pacemaker vs sinus node

pacemaker

noun
  • A set of nerves which stimulate the heart to beat. 

  • One who sets the pace in a race, to guide the others. 

  • A medical implement that is used to stimulate a heart to beat by simulating the action of the natural pacemaker. 

sinus node

noun
  • Synonym of sinoatrial node. 

How often have the words pacemaker and sinus node occurred in a corpus of books? (source: Google Ngram Viewer )