Submitted by Dawn on Sat, 01/21/2012 - 23:16
Today's expert is Jason E. Roediger, CCT, CRAT, who is a highly respected Cardiovascular Technician at the Dept. of Veterans Affairs, Hunter Holmes McGuire VA Medical Center in Richmond, VA. He is known for holding numerous certifications in all levels of ECG interpretation, and also for scoring 100% on the Level IV Advanced ECG Board Certification exam that is usually reserved for cardiologists.
Answer: Always? No. Usually, Yes.
There are exceptions to several "golden rules" in electrocardiography and this one is not exempt. One of the chronic issues contributing towards widespread confusion in understanding electrical axis is a lack of continuity in terminology. There is no general concensus on how to refer to an axis in the right upper quadrant. Depending on which author you are reading, it has traditionally been known by multiple names: Northwest axis. . . upper right quadrant. . . extreme right axis. . . right superior axis. . . "no-man's-land" (i.e., "N-M-L".). . . etc. Because my first exposure to electrical axis was through Dr. Marriott's textbooks and he prefered to use "N-M-L", I have personally latched on to that particular name as well. Even though some persist in calling it an "extreme left axis" or "far left axis deviation", this practice is frowned upon and discouraged. It's important to note that an axis in "N-M-L" is not synonymous with an "indeterminate" axis which occurs when the QRS is essentially isodiphasic or equphasic in all 6 limb leads and therefore the polarity of the QRS cannot be discerned in leads I and aVF.
Definition: An axis in "N-M-L" is recognized when the QRS complex has a predominantly or wholly negative deflection (i.e., down) in leads I and aVF. The axis is −90 to −180 degrees.
Irregardless of which descriptive name you prefer, in the context of a wide QRS complex tachycardia, this particular axis is highly predictive of ventricular tachycardia and is rarely encountered in "conducted" rhythms however some examples of aberrant SVT have been published with an axis in "N-M-L".
In summary: An axis in "N-M-L" implies (but is not proof of) an apical origin to the rhythm and should make one think of and exclude the possibility of ventricular tachycardia. As a general rule, until it is proven otherwise, assume any wide QRS complex tachycardia is ventricular tachycardia. Even though this one clue carries significant weight in supporting the interpretation of ventricular tachycardia, that conclusion can not be made based solely on this single criteria. This axis is just one of a long list of criteria and should be used in conjunction with all of them as they carry alot of strength when used collectively.
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Comments
On "N-M-L" Axis ...
Excellent point made by Jason regarding an axis in "N-M-L". To this I'd propose adding, "N-W-L" (no-woman's-land) - and/or to be gender neutral, "N-P-L" (no-person's land). My understanding of why the term "indeterminate" is desirable - is because one "cannot determine" if an axis found in this upper right quadrant (between -90 to -180 degrees) represents marked left vs marked right axis deviation - therefore "indeterminate". While true that the more common "N-M-L" axis is a different entity than that axis in which all 6 limb leads are isodiphasic - I'd pose the question of whether we truly can figure out a specific number of degrees for any axis situated in this upper right quadrant ... Regardless of what the specific degree axis might be - Jason makes the excellent point that the finding of bizarre axis deviation (such as the totally negative QRS complexes seen in the inferior leads in his post on the WCT below ) is a strongly suggestive finding that this WCT is VT. (Jason also totally makes the point that there are MANY additional reasons why this WCT is VT). Looking at axis during a tachycardia is easy to do - and is "high yield" for suggesting VT when axis deviation is marked.
Ken Grauer, MD www.kg-ekgpress.com [email protected]
Received via email from Darlene Hutton:
Another cause of extreme axis
Permalink Submitted by QRSjunkie on Sun, 03/11/2012 - 10:13
Excellent reading from Ken and Jason, thank you. I have also used NPL (no person's land) in keeping with our gender-sensitive environment but prefer using the term 'extreme' as this axis is either an extreme right or left axis gone beyond their 'defined' borders.
There is one other reason for an extreme axis other than VT, and that is in the setting of someone who has had transmural necrosis in the inferior and laterial wall of the left ventricle. This amount of muscle damage in a STEMI is almost unheard of now because of our rapid ECG assessment and interventions in the cath lab. However, for those of us who provided care to these patients prior to reperfusion options such as primary angioplasty or fibrinolytics, back in the late 80s and early 90s, you will recall that when a STEMI presented there was little we could do to stop the process and the final outcome was that these STEMIs would all end up with transmural tissue death and permanent Q waves on their ECG.
Left ventricular inferior and lateral wall necrosis that extends transmurally, resulting in Q wave, will alter the axis from a normal axis to an extreme axis as Leads I, II, III, aVL, aVF will all have Q waves making these QRS complexes all predominantly below the isoelectric line.
Note from ECG Guru: Darlene Hutton, RN, BScN, MSN, is the co-owner of QRS Educational Services.
Dawn Altman, Admin
Great Discussion Topic!
Great presentation, Jason! Thank you. There are two other possible causes of a mean QRS axis in the northwest quadrant: hyperkalemia and congenital heart disease (specifically transposition of the great vessels and single ventricle). Among the guises that hyperkalemia can assume is an extreme axis in the northwest quadrant. This is mentioned from time to time in articles on hyperkalemia, though in 35 years of practice I don't recall seeing a case. Also, you aren't likely to see many of these types of congenital hearts either unless you are a pediatric cardiologist or a neonatal critical care specialist.
Jerry W. Jones MD FACEP FAAEM
https://www.medicusofhouston.com
Twitter: @jwjmd