Tachycardias Flashcards
What is a narrow complex tachycardia?
HR > 100bpm
QRS complex <120ms
Give some examples of irregular narrow complex tachycardias
Sinus arrhythmia
AF
Atrial flutter with variable block
How is narrow complex tachycardia managed?
Identify and treat the underlying rhythm E.g. treating sinus tachycardia secondary to dehydration with IV fluids.
If AVNRT or AVRT are suspected consider blocking AVN transiently, this will break circuit of AV re-entry rhythm allowing sinus rhythm to re-establish:
Vagal manœuvres (carotid sinus massage, valsava manoeuvre (blowing into syringe)
IV adenosine
Describe normal conduction in the heart
Initiated by the SAN
Electrical activity spreads around the atria
The AVN receives activity, pauses and then passes it on down the bundle of His which splits into the left and right bundle branches. These acute depolarisation of the ventricular myocardium from bottom to top.
Describe conduction in sinus tachycardia. Give causes
Conduction occurs normally but impulses are initiated at a high frequency.
Causes: infection, pain, exercise, anxiety, dehydration, bleed, systemic vasodilation (Sepsis), drugs, anaemia, fever, PE, hyperthyroidism
Describe conduction in focal atrial tachycardia
A group of atrial cells act as a pace maker, outpacing the SAN. P wave shape is different to sinus
Describe conduction in atrial flutter
Electrical activity circles the atria 300 times per minute giving a sawtooth baseline.
AVN passes some of these impulses on, resulting in ventricular rates that are factors of 300
Describe conduction in AVRT (Atrioventricular Re-entry Tachycardia
Accessory pathway (e.g. Bundle of Kent in WPW) allows electrical activity from the ventricles to pass to the resting atrial myocytes, creating a circuit: atria - AVN - ventricles - accessory pathway - atria.
This direction is called orthodromic conduction and results in narrow QRS complexes as ventricular depolarisation is triggered via the bundles of His.
Conduction in the other direction is called antidromic and results in broad QRS.
Describe conduction in AVNRT - atrioventricular nod re-entry tachycardia.
Circuits from within the AVN causing narrow complex tachycardias
Describe conduction in junctional tachycardia
Cells in the AVN become the pacemaker, giving narrow QRS complexes as impulses reach the ventricles through the normal routes
What can bundle branch block cause in narrow complex tachycardias
Can make them broad complex
Describe the conduction in ventricular tachycardia.
Result from circuits similar to atrial flutter or from focuses of rapidly firing cells.
QRS is broad
When a circuit is in action and its plane rotates, ECG shows broad complex tachycardia with regularly increasing and decreasing amplitudes - this is called tornadoes de pointes.
What is a broad complex tachycardia?
ECG rate > 100 QRS > 120ms
How are broad complex tachycardias managed?
Identify the underlying rhythms and treat accordingly
If in doubt treat as VT
What are differentials for broad complex tachycardia?
Ventricular fibrillation - chaotic no pattern
Ventricular tachycardia
Torsade de pointes (polymorphic VT) - VT with varying axis
Narrow complex tachycardia in combination with BBB
