ABNORMALITIES OF THE S-T SEGMENT .1.

The usual normal S-T segment of the surface electrocardiogram (ECG) co ntributes little to the diagnostic procedure. When the S-T segment is too long or too short, or when it is displaced upward or downward, it is commonly abnormal. Under such circumstances, and S-T segment abnorm ality usually contributes considerable diagnostic information. When th e Grant method of ECG interpretation is used, it is possible to percei ve abnormalities of the S-T segment that may otherwise be ignored or m isinterpreted. This paper describes the method of identification and t he significance of primary and secondary S-T segment abnormalities. Wh en a mean vector constructed for the S-T segment displacement seen in 12 ECG leads is relatively parallel with a mean vector representing th e T wave, it is, with a few exceptions, part of the repolarization pro cess and is therefore part of the T wave. This may be called a seconda ry S-T segment abnormality. When a mean vector constructed for the S-T segment displacement seen in 12 ECG leads is not relatively parallel with a mean vector representing the T wave, it is, with a few exceptio ns, not part of the repolarization process and is therefore not part o f the T wave. This may be called a primary S-T segment abnormality.