This chapter presents brief introductory notes about some special features of the female electrocardiogram (ECG). ECGs are generally displayed as one-dimensional functions of time with different ECG leads grouped in various conventional sequences to provide some two-dimensional (2-D) information such as chest leads V1 through V6. The mean horizontal plane (XZ) QRS and T vector loops of normal adult women show that the spatial direction of the initial repolarization sequence in horizontal plane is predominantly reverse and terminal repolarization concordant with depolarization sequence. Frontal plane QRS and T vector loops both are narrow and directed to the left indicating that spatial direction of repolarization sequence in frontal plane is predominantly reverse with respect to depolarization sequence.

Two-dimensional display of vector loops in principal planes is reasonably effective for illustrating ECG data of an individual person or mean ECG data of a group of individuals. However, these display formats reveal no information about the scatter or clustering of directional information at various time points of excitation or repolarization sequence. Directional distributions of vectorial data require in essence three-dimensional displays. Novel three-dimensional display procedures are introduced in this chapter for this purpose. Of particular importance is information obtained about three-dimensional distribution at time points of peak QRS peak and T peak vectors. While the spatial distribution of T peak vector is relatively tightly clustered at time point T peak and remain tightly clustered throughout repolarization, spatial directions of QRS vectors vary widely in the course of depolarization. The latter finding corresponds to QRS vectors rotating over 180° through the depolarization sequence.

Among the most characteristic features in female ECG with distinctive gender differences are ST segment patterns in anterior chest leads particularly in V2. The ST segment amplitude increases slowly from the J-point (end of QRS) until the onset of the T wave and then increases more rapidly until T wave peak. The slowly ascending ST segment with a relatively tall positive T wave in V2 represents a characteristic female (‘U’-shaped) waveform with a positive convexity.