is the most likely mechanism of this patient's condition.
- Other Likely diagnoses:
- Ventricular Septal Defect (VSD): Similar to ASD, VSD can cause a left-to-right shunt, leading to increased pulmonary blood flow and potentially elevated pulmonary vascular resistance. However, the clinical presentation and the specific murmur's location and characteristics might differ.
- Patent Ductus Arteriosus (PDA): This condition involves the failure of the ductus arteriosus to close after birth, leading to a left-to-right shunt from the aorta to the pulmonary artery. It can also increase pulmonary vascular resistance but typically presents with a continuous murmur ("machinery" murmur) best heard at the left upper sternal border.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
- Eisenmenger Syndrome: Although less likely given the patient's current age and the fact that she has not shown more severe symptoms, Eisenmenger Syndrome is a condition where a long-standing left-to-right shunt (from conditions like VSD, ASD, or PDA) reverses to become a right-to-left shunt due to elevated pulmonary vascular resistance. This would lead to cyanosis and significant morbidity. Early detection and management of the underlying defect can prevent this outcome.
- Rare diagnoses:
- Total Anomalous Pulmonary Venous Connection (TAPVC): A rare congenital heart defect where all four pulmonary veins are malpositioned and make anomalous connections to the systemic venous circulation. This condition often presents with severe respiratory distress and cyanosis in infancy.
- Truncus Arteriosus: A rare congenital heart defect where a single blood vessel comes out of the heart, instead of the usual two separate vessels, leading to both ventricles pumping blood into this common vessel. It often presents with symptoms of heart failure and a harsh systolic ejection murmur.
The key to this question is recognizing the signs that point towards an increase in pulmonary vascular resistance as the most likely mechanism, given the clinical presentation and the effects of long-standing left-to-right shunt lesions on the pulmonary vasculature.