A Changing Heart Murmur

A 4-year-old male, diagnosed to have a small, pressure-restrictive, perimembranous ventricular septal defect (VSD) at 11 months of age, presents to clinic for follow-up. His mother states that he is asymptomatic but is concerned about the "loud noise that his chest made." On physical exam, both height and weight are in the 95th percentile. There is a prominent precordial impulse with a palpable thrill and a grade V/VI harsh systolic ejection murmur in the left upper sternal border with radiation to the back. There are no diastolic murmurs, clicks nor gallops. Breath sounds are clear and equal. There is no hepatosplenonomegaly, with good pulses and perfusion.

Figure 1: Electrocardiogram (ECG)

Figure 1

Video 1: Parasternal Short-Axis View

Figure 2: Doppler Still Frame Across the Right Ventricular Outflow Tract (RVOT)

Figure 2

Video 2: Parasternal Long-Axis View

Video 3: Apical Right Ventricular Outflow Tract (RVOT) View With Color Doppler

Video 4: Apical LVOT View With Color Doppler

Which of the following statements describes the most likely etiology of this patient's changing murmur?

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