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Third-degree AV Block and Junctional Escape Rhythm With Right Bundle Branch Block and Prolonged QTc Interval

Sat, 01/26/2013 - 13:48 -- Dawn

This ECG is from a 70 year old woman for which we have, unfortunately, no clinical information.  It shows a sinus rhythm with a rate of about 72 bpm (NSR) with AV dissociation caused by third-degree heart block.  The escape rhythm is junctional at a rate of 38 bpm.  There appears to be a right bundle branch block, based on the QRS duration of 132 ms, and a wide S wave in Leads I and V6.  The precordial leads do not show the usual RBBB pattern of rSR' in V1 and V2, and the r wave progression is poor (non-existent).  This is felt to be due to poor lead placement (a good teaching point).  Of interest, the ECG machine has reported a "severe right axis deviation" based on the tall upright R wave in aVR and the deep S in avF.  In RBBB, the first part of the QRS represents left ventricular depolarization, and the terminal wave represents the delayed right ventricle.  In effect, the two ventricles have their own electrical axes, which we can see because the ventricles are not depolarizing simultaneously.  The axis of the LV appears to be normal in this tracing.

In addition to the above, this patient has a very prolonged QT interval.  The QT is longer in bradycardic rhythms, but when corrected to a standard of 60 bpm (QTc), this patient's QT interval is still prolonged at QTc: 552 ms.  Without clinical data, we cannot speculate  as to why this patient's QTc is prolonged, but it can be a very dangerous situation.  Follow the links for more information on QT prolongation and Torsades de Pointes and Long QT Syndrome.

As always, we welcome comments from our members adding insight to this interesting ECG, and also questions you would like to ask our Guru members.

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ekgpress@mac.com's picture
VERY interesting tracing - because QRS morphology continually changes in the lead II rhythm strip at the bottom !!! I'll make the following points:
  • Regular atrial rhythm as noted by Dawn at 72/minute
  • Completely regular escape rhythm at just under 40/minute. As per my title - the VERY interesting aspect of this tracing to me is how QRS morphology continually changes in the lead II rhythm strip. Normally this would make me think that at least some of the P waves were conducting - however, IF that were the case - then I would NOT expect the escape rhythm to be so absolutely regular. Instead - one usually sees an early beat as a clue that there is conduction. If I were at the bedside treating this patient - I'd definitely like a LONGER rhythm strip before committing myself to what the degree of AV block is. I'd like to be certain that P waves are truly occurring at all parts of the cycle and failing to conduct despite being given opportunity to do so ... Not having this, I agree with Dawn that there most likely is complete AV block given the absolutely regular escape rhythm.
  • This leaves me having to explain the changing QRS morphology in the lead II rhythm strip ... which I find easiest to do by postulating junctional escape (as per Dawn) - albeit with VARYING DEGREES of BBB. 
  • We only see 1 QRS complex in lead V1. It is a low amplitude positive complex. It does not have an rSR' - yet given that it is positive, widened - and given that there IS a wide terminal S wave in both leads I and V6 - this is consistent with RBBB.
  • QRS morphology in the limb leads changes in leads I, II, III - but not truly in a pattern of one or the other of the hemiblocks ... (the 2nd beat in lead II is consistent with LAHB - but the Qr in lead III really isn't, nor is the predominantly negative QRS in lead I ). So my best guess is 3rd Degree AV Block with slow junctional escape manifesting varying degrees of RBBB.
  • As to "R wave progression" - given the already positive QRS in lead V1 - what we see in leads V2,V3 is consistent with RBBB. NOTE however that QRS morphology is again changing in leads V4,V5,V6 (predominantly positive in the first complex for these leads - and predominantly negative for the 2nd complex for these leads). Given non-sinus mechanism and RBBB of varying degrees - I don't think we are able to speak intelligently about "r wave progression" for this tracing ...
  • As to "axis" - I also don't think we can say much given the non-sinus mechanism - presumed junctional escape - and very atypical RBBB morphology with changing degrees of conduction block ...
  • Finally - as to the QT interval - it does measure long. That said - BBB is clearly a cause of QT lengthening - and given that the QTc (= corrected QT interval) = measured QT over the square root of the R-R interval - the acceptable QTc lengthens when the rate slows. This is why you see above the tracing that the computer calculated a measured QT = 590ms - but a QTc of only 552ms - which is long, but not overly so. Clinically correlation of course will be everything - but I'm less worried about the QTc in this patient than I am about presumed 3rd degree AV block with junctional escape and significant bundle branch impaired conduction.
 

Ken Grauer, MD  www.kg-ekgpress.com   [email protected] 

Submitted by VinceD on

Great thoughts Dr. Grauer. I too was a bit perplexed by that changing QRS morphology - it definitely exceeds what I consider to be WNL for respiratory variation. I'm glad you already covered the possibilities far better than I could have.

Vince D

Submitted by Dee on



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I found out 2 years ago that I have LongQT. Then genetic test came back I know it's LQTS1 . My ECG showed a long QT for years before that. Most doctors I've seen have no clue what to read and even more concerning don't seem to care enough to study up. Cardiologists even go into a blank stare too. I came to your blog after searching the internet for hours to find my way.Sudden death is not as rare as one is led to believe, so I fail to see why the patient has to be the person fighting their way through the system to avoid the dreaded moment of crisis. Just because it's genetic doesnt mean you ignore it in your training. ( it's often acquired and can be temporary too)There's an ECG machine in modern ambulances and ER and teaching hospital should have an electrophysiologist and he should train the ER nurses to read this. Before anymore patients die while people scratch their heads. Secondly train Aneasthetists so I dont have to beg them to consider my condition while they glaze over. I can only.imagine what families go though who have no insurance. Because genetic testing costs. Since the list of medicines that can cause LongQT leading to Tosades is long and includes every class of drugs. I fail to see how anybody from GPs who prescribe to Emergency medicine isn't trained to at least know the syndrome.Thankyou for the blog 

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