ECG Arrhythmias (a.k.a. non-sinus rhythm) can be quite difficult to distinguish. As a starting point it is always ideal to identify the QRS complex and its rate (in relation to the ventricles), identify the P wave and its rate (in relation to the atria), and the relationship between the P wave and the QRS complex.
Identifying ECG Arrhythmias
STEP 1: The Ventricle
- is the heartbeat FAST (>100bpm) or SLOW (<60bpm)?
- is it REGULAR or IRREGULAR? can you hear any extra beats?
- is it NARROW <120ms) or WIDE (>120ms)
STEP 2: The Atrium
- focus on the P wave in the II and VI ECG lead reading
- note the rate
- note the morphology
Step 3: The Relationship between the Ventricle and the Atrium
- is there any relationship between the P Wave and the QRS Complex?
- is every P Wave followed by a QRS Complex?
- is every QRS Complex preceded by a P Wave?
- what is the ratio of P:QRS?
- can you note an AV dissociation where the atria and ventricles beat independently of each other?
- determine the PR interval – does it change?
- determine the RR interval – does it change?
Normal Sinus Rhythm
A normal sinus rhythm features a good relationship between the ventricles and the atria, with a heart rate between 60-100bpm.
Bradycardia
Bradycardia presents with a heart rate of less than 60bpm.
Tachycardia
Tachycardia presents with a heart rate of over 100bpm; may present as:
NARROW COMPLEX, REGULAR OR IRREGULAR:
- Regular Tachycardia: sinus tachycardia OR atrial flutter
- Irregular Tachycardia: atrial fibrillation with no P Waves OR atrial flutter with variable AV conduction
WIDE COMPLEX, REGULAR OR IRREGULAR:
- Regular Tachycardia: sinus tachycardia (VT with aberrant conduction)
- Irregular Tachycardia: atrial fibrillation (with aberrant conduction)
Atrial Fibrillation presents with absent, very hard to identify P wave, indicating issues within the atrial chambers functionality.
Ventricular Tachycardia presents with an absent P wave, high heart rate, and with a wide and somewhat weird-looking QRS complex.
AV Block
1° AV Block = Delayed Block – PROLONGED but CONSTANT PR interval (>200ms) + P wave with every QRS complex.
2° AV Block Mobitz Type 1 a.k.a. Wenchenbach = Intermittently Blocked – PROGRESSIVELY LENGTHENING PR intervals until a P Wave fails to conduct, leading to a DROPPED QRS complex (missed beat); next cycle restarts with a normal PR.
2° AV Block Mobitz Type 2 = Intermittently Blocked – P waves NOT ALWAYS FOLLOWED by QRS complex + CONSTANT NORMAL or PROLONGED PR interval.
High Grade AV Block = Intermittently Blocked – consecutive P Waves are not followed by QRS complex + CONSTANT NORMAL or PROLONGED PR interval.
3° AV Block = Completely Blocked – NO RELATIONSHIP a.k.a. dissociation BETWEEN P wave and QRS complex; PR interval is different with each beat and P Waves are usually faster than QRS complexes.
The Escape Rhythm
In complete heart block (3° AV Block), the heart functions through the:
- Junctional escape beating @ 40-50bpm indicating block in the AV node;
- Ventricular escape beating @ 20-40bpm indicating block in the His-Purkinje site. This is unreliable and results in asystole.
Ventricular Fibrillation happens when the ventricles fibrillate without prefilling, pushing no blood volume out to circulation = no cardiac output. This is a SHOCKABLE RHYTHM.
Asystole presents with an absence of electrical impulses as an almost flat line on an ECG. Prior to this rhythm, the patient may present with agonal breathing. CPR should be performed. Asystole is NOT A SHOCKABLE RHYTHM.
Practice Interpreting ECG Arrhythmias
ECG Simulator: https://skillstat.com/tools/ecg-simulator/
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