Narrow complex tachycardias Flashcards
Describe what a narrow complex tachycardia is?
ECG shows a rate of >100BPM but a QRS complex duration of <120ms
Narrow QRS complex as ventricles are depolarised via the normal conduction pathways
What is sinus tachycardia?
What are the causes?
Conduction occurs normally in sinus rhythm, but impulses are initiated at a high frequency.
Causes -
- Infection, pain, exercise, anxiety, dehydration, bleeding, sepsis, anaemia, fever, PE, hyperthyroidism, pregnancy
- Autonomic neuropathy
- Drugs eg caffeine, nicotine, salbutamol
What is focal atrial tachycardia?
How do you know it’s this compared to sinus tachycardia?
A group of atrial cells act as a pace maker, outpacing the SAN.
P wave will be a different morphology to sinus rhythm. Classically there are inverted P waves in the inferior leads.
What is atrial flutter?
Why can it cause a heart ‘block’
What are the classical ECG signs?
Electrical activity circles the atria 300 times a minute, giving a sawtooth baseline. It is a classic example of a macro-reentrant circuit.
Due to the fast atrial rate, the AVN causes a block. Classically a 2:1 block aka 2 P waves for every QRS.
- Rate of depolarisation >250bpm
- Typical sawtooth pattern
- Best seen in inferior leads
What is a ‘supraventricular tachycardia’?
A tachyarrythmia derived from reentrant circuits involving the AVN.
What are the two types of SVT?
Are they easy to distinguish on an ECG?
- AVNRT - Atrioventricular nodal reentrant tachycardia
- AVRT - Atrioventricular reentrant tachycardia
No
What is AVNRT?
In what patients does it present?
What would distinguish it on an ECG?
Circuits form within the AVN, causing narrow complex tachycardias.
Occurs in patients with structurally normal hearts and is the most common.
Usually absent P waves.
What is AVRT?
An accessory pathway allows electrical activity from the ventricles to pass to the resting atrial myocytes, creating a circuit.
Occurs in younger patients.
What is orthodromic conduction?
Is it more common?
What does the ECG show?
Antegrade conduction via the AVN, retrograde conduction via the accessory pathway.
Yes
ECG shows:
- Rapid, narrow complex QRS
- Absent P waves
What is antidromic conduction?
What does the ECG show?
Antegrade conduction via accessory pathway, retrograde conduction via the AVN.
ECG shows:
- Appearance similar to VT
- Rapid broad complex QRS
- Absent P waves
What is Wolff-Parkinson-White syndrome?
It is a preexcitation syndrome that is characterized by congenital accessory pathway and episodic tachyarrhythmias
What is the structural abnormality in WPW called?
Which direction of conduction does it allow?
Which conduction will show ECG symptoms at rest?
Bundle of Kent
Antegrade and retrograde
Antegrade - Can be seen on the resting ECG
Retrograde - Conceals the accessory pathway
What pattern does the ECG show with WPW?
- Short PR interval as no AVN conduction delay
- Early slurred upstroke in the QRS complex, called a delta wave
What is the concern with WPW?
- Development of AF
- Will be conducted to the ventricles, leading to VF
What is AF called when it causes tachycardia?
AF with fast ventricular response
