ECG Exigency 013
Before you can wonder any longer whether this Midsummer Night’s Dream, a Friday night in ED, is about to become a Tempest, the nurse pokes his ECG in front of you.
You feel pretty smart because you have just read up about Super Axis Man (SAM). So you say (insert posh voice here):
You get strange looks from the nurse, so you confidently tell him,
The nurse, still bewildered about your comments on touching an ECG, and wondering about the method in your madness, says
Bah you think — the nurse doth protest too much. But you humor him.
Barely conscious, the patient, gasping, looks at you and says…
Q1. What is the definition of wide complex tachycadia?
- The QRS-complex needs to be wide. Wide is >120ms (or >3 small squares).
- The patient needs to be tachycardic, >100/min.
The differential diagnosis in WCT includes ventricular tachycardia (VT), supraventricular tachycardia (SVT) with aberrancy and pacemaker rhythms.
Q2. What clinical features help differentiate VT from SVT?
- If the patient has no prior history of tachycardia, or they have a history of structural cardiac disease, a known pacemaker or ICD this makes VT more likely. A history of AVNRT or other previous SVT makes SVT more likely.
- The patient who is unstable, has cardiac failure, a midline sternotomy scar, a pacemaker or ICD, cannon a-waves or heart sound fluctuations (esp S1) make VT more likely.
- VT is more common generally (80%, but up to 95% in IHD). VT is more likely with extreme right axis, minor rate variation and chest lead concordance. SVT is more likely with a rate that is exactly 150/min and a narrower QRS-complex width (120-140ms).
Bill looks at you, and whispers longingly:
Q3. What algorithms may help you differentiate SVT with aberrant conduction from VT?
The Brugada Criteria
- sensitivity: 98.7%
- specificity: 96.5%
- test accuracy: 90%.
However other authors have reported lower values with independent application of the criteria.
The Vereckei Criteria
- sensitivity: 95.7%
- specificity: 73.4%
- test accuracy: 90%.
These are remarkably similar to the above values for the Brugada Criteria.
Interestingly, in the same paper Vereckei evaluated the same 453 ECGs used to develop his criteria, using Brugada criteria — with a test accuracy of 85%. Furthermore, 18 WCTs were incorrectly diagnosed by both criteria.
Things I like about these criteria…
- They involve a simple four step process.
- Most steps in both the Brugada and Vereckei are simple to remember, and easy to rapidly apply.
Things I don’t like about these criteria…
- Step 4 in the Brugada criteria and step 3 in the Vereckei criteria are complicated.
- VT is a medical emergency. Both criteria get it wrong about 10% of the time…
- 10% is too high for my liking.
So, is all this Vereckei and Brugada business Much Ado About Nothing? Are they Measure For Measure the same thing?
- A more pragmatic way of looking at the algorithm is that yes, both may help you equally in making the diagnosis in a stable patient. But in the unstable patient, the distinction between SVT and VT is academic, because you have a 10% chance of getting it wrong. I think that is too high.
- If someone has a WCT and they are haemodynamically compromised, they need urgent action — a DC shock would be my preference, or a very quick acting antiarrhythmic.
Or, as Bill was saying to me by this stage —
- Brugada P, Brugada J, Mont L, Smeets J, Andries EW. A new approach to the differential diagnosis of a regular tachycardia with a wide QRS complex. Circulation. 1991 May;83(5):1649-59. PMID: 2022022. [fulltext]
- Vereckei A, Duray G, Szénási G, Altemose GT, Miller JM. Application of a new algorithm in the differential diagnosis of wide QRS complex tachycardia. Eur Heart J. 2007 Mar;28(5):589-600. Epub 2007 Feb 1. PMID: 17272358.