A schematic representation of the generation of the P-QRS-T complex is shown
The intracellular fluid of myocardial cells is electrically negative (approx.
85 mV) in relation to the extracellular fluid. Conversely the extracellular fluid
is positive in relation to the intracellular fluid.
It is differences in current charges in the extracellular fluid that create the
potential difference recorded by the ECG.
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Fig. 3.1 Generation of the ECG and depolarisation of
the heart as an electrical impulse travels from the sinoatrial (SA) node. The ECG
recorder is attached in such a way that the negative electrode is at the base of
the heart and the positive at the apex; this approximates to lead II. (Modified from
Tilley (1992) with kind permission.)