Left bundle branch block
| Left bundle branch block | |
 | |
|---|---|
| ECG characteristics of a typical LBBB showing wide QRS complexes with abnormal morphology in leads V1 and V6 | |
| ICD-10 | I44.7 |
| DiseasesDB | 7352 |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]
Synonyms and related keywords: LBBB
Overview
Left bundle branch block (LBBB) is a cardiac conduction abnormality seen on the electrocardiogram (ECG) whereby there is an impairment of transmission of the cardiac electrical impulse along the fibers of the left main bundle branch, or both the left anterior fascicle and left posterior fascicle. This conduction disturbance is characterized by wide (greater than or equal to 0.12 seconds) QRS complexes. In this condition, activation of the left ventricle is delayed, which results in the left ventricle contracting later than the right ventricle.
Classification
New Left Bundle Branch Block
New LBBB is defined as the presence of a new left bundle branch block and:[1]
- A prior ECG with normal QRS duration (<110 ms)12 within 24 hours before the LBBB tracing without T-wave abnormalities.
- Acute-onset illness with LBBB on the admission tracing resolving within 24 hours without T-wave abnormalities on the subsequent narrow QRS tracings (to exclude LBBB lasting more than 24 hours) in patients with no history of LBBB.
Old Left Bundle Branch Block
An old LBBB is defined as an[2] LBBB that has existed for more than 24 hours (by prior tracings or reports in the electronic medical record).
Left Bundle Branch Block of Unknown Duration
The LBBB duration is unknown on tracings obtained within the first 24 hours of admission in which there is not any prior EKG information.[3]
Causes of LBBB
Common Causes
The most common causes of LBBB include:
- Hypertension
- Coronary heart disease
- Congestive heart failure
- Hypertrophic obstructive cardiomyopathy
- Valvular heart disease
Causes of LBBB in Alphaetical Order
- Chagas disease
- Coronary Artery Disease
- Dilated cardiomyopathy
- Endocarditis
- Hemochromatosis
- Hypertension
- Hypertrophic obstructive cardiomyopathy (HOCM)
- Ischemic heart disease
- Left ventricular hypertrophy
- Left ventricular outflow tract surgery
- Lyme disease [4]
- Myocardial infarction
- Myocardial ischemia
- Myocarditis
- Primary disease of the cardiac electrical conduction system
- Progressive conduction system disease
- Rheumatic fever with aortic valve involvement
- Sarcoidosis
- Scleroderma
- Septal myomectomy
Differentiating LBBB from other Disorders
LBBB must be differentiated from:
- Left anterior fascicular block (LAFB) where there is block of only the anterior fascicle
- Left posterior fascicular block (LPFB) where there is block of only the posterior fascicle
- Left ventricular hypertrophy which also causes tall QRS complexes
Epidemiology and Demographics
LBBB is uncommon among patients under 50 years of age (<0.5%). It occurs in 6% to 8% of patients over the age of 50.
Natural History, Complications, Prognosis
LBBB is often a marker of underlying heart disease, and may be associated with adverse outcomes as a result of the underlying disease, or it may be involved directly in adverse outcomes itself.
Complications
Pulmonary arterial line placement [5] in a patient with LBBB can result in complete heart block if the right bundle branch is traumatized during the process.
Prognosis
Age Under 50 Years
In patients under the age of 50, LBBB does not appear to be associated with an adverse prognosis.
Age 50 and Over
It is notable that when LBBB is the presenting feautre of acute MI, one half the time the patient will have no chest pain. Unfortunately patients whose only manifestation of acute MI is left bundle branch block are less frequently treated with reperfusion therapy, and have a poorer prognosis.[6]
Diagnosis
Electrocardiographic Criteria
The criteria to diagnose a left bundle branch block on an electrocardiogram includes the following:
- The heart rhythm must be supraventricular in origin. A wide QRS complex that is not preceded by P waves would not qualify.
- The QRS duration must be greater than or equal to 120 milliseconds.
- There should be a QS or rS complex in lead V1.
- There should be a monophasic R wave in leads I and V6.
The T wave deflection should be opposite of the terminal deflection of the QRS complex. This lack of concordance in direction is known as appropriate T wave discordance, and it is expected in patients with a left bundle branch block. A concordant T wave may suggest the presence of either ischemia or myocardial infarction.
The EKG below shows a case of left bundle branch block depicting an RsR' pattern (M pattern) in lead V6, and a wide QRS complex in both leads V1 and V6.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:LBBB.png
EKG Examples
The EKG below shows an RsR' pattern (M pattern) in leads V4, V5, and V6 suggesting a left bundle branch block. Also seen are wide QRS complexes throughout the precordium, and ST segment depression in leads II, V5, and V6.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:E23.jpg
The EKG below shows a left axis deviation with an RsR' pattern (M pattern) in all limb leads (leads I, II, III, aVR, aVL, and aVF) and in lead V6, depicting a left bundle branch block. Tachycardia is also present with a rate of more than 100 beats per minute.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:12leadLBTB.png
The EKG below shows a left axis deviation with an RsR' pattern (M pattern) throughout the precordium, depicting a left bundle branch block. The EKG also shows wide QRS complexes and a prolonged PR interval.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:12leadLBTB002.jpg
The EKG below shows an RsR' pattern (M pattern)in leads V5, V6, and aVL depicting a left bundle branch block. There is also notching of the QRS complex in lead I and ST segment elevation seen in leads V1, V2, V3, V4, and aVR.
The EKG below shows an RsR' pattern (M pattern) in leads II, aVL, and aVF depicting a left bundle branch block. There is also ST segment elevation in leads V1, V2, and aVR. There is widening of the QRS complexes throughout the precordial leads.
The EKG below shows an RsR' pattern (M pattern) in leads I, II, aVL, and V4 depicting a left bundle branch block. The EKG also shows left axis deviation with left ventricular hypertrophy, and ST segment elevations in V1, V2, and V3 as well as an ST segment depression in V6. There is widening of the QRS complexes throughout the precordial leads.
The EKG below shows an RsR' pattern (M pattern) in leads V1, V4, V5, and aVL depicting a left bundle branch block. The EKG also shows ST depression with T wave inversion in lead V6 indicating a left ventricular strain pattern. Wide QRS complexes are seen throughout the EKG. The EKG also shows evidence of left ventricular hypertrophy.
The EKG below shows an RsR' pattern (M pattern) in leads III, aVL, aVF, and notching of the QRS complex in V5 depicting a left bundle branch block. Wide QRS complexes are seen throughout the EKG.
The EKG below shows an irregular rhythm with an RsR' pattern (M pattern) in leads II, V5, and V6. Q waves are seen in leads I, aVL, V5, and V6. There is evidence of left ventricular hypertrophy and left axis deviation.
The EKG below shows a left bundle branch block.
The EKG below shows an RsR' pattern (M pattern) in leads V4 and V5 depicting a left bundle branch block. The EKG also shows sinus rhythm, prolonged PR interval (greater than 200ms), and wide QRS complexes (> 120ms). The loss of the septal Q waves and the tall broad R waves in leads I, aVL, and V6 are diagnostic of a left bundle branch block.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:E203.jpg
Reading Ischemia In The Presence Of LBBB
LBBB can simulate an MI due to the associated secondary ST changes and pseudoinfarction q waves that it is associated with. It can mask the EKG changes of an MI.
Sgarbossa Criteria
An EKG scoring system was developed, and the independent criteria were assessed on patients from the GUSTO-1 trial. These patients were scored from 0-5 for the presence of LBBB in the context of an acute myocardial infarction.[7]
| Criteria | Score |
| 1.ST-segment elevation ≥ 1 mm and concordant with QRS complex | 5 |
| 2.ST-segment depression ≥ 1 mm in lead V1,V2 or V3 | 3 |
| 3.ST-segment elevation ≥ 5 mm and discordant with QRS complex | 2 |
Pseudoinfarct Patterns: Simulation of an Anterior MI
- LBBB can cause a poor R wave progression. In the presence of LBBB, there is often a decrease in the amplitude of R waves to the mid precordium in the absence of a septal infarct.
- QS complexes are often seen in the right precordial leads in uncomplicated LBBB, and they may even extend as far out as V5 or V6.
- Non infarctional Q waves may be seen in aVL.
- The electrical basis for the appearance of q waves is that LBBB causes a loss of the normal septal R waves in the right precordial leads. The septum is no longer being depolarized from left to right as it normally does because of the delay in conduction down the left bundle. Therefore, there is a loss of the early R wave.
- There can occasionally be Rs complexes in V1. These unanticipated initial positive forces are due to early RV depolarization and may actually mask the q waves (i.e. loss of initial septal forces) that accompany an anteroseptal MI.
Simulation of an Inferior MI
- Noninfarctional QS complexes can be seen in leads II, III, and aVF in LBBB.
- There are a number of autopsy cases were there are QS waves inferiorly without evidence of an MI.
- There are several reported cases of intermittent LBBB in which the inferior QS waves were present only in the aberrantly conducted beats.
- Conversely, LBBB may mask the development of Q waves in an MI.
Secondary ST segment and T Wave Changes
- Primary ST segment and T wave changes are repolarization changes that are seen with ischemia or electrolyte imbalance. They reflect actual changes in the myocardial action potentials.
- Secondary ST segment and T wave changes occur when the sequence of ventricular activation is altered without any disturbance in the electrical properties of the myocardial cells such as is seen in LBBB.
- As a result of secondary ST segment and T wave wave changes, the QRS and the T wave vectors are oriented in opposite directions which is known as discordance of the QRS and T wave vectors.
- Thus, the QRS is often predominantly negative in the right precordial leads while the T wave is oriented positively. In those leads where there is a tall positive R wave there is a negative T wave.
- These secondary ST segment and T wave changes often mimic infarction, and furthermore they may mask the ST segment and T wave changes of an MI.
- Sometimes primary ST segment and T wave changes will be superimposed on the LBBB pattern and the following suggests the diagnosis of ischemia or infarction:
- ST segment elevation in leads with a predominant R wave. In uncomplicated LBBB, the ST segment is isoelectric or depressed.
- T wave inversions in the right to midprecordial leads or in other leads with a predominantly negative QRS. In other words there is an absence of discordance, and there is the presence of concordance.
- Morphology: In leads with a predominant R wave, the ST segment begins to slope downwards and blends into the T wave. The ascending limb of the T wave ascends back to the baseline at a more acute angle.
- The ischemic T waves have a more symmetric appearance and a slightly upwardly bowed ST segment.
- ST segment and T wave elevations simulating acute infarction: The ST segment can be markedly elevated (up to 10 mm or more at the J point ) in leads with a QS or rS segment in uncomplicated LBBB. In addition, there can be a loss of R wave progression.
- T wave inversions in intermittent LBBB: May develop deep T wave inversions in the right to midprecordial leads of normally conducted beats in the absence of CAD. These T wave inversions are deepest in leads V1 to V4 with a symmetric or coved appearance.
Etiology of Q Waves
- As described earlier, in LBBB there is a loss of depolarization from left to right, which produced an initial r wave in the right precordial leads.
- Now there is depolarization from right to left. Consequently the initial r wave is lost, and the non infarctional QS complexes may appear in the precordial leads.
- The reversal of septal activation results in RS complexes in the left precordial leads.
Can You Read a Left Ventricular Free Wall Infarction In the Presence of a LBBB?
- No. This pattern of infarction results in abnormal q waves in the midprecordial to lateral precordial leads.
- In LBBB the initial septal depolarization forces are directed from right to left. These leftward septal forces will produce an initial R wave in the midprecordial to the lateral precordial leads, masking the loss of potential q waves produced by the infarction.
- Therefore left ventricular free wall infarction by itself will not produce diagnostic q waves in the presence of a LBBB.
- Poor R wave progression is seen in uncomplicated LBBB.
Can You Read a Septal Infarction in the Presence of LBBB?
- Yes. Again the septal forces are directed to the left in LBBB.
- If enough of the septum is infarcted to eliminate these initial leftward septal forces, abnormal QR, QRS, or qrs types of complexes may appear in the midprecordial to lateral precordial leads.
- These initial q waves may reflect posterior and superior forces from the spared basal portion of the septum.
- Small q waves of 0.03 sec or less may be seen in leads I, V5 to V6 in uncomplicated LBBB.
- The presence of q waves laterally is an example of false localization. [8]
Physical Examination
Heart
Paradoxical split of the second heart sound
Treatment
Treatment is directed at the underlying cause of left bundle branch block, such as ST elevation myocardial infarction. Patients with syncope and LBBB may have a rhythm disturbance that requires a pacemaker. Given the dysynchrony that occurs with left ventricular contractility, cardiac resynchronization therapy in heart failure patients may be of benefit.
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Related Chapters
References
- ↑ Shvilkin A, Bojovic B, Vajdic B, Gussak I, Ho KK, Zimetbaum P, Josephson ME. Vectorcardiographic and electrocardiographic criteria to distinguish new and old left bundle branch block. Heart Rhythm 2010;7:1085–1092.
- ↑ Shvilkin A, Bojovic B, Vajdic B, Gussak I, Ho KK, Zimetbaum P, Josephson ME. Vectorcardiographic and electrocardiographic criteria to distinguish new and old left bundle branch block. Heart Rhythm 2010;7:1085–1092.
- ↑ Shvilkin A, Bojovic B, Vajdic B, Gussak I, Ho KK, Zimetbaum P, Josephson ME. Vectorcardiographic and electrocardiographic criteria to distinguish new and old left bundle branch block. Heart Rhythm 2010;7:1085–1092.
- ↑ http://onlinelibrary.wiley.com/doi/10.1111/j.1540-8159.1990.tb04009.x/abstract
- ↑ Morris D, Mulvihill D, Lew WY (1987). "Risk of developing complete heart block during bedside pulmonary artery catheterization in patients with left bundle-branch block". Archives of Internal Medicine. 147 (11): 2005–10. PMID 3675104. Retrieved 2012-10-17. Unknown parameter
|month=ignored (help) - ↑ Shlipak M, Go A, Frederick P, Malmgren J, Barron H, Canto J. Treatment and outcomes of left bundle-branch block patients with myocardial infarction who present without chest pain. J Am Coll Cardiol. 2000;36(3):706-712.
- ↑ Sgarbossa EB, Pinski SL, Barbagelata A, Underwood DA, Gates KB, Topol EJ, Califf RM, Wagner GS (1996). "Electrocardiographic diagnosis of evolving acute myocardial infarction in the presence of left bundle-branch block. GUSTO-1 (Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries) Investigators". N. Engl. J. Med. 334 (8): 481–7. PMID 8559200. Unknown parameter
|month=ignored (help) - ↑ Myocardial Infarction, Electrocardiographic Differential Dx, Ary L. Goldberger, 3rd ed., Mosby Co., St. Louis, 1984, p.85 93.