Unmasking of atrial repolarization waves using a simple modified limb lead system.

Objective: In the present study, a modified limb lead (MLL) system was used to record the Ta wave in sinus rhythm and with AV block in male patients.

Methods: Eighty male subjects (mean age 36 ± 7 years) in sinus rhythm and 20 male patients with AV block (mean age 72 ± 5 years) were included in this study. Standard limb lead (SLL) ECGs and MLL ECGs were recorded for 60 seconds each with an EDAN SE-1010 PC ECG system.

Results: In sinus rhythm subjects, the observable Ta wave duration was 109 ± 4.7 ms, the P-Ta duration was 196 ± 5.1 ms, and the corrected P-Ta duration was 238 ± 7.2 ms. The Ta wave peak amplitude was -42 ± 8 µV. In AV block patients, the Ta wave duration was 314 ± 28 ms the P-Ta duration was 418 ± 29 ms and the corrected P-Ta duration was 46 ± 31 ms, while the Ta wave peak amplitude was -37 ± 9 µV. A correlation was found between the P and Ta wave amplitude, and no correlation was found between the P and Ta wave duration or the Ta amplitude and Ta duration in sinus rhythm and AV block subjects.

Conclusion: The end of the Ta wave is not observable in sinus rhythm subjects, as it extends into the QRS complex and ST segment. In AV block patients, the Ta wave duration was generally three times longer than the observable Ta duration in sinus rhythm subjects.