Crossword Genius

Frontrunner from UN maybe lacking empathy at first (9)

Ross

I believe the answer is:

pacemaker

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'frontrunner' is the definition.
(a pacemaker runs at the front)

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for pacemaker that I've seen before include "Device inserted into chest to stimulate heart" , "Heart patient's aid" , "Electrical device put in heart to stimulate pulse" , "Device inserted in body to strengthen heartbeat" , "Implanted device to control the heartbeat" .)

I've seen this clue in The Times.
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