Normal limits of ECG measurements related to atrial activity using a modified limb lead system.

Objective: The present study was designed to derive the normal limits of a new ECG lead system aimed at enhancing the amplitude of atrial potentials through the use of bipolar chest leads.

Methods: Sixty healthy male subjects, mean age 38.85±8.76 years (range 25 to 58 years) were included in this study. In addition to a standard 12-lead ECG, a modified limb lead (MLL) ECG was recorded for 60 sec with the RA electrode placed in the 3rd right intercostal space slightly to the left of the mid-clavicular line, the LA electrode placed in the 5th right intercostal space slightly to the right of the mid-clavicular line and the LL electrode placed in the 5th right intercostal space on the mid- clavicular line.

Results: In the frontal plane, the modification of limb electrode positions produced significant changes compared to standard limb lead I and II. The mean P wave amplitude was 111±17μV in MLL I and 64±16μV in standard limb lead (SLL) I (p<0.001). Similarly it was 118±22μV in MLL II and 100±27μV in SLL II. No statistically significant changes were seen in V1-V6 due to modification of the Wilson central terminal electrode positions.

Conclusion: The modification of limb electrode placement leads to changes in the amplitude of the P waves in the MLL leads I and II compared to SLL leads I and II in healthy subjects. These changes may be of importance in the detection of atrial electrical activity.