Narrow Complex Tachycardias

Narrow complex tachycardias are defined as HR > 100 bpm with a QRS < 120ms (3 small squares.

Summary of the Regular Type

Summary of the Irregular Type

Management

The most important thing to do first in these cases is an A-E assessment in order to find out if the patient is stable or unstable. Signs the patient is unstable are Shock, Syncope, Heart failure, and Myocardial ischaemia.

Unstable - Synchronised DC cardioversion

Stable - Find out if the rhythm is regular or irregular:

• Regular (SVT) - Try vagal manouveres (valsalva or carotid sinus stimulation) first. If no improvement, give IV Adenosine 6mg rapid blous (try 12mg, then 18mg if not helping).

  • Adenosine works to transiently block the AV node

• Irregular (AF) - If < 48 hours, pharmacological cardioversion (flecanide, amiodarone). If > 48 hours, rate control (Metoprolol/Bisoprolol, Verapamil) and anticoagulate.

N.B. Carotid sinus stimulation tends not to be that helpful, so the valsalva manoeuvre is more commonly used (blowing into an empty syringe).

N.B. Bisoprolol is the best cardio-specific BB, but it takes around 24 hrs for its effect to clear, therefore it can’t be easily reversed if it brings the HR and BP down too much. Metoprolol tends to be the better option initially as it can be stopped more easily.

N.B. Adenosine causes transient, complete blockage of the AV node.

Types of Shock

• Unsynchronised (same as defibrillation) - High-energy shock delivered at any random phase of the cardiac cycle.

• Synchronised - Lower-energy shock that's delivered in time with an R-wave to reset the heart's rhythm.