Introduction - ECG Acquisition and Automated Remote Processing - page 5

(a) (b)

(c)

SA node

P-wave

AV node

Bundle of His

QRS -
complex

Right Bundle
Branch

Left Bundle

Branch

T- w a v e

Anterior Fascicle Posterior Fascicle

Fig. 1.3 Electrical conduction system through heart schematic. a Electrical conducting system
of heart. b ECG wave. c Conduction pathway sequence

1.4 ECG Clinical Signatures

A complete cardiac cycle is represented by P-QRS-T waves, connected by some
equipotential segments in a typical ECG wave, called a 'beat.' Most of the
diagnostic information is contained in the morphology and wave duration and
intervals of constituent waves. For ECG interpretations, some conventions are
used for the wave durations and intervals, defined as follows:

Onset: the start or initiation of an electrical activity (repolarization or

depolarization).
Offset:

the end or termination of an electrical activity (repolarization or

depolarization).
Wave duration (or width): time gap between the onset and offset of the same wave.
Interval: onset of one wave and offset of the other wave (or next wave).
Segment: offset of one wave and onset of the following wave.