Wednesday, November 5, 2014

Cold symptoms and bradycardia. What is this pre-excitation?

A young man presented to the ED for cough and runny nose and was bradycardic, so an ECG was recorded:
There is sinus rhythm with complete AV dissociation due to complete (third degree) AV block.  The escape has a slurred upstroke.  Is this a delta wave?



The patient stated that he knows he has this and that whenever he feels weak he just takes some methamphetamine and he feels fine!  He refused any treatment or evaluation.


The rhythm is interesting, though, and we have some disagreement about whether it is an nodal escape with a fasciculo-ventricular accessory pathway, or a ventricular escape with "Pseudo" Delta waves.  In any case, there must be some pre-excitation.

If it is fasculo-ventricular, as our EP expert says (and I defer to him), then this is a potential ladder diagram, as drawn by Christopher Watford:


K. Wang has graciously offered to let me insert pages 212 and 213 on Pseudo Delta waves from his great Atlas of Electrocardiography:






It seems to me that Pseudo Delta waves are only "Pseudo" in that the do not necessarily represent an accessory pathway, the way we normally associate delta waves with WPW.

However, it also seems that any delta wave implies some pre-excitation.  Ventricular beats often take some time to reach the conducting fibers and will thus often have pre-excitation of some sort.

11 comments:

  1. I've had a patient develop bradycardia with phenylephrine. Any chance that the bradycardia ± AV block is caused by the methamphetamine use?

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    Replies
    1. Brooks,
      I don't see how it would be. do you?
      Steve

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    2. Not sure myself, just thinking that meth might cause a reflex bradycardia through the same putative mechanism as phenylephrine (stimulation of baroreceptors).
      I found one study that found a surprisingly high prevalence of bradycardia in chronic meth users, much higher than the rate of tachycardia:https://www.google.com/url?sa=t&source=web&rct=j&ei=RKRyVNCfHITGsQSRu4LQBg&url=http://cfenet.ubc.ca/sites/default/files/uploads/Health%2520Conditions.pdf&ved=0CBwQFjAA&usg=AFQjCNHkAXxv1qpF_0rjeyl1alShUFF2Xg&sig2=nhCMMEUFBx2QYrgDLTQuIA

      Delete
    3. But that would be acute intoxication right?

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    4. Oddly enough, the bradycardia was seen in a (presumably) abstinent population, having completed meth detox.

      Something to keep an eye out for in the future, I suppse.

      Delete
  2. only delta wave (with normal PR interval) is also preexcitation? qrs with delta wave in AF is also preexcitation? what is pseudo delta wave? can you recommend article/literature for this subject?

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  3. how do you differentiate preexitation vs aberrancy in AF?

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    Replies
    1. Pre-excitation is a fusion beat: there is some depolarization of the ventricle PRIOR to the arrival of an impulse through the conducting system. They fuse, with a delta wave representing the pre-excitation and the narrow part of the QRS the depolarization through the conducting system.

      Aberrancy is conducted FIRST via the conducting system and only later through non-conducting tissue. For instance, RBBB has normal conduction through the left conducting system, but the delay comes later when the right ventricle is depolarized through ventricular conduction alone.

      So one might conceive it such: pre-excitation has the slow conduction at the beginning of the QRS, aberrancy has it at the end of the QRS

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  4. Hello, I'm still just getting the basics down but would the inverted T waves in II and avF and the tall T waves in several of the precordial leads be indicative of anything?

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    Replies
    1. With abnormal QRS's such as this, you expect discordance (ST-T opposite direction from QRS). Just like in paced rhythm or LBBB or PVCs.

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