- Required Reading: Introduction to Arrhythmia Diagnosis
- Narrow QRS is ≤ 120ms
- Narrow QRS = Simultaneous activation of both ventricles
- A narrow QRS tachycardia activates both ventricles simultaneously.
- Atrial tachycardias generally have a narrow QRS because their ventricular activation occurs via the AV node and the ventricular conduction system (His-Purkinje system), which leads to simultaneous activation of both ventricles.
- NOTE: Atrial tachycardias can have a wide QRS, often in the presence of a RBBB, LBBB, or pre-excitation.
- NOTE: The term “SVT – Supraventricular Tachycardia” refers to narrow-QRS REGULAR tachycardia. Even though atrial fibrillation is “supraventricular”, it is not classically called SVT.
- Describe the ECG & Frame the Problem
- Step 1: Narrow vs. Wide (≥120ms?)
- Step 2: Regular vs. Irregular (use calipers)
- Present a differential diagnosis (see Tables)
- Narrow the differential diagnosis (understanding the mechanisms of arrhythmia)
|DDx of an IRREGULAR narrow QRS Tachycardia:|
NOTE: List not exhaustive, other mechanisms exist
|Differential Diagnosis of a REGULAR Narrow QRS Tachycardia|