Learn EP · Lesson 5 of 6
Pacing Fundamentals
Programmed stimulation lets the EP team ask controlled questions about capture, conduction, refractoriness and tachycardia behavior.
Core language
Drive trainA sequence of paced beats at a defined cycle length used to establish a controlled rhythm state.
ExtrastimulusAn additional paced stimulus introduced at a chosen coupling interval after the drive train.
CaptureThe pacing stimulus successfully depolarizes the intended myocardium.
RefractorinessA tissue may fail to respond when a stimulus arrives while it is not yet excitable.
What to watch after every paced beat
Did it capture?
Confirm the tissue actually responded to the stimulus.
Where did it go?
Compare activation sequence across intracardiac and surface channels.
What changed?
Look for delay, block, pathway changes, initiation or termination of tachycardia.
Important: Advanced EP pacing maneuvers are not cookbook algorithms. Their diagnostic value depends on the exact pacing site, timing, tachycardia mechanism and complete intracardiac context.
Learning objectives
RecognizeUnderstand drive trains, extrastimuli, coupling intervals and capture.
ObserveTrack what changes in conduction as stimulus timing changes.
Think mechanisticallyTreat pacing as a controlled question rather than a memorized maneuver.
Pacing logic: stimulus → response
Every paced beat has a chain of questions:
Did the stimulus capture? → Which tissue activated first? → What was the activation sequence? → Did conduction time change? → Was there block, pathway change, initiation or termination?
Did the stimulus capture? → Which tissue activated first? → What was the activation sequence? → Did conduction time change? → Was there block, pathway change, initiation or termination?
Pacing checkpoint
Question 1
A pacing spike is visible, but there is no local depolarization immediately following it. What should you consider first?
Question 2
Why are progressively earlier extrastimuli useful during programmed stimulation?
Trusted resources
Heart Rhythm Society — EP Lab Standards
Laboratory processes, protocols, equipment, personnel, safety and quality.
Open HRS resource →
Laboratory processes, protocols, equipment, personnel, safety and quality.
Open HRS resource →
ESC/EHRA — Heart Rhythm learning references
Recommended reading and competency topics for invasive electrophysiology.
Open ESC resource →
Recommended reading and competency topics for invasive electrophysiology.
Open ESC resource →
Educational scope: This lesson explains foundational concepts. It does not teach independent performance or interpretation of invasive EP procedures. Follow institutional training, current professional guidance, and manufacturer instructions.
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