Robert Vroman wrote:

<snip>

"As far as the subsequent discussion of rates goes, my understanding is that the category of SVT is not really considered until the rate is over 150. That is because at rates less than that if P waves are present they will be seen. However the key word is considered, and this classification should be a last ditch usage. It is very possible to be able to identify the actual rhythm at rates over 150, and it can indeed be sinus as well as others.  I have often heard 180 used as the theoretical upper limit of the sinus node. However is there any evidence to support this? In school I remember learning the formula Paul mentioned (220 – age). Also I have not seen it this year in the coverage of the Tour de France, but I remember a few years ago they would show the riders heart rates which were many times above 180. I would assume those were sinus rhythms."

I see the disconnect now.

Once you accept that sinus tachycardia is a form of SVT, this view is no longer tenable. As the most frequently encountered SVT, sinus tachycardia is the first heart rhythm I consider when I'm dealing with a narrow complex tachycardia, and as Paul mentioned, you always have to consider whether or not it's a compensatory tachycardia. I consider the Hs and Ts for all tachycardias. The other issue with regard to atrial complexes is that when you have sinus tachycardia with 1AVB, the P waves can be obscured by the preceding T wave at rates below 150. What would you call junctional tachycardia at 140 beats/min? Something other than SVT? On occasion I've seen 2:1 atrial tachycardia that was mistaken for sinus tachycardia because every other atrial complex was buried in the QRS/T complex. While atrial flutter with 2:1 conduction is often right at 150, sometimes it's faster and sometimes it's slower. It's still SVT. Same with AF w/RVR. That's the problem with imprecise definitions and ambiguous umbrella terms like SVT that are used as if they are actual heart rhythms as opposed to a specific category of heart rhythms. By definition, a tachycardia is a heart rate > 100. By definition, if it's supraventricular then it's anything that originates above the ventricles. Why complicate matters by throwing in arbitrary criteria that add no value in terms of figuring out the diagnosis and can in fact be misleading?

Tom