Objective: This study aims to characterize P and Ta wave of Modified Limb Lead (MLL) Electrocardiogram (ECG) in Normal Sinus Rhythm (NSR) and Atrioventricular Block (AVB). Methods: ECGs were recorded using MLL configuration from 100 NSR volunteers (mean age 31 years, 35 women) and 20 male AVB patients (mean age 72 years). Amplitudes and durations of P, Ta wave, and PTa Interval (PTaI) were measured, plotted, and analyzed for both the groups. Results: P-wave amplitudes were larger in AVB, and also P, Ta waves correlated significantly in both groups with higher correlation in AVB (NSR: [Formula: see text]; AVB: [Formula: see text]). Ta-wave duration ([Formula: see text] ms) was longer than P-wave duration ([Formula: see text] ms) in AVB patients and was opposite to P-wave polarity in all the leads. PP Interval (PPI) correlated significantly with P wave (NSR: [Formula: see text]; AVB: [Formula: see text]), Ta wave ([Formula: see text]; [Formula: see text]), PTaI ([Formula: see text]; [Formula: see text]), and corrected PTaI ([Formula: see text]; [Formula: see text]). Conclusion: P-wave right axis shift leads to the higher P-wave amplitude in AVB which may be due to the advancing age and atrial chamber enlargement. In NSR, the duration of observable Ta wave was longer than P wave, whereas in AVB, the Ta wave duration was 3–3.5 times longer than P wave.

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