QuestionSBA
QuestionChoice
This ECG is not in keeping with someone who is presenting with anxiety. Anxiety can present with palpitations, however they would have a normal ECG or sinus tachycardia. In this case, the ECG is abnormal meaning anxiety is not the single best answer
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d
Anxiety
QuestionChoice
This ECG does not show ventricular tachycardia. Ventricular tachycardia is a broad complex tachycardia (QRS complexes >120ms) whereas this ECG is a narrow complex tachycardia (QRS complexes <120ms). Therefore this ECG is more in keeping with supraventricular tachycardia
33540
c
Ventricular tachycardia
QuestionChoice
This ECG does not show atrial fibrillation. While supraventicular tachycardia and atrial fibrillation can both be classified as narrow complex tachycardias and both have absent P waves, the key difference is that atrial fibrillation is an irregularly irregular rhythm and supraventricular tachycardia is a regular rhythm. As the rhythm of this ECG is regular, this is more in keeping with a supraventricular tachycardia
33539
b
Atrial fibrillation
QuestionChoice
This is a typical ECG demonstrating supraventricular tachycardia. Key features in keeping with supraventricular tachycardia are a ventricular rate >100, regular ventricular rhythm, QRS complexes <120ms and the absence of P waves. This condition is also relatively common in young patients with no underlying cardiac disease
33538
a
Supraventricular tachycardia (SVT)
QuestionChoice
This ECG does not show Wolff-Parkinson-White syndrome. The triad of features in Wolff-Parkinson-White syndrome are delta waves (slurred upstroke in the QRS), wide QRS and a short PR interval. Although Wolff-Parkinson-White syndrome is associated with supraventricular tachycardia, there is nothing that suggests this patient has an underlying diagnosis of Wolff-Parkinson-White syndrome in the question. Therefore, the single best answer is supraventricular tachycardia
33542
e
Wolff-Parkinson-White syndrome
QuestionComment
Whoever decided to include the answer on the bloody ECG shouldn't have been let into med school
22420
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subscriber
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# Summary

Narrow complex tachycardia is a term used to describe a dysrhythmia with a heart rate greater than 100bpm and a narrow QRS complex (<120ms) on an ECG. It can be categorised as regular or irregular. Regular narrow complex tachycardias include sinus tachycardia, atrial flutter, atrioventricular re-entry tachycardia (AVRT), atrioventricular nodal re-entry tachycardia (AVNRT), and junctional tachycardia. Irregular narrow complex tachycardias include atrial fibrillation, atrial flutter with variable block, and multifocal atrial tachycardia. Symptoms may include palpitations, lightheadedness, dyspnoea, chest pain, and syncope. Management involves identifying and addressing reversible causes, performing vagal manouevres, administering medications like adenosine or beta-blockers, and performing synchronised DC cardioversion in those presenting with adverse features. Long-term management may involve cardiac ablation. Complications may include heart failure and cardiac arrest, but the prognosis is generally good.

# Definition 

A narrow complex tachycardia refers to a dysrhythmia that has a heart rate greater than 100bpm and a QRS complex that is less than 120ms. 

An important distinction to make is between a supraventricular tachycardia (SVT) and a sinus tachycardia. Sinus tachycardias frequently change rate and gradually speed up or slow down over seconds to minutes. On the other hand, an SVT starts suddenly then stays at the same rate until it ends.

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# Epidemiology 

Narrow complex tachycardias are common. 

# Pathophysiology

The pathophysiology of different narrow complex tachycardias is diverse and discussed further below.

# Classification 

Narrow complex tachycardias can be classified according to whether the rhythm is regular or irregular. 

## Regular Narrow Complex Tachycardias 

* **Sinus tachycardia**: physiological or pathological (secondary to pain, sepsis or illness). 
* **Focal atrial tachycardia**: autonomous atrial cells acting like the sino-atrial node. There is abnormal p wave morphology. 
* **Atrial flutter**: characterised by a **sawtooth baseline**. The electrical activity in the atria is at 300bpm. The AVN acts as a safety mechanism and filters through this high frequency and usually gives a ventricular rate of 150bpm or 75bpm (see below for atrial flutter with variable block). 
* **Atrioventricular re-entry tachycardia (AVRT)**: there is an accessory pathway between the atria and the ventricles that is not filtered by the AVN. Associated with Wolff-Parkinson White. 
* **Atrioventricular nodal re-entry tachycardia (AVNRT)**: there are re-entrant circuits within or near to the AVN causing a supraventricular tachycardia. 
* **Junctional tachycardia**: atrioventricular node becomes the pacemaker and causes ventricular contraction greater than 100bpm. 

## Irregular Narrow Complex Tachycardias

* **Atrial Fibrillation**: irregularly irregular rhythm with no discernible p waves.
* **Atrial Flutter with Variable Block**: atrial flutter but the atrioventricular node has a variable block of the high frequencies generated by the atria leading to an irregular rhythm. 
* **Multifocal atrial tachycardia**: similar to atrial tachycardia but there are multiple groups of autonomous atrial cells acting as the sino-atrial node leading to an irregular rhythm. It is commonly found in those with severe COPD. 

# Symptoms

* Palpitations 
* Lightheadedness 
* Dyspnoea
* Chest pain 
* Syncope 

# Signs 

* Tachycardic: regular or regularly irregular or irregularly irregular. 
* Haemodynamic instability: shock, chest pain, heart failure or syncope. 

# Investigations

## Bedside

* **ECG**: hallmark for investigation of narrow complex tachycardias. Sometimes the tachycardia can obscure the underlying rhythmn. 
* **24 hour tape**: narrow complex tachycardias are often paroxysmal and so 24 hour tapes are used to capture dysrhythmias. 

## Bloods 

* **FBC, TFTs, dyselectrolytaemias**: used to identify any clear precipitant for sinus tachycardia or other dysrhythmias. 

## Imaging

* **Echocardiogram**: useful in identifying structural heart disease that prediposes to arrhythmia e.g. dilated left atrium predisposes to atrial fibrillation. 
* **Loop recorder**: small device inserted subcutaneously to monitor heart rate and rhythmn continuously. They look like a USB stick on CXR! 
* **Cardiac catheterisation**: electrophysiologists can identify arrhythmogenic foci and ablate them. 

# Management

Management of narrow complex tachycardias is according to the Resuscitation Council Adult Tachycardia Algorithm (2021).

## Initial management

For emergencies, always follow an A-E structure. Identify reversible causes (dyselectrolytaemias, drugs, cardiac causes etc.) 

*If there are adverse signs (e.g. shock, syncope, heart failure, myocardial ischaemia):* 

* **1st line** = **synchronised DC cardioversion +/- amiodarone.**

*If there are no adverse signs:* consider whether the rhythmn is regular or irregular. 

*Regular*

* **1st line** = **vagal manouevres** including Valsalva manouevre and carotid sinus massage. Increasing vagal input can help terminate the SVT. 
* **2nd line** = **IV adenosine**. Initially give a 6mg bolus. If this is unsuccessful give 12mg. If this is still unsuccessful give 18mg. 
* **3rd line** = **verapamil or beta-blocker** 
* **4th line** = **synchronised DC cardioversion**

*Irregular*

* Probable atrial fibrillation and to treat with **beta-blockers**.  
* If there are signs of heart failure **digoxin** may be trialled. 
* If onset >48h the patient will need to be anticoagulated. 

## Further management 

Longer-term other treatments for persistent, recurrent SVT may be trialled including cardiac ablation of arrhythymogenic foci. 

# Complications

Paroxysmal SVT can lead to unpleasant symptoms for patients. Over time, paroxysmal SVT can lead to weakening of the heart muscles and lead to heart failure. SVT with adverse signs can lead to cardiac arrest and death. 

# Prognosis 

SVT is commonly a benign condition that does not shorten life expectancy. 

# NICE Guidelines

[NICE Guidelines for Palpitations](https://cks.nice.org.uk/topics/palpitations/management/current-palpitations/)

# References

[Click here to see the flowchart on the Resus Council website about managing peri-arrest rhythms](https://www.resus.org.uk/library/2021-resuscitation-guidelines/adult-advanced-life-support-guidelines)

[BNF Arrhythmias Treatment Summary](https://bnf.nice.org.uk/treatment-summaries/arrhythmias/)
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Acute narrow complex tachycardias
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A 28 year old female presents to the emergency department with palpitations. Her ECG is shown below:

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What is the most likely diagnosis?
a