Supraventricular Tachycardia

Supraventricular Tachycardia (SVT)

SVT is a broad term for a number of tachyarrhythmias that originate above the ventricular electrical conduction system (purkinje fibers).

Classic Paroxysmal SVT has a narrow QRS complex & has a very regular rhythm. Inverted P waves are sometimes seen after the QRS complex. These are called retrograde p waves

Supraventricular Tachycardia EKG Rhythm Strip

The heart fills during diastole, and diastole is normally 2/3 the cardiac cycle. A rapid heart rate will significantly reduce the time which the ventricles have to fill. The reduced filling time results in a smaller amount of blood ejected from the heart during systole. The end result is a drop in cardiac output & hypotension.

With the drop in cardiac output, a patient may experience the following symptoms. These symptoms occur more frequently with a heart rate >150 beats per minute:

  • Shortness of air (S)
  • Palpitation feeling in chest (S)
  • Ongoing chest pain (U)
  • Dizziness (S)
  • Rapid breathing (S)
  • Loss of consciousness (U)
  • Numbness of body parts (S)

The pathway of choice for SVT in the tachycardia algorithm is based on whether the patient is stable or unstable. The symptoms listed above that would indicate the patient is unstable are noted with the letter (U). Stable but serious symptoms are indicated with the letter (S).

Unstable patients with SVT and a pulse are always treated with cardioversion. The appropriate voltage for cardioverting SVT is 50-100 J. This is what AHA recommends and also SVT converts quite readily with 50-100 J.



    • says

      Persistent SVT will probably require an electrophysiology study to determine the mechanism of the disorder. This will allow for proper treatment of the arrhythmia.

      Kind regards,

    • says

      A vagal maneuver is a technique by which you attempt to increase intrathroacic pressure which will stimulate the vagus nerve. This can result in slowed conduction of electrical impulses through the AV node of the heart. There are a number of ways to do it here are a couple:

      1. Cough Method: Have the patient cough forcefully. This is a simple form of vagal maneuver. The idea is to increase intrathroacic pressure which will stimulate the vagus nerve. This can result in slowed conduction of electrical impulses through the AV node of the heart.
      2. Straw Method: Have the patient blow forcefully through a straw for 3-5 seconds.
      3. Bear down Method: Have the patient bear down and strain. Kind of like how a person might strain when having a bowel movement.
      4. Syringe Plunger Method: First, show the patient how easy it is to move the plunger by pulling it back and forth in within the syringe and then have the patient. Have the patient place their mouth over the exit end of the syringe and attempt to blow the plunger out of the syringe. Have them blow for 3-5 seconds.
      5. Abdominal Pressure Method: Press into the pts abd while they contract and resist pressing into their abd.
      6. Ice Method: Quote from a healthcare provider: “We had a kid (approximately 12 yrs old) present to our ER in SVT, instead of using drugs and vagal maneuvers we dunked his face in a bucket of ice twice and it immediately & effectively brought the heart rate down. We observed him for a period of time and the kid was fine. Worked wonders! Young army doctor’s idea!”

      Hope this helps. Kind regards, Jeff

  1. ChrisL says

    If pt has not converted after vagaries man. and has had a total of 18mg of Adenosine admin per our protocol, should we consider cardioverting? Or monitor pt en route and call MD at receiving facility for consultation?

    • says

      At this stage, a cardiologist should be involved in the next treatment options. As long as the patient is stable, this would be the case. At any point if the patient becomes unstable you would perform cardioversion.

      Kind regards,

    • says

      Yes, premature atrial tachycardia (PAT) would be considered a of supraventricular tachycardia. Not sure what you mean by PAF, but if you mean atrial fibrillation with a rapid ventricular rate then yes, this would also fit the criteria for SVT.

      Kind regards,

      • Michaela says

        We usually refer : PAT and PAF as paroxysmal atrial tach and paroxysmal atrial fibrillation when the event starts suddenly, and many SVT events do start suddenly

    • says

      The 4 most common types of SVT are A-V Nodal Reentry Tachycardia, A-V
      Reentry Tachycardia, atrial tachycardia and atrial flutter. These rhythms are regular in nature and have a rate > 150. To distinguish the difference between the re-entry tachycardias and the other types really requires a 12 lead ECG. The diagnostic criteria to determine that it is a reentrant tachycardia is actually quite complex. I attached a pic from my 12 lead ecg pocket reference that will help. Reentry tachycardias are very easy to convert and often vagal maneuvers will suffice to terminate the tachycardia.

      Kind regards,

  2. Linsey says

    Lets say I have a pt hooked up to a basic tele monitor and she goes into SVT. Vagal maneuvers are attempted and doctor orders Adenosine. Would you then hook her up to the code cart prior to giving the Adenosine.?

    • Linsey says

      Oh and the patient is in stable condition.
      And would your answer be different if the patient had multiple reentrys into SVT and successful Adenosine administrations? Or maybe just having the code cart at bedside? Can Adenosine cause lethal arrhythmias?

      • says

        The crash cart would not be necessary, but it could be close at hand in the case that the patient becomes unstable. Adenosine does not normally precipitate lethal arrhythmias.

        Kind regards,

    • says

      Having the code cart prior to giving adenosine would not be necessary. It would not hurt, but it would not be necessary. Adenosine rapid IV push will not usually precipitate pulseless VT or VF.

      Kind regards,

  3. says

    What’s the difference between a stable and unstable patient. Does dsypnoea and palpitations in a patient discovered to have an SVT make him unstable. Would it be right to shock him immediately or better to do Valhalla manoeuvre then adenosine algorithm.

    • says

      The main indication of a patient that is unstable are as follows:
      1. Altered mental status
      2. SBP less than 90 (hypotension)
      3. Signs of shock
      4. Ischemic chest discomfort
      5. Acute heart failure

      The patient with dyspnea and palpitations would not necessarily be unstable, and it would most likely be ok to attempt vagal maneuvers then adenosine prior to any attempt with cardioversion.

      Kind regards,

  4. says

    In the third example on the video it states that you can see p waves. Well, if that’s true, then where are the T waves? In the explanation blurb at the beginning it says that p waves can be buried in the qrs. How are you ever supposed to know if you are looking at p waves or t waves?

    • says

      With SVT, It can be difficult to differentiate the p-waves from the t-waves. Most of the time p-waves will not be present due to the rapid HR involved with SVT.
      One way to differentiate is to give adenosine to temporarily slow the heart rate. This will give you a better look at the underlying rhythm and help to diagnose the underlying rhythm.

      Kind regards,


        Ni jeff. Another forma to find p waves and t waves in some cases justo gain 2 mV and increase TVE speed 50mm/sec. Bye!

  5. says

    Will synchronised cardioversion always convert an unstable SVT? and if not is it acceptable to administer adenosine in the case of a “SVT refractory to cardioversion”.

  6. says

    How can you tell the difference between SVT and Atrial Tachycardia? The strip I have has a rate of 180, regular rate, distinguishable P waves. I say SVT but it’s Atrial Tach?

    • says

      Atrial tachycardia is a form of SVT. Atrial tachycardia means that the tachycardia originates in the atria but not from the SA node.

      When describing a tachycardia that originates in the atria but outside of the sinus note, another term used is supraventricular. Thus, atrial tachycardia is essentially the same thing as SVT.

      Kind regards,

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