4.1.5 Heart score
The measurement of heart score was popularised in Australia by Steel and co-workers in the 1960s and is still widely used in the southern hemisphere. It is measured by calculating the mean duration of the QRS complex in the three-limb leads. Steel found the measurement to correlate closely with athletic perforand heart weight. However, later studies have failed to find a strong correlation between these factors. The method has little basis in electrobecause the majority of the myocardium is electrically silent at the body surface (see section 1.5.6). In addition, precise measurement of the duraof the QRS complex is difficult because the ST segment is slurred in many normal animals. There are a number of reasons why the measurement may be increased in athletic animals. However, in the author's view, measurement of heart score is a misleading technique in individual horses and has no clinical value.