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The morphologic (4th) criteria for diagnosing VT using the Brugada criteria are the most complicated and difficult to memorize. They are divided based on whether the EKG has more of a RBBB or a LBBB appearance. This is determined by looking at V1 and determining if there is a dominant R wave (RBBB criteria) or S wave (LBBB criteria). Within this division, there are specific features to look at in V1/V2 and V6.
RBBB Criteria
RBBB Criteria
There are 3 main morphologic findings that would indicate VT in V1/V2. They are a smooth, monophasic R wave, taller left rabbit ear, and qR pattern. The taller left rabbit ear sign typically does not have the RSR' pattern, but is actually notching of the downstroke of the R wave.
There are 2 main morphologic findings in V6 that would indicate VT: QS waves and R/S ratio<1 (rS wave, in other words).
LBBB Criteria
LBBB Criteria
Again for V1/V2, there are 3 morphologic criteria that indicate VT: initial R wave >30-40ms, Josephson's sign, and RS interval>60ms. Josephson's sign is notching or slurring of the S wave. The RS interval is, again, defined as the time from onset of the R wave to the nadir of the S wave.
There are 2 patterns, again, in V6 that are indicative of VT: QS pattern (same as RBBB criteria) and qR pattern. SVT with a LBBB does not have Q waves in V6.
Example:
Source: EmDocs
Taller left rabbit ear indicative of VT (there are also other signs that indicate VT here)
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