Pacemaker Rhythm Interpretation Flashcards

A CCT is reviewing an ECG strip that shows a regular vertical spike immediately preceding each P wave, followed by a normal QRS complex. The patient's heart rate is 70 bpm. Which of the following is the most accurate interpretation?

Answer: Atrial paced rhythm

This ECG demonstrates a normally functioning atrial pacemaker. The pacemaker spike initiates atrial depolarization, creating the P wave. The impulse then travels normally through the AV node and ventricles, resulting in a native QRS complex.

An ECG rhythm strip from a patient with a pacemaker shows distinct pacing spikes that are not followed by any electrical activity (neither a P wave nor a QRS complex). This finding is best described as which type of pacemaker malfunction?

Answer: Failure to capture

Failure to capture occurs when the pacemaker delivers an electrical stimulus (the spike), but the stimulus is insufficient to depolarize the myocardium. As a result, no P wave or QRS complex is generated after the spike.

Which of the following ECG findings is most characteristic of a ventricular-paced rhythm originating from a lead in the right ventricle?

Answer: A pacing spike followed by a wide QRS complex with a Left Bundle Branch Block (LBBB) morphology

When the right ventricle is paced, the depolarization spreads slowly and abnormally to the left ventricle, bypassing the normal conduction pathway. This results in a wide QRS complex (>0.12s) that typically has a Left Bundle Branch Block (LBBB) appearance.

A technician observes a rhythm strip where pacemaker spikes appear at a fixed rate, including some that fall shortly after the patient's own native QRS complexes. This indicates that the pacemaker is not recognizing the patient's intrinsic beats. What is this malfunction called?

Answer: Undersensing

Undersensing is the pacemaker's inability to 'see' or detect the patient's intrinsic cardiac activity. Because it fails to sense the native beat, it fires inappropriately, leading to competitive pacing where pacemaker spikes can occur soon after a native QRS.

A patient's ECG shows two distinct pacing spikes. The first spike is followed by a P wave, and after a short, fixed delay, a second spike appears, followed by a wide QRS complex. This pattern is consistent with which pacing mode?

Answer: Dual-chamber AV sequential pacing (DDD)

This describes AV sequential pacing, a function of a dual-chamber pacemaker. The first spike captures the atrium, and the second spike captures the ventricle after a programmed AV delay, mimicking the natural sequence of cardiac contraction.

A CCT is monitoring a patient whose pacemaker is programmed to a lower rate of 60 bpm. The patient's intrinsic heart rate drops to 50 bpm, but no pacing spikes appear on the ECG, resulting in a long pause. This scenario most likely represents which pacemaker malfunction?

Answer: Oversensing

Oversensing occurs when the pacemaker incorrectly interprets electrical signals (e.g., muscle artifact, tall T-waves, or EMI) as intrinsic cardiac activity. This false detection inhibits the pacemaker from delivering a pacing stimulus when it is actually needed, causing a pause or a rate drop.