Differentiating Wide Complex Tachycardias

Answer: This ECG was orthodromic AVRT with RBBB, LPFB Abberrancy.

Clinical Context:

A 40 year old female with no medical history is less likely to present with Scar related VT due to ischaemic heart disease.

However, VT remains a possible diagnosis due to several non ischaemic cardiomyopathies or due to idiopathic VT. I’ve listed a short list of some which need to be considered, however, for the sake of brevity & not labouring the point, this list is severely truncated & by no means exhaustive and presentations can deviate significantly from those listed here:

1.Idiopathic VT

• Most commonly from the LVOT or RVOT (review VT localisation lectures from EP/ECG in Practice).

2.ARVC (AVC):

• Most commonly an RV free wall or Moderator band/Apical VT, however RVOT also common.

3. Dilated Cardiomyopathy:

• Diffuse cardiomyopathy. VT sites more commonly LV.

4. Cardiac Sarcoid:

• Wide variety of VT morphologies with a possible skew towards Septal circuits.

This ECG morphology does not fit with several of these presentations, although that does not exclude them as a diagnosis.

Analysing the ECG

80% of Wide complex tachycardias are VT purportedly.

• This means, if you are diagnosing SVT, you better have a good reason.
• Most of the time, this good reason is that the ECG exhibits perfect examples of Bundle Branch Blocks and has ABSENT features of VT.

This ECG has an overall look that is consistent with a RBBB & LPFB.

• With the exception of the bundle branch VT’s or Fascicular VT’s, most VT’s do not display perfect Bundle branch & Fascicular block morphologies.

A corner stone of VT vs SVT analysis is a very strong understanding of the features of bundle branch blocks & fascicular blocks, so that you can recognize when these features are present (and therefore the wide complex tachycardia is likely SVT with aberrancy) and not present (making VT a more likely diagnosis).

This ECG exhibits features of RBBB, LPFB.

VT Features which are notably absent in this ECG

My Two cents:

• Most wide complex tachycardias are VT, so erring on the side of caution is always desirable.
• Diagnosis of SVT with aberrancy hinges on a strong understanding of the features of Bundle Branch Blocks & Fascicular Blocks.
• It also hinges on a strong understanding of the absent features of VT, such as extreme axis or precordial concordance, which almost always predict VT and are almost always absent in true SVT’s.

Thanks for tuning in :)
Cheers
Mitch & the CPiP team

Differentiating VT from SVT with aberrancy is taught in more depth in ECG in Practice.