EMConference: Pacemaker Basics

What is pacing? When the heart does not initiate a stimulus to cause the heart to beat, the pacemaker can. If the heart beats too slow, the pacemaker kicks in and will take over. However, it is battery operated so to conserve the battery and prevent R on T phenomenon, the pacemaker only kicks in when it needs to, i.e. if the heart is not doing its job.  

Indications for permanent pacing: 

  • Sinus bradycardia 

  • AV conduction disease-usually infranodal even if symptomatic 

  • Fascicular blocks 

  • Carotid sinus disease 

  • HOCM 

  • CHF 

The chamber(s) that can be paced: 

  • Atria-usually used in people with sinus node dysfunction 

  • Ventricle-the pacing stimulus begins in the ventricle, usually used in people with atrial fibrillation 

  • Atria and Ventricle-both the atria and the ventricle can be paced, used in patients with impaired AV conduction 

  • Bi-ventricular pacing-usually used in severe heart failure for cardiac resynchronization therapy 

Pacemaker terminology:

  • Usually there are 5 letters to help identify a pacemaker type, in the ED we are more concerned about the first 3 

  • Sensing-the ability of the pacemaker to sense the native cardiac depolarization 

Letter 1 

Letter 2 

Letter 3 

Chamber paced 

Chamber sensed  

Response to sensing 














  • DDD= means both the atria and/or the ventricle can be paced, both can be sensed, and the pacemaker can trigger pacing or inhibit pacing in response to what it senses 

  • VVI= means only the ventricle is paced, only ventricular stimulus is sensed, and the pacemaker will not pace if there is inherent ventricular activity 

  • AAI=only the atrium is paced, only the atrial is sensed, and the pacemaker will not pace in response to native atrial activity  

  • VOO/DOO=the heart will pace at the set rate no matter what the native cardiac activity is 


  • EmRAP 

  • CanadianEM 

  • LITFL 

  • Radiopedia 

  • AHA 

  • EmDOCS 

  • Leclercq C. Upgrading from right ventricular pacing to biventricular pacing in pacemaker patients with chronic heart failure. Heart 2008;94:102-107. 

  • Mulpuru SK, Madhavan M, McLeod CJ, Friedman AM,  Cha M, Friedman PA. Cardiac Pacemakers: Function, Troubleshooting, and Management. Part 1 of a 2 part series. Journal of the American College of Cardiology 2017:69:189-210.