ECG Blocks

Question 1

What is a first degree block?

Answer 1

When the electrical signal starts at SAN, but is delayed at the AVN.

Question 2

What are the causes of a first degree block?

Answer 2

• AVN damage
• Hypoxia
• Increased vagal tone
• Drug toxicity

Question 3

What is the key characteristic that is shown in a first degree block?

Answer 3

• P-R interval is >0.2
• P-R interval is consistently delayed

Question 4

What is a Type 1 second degree heart block?

Answer 4

Where the electrical signal that starts at the SAN gradually increases in delayed att the AVN, till a point where it is not passed through the AVN. This eventually reverts back to normal complex.

Question 5

Define a Second degree, type 2 block?

Answer 5

Where the AVN conducts most beats, but blocks every 2nd, 3rd or 4th beath.

Question 6

What are the characteristics of a Secondary degree, type block?

Answer 6

• Rate normal/slow
• P waves normal,
• Not every P has a QRS
• Atrial regular, ventricular irregular
• P - R interval is normal,

Question 7

Define 2:1 AV block.

Answer 7

Where the AVN conducts every second signal from the SAN.

Question 8

What occurs with the hearts conductive pathway in a 3rd degree heart block?

Answer 8

• There is no signal passed through the AVN, meaning ventricles depolarise autonomsly.

Question 9

What are the characteristics for a 3rd degree bundle branch block?

Answer 9

• Vertricular rate 20-40
• Atrial and ventricular rate regular
• Radial pulse feels bradycardic
• No relationtionship between the P waves and the QRS complex.

Question 10

What are the causes of 3rd degree heart block?

Answer 10

• Mi
• Conductive system damage
• Drug toxicity
• Increased vagal tone

Question 11

What is the clinical significance of a 3rd degree heart block?

Answer 11

• Decreased Cardiac output
• Hypotenssion
• Hypoperfusion
• May progress quickly to VF

Question 12

What is the pre-hospital treatment for 3rd degree heart block?

Answer 12

• Atropine may increase SAN and AVN activity
• Treatment of bradycardia symptoms,

Question 13

In what direction does the septum depolarise?

Answer 13

• Left to right

Question 14

Why does the QRS get wider in bundle branches?

Answer 14

Delay going down the bundle branches, due to areas not conducting impulse.

Question 15

What leads are right bundle branch most likely to show in?

Answer 15

• V1 and V2

Question 16

What leads are likely to show left bundle branch block?

Answer 16

• V5, V6 and L1

Question 17

What are the characteristics of a right bundle branch block?

Answer 17

• QRS >0.21 (210ms)
• V1 shows RSR complex
• V1 and V6 show slurred S wave

Question 18

What are the common causes or right bundle branch block?

Answer 18

• Diseases of the right side of the heart,
• Diseases of the lings (PE, Pulmonary hypotension)

Question 19

What is the clinical significance of a right bundle branch block?

Answer 19

• Can be normal
• Can indication problems of the right side of the heart,
• Can be a sign of atrial septal defect

Question 20

What are the characteristics of a left bundle branch block?

Answer 20

• QRS ?0.12 (120ms)
• V1 is broad and monomorphic
• L1 and V2 broad complex R wave, with no Q wave

Question 21

In a left bundle branch block, which side of the septum depolarises first?

Answer 21

Right side

Question 22

What are the common causes of Left bundle branch block?

Answer 22

• Hypertension
• Coronary atery disease
• infiltrative diseases of the heart
• dilated cardio myopathy
• Rheumatic heart diseases
• Benighn/ Idiopathic causes