June 2017

Initial Approach

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Tim V. -

You mention to distinguish v tach from SVT with aberrancy to use adenosine. Amal says that 20% of v tach responds to adenosine so be wary of this approach. Thanks for the review.

Jess Mason -

Yes, we are planning to discuss this in further detail in another segment. This would change the disposition, of course.

Mike -

Fantastic summary of arrhythmias; thank you very much. I have have two questions.

First, it seems as if many providers are very anxious and leery of cardioversion both with definite onset of A. fib less than 12-24 hours (never mind up to 48 hours), and in cases of A. flutter, refractory SVT, etc. I'm quick to cardiovert and have good success. Are there any significant adverse affects of cardioversion?

Second, I've pretty much abandoned the use of adenosine. I've had variable success and patients hate it. A few have told me to do anything else but give them "the medicine" that makes them feel as if they're dying. I either give diltiazem or cardiovert, figuring that both with take care of either A. flutter or SVT. What are your thoughts?

Stephanie S. -

Hello, excellent summary and approach!
I was wondering where the information on "the primacy of rate" came from - the idea of a heart rate > 140 being maladaptive and actually decreasing cardiac output. Cardiac Output = HR x SV, but the bodies beat-to-beat fine tuning of autonomic input on the heart makes this a very complex relationship. Reading through all my textbooks (Lilly's pathophysiology of heart disease, Boron and Baulpeeps medical physiology, and Tintinallis Emegency Medicine) and doing a search through some physiology papers online has become very confusing, and much of it has to do with exercise (where there is also a large change in Systemic Vascular Resistance). Nobody seems to directly relate HR at rest (as in arrhythmia) with Cardiac output. Can you please share your sources so I can read more into this? Thanks!

Terence P. -

Hey there, great stuff. A nitpick, but i noticed it in audio and written. Isn't three small squares (delineation point for wide or narrow QRS) 120 ms? I see it listed and on audio as .12 ms. Again, a nitpick.

Jess Mason -

Yes it should be 120 ms.

@JamesPowellMD -

Hello, I just re-watched your C3 review on tachyarrhythmias: very good approach! I have the same question as Stephanie above, which I noticed was never answered. Was hoping you could share some sources for this, specifically where does the number 140 for primacy of rate come from? In your summary it said “Once the ventricular rate exceeds about 140, heart rate no longer increases cardiac output (CO); CO rather begins to decrease...”
Thanks!

Mel H. -

This 140 number is less science than experience - over that number cardiac output seems to go down as the patient decompensates, but of course that is a ball park.

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Tachydysrythmias Full episode audio for MD edition 69:45 min - 97 MB - M4AC3 2017 June Board Review Answers 182 KB - PDFC3 2017 June Board Review Questions 543 KB - PDFC3 Tachyarrhthmias MP3 Files 93 MB - ZIPC3 - Tachyarrhythmias - Written Summary 512 KB - PDF