Tachyarrhythmias Flashcards
(26 cards)
Definition of narrow complex tachycardia?
Rate >100bpm
QRS complex <120ms
- narrow QRS complxes maen that the ventricles are being depolarised by normal conduction pathway
Causes of regular narrow complex tachycardia
Sinus tachycardia
Focal atrial tachycardia
Atrial flutter
Atrioventricular re-entry tachycardia e.g. WPW syndrome
Atrioventricular nodal re-entry tachycardia (SVT)
What are the causes of sinus tachycardia
Infection Pain Anxiety Exercise Bleeding Dehydration Sepsis - due to systemic vasodilation (to keep BP up) Drugs - caffeine, nicotine, salbutamol Anaemia Pregnancy CO2 retention Autonomic neuropathy Fever Pulmonary embolism Hypertyroidism
What is focal atrial tachycardia + ECG changes
A group of atrial cells acting as the pacemaker, and out-pacing the sinoatrial node >150bpm
P wave becomes superimposed onto the preceding T-wave
What is atrial flutter
Rate >250bpm in the atria, leading to a saw-tooth baseline
- ?P waves can’t be seen
AV node passes on some of the impulses, so the ventricular rate is a multiple of the atria rate
- e.g. atria 300bpm = 100bpm (3:1 AV block)`
What is atrioventricular re-entry tachycardia
An accessory pathway that allows electrical activity from the ventricles to pass to the resting atrial monocytes, creating a circuit
e.g. Wolff-Parkinson-White syndrome
What is atrioventricular nodal re-entry tachycardia + ECG signs
New circuits form within the AV node, which constantly stimulate the ventricles to contact
- causes p waves to be very close to the QRS/not visible
What are the irregular narrow-complex tachycardias
Sinus arrhythmia
Atrial fibrillation
Atrial flutter with variable block
Multi-focal atrial tachycardia
What is a sinus arrhythmia
A normal variant - rate changes on inspiration and expiration
- sinus tachycardia + ectopic beats
What is multi-focal atrial tachycardia
Like focal atrial tachycardia, but with multiple groups of cells taking it in turns to initiate cardiac cycle
- associated with COPD
How are narrow-complex tachyarrhythmias managed
Oxygen, 12-lead ECG and IV access
No adverse signs
- if irregular rhythm; probably AF
- regular rhythm; by definition is an SVT, and vagal manoeuvres should be attempted
- adenosine if this doesn’t work
- bet-blockers for possible atrial flutter if this fails
Adverse signs
- get help
- sedation and DC cardioversion (up to 3)
- correct electrolytes
- amiodarone and repeat shock as needed
Describe the use of adenosine in SVT
6mg bolus IV with 0.9% saline flush while recording a 12-lead rhythm strip
12mg bolus IV after 2 mins if initial dose unsuccessful
Max one more 12mg dose before attempting verapamil
What are the side effects of adenosine?
Chest tightness
Dyspnoea
Headache
Flushing
Contraindications of adenosine
Asthma
2nd/3rd degree heart block
Sinoatrial disease
Definition of broad-complex tachycardia?
Heart rate >100bpm
QRS >120ms
- no clear QRS complexes indicates VF or asystole
Possible causes of a broad-complex tachycardia
Ventricular fibrillation
Ventricular tachycardia
Any cause of narrow-complex tachycardia + BBB/metabolic causes of a wide QRS
Antidromic AVRT
Describe ventricular fibrillation + ECG
Ventricles attempt to contract at rates up to 500bpm, this leads to a loss of cardiac output
Chaotic and no discernible pattern on ECG
Describe ventricular tachycardia + ECG
Foci in ventricles discharge at a high frequency, causing an abnormal spread or charge through the ventricles = wide and abnormal QRS
Broad and regular QRS complex and no P waves
What is Torsade de pointes
Polymorphic ventricular tachycardia - VT with a varying axis
- looks like ventricular fibrillation
What in the history and examination could help you differentiate an SVT + BBB and VT?
Recent MI - most likely VT as it can cause ventricular damage
12-lead ECG
Response to certain medications
What ECG findings suggest a patient is experiencing VT, not SVT + BBB?
Positive or negative QRS concordance in all leads
QRS >160ms
Marked left axis deviation
AV dissociated (p waves are independent of the QRS complexes)
Fusion or capture beats
RSR’ pattern - where R is taller than R’
How is a broad-complex tachycardia managed?
Oxygen, 12-lead ECG and IV access
No adverse signs
- correct electrolyte abnormalities
- give amiodarone if rhythm is regular (adenosine instead if known history of SVT + BBB)
- seek expert help and give IV magnesium
- if none of this is successful; sedation and shock is required
Averse signs
- sedation and DC cardioversion (up to 3)
- correct electrolytes
- amiodarone and further cardioversion as needed
How should the patient be managed once the VT is corrected?
Establish the cause
Maintain anti-arrhythmics (if MI was the cause) for 12-24 hours
- solatol or amiodarone
ICD or surgical isolation of arryhythmic area if required
Why does VF require a non-synchronised DC shock?
Synchronised shocks use the R wave to trigger defibrillation - and VF doesn’t have an R waves
