The criteria to diagnose a left bundle branch block on the electrocardiogram:

Left anterior fascicular block is a cardiac condition, distinguished from left bundle branch block.

Bundle branch block, especially left bundle branch block, can lead to cardiac dyssynchrony.

Intraventricular conduction defects and bundle branch block, especially left bundle branch block, are also common.

Left bundle branch block widens the entire QRS, and in most cases shifts the heart's electrical axis to the left.

Isolated instances of arrhythmias, such as supraventricular extrasystoles, atrial fibrillation and left bundle branch block have been reported during chronic flupirtine therapy.

Intraventricular conduction abnormalities (e.g., right or left bundle branch block, WPW, etc.)

However, some cardiac conduction abnormalities such as left bundle branch block (LBBB) allow the P2 sound to be heard before the A2 sound during expiration.

An ECG that reveals ST segment elevation or new left bundle branch block suggests complete blockage of one of the main coronary arteries.

Left bundle branch block (LBBB) is a cardiac conduction abnormality seen on the electrocardiogram (ECG).

Aortic stenosis, hypertrophic cardiomyopathy, left bundle branch block (LBBB), and a ventricular pacemaker could all cause a reverse splitting of the second heart sound.

If M occurs slightly after T, then the patient likely has a dysfunction of conduction of the left side of the heart such as a left bundle branch block.

These include incomplete left bundle branch block, complete left bundle branch block and complete right bundle branch block.

Sgarbossa's criteria is a set of electrocardiographic findings generally used to identify acute myocardial infarction in the presence of a left bundle branch block (LBBB) or a paced rhythm.

If this indicates acute heart damage (elevation in the ST segment, new left bundle branch block), treatment for a heart attack in the form of angioplasty or thrombolysis is indicated immediately (see below).

Pharmacologic agents such as Adenosine, Lexiscan (Regadenoson), or dipyridamole is generally used when a patient cannot achieve adequate work level with treadmill exercise, or has poorly controlled hypertension or left bundle branch block.

An electrocardiogram (ECG/EKG) may be used to identify arrhythmias, ischemic heart disease, right and left ventricular hypertrophy, and presence of conduction delay or abnormalities (e.g. left bundle branch block).

Some authors consider left bundle branch block (LBBB) to be a technical bifascicular block, since the block occurs above the bifurcation of the left anterior and left posterior fascicles of the left bundle branch.

The clinician must therefore be well versed in recognizing the so-called ECG mimics of acute myocardial infarction, which include left ventricular hypertrophy, left bundle branch block, paced rhythm, early repolarization, pericarditis, hyperkalemia, and ventricular aneurysm.

Poor R wave progression is commonly attributed to anterior myocardial infarction, but it may also be caused by left bundle branch block, Wolff-Parkinson-White syndrome, right and left ventricular hypertrophy as well as by faulty ECG recording technique.

If the ECG confirms changes suggestive of myocardial infarction (ST elevations in specific leads, a new left bundle branch block or a true posterior MI pattern), thrombolytics may be administered or primary coronary angioplasty may be performed.