Bundle Branch Blocks ECG PDF

Faculty of Nursing Electrocardiogram (ECG) Technician Program ECG Rhythm Analysis Bundle Branch Blocks Prepared By: Dr. Esraa E. Ahmed 1445 AH (2024) Updated by Dr. Hayam Asfour  Learning Objective By the end of this lecture, the traine...

Faculty of Nursing Electrocardiogram (ECG) Technician Program ECG Rhythm Analysis Bundle Branch Blocks Prepared By: Dr. Esraa E. Ahmed 1445 AH (2024) Updated by Dr. Hayam Asfour  Learning Objective By the end of this lecture, the trainees must be able to: 1. Tell the concept of infra-nodal block and its clinical significance. 2. Know LBBB ECG criteria. 3. Know RBBB ECG criteria. 4. Identify Complete and incomplete Bundle branch blocks. 5. Identify Fascicular blocks. Left anterior. Left posterior. Bi-fascicular. Tri-fascicular. Clinical significance. The cardiac conduction system Electrical impulses travel through the heart via a specific conduction pathway. The sinoatrial node (SAN) acts as the initial pacemaker before the impulse spreads throughout the atria and towards the atrioventricular node (AVN). The depolarisation wave travels through the heart’s septum via the Bundle of His and Purkinje fibres. These are organised into the left and right bundle branches. The right bundle branch depolarises the right ventricle, and the left bundle branch depolarises the left ventricle simultaneously. The septum is depolarised by the left bundle branch, resulting in the septum being depolarised from left to right. ECG basics The ECG is a graphical representation of the net direction of electrical depolarisation in the heart at any one time. Different leads look at the heart from different angles (the most important to know for understanding bundle branch blocks is that V1 views the heart from the right and V6 from the left). An upwards spike means the net depolarisation is heading towards that lead. A downward spike means the net depolarisation is heading away from that lead. ECG basics There is a greater muscle mass on the left side of the heart compared to the right, so depolarisation within the left ventricles has a greater impact on the ECG trace. The right and left ventricles should depolarise simultaneously, producing one uniform R wave. Ventricular depolarisation using normal pathways is complete within 120ms. Depolarisation takes longer when these pathways are disrupted or changed in any way, causing broad QRS complexes. A broad QRS complex always indicates abnormal ventricular depolarisation.  Components of an ECG trace. ECG Definition component P wave Atrial depolarisation PR interval Conduction through the AVN to the ventricles QRS complex Ventricular depolarisation Q wave The first downward deflection R wave Any upwards deflection S wave Any downward deflection after an R wave T wave Ventricular repolarisation  In normal cardiac conduction 1.The sino-atrial node acts as the initial pacemaker 2.Depolarisation reaches the atrioventricular node 3.Impulses travel simultaneously down the bundle of His via the left and right bundle branches. The septum is depolarised from the left. 4.Both the left and right ventricular walls are depolarised simultaneously.  In normal cardiac conduction The main feature of bundle branch blocks is the broadening of QRS complexes. It is important to ensure other causes of broad complexes are excluded. As the problem is below the atria, the P waves and the PR intervals are normal.  Tell the concept of infra-nodal block and its clinical significance Delay or blockage of conduction of the electrical impulse in the bundle branches is called a bundle branch block. Bundle branch blocks are frequently found in patients with cardiac disease but are occasionally found in the normal heart. Their presence alone does not require treatment. Right bundle branch block is of minor clinical significance, except as an indicator of possible coronary heart disease. Left bundle branch block is rare in the otherwise normal individual and is most seen in ischemic heart disease. It therefore carries a more severe prognosis than right bundle branch block.  Know RBBB ECG Criteria A delay or blockage of the conduction in the right bundle branch is called right bundle branch block. A normal impulse is initiated in the SA node and causes the atria to depolarize. The impulse then travels through the AV node and reaches the bundle branches. If the right bundle branch is blocked, the impulse will go down the left bundle branch. The initial activation in the ventricles remains the same as that in normal depolarization (i.e. from left to right).  Know RBBB ECG Criteria ▪ Lead V1 will have an initial R wave inscribed, as the initial impulse is travelling towards that electrode. ▪ The left ventricle depolarizes first and inscribes an S wave in V1, as the forces of depolarization are now travelling away from V1. ▪ The right ventricle then depolarizes. As the wave of depolarization moves towards V1, an R’ is inscribed. ▪ Again, the opposite pattern will be inscribed in V6. ▪ The entire QRS complex will be widened (greater than 0.12 seconds) owing to the conduction delay. Thus, the pattern of right bundle branch block is a broad positive complex in V1. Know RBBB ECG criteria The sequence of conduction in right bundle branch block. Know LBBB ECG Criteria Right bundle branch block ECG.  Know RBBB ECG Criteria ▪ Bundle branch block is diagnosed by looking at the width and configuration of the QRS complexes. 1. QRS complex widened to greater than 0.12 seconds (3 small squares). 2. RSR’ pattern in V1-V3: an initial small upward deflection (R wave), a larger downward deflection (S wave), then another large upward deflection (a second R wave, which is indicated as R’) (rabbit ears) or a tall, broad R wave; there is also ST-segment depression and T-wave inversion. 3. Wide, slurred S wave in lateral leads: I, aVL, V5-V6 WiLLiaM MaRRoW mnemonic The WiLLiaM MaRRoW mnemonic can be used to quickly recognise left and right bundle branch blocks by looking at V1 and V6: WiLLiaM refers to the ECG appearance of left bundle branch block MaRRoW refers to the ECG appearance of right bundle branch block The middle letters of the names help you remember which bundle branch block each name is referring to (two Ls in WiLLiaM = left bundle branch block, two Rs in MaRRoW = right bundle branch block). Each name’s first and last letter helps you recognise the ECG features of the associated bundle branch block.  WiLLiaM MaRRoW mnemonic To recognise right bundle branch block, we use the name MaRRoW and look at the first and last letters: M: complexes in V1 resemble the letter M: initial small upward deflection (r wave), a larger downward deflection (S wave), then another large upward deflection (second R wave) W: complexes in V6 resemble a W: initial small downward deflection (Q wave), then a larger upward deflection (R wave), and then a wide downward deflection (S wave) Pathophysiology In right bundle branch block: 1.The sino-atrial node acts as the initial pacemaker 2.Depolarisation reaches the atrioventricular node 3.Depolarisation through the bundle of His occurs only via the left bundle branch. The left branch still depolarises the septum as normal. 4.The left ventricular wall depolarises as normal. 5.The right ventricular walls are eventually depolarised by the left bundle branch, this occurs by a slower, less efficient pathway. Clinical relevance RBBB can be either physiological or the result of damage to the right bundle branch. Causes of damage include underlying lung pathology (COPD, pulmonary emboli, cor pulmonale), primary heart muscle disease (ARVC), congenital heart disease (e.g. ASD), ischaemic heart disease and primary degeneration of the right bundle.  Know LBBB ECG Criteria ▪ In left bundle branch block, there is a delay or blockage of conduction in the main left bundle branch. This affects the normal depolarization in the ventricles. ▪ In left bundle branch block, the impulse begins in the SA node and depolarizes the atria, then travels through the AV node to the left and right bundle branches. ▪ On finding the left bundle branch blocked, the impulse travels down the right bundle branch.  Know LBBB ECG Criteria ▪ The septum is unable to depolarize from left to right as normal and instead depolarises from right to left. ▪ As V6 sits opposite V1, it will be affected in the opposite way. ▪ If V1 is our electrode, the impulse will initially be travelling away from it, as the septum depolarises. ▪ This causes a negative deflection (Q wave) to be inscribed. However, this is often not visible. Right ventricular depolarisation follows.  Know LBBB ECG Criteria ▪ If VI is our electrode, the impulse would now travel towards the electrode so a small positive deflection (R wave) would be inscribed. The left ventricle is then depolarized. ▪ The impulse is now travelling away from V1 and so a negative deflection (S wave) would be inscribed. Thus, the pattern of left bundle branch block in V1 is negative. As V6 sits opposite V1, it will be affected in the opposite way. The entire QRS complex in left bundle branch block will be widened (greater than 0.12 seconds) owing to the conduction delay. Know LBBB ECG criteria The conduction sequence of left bundle branch block. Know LBBB ECG Criteria Left bundle branch block ECG.  Know LBBB ECG Criteria ▪ Bundle branch block is diagnosed by looking at the width and configuration of the QRS complexes. 1. QRS complex widened to greater than 0.12 seconds (3 small squares) 2. Dominant S wave in V1 3. Broad or notched R wave with prolonged upstroke in leads V5, V6, I, and aVL with ST-segment depression and T-wave inversion. 4. Absence of Q waves in lateral leads 5. Prolonged R wave >60ms in leads V5-V6 6. Left axis deviation may be present.  WiLLiaM MaRRoW mnemonic WiLLiaM MaRRoW mnemonic can be used to quickly recognise left and right bundle branch blocks by looking at V1 and V6. To recognise left bundle branch block, we use the name WiLLiaM and look at the first and last letters: W: complexes in V1 resemble the letter W: deep downward deflection (dominant S wave), which may be notched M: complexes in V6 resemble the letter M: broad, notched or ‘M’ shaped R wave in V6 Pathophysiology In left bundle branch block: When viewed from the right-hand side (V1), net depolarisation travels away (towards the left), resulting in negative ECG deflections. The first downward deflection represents the right ventricle, and the slightly delayed 2nd downward deflection corresponds to the depolarisation of the left ventricle. When viewed from the left-hand side (V6), where the net depolarisation is travelling towards the detector, deflections are positive on the ECG. Again, there will be two peaks (RR) due to the delay in left ventricular depolarisation.  Pathophysiology In left bundle branch block: In left bundle branch block: 1.The sino-atrial node acts as the initial pacemaker 2.Depolarisation reaches the atrioventricular node 3.Depolarisation down the bundle of His occurs only via the right bundle branch. The septum is abnormally depolarised from right to left. 4.The right ventricular wall is depolarised as normal. The left ventricular walls are eventually depolarised by the right bundle branch, this occurs by a slower, less efficient pathway. Clinical relevance LBBB is always pathological. Left bundle branch block may be due to conduction system degeneration or myocardial pathologies such as ischaemic heart disease, cardiomyopathy and valvular heart disease. LBBB may also occur after cardiac procedures, which damage the left bundle branch or His bundle. A STEMI presenting as chest pain with LBBB is exceedingly rare.  Identify Complete and incomplete Bundle branch blocks ▪ An incomplete block means that electrical signals are being conducted better than in a complete block. Still, right bundle branch block indicates a higher risk for heart disease and, sometimes, the eventual need for a pacemaker. Identify Fascicular (Hemiblock) Blocks ▪ The left bundle branch has two main divisions or fascicules – the anterior fascicule and the posterior fascicule. If either of these fascicules becomes blocked, it is called a hemiblock. ▪ The blockage may be the result of conduction system disease in the fascicles or may occur when there is disease or fibrosis surrounding the fascicles (in other words, with a myocardial infarction). ▪ The major effect that hemiblocks have on the ECG is axis deviation.  Left Anterior Hemiblock ▪ If conduction down the anterior fascicule is blocked, this is known as left anterior hemiblock. ▪ Due to the blockage, the current flows mainly down the posterior fascicle to the inferior surface of the heart. ▪ Left ventricular myocardial depolarization then occurs, progressing in an inferior-to superior and right-to-left direction. ▪ The axis deviation is therefore redirected upward and slightly leftward, inscribing tall positive R waves in leads I and AVL and deep S waves in II, III and AVF. ▪ This results in left axis deviation.  Left Anterior Hemiblock Pathway of current in left anterior hemiblock ECG showing left anterior hemiblock  Left Anterior Hemiblock ▪ Left anterior hemiblock is diagnosed by looking for left or right axis deviation. 1. Normal QRS duration and no ST-segment or T-wave changes. 2. Left axis deviation greater than −30°. 3. No other cause of left axis deviation is present.  Left Posterior Hemiblock ▪ In left posterior hemiblock, the reverse occurs. ▪ Due to a blockage in the posterior fascicule, the current flows down the left anterior fascicle, and ventricular myocardial depolarization follows in a left-to-right direction. ▪ The axis deviation is directed downward and rightward, ▪ inscribing tall R waves in II, III and AVF, and deep S waves in the leads I and AVL. ▪ This results in a right axis deviation.  Left Posterior Hemiblock Pathway of current in left posterior hemiblock ECG of left posterior hemiblock  Left Posterior Hemiblock ▪ Left posterior hemiblock is diagnosed by looking for left or right axis deviation. 1. Normal QRS duration and no ST-segment or T-wave changes. 2. Right axis deviation. 3. No other cause of right axis deviation is present. Left anterior hemiblock is more common than left posterior hemiblock because the posterior fascicle is much thicker anatomically and has a dual blood supply from the left and right coronary arteries.  Bi-fascicular Block ▪ Left anterior and left posterior hemiblock are sometimes accompanied by right bundle branch block. This is referred to as a bi-fascicular block. ▪ In such cases, the QRS complex is widened (rather than the narrow QRS complexes that accompany hemiblocks). ▪ Conduction to the ventricles is via the single remaining fascicle. A right bundle branch block with a left anterior hemiblock will manifest itself on an ECG with a right bundle branch pattern plus a left axis deviation. A right bundle branch block with a left posterior hemiblock will manifest itself on an ECG with a right bundle branch pattern plus a right axis deviation.  Bi-fascicular Block ECG showing right bundle branch block and left anterior hemiblock  Bi-fascicular Block ECG showing right bundle branch block and left posterior hemiblock A bi-fascicular block can occur due to ischaemic heart disease or as part of a degeneration of the conduction system.  Bi-fascicular Block The features of a right bundle branch block combined with the left anterior hemiblock are as follows: Right Bundle Branch Block Left Anterior Hemiblock ▪️QRS wider than 0.12 seconds ▪️Left axis deviation ▪️RSR′ in V1 and V2 The features of a right bundle branch block combined with the left posterior hemiblock are as follows: Right Bundle Branch Block Left Posterior Hemiblock ▪️RSwider than 0.12 seconds ▪️Right axis deviation ▪️RSR′ in V1 and V2  Tri-fascicular Block ▪ This term applies to the presence of conducting disease in the right bundle branch and the two fascicles of the left bundle branch. ▪ Tri-fascicular block can be incomplete or complete, depending on whether or not all three fascicles have completely failed.  Tri-fascicular Block ▪ The following ECG manifestations are found with incomplete tri- fascicular block: If the right bundle branch and the left anterior fascicle are completely blocked, while the left posterior fascicle is incompletely blocked, the pattern of right bundle branch block, left axis deviation and first-degree AV block occurs. If the right bundle branch and the left posterior fascicle are completely blocked, while the left anterior fascicle is incompletely blocked, the pattern of right bundle branch block, right axis deviation and first-degree AV block occurs. If all three fascicles are completely blocked, complete third-degree AV block occurs.  Tri-fascicular Block ECG showing RBBB, left axis deviation and first-degree AV block.  Tri-fascicular Block ECG showing RBBB, left axis deviation and Mobitz Type II second degree AV block.  Summary: Bundle Branch Blocks ▪ Assess rhythm strip – are the QRS complexes wider than 0.12 seconds? ▪ If yes, it is either a ventricular rhythm or a bundle branch block. ▪ Go to V1 on the ECG – is it broad and positive or broad and negative? ▪ Is it a WILLIAM or MARROW pattern?! Summary: Hemiblocks, Bi-fascicular Blocks and Tri-fascicular Blocks ▪ Left anterior hemiblock results in left axis deviation. The QRS is of normal duration. ▪ Left posterior hemiblock results in right axis deviation. The QRS is of normal duration. ▪ A right bundle branch block with a left anterior hemiblock will manifest itself on an ECG with a right bundle branch pattern plus a left axis deviation. ▪ A right bundle branch block with a left posterior hemiblock will manifest itself on an ECG with a right bundle branch pattern plus a right axis deviation. Summary: Hemiblocks, Bi-fascicular Blocks and Tri-fascicular Blocks ▪ If the right bundle branch and the left anterior fascicle are completely blocked, while the left posterior fascicle is incompletely blocked, the pattern of right bundle branch block, left axis deviation and first-degree AV block occurs. ▪ If the right bundle branch and the left posterior fascicle are completely blocked, while the left anterior fascicle is incompletely blocked, the pattern of right bundle branch block, right axis deviation and first-degree AV block occurs. ▪ If all three fascicles are completely blocked, complete third- degree AV block occurs.  References ▪ The Only EKG Book You’ll Ever Need, 8th edition. Thaler. Lippincott Williams and Wilkins. 2015, Chapter 11, 13 pp 79-81, 85-90. https://t.me/MedicalEbooksLibrary ▪ https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ve d=2ahUKEwjC2tjc_97- AhURnf0HHY3YBJgQFnoECBEQAQ&url=https%3A%2F%2Fcmc.marmot.org%2FRecord%2F.b50739359&usg=AOvVaw0iaawp5Qc- mfDWU3vf86O2 ▪ https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ca d=rja&uact=8&ved=2ahUKEwjf9tX1gd_- AhUf8rsIHXeOBZIQFnoECBkQAQ&url=https%3A%2F%2Fwww.perlego.c om%2Fbook%2F1284136%2Fthe-ecg-workbook-4th-edition- pdf&usg=AOvVaw3N23Mt-70n139DzqOwHkAF Thank You!