Male patient with chest pain and wide complex rhythm

EMS is called to the residence of a 78 year old male.

It’s the middle of the night. The patient’s spouse meets you at the front door and brings you back to the bedroom.

The patient is sitting on the edge of his bed. He is highly anxious and complaining of chest discomfort and palpitations.

  • Onset: During sleep
  • Provoke: Running made the sensation feel better earlier the previous day
  • Quality: An “electric” sort of “full” feeling in his chest
  • Radiate: The sensation does not radiate
  • Severity: 5/10
  • Time: Started earlier the previous day but went away after running

The patient takes several deep breaths during EMS evaluation and seems upset that it doesn’t correct the problem.

Skin is pink, warm, and moist.

Breath sounds are clear bilaterally.

Vital signs are assessed.

  • HR: 100
  • RR: 20
  • NIBP: 160/98
  • SpO2: 98% on RA
  • Temp: 98.4 F / 36.9 C

The cardiac monitor is attached.


A 12-lead ECG is obtained.


And another.


What’s going on here? The computerized interpretation says “Ventricular pre-excitation, WPW pattern type B”. Is that possible?

No, this is just a typical ventricular paced rhythm (with the pacing lead in the apex of the right ventricle). To me, this falls into the list of reasons why “axis matters.”

Whenever you see a wide complex rhythm with left bundle branch block morphology in lead V1 and left axis deviation, you should consider the possibility of paced rhythm. Sometimes, as in this case, you will also see negative concordance of QRS complexes in the precordial leads (all of the QRS complexes are negatively deflected).

I have noticed on many occasions that inability to recognize a paced rhythm can lead to incorrect interpretations of the 12-lead ECG. That’s why it’s important to look (and feel) for a pacemaker when you do your physical exam!

You do perform a physical exam, right? (Say yes.)

Undressing your patients from the waist up (while preserving their dignity) helps with proper lead placement, reveals surgical scars and implantable medical devices, and allows you to assess breath sounds more accurately.

When you suspect the possibility of a ventricular paced rhythm you should scrutinize leads V3-V5 for pacer spikes.

This makes sense when you think about it because these leads are in close proximity to the apex of the right ventricle. One of the few drawbacks to setting the high frequency / low pass filter to 40 Hz (from 150 Hz) is that it makes pacing spikes more difficult to appreciate.


This case is also a nice example of appropriate T-wave discordance. In other words, generally speaking, the T-waves are deflected opposite the majority of the QRS complex, which suggests a secondary ST/T-wave abnormality (as opposed to the primary ST/T-wave abnormalities of ischemia or acute injury).

Since all of the precordial leads show negative QRS complexes, let’s arrange them smallest to largest and see if we notice anything.

paced_t-wave_discordance wm

See how the T-waves gets larger as the S-wave get deeper? This is the rule of proportionality, which states that repolarization is proportional to depolarization.

This patient may be suffering ACS but the ECG does not meet Sgarbossa’s criteria to identify acute STEMI in the presence of left bundle branch block or paced rhythm.

Further reading

Identifying Acute STEMI in the Presence of Paced Rhythm

Making Sense of Sgarbossa’s Criteria – Chest Pain and Left Bundle Branch Block


  • Saleh Awdaly says:

    Very nice case, hits more than one important point such a pacemaker manifestation and detection, diagnosis of IHD in the presence of LBBB and pacemaker . Regarding this case the proportion between negative R and positive T waves is quite enough to exclude the possibility of myocardial infarction, because in in myocardial infarction this proportion is probably lost and the R waves or opposite S waves become shorter or at least the T waves becoming taller than preceding waves ,moreover a further confirm by biomarkers is mandatory and serial ECGs .

  • Saleh Awdaly says:

    In addition to the above mentioned points the best method to detect the pacemaker spikes is by moving the ECG electroides little bit down ?!
    Thank you for your nice case .

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