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.

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 synchronized 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.

Below is a short video which will help you quickly identify supraventricular tachycardia on a monitor.
Please allow several seconds for the video to load. (4.37 mb)

Click for next Rhythm Review: Atrial Flutter

Questions Asked On This Page

1. Q: What are vagal maneuvers?

   A: A vagal maneuver is a technique by which you attempt to increase intrathoracic pressure which stimulates the vagus nerve. This can result in slowed conduction of electrical impulses through the AV node of the heart. The following methods can be used.

   1. Cough Method: Have a patient cough forcefully. This is a simple form of vagal maneuver. A cough stimulates an increase in intrathoracic 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. Now instruct 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 patient’s abdomen while they contract and resist pressing into their abdomen.
   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!”

2. Q: I can’t distinguish the sinus tachycardia example from the three re-entry SVT examples on the pre-test no matter how long I stare at the strips…they look identical to me. Help please, and thanks.

   A: On the Pretest at the AHA website, Look at each image carefully. Don’t try to over-observe. Just look at each one and notice how many QRS complexes there are.
   There are almost double the amount of QRS complexes in all of the SVT when compared to the Sinus Tachycardia. This is the easiest way to tell SVT from Sinus tachycardia. Also, P-waves are only clear in the sinus tachycardia. Most of the time with SVT you will not be able to see the p-waves. SVT rate will usually be greater than 150 and Sinus tachycardia will be less than 150.

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3. Q: Let me get this straight. Svt is a heart rate greater than 150 with conduction at or above the av node?

   A: That is correct.

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4. Q: When is putting pressure on the jugular used for SVT?

   A: Applying pressure or lightly massaging carotid artery would be considered a vagal maneuver. This or any type of vagal maneuver would be performed for symptomatic SVT if the patient is stable and the QRS complex is less than 0.12 second.

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5. Q: What is the easiest way of recognizing reentry supraventricular tachycardia on a rhythm strip?

   A: The four most common types of SVT are A-V Nodal Reentry Tachycardia, A-V Reentry Tachycardia, atrial tachycardia, and atrial flutter. These rhythms are regular and have a rate > 150.

   To distinguish the difference between the re-entry tachycardias and the other types requires a 12 lead ECG. The diagnostic criteria to determine that it is a reentrant tachycardia is complex. Reentry tachycardias are very easy to convert, and often vagal maneuvers will suffice to terminate the tachycardia.

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6. Q: For adenosine IVP, how many ccs of normal saline DO WE USE SINCE IT HAS A SHORT HALF LIFE?

   A: You would follow the dosage of adenosine with 10 ml of NS. You should have the 10 ml on a double port IV or put the 2nd port on with a stop-cock. This way you can push the adenosine in rapidly, and then with as short a time as possible, you can forcefully push the 10ml bolus of NS in. You must push both extremely fast. The faster, the better.

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7. Q: How can I distinguish between SVT and sinus tach?

   A: The rate for SVT will usually be greater than 150. With sinus tachycardia, the rate will usually be less than 150. Sinus tachycardia is usually related to some underlying cause like hypovolemia, fever, or sepsis and the rate will not exceed 150.
   This is the easiest way to determine the difference.
   For SVT, the symptoms can arise suddenly and may resolve without treatment. The rate for SVT will typically be 150-270/min and will often be accompanied by the following symptoms: pounding heart, shortness of breath, chest pain, rapid breathing, dizziness, or loss of consciousness.

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8. Q: What should be the duration of time to perform vagal maneuvers.

   A: Vagal maneuvers should be attempted for 5 to 10 seconds. This should be enough time to stimulate the vagus nerve.

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9. Q: What’s the difference between a stable and unstable patient. Does dyspnea 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 Valsalva maneuver then adenosine algorithm?

   A: 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 before any attempt with cardioversion.

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10. Q: Will synchronized cardioversion always convert an unstable SVT? And if not, is it acceptable to administer adenosine in the case of an “SVT refractory to cardioversion.”

    A: Synchronized cardioversion works over 90% of the time for standard SVTs which are AVRT and AVNRT. Adenosine is not the treatment of choice for unstable SVT.

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11. Q: 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 complexes. How are you ever supposed to know if you are looking at p waves or t waves?

    A: 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 with the diagnosis.

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12. Q: 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?

    A: 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.

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13. Q: I was under the impression that adenosine can be given just two times (6mg, 12mg). Please advise.

    A: Giving a second dose of 12mg (6-12-12) of adenosine is fine. This is not clear in the manual. For many years AHA listed 6-12-12 and then in 2010 it changed to 6-12. Honestly, I have never gotten a clear answer from AHA on this matter. I have been told and have seen that at times the 2nd dose of 12 mg may be necessary. It can be given.

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14. Q: How I can identify the SVT wide QRS related to antidromic re-entry and stable patient with monomorphic ventricle tachycardia in ECG?

    A: This can be very difficult. Differentiation of VT from SVT with aberrancy is not always possible. This web page goes much more into detail on the subject.

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15. Q: If a patient is unstable, do you go straight to cardioversion? And if so when do you give adenosine? What about is stable?

    A: Yes, if the pt. is unstable, you go straight to cardioversion. In general, if the patient is stable with narrow complex SVT, you could attempt vagal maneuvers and then adenosine if vagal maneuvers fail.

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16. Q: Today I took the pre-assessment on the AHA student site and the rhythm section had several reentry tachycardias—what is the difference from other tachycardias and what do I look for on the rhythm strip. I have minimal EKG knowledge and am struggling a bit.

    A: The most common re-entry tachycardia is SVT. The major difference is the rate will usually be greater than 150/min (often greater than 170), and there will be no p-waves present. The pathophysiology of re-entry tachycardia is a bit complicated to explain without some visuals. Here is a web page about the subject.

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17. Q: How can you tell the difference between rapid A-Fib and PSVT when the rate is so high? Both can be treated very differently.

    A: This can be a difficult thing. I have seen adenosine used as a diagnostic tool to differentiate between the two, and it works well.
    When you give adenosine, it slows the heart and allows you to see the underlying rhythm. When adenosine is given, and the rate temporarily slows, you will see the difference. If atrial fibrillation is present, you will see an irregular rhythm with no p-waves. If the rhythm is SVT, you should see a regular rhythm when the rate is slowed.

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18. Q: If PAT is symptomatic what is the ACLS treatment, is it cardioversion or adenosine?

    A: PAT is a form of SVT which originates within the atria but outside of the sinus node. Atrial flutter and multifocal atrial tachycardia are specific types of atrial tachycardia.
    If a patient is symptomatic and UNSTABLE, then the treatment would be cardioversion.
    If a patient is symptomatic and STABLE, then the treatment would vary depending on the cause of the PAT. In many cases, PAT will be asymptomatic and needs no treatment. However, in other cases such as toxicity, caffeine, or scarring on the heart. There are different treatments for each.

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19. Q: I’ve read some literature, the atrial tachycardia were classified as PSVT and SVT, how to differentiate them? Or is it just the same?

    A: Technically atrial tachycardia is different from SVT when it comes to SVT as presented within ACLS. When you think of arrhythmias, think of them in the two categories.

    1. Arrhythmias above the ventricles (supraventricular)
    2. Arrhythmias in the ventricles

    SVT is a very generic term, and within the framework of ACLS (I wish AHA would be more specific), SVT for ACLS purposes is typically referring to AVNRT and AVRT.
    Atrial tachycardia is a type of SVT because it is supraventricular (above the ventricles), but because of the general nature of the word SVT and how the AHA ACLS provider manual uses the word, it can be confusing.
    This can get a bit technical and so I have provided a link to a great article about SVT that may hopefully help clarify things for you.
    Supraventricular Tachycardia Explained.

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20. Q: Is there a way to distinguish between atrial tachycardia and SVT? I know AT is a form of SVT. However, I was taking a practice test for my NREMTP and was given a rhythm strip for interpretation… HR 170 regular narrow QRS, p waves buried in the T wave… I chose SVT, but the answer said AT.

    A: It can be difficult to distinguish between AT and SVT. Here are two things that may help.

    1. Typically, the rate for SVT is going to be extremely high. Greater than 200. Not always but typically. If the rate is below 200 question whether it is SVT.
    2. With AT you can often make out inverted P-waves (Lead II) that are buried in the T-wave. Retrograde p-waves are typical because the electrical impulse is being generated within the atrial from a different than normal position (Ectopic).

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21. Q: Does SVT- AVNRT, and AVRT need to EP study?

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

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22. Q: If pt has not converted after vagal maneuvers 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?

    A: 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.

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23. Q: How can we treat SVT in a hypotensive patient <90 systolic, while refusing dc shock?

    A: If the patient refuses cardioversion, you could attempt adenosine as prescribed for SVT in the AHA ACLS tachycardia algorithm.

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24. Q: What happened to Adenocard in the algorithm?

    A: Adenocard (adenosine) it’s still part of the tachycardia algorithm. All of this information is covered on the site pages that review the tachycardia algorithm.