Lacking a cause, worried about pulse? (8)
I believe the answer is:
resonate
'pulse?' is the definition.
(thesaurus)
'lacking a cause worried' is the wordplay.
'lacking' indicates named letters should be taken away.
'cause' becomes 'reason' (I've seen this before).
'worried' becomes 'ate' (something worrying may eat someone up).
'reason' with 'a' removed is 'reson'.
'reson'+'ate'='RESONATE'
'about' is the link.
(Other definitions for resonate that I've seen before include "Echo" , "Resound" , "provide vibrant sounds" , "Vibrate at the same frequency" , "Sound deeply and clearly" .)