Tom B. Posted May 27, 2009 Posted May 27, 2009 As I explained in a recent interview with EP Lab Digest, the cardiologist who's "right" can generally provide an explanation of "why". Tomas Garcia MD used to remind us at the EKG Club that the most common reason cardiologists fail their 3-part board exam is ECG interpretation! Tom These are very good strips; the kind that if you showed them to 10 cardiologists, you would probably get 8 different interpretations.
Brandon Oto Posted February 17, 2010 Posted February 17, 2010 My apologies for the outrageous thread resuscitation, but these strip teases seem like they should be lasting resources. If Tom's still reading, I hope he'll be willing to add a little info. 5. Look at signs of AV dissociation --- This is the best evidence that a rhythm is VT, but it's only present 50% of the time, and it's not easy to appreciate on most ECGs. Tom, What do you mean by the above? I agree that P-wave association is hard to note in most VT, but by saying it's only present 50% of the time, do you mean that some VT DOES have AV association? Surely that makes no sense unless you're thinking of retrograde conduction.
Tom B. Posted February 18, 2010 Posted February 18, 2010 My apologies for the outrageous thread resuscitation, but these strip teases seem like they should be lasting resources. If Tom's still reading, I hope he'll be willing to add a little info. Tom, What do you mean by the above? I agree that P-wave association is hard to note in most VT, but by saying it's only present 50% of the time, do you mean that some VT DOES have AV association? Surely that makes no sense unless you're thinking of retrograde conduction. Brandon - I'm not 100% sure I understand the question, but some VT does have AV dissociation. In other words, the ventricles are in a self-sustained ventricular tachycardia and the atria are in sinus rhythm (for example). So the ventricular rate might be 180 and the atrial rate might be 80. When that occurs, a trained eye might be able to march out the P-waves running through the VT. This is much easier sitting down inside the hospital with a rhythm strip laid out on the desk and a pair of calipers in your hand. Other times, VA conduction is intact, so you will have retrograde activation of the atria. That's why a 1:1 relationship between atrial complexes and ventricular complexes is no help when differentiating between VT and SVT with aberrancy. If the episodes of a wide complex tachycardia are paroxysmal, you might say, "Then if the tachycardia ends with an atrial complex it must have been VT." Unfortunately, even that isn't true, since the tachycardia could end with a blocked atrial complex. Does that answer your question? Thanks, Tom
Brandon Oto Posted February 19, 2010 Posted February 19, 2010 Brandon - I'm not 100% sure I understand the question, but some VT does have AV dissociation. In other words, the ventricles are in a self-sustained ventricular tachycardia and the atria are in sinus rhythm (for example). So the ventricular rate might be 180 and the atrial rate might be 80. When that occurs, a trained eye might be able to march out the P-waves running through the VT. This is much easier sitting down inside the hospital with a rhythm strip laid out on the desk and a pair of calipers in your hand. Other times, VA conduction is intact, so you will have retrograde activation of the atria. That's why a 1:1 relationship between atrial complexes and ventricular complexes is no help when differentiating between VT and SVT with aberrancy. If the episodes of a wide complex tachycardia are paroxysmal, you might say, "Then if the tachycardia ends with an atrial complex it must have been VT." Unfortunately, even that isn't true, since the tachycardia could end with a blocked atrial complex. Does that answer your question? Thanks, Tom Thanks for answering, Tom. What I meant is that VT by definition is ventricular, so I was confused when you suggested that 50% of VT might show AV association. I see now that you meant about half of them will demonstrate retrograde conduction, thereby associating P waves and QRS complexes even though the actual rhythm isn't originating supraventricularly. Is that 50% stat a general illustration, by the way, or is that the actual percentage? Do about half of the AV nodes out there have some quality that allows retrograde conduction, and half do not?
Tom B. Posted February 19, 2010 Posted February 19, 2010 Thanks for answering, Tom. What I meant is that VT by definition is ventricular, so I was confused when you suggested that 50% of VT might show AV association. I see now that you meant about half of them will demonstrate retrograde conduction, thereby associating P waves and QRS complexes even though the actual rhythm isn't originating supraventricularly. Is that 50% stat a general illustration, by the way, or is that the actual percentage? Do about half of the AV nodes out there have some quality that allows retrograde conduction, and half do not? Brandon - The 50% statistic is cited frequently in medical textbooks and the peer reviewed literature. You can check out a Google search for examples. I'm not sure why. Apparently some AV nodes allow antegrade AV conduction but not retrograde VA conduction. You'd think if it would allow one it would allow the other, but clearly that's not the case! Tom
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