The ST segment/heart rate relationship as an index of myocardial ischaemia

Changes in myocardial ischaemia during isosorbide dinitrate or indoramin therapy in patients with stable angina using relations between the ST segment and heart rate

The effect of isosorbide dinitrate or indoramin on myocardial ischaemia was examined in patients with stable angina pectoris. In a prospective trial, randomization resulted in 8 and 9 patients, respectively, given isosorbide dinitrate in a dose of 30-90 mg daily, and indoramin in a dose of 75-225 mg daily; 2 of these patients were serially examined during the two types of therapy. Changes in myocardial ischaemia were assessed by exercise testing using 12 standard electrocardiographic leads and a bipolar lead CM5. Individual and group comparisons showed that isosorbide dinitrate resulted in an increase in ST segment depression, the maximal ST/heart rate slope and the ratio of net ST segment depression to increases in heart rate (at least P less than 0.01). In contrast, with indoramin therapy there were no significant changes in these indices. The results in these patients suggest that isosorbide dinitrate leads more consistently to increases in the severity of myocardial ischaemia than indoramin, although this effect on ischaemia is apparently less than the benefit of these agents on exercise performance.

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

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.(ABSTRACT TRUNCATED AT 250 WORDS)