Differential Diagnosis of Wide Complex Tachycardias – Part 3

Let’s look at another unusual case.

This was the ECG of a chest pain patient in the emergency department.


Let us assume for a moment that the patient is hemodynamically stable but diaphoretic and complaining of severe substernal chest pressure.

What does this 12 lead ECG show?

It’s a regular rhythm. The rate is 120. The QRS duration is 150 ms (0.15 s). This is a regular wide complex tachycardia.

No P waves are apparent. Could this be slow VT?

Let’s look at QRS morphology.

The pattern in lead V1 is RBBB and there is a left axis deviation. This is a bifascicular pattern (RBBB/LAFB).

Suddenly, there is a rhythm change on the monitor.

What happened?

Atrial complexes can be seen in several leads at a rate very similar to the rate of the wide complex tachycardia.

This was some type of SVT with bifascicular block.

The PR interval was sufficiently long that it was buried in the previous T wave, making this a so-called “trifascicular” block (1°AVB, RBBB, LAFB).

Think about it. If the right bundle branch is blocked, and the left anterior fascicle of the left bundle branch is blocked, then ventricular activation occurs only through the left posterior fascicle of the left bundle branch.

When 1°AVB occurs in this setting, there’s either a delay in the AV node, or a delay in the left posterior fascicle of the left bundle branch. Either way, with a chest pain patient (or a syncope patient) you have to be concerned that the last remaining connection between the atria and ventricles is vulnerable.

These patients can suddenly convert to 3°AVB without an escape rhythm, especially if they take oral antiarrhythmics.

So be careful when considering IV antiarrhythmics for these patients, and consider applying the Combo-Pads as a precaution.

The 2005 AHA ECC Guidelines frown upon TCP for asystolic arrest, but in the setting of bifascicular block and chest pain (or a recent history of syncope), it seems to me that immediate TCP is a reasonable intervention if the Combo-Pads are already applied as a precaution in anticipation of the possibility!

Just remember, this would not be the time to get shy about dialing up the milliamperes!

See also

Differential diagnosis of wide complex tachycardias – Part 1

Differential diagnosis of wide complex tachycardias – Part 2

Differential diagnosis of wide complex tachycardias – Part 3

Differential diagnosis of wide complex tachycardias – Part 4

Differential diagnosis of wide complex tachycardias – Part 5

Differential diagnosis of wide complex tachycardias – Part 6

 

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