Heart Blocks

Question 1

What’s the Block?

Answer 1

1st Degree Heart Block

• PR interval > 0.20secs (5 small squares)
• Usually regular
• Usually benign
• No specific treatment required

Question 2

What’s the Block?

Answer 2

2nd Degree Heart Block Mobitz 1 (Wenckebach)

• PR interval extends until a P wave is not followed by a corresponding QRS complex
• Following PR interval is short/normal and the cycle starts again
• QRS complex must be seen at least twice in a row in order to see this pattern
• Usually benign, asymptomatic pt do not require treatment, permanent pacing rarely required
• Symptomatic pt usually respond to atropine

Question 3

What’s the Block?

Answer 3

2nd Degree Heart Block Mobitz 2

• Intermittently P waves are not followed by a QRS, with no real pattern
• P waves remain at a constant rate
• Whenever there is a QRS, the PR interval remains constant throughout
• Type 2 is of greater concern than Type 1 and sometimes requires pacing
• Extended RR interval will be an exact multiple of the number of dropped beats
• Likely to progress into bradycardia or 3rd degree block, can cause syncope and sudden cardiac death
• Immediate admission for cardiac monitoring and likely permanent pacing

Question 4

What’s the Block?

Answer 4

3rd Degree/Complete Heart Block

• No relationship between the P waves and the QRS complexes
• Usually more P waves than QRS complexes
• P & QRS are both regular but independantly of each other
• Ventricular response is usually bradycardic and the QRS are often wide and bizarre
• Typically pt will present as severe bradycardia with independant atrial/ventricular rates
• P likely to suffer ventricular standstill causing syncope or sudden cardiac death
• Urgent admission for cardiac monitoring, usually permanent pacing

Question 5

What’s the Block?

Answer 5

Left Bundle Branch Block (LBBB)

• Wide QRS with possible absence of Q in lateral leads
• Tall R waves Lateral I, V5-V6
• Deep S waves anterior V1-V3
• Broad ‘notched’ or ‘M’ shaped R wave in lateral leads

Traditionally LBBB accompanied by chest pain was criteria for thrombolysis

Question 6

What’s the Block?

Answer 6

Right Bundle Branch Block (RBBB)

• Broad QRS > 120 ms
• RSR’ pattern in the anterior leads V1-3 (‘M-shaped’ QRS complex)
• Wide, slurred S wave in the lateral leads (I, aVL, V5-6)

Question 7

What’s the Rhythm?

Answer 7

Bifascicular Block

RBBB

+

Left Axis Deviation

Question 8

What’s the Rhythm?

Answer 8

Trifascicular Block

RBBB

+

Left Axis Deviation

+

1st Degree Heart Block

May progress to 3rd degree/complete heart block then require permanent pacing