A 12-year-old boy presents with a heart murmur detected on routine examination. Vital signs show BP 110/72 mmHg, HR 88 bpm, RR 18/min, temperature 37°C, and SpO2 98% on room air. Physical examination reveals a fixed split S2 that does not vary with respiration. Chest X-ray shows mild cardiomegaly. Transthoracic echocardiography confirms a secundum atrial septal defect with a 15-mm defect size and normal left ventricular function. He denies dyspnea on exertion. Which mechanism best explains the fixed splitting of S2?
- A)Right ventricular stroke volume remains persistently increased throughout the respiratory cycleGABARITO
- B)Inspiration equally increases both left and right ventricular filling
- C)Pulmonic valve closure is fixed early because pulmonary artery pressure is low
- D)The aortic valve closes late due to left ventricular outflow obstruction
- E)The murmur is generated by turbulence across the septal defect itself
Explicação
In an ASD, left to right shunting causes chronically increased right ventricular filling and a persistently prolonged right ventricular ejection time. Because the right sided volume load remains elevated regardless of respiratory phase, splitting of S2 becomes... Ver explicação completa e trilha adaptativa →