So really, when we think about wide complex rhythms,
we wanna think about whether the patient is in ventricular tachycardia
or supraventricular tachycardia with aberrant conduction.
And there are some clinical features
that will help us distinguish between the two.
So, older patients are much more likely to be in V-tach
compared to younger patients.
Patients with a history of heart disease, either ischemic heart disease,
heart failure, cardiomyopathy,
again, more likely to be having a ventricular dysrhythmia
and definitely patients who have a family history
for ventricular rhythm disturbance, again, are more likely to be in V-tach.
On the ECG, there are a number of different features that you can look for
and we’re not gonna cover them in a lot of detail here
but you can look for AV dissociation, fusion or capture beats,
extreme axis deviation, QRS concordance, or Brugada’s sign
which is defined as a hundred milliseconds
from the QRS complex to the bottom of the S wave.
In other words, prolongation of that latter part of the QRS complex.
The bottom-line is that these things are really interesting to think about and talk about,
and they make for good conversation on rounds,
but ultimately, it’s very, very difficult to reliably differentiate
between V-tach and supraventricular tachycardia with aberrancy.
There are a lot of different criteria that people use for this.
There’s the Brugada criteria, the modified Brugada criteria,
there’s a whole bunch of different ones.
But none of them has been shown to be completely reliable in clinical practice
and therefore, they’re not completely safe to use in clinical practice.
So, this is a pearl for you, pay attention.
The bottom-line is that all wide-complex tachycardia
should be assumed to be V-tach until proven otherwise.
It’s very difficult to differentiate between V-tach, and supraventricular tachycardia
with aberrant conduction on clinical grounds,
so when in doubt, assume that it’s V-tach, and you’ll be safe.
Now, why is this so important? Well, very simply,
V-tach is a life-threatening rhythm disturbance
and you have to treat it aggressively
where supraventricular tachycardia is more benign
and you don’t have to be quite as assertive with your management.
More importantly, ventricular tachycardia’s not gonna respond
to the kinds of treatments that we use for supraventricular rhythms.
So you’re not gonna be effective in treating V-tach
if you’re trying to treat it like a supraventricular rhythm.
But the most important thing is that in some situations,
use of medications that are designed for supraventricular rhythms
can actually be harmful in certain situations in wide-complex tachycardia.
You can actually kill patients by treating their wide-complex tachycardia
as though it is supraventricular in origin, and let’s talk about an example of that.
So, Wolff-Parkinson-White is one condition where it’s very, very dangerous
to use AV nodal blocking agents which are used for supraventricular rhythms
to try to terminate wide-complex tachycardia.
So, in patients with WPW, there are two conduction pathways.
There’s a normal conduction pathway and there’s an accessory pathway.
Now, if you use an AV-nodal blocker to try to slow down a heart rate
in a patient with WPW, it’s gonna work on the normal pathway,
that runs through the AV node.
However, these patients have a second pathway, an accessory pathway,
and your AV-nodal blocker is not gonna work on that accessory pathway.
So what’s gonna happen?
You’ve got all kinds of electricity whizzing around the heart.
You block one pathway, so you’re gonna end up forcing the electricity down
the other pathway which can actually accelerate conduction
through the accessory pathway and cause the heart rate to further increase
or you can precipitate ventricular fibrillation.
So, this is a potentially lethal error in these patients.
Now, very simply, if you treat the patient as though they have ventricular tachycardia
and you don’t use AV-nodal blockers,
you use the types of medicines that we’re gonna talk about for V-tach,
you don’t have this problem because you’re gonna block both the normal
and the accessory pathway simultaneously
and you won’t set your patient up for this type of risk.
So, how do you diagnose ventricular tachycardia?
Like we said, you have to have tachycardia so the rate has to be greater than 100.
It’s usually much higher than that though, it’s usually in the 150 to 200 range,
about 180 is pretty average for V-tach.
You have to have a wide QRS complex
which we already said is greater than 120 milliseconds,
and you have to have a regular rate.
Now, there might be some minimal beat to beat variability,
you certainly can see that but in general,
you should see the QRS complex is coming along at a regular rate.