Determination of the electrical heart axis in the frontal plane by analysis of the limb leads:
Case 1 - QRS complex predominantly positively deflected in lead I and predominantly negatively deflected in lead II is conclusive for left heart axis deviation.
A positively deflected QRS complex in lead I implies that the electrical heart axis is situated between –90 degrees and +90 degrees with reference to the horizontal line.
A negatively deflected QRS complex in lead II implies that the electrical heart axis is situated between +150 degrees and -30 degrees with reference to the horizontal line.
The animation shows the possible area in which the heart axis may be situated in this case. Click the play button.
Case 2 - QRS complex predominantly negatively deflected in lead I and predominantly positively deflected in lead aVF is conclusive for right heart axis deviation.
A negatively deflected QRS complex in lead I implies that the electrical heart axis is situated between +90 degrees and -90 degrees with reference to the horizontal line.
A positively deflected QRS complex in lead aVF implies that the electrical heart axis is situated between 0 degrees and +180 degrees with reference to the horizontal line.
The animation shows the possible area in which the heart axis may be situated in this case. Click the play button.
Case 3 - QRS complex predominantly negatively deflected in lead I and predominantly negatively deflected in lead aVF is conclusive for extreme heart axis deviation.
A negatively deflected QRS complex in lead I implies that the electrical heart axis is situated between +90 degrees and -90 degrees with reference to the horizontal line.
A negatively deflected QRS complex in lead aVF implies that the electrical heart axis is situated between +180 degrees and 0 degrees with reference to the horizontal line.
The animation shows the possible area in which the heart axis may be situated in this case. Click the play button.
Case 4 - QRS complex predominantly positively deflected in lead I and predominantly positively deflected in lead II is conclusive for normal heart axis.
A positively deflected QRS complex in lead I implies that the electrical heart axis is situated between -90 degrees and +90 degrees with reference to the horizontal line.
A positively deflected QRS complex in lead II implies that the electrical heart axis is situated between -30 degrees and +150 degrees with reference to the horizontal line.
The animation shows the possible area in which the heart axis may be situated in this case. Click the play button.
