Q. Duration limit of the QRS?

The duration of the QRS is usually reduced slightly during exercise. Because catecholamines increase conduction velocity in the Purkinje fibers and through the ventricular muscle. A number for studies show that ischaemia reduces the conduction velocity. The greatest prolongation is found in those with three vessel disease.

Athens Score

Changes in R-waves, S-waves and Q-waves have all shown some usefulness, but each is a weak predictor of CAD. Therefore, Michaelides and colleagues, have proposed an index or score to combine these factors. By combining the amplitude changes of the three waves in the formula mm = (DR - DQ - DS) aVF + (DR - DQ- DS) V5 and using a cutoff of less than 5 mm, they were able to obtain a sensitivity of 75 per cent and a specificity of 73 per cent. This was better than using ST depression alone.