Conduction system
Bradycardia mechanisms
Bradycardia - Classification
- Sinus node disease
- Atrioventricular block
Sinus bradycardia
- Sinus node
- Sinus bradycardia
- Sinus arrest
- SA junction
- Second degree type 1 SA block
- Second degree type 2 SA block
AV block
- First degree
- Second degree type 1
- Second degree type 2
- Third degree
Learning point - Degree of AV block
- First degree - Every P wave conducted
- Second degree - Some P waves conducted, some not
- Third degree - No P waves conducted
ECGs
Always measure !
Differential diagnosis
- Sinus arrhythmia
- Sinus pause
- SA block - second degree type 1
- SA block - second degree type 2
RR intervals - expected
How to measure
Ladder diagrams
AV block or SND ?
Learning point - Distinguish AVB from SND
- P > QRS - AV block
- P = / < QRS - Sinus node disease
Ladder diagram
Similar ECG - misdiagnosed as AV block
Asymptomatic young male
Patient with slow pulse rate - Sinus bradycardia ?
Teaching points - 2:1 block
- May be mistaken as sinus bradycardia
- Especially with PR prolongation
- Can be either type 1 or type 2
2 to 1 block - Supra His (type 1) or infra His (type 2)
- QRS width
- PR interval
Intermittent improved conduction helps make a diagnosis
Infra His
Supra His 2 to 1 block
Middle aged female with syncope
EP study - Intra His block
82 year old with syncope
54 M with syncope
Female with syncope
Summary
- SND / AV block - prognosis, need for treatment different
- P waves are key
- In AV block, differentiating supra- vs infra- His block is important
- ECG gives clues, but EP if in doubt