Pacemaker Rhythm Interpretation Flashcards
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Read the first 6 Pacemaker Rhythm Interpretation flashcards as text
On an ECG, what is the characteristic appearance of a pacemaker spike followed by a wide QRS complex?
Answer: A thin vertical spike immediately followed by a broad, LBBB-morphology QRS greater than 0.12 seconds
Ventricular paced beats produce a sharp spike (the pacemaker stimulus artifact) immediately followed by a wide QRS complex resembling LBBB morphology, because ventricular activation spreads cell-to-cell rather than via the His-Purkinje system.
What is pacemaker failure to capture?
Answer: The pacemaker fires (spike visible) but does not depolarize the myocardium (no QRS follows)
Failure to capture occurs when a pacemaker spike is visible on the ECG but is not followed by a QRS complex (or P wave for atrial pacing), meaning the electrical stimulus failed to depolarize the myocardium.
What does the middle letter in a three-letter pacemaker code represent? (e.g., DDD, VVI, VDD)
Answer: The chamber sensed by the pacemaker
In the NBG pacemaker code (first three letters), the first letter indicates the chamber paced, the second letter indicates the chamber sensed, and the third letter indicates the response to sensing (I=inhibited, T=triggered, D=dual).
A patient with a DDD pacemaker shows pacing spikes before both P waves and QRS complexes on the ECG. What pacemaker mode is currently functioning?
Answer: AV sequential (DDD) pacing — both atrium and ventricle are being paced
Visible pacing spikes before both P waves and QRS complexes confirms that both the atrium and ventricle are being paced sequentially (DDD or DOO mode), which is the most physiologic form of pacing.
What is undersensing in a pacemaker, and what ECG pattern does it produce?
Answer: The pacemaker fails to detect intrinsic cardiac activity and fires at inappropriate times, producing spikes that may fall on T waves
Undersensing means the pacemaker's sensing circuit fails to detect the patient's own heartbeats, so it fires according to its escape interval as if no intrinsic beat occurred, potentially producing spikes falling on T waves (R-on-T phenomenon).
Which pacemaker code indicates rate-responsive pacing?
Answer: A fifth letter 'R' added after the standard three-letter code, as in DDDR or VVIR
Rate-responsive pacing is indicated by the letter 'R' as the fourth position in the NBG code (e.g., DDDR, VVIR, AAIR), indicating the pacemaker can vary its rate in response to physiologic demand (activity, minute ventilation, etc.).