CONTENTS

This differential diagnosis applies to wide-complex ECGs (>120 ms) of supraventricular origin. The differential diagnosis includes the following entities:

• Initial considerations
• Differential diagnosis:
  • Abnormal P-waves:
    • WPW
    • AIVR or slow VT
  • Hyperkalemia
  • Hypothermia
  • MI with pseudo-wide QRS
  • RBBB or sodium-channel blocker
  • LBBB or LVH
  • IVCD

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initial considerations when approaching wide complex ECG

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causes of QRS >200 ms

• Hyperkalemia.
• Acidosis.
• Sodium channel blocker toxicity.
• Shark-fin (STE with hyperacute T-wave that seems to widen the QRS complex).
• Ventricular tachycardia.

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causes of wide QRS complex

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WPW (aka, preexcitation)

• i) Delta-wave
• ii) PR interval short (<120 ms)

AIVR or slow VT

• Make sure there are P-waves.
• (Note, however, that hyperkalemia can cause wide complexes and absent P-waves)

hyperkalemia

clues suggesting hyperkalemia 📖

• [1] Extremely prolonged QRS (e.g., >200 ms).
• [2] Relatively peaked T-waves are usually the most helpful clue:
  • Wide-complex ECGs usually have broad T-waves.
  • Hyperkalemia may cause “relative peaking” of the T-waves, which is contrary to what would be expected given the prolongation of the QRS complex.
• [3] High-amplitude T-waves (>10 mm) may also be seen.

additional features of hyperkalemia may include:

• 🔑  Bradycardia, blocks, and/or pauses.
• 🔑  Infarct mimic (STE in V1-V2; often triangular STE diving into TWI).
• 🔑 Terminal right axis deviation (large S-I +/- S-V6; RSR' in V1).

hypothermia 📖

• All intervals prolonged
• Osborne wave

MI with pseudo-wide QRS

ST segment changes can mimic a wide QRS complex because the ST deviation makes it challenging to determine where the QRS complex ends.  The key clue here is that the QRS complex may look relatively narrow in some leads but broad in others.  To interpret the ECG, find a lead where the QRS complex seems relatively well-defined.  Drop a line from the end of that QRS complex down to the rhythm strip at the bottom of the ECG to time-stamp the end of the QRS complex.

occlusive MI with pseudo-QRS prolongation

• Bundle-branch block plus occlusive MI generates a huge jumbled QRS complex.
• Key characteristics:
  • (1) It can resemble a “shark fin” – a distinctive morphology that should be recognized.
  • (2) Often, one lead where QRS is narrower than other leads can help sort this out from hyperkalemia (which may look somewhat similar, but in hyperkalemia, all the QRS complexes are large).

RBBB or sodium-channel blocker

discussed further here: 📖

LBBB vs. LVH

discussed further here: 📖

IVCD (diagnosis of exclusion)

diagnostic criteria for IVCD

• [1] QRS >120 ms.
• [2] None of the above diagnoses.

interpretation of the remainder of the ECG

• Intervals:
  • PR reduction: re-consider WPW.
  • QT will usually be prolonged.
• Axis: variable, depending on IVCD.
• Chamber:
  • Atria are unaffected.
  • LVH is probably present if an S-wave >35-30 is seen in any precordial lead.
• Morphology:
  • Limited interpretability.

causes of IVCD may include:

• Antiarrhythmic medications (especially IA and IC agents).
• Hyperkalemia.
• Hypothermia.
• Metabolic abnormalities.
• LVH.
• Cardiomyopathy. (O'Keefe 2021)

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questions & discussion

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