Comparison between manual and computer measurement of ST-segment amplitude during exercise

Abstract

Several studies have shown that the maximal ST HR slope may be used as a reliable index of myocardial ischemia as assessed by coronary angiography, but this involves laborious training and derivation, particularly with respect to the measurement of ST segment amplitude, which is obtained by averaging values measured in at least 10 cardiac cycles in the steady state. The authors compared manual measurement of ST-segment amplitude with computer-processed beat using cardiac cycles in six consecutive patients with standard 12-lead records obtained over 5 seconds and a beat processed by the recorder to represent each lead (modal beat, over 10 seconds). All recordings were made in the steady state. Two patients had myocardial ischemia, as assessed by means including the maximal ST HR slope and the occurrence of ST-segment depression at the end of exercise. Comparisons were made between measurements in 324 pairs of ST-segment amplitude obtained, respectively, from manually averaged recorded beats (average beat) and the modal beat during each step of the exercise test. The level of the ST-segment, (80 msec after the end of QRS complex) was independently obtained from the two records in a blinded fashion. The group data showed that the modal beat gave significantly lower values of ST-segment amplitude than the average beat. Similar results were obtained when 286 pairs of positive amplitudes were compared in the range of 0–7.25 mm. In the remaining 38 pairs in which ST-segment depression was found, the amplitude in the modal beats was not significantly different from the average beats. When the amplitude was assessed in 10–12 average beats of cardiac cycles in 45 pairs, the protocol for obtaining the maximal ST HR slope, no significant difference was found between average beats of 0.59 mm and modal beats of 0.69 mm. Cardiac cycles less than 10 were assessed to examine the influence of ST-segment amplitude and small numbers of recorded beats. Irrespective of the number of beats, amplitudes of values less than 2.45 mm in average beats were not significantly different from those in modal beats. The results show that the ECG recorder processing accuracy was better in cardiac beats with ST-segments having a low amplitude or a negative value than a highly positive amplitude. This should be useful in assessments of the level of the ST-segment at the end of exercise.