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A bundle branch block can be diagnosed when the duration of the QRS complex on the ECG exceeds 120 ms. A right bundle branch block typically causes prolongation of the last part of the QRS complex and may shift the heart's electrical axis slightly to the right.
So if the block happens on the right side, it’s referred to as a right bundle branch block. So with this type, the electrical signal starts at the SA node, contracts the atria, moves through the AV node, splits at the bundle of His, and then moves down the left bundle branch but is blocked on the right bundle branch.
Infra-Hisian blocks may occur at the left or right bundle branches ("bundle branch block") or the fascicles of the left bundle branch ("fascicular block" or "Hemiblock"). SA and AV node blocks are each divided into three degrees, with second-degree blocks being divided into two types (written either "type I or II" or "type 1 or 2").
Left bundle branch block (LBBB) is a conduction abnormality in the heart that can be seen on an electrocardiogram (ECG). [1] In this condition, activation of the left ventricle of the heart is delayed, which causes the left ventricle to contract later than the right ventricle .
When a bundle branch or their fascicles becomes injured (by underlying heart disease, myocardial infarction, or cardiac surgery), it may cease to conduct electrical impulses appropriately, resulting in altered pathways for ventricular depolarization. This condition is known as a bundle branch block. [3]
The key indication for CRT is left bundle branch block (LBBB) of the heart, a cardiac abnormality leading to delayed left ventricular contraction. LBBB causes a QRS prolongation of ≥120 ms on the electrocardiogram, contributing to poor left ventricular coordination and reduced systolic function, thereby reduced ejection fraction (<35%).
The distal portion of the AV node is known as the bundle of His. [8] The bundle of His splits into two branches in the interventricular septum: the left bundle branch and the right bundle branch. The left bundle branch activates the left ventricle, while the right bundle branch activates the right ventricle.
A second, and clinically distinct, definition of trifascicular block is a circumstance in which right bundle branch block (RBBB) and left bundle branch block occur in the same patient, but at distinct points in time. For example, a patient that is found to have a RBBB one day and a LBBB another can be said to have "alternating bundle branch ...