Questions and Answers
What pattern will a right bundle branch block with a left anterior hemiblock show on an ECG?
What pattern will a right bundle branch block with a left posterior hemiblock show on an ECG?
What occurs when the right bundle branch and the left anterior fascicle are completely blocked?
Right bundle branch block, left axis deviation, and first-degree AV block.
What occurs when the right bundle branch and the left posterior fascicle are completely blocked?
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Complete third-degree AV block occurs when all three fascicles are completely blocked.
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What is the concept of infra-nodal block?
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What are the ECG criteria for Left Bundle Branch Block (LBBB)?
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What are the ECG criteria for Right Bundle Branch Block (RBBB)?
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What do broad QRS complexes indicate?
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What does the WiLLiaM MaRRoW mnemonic help to remember?
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What is the cause of left axis deviation in Left Anterior Hemiblock?
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Right Bundle Branch Block (RBBB) is usually of major clinical significance.
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What is identified in Complete Bundle Branch Blocks?
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Which of the following best describes bi-fascicular block?
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What happens in Left Posterior Hemiblock?
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What occurs in Tri-fascicular Block?
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Study Notes
Learning Objectives
- Understanding infra-nodal block and its clinical importance.
- Knowledge of Left Bundle Branch Block (LBBB) and Right Bundle Branch Block (RBBB) ECG criteria.
- Identification of complete and incomplete bundle branch blocks.
- Recognition of fascicular blocks including left anterior, left posterior, bi-fascicular, and tri-fascicular blocks.
Cardiac Conduction System
- Electrical impulses in the heart travel through a specific pathway: sinoatrial node (SAN) → atrioventricular node (AVN) → Bundle of His → Purkinje fibres.
- The right bundle branch depolarizes the right ventricle, while the left bundle branch depolarizes the left ventricle.
- The septum depolarizes from left to right.
ECG Basics
- An ECG is a graphical representation of electrical depolarization in the heart.
- Lead V1 views the heart from the right; V6 views from the left.
- Direction of deflection in the ECG trace indicates net depolarization towards or away from the electrode.
- Left ventricular depolarization affects the ECG more significantly due to greater muscle mass on that side.
Key ECG Components
- P wave: Atrial depolarization
- PR interval: Conduction through the AV node
- QRS complex: Ventricular depolarization
- T wave: Ventricular repolarization
Bundle Branch Blocks (BBBs)
- Main Characteristic: Broadening of QRS complexes (> 0.12 seconds).
- P waves and PR intervals remain normal since the issue arises below the atria.
Right Bundle Branch Block (RBBB)
- Impulse travels only down the left bundle branch, leading to delayed right ventricular depolarization.
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ECG Criteria:
- Broad positive complex in V1 due to initial R wave followed by a deep S wave and a secondary R wave (R’).
- Widened QRS complex (> 0.12 seconds) with RSR’ pattern in V1-V3.
- Slurred S wave in lateral leads I, aVL, V5, V6.
Left Bundle Branch Block (LBBB)
- Impulse travels only via the right bundle branch when the left bundle branch is blocked.
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ECG Criteria:
- Broad or notched R wave in V5, V6, I, and aVL with ST-segment depression and T-wave inversion.
- Dominant S wave in V1 and widened QRS complex (> 0.12 seconds).
- Absence of Q waves in lateral leads; may show left axis deviation.
Hemiblocks
- Fascicular blocks affecting either the anterior or posterior divisions of the left bundle branch.
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Left Anterior Hemiblock:
- Current primarily flows through the posterior fascicle leading to left axis deviation.
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Left Posterior Hemiblock:
- Current flows down the left anterior fascicle, resulting in right axis deviation.
Bi-fascicular Block
- Combination of RBBB with either left anterior or left posterior hemiblock.
- Results in a widened QRS complex with specific axis deviations depending on the associated hemiblock.
Tri-fascicular Block
- Involves right bundle branch and both fascicles of the left bundle branch.
- Can be incomplete or complete, influencing conduction and potentially leading to third-degree AV block.
Clinical Relevance
- RBBB can signify minor issues unless associated with underlying conditions such as ischemic heart disease.
- LBBB is always pathological, linked to myocardial pathologies, and can occur post-cardiac procedures.
Mnemonics for Recognition
- WiLLiaM: Used for LBBB recognition (indicating patterns in V1 and V6).
- MaRRoW: Used for RBBB recognition (indicating patterns in V1 and V6).
Summary Notes
- Assess QRS duration for potential bundle branch blocks; if QRS is > 0.12 seconds, evaluate further.
- Identify patterns in V1 and V6 to differentiate between various bundle branch and fascicular blocks.
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Description
This quiz focuses on the analysis of ECG rhythms, specifically addressing Bundle Branch Blocks. Trainees will explore the concepts of infra-nodal blocks, LBBB and RBBB ECG criteria, and the identification of complete and incomplete blocks. Enhance your understanding of these critical electrocardiographic concepts.
