ECG Exercise 30 - Pacemaker Basics

Last updated 10/30/26

Below is an ECG Exercise focused on paced rhythm strips. Work through every strip with the same system:

Mode - single or dual chamber? Spikes in the atrium, ventricle, or both?
Rate - measure spike to spike (1 big box = 200 ms; 60,000 ÷ interval = ppm)
Capture - is every spike followed by a depolarization?
Sensing - do native beats inhibit the device and reset its timing?
Underlying rhythm
What to do next

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Pacemakers can only do two things: capture and sense. Almost every abnormal paced strip is a capture problem, a sensing problem, or a programmed feature doing exactly what it was designed to do.

Rhythm Strip 1

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Single or dual chamber?

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What is the rate?

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Is there capture in both chambers?

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Which of the 4 dual-chamber states is this? What is the AV delay?

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Can you assess sensing on this strip?

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Pacer Strip 1 - original schematic · See also: Kenny, Easy Tracings #3, #7, #9, #11, #17, #18, #32, #33

Rhythm Strip 2

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Where are the spikes?

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What is the rate? Is pacing above the base rate a malfunction?

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Which dual-chamber state is this? Why is there no atrial spike?

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What is the most likely indication for this pacemaker?

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If the sinus rate rose to 150, would the ventricle follow?

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Pacer Strip 2 - original schematic · See also: Kenny, Easy Tracing #16

Rhythm Strip 3

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What is the mode and rate?

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Is there capture?

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Why is this strip dangerous?

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What are the causes of loss of capture?

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ED management?

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Pacer Strip 3 - original schematic · See also: Kenny, Easy Tracings #15, #25

Strip 4

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What is wrong with the first three spikes?

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Why don't the first three spikes capture? Is this a capture problem?

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What is the risk?

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What are the causes of undersensing? What should you rule out first?

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Pacer Strip 4 - original schematic · See also: Kenny, Easy Tracings #13, #14, #21, #23

Strip 5

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Loss of capture or oversensing?

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What is the squiggly baseline?

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How can you confirm it at the bedside?

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What would this same noise do in an ICD?

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Pacer Strip 5 - original schematic · See also: Kenny, Easy Tracings #8, #10, #22

Strip 6

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Label each of the 5 complexes

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Which beats confirm capture?

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Is sensing appropriate?

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Is this a malfunction?

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Pacer Strip 6 - original schematic · See also: Kenny, Easy Tracings #6, #25, #28, #29, #34

Strip 7

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What is missing on beats 2 and 3?

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What is the most likely explanation?

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Why is it dangerous?

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How do devices prevent it?

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Pacer Strip 7 - original schematic

Strip 8

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What starts the tachycardia?

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What is the notch after the PVC and on every paced T wave?

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What is the rate of the tachycardia, and why that number?

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Explain the mechanism

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How do you treat it in the ED?

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Pacer Strip 8 - original schematic

Strip 9

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Compare the atrial rate with the ventricular rate

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What happens to the AV delay (P to ventricular spike)?

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Why does the AV delay lengthen, and why is a beat dropped?

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Is this a malfunction? What is the real ED question?

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Pacer Strip 9 - original schematic

Strip 10

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What is the atrial-to-ventricular ratio?

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Is the AV delay getting longer?

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The sensed AV delay is 200 ms and PVARP is 240 ms. At what atrial rate does 2:1 block start?

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How would this patient present, and how is it fixed?

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Pacer Strip 10 - original schematic

Strip 11

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Which chamber is being paced?

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What is the rate?

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Which dual-chamber state is this, and what does it tell you about the patient?

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Is this an AAI or a DDD pacemaker?

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Pacer Strip 11 - original schematic · See also: Kenny, Easy Tracings #1, #19, #35

Strip 12

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What is the mode and rate?

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What are the small bumps between and on the paced beats?

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Is the pacemaker malfunctioning?

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How would you check ventricular sensing in this patient?

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Pacer Strip 12 - original schematic · See also: Kenny, Easy Tracings #2, #20

Strip 13

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What is the mode and dual-chamber state?

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What goes wrong on beats 3 and 6?

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What does the absence of an escape beat tell you?

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Most likely cause and next steps?

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Pacer Strip 13 - original schematic · See also: Kenny, Easy Tracing #4

Strip 14

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What are the two tall complexes without spikes?

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Were the PVCs sensed? How can you tell?

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Is this pacemaker working properly?

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Pacer Strip 14 - original schematic · See also: Kenny, Easy Tracing #5

Strip 15

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This patient has a DDD pacemaker. Where are the spikes?

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Is the pacemaker broken?

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What can't you assess on this strip, and how would you?

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Pacer Strip 15 - original schematic · See also: Kenny, Easy Tracings #24, #31

Strip 16

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What is the underlying rhythm?

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Why is there only one paced beat?

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Does this pacemaker prevent AF with RVR?

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What two sensing problems are common in AF?

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Pacer Strip 16 - original schematic · See also: Kenny, Easy Tracings #12, #22, #30

Strip 17

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The base rate is programmed to 70. Why aren't the first three native beats (~55 bpm) paced?

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Why does pacing start where it does, and at what rate?

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Why use hysteresis? Is this a malfunction?

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Pacer Strip 17 - original schematic · See also: Kenny, Easy Tracings #14, #26

Strip 18

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Name the dual-chamber state of each beat

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Is anything wrong?

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Why did beats 5-7 conduct when beats 1-2 were ventricular paced?

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Pacer Strip 18 - original schematic · See also: Kenny, Easy Tracing #27

Pacemaker Pearls

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No spike where one should be - what are the two explanations?

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What does a magnet do?

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Differential for a regular paced tachycardia at ~120 in a DDD patient

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Memory aids

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Reference: Kenny T. The Nuts and Bolts of Paced ECG Interpretation. Wiley-Blackwell; 2009