Pacemaker Rhythm Interpretation Flashcards
6 cards from real CCT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Pacemaker Rhythm Interpretation flashcards as text
A pacemaker-dependent patient's ECG shows no pacing spikes and no intrinsic rhythm. What is the most urgent concern?
Answer: Complete pacemaker failure (failure to output) in a patient who has no escape rhythm, which is an immediately life-threatening emergency
Failure to output (no spikes despite no intrinsic rhythm) in a pacemaker-dependent patient is a cardiac emergency — without any electrical activity, the patient has no cardiac output and will rapidly deteriorate.
What is 'pacemaker syndrome,' and in which pacing mode does it most commonly occur?
Answer: Symptoms (fatigue, dizziness, pulsations in neck) caused by loss of AV synchrony, most common with VVI pacing
Pacemaker syndrome describes the hemodynamic and symptomatic consequences of AV dissociation caused by ventricular-only pacing (VVI), where the atria contract against closed AV valves, causing retrograde cannon A waves and reduced cardiac output.
On ECG, how can you distinguish a right ventricular apex pacemaker from a left ventricular pacemaker (as in CRT devices)?
Answer: RV apex pacing shows LBBB morphology in precordial leads; LV pacing shows RBBB morphology
RV apex pacing depolarizes the heart starting from the right ventricle and spreading leftward, producing a LBBB-like pattern. LV epicardial pacing (as in CRT) activates the left ventricle first, producing a RBBB-like pattern.
What is the significance of a 'pacing spike' that falls directly on a T wave in a pacemaker patient?
Answer: It represents an R-on-T phenomenon from undersensing that could theoretically induce ventricular fibrillation
A pacing spike landing on the T wave (R-on-T phenomenon) results from undersensing — the pacemaker failed to detect the preceding intrinsic QRS and therefore fired at its escape interval, which happened to coincide with the vulnerable period (T wave) of ventricular repolarization.
What is the most common reason for pacemaker oversensing, and what does it produce on ECG?
Answer: Sensing of T waves or muscle (myopotential) artifact, causing inappropriate inhibition of pacing and long pauses
Oversensing occurs when the pacemaker detects signals that are not true cardiac events (T waves, myopotentials, electromagnetic interference) and interprets them as intrinsic beats, causing it to inappropriately inhibit pacing, producing pauses.
A patient with a VVIR pacemaker programmed to 60 bpm shows QRS complexes at a rate of 80 bpm with no pacemaker spikes. What is the most likely explanation?
Answer: The patient's intrinsic heart rate (80 bpm) exceeds the pacemaker's programmed lower rate (60 bpm), appropriately inhibiting pacing
In demand (inhibited) pacing modes like VVI, if the patient's intrinsic rate exceeds the programmed lower rate, the pacemaker appropriately senses the intrinsic beats and inhibits its output. This is normal pacemaker behavior, not a malfunction.