A 16-year-old boy is evaluated in the office due to leg cramps. He plays soccer but frequently stops in the middle of practice due to cramps in both legs. The patient is afebrile. Blood pressure is 170/90 mm Hg bilaterally in upper extremities. Point of maximal impulse is nondisplaced. S1 is normal, and S2 is physiologically split. An S4 is heard, as well as a continuous murmur best auscultated over the back at the left paravertebral area. Distal pulses in the radial arteries are prominent. Dorsalis pedis and posterior tibial pulses are difficult to palpate. The rest of the physical examination is unremarkable. Which of the following is the most likely cause of this patient's continuous murmur?
1) Increased blood flow across the tricuspid valve
2) Increased blood flow through collateral blood vessels
3) Increased cardiac output due to low systemic vascular resistance
4) Increased pulmonary arterial blood flow
5) Persistence of the ductus arteriosus