Med in Small Doses - SVT Tachyarrhythmias


This post is on some common and important SVT/Atrial Tachyarrhythmias (e.g. Atrial Fibrillation). See Cardiac Arrhythmias for a complete overview. A Quick Guide to ECG will also give you tips on how to approach an ECG. Remember Bundle Branch Blocks effect ECG interpretation.

Typically Narrow complex (QRS<0.12)
EXCEPTION: SVT + Bundle Branch Block cause Board complex.

Supraventricular tachycardia: causes SNAP
S inus tachy
N odal tachy
A fib
P aroxysmal atrial tachy

Irregular
Atrial Fibrillation (AF): most important arrhythmia. irregular, irregular pulse. Loss of P waves.

Adapted from AFib by J.Heuser

RFs: IHD, HTN, Chronic EtOH use, cardiomyopathy, Congenital HD, Valvular lesions

Causes PIRATES:
P ulmonary: PE, COPD
I atrogenic
R heumatic heart: mirtral regurgitation
A therosclerotic: MI, CAD
T hyroid: hyperthyroid
E ndocarditis
S ick sinus syndrome

Complications: ↓ CO, embolic stroke, ↑ ventricular response.

Tx: Rate control (Beta-blockers, CCB, digoxin), rhythm control (DC cardioversion, amiodarone, flecainide) & anticoagulation.
  • AF < 48h – Cardiovert immediately with a bit of heparin
  • AF > 48h – Look for a clot. Rhythm control or rate control + anticoagulation.

Management ABCD
A nti-coagulate
B eta-blocker to control rate
C ardiovert
D igoxin

Multifocal atrial tachycardia (MAT): P-waves of at least 3 different morphologies that all fall before irregular, narrow QRS complexes.

Regular
Sinus Tachycardia (rate > 100 bpm)
Causes: exercise, pain, anxiety, hypovolaemia, PE, hyperthyroidism.
Management Priority: Search for a cause.

AVNRT: nodal problem.
  • Most common regular SVT tachycardia.
  • Females > Males

AVRT: accessory pathway.
  • Most common WPW. Short PR intervals. Delta waves.

General Tx: Valsalva manoeuvre, Carotid Sinus Massage (CSM), ocular pressure. Adenosine, DC cardioversion.

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