Pacemaker Rhythm Analysis Flashcards

A CRAT observes a rhythm strip where a pacemaker spike is visible, but it is not followed by a P wave or a QRS complex. This occurs intermittently throughout the strip. What pacemaker malfunction does this represent?

Answer: Failure to capture

Failure to capture occurs when the pacemaker delivers an electrical stimulus (the spike), but it fails to depolarize the myocardium. On the ECG, this is seen as a pacing spike that is not followed by the expected cardiac electrical activity (a P wave for atrial capture or a QRS complex for ventricular capture). [1, 3, 4]

Which of the following ECG characteristics is the hallmark of a normally functioning ventricular-paced rhythm?

Answer: A wide, bizarre QRS complex preceded by a pacing spike.

When a pacemaker stimulates the ventricle directly (typically the right ventricle), the electrical impulse spreads through the ventricular muscle in an abnormal, slower pathway, rather than the rapid His-Purkinje system. This results in a wide QRS complex (>0.12 seconds), similar in appearance to a bundle branch block or a PVC. [2, 12, 16]

A patient's intrinsic heart rate is 50 bpm. Their pacemaker is programmed with a lower rate limit of 60 bpm, but no pacing spikes are visible on the ECG strip. This observation is most consistent with which pacemaker issue?

Answer: Failure to pace (failure to fire)

Failure to pace, also called failure to fire or output failure, is the inability of the pacemaker to deliver a stimulus when it is needed. [1, 7] In this scenario, since the patient's heart rate has fallen below the programmed lower limit, the pacemaker should be firing, but the absence of pacing spikes indicates it is not delivering any output. [4, 7]

A technician is analyzing a rhythm strip and notes pacing spikes that appear at a fixed rate, with some spikes falling directly on the patient's own native QRS complexes and T waves. This indicates the pacemaker is not recognizing the patient's intrinsic rhythm. What is this malfunction called?

Answer: Undersensing

Undersensing occurs when the pacemaker fails to detect the patient's intrinsic cardiac activity (P waves or R waves). Because it doesn't 'see' the native beats, it paces asynchronously at its set rate, which can result in pacing spikes appearing inappropriately, such as within or on top of the patient's own QRS complexes. [1, 4, 7]

A patient with a DDD pacemaker has an underlying sinus bradycardia. The ECG shows a pacing spike immediately followed by a P wave, which is then followed by a second pacing spike and a wide QRS complex. This pattern repeats consistently. What is the correct interpretation?

Answer: AV sequential pacing

This pattern represents normal AV sequential pacing in a dual-chamber (DDD) pacemaker. The first spike paces the atrium because the intrinsic rate is too slow. The pacemaker then waits for a programmed AV delay. If an intrinsic QRS does not appear within that time, the pacemaker delivers a second stimulus to pace the ventricle. This ensures both atrial and ventricular contraction are synchronized. [2, 11, 13]

A CRAT notices on a patient's monitor that the pacemaker intermittently stops firing, causing long pauses, especially when the patient moves their arm or coughs. The technician suspects the pacemaker is incorrectly identifying muscle artifact as cardiac signals. This malfunction is known as:

Answer: Oversensing

Oversensing is when the pacemaker incorrectly interprets non-cardiac electrical signals (like skeletal muscle artifact, T-waves, or EMI) as intrinsic cardiac activity. This misinterpretation inhibits the pacemaker from delivering a pacing stimulus when it's actually needed, potentially leading to pauses or syncope. [1, 5, 6]