Narrow Complex Tachycardias
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Article at a Glance
- Paroxysmal supraventricular tachycardia (PSVT) is a term that encompasses several rapid and narrow complex tachycardias.
- Reentrant circuits are responsible for many types of supraventricular tachycardia (SVT).
- Vagal maneuvers include the Valsalva maneuver and carotid sinus massage.
- Adenosine is an effective and safe treatment for narrow and rapid SVTs.
- Calcium channel blockers and β-blockers provide longer-lasting atrioventricular (AV) nodal blockade.
Adult Tachycardia Algorithm with a Pulse
Regular Narrow QRS Complex: Supraventricular Tachycardia
Most SVTs are caused by a reentrant circuit that produces impulses that travel in a circular manner within the myocardium.1 A QRS complex that measures less than 0.12 seconds is considered to be narrow and is characteristic of SVT. SVT can also present as wide QRS complexes (greater than 0.12 seconds) if there is a preexisting bundle branch block or rate-dependent aberrancy.
Related Video – ECG Rhythm Review – Supraventricular Tachycardia (SVT)
These reentrant circuits can occur in the atrial myocardium, causing atrial fibrillation (an irregular narrow complex tachycardia) or atrial flutter (a very rapid, regular narrow complex tachycardia). They can also occur in the AV node itself.
If the circuit has both limbs in the AV node, then the result is an AV nodal reentry tachycardia (AVNRT). If the circuit has one limb in the AV node and the other in an accessory pathway, then the result is an AV reentry tachycardia (AVRT). These rhythms are commonly referred to as paroxysmal supraventricular tachycardia (PSVT). They create a regular rate exceeding 150 beats per minute.
There is no P-wave evident in AVNRT.
Related Video – ECG Rhythm Review – Atrial Fibrillation
Related Video – ECG Rhythm Review – Atrial Flutter
Supraventricular tachycardias can also be caused by an excited automatic focus. This excited automatic focus results in a gradual increase or decrease in the heart rate, similar to that of impulses arising from the sinoatrial node.
These automatic foci can also cause ectopic atrial tachycardias, multifocal atrial tachycardias, and junctional tachycardias. They are difficult to treat and may not respond to synchronized cardioversion but can be controlled with drugs that slow the conduction through the AV node, which in turn slows the ventricular rate.
Read: Rhythm-based Management In Cardiac Arrest
Treatment: Vagal Maneuvers
Vagal maneuvers and adenosine are the preferred initial management for PSVT. Vagal maneuvers, such as the Valsalva maneuver or carotid massage, can terminate up to 25% of PSVTs.2 However, for other SVTs, these maneuvers will only temporarily slow the ventricular rate and will not terminate the tachyarrhythmia. Slowing the rate temporarily can make it easier to identify the rhythm.
The Valsalva maneuver is a breathing method used to slow down the heart. It is performed by breathing out through the mouth while holding the nose tightly closed.
Treatment: Adenosine
Due to its fast half-life, adenosine is given at a dose of 6 mg via rapid intravenous (IV) push through a large vein, followed by a 20 mL flush of normal saline.3 It is the preferred treatment for regular and narrow tachycardias, but it must be used with caution in patients who may have Wolff-Parkinson-White syndrome because it can cause atrial fibrillation. Therefore, a defibrillator should always be on standby.
As with vagal maneuvers, adenosine is a temporary intervention in treating SVTs other than PSVT.
Adenosine is given through a rapid intravenous (IV) push.4
Related Video -Adenosine – ACLS Drugs
Amiodarone is an option for treating wide complex stable wide complex SVT. Amiodarone has a slower therapeutic effect compared with adenosine. It also has a risk of proarrhythmic effects. Therefore, adenosine is favored over amiodarone as a first line drug.
Related Video – Amiodarone – ACLS Drugs
Adenosine is safe to use in patients who are pregnant but is contraindicated in patients with asthma.
The dose should be reduced to 3 mg if it will be given via a central line or if a patient has taken dipyridamole or carbamazepine. Higher doses may be necessary for patients who have high levels of theophylline, caffeine, or theobromine in their system.
After successful cardioversion with adenosine, the patient must be monitored continuously. If there is a recurrence of PSVT, adenosine may be administered again or a longer-acting AV nodal blocking agent, such as diltiazem or a β-blocker, may be administered.
If, after treatment with adenosine, the patient experiences another form of SVT, then a longer-acting AV nodal blocking agent may be administered to produce a longer-lasting control of ventricular rate.
Treatment: Calcium Channel Blockers and Beta-Blockers
As previously mentioned, persistent PSVT, recurring PSVT, or other forms of SVT occurring after treatment of PSVT can be treated with longer-acting AV nodal blocking agents, such as calcium channel blockers (diltiazem or verapamil) or β-blockers.
Related Video – Verapamil vs. Cardizem – ACLS Drugs
Related Video – Beta Blockers – ACLS Drugs
These longer-acting agents affect the nodal tissue to terminate the reentry circuit of PSVT that is dependent on the AV node. Their longer duration results in a sustained termination of PSVT and control of atrial tachyarrhythmias. Studies have shown that verapamil and diltiazem can successfully convert PSVT to normal sinus rhythm.5
Verapamil is administered at a dose of 2.5–5 mg IV slowly over two minutes. For older patients, it is administered over three minutes. Repeated doses of 5–10 mg every 15–30 minutes may be necessary to achieve the desired effect.
Verapamil is reserved for patients with narrow complex reentry SVT or other arrhythmias that are supraventricular in origin. It is contraindicated in patients with wide complex tachycardias and patients with heart failure.
Verapamil and diltiazem are calcium channel blockers.
Diltiazem is administered at a dose of 15–20 mg IV slowly over two minutes. It can also be repeated if the desired effect has not been reached after 15 minutes, using a dose of 20–25 mg. A maintenance infusion of 5–15 mg/hour titrated to the desired heart rate can also be administered.6
Metoprolol, atenolol, propranolol, esmolol, and labetalol are types of β-blockers used to treat SVT. Their therapeutic effect is achieved by antagonizing the sympathetic tone of the nodal tissue, which slows conduction.
These drugs also have negative inotropic effects that can potentially reduce cardiac output, and therefore, they should be used with caution in patients with heart failure. Other side effects of β-blockers include bradycardia, AV conduction delays, and hypotension. These drugs must also be used with caution in patients with obstructive pulmonary disease.
The use of adenosine, calcium channel blockers, β-blockers, or digoxin is contraindicated in patients with pre-excited atrial fibrillation or flutter that conducts to the ventricles through the AV node and an accessory pathway, as these drugs are unlikely to slow the ventricular rate and may even increase it. These drugs must not be used in these situations.
Combining AV nodal blocking agents may cause profound bradycardia. Therefore, the clinician should avoid overlapping these treatments, keeping in mind that this can potentiate their effects.
It is important for clinicians to understand the various presentations of tachycardia. This article describes the different types of supraventricular tachycardias and methods for managing them, including using the Valsalva maneuver and pharmacologic methods, such as adenosine and calcium channel blockers.
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Editorial Sources
ACLS Certification Association (ACA) uses only high-quality medical resources and peer-reviewed studies to support the facts within our articles. Explore our editorial process to learn how our content reflects clinical accuracy and the latest best practices in medicine. As an ACA Authorized Training Center, all content is reviewed for medical accuracy by the ACA Medical Review Board.
1. Amandeep Goyal; Benjamin Senst; Poonam Bhyan; Roman Zeltser. Reentry Arrhythmia. National Library of Medicine. 2022.
2. Logan J. Niehues; Victoria Klovenski. Vagal Maneuver. National Library of Medicine. 2021.
3. Shashank Singh; Rebecca McKintosh. Adenosine. National Library of Medicine. 2021.
4. Adenosine. McGuff Medical Products. 2021.
5. Brubaker S, Long B, Koyfman A. Alternative treatment options for atrioventricular-nodal-reentry tachycardia: An emergency medicine review. J Emerg Med. 2018
6. Medscape. diltiazem (Rx). 2022
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