The genesis of indeterminate axis: a quantitative vectorcardiographic analysis

Area of Science:

• Cardiology
• Electrophysiology
• Medical Imaging

Background:

• The electrical basis of an indeterminate QRS axis in vectorcardiography is not well understood.
• Previous studies have not fully elucidated the underlying vectorcardiographic characteristics.

Purpose of the Study:

• To investigate the vectorcardiographic features associated with an indeterminate QRS axis.
• To clarify the relationship between QRS loop morphology and terminal QRS forces.

Main Methods:

• Frank lead vectorcardiograms (VCGs) were recorded from ten subjects with indeterminate QRS axis.
• Analysis included frontal and transverse plane QRS loop characteristics and terminal force orientation.
• Comparison with established normal values from larger subject cohorts.

Main Results:

• Subjects exhibited narrow frontal plane QRS loops, significantly smaller than normal values.
• Terminal QRS forces showed a characteristic posterior, rightward, and superior orientation in the transverse plane.
• Prominent S waves were observed in precordial leads V5 and V6, significantly exceeding normal amplitudes.

Conclusions:

• The indeterminate QRS axis appears to be an epiphenomenon of the QRS loop's orientation relative to the frontal plane.
• Posterior, rightward, and superior terminal QRS force orientation is a key underlying factor.
• These findings provide a clearer vectorcardiographic understanding of the indeterminate QRS axis.