Ask the doctor: Does the length of the ST segment on an electrocardiogram matter?

I have an electrocardiogram as part of my yearly checkup. After the last one, my doctor mentioned that my ST segment was longer this year than it was last year. He recommended that I have a stress test to check this out. I passed with flying colors. When I asked the cardiologist who did the stress test about the ST segment, he said the length isn?t really important, that the height and shape are what matter. Can you explain?