The Case
A 96-year-old female with a history of coronary artery disease, hypertension, and complete heart block status post dual-chamber pacemaker (remote) presents to the ED by EMS with generalized weakness and lethargy.
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EKG Characteristics
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Rate
130
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Rhythm
Wide Complex Tachycardia, Paced
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Intervals
QRS 180, QT/QTc 406/596
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Axis
Left axis deviation
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ST Segments
Non-specific
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Additional Features
Paced Rhythm with LBBB morphology
Diagnosis
Pacemaker-Mediated Tachycardia
Questions
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What is the differential diagnosis for these ECG findings?
Pacemaker Associated Tachycardia, Rapidly-Sensed Atrial Rate (with underlying atrial tachycardia), Ventricular Arrhythmia
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What is the next best step in evaluating this patient?
Applying a magnet to the pacemaker inhibits its ability to sense atrial rhythms and reverts it to an asynchronous pacing mode. Terminating the tachycardia by applying a magnet suggests a pacemaker-mediated tachycardia and further pacemaker interrogation and evaluation should occur. If there is no change with the magnet application, an underlying arrhythmia is likely present, and standard ACLS algorithms should be applied.
Discussion
Discussion:
Pacemaker-mediated tachycardia is typically caused by atrial sensing of a ventricular impulse through a retrograde AV node or a re-entrant pathway. Other forms of pacemaker-mediated tachycardia include sensor-induced tachycardia caused by malfunctioning physiologic sensors, which normally increase the pacemaker rate based on underlying physiologic parameters. Consider a pacemaker-mediated tachycardia when a patient presents with a regular, paced tachycardia at or around 130 bpm, a standard upper limit of pacemaker rate. P-waves are typically absent. This rhythm will be terminated with magnet application.
A pacemaker-mediated tachycardia’s primary differential diagnosis includes a rapidly-sense atrial rate, which occurs when any (native) atrial tachycardia (sinus tachycardia, atrial fibrillation, etc.) results in rapid ventricular pacing. The ECG will demonstrate a native atrial rhythm with a paced ventricular rhythm. In this situation, non-paced P-waves are likely to be present.
Consider secondary/physiologic etiologies of tachycardia (infection, dehydration, bleeding, embolism, substance use/withdrawal) in addition to underlying atrial arrhythmias. This rhythm will not result in cessation with magnet application.
ED Course:
The patient presented mild hypotension but was alert without signs of respiratory distress and a reassuring perfusion exam.
EKG initially showed a ventricular paced rhythm at 130 with expected left-bundle branch block morphology and no evidence of ischemia per Modified Sgarbossa’s criteria.
The chest X-ray demonstrated normal pacemaker lead placement with mild pulmonary edema. The patient was connected to Zoll Pads, a magnet was obtained, and Electrophysiology was consulted.
During EP evaluation, the patient’s rhythm reverted to her baseline, paced rhythm without intervention.
EP interrogated the device, which determined that an inappropriate rate response parameter, likely related to the battery replacement three days prior, confirming a sensor-induced pacemaker-mediated tachycardia.
The patient was ultimately admitted, treated with gentle diuretics, and underwent re-programming of her pacemaker.
Pearls
- Consider pacemaker-mediated tachycardia in patients presenting with paced, wide-complex tachycardia, especially when the rate remains constant at 130, the typical upper limit of pacemaker settings.
- Magnet application can differentiate pacemaker-mediated tachycardia from a rapidly sensed atrial rate by reverting the pacemaker to an asynchronous pacing mode.