ECG and VCG changes in experimental hemiblock and bifascicular block

Area of Science:

• Cardiology
• Electrophysiology
• Cardiac Imaging

Background:

• Understanding ECG/VCG changes in fascicular blocks is crucial for diagnosing conduction abnormalities.
• Hemiblocks, specifically left anterior fascicular block (LASB) and left posterior fascicular block (LPSB), can present in isolation or with other conduction defects like right bundle branch block (RBBB).

Purpose of the Study:

• To investigate the electrocardiographic (ECG) and vectorcardiographic (VCG) alterations in QRS configuration.
• To differentiate changes associated with isolated LASB and LPSB versus those combined with RBBB in canine hearts.
• To determine the diagnostic significance of initial versus terminal QRS forces in hemiblock diagnosis.

Main Methods:

• Induction of LASB and LPSB, both isolated and combined with RBBB, in canine models.
• Analysis of ECG and VCG parameters, including QRS axis deviation and QRS duration.
• Comparison of QRS loop changes, focusing on initial, main, and terminal parts.

Main Results:

• LASB caused superior-leftward QRS axis deviation without significant QRS prolongation; adding RBBB prolonged QRS significantly and rotated the axis counterclockwise.
• LPSB caused inferior-rightward QRS axis deviation without significant QRS prolongation; adding RBBB significantly prolonged QRS and rotated the axis clockwise.
• Neither LASB nor LPSB altered the initial QRS loop forces, but affected main and terminal forces, with no change in QRS loop rotation direction.

Conclusions:

• Changes in the terminal forces of the QRS loop are more diagnostically significant for hemiblock than initial forces.
• Combined fascicular blocks with RBBB lead to significant QRS duration prolongation, offering a distinct diagnostic signature.
• Vectorcardiography provides valuable insights into the spatial characteristics of QRS abnormalities in fascicular blocks.