Back to basics: what's going on here?

 Written by Pendell Meyers

A man in his 70s presented with history of pacemaker presented with shortness of breath with exertion and presyncope.

Here is his triage ECG with minimal symptoms:

What do you think?

The ECG shows pacemaker failure with inability to capture or sense, with either underlying atrial fibrillation or junctional escape rhythm. The QRS shows LVH and there are diffuse ST-T abnormalities likely in part appropriate for the LVH, though memory T waves are also a consideration.

Smith: I think this is atrial fibrillation with a very slow ventricular response.  Junctional rhythm should be fairly regular.  The QRS is not wide, so it is not a ventricular escape.

The patient was found to have a fractured lead, which was replaced successfully without complications and with resolution of symptoms.

He did well.

Smith: this can usually be seen on chest x-ray.  Here are multiple examples.

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MY Comment, by KEN GRAUER, MD (8/19/2024):

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"The patient has a pacemaker." Awareness of this information means that the emergency provided is immediately charged with assessing whether or not the device is correctly functioning.

• Given the ever increasing complexity of pacemakers (with an ever increasing array of complex new features) — determining whether the pacemaker is appropriately working is not always a simple task — especially since emergency providers are rarely privilege to knowing the parameters that the pacemaker has been programmed for.
• Adding to this challenge is the clinical reality that pacemaker troubleshooting is not a common enough problem to provide sufficient exposure to the full gamut of potential malfunctions to most non-cardiology emergency providers.
• Finally — Most of the time, the pacemaker will be working correctly. This makes recognition of occasional malfunction that much more difficult.

We've periodically reviewed cases regarding Pacemaker Troubleshooting (See the February 18, 2024 post — the January 13, 2024 post — the October 19, 2022 post — the August 3, 2022 post — the May 21, 2023 post — the June 19, 2024 post — and the November 9, 2018 post, to name a number of them).

• On many occasions when determining pacemaker function has been difficult — the problem was that pacemaker spikes were not readily evident. Suboptimal filter settings is a major reason this may occur (See My Comment in the January 13, 2024 post).

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Today's CASE:

For clarity in Figure-1 — I've reproduced today's ECG. That there is pacemaker malfunction is easy to diagnose.

• Regular pacing spikes are seen throughout ECG #1 — at a rate of ~70/minute (YELLOW lines highlighting pacer spikes in each of the leads in which they are seen — with these pacer spikes being regularly spaced at an interval of 4.3 large boxes).
• However, there is complete pacer-ventricular dissociation — in that there is no relation between pacer spikes and neighboring QRS complexes. Instead — the narrow QRS complexes continue at their inherent rate (ie, The pacemaker fails to sense and respond to native beats).
• No P wave and no QRS ever follows any of the regular pacing spikes (a result of the fractured pacing lead). Regardless of whether we are seeing atrial or ventricular spikes from the pacemaker — there is failure to capture.

Figure-1: I've added YELLOW lines for those pacer spikes that are seen.

LEARNING Points:

• If having trouble seeing pacing spikes — Check the filter settings (as per My Comment in the January 13, 2024 post). If filter settings are not optimal — then repeat the ECG at the more optimal 0.05 Hz-to-150 Hz setting.
• Overall — pacing spikes are easy to see for most beats in today's tracing. But I never would have guessed that this patient had a pacemaker if I wasn't told and if all beats looked like beat #2 in the 3 long lead rhythm strips. It is only because I saw regular pacing spikes everywhere else in each of the long lead rhythm strips, that I knew to look more closely at simultaneously-recorded lead III — which does show a subtle pacer spike (that darkens the terminal descent of the QRS in this lead).
• As is often the case — assessing pacemaker function becomes easier as soon as we can identify all pacer spikes.
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• Finally — I find it insightful (and clinically useful) to always try to determine WHY the patient has a pacemaker. As per Dr. Meyers — the underlying rhythm is either slow AFib or a junctional escape rhythm (There is a fairly-but-not-completely regular underlying bradycardic rhythm — with narrow QRS — and no P waves). Given the patient's age (in his 70s) — and an underlying rhythm of either slow AFib or slow junctional escape — the most likely reason for pacing is SSS (Sick Sinus Syndrome). It appears from ECG #1 that this patient will still need permanent pacing.

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NOTE: For nice basic reviews of pacemaker terminology, normal pacemaker function — and the more common general categories of potential pacemaker malfunction — You may find the following of interest:

• Liaquat and Alzahrani — StatPearls, 2023.
• Burns and Buttner — LITFL (Life-In-The-Fast-Lane) — in the June 4, 2021 and July 7, 2022 posts.