Comparison of glucose-insulin-thallium-201 infusion single photon emission computed tomography (SPECT), stress-redistribution-reinjection thallium-201 SPECT and low dose dobutamine echocardiography for prediction of reversible dysfunction

Evaluation of myocardial viability with thallium-201 infusion MPSPECT after oral glucose application in patients with chronic coronary artery disease

AIM

The aim of this study was to evaluate the myocardial viability in nondiabetic patients with chronic coronary artery disease (CCAD) or past myocardial infarction (MI), using thallium-201 infusion myocardial perfusion single-photon emission computed tomography (MPSPECT) imaging after oral glucose application (Glu+Tl-infusion).

MATERIALS AND METHODS

In this study, 33 nondiabetic patients (three female, 30 male, mean age: 55.24+/-11 years, range: 33-77 years) with MI history or known CCAD were included. Rest/redistribution/24 h-late-MPSPECT imaging was performed for all patients. In all patients in whom fixed perfusion defect was observed on any wall of the left ventriculi, after 24 h-late-MPSPECT imaging, 75 g oral glucose was given. Thirty minutes later, 1 mCi thallium-201 in 100 ml of physiological saline solution was applied in a period of 20 min by slow infusion. After infusion at the 10th minute, MPSPECT imaging was performed. Perfusion was evaluated visually for a total of 3432 segments with the 26-segment 5-point scoring technique. Scoring measured perfusion as 0 = no perfusion defect, 1 = mildly reduced, 2 = moderately reduced, 3 = severely reduced, and 4 = absent uptake. Scores '0 and 1' were considered normal and scores '2-4' were considered abnormal.

RESULTS

For serum insulin levels measured after glucose application, a significant increase was determined, according to the period before glucose application (P<0.001). When compared with rest MPSPECT images, segmental perfusion improvement both in redistribution and in the 24 h-late-MPSPECT images were 16.3 and 18.3%, respectively. This ratio was found to be 27.2% for Glu+Tl-infusion images. The ratios of segments in which perfusion was worsening were calculated to be 9.4, 14.5, and 7.3%, respectively, for redistribution, 24 h-late-MPSPECT, and Glu+Tl-infusion images. When this evaluation was made for all three vessel areas, again the highest perfusion improvement and the lowest perfusion worsening were detected for Glu+Tl-infusion images. In addition, when this evaluation was made for the three vessel areas according to the coronary narrowing degree, again the highest perfusion improvement was detected for Glu+Tl-infusion images, in segments in the left anterior descending artery, and right coronary artery areas with >/=90% narrowing. In rest images, in segments with segmental scores of 3 and 4, when the total reversibility ratio was evaluated, this ratio was calculated to be 0.7% for redistribution images and 4.5% for 24 h-late-MPSPECT. The highest total reversibility ratio in these segments was detected with Glu+Tl-infusion images to be 10.3%. When we evaluated the patients with respect to the MI history time, the highest segmental perfusion improvement was detected in patients with 0-3 months of MI history.

CONCLUSION

We conclude that in nondiabetic patients who are known to have CCAD or past MI history, Glu+Tl-infusion is an easily applicable method that gives better results for the evaluation of myocardial viability.

Comparison of thallium deposition with segmental perfusion in pigs with chronic hibernating myocardium

Viable, chronically dysfunctional myocardium with reduced resting flow (or hibernating myocardium) is an important prognostic factor in ischemic heart disease. Although thallium-201 imaging is frequently used to assess myocardial viability in patients with ischemic cardiomyopathy, there are limited data regarding its deposition in hibernating myocardium, and this data suggest that thallium retention may be supernormal compared with control myocardium. Accordingly, pigs (n=7) were chronically instrumented with a 1.5 mm Delrin stenosis on the proximal left anterior descending coronary artery (LAD) to produce hibernating myocardium. Four months later, severe anteroapical hypokinesis was documented with contrast ventriculography (wall motion score, 0.7+/-0.8; normal=3), and microsphere measurements confirmed reduced resting flow (LAD subendocardium, 0.78+/-0.34 vs. 0.96+/-0.24 ml.min(-1).g(-1) in remote; P<0.001). Absolute deposition of thallium-201 and insulin-stimulated [18F]-2 fluoro-2-deoxyglucose (FDG) were assessed over 1 h and compared with resting flow (n=704 samples). Thallium-201 deposition was only weakly correlated with perfusion (r2=0.20; P<0.001) and was more homogeneously distributed (relative dispersion, 0.12+/-0.03 vs. 0.29+/-0.10 for microsphere flow; P<0.01). Thus after 1 h relative thallium-201 (subendocardium LAD/remote, 0.96+/-0.16) overestimated relative perfusion (0.78+/-0.32; P<0.0001) and underestimated the relative reduction in flow. Viability was confirmed by both histology and preserved FDG uptake. We conclude that under resting conditions, thallium-201 redistribution in hibernating myocardium is nearly complete within 1 h, with similar deposition to remote myocardium despite regional differences in flow. These data suggest that in this time frame thallium-201 deposition may not discriminate hibernating myocardium from dysfunction myocardium with normal resting flow. Since hibernating myocardium has been associated with a worse prognosis, this limitation could have significant clinical implications.

Beneficial effect of coronary artery bypass grafting as assessed by quantitative gated single-photon emission computed tomography

The development of quantitative gated single-photon emission computed tomography (SPECT) has enabled the assessment of left ventricular perfusion, function and wall thickness in a single examination. Accordingly, the present study used gated SPECT to assess the benefit of coronary artery bypass grafting (CABG) in patients with coronary artery disease; 47 of those patients were evaluated before and 5 months after CABG. As a result of coronary revascularization, a significant improvement was observed in global ejection fraction (50+/-12 --> 53+/-11%; p<0.05). In 107 revascularized territories, the average regional reversible defect score (0.8+/-0.5 --> 0.2 +/-0.3; p<0.0001), average regional perfusion score at rest (0.6+/-0.6 --> 0.3+/-0.4; p<0.0001), average regional wall motion score (0.9+/-0.7 --> 0.7+/-0.5; p<0.05), and end-diastolic wall thickness (8.1+/-1.3 --> 8.6+/-1.5 mm; p<0.0005) all improved significantly. Even in 34 non-revascularized territories, the average regional reversible defect score (0.5+/-0.7 --> 0.2+/-0.5; p<0.03), average regional wall motion score (0.8+/-1.1 --> 0.5 +/-1.0; p<0.03) and end-diastolic wall thickness (8.0+/-1.4 --> 9.1+/-2.0 mm; p<0.03) all improved significantly. These results indicate that improvement in myocardial ischemia, hibernation and left ventricular function with CABG can be assessed in detail with gated SPECT.

Effect of dobutamine on regional diastolic left ventricular asynchrony in patients with left ventricular hypertrophy

Dobutamine improves systolic as well as diastolic function, but its effect on left ventricular (LV) asynchrony is unknown. An on-line automated segmental motion analysis (A-SMA) system was developed, based on an automatic border detection technique, to evaluate the effect of dobutamine on LV asynchrony in patients with LV hypertrophy (LVH). Low dose (5 microg x kg (-1) x min(-1)) dobutamine stress echocardiography was performed in 15 patients with LVH and in 15 healthy subjects. Short-axis LV views were obtained and divided into 4 wedge-shaped segments using A-SMA. The time - area curve and its first derivative curve in each segment were displayed. Total normalized peak filling rates (nPFR) were obtained. Systolic and diastolic asynchronies were assessed from the coefficient of variation (CV) of the regional time intervals from end diastole to the peak ejection rate (T-PER), and from end systole to the peak filling rate (T-PFR), respectively. At baseline, the CV of T-PER and T-PFR in patients with LVH were greater than those in healthy subjects (CV-T-PER: 18.8+/-9.2 vs 9.6+/-4.3%, CV-T-PFR: 19.5+/-7 vs 8.1+/-4.1%, both p<0.01). During dobutamine infusion, differences among groups at baseline disappeared and systolic and diastolic asynchronies improved (CV-T-PER: 7.3+/-4.8 vs 5.7+/-2.1%, CV-T-PFR: 6.8+/-3.5 vs 5.1+/-1.3%, both p>0.05). Total nPFR increased (from 3.2+/-1.0 /s to 5.6+/-1.3 /s, p<0.01) with dobutamine infusion in patients with LVH. Dobutamine improved LV diastolic asynchrony, as evaluated by A-SMA, in patients with LVH demonstrating that the lusitropic effect of dobutamine improved LV regional diastolic asynchrony, playing an important role in the improvement of global LV diastolic filling.

Reverse Redistribution Phenomenon on Rest 99mTc-Tetrofosmin Myocardial Single Photon Emission Computed Tomography Involves Impaired Left Ventricular Contraction in Patients With Acute Myocardial Infarction

The purpose of this study was to investigate the clinical significance of the reverse redistribution (RR) phenomenon on technetium-99m ((99m)Tc)-tetrofosmin myocardial single photon emission computed tomography (SPECT) performed at rest. Twenty-five patients underwent myocardial SPECT 3 weeks after the onset of acute myocardial infarction. Myocardial images were acquired at 40 min (early) and 4 h (delayed) after the injection of 740 MBq of (99m)Tc-tetrofosmin. The regional myocardial uptake of the tracer in 26 segments of the left ventricular (LV) wall was visually scored from 0 (no activity) to 3 (normal activity), and then the RR was defined as a decrease of more than 1 point in the activity score on the delayed image compared with that on the early image. Regions with an activity score of 3 on both the early and delayed images were defined as normal, and those with a score of 0 or 1 on the early image were considered to have a fixed defect. The regional myocardial (99m)Tc-tetrofosmin uptake and washout rate were also quantitatively assessed in each region. In addition, exercise stress electrocardiograph-gated SPECT with (99m)Tc-tetrofosmin was performed within 1 week of the rest study, and the percent count increase (%CI) during myocardial contraction in each corresponding region was studied. RR was observed in 18 of the 25 patients. The regional washout rate of (99m)Tc-tetrofosmin was significantly higher in the RR regions (45.0+/-3.8%) than in either the normal regions (36.4+/-4.1%, p<0.001) or in those with a fixed defect (39.7+/-3.9%, p<0.001). The %CI in the RR regions (10.4+/-10.4%) was significantly less than that in the normal regions (23.5+/-10.1%, p<0.001); however, no significant difference was found between the RR regions and those with a fixed defect (8.0+/-7.2%). In patients with acute myocardial infarction, the regions showing the RR phenomenon on (99m)Tc-tetrofosmin SPECT have severely impaired LV wall contraction after exercise.