eLFH - The Electrocardiogram Part 2 Flashcards
Types of Heart Block
1st Degree Heart Block
2nd Degree Heart Block - Mobitz Type 1 (Wenckebach)
2nd Degree Heart Block - Mobitz Type 2
3rd Degree Heart Block
1st degree heart block definition
Prolongation of PR interval
Delay at the AV node
2nd degree heart block - Mobitz type 1 definition
Progressive prolongation of PR interval until P wave is not conducted to ventricles and process restarts
2nd degree heart block - Mobitz type 2 definition
Intermittent failed conduction via AV node from atria to ventricles
Commonly 2:1 or 3:1 block
3rd degree heart block definition
Complete dissociation of atrial and ventricular activity
Aka complete heart block
Components of Left Bundle branch
Anterior fascicle
Posterior fascicle
Causes of LBBB
IHD
LVH - HTN, AS
Cardiomyopathy
Pacing of right ventricle
Causes of RBBB
IHD
HTN
Cardiomyopathy
RV strain - PE, COPD, ASD
ECG changes in LBBB
Broadened QRS
V1 negative at end of QRS
V6 positive at end of QRS
‘WiLLiaM’
Reason for ECG changes in LBBB
Normal left bundle branch conduction is blocked
Septum and left ventricle reliant on depolarisation spreading from right ventricle
Septum still depolarises first but now from right to left - initial V1 small downstroke, V6 small upstroke
Then right ventricle depolarises which may be hidden by ongoing septal depolarisation - V1 small upstroke, V6 small downstroke
Lastly left ventricle depolarises making biggest contribution to QRS as it is largest - V1 large upstroke, V6 large downstroke
ECG changes in RBBB
Broadened QRS
V1 positive and end of QRS
V6 negative at end of QRS
‘MaRRoW’
Reason for ECG changes in RBBB
No longer conduction down right bundle branch
Septum depolarises left to right - initial V1 small upstroke, V6 small downstroke
Then left ventricle depolarises normally - V1 large downstroke, V6 large upstroke
Right ventricle conduction delayed and spreads from LV - V1 large upstroke, V6 large downstroke
Left anterior hemiblock definition
Block of anterior fascicle of left bundle branch
More common than left posterior hemiblock as coronary blood supply more vulnerable to anterior fascicle
ECG changes with left anterior hemiblock
Left axis deviation in otherwise normal ECG
Left posterior hemiblock definition
Block of posterior fascicle of left bundle branch
Uncommon and less clinically significant
Bifasicular block definition
RBBB + Left fascicular hemiblock (usually anterior)
Bifasicular block ECG changes
RBBB
Left axis deviation
Trifasicular block definition
Bifasicular block + 1st degree heart block
Trifasicular block ECG changes
RBBB
Left axis deviation
Prolonged PR interval
Trifasicular block importance
Risk of developing complete heart block
Indications for pacemaker insertion
3rd degree heart block
2nd degree HB Mobitz Type 2
2nd degree HB with symptoms
Bifasicular or Trifasicular block with intermittent 3rd degree or 2nd degree Mobitz type II
Sinus node dysfunction with symptomatic bradycardia and significant pauses
Pacemaker categories
External or Transvenous
Temporary or Permanent
Pacing lead placement
Usually either RA and/or RV
Biventricular pacemakers inserted for cardiac resynchronisation therapy - LV paced via coronary sinus
ECG findings in Atrial pacing vs Ventricular pacing vs Dual chamber pacing
Atrial pacing - pacing spike directly precedes P waves
Ventricular pacing - pacing spike directly precedes QRS (QRS similar to RBBB appearance as RV is being paced)
Dual pacing - pacing spike directly precedes both P wave and QRS
Coronary blood supply to AV node
Right coronary artery
Therefore inferior MI can cause complete heart block
Drug to avoid in SVT with WPW
Digoxin as it acts to block AV node, therefore faster atrial rate would be transmitted directly to ventricles via accessory pathway
Results in VT
