Mechanism for abnormal thallium-201 myocardial scintigraphy in patients with left bundle branch block in the absence of angiographic coronary artery disease

Patients with left bundle branch block (LBBB) often show abnormal images on exercise thallium (T1)-201 scintigraphy without evidence of significant coronary stenosis. We investigated the mechanism for this phenomenon. Six patients with LBBB and without significant coronary stenosis underwent T1-201 SPECT, ECG-gated SPECT imaging with Tc-99m-methoxyisobutyl-isonitrile (MIBI), and atrial pacing stress test. The % count amplitude in Tc-99m-MIBI images was calculated as [(maximal counts) - (minimal counts)]/(minimal counts) x 100. Though all patients had a low count in the septal and inferior wall in T1-201 SPECT images, there was no ischemic production of lactate during an atrial pacing stress test. Nevertheless, gated SPECT images showed attenuated septal activity during systole. In patients with LBBB, the ratios of % count amplitude at the septum to that at the lateral wall at rest (0.47 +/- 0.05, mean +/- SE) were significantly less than the controls (n = 5, 0.83 +/- 0.12, p = 0.014). In conclusion, these results suggest that abnormal T1-201 SPECT images of the septum in patients with LBBB are partially caused by impaired septal wall thickening during systole. Such an abnormal wall motion may reduce blood flow demands to the septum, resulting in reduction of coronary blood flow with little ischemia.

Intracellular sodium accumulation during ischemia as the substrate for reperfusion injury

To elucidate the role of intracellular Na+ kinetics during ischemia and reperfusion in postischemic contractile dysfunction, intracellular Na+ concentration ([Na+]i) was measured in isolated perfused rat hearts using 23Na nuclear magnetic resonance spectroscopy. The extension of the ischemic period from 9 minutes to 15, 21, and 27 minutes (at 37 degrees C) increased [Na+]i at the end of ischemia from 270.0+/-10.4% of preischemic level (mean+/-SE, n=5) to 348.4+/-12.0% (n=5), 491.0+/-34.0% (n=7), and 505.3+/-12.1% (n=5), respectively, whereas the recovery of developed pressure worsened with the prolongation of the ischemic period (95.1+/-4.2%, 84.3+/-1. 2%, 52.8+/-13.7%, and 16.9+/-6.4% of preischemic level). The kinetics of [Na+]i recovery during reperfusion was analyzed by the fitting of a monoexponential function. When the hearts were reperfused with low-[Ca]o (0.15 mmol/L) solution, the time constants of the recovery (tau) after 15-minute (8.07+/-0.85 minutes, n=5) and 21-minute ischemia (6.44+/-0.90, n=5) were significantly extended, with better functional recovery (98.5+/-1.4% for 15-minute [P<0.05]; 98.0+/-1.0% for 21-minute [P<0.05]) compared with standard reperfusion ([Ca]o=2.0 mmol/L, tau=3.58+/-0.28 minutes for 15-minute [P<0.0001]; tau=3.02+/-0.20 for 21-minute [P<0.0001]). A selective inhibitor of Na+/Ca2+ exchanger also decelerated the [Na+]i recovery, which suggests that the recovery reflects the Na+/Ca2+ exchange activity. In contrast, high-[Ca]o reperfusion (5 mmol/L) accelerated the [Na+]i recovery after 9-minute ischemia (tau=2.48+/-0.11 minute, n=5 [P<0.0001]) and 15-minute ischemia (tau=2.10+/-0.07, n=6 [P<0. 05]), but functional recovery deteriorated only in the hearts with 15-minute ischemia (29.8+/-9.4% [P<0.05]). [Na+]i recovery after 27-minute ischemia was incomplete and decelerated by low-[Ca]o reperfusion, with limited improvement of functional recovery (42. 5+/-7.9%, n=5 [P<0.05]). These results indicate that intracellular Na+ accumulation during ischemia is the substrate for reperfusion injury and that the [Na+]i kinetics during reperfusion, which is coupled with Ca2+ influx, also determines the degree of injury.

Comparison of dual-head coincidence gamma camera FDG imaging with FDG PET in detection of breast cancer and axillary lymph node metastasis

Dual-head coincidence gamma camera 18F-fluorodeoxyglucose (FDG) imaging was compared with FDG PET in the detection of breast cancer and axillary lymph node metastasis.

METHODS

Both coincidence gamma camera FDG imaging and FDG PET were performed in a cylindrical phantom containing spheres of different sizes and activity ratios (5:1, 10:1 and 15:1) and in 30 women (age range 32-78 y) with suspected breast cancer. Biopsies or mastectomies were performed in all patients. Images were visually assessed, and the count ratio between tumor and normal tissue (T/N ratio) was calculated.

RESULTS

In the phantom studies, coincidence gamma camera imaging visualized the smallest sphere (1.0 cm) at a ratio of 15:1 but not at ratios of 5:1 and 10:1. Coincidence gamma camera imaging visualized the other spheres (> or =1.3 cm) at all ratios. PET visualized all spheres at all ratios. In the clinical studies, 22 of 26 breast carcinomas detected by PET were also detected by coincidence gamma camera imaging.. Coincidence gamma camera imaging detected all of the carcinomas > or =2 cm in diameter (n = 10) and 12 of 16 carcinomas <2 cm. In breast carcinomas detected by both PET and coincidence gamma camera imaging, the T/N ratio in non-attenuation-corrected PET (7.12 +/- 7.13) was significantly higher than in coincidence gamma camera imaging (2.90 +/- 1.47, P < 0.005). Four of 8 axillary lymph node metastases detected by PET were detected by coincidence gamma camera imaging. Of 9 axillary lymph node metastases <1.0 cm in diameter, 7 and 3 were detected by PET and coincidence gamma camera imaging, respectively.

CONCLUSION

Coincidence gamma camera imaging is useful in detecting breast carcinoma > or =2 cm in diameter but is not reliable for breast carcinoma <2 cm in diameter. Coincidence gamma camera imaging may be useless or even dangerous in the detection of axillary lymph node metastasis.

Applicability of 99mTc-HL91, a putative hypoxic tracer, to detection of tumor hypoxia

To elucidate the applicability of 99mTc-HL91 (HL91) a putative hypoxic tracer, to the imaging of hypoxia in tumors, a biodistribution study of the tracer was performed. The intratumoral distribution of HL91 was compared with that of 14C-deoxyglucose (DG) and the expression of glucose transporter 1 (GLUT1) in an implanted tumor.

METHODS

Biodistribution of HL91 after intravenous injection into Wistar rats with rat mammary tumor (Walker-256) was studied by determining blood and tissue levels of radioactivity from 15 min to 6 h after injection. Dual ex vivo autoradiography was performed on sections of the tumor using HL91 (74 MBq) and DG (185 kBq). The same sections were immunohistologically analyzed with anti-GLUT1 antibody. Tumor tissue was histologically divided into areas of viable cancer cells, necrosis and granulation tissue. The viable cancer cell area was further divided into normoxic and hypoxic areas. Uptake of both tracers in each area was measured quantitatively. The intensity of GLUT1 staining (relative optical density [ROD]) in each area was evaluated by densitometry.

RESULTS

The uptake of HL91 in the tumor reached a maximal value (0.897 +/- 0.118% ID [injected dose], mean +/- SD, n = 5) at 120 min after intravenous injection of HL91, then gradually decreased. The tumor-to-muscle ratio continued to increase until 360 min (4.34 at 120 min, 7.01 at 240 min and 10.4 at 360 min). HL91 accumulated to significantly higher levels in the hypoxic area than those in the other tissues (P < 0.0001). Uptake of DG and expression of GLUT1 were significantly higher in the hypoxic area than in the normoxic area (P < 0.0001). In the viable cancer cell area, uptake of HL91 and expression of GLUT1 were strongly correlated (r = 0.624-0.868, mean r = 0.743, P < 0.0001), and DG uptake was moderately correlated with GLUT1 expression (r = 0.328-0.669, mean r = 0.505, P < 0.0001).

CONCLUSION

These results indicate that HL91 can be used to detect tumor hypoxia.

Feasibility of fluorodeoxyglucose dual-head gamma camera coincidence imaging in the evaluation of lung cancer: comparison with FDG PET

The purpose of this study was to elucidate the feasibility of fluorodeoxyglucose gamma camera coincidence imaging (FDG GCI) in the evaluation of lung cancer in comparison with FDG PET.

METHODS

Twenty-three patients with recently diagnosed lung cancer were examined with both FDG PET and FDG GCI on the same day. Pulmonary lesions were analyzed visually and semiquantitatively using the ratio of lesion-to-background counts (L/B ratio). The L/B ratio of FDG PET without attenuation correction (AC) was also calculated and compared. Nodal stations were only visually analyzed.

RESULTS

FDG GCI and FDG PET could detect 22 and 23, respectively, of 23 pulmonary lesions by visual analysis (95.7% versus 100%). The L/B ratio of FDG GCI was 4.26 +/- 2.55, and significantly lower than that of FDG PET (9.29 +/- 4.95; P < 0.01). The L/B ratio of FDG PET was significantly higher with AC than that without AC (9.29 +/- 4.95 vs. 6.66 +/- 4.65; P < 0.01). When the L/B ratio threshold was set at 5.0 for FDG PET and 2.7 for FDG GCI, their sensitivity was 87.0% and 73.9%, respectively. Of the 3 and 6 patients with false-negative results on semiquantitative analysis, the lesions in 3 patients on FDG PET and 4 patients on FDG GCI were less than or equal to 2.0 cm in greatest diameter, respectively. In the assessment of mediastinal involvement, FDG PET was 77.8% sensitive, 78.6% specific and 78.3% accurate, whereas FDG GCI was 77.8% sensitive, 92.9% specific and 87.0% accurate. In the hilar regions, FDG PET was 100% sensitive, 84.2% specific and 87.0% accurate, whereas FDG GCI was 75.0% sensitive, 89.5% specific and 87.0% accurate.

CONCLUSION

In this study, FDG GCI yielded results comparable to FDG PET on visual analysis to detect pulmonary lesions and lymph node metastases. However, the lesion-to-background contrasts of pulmonary lesions and nodal involvement were lower in FDG GCI than in FDG PET. Comparison between the L/B ratio of FDG PET with and without AC indicated that, with AC, FDG GCI would be closer to FDG PET in the evaluation of lung cancer.

Comparison between the decrease of dopamine transporter and that of L-DOPA uptake for detection of early to advanced stage of Parkinson's disease in animal models

Early diagnosis of Parkinson's disease (PD) is important for the potential application of neuroprotective therapies. The purpose of this study was to assess the detection of the early changes of PD by either imaging the dopamine transporter (DAT) or uptake of L-3,4-dihydroxyphenylalanine (L-DOPA). An early to advanced stage model of PD was induced in rats by stereotaxic injection of 1-10 microg 6-hydroxydopamine (6-OHDA) into the substantia nigra pars compacta. Using adjacent sections of the same animals, the binding of [I-125]beta-CIT, which labels DAT and the uptake of [C-14]L-DOPA, were evaluated 4 weeks after induction of the lesion. Any decrease in dopaminergic neurons was evaluated by in situ hybridization histochemistry (ISH) by detection of DAT mRNA-positive neurons. In addition, the expression levels of DAT, dopa decarboxylase (DDC), and vesicular monoamine transporter (VMAT2) in each neuron were studied with ISH. Our results show a decrease in both [I-125]beta-CIT binding and [C-14]L-DOPA uptake in parallel with a decrease in DA neurons from early to advanced stage models of PD. The decrease in [C-14]L-DOPA uptake was smaller than that in [I-125]beta-CIT binding in the same animal (P < 0.0001). Expression levels of DAT, DDC, and VMAT2 mRNAs were also decreased with the progression of the disease. Although ISH failed to detect the origin of the discrepancy between [I-125]beta-CIT and [C-14]L-DOPA levels, it was concluded that [C-14]L-DOPA levels underestimated the decrease of dopaminergic neurons and that [I-125]beta-CIT levels more precisely reflected the decrease.

Genetic polymorphisms of drug-metabolizing enzymes and susceptibility to head-and-neck squamous-cell carcinoma

We have investigated the association between the polymorphisms of drug-metabolizing enzymes and susceptibility to head-and-neck squamous-cell carcinoma (HNSCC). PCR-based analysis was performed on 145 Japanese patients and 164 healthy Japanese controls to determine genotypes of polymorphisms in CYP1A1, CYP2E1, GSTM1, GSTP1, and NAT2. Patients and controls were compared by multivariate analysis. The CYP1A1 Val/Val genotype was seen more frequently in patients than in controls [odds ratio (OR) 4.1, p = 0.038). The frequency of the slow plus intermediate NAT2 genotypes was also higher in patients (OR 2.0, p = 0.039). When we analyzed the distributions of the genotypes in 69 laryngeal and 45 pharyngeal cancer patients, laryngeal cancer patients had a higher frequency of NAT2 slow or intermediate genotype (OR 2.7, p = 0.011) and GSTP1 AA genotype (OR 2.4, p = 0.047) than controls. Pharyngeal cancer patients had a higher frequency of the CYP1A1 Val/Val genotype than controls (OR 5.7, p = 0.034), suggesting that different organs may be responsive to different chemicals from the environment. Furthermore, 23 patients who developed multiple cancers (HNSCC plus other) were compared with 115 patients with HNSCC alone. There was no significant difference in the polymorphisms between the 2 groups, though excessive alcohol consumption (more than 50 g/day of ethanol) appeared to be a risk factor for multiple cancers (p = 0.053).

Genetic polymorphisms of drug-metabolizing enzymes and susceptibility to head-and-neck squamous-cell carcinoma

We have investigated the association between the polymorphisms of drug-metabolizing enzymes and susceptibility to head-and-neck squamous-cell carcinoma (HNSCC). PCR-based analysis was performed on 145 Japanese patients and 164 healthy Japanese controls to determine genotypes of polymorphisms in CYP1A1, CYP2E1, GSTM1, GSTP1, and NAT2. Patients and controls were compared by multivariate analysis. The CYP1A1 Val/Val genotype was seen more frequently in patients than in controls [odds ratio (OR) 4.1, p = 0.038). The frequency of the slow plus intermediate NAT2 genotypes was also higher in patients (OR 2.0, p = 0.039). When we analyzed the distributions of the genotypes in 69 laryngeal and 45 pharyngeal cancer patients, laryngeal cancer patients had a higher frequency of NAT2 slow or intermediate genotype (OR 2.7, p = 0.011) and GSTP1 AA genotype (OR 2.4, p = 0.047) than controls. Pharyngeal cancer patients had a higher frequency of the CYP1A1 Val/Val genotype than controls (OR 5.7, p = 0.034), suggesting that different organs may be responsive to different chemicals from the environment. Furthermore, 23 patients who developed multiple cancers (HNSCC plus other) were compared with 115 patients with HNSCC alone. There was no significant difference in the polymorphisms between the 2 groups, though excessive alcohol consumption (more than 50 g/day of ethanol) appeared to be a risk factor for multiple cancers (p = 0.053).

Technetium-99m HL91 uptake as a tumour hypoxia marker: relationship to tumour blood flow

Technetium-99m HL91 (HL91) is a potential agent for imaging hypoxic tissue in vivo. To elucidate the relationship between hypoxia and blood flow in a tumour, dual-tracer autoradiography with HL91 and carbon-14 iodoantipyrine (IAP) was performed in a tumour-bearing rat model. The distribution of each tracer was analysed visually and semiquantitatively. In the tumours with central necrotic areas, HL91 uptake was marked around the necrotic areas whereas IAP uptake was marked at the periphery of the tumours, around the areas of marked HL91 uptake. Normalized HL91 uptake (%HL91) was highest in the low normalized IAP uptake (%IAP) fraction in the non-necrotic areas. There was a weak negative correlation between %HL91 and %IAP in the non-necrotic areas (r = -0.322, P<0.0001). In tumours with few or no necrotic areas, HL91 uptake was heterogeneous throughout the tumours, while IAP uptake predominantly occurred at the periphery of the tumours. %HL91 was higher in the inner two-thirds of the tumour than in the outer third. There was again a weak negative correlation between %HL91 and %IAP (r = -0.354, P<0.0001). This study confirmed that high HL91 uptake is related to low blood flow. The marked HL91 uptake around the necrotic region suggests the presence of chronic hypoxia in a tumour.

Lumped constant for deoxyglucose is decreased when myocardial glucose uptake is enhanced

Quantification of myocardial glucose uptake by positron emission tomography with [18F]fluorodeoxyglucose (FDG) requires the "lumped constant" (LC), which corrects the difference of affinity between glucose and FDG to glucose transporters and phosphorylating system. Since LC was introduced, it has been considered to be constant. However, this has recently been questioned. To elucidate the constancy of LC by other than radioisotope techniques, the accumulation rate of sugar phosphates (d[SP]/dt) was measured in isolated, perfused rat hearts by 31P NMR spectroscopy with 2-deoxyglucose (DG). We postulate alpha as the affinity of DG to transporters and the phosphorylating system relative to that of glucose. Theoretically, alpha is equivalent to LC. We determined alpha by measuring d[SP]/dt at DG concentration ([DG]) = 10, 7, 5, and 3 mmol/l, keeping the total of glucose concentration ([glucose]) and [DG] to 10 mmol/l. When the glucose uptake was enhanced by insulin (10 mU/ml) or stunning, calculated alpha was reduced (insulin stimulated, 0.15; stunning, 0.19) compared with the control (0.59). These results indicate that LC can be evaluated by methods without radiolabeled tracers and is smaller when glucose uptake is augmented.

Mechanism of impaired left ventricular wall motion in the diabetic heart without coronary artery disease

OBJECTIVE

To elucidate whether impairment of the myocardial free fatty acid (FFA) metabolism and small vessel abnormalities in the myocardium are etiologic or contributory factors of myocardial dysfunction in patients with NIDDM without any significant coronary artery disease.

RESEARCH DESIGN AND METHODS

We performed myocardial imaging with 123I-labeled beta-methyl-p-iodophenyl pentadecanoic acid (BMIPP), a branched analog of FFA, and dipyridamole-infusion 201thallium scintigraphy (Dip) in nine patients who demonstrated left ventricular wall motion abnormalities without any significant coronary artery disease and in fifteen control cases. As an index of myocardial FFA metabolism, the heart-to-mediastinum count ratio (H/M) of BMIPP was calculated from the mean count in the regions of interest at the heart and the upper mediastinum.

RESULTS

Nine patients with reduced wall motion documented by left ventriculography (LVG), (hypokinetic group) demonstrated significantly lower BMIPP uptake (2.1 +/- 0.2, mean +/- SD) than fifteen patients with normal wall motion (normokinetic group) (2.3 +/- 0.2, P < 0.05). Regional ventricular wall motion observed by LVG, regional BMIPP uptake, and regional redistribution phenomenon (RD) were evaluated for five regions of the left ventricle: anterior, septal, apical, lateral, and inferoposterior regions. Wall motion was abnormal in 24 out of 120 regions. Regional BMIPP uptake was reduced in 47 regions. RD in Dip was observed in 23 regions. In regional analysis, the existence of defect in the BMIPP image showed significant correlation with wall motion abnormality (P < 0.01), but there was no significant relationship between the RD in Dip and regional wall motion abnormality (P = 0.16). Myocardial biopsy specimens obtained from the right ventricle of 20 patients showed no pathologic changes, with the exception of two patients.

CONCLUSIONS

Our findings suggest that impairment of myocardial FFA metabolism rather than small vessel abnormalities in the myocardium is responsible for modest left ventricular dysfunction in patients with diabetes.

Glucose tolerance and myocardial F-18 fluorodeoxyglucose uptake in normal regions in coronary heart disease patients

To elucidate the relation between glucose tolerance and myocardial uptake of F-18 fluorodeoxyglucose (FDG), FDG-PET with 75 g oral glucose loading was performed on 43 coronary artery disease patients (twice in 2 patients). The patients were divided into 4 groups based on the blood glucose level (BS) and the insulinogenic index (II): group 1, normal (n = 9); group 2, impaired glucose tolerance (IGT, n = 12); group 3, mild diabetes mellitus (DM) (II > 0.4, n = 12); and group 4, severe DM (II < or = 0.4, n = 12). Percent (%) dose uptake of FDG in the normal regions of the myocardium was not significantly different in groups 1, 2, and 3, but it was much lower in group 4 than in groups 1 and 2. In groups 2, 3, and 4, % dose uptake showed a definite negative correlation with BS 60 min after glucose loading (r = -0.450, p < 0.05), and a close positive correlation with II (r = 0.363, p < 0.05). These findings indicate that myocardial FDG uptake in normal regions is not greatly impaired in patients with IGT or mild DM. Myocardial viability can be assessed by oral glucose loading in patients with IGT and mild DM as well as in patients with normal glucose tolerance.

Estimation of shunt flow in coronary-pulmonary fistula by lung perfusion scintigraphy with technetium-99m macroaggregated albumin

The shunt flow from the coronary artery to pulmonary arteries was evaluated in 6 patients with coronary-pulmonary fistula by lung perfusion scintigraphy with technetium-99m macroaggregated albumin. In 2 patients, whose degree of visualization of pulmonary arteries by coronary angiography was relatively high, lung perfusion scintigrams demonstrated the defects at the distal of coronary-pulmonary fistulas.

Metabolic changes in hibernating myocardium after percutaneous transluminal coronary angioplasty and the relation between recovery in left ventricular function and free fatty acid metabolism

To elucidate the changes in oxidative metabolism in hibernating myocardium after coronary revascularization, we performed myocardial single-photon emission computed tomography with a free fatty acid analog, I-123 beta-methyliodophenylpentadecanoic acid (BMIPP), and thallium-201 before and 1 month after percutaneous transluminal coronary angioplasty (PTCA) in 11 patients with angina pectoris caused by single artery stenosis. All patients had improvement in wall motion after PTCA at the region with coronary stenosis; the wall motion abnormality score evaluated by left ventriculography decreased from 5.5+/-0.8 (mean +/- SE) to 2.1+/-0.9, p <0.01) after PTCA. The defect score of I-123 BMIPP images was significantly larger than that of thallium-201 images either before (14+/-1.3 vs 8.9+/-1.1, p <0.01) or 1 month after (7.4+/-1.5 vs 3.7+/-0.8, p <0.01) PTCA. The decrease in the defect score of both images was significant (p <0.01). Changes in the wall motion abnormality score showed a significant correlation with both the change in the defect score of thallium-201 images (r = 0.58, p < 0.01) and that of I-123 BMIPP images (r = 0.75, p <0.01). These results indicate that the metabolism of free fatty acid is impaired in hibernating myocardium, and that improvement in left ventricular function after successful PTCA is strongly associated with the recovery of oxidative metabolism.

Difference in the mechanisms for compensating ischemic acidosis in diabetic rat hearts

To elucidate the difference in the mechanisms for alkalization during ischemic acidosis between diabetic and non-diabetic hearts, intracellular pH (pHi) was measured by phosphorus-31 magnetic resonance spectroscopy. Diabetes was induced by the injection of streptozotocin. The accumulation of proton ion (DeltaH+) during 15 min global ischemia at 37 degreesC was calculated from pH i. There were no significant differences in DeltaH+ between diabetic (DM: 0. 54+/-0.03 micromol/l,n=6; mean+/-s.e.m.) and non-DM hearts (0.57+/-0.04, n=6), when perfused with bicarbonate buffer. However, perfusion with HEPES buffer revealed a significant increase of DeltaH+ in DM (0.85+/-0.07, n=5) compared with non-DM (0.61+/-0.06, n=5P<0.05). On the contrary, the addition of a Na+/H+ exchange inhibitor (EIPA; 1 micromol/l) to bicarbonate buffer significantly increased DeltaH+ in non-DM (1.09+/-0.10, n=4) compared with DM (0.71+/-0.03, n=5P<0.01). Perfusion with HEPES buffer and EIPA equally increased DeltaH+ in both groups (DM 1.13+/-0.13, n=4; non-DM 1.15+/-0.14, n=4). Thus, the activity of Na+/H+ exchanger during ischemic acidosis, assessed as the increase of DeltaH+ induced by addition of EIPA to bicarbonate buffer, was higher in non-DM (0.52) than DM (0.17). In contrast, the contribution of bicarbonate-dependent systems evaluated by the deference of DeltaH+ between the bicarbonate buffer and the HEPES buffer was markedly bigger in DM (0.31) than non-DM (0.04). These results indicate that Na+/H+ exchange is a major mechanism to compensate ischemic acidosis in non-DM hearts, whereas bicarbonate-dependent systems compensate the depressed activity of Na+/H+ exchange in DM.

Mechanism for the cardioprotective effects of the calcium channel blocker clentiazem during ischemia and reperfusion

To elucidate whether or not Ca channel blockers have an intrinsic benefit that cannot be attributed to the reduction of Ca2+ entry by pretreatment, time-averaged intracellular Ca2+ concentration ([Ca2+]i) and energy-related phosphates were measured in isolated ferret hearts using nuclear magnetic resonance. In the drug-free ischemic group, [Ca2+]i increased significantly during 30 min of global ischemia at 30 degrees C and during 0-5 min of reperfusion. After 30 min of reperfusion, isovolumic left ventricular developed pressure recovered only to 63+/-7% of the pre-ischemic level (mean+/-SEM; N=5). Pretreatment with the Ca channel blocker clentiazem (10(-7) mol/L) itself depressed developed pressure by 53+/-9%. In the clentiazem group, [Ca2+]i showed no significant changes during ischemia or reperfusion. Recovery of developed pressure (87+/-8% of untreated level) was significantly higher than in the non-treated group (p<0.05). Nevertheless, when the negative inotropism of clentiazem was offset by increasing [Ca]o from 2 to 3 mmol/L, no beneficial effects of clentiazem were observed; [Ca2+]i increased significantly during 0-5 min of reperfusion, and developed pressure recovered only 60+/-7% of untreated level. These results indicate that reduction of Ca2+ entry from the extracellular space to the myocyte, as reflected by negative inotropism during pretreatment, is required for clentiazem to protect myocardium in a model of global ischemia and reperfusion.

SPECT findings in mitochondrial encephalomyopathy

We investigated the alterations in regional cerebral blood flow (rCBF) in mitochondrial encephalomyopathy (MEM), using [123I]N-isopropyl-p-iodoamphetamine (IMP) or 99mTc-hexamethyl propyleneamine oxime SPECT in 10 MEM patients.

METHODS

Four of the patients had MEM with lactic acidosis and strokelike episodes (MELAS), 2 had Kearns-Sayre syndrome (KSS), 1 had myoclonic epilepsy with ragged red fibers (MERRF) and 3 had cytochrome C oxidase deficiency (CCOD). Cerebral perfusion reserve was obtained from 6 patients (3 MELAS, 1 MERRF, 1 KSS, 1 CCOD) for a comparative analysis using the split-dose 123I-IMP SPECT method before and after the injection of acetazolamide.

RESULTS

All patients with MELAS showed focal hypoperfusion in the parietal and/or occipital lobes. Follow-up studies (3 MELAS patients) revealed extension or improvement in the abnormal perfusion. The hypoperfused lesions were correlated with abnormal CT/MRI findings. Perfusion was normal in 1 MERRF, 2 KSS and 3 CCOD patients, whereas CT/MRI findings in 1 MERRF, 1 KSS and 1 CCOD patient were abnormal. The cerebral perfusion reserve in 3 MELAS patients was decreased significantly compared with that in patients with other types of MEM (MELAS 7.4%, other MEM 33.8%; p < 0.05).

CONCLUSION

The rCBF was altered specifically in patients with MELAS, suggesting that brain perfusion SPECT will be useful in diagnosing and assessing such patients. The decreased cerebral perfusion reserve in patients with MELAS may represent an important feature of the pathogenesis of the strokelike episodes. The SPECT findings of patients with other types of MEM (MERRF, KSS and CCOD) were normal.

Assessment of reperfused myocardium using a new ischaemia-avid imaging agent, technetium-99m HL91: comparison with myocardial glucose uptake

We evaluated the efficacy of a new ischae-mia-avid imaging agent, technetium-99m labelled 4,9-diaza-3,3,10,10-tetramethyldodecan-2,11-dione dioxime (99mTc- HL91) as a marker of myocardial viability in ischaemic and reperfused myocardium. The left coronary artery of rats was ligated for 15 or 60 min and released. The myocardium was reperfused for 60 min [stunned myocardium, or acute myocardial infarction (MI)] or 7 days (subacute MI). Thereafter, 99mTc-HL91 and carbon-14 2-deoxyglucose (DG) were co-injected 30 min before sacrifice. We evaluated the myocardial accumulation of 99mTc-HL91 and DG by dual-tracer ex vivo autoradiography. The uptake of each tracer in the myocardial region was normalized by that in the septum (control), and expressed as percent uptake (%HL or %DG, respectively). Individual hearts were also histopathologically examined. The %HL in the stunned myocardium (n = 8) and in the septum were identical (101%+/-15%, mean+/-SD, P = ns), whereas the %DG was significantly increased (149%+/-27%, P<0.05) compared with that in the septum. These results suggest that 99mTc-HL91 cannot visualize stunned myocardium, whereas DG can. In acute MI (n = 7), the %HL (423%+/-96%, P<0.005) and the %DG (318%+/-91%, P<0.001) in the non-infarcted area at risk were significantly augmented compared with those in the septum. The %DG (181%+/-17%) in the infarcted area was also augmented (P<0.001), whereas the %HL (106%+/-25%) in the infarcted area was identical to that in the septum (P = ns). These results indicate that 99mTc-HL91 detected viable myocardium in the area at risk. In subacute MI (n = 8), the%HL in the infarcted area (101%+/-45%) and in the septum was identical, whereas %DG (292%+/-57%) was significantly higher than that in the non-infarcted risk area or the septum (P<0.0001). These findings suggest that DG detected viable myocardium in the area at risk, but that 99mTc-HL91 was not retained. We conclude that 99mTc-HL91 is a potent marker of myocardial viability when used during the early acute phase after reperfusion.

Alteration of intracellular Na+ during ischemia in diabetic rat hearts: the role of reduced activity in Na+/H+ exchange against stunning

To elucidate the contribution of reduced activity of Na+/H+ exchange in streptozotocin-induced diabetic hearts against stunning, intracellular Na+ concentration ([Na+]i) was measured in isolated rat hearts using 23Na-MRS. The recovery of left ventricular developed pressure in hearts reperfused after 15 min global ischaemia at 37 degreesC was significantly better in diabetic ones (102.9+/-2.0% of pre-ischemic level, mean+/-s.e., n=6; P<0.05), and non-diabetic ones pre-treated with potent Na+/H+ exchange inhibitor, EIPA (1 mu mol/l; 93.8+/-2.3%, n=5; *P<0.05) than non-treated, non-diabetic hearts (75.1+/-2.5%, n=8). When diabetic hearts were pre-treated with EIPA, the recovery (101.2+/-2.6%, n=5) was identical to that of non-treated, diabetic hearts. [Na+]i in non-diabetic hearts increased to 329.1+/-8.1% of pre-ischemic level during 15 min ischemia, whereas the increase in [Na+]i in diabetic hearts significantly suppressed to 199.8+/-10.3% (P<0.001). EIPA attenuated the increase of [Na+]i during ischemia to 189.1+/-9.0% in non-diabetic hearts ( P<0.001) and to 155.3+/-4.6% in diabetic hearts (P<0.05). Thus, the EIPA-dependent Na+ accumulation during ischemia, i.e. Na+ influx probably mostly via Na+/H+ exchange was smaller in diabetic hearts by 69.7% compared with that in non-diabetic hearts. These results indicate that the cardiac protection against stunning in streptozotocin-induced diabetic hearts is mediated by the attenuation of Na+ accumulation during ischemia, which is caused by the reduced activity in Na+/H+ exchanger.

Evaluation of left ventricular ejection fraction from radial long-axis tomography: a new reconstruction algorithm for ECG-gated technetium-99m sestamibi SPECT

Radial long-axis tomography can provide views similar to contrast left ventriculography (LVG) including the basal and apical areas of the left ventricle, not possible in routine short-axis tomography. We applied this method to ECG-gated Tc-99m Sestamibi (MIBI) myocardial SPECT images to estimate the left ventricular ejection fraction (LVEF).

METHODS

ECG-gated Tc-99m MIBI SPECT was performed with a temporal resolution of 10 frames per R-R interval. LVEF was calculated on the basis of left ventricular volume estimates at end diastole (ED) and end systole (ES) with using an ellipsoid body model. To validate this method, LVEF's derived from ECG-gated Tc-99m MIBI SPECT were compared with those from LVG in 11 patients with coronary artery disease.

RESULTS

There was a close linear correlation between LVEF values calculated from Tc-99m MIBI SPECT and those from LVG (r = 0.89, p < 0.001), although the gated SPECT underestimated LVEF compared to LVG. The technique showed excellent reproducibility (intra-observer variability, r = 0.96, p < 0.001; inter-observer variability, r = 0.71, p < 0.005).

CONCLUSION

The radial long-axis tomography technique gives a good estimate of LVEF, in agreement with estimates based on LVG. ECG-gated Tc-99m MIBI SPECT can, therefore, be applicable to assess myocardial perfusion and ventricular function at the same time.

Contribution of hypoxia to the development of cardiomyopathy in hamsters

OBJECTIVE

It has been hypothesized that microvascular spasms cause cardiomyopathy. To elucidate the contribution of hypoxia to the development of cardiomyopathy, the newly-developed hypoxia tracer, Tc-99m nitroimidazole, was applied to detect myocardial hypoxia in a hamster model.

METHODS

Tc-99m nitroimidazole (180 MBq) and I-125 iodoantipyrine (370 kBq) were injected into cardiomyopathic Syrian hamsters or control hamsters at age 10, 25, and 40 weeks (n = 6 in each group). The myocardial uptake of Tc-99m nitroimidazole was measured and dual tracer autoradiography was performed.

RESULTS

Histologic study revealed that the cardiomyopathic hamsters at age 10, 25 and 40 weeks were in the myocytolytic stage, the fibrotic and healing stage, and the hypertrophy and dilatation stage, respectively. Tc-99m nitroimidazole uptake was significantly greater in the cardiomyopathic hamsters than in the controls at age 25 weeks (cardiomyopathic hamsters, 33.3 +/- 4.7% g dose/g; control, 25.2 +/- 3.1), whereas there were no significant differences between both strains at age 10 and 40 weeks. The quantified concentration of I-125 iodoantipyrine in the cardiomyopathic hamster at age 40 weeks was significantly lower than that in the controls. When the Tc-99m nitroimidazole uptake was normalized by I-125 iodoantipyrine concentrations, the cardiomyopathic hamsters at age 25 and 40 weeks showed significantly greater uptake than the controls.

CONCLUSION

The myocardium in cardiomyopathic hamsters was hypoxic at the fibrotic and healing stage and may be hypoxic at the hypertrophy and dilatation stage. This may contribute to the development of cardiomyopathy.

Quantification of systolic count increase in technetium-99m-MIBI gated myocardial SPECT

This study was performed to clarify the validity of quantification of myocardial wall thickening by the count increase method using electrocardiography (ECG)-gated SPECT.

METHODS

We performed a phantom study to examine the quantification of this method and to clarify the relationship between the changes of relative counts and objective size (such as myocardial wall) under various conditions. In addition, in volunteers, the percent count increase (%CI) was analyzed in left ventricular segments based on circumferential profile curve analysis by ECG-gated SPECT with 99mTc-MIBI (methoxyisobutyl-isonitrile), and it was compared with the regional systolic wall thickness (%Th) assessed by echocardiography during low-dose dobutamine infusion.

RESULTS

In our phantom study, the relative count changes were correlated linearly with the object size only within less than 20 mm. Recovery coefficient curves were influenced by acquisition parameters such as type of collimator, diameter of camera rotation, counts and photon scattering. In ECG-gated SPECT, the %CI value was increased gradually at each stage after dobutamine infusion, in relation to the increase of the %Th seen on echocardiography, although there are significant large deviations between these two parameters.

CONCLUSIONS

In this study, quantitative analysis based on the %CI in ECG-gated SPECT may underestimate regional wall thickening. These data should be considered in the evaluation of the %CI as an index of myocardial function.

Glucose-loading thallium-201 myocardial SPECT

This study was designed to evaluate the feasibility of assessing myocardial viability using glucose loading followed by 201Tl SPECT.

METHODS

First, the effect of insulin on the kinetics of 201Tl uptake was evaluated in isolated perfused rat hearts. Second, glucose-loading 201Tl myocardial SPECT was performed in 13 nondiabetic patients with histories of anterior myocardial infarction. Thirty minutes before acquiring rest 201Tl SPECT, 20 g of glucose were intravenously injected into the fasting subjects. Thallium perfusion defects were compared to those of conventional rest-redistribution SPECT images obtained within a 2-wk interval. SPECT images were divided into 21 segments, and a defect score in 17 segments was calculated as a sum of the semiquantitative defect scores (0 = normal; 1 = mildly decreased uptake; 2 = severely decreased uptake; 3 = absence of uptake).

RESULTS

Thallium-201 uptake in isolated hearts showed a significant increase of 26% after insulin loading. Eleven (24%) of 45 segments showing perfusion defects on the conventional rest SPECT images demonstrated 201Tl uptake on glucose-loading SPECT imaging. Defect scores decreased significantly on the glucose-loading SPECT images (9.9 +/- 2.2 in early images; mean +/- s.e.) compared with the conventional rest-redistribution SPECT images (12.6 +/- 6.9 in delayed images, p < 0.05).

CONCLUSION

Glucose-loading SPECT represents a superior method for assessing myocardial viability using 201Tl.