Pacing Spikes Without Capture After Pacemaker Insertion
A 79-year-old woman received a dual-chamber pacemaker 6 hours ago for complete AV block. Telemetry shows atrial pacing spikes at 70/min followed by P waves, and ventricular pacing spikes at 70/min with no QRS complex after most spikes; the underlying ventricular escape rhythm is 34 beats/min and wide. She is drowsy, blood pressure is 92/54 mmHg, and her extremities are cool. Her respiratory rate is 22/min and SpO2 is 93% on room air. The technician notes that the patient has been shivering since returning from the procedure and that the monitor has been beeping frequently. The pacemaker programmer is not on the unit, and the nurse is on the phone with the physician. The technician must decide whether the rhythm represents failure to capture or undersensing, and whether to activate a rapid response.
1. Differentiate failure to capture from undersensing and from oversensing using the strip findings described.
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Failure to capture: a pacing spike is delivered but does not produce a depolarization. Here the ventricular pacing spikes occur at 70/min and are followed by no QRS complex, which is failure to capture. The atrial spikes do capture because each is followed by a P wave.
Undersensing: the pacemaker fails to see intrinsic activity and therefore delivers a spike when it should have been inhibited. The spike would fall within or immediately after an intrinsic P or QRS. That is not the pattern here; the ventricular spikes are not falling on intrinsic ventricular beats.
Oversensing: the pacemaker senses non-cardiac signals (muscle artifact, shivering, lead noise) and inappropriately inhibits pacing, producing pauses. Here the ventricular spikes are present at the programmed rate, so oversensing is not the primary problem.
Caveat about shivering: shivering can create artifact that mimics pacing spikes or QRS complexes. Confirm that the spikes are true by checking multiple leads and looking for sharp, vertical, simultaneous spikes. True failure to capture is a clinical emergency when the patient is symptomatic and the underlying escape rate is only 34/min.
2. State your immediate actions and escalation, and explain why shivering matters for both the patient and the monitor.
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Immediate actions:
- Stay with the patient and assess airway, breathing, circulation, mental status, and blood pressure.
- Activate the rapid response team: the patient is symptomatic (drowsy, hypotensive, cool) with a bradycardic escape rhythm and failure to capture.
- Apply defibrillator pads and prepare for transcutaneous pacing; ensure IV access and continuous pulse oximetry.
- Check the pacemaker connections, dressing, and cables; notify cardiology and the device representative. Do not reprogram the device without a programmer and an order.
- Document the time, programmed rate, capture status, underlying rhythm, and interventions.
Why shivering matters:
- It increases oxygen consumption and cardiac workload in a patient who is already hypotensive and bradycardic.
- It can be a sign of hypothermia, sepsis, or a transfusion reaction, so the cause needs evaluation.
- Muscle artifact can mimic pacing spikes or QRS complexes and can confuse the monitor's rhythm analysis; verify the tracing in multiple leads and treat the patient, not the alarm.
3. What monitoring parameters would you prioritize over the next hour, and what changes would prompt you to escalate again?
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Priorities:
- Continuous ECG with beat-by-beat attention to each pacing spike and the presence of capture (P after atrial spike, QRS after ventricular spike).
- Underlying escape rhythm and rate; a falling escape rate is an emergency.
- Blood pressure every 5 minutes, SpO2, respiratory rate, mental status, skin temperature, and urine output.
- Temperature and signs of shivering or infection.
- Documented device settings if the programmer arrives, and a repeat 12-lead ECG.
Escalate again if:
- Capture disappears entirely or the underlying ventricular rate falls below 30/min.
- Systolic blood pressure falls further or the patient becomes unresponsive.
- The rhythm degenerates into ventricular tachycardia or fibrillation.
- Transcutaneous pacing becomes necessary because the device is not capturing.
- Chest pain, worsening dyspnea, or a new arrhythmia appears.
The technician's role is continuous surveillance and timely communication; the decision to reprogram or revise the lead belongs to the clinician.