The interpretation of gross left axis deviation in the electrocardiogram

Area of Science:

• Cardiology
• Electrophysiology
• Medical Diagnostics

Background:

• Left axis deviation (LAD) in electrocardiograms (ECGs) can indicate conduction defects.
• Distinguishing LAD patterns in heart disease patients from normal subjects is challenging.

Purpose of the Study:

• To investigate vector angle discrepancies in patients with left axis deviation.
• To evaluate the diagnostic criteria for left anterior fascicular block.

Main Methods:

• Analysis of mean angles from maximum deflections versus areas in 94 patients with LAD.
• Comparison of frontal plane vector angles (maximum and 50 msec) between patient and normal groups.
• Assessment of initial vector orientation (spatial and azimuth) in normal and LAD subjects.

Main Results:

• Marked disparity in mean vector angles in LAD patients compared to a close correlation in normal subjects.
• Considerable variation in frontal plane angles and initial vector orientation in LAD patients.
• Rightward initial vector observed in 60% of LAD patients, unlike 80% of normals, suggesting left anterior fascicular conduction defects.

Conclusions:

• A rightward 5-10 msec vector (Q wave in lead 1) is not essential for diagnosing left anterior fascicular block.
• Rigid criteria to reliably distinguish aberrant excitation patterns in LAD from normal ECGs were not established.
• Old infarction patterns were not obscured by anterior fascicular block.