Narrow Complex Tachycardia

Question 1

Definition of narrow complex tachycardia.

Answer 1

Rate > 100 bpm

QRS complex duration < 120 ms

This occurs when the ventricles are depolarised via the normal conduction pathways.

Question 2

Divisions of narrow complex tachy.

Answer 2

Regular narrow and irregular narrow.

Question 3

Irregular narrow complex tachys.

Answer 3

Most commonly AF

Can also be sinus arrhytmia (sinus with frequent ectopic beats)

Atrial flutter with variable block

Multifocal atrial tachycardia (usually associated with COPD).

Question 4

Regular narrow complex tachys.

Answer 4

Sinus tachycardia most commonly.

Focal atrial tachycardia

Atrial flutter

Atrioventricular re-entry tachycardia (AVRT)

Atrioventricular nodal re-entry tachycardia (AVNRT)

Junctional tachycardia

Question 5

Common causes of sinus tachycardia.

Answer 5

Infection

Pain

Exercise

Anxiety

Dehydration/Hypotension

Bleed

Systemic vasodilation

Drugs

Anaemia

Fever

PE

Hyperthyroidism

Pregnancy

CO2 retention etc…

Question 6

Explain focal atrial tachycardia.

Answer 6

A group of atrial cells act as a pacemaker that outpaces the SAN.

The P-wave morphology is different to sinus tachycardia because of this.

Question 7

Explain atrial flutter.

Answer 7

Electrical activity circles the atria 300 times per minute.

This gives a sawtooth baseline. The AVN passes some impulses on leading to ventricular rates that are factors of 300 (150 (most common), 100, 75)

Atrial flutter is caused by a “re-entrant rhythm” in either atrium. This is where the electrical signal re-circulates in a self-perpetuating loop due to an extra electrical pathway.

Question 8

Explain atrioventricular re-entry tachycardias.

Answer 8

An accessory pathway such as bundle of Kent in Wolff-Parkinson-White allows electrical activity from the ventricles to pass to the resting atrial myocytes creating a circuit.

This results in a narrow QRS complex as ventricular depolarisation is triggered via the bundles of His still, it’s called an orthodromic conduction.

The reverse way is called antidromic and gives a broad QRS + delta waves.

Question 9

Explain atrioventricular nodal re-entry tachycardias.

Answer 9

Circuits form within the AVN. This causes narrow complex.

Question 10

Explain junctional tachycardia.

Answer 10

Cells in the AVN become the pacemaker.

This gives a narrow QRS as impulses reach the ventricles through the bundle of His still.

However the P wave may be inverted (because the conduction goes in reverse) and also late.

Question 11

ECG of AF.

Answer 11

Absent p waves and irregular QRS complexes + NCT.

Question 12

Atrial flutter on ECG.

Answer 12

Atrial rate = 260-340 bpm

Sawtooth baseline due to a re-entrant circuit usually in the right atrium.

Ventricular rate is often 150 bpm.

Question 13

Atrial tachycardia on ECG.

Answer 13

Abnormally shaped P waves that may outnumber QRS.

Question 14

Multifocal atrial tachycardia on ECG.

Answer 14

3 or more P-wave morphologies + irregular QRS complex.

Question 15

Management algorithm of narrow complex tachycardia Pt 1.

Answer 15

1 - Give O2 if SaO2 < 90% + IV access + 12 lead ECG

2 - Check for adverse signs such as;
Shock
Chest pain/ischaemia on ECG
Heart failure
Syncope
If one of the following signs are present treat as haemodynamically unstable.

Question 16

Treatment of NCT in patient with adverse signs.

Answer 16

1 - Get expert help.

2 - Sedate patient

3 - Do up to 3 synchronized DC shocks - 70 to 120J for the first, then 120 to 360J subsequently.

4 - Check and correct K+, Mg2+ and Ca2+

5 - Amiodarone 300mg IV over 20 minutes or more.
Consider repeat shock then give 900mg amiodarone over 24h IVI via central line.

Question 17

If there is NCT but the patient is stable, what should be assessed?

Answer 17

Is the rhythm regular or irregular?

Question 18

If the rhythm is irregular, how should it be treated?

Answer 18

It is most probably AF, so treat as AF.

(This will be detailed in other flashcards)

Question 19

Treatment of NCT in stable patient with regular rhythm.

Answer 19

1 - Start continuous ECG trace and perform vagal manoeuvres (valsalva, carotid sinus massage) CId if digoxin toxicity, acute ischaemia or carotid bruit (carotid bruit + massage might lead to emboli)

2 - If vagal manoeuvres fail -> Give adenosine 6mg bolus IV, then 12 mg and then 12 mg again if necessary.
Verapamil 2.5-5mg over 2 min can be given if adenosine is CId.

3 - If sinus rhythm is not achieved as of yet -> Possible atrial flutter and seek expert help. Control rate with e.g. b-blockers.

3 - If sinus rhythm is achieved -> Probably paroxysmal re-entrant SVT so assess ECG for e.g. WPW.

Question 20

Treatment of acute irregular NCT (AF).

Answer 20

Control rate;
B-blockers like metoprolol 1-10 mg IV
Rate-limiting Ca2+ blocker like verapamil 5-10mg IV
Digoxin can be given if there is HF
Amiodarone can also be given

Do not give them in combination!

Consider anticoagulation with warfarin or DOAC to reduce risk of stroke.

If onset is definitely less than 48h or if effectively anticoagulated for over 3 weeks consider DC cardioversion under sedation or chemical cardioversion with fleicanide 300mg PO or amiodarone 300 mg IVI over 20-60 min and then 900mg over 24h.

Question 21

Specific treatment of sinus tachycardia.

Answer 21

Treat underlying cause

Question 22

Specific treatment of superventricular tachycardia.

Answer 22

If adenosine fails use verapamil. Do not give this if on b-blocker as well.

Can also give atenolol.

DC cardioversion if unsuccessful.

Question 23

Specific treatment of AF/flutter

Answer 23

Discussed earlier.

Question 24

Specific treatment of atrial tachycardia.

Answer 24

This is rare and may be due to digoxin toxicity.

Withdraw digoxin.

Maintain K+ at 4-5 mmol/L

Question 25

Specific treatment of Multifocal atrial tachycardia.

Answer 25

This is most commonly due to COPD.

Correct hypoxia and hypercapnia.

Consider verapamil if rate remains >110 bpm.

Question 26

Specific treatment of junctional tachycardia.

Answer 26

First try vagal manoeuvres.

Adenosine if unsuccessful

If still unsuccessful try b-blockers.

If this still won’t do the trick consider radiofrequency ablation.

Question 27

Tachycardia treatment summary

Answer 27

Unstable patient:

Consider up to 3 synchronised shocks

Consider an amiodarone infusion

In a stable patient:

Narrow complex (QRS < 0.12s)

Atrial fibrillation – rate control with a beta blocker or diltiazem (calcium channel blocker)

Atrial flutter – control rate with a beta blocker

Supraventricular tachycardias – treat with vagal manoeuvres and adenosine

Broad complex (QRS > 0.12s)

Ventricular tachycardia or unclear – amiodarone infusion

If known SVT with bundle branch block treat as normal SVT

If irregular may be AF variation – seek expert help