The BSPM data were analyzed and displayed using a VAX 11/780 computer. The 15-s recordings at each lead were averaged using previously tested algorithms with the PR segment as baseline. In addition, editing of each analog-form averaged lead was performed; leads judged unacceptable because of noise or baseline drift were deleted and replaced by interpolated data from surrounding leads.
Using superimposed Frank X, Y and Z leads to determine the time instants of QRS offset and peak of the T wave, the time integral of, or area under, the ST segment curve was computed at each electrode site. For this exercise study, the duration of the ST segment was defined as one half the time from QRS offset to the peak of the T wave (Fig 1). The ST segment time integrals were expressed in jiV*s. flovent inhaler
The BSPM display format was as individual and group mean ST segment isointegral contour maps at the various protocol times (Fig 2). Individual (Fig 2 and 3) and group mean (Fig 4 and 5) temporal difference maps also were constructed by subtracting resting maps from maps at cessation of exercise and at 5 min of recovery, respectively. From these subtraction maps the body surface sum of negative change in ST integral values (sum ST decrease) was determined and utilized as the quantitative index of electrocardiographic ischemia for this study (Fig 2 to 5).
Figure 1. Signal-averaged 12-lead electrocardiograms of a CAD patient (patient 5; Tables 1 and 2) at rest, at immediate cessation of exercise and at 5 min recovery. The shaded areas in each panel represent the ST integral, the area under the ST curve.
Figure 2. ST segment isointegral maps for the same study subject as illustrated in Figure 1. Each rectangle represents the torso, unrolled. The left half of each map represents the front of the body; the right half, the back. The contour lines join points of equal ST integral value and progress logarithmically. The maxima and minima are numerically identified. In the top four maps, solid lines represent positive ST integral values; dashed lines, negative values. From rest to immediate cessation of exercise, anterior, lateral and inferior ST distributions changed from positive to markedly negative. By 5 min of recovery they had returned toward normal, but there was still an area of ST negatively centered over the precordium. The bottom two maps are temporal subtraction maps in which dashed lines indicate a relative decrease in ST integral values between the respective study times. The torso sum of this decrease in ST integral values was utilized as the quantitative index of electrocardiographic ischemia for this study. In this patient with total occlusion of the left anterior descending coronary artery the sum of ST integral decrease between rest and immediate cessation of exercise was — 9,043 |iV«s, improving to — 6,202 jjlV*s by 5 min of recovery.
Figure 3. Isointegral ST maps of a study subject (patient 35; Tables 1 and 2) with three-vessel CAD.
Figure 4. Croup mean ST isointegral maps for the five study groups (Tables 1 to 3).
Figure 5. Croup mean ST isointegral maps of the component subgroups of CAD patient group 1 (Tables 1 and 2). The maps in the left column are the average ST integral appearances for the 14 patients with isolated left anterior descending CAD; those in the middle column, from four patients with isolated right CAD; and, the maps in the right column, from the five patients with isolated circumflex CAD. There were some spatial differences in ST integral patterns from rest, to exercise, to recovery; however, there was also marked overlap.
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