Narrow complex tachycardias – Part I

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.

The paramedic in charge of the call diagnosed the heart rhythm as SVT.

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.

Do you see why it's important to include sinus tachycardia in the differential diagnosis for tachycardias?

Failure to consider sinus tachycardia can have serious consequences and put the patient at risk for iatrogenic harm.

See also:

Narrow complex tachycardias – Part I

Narrow complex tachycardias – Part II

Narrow complex tachycardias – Part III


  • Anonymous says:

    You stated the patient was conscious, but she obviously didn't volunteer either her surgery that day or her bleeding. Beating up on the medic crew may not be appropriate because the patient may have been too embarrassed to mention those details to a crew of male firefighters. She may not have had the same apprehension when speaking with a female nurse in the ER. But I see what you are getting at here.

  • Tom B says:

    Anonymous – The problem is that the crew didn't obtain an appropriate history, making the issue of the patient's comfort level somewhat irrelevant.I'm not here to protect the egos of paramedics, and criticism isn't "beating up". The paramedic in this case knows he was wrong.The best lessons I've learned in EMS (and in life) have been from failure.Live and learn.If you can learn from someone else's mistakes, all the better. After all, it's not about us, it's about quality patient care.Regardless, I'm glad you see what I'm getting at.Tom

  • Brian T says:

    Hey Tom-I am sure you are familiar with the old "220 minus age" rule of thumb for determining the upper limit of SA node pacing ability. I am curious what your opinion is on this, and if you know if it is based on research or anecdote.

  • Tom B says:

    Brian T -Yes, I've heard that. Dr. Fowler teaches it in his lectures. (If you haven't seen them, you should check out and click on "SEE DR. RAYS LECTURES!!")I definitely think it's worth considering. I'm trying to decide whether or not I've ever seen a 70 year old with a sinus rate above 150.Maybe that's where the 150 rule for SVT comes from! :)Tom

  • Tom B says:

    Anonymous – I reconsidered your feedback and removed the sarcastic comment(s).Tom

  • Shaggy says:

    Without knowing of the vaginal bleeding, this case screams out HYPOVOLEMIA!. Besides, it may just be me, but I swear it looks like sinus tach. Either way, ACLS and Paramedic training traditionally focused not only on arrythmia recognition but the treatment of the arrythmia and less on treating the underlying causes. It took many years to deprogram myself of this ideology.

  • Anonymous says:

    That Medic crew fully deserves a beating. Anyways, I probably deserve a beating to, because this subject has always confused me. I was renewing my ACLS when I recieved a sinus tach at 180 with clearly visible P waves. I was hoping for the typical SVT we all see. Anyways, I was not thinking Adenosine for this pt because of the clear P waves. What to do?

  • MrFussy says:

    As a trainee EMT i'm interested in your take on vagal stimulation in tachycardia's. Blowing in a 20ml syringe, carotid massage or even positioning in the supine position (not relevant to the given scenario) to name but a few.Are these practised before drugs administered?

  • Tom B says:

    Use common sense with the "blowing into the syringe" thing. If the patient is hypertensive, with a flushed face, and has a history of CVA for example, you might not want the poor guy's head to explode.We don't do carotid sinus massage, because we don't want to break off a piece of plaque and cause a stroke. The docs are trained to listen for bruits, so let them try it. Positioning in the supine position? I wasn't aware that stimulated the vagus nerve. Is that what you meant?It seems to me that having the patient bear down with abdonimal pressure is best and ice cold water to the face is second best, albeit impractical in the back of an ambulance.But yes, I would suggest trying vagal maneuvers before reaching for drugs!Tom

  • Tracey says:

    Excellent synopsis of Narrow Complex Tachycardia……!

  • Jeff says:

    Might need to play detective but question question question it will get answer also look around when you approach Pt for clues .

  • Jake says:

    I have to ask: Is it verified that the crew did not attempt to obtain a complete history, or did the patient not provide that particular detail when asked? I can't count the number of times that I've been made to look like an idiot after asking a patient "Have you ever had X?" and they say "no", and then when I'm handing them off to the ER they volunteer "I have a history of X." It's even more common when it's something a patient might consider embarrasing or shameful. Abortions, unexpected/undesired pregnancy, and vaginal issues are just some things that top that list, especially if the medic is male.
    I just can't imagine not trying to get a history before treating this patient. An otherwise healthy 18 y/o does not just go into SVT for no reason.*
    * Okay, it might happen, but it's so unusual that this statement is at least a valid starting assumption.

  • Yes, I know for a fact that the treating paramedic didn't even ask.

  • tedbohne says:

    sinus tachycardia secondary to hypovolemia.  meds? previous hx?  WTFO?

  • Jerry says:

    Sounds like a bunch of rookies on here. Tachycardia is Tachycardia and SVT is SVT. We were taught common sense back in the day, what I see coming out of school today is a lot of dangerous people with tunnel vision leading their way.I had this same situation and had a Supv. on board with me and ened up calling med-control to shut him and his Adenosine down, 300 cc bolus later, broke into to the prettiest NSR you ever saw. Electrolyte imbalance which LR or NSL will take care of most of the time. Folks today just want "to start a line" or "drop a tube" without even knowing why they are doing it. After 20 years it's is scary to me what they are pushing out of school.

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