Embedded Files
The first 3 Brugada criteria are rather straightforward methods for objective evaluation. The Brugada algorithm is an easy to follow decision tree, though the last step (morphologic criteria) is much more complicated. They have very high specificities for determining if VT is present, though have quite variable sensitivities.
The first criteria is absence of an RS complex in all precordial leads. In other words, there is complete concordance of the QRS segment-it is either completely negative or completely positive in all precordial leads. If this is present, one can diagnose VT. If this is not present (ie RS waves present), then one moves onto step 2. Bundle branch blocks (most common cause of aberrant conduction) should not produce concordance throughout all precordial leads.
The second criteria is the R to S interval. Specifically, one measures the beginning of the upstroke of the R wave to the nadir of the S wave. If this timeframe is >100ms, then one can diagnose VT. If it is less than this, then one moves onto step 3. This is because SVT with aberrancy has conduction speeds that are initially fast and then slow down (ie due to bundle branch block). In contrast, VT originates in scar tissue of the myocardium and is slow to propagate until reaching the conduction system.
Source: LITFL
RS interval measurement, starting with the beginning of the upstroke of the R wave to the nadir of the S wave
The third criteria is AV dissociation. If there is AV dissociation present, then the QRS complexes must originate in the ventricles and, therefore, be VT in a wide complex tachycardia (if it is slow, there is a 3* AV block with an escape rhythm). P waves may be present on an EKG with VT as the sinus node is still firing, attempting to provide electrical activity to the heart unsuccessfully. These can be difficult to find. As is always the case for P waves, it is best to look for and evaluate them in V1 and lead II. AV dissociation would be present if there is not always a P for QRS and QRS for P (activity of QRS complex 'dissociated' from activity of P waves). If AV dissociation is not identified, then one should move onto step 4 (morphologic criteria on another page).
Examples:
Source: Steve Smith's blog
This EKG meets criteria for VT in a multitude of ways. For the above criteria, the RS interval is >100ms, indicating VT.
Source: Steve Smith's blog
The above EKG but annotated. The green arrows indicate the beginning and ending of the QRS complex. The black arrow indicates the nadir of the S wave (black lines are beginning of QRS complexes), which is >100ms.
Source: Medicus of Houston
This EKG indicates VT with positive concordance throughout the precordial leads.
Page updated
Google Sites
Report abuse