Variable threshold of exertional ischaemia in patients with positive exercise test at low workload.

In order to determine individual variability of ischaemic threshold on different days, 18 patients with exertional ischaemia at low workload were studied. All patients performed two exercise tests during different days in the morning and three on the same day at 9 am, 2 pm and 5 pm. The test performed in the morning on different days resulted in a significant difference in the mean values of rate pressure product at the ischaemic threshold as a consequence of individual variability observed in 10 patients. In 8 of these patients the differences were greater than 4000 mmHg beats min-1. Two patients showed respectively, 1 and 5 negative exercise tests despite the greater values of rate pressure product reached. Only 3 patients showed circadian variation of the ischaemic threshold; in these 3 patients variations of rate pressure product at the ischaemic threshold were also observed between different days. These data indicate that in patients with exertional ischaemia at low workload the rate pressure product at the ischaemic threshold shows considerable variability between tests performed on different days.