ECG Blocks Flashcards
What is a first degree block?
When the electrical signal starts at SAN, but is delayed at the AVN.
What are the causes of a first degree block?
- AVN damage
- Hypoxia
- Increased vagal tone
- Drug toxicity
What is the key characteristic that is shown in a first degree block?
- P-R interval is >0.2
- P-R interval is consistently delayed
What is a Type 1 second degree heart block?
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.
Define a Second degree, type 2 block?
Where the AVN conducts most beats, but blocks every 2nd, 3rd or 4th beath.
What are the characteristics of a Secondary degree, type block?
- Rate normal/slow
- P waves normal,
- Not every P has a QRS
- Atrial regular, ventricular irregular
- P - R interval is normal,
Define 2:1 AV block.
Where the AVN conducts every second signal from the SAN.
What occurs with the hearts conductive pathway in a 3rd degree heart block?
- There is no signal passed through the AVN, meaning ventricles depolarise autonomsly.
What are the characteristics for a 3rd degree bundle branch block?
- Vertricular rate 20-40
- Atrial and ventricular rate regular
- Radial pulse feels bradycardic
- No relationtionship between the P waves and the QRS complex.
What are the causes of 3rd degree heart block?
- Mi
- Conductive system damage
- Drug toxicity
- Increased vagal tone
What is the clinical significance of a 3rd degree heart block?
- Decreased Cardiac output
- Hypotenssion
- Hypoperfusion
- May progress quickly to VF
What is the pre-hospital treatment for 3rd degree heart block?
- Atropine may increase SAN and AVN activity
- Treatment of bradycardia symptoms,
In what direction does the septum depolarise?
- Left to right
Why does the QRS get wider in bundle branches?
Delay going down the bundle branches, due to areas not conducting impulse.
What leads are right bundle branch most likely to show in?
- V1 and V2
What leads are likely to show left bundle branch block?
- V5, V6 and L1
What are the characteristics of a right bundle branch block?
- QRS >0.21 (210ms)
- V1 shows RSR complex
- V1 and V6 show slurred S wave
What are the common causes or right bundle branch block?
- Diseases of the right side of the heart,
- Diseases of the lings (PE, Pulmonary hypotension)
What is the clinical significance of a right bundle branch block?
- Can be normal
- Can indication problems of the right side of the heart,
- Can be a sign of atrial septal defect
What are the characteristics of a left bundle branch block?
- QRS ?0.12 (120ms)
- V1 is broad and monomorphic
- L1 and V2 broad complex R wave, with no Q wave
In a left bundle branch block, which side of the septum depolarises first?
Right side
What are the common causes of Left bundle branch block?
- Hypertension
- Coronary atery disease
- infiltrative diseases of the heart
- dilated cardio myopathy
- Rheumatic heart diseases
- Benighn/ Idiopathic causes
