CCT Pacemaker Rhythm Interpretation 2

Question 1

On an ECG, what is the characteristic appearance of a pacemaker spike followed by a wide QRS complex?

Accepted Answer

A thin vertical spike immediately followed by a broad, LBBB-morphology QRS greater than 0.12 seconds

Answer

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.

Question 2

What is pacemaker failure to capture?

Accepted Answer

The pacemaker fires (spike visible) but does not depolarize the myocardium (no QRS follows)

Answer

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.

Question 3

What does the middle letter in a three-letter pacemaker code represent? (e.g., DDD, VVI, VDD)

Accepted Answer

The chamber sensed by the pacemaker

Answer

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).

Question 4

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?

Accepted Answer

AV sequential (DDD) pacing — both atrium and ventricle are being paced

Answer

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.

Question 5

What is undersensing in a pacemaker, and what ECG pattern does it produce?

Accepted Answer

The pacemaker fails to detect intrinsic cardiac activity and fires at inappropriate times, producing spikes that may fall on T waves

Answer

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).

CCT - Certified Cardiographic Technician Exam Practice Test

CCT - Certified Cardiographic Technician Exam Practice Test

CCT Pacemaker Rhythm Interpretation 2