Quantitative Evaluation of Serial 201-Tl Myocardial Scintigrams after Stress Testing in Ischemic Heart Disease

Abstract

For the quantitave evaluation of transient myocardial ischemia, serial 201-Tl myocardial scintigrams were performed at rest and under stress testing at intervals of one week in ischemic heart disease. Eight normal adults and forty-two patients with ischemic heart disease were studied by stress testing. The stress testing was multistage exercise by sitting bicycle ergometer to submaximal level. And 201-Tlwas injected 3 mCi intravenously one minute before the end of the test. In this study GCA-401 (Toshiba) as gammacamera, GAMMA 11 PDP 11/34 (DEC)as minicomputor and SIEMENS ELEMA 380B (Siemens) as bicycle ergometer were used. Myocardial scintigrams in three views (anterior, left anterior oblique and left lateral projectons)were obtained at ten minutes, one and two hours (phase 0,1 and 2) after the 201-Tl bolus injection.
The author showed that the washout rate was correlated with the peak double product (mmHg beats/min, × 10²). Based on the conception of 201-T1 redistribution report ed by Gewirtz et al., removing the influence of stress level using the correction of the washout rate the quantitative method was designed.
The myocardial wall was g eometrically divided into five segments each view. One segment was situated at apical region. The remained two segmeuts were placed at septal region and other two segments at postero-lateral region using the ROI of 7 × 7 matrix by manual. The washout rate from phase i to j (WRij) was defined as WRij= (maxCtsi-maxCtsj) /maxCtsi where maxCtsi denoted maximal Cts at phase i in the relevant view. The washout rate 02 (WR02)showed the decreasing rate of the net rate of 201-Tl for two hours after the injection.
The redistribution index (cRdsij) in each segment was defined as cRdsij= [Ctsi × WRij + (Ctsj-Ctsi) ]/maxCtsi, where Ctsi denoted mean Cts at phase i in the segment. cRds02 showed the redistributed counts which were estimated by adding WR02 for two hours.
The infarcted segment was identified by the findings of ECG and VC G. In remained segments, the ischemic segment was identified as 70% or less of maxCts 0 in phase 0 scintigram, while normal segment as 80% or more. The segments from 70% to 80% of maxCts 0 were removed from this study. ΣcRdsij denoted the sum of 15 cRdsij. MaxcRdsij indicated as the maximum of 15 cRdsij. Mean values (±SD) of cRds02 in the normal, ischemic and infarcted segments were -6.3 ±5.4, 9.9 ±6.9 and 3.4 ± 7.4%, respectively, and the differences were statistically significant each other (p<0.001). Mean values (± ±SD) of ΣcRds02 in normal, angina pectoris and MI groups were -48.3 ±46.8, 95.0 ±67.8 and 62.9 ± 35.8 resqectively. Between normal and angina pectoris group, and between normal and MI group, the differences were statistically significant respectively (p<0.001, q<0.01). When the peak double product attained at the test was 200 or more, it was significantly correlated with WR02 (r=0.81, p<0.01). All the thirty-two patients with angina except two showed that WR12 was greater than WR01, but eight normal cases showed that WRO1 was greater than WR12.
RI angiography was performed in the twenty-eight cases who had myocardial scintigram under stress testing in order to evaluate LV function using ejection fraction (EF), mean ejection rate (mER) and maximal ejection rate (maxER). The equilibrilium method at LAO 45°projection was used after 99m-Tc HSA 15 mCi intravenously at supine position. The indices were calculated from LV volume curve after the addition of six hundred cardiac cycle. The differences between MI with angina and MI without angina were significant statistically using maxcRds02, mER and EF (p<0.05, p<0.05 and p<0.01), though not significaut using maxER. As maxER decreased 4.00 or less, maxcRds02 increased. It was useful that twentyeight cases conld be classified to four groups (normal, angina pectoris.