Left axis deviation causes

Pathological left axis deviation (LAD) is a condition where the heart’s main axis is shifted to the left. This can be caused by a number of different conditions, including heart disease, lung disease, and certain types of cancer. LAD can also be a normal variant in some people. In most cases, LAD is not a serious condition and does not require treatment. However, in some cases, LAD can be a sign of a more serious underlying condition and may require further evaluation and treatment. A Left axis deviation can be benign and isolated in up to 40% of cases, but it is frequently associated with current heart disease and should be monitored. The left axis deviation is a major QRS vector with a temperature range of -30C to -90C. Normal is defined as the electrical axis falling between -30 and +90. Electrical axis deviation occurs if the electrical axis is between -30 and -90. The electrical axis should be between 90 and 180 to calculate the right axis deviation. What Is The Range For Left Axis Deviation? Image Source: howmed.net The left axis deviation is the major vector, falling between -30 and -90 degrees. The QRS axis is shifted 90 degrees to 180 degrees on either the right or left axis, resulting in the right axis deviation. Lung disease, Left axis deviation (LAD) is the most common abnormality observed in adults, affecting more than 8% of patients. Left anterior hemiblocks or left anterior fascicular blocks are the two most common forms of LAD (45% or more). If a patient ha...

Left bundle branch block (LBBB): ECG criteria and clinical implications Leftbundle branch block (LBBB) is the consequence of anatomical or functional dysfunction in the leftbundle branch, causing the impulse to be blocked. Depolarization of the leftventricle will be carried out by impulses spreading from the rightventricle.Because the left bundle branch is dysfunctional, the impulse will spread (through the leftventricle) partly or entirely outside of the conduction system; such impulse conduction is slow and therefore the QRS duration becomes prolonged. The hallmark of leftbundle branch block (LBBB) isQRS duration ≥0,12 seconds, deep and broad S-wave in V1/V2 and broad clumsy R-wave in V5/V6.Refer to Figure 1, where the difference between normal conduction, right bundle branch block ( Figure 1. These ECGs show the difference between normal conduction, left bundle branch block (LBBB) and right bundle branch block (RBBB). As evident from these ECGs, the cardinal difference between normal conduction and bundle branch blocks is the QRS duration: bundle branch blocks are caused by dysfunctional bundle branches, which results in slow (and abnormal) activation of ventricular myocardium and thus prolonged QRS duration. A QRS duration of 120 ms (0.12 s) is required to diagnose bundle branch block. Also note that both left bundle branch block (LBBB) and right bundle branch block (RBBB) cause marked ST-T changes, including ST elevations, ECG criteria for left bundle branch block (LB...

• QRS duration > 120ms • Dominant S wave in V1 • Broad monophasic R wave in lateral leads (I, aVL, V5-6) • Absence of Q waves in lateral leads • Prolonged R wave peak time > 60ms in leads V5-6 LBBB: Left Bundle Branch Block V1: Dominant S wave V6: broad, notched (‘M’-shaped) R wave Associated features include: • Left axis deviation (LAD); • Poor R wave progression in precordial leads, and • Appropriate discordance (discussed below) Electrophysiology In normal cardiac conduction, impulses travel equally down the left and right bundles, with the septum activated from left to right and the formation of small Q waves in lateral leads • In LBBB, conduction delay means that impulses travel first via the right bundle branch to the RV, and then to the LV via the septum • Septal activation is thus reversed eliminating lateral Q waves • The overall depolarisation vector from the right to left ventricle produces tall R waves in lateral leads (I, V5-6) and deep S waves in the right precordial leads (V1-3). The delay between activation of the RV and LV produces the characteristic “M-shaped” R wave seen in lateral leads • Delayed overall conduction time to the LV extends the QRS duration to > 120 ms Sequence of conduction in LBBB: 1) Conduction delay means impulses travel first via the right bundle branch (black arrow) 2) Septum is activated from right-to-left (yellow arrows) 3) Overall depolarisation vector is directed towards lateral leads (red arrow) What about the ST elevation? • Ap...

Clinically, bifascicular block presents with one of two ECG patterns: • Right bundle branch block ( • RBBB and left posterior fascicular block ( * Some authors describe Left bundle branch block ( LBBB) as a bifascicular block, as it may indicate LAFB + LPFB. However, clinically the term bifascicular block is reserved for RBBB with either LAFB or LPFB Electrophysiology Bifascicular block involves conduction delay below the atrioventricular node in two of the three fascicles: • Conduction to the ventricles is via the single remaining fascicle • The ECG will show typical features of RBBB plus either left or right axis deviation. • RBBB + LAFB is the most common of the two patterns. This is due to a single coronary artery blood supply (LAD) to the anterior fascicle • RBBB + LPFB is less common due to a dual blood supply (right and left circumflex arteries), and this combination may be associated with more extensive underlying cardiac pathology Clinical significance Bifascicular block is often associated with structural heart disease (50-80%) and extensive fibrosis of the conducting system. There is a risk of progression to complete heart block with additional damage to the third remaining fascicle, however clinical context is important: • Overall rate of progression to complete heart block is 1-4% per year • In symptom free patients, these figures are ~1% per year • Patients presenting with syncope have a 17% annual risk of progression • Syncope or presyncope in the context of...

Open Access is an initiative that aims to make scientific research freely available to all. To date our community has made over 100 million downloads. It’s based on principles of collaboration, unobstructed discovery, and, most importantly, scientific progression. As PhD students, we found it difficult to access the research we needed, so we decided to create a new Open Access publisher that levels the playing field for scientists across the world. How? By making research easy to access, and puts the academic needs of the researchers before the business interests of publishers. We are a community of more than 103,000 authors and editors from 3,291 institutions spanning 160 countries, including Nobel Prize winners and some of the world’s most-cited researchers. Publishing on IntechOpen allows authors to earn citations and find new collaborators, meaning more people see your work not only from your own field of study, but from other related fields too. Axis deviation indicates possible presence of various conditions. It also affects the QRS and T morphologies. The limits of axis deviations are as such arbitrary and the approximate degree of axis itself can be easily determined. Various conditions often shift the QRS axis without fulfilling the defined limits of deviations in the initial stage. The associations with various conditions may be missed if such partial shift of the axis is disregarded. Isolated left axis deviation is relatively common in the general population and...

• QRS duration > 120ms • Dominant S wave in V1 • Broad monophasic R wave in lateral leads (I, aVL, V5-6) • Absence of Q waves in lateral leads • Prolonged R wave peak time > 60ms in leads V5-6 LBBB: Left Bundle Branch Block V1: Dominant S wave V6: broad, notched (‘M’-shaped) R wave Associated features include: • Left axis deviation (LAD); • Poor R wave progression in precordial leads, and • Appropriate discordance (discussed below) Electrophysiology In normal cardiac conduction, impulses travel equally down the left and right bundles, with the septum activated from left to right and the formation of small Q waves in lateral leads • In LBBB, conduction delay means that impulses travel first via the right bundle branch to the RV, and then to the LV via the septum • Septal activation is thus reversed eliminating lateral Q waves • The overall depolarisation vector from the right to left ventricle produces tall R waves in lateral leads (I, V5-6) and deep S waves in the right precordial leads (V1-3). The delay between activation of the RV and LV produces the characteristic “M-shaped” R wave seen in lateral leads • Delayed overall conduction time to the LV extends the QRS duration to > 120 ms Sequence of conduction in LBBB: 1) Conduction delay means impulses travel first via the right bundle branch (black arrow) 2) Septum is activated from right-to-left (yellow arrows) 3) Overall depolarisation vector is directed towards lateral leads (red arrow) What about the ST elevation? • Ap...

Open Access is an initiative that aims to make scientific research freely available to all. To date our community has made over 100 million downloads. It’s based on principles of collaboration, unobstructed discovery, and, most importantly, scientific progression. As PhD students, we found it difficult to access the research we needed, so we decided to create a new Open Access publisher that levels the playing field for scientists across the world. How? By making research easy to access, and puts the academic needs of the researchers before the business interests of publishers. We are a community of more than 103,000 authors and editors from 3,291 institutions spanning 160 countries, including Nobel Prize winners and some of the world’s most-cited researchers. Publishing on IntechOpen allows authors to earn citations and find new collaborators, meaning more people see your work not only from your own field of study, but from other related fields too. Axis deviation indicates possible presence of various conditions. It also affects the QRS and T morphologies. The limits of axis deviations are as such arbitrary and the approximate degree of axis itself can be easily determined. Various conditions often shift the QRS axis without fulfilling the defined limits of deviations in the initial stage. The associations with various conditions may be missed if such partial shift of the axis is disregarded. Isolated left axis deviation is relatively common in the general population and...

Left bundle branch block (LBBB): ECG criteria and clinical implications Leftbundle branch block (LBBB) is the consequence of anatomical or functional dysfunction in the leftbundle branch, causing the impulse to be blocked. Depolarization of the leftventricle will be carried out by impulses spreading from the rightventricle.Because the left bundle branch is dysfunctional, the impulse will spread (through the leftventricle) partly or entirely outside of the conduction system; such impulse conduction is slow and therefore the QRS duration becomes prolonged. The hallmark of leftbundle branch block (LBBB) isQRS duration ≥0,12 seconds, deep and broad S-wave in V1/V2 and broad clumsy R-wave in V5/V6.Refer to Figure 1, where the difference between normal conduction, right bundle branch block ( Figure 1. These ECGs show the difference between normal conduction, left bundle branch block (LBBB) and right bundle branch block (RBBB). As evident from these ECGs, the cardinal difference between normal conduction and bundle branch blocks is the QRS duration: bundle branch blocks are caused by dysfunctional bundle branches, which results in slow (and abnormal) activation of ventricular myocardium and thus prolonged QRS duration. A QRS duration of 120 ms (0.12 s) is required to diagnose bundle branch block. Also note that both left bundle branch block (LBBB) and right bundle branch block (RBBB) cause marked ST-T changes, including ST elevations, ECG criteria for left bundle branch block (LB...

Pathological left axis deviation (LAD) is a condition where the heart’s main axis is shifted to the left. This can be caused by a number of different conditions, including heart disease, lung disease, and certain types of cancer. LAD can also be a normal variant in some people. In most cases, LAD is not a serious condition and does not require treatment. However, in some cases, LAD can be a sign of a more serious underlying condition and may require further evaluation and treatment. A Left axis deviation can be benign and isolated in up to 40% of cases, but it is frequently associated with current heart disease and should be monitored. The left axis deviation is a major QRS vector with a temperature range of -30C to -90C. Normal is defined as the electrical axis falling between -30 and +90. Electrical axis deviation occurs if the electrical axis is between -30 and -90. The electrical axis should be between 90 and 180 to calculate the right axis deviation. What Is The Range For Left Axis Deviation? Image Source: howmed.net The left axis deviation is the major vector, falling between -30 and -90 degrees. The QRS axis is shifted 90 degrees to 180 degrees on either the right or left axis, resulting in the right axis deviation. Lung disease, Left axis deviation (LAD) is the most common abnormality observed in adults, affecting more than 8% of patients. Left anterior hemiblocks or left anterior fascicular blocks are the two most common forms of LAD (45% or more). If a patient ha...

Clinically, bifascicular block presents with one of two ECG patterns: • Right bundle branch block ( • RBBB and left posterior fascicular block ( * Some authors describe Left bundle branch block ( LBBB) as a bifascicular block, as it may indicate LAFB + LPFB. However, clinically the term bifascicular block is reserved for RBBB with either LAFB or LPFB Electrophysiology Bifascicular block involves conduction delay below the atrioventricular node in two of the three fascicles: • Conduction to the ventricles is via the single remaining fascicle • The ECG will show typical features of RBBB plus either left or right axis deviation. • RBBB + LAFB is the most common of the two patterns. This is due to a single coronary artery blood supply (LAD) to the anterior fascicle • RBBB + LPFB is less common due to a dual blood supply (right and left circumflex arteries), and this combination may be associated with more extensive underlying cardiac pathology Clinical significance Bifascicular block is often associated with structural heart disease (50-80%) and extensive fibrosis of the conducting system. There is a risk of progression to complete heart block with additional damage to the third remaining fascicle, however clinical context is important: • Overall rate of progression to complete heart block is 1-4% per year • In symptom free patients, these figures are ~1% per year • Patients presenting with syncope have a 17% annual risk of progression • Syncope or presyncope in the context of...