Coarctation of the aorta and radiofemoral delay
Coarctation of the aorta is a congenital narrowing of part of the aorta, usually just beyond the left subclavian artery (the branch to the left arm).
Remember
In a young person, high arm blood pressure with weak, delayed pulses in the groin (the femoral pulses) suggests coarctation: the narrowing usually lies beyond the arm branches, so the arms sit before it with high pressure and the legs sit after it with weak, late pulses.
Memory aid
a kinked garden hose, with high pressure before the kink and a trickle after it
Picture the narrowing as the kink: pressure is high before it, in the head and arms, and only a trickle gets past it to the legs.
In coarctation of the aorta, the aorta has a congenital narrowing, usually just beyond the left subclavian artery (the branch that supplies the left arm). The narrowing is usually close to the ductus arteriosus (the foetal channel joining the aorta and the pulmonary artery).
Think of a kinked hose. Blood struggles to flow past the narrowing, so pressure builds upstream (towards the heart), in the head and arms. That gives hypertension and strong arm pulses. Beyond the narrowing, downstream (in the lower body), flow and pressure fall, so the legs have reduced perfusion.
Blood has to squeeze through the narrowed segment to reach the legs, so the femoral pulse (in the groin) arrives later and feels weaker than the radial pulse (at the wrist). Feeling both together shows radiofemoral delay, and the femoral pulses are weak, late or even absent. Poor blood supply to the leg muscles can cause claudication, which is cramping or tiredness in the legs when walking.
The aortic arch (the part of the aorta where the vessels to the head and arms arise) gives off three branches in turn: the brachiocephalic trunk (to the right arm and right side of the head), the left common carotid artery and the left subclavian artery (to the left arm). If the narrowing lies after all three, the arms are upstream and the legs downstream, so the delay is between radial and femoral pulses. If it lies between the brachiocephalic trunk and the left subclavian artery, there can also be a delay between the two radial pulses, because the left arm lies beyond it.
Mild coarctation may go unnoticed until adolescence or adulthood, so in a young person with hypertension, compare the blood pressure in all four limbs.
Key facts
- Usual site
- just beyond the left subclavian artery, near the ductus arteriosus.
- Arms
- high blood pressure and strong pulses, because they sit upstream of the narrowing.
- Legs
- they sit downstream, so the femoral pulses are weak and delayed, and poor blood supply can cause fatigue or cramping when walking (claudication).
- Key sign
- radiofemoral delay, with strong radial pulses and weak or absent femoral pulses.
- Other site
- if the narrowing lies between the brachiocephalic trunk and the left subclavian artery, there can also be a delay between the two radial pulses.
- Examination
- compare the blood pressure and pulses in all four limbs.
Exam traps
- A delay between the two radial pulses does not fit this picture. It occurs when the narrowing lies between the brachiocephalic trunk and the left subclavian artery, so the two arms differ, whereas the problem here is arms against legs.
- In coarctation, blood pressure is not higher in the legs. The pattern is reversed, because pressure upstream of the narrowing, in the arms, is high and the pressure in the legs is low.
- Bounding femoral pulses with reduced radial pulses is the opposite pattern. Coarctation typically lies beyond the vessels supplying the arms, so it weakens the pulses below it, not the pulses in the arms.
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