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Matters of the heart - SVT

Patrick McMurray

What is Supraventricular Tachycardia (SVT)?

Supraventricular Tachycardia is a fast heart rate where the problem causing the arrhythmia is originating in the atria, which is above (supra) the ventricles. It is an umbrella term that covers four arrhythmias. 

  • Paroxysmal Supraventricular Tachycardia (PSVT)

  • Wolff Parkinson White Syndrome (WPW)

  • Atrial Fibrillation (AFib)

  • Atrial Flutter (Aflutter)

We will cover Atrial Fibrillation and Atrial Flutter in more detail in next week’s post. So I am going to focus on PSVT and WPW in this post.

I want to be very clear about this though, it is important to know that SVT is an umbrella term and why BUT it is also important to know how the term is frequently used in the clinical setting.

The term SVT is most often synonymous with PSVT and you will not likely hear Atrial Fibrillation referred to as SVT unless there is a Rapid Ventricular Response (RVR), and even then, it is likely referred to as AFib RVR. Pictured below:

 (Source)

I always believe that knowledge is power and that it is important to know BOTH clinical slang and technical slang. If someone says the patient is in SVT, you need to know how to read the ECG/EKG to know which SVT they are in.

So lets differentiate!

What is Paroxysmal Supraventricular Tachycardia (PSVT)?

The term Paroxysmal means sudden onset and PSVT is often used synonymously as SVT. Although not generally dangerous, PSVT is uncomfortable and typically occurs in a younger patient population, usually after intense exercising. The heart inherently has one electrical pathway, the Sinoatrial (SA) node to the Atrioventricular (AV) node, to the Bundle of His to the Purkinje Fibers. The AV node is located between the atria and the ventricles and will slow down the electrical impulse to allow time for the ventricles to fill. In PSVT the electrical pathway will become interrupted with an additional impulse that continues to circulate and fire in the atria.

One cause of PSVT occurs when the patient has two pathways in their AV node causing the additional circuit, then this is called Atrioventricular Nodal Reentrant Tachycardia (AVNRT). The EKG/ECG typically is a narrow complex tachycardia with a rate above 120 bpm.

 (Source)

 Note: The p wave is not discernable.

Another cause of PSVT can be when there are two pathways between the AV node and the ventricles. This is called Atrioventricular Reciprocating Supraventricular Tachycardia. There can be multiple different abnormal pathways between the AV node and the ventricles, such as the Bundle of Kent in Wolff-Parkinson-White Syndrome.

Video-https://youtu.be/36MT8hR-gDg

What is Wolff-Parkinson-White (WPW) Syndrome?

Wolff-Parkinson-White Syndrome is congenital and usually harmless. In WPW the additional electrical pathway does not go through the AV node, skipping the “slow down” part. This additional pathway is called the Bundle of Kent. Patients with the Bundle of Kent present will mostly be in a sinus rhythm, but have the ability to start a re-entry circuit, increasing the amount of excitation circulating in the heart, thus increasing the heart rate (tachycardia).

Video- https://youtu.be/9MDRKId2d0Q

What does WPW look like?

 (Source)

Note: There is a Delta wave between the P wave and the R wave.

This EKG/ECG is WPW in Sinus Rhythm. The delta wave is where the AV node is supposed to be getting the signal and passing it on. However, in WPW as discussed earlier, there is an additional pathway that skips over the AV node creating a slope in the ECG/EKG.

When WPW becomes tachycardic, the patient may start to become symptomatic. Signs and Symptoms as well as treatment of WPW are the same as all PSVTs (AKA SVT) and so I will cover them as just SVT.

What are the Signs and Symptoms of Supraventricular Tachycardia (SVT)?

So symptoms will be the same as any tachycardia. A patient may experience some, none, or all of the following symptoms:

  • Dizziness

  • Lightheadedness

  • Hypotension

  • Palpitations

  • Fluttering chest sensation

  • Chest pain

  • Chest tightness

  • Fatigue

  • Syncope

  • Shortness of Breath

  • Difficulty in Breathing

 

How do you treat Supraventricular Tachycardia (SVT)?

Supraventricular Tachycardias not only have the same signs and symptoms, but they mostly have the same treatment. Treatment is sort of conducted in phases.

Phase 1: Vagal Maneuvers

  • Have the patient try to push like trying to have a bowel movement

  • Submerge the patients face in ice cold water

  • Massage the patient's carotids (Done by the doctor only!)

Phase 2: Medications

The key to which medication to give is based on the EKG. This is why it is important to look at the EKG/ECG.

  • If the rhythm is regular and the QRS complex is narrow (not wide) give:

  • This medication is given via rapid bolus and causes a short pause of asystole.

  • Make sure to have the patient on the AED while giving this med in the event that the heart doesn’t start back up after the asystole.

  • Also make sure the 12-lead EKG is hooked up to the patient before, during and after the administration of adenosine.

  • If the rhythm is irregular consider Antiarrhythmics:

  • Is an antiarrhythmic cardiac glycoside

  • Slows AV conduction and prolongs AV refractory period

  • Small window of therapeutic effect and can easily become toxic so administer with caution and while monitoring the patient

  • Is a calcium channel blocker

  • Needs to be used with caution if a patient has heart failure or hypotension

  • Is a calcium channel blocker

  • Less side effects than verapamil but less effective.

Phase 3: Procedure

  • Ablation

  • This can be used as treatment OR prevention

  • Is very effective but is only used after control with medication doesn’t work because of the risks involved

  • This procedure requires scarring the tissues and sedation

Extended care of patients with SVT

SVT can occur again and the patient will need to be educated on what to avoid and how to manage their medications.

  • Avoid triggers

  • Exercise

  • Caffeine

  • Alcohol

  • Stress

  • Smoking

  • If prescribed antiarrhythmic medications, take them as prescribed. Such as:

  • Amiodarone

  • Procainamide

  • Calcium channel blockers

  • Diltiazem (Cardizem)

  • Verapamil

  • Beta-Blockers

  • Metoprolol

  • Atenolol

So like we discussed, SVT not a life-threatening arrhythmia initially, but can become life threatening (your heart can only sustain beating that fast for so long). Treatment is based on the specific rhythm and some trial and error. There are many different types of SVT, so make sure you know the differences between them!

Sources

Merck Manuals

Life in the Fast Lane

Cardiology Advisor

Mayo Clinic

Written by: Susan DuPont of BossRN.com who is a full time nurse in a level I trauma Emergency Room. In her spare time she loves the outdoors, fishing, and hunting.