ECG-ARRHYTHMIA CLASSIFICATION

SUMMARY

1. SINUS ARRHYTHMIA: variation of the HR during respiration, particularly in young people
- Increases with inspiration due to vagal inhibition of the cardio-inhibitory area of the medulla (note: double negative) due to stretch receptors in the lungs
- Decreases in expiration

2. SICK SINUS SYNDROME: pathologies related to SA node

3. HEART BLOCK (AV nodal vs infranodal block):
a. First degree: PR interval > 0.2s 
b. Second degree: Mobitz I (progressively lengthening PR interval until a QRS complex is dropped) & II (2:1, 3:1, 4:1 P waves consistently not being followed by QRS complexes)
c. Third degree: none of the P waves are conducted to the ventricles

4. SUPRAVENTRICULAR ARRHYTHMIAS:
a. Atrial flutter: circus rhythm running b/w IVC and TV causing atrial rate ~300/min commonly with 2:1 AV block
b. Atrial fibrillation: most common sustained arrhythmia, irregularly irregular ventricular response with rate 120-180/min in the absence of treatment
c. Multifocal atrial tachycardia: ECG shows atrial rate > 100/min & P waves of 3 or more distinct morphologies
d. Supraventricular tachycardia: narrow QRS complex tachycardias arising above the ventricles (key is to recognize the P wave in relation to QRS complexes)
e. Wolff-Parkinson-White syndrome: a/w an accessory/aberrant pathway (bundle of Kent) b/w atria & ventricles which bypasses the AV node & 'pre-exciting' the ventricle 

5. VENTRICULAR ARRHYTHMIAS:
a. Premature ventricular contractions: premature ventricular beats with a compensatory pause
b. Ventricular tachycardia: defined as 3 or more sequential QRS complexes of ventricular origin at rate > 100/min, divided into monomorphic vs. polymorphic VT and sustained vs. non-sustained VT