arrhythmia vs dysrhythmia

arrhythmia

noun
  • An irregular heartbeat; a lack of a regular pulse 

  • A disease entity involving such beats, such as atrial fibrillation, ventricular tachycardia, AV nodal reentrant tachycardia, or others. 

dysrhythmia

noun
  • A disturbance to an otherwise normal biological rhythm, especially that of the heart. 

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