EP 101

Back to Basics: Deciphering Pacemaker ECGs

Christine Chiu-Man, MSc

Christine Chiu-Man, MSc

Oftentimes, the first sign of pacemaker malfunction is shown on the electrocardiogram (ECG). Yet, the interpretation of pacemaker ECG can be daunting, as one needs to be familiar with timing cycles and the manufacturer-specific programmable features of the device. A pacemaker electrocardiogram includes rhythm assessment from the 12-lead ECG, Holter, event recorder, or stress exercise testing. The purpose of the assessment is to find out if the pacemaker is sensing and capturing, as well as if the programmed settings are appropriate for the patient.

Similar to arrhythmia interpretation, a systematic approach should be used when deciphering pacemaker ECGs. We need to know the basics of pacemaker timing cycles for single- and dual-chamber pacing. We should have a list of differential diagnoses that we work through on the rhythm strip. Table 1 shows the four basic rules that we can use to navigate through a pacemaker ECG. Table 2 provides some examples of pacemaker features that will show changes in the pacemaker timing cycle. The best way to learn is to practice. Figure 1 is a practice ECG — take a look and see if there is pacemaker malfunction such as a sensing or capture problem.

Disclosure: The author has no conflicts of interest to report regarding the content herein.   


  1. Chiu-Man C, Nygren A, de Souza L. Chapter 3.3: Pacemaker timing cycles, programming, and troubleshooting. In: Tsiperfal A, Ottoboni L, Beheiry S, Al-Ahmed A, Natale A, Wang P. Cardiac Arrhythmia Management: A Practical Guide for Nurses and Allied Professionals. Wiley-Blackwell. 2011. Pages 181-230.