I've come to dislike the term "SVT" (supraventricular tachycardia).
In the first place, it's not an arrhythmia. It's an umbrella term that covers a group of arrhythmias which require the AV node for their maintenance.
Most importantly, it includes sinus tachycardia!
For some reason, this is a difficult concept for many clinicians to grasp, partly because of myths passed on from generation to generation.
For example, my least favorite of all.
"If the rate is 150 or greater, it's SVT."
Does it mean that junctional tachycardia at a rate of 149 is not SVT? Does that mean that sinus tachycardia can't be 151? 161? 171?
As Ray Fowler, M.D. often reminds us, the maximum sinus rate (give or take a few %) is 220 minus age.
I think the term "SVT" is less helpful than the term "narrow complex tachycardia" for figuring out a differential diagnosis.
Because at first glance, you won't always know it's SVT, but you should be able to figure out whether or not a tachycardia has narrow QRS complexes.
Regardless, there's no point in wasting precious time and energy making this more difficult than it needs to be.
A tachycardia is a heart rate equal to or greater than 100. A supraventricular rhythm originates above the ventricles. A narrow QRS rhythm has a QRS duration < 120 ms.
From the AHA ECC 2005 Guidelines, Part 7.3: Management of Symptomatic Bradycardia and Tachycardia:
Narrow–QRS-complex (SVT) tachycardias (QRS duration < 0.12 s) in order of frequency
- Sinus tachycardia
- Atrial fibrillation
- Atrial flutter
- AV nodal reentry
- Accessory pathway–mediated tachycardia
- Atrial tachycardia (ectopic and reentrant)
- Multifocal atrial tachycardia (MAT)
- Junctional tachycardia
In other words:
Sinus tachcyardia is, by far, the most common form of SVT!
This is important because the first arrhythmia you should consider when faced with a narrow complex tachycardia (or SVT) is sinus tachycardia!
And what antiarrhythmic do we use for sinus tachycardia?
All together now!
We consider the Hs and Ts (as we should for any arrhythmia before reaching into the drug box) and we treat the underlying cause.
Let me give you an example.
An 18 year old female calls 9-1-1 and complains of palpitations.
EMS responds to the scene and finds her lying on the floor with absent radial pulses and a pressure of 80/40.
However, she's conscious, alert, and oriented to person, place and time.
The cardiac monitor is attached.
An IV was started, and the patient received adenosine 6/12/12.
It didn't resolve the arrhythmia.
Because had they asked, the patient had an elective abortion earlier that day.
She had vaginal bleeding and soaked through at least 8 maxipads.
In light of this new information, what is the heart rhythm?
How about sinus tachcyardia?
How about appropriate and compensatory sinus tachycardia?
So what was the patient's problem? If you don't know, it's on this list and it starts with an H.
Failure to consider sinus tachycardia can have serious consequences and put the patient at risk for iatrogenic harm.
Narrow complex tachycardias – Part I