Intraventricular block (synonyms: IV block; fascicular block; thigh block; ICD-10-GM I45.4: nonspecific intraventricular block) is a cardiac arrhythmia that belongs to the group of conduction disorders.
In thigh block, there is an excitation conduction disturbance of the heart below the His bundle (lat. fasciculus atrioventricularis). The His bundle is part of the conduction system. It lies distal to the atrioventricular node (lat. nodus atrioventricularis; “atrioventricular node“; AV node) toward the apex of the heart.
In intraventricular block, the following forms are distinguished according to the number of fascicles (substructures consisting of multiple nerve or muscle fibers) involved:
- Unifascicular block
- Bifascicular blocks – e.g., right bundle branch block and left anterior hemiblock.
- Trifascicular blocks – all legs below the His bundle.
According to the localization, a distinction is made between:
- Left bundle branch block (LSB)
- Left anterior hemiblock (LAH, LAHB).
- Left posterior hemiblock (LPH, LPHB).
- Right bundle branch block (RSB)
The following degrees of severity of intraventricular block can be differentiated:
- Severity I – incomplete block
- Severity II – intermittent block
- Severity III – permanent (durable) block
Course and prognosis: the main focus is the therapy of the underlying disease. If there is an isolated unifascicular block, it does not require therapy. While a bifascicular block is an indication for implantation of a pacemaker only if clinical symptoms are present, a trifascicular block is a clear indication for implantation of a pacemaker. If trifascicular block is not treated, arrhythmias and syncope (brief loss of consciousness) may occur.
