Serial assessment of denervated but viable myocardium following acute myocardial infarction in dogs using iodine-123 metaiodobenzylguanidine and thallium-201 chloride myocardial single photon emission tomography.

Iodine-123 metaiodobenzylguanidine (mIBG) is taken up by sympathetic nerve endings, allowing scintigraphic imaging of myocardial sympathetic innervation. We investigated the denervated but viable canine myocardium after acute myocardial infarction by serial mIBG and thallium-201 chloride (201TlCl) single photon emission tomography (SPET). In 12 dogs, acute myocardial infarction was produced by ligation of the left circumflex coronary artery. Images of mIBG and thallium SPET were obtained 6 h, 1, 4 and 6 weeks later. The defect size was calculated in percentage points from short axial views, and the 123I-mIBG/201TlCl ratio was determined. The uptake ratio was high at 1 week but gradually decreased. Three dogs were killed at each time point, and tissue samples were obtained from infarcted (both 201TlCl and 123I-mIBG defects), peri-infarcted (123I-mIBG defect and 201TlCl normal) and normal myocardium (both mIBG and 201TlCl normal). The changes in tissue content of noradrenaline in these lesions were measured. Noradrenaline tissue content gradually recovered in the peri-infarcted area. However, no recovery was noted in the infarcted area at 6 weeks. We conclude that sympathetic denervation and re-innervation occur following acute myocardial infarction, and the denervated but viable myocardium could be detected non-invasively by combined mIBG and thallium SPET.     

Serial assessment of denervated but viable myocardium following acute myocardial infarction by using 123I-MIBG and 201TlCl myocardial SPECT

123I-MIBG is taken up by sympathetic nerve ending and provides a scintigraphic image of myocardial sympathetic innervation. We investigated the scintigraphic detection of denervated but viable myocardium following acute myocardial infarction by serial 123I-MIBG and 201TlCl myocardial SPECT. Fourteen patients were studied at acute (10 +/- 2 days) and chronic stage (86 +/- 10 days). Simultaneous dual SPECT was carried out after IV administration of 111 MBq (3 mCi) of 201TlCl and 123I-MIBG. The defect size of 123I-MIBG and 201TlCl were compared visually by using Bull's eye display generated from each myocardial SPECT. In all patients, 123I-MIBG defect showed larger compared to 201T1Cl defect at acute stage, which suggest the existence of denervated but viable myocardium. Of these patients, seven showed significant improvement of both defects, though 123I-MIBG defect showed slightly larger compared to 201TlCl defect, even at chronic stage. These patients had exercise induced thallium transient defect at infarcted area. The remaining 7 patients had no improvement of both defects at chronic stage, which suggest the complete scar at infarcted area. In addition to above study, 4 patients of old myocardial infarction demonstrated larger 123I-MIBG defect compared to 201TlCl defect even at old stage, which thought to be pathogenesis of ventricular tachycardia. In conclusion, 123I-MIBG could evaluate sympathetic denervation and reinnervation noninvasively in the patients with acute myocardial infarction.     

Dynamic myocardial scintigraphy with 123I-labeled free fatty acids in patients with myocardial infarction

We have already shown that myocardial imaging properties of radio-iodinated long-chain free fatty acids (¹²³I-FFA) and thallium 201 (²⁰¹Tl) are comparable in detecting areas of inadequate myocardial perfusion (van der Wall et al. 1980). Besides confirming our earlier observations, the present study tests the potential of ¹²³I-FFA, hexadecenoic acid (¹²³I-16-HA), and heptadecanoic acid (¹²³I-17-H^oA), in assessing regional myocardial metabolism in 30 patients within a week of proven myocardial infarction. The clearance rates (t_1/2) of FFA were estimated from mono-exponential time-activity curves, obtained by external detection over infarcted and normally perfused areas during a 30-min period after IV administration of 3–5 mCi ¹²³I-16-HA or ¹²³I-17-H^oA. Six normal subjects served as controls. The t_1/2 values in the infarcted areas were found to be significantly lower (18.5±2.5 min; mean±SD, with ¹²³I-16-HA and 16.8±3.5 min with ¹²³I-17-H^oA) than in noninfarcted areas (34.0±8.4 min with ¹²³I-16-HA and 34.8±7.7 with ¹²³I-17-H^oA). The t_1/2 values in the control group (27.5±3.0 min with ¹²³I-17-H^oA) were not significantly different from values found in noninfarcted areas in the patient group. Our findings of faster FFA turn-over rates in infarcted tissue are in contrast to previous studies, which have shown prolonged turn-over rates in reversibly ischaemic myocardium. We coclude that the study of turn-over rates of FFA provides a means to distinguish normally perfused, reversibly ischaemic and irreversibly ischaemic myocardium.     

Clinical significance of denervated but viable myocardium in patients with recanalized acute myocardial infarction.

In patients with acute myocardial infarction (MI), myocardial sympathetic innervation evaluated by 123I-metaiodobenzylguanidine myocardial scintigraphy is more sensitive to ischaemia than the associated perfusion abnormality of 201Tl myocardial scintigraphy. The purpose of this study was to evaluate the scintigraphic indices related to the recovery of left ventricular function after acute MI. 123I-metaiodobenzylguanidine and 201Tl-chloride imaging were performed in 15 patients (mean age 60 years, 13 men and 2 women) 2 weeks after the onset of acute MI. Using a 20-segment visual interpretation of the 201Tl image, myocardial segments were classified into persistent defect, redistribution or reverse redistribution, and normal 201Tl uptake. The extent of denervated segments showed a fair correlation with the ejection fraction on admission (r = -0.53, P = 0.04), whereas the extent of persistent defect had a close correlation with the ejection fraction at 4 months (r = -0.79, P = 0.01). There was a good correlation between the extent of denervated but viable myocardium and the change in ejection fraction from admission to 4 months (r = 0.68, P = 0.01). Thus, denervated but viable myocardium is a scintigraphic index related to the functional recovery of left ventricular pump function after acute MI.     

Recovery of impaired left ventricular function in patients with acute myocardial infarction is predicted by the discordance in defect size on123I-BMIPP and201TI SPET images

A discrepancy between myocardial perfusion defect and wall motion abnormalities is frequently found early after coronary reperfusion in patients with acute myocardial infarction. The purpose of this study was to assess recovery of impaired left ventricular function by reference to the discordance in defect size between myocardial fatty acid uptake and myocardial perfusion using combined single-photon emission tomographic (SPET) imaging early after coronary perfusion therapy. In 37 patients with acute myocardial infarction, iodine-123 15(p-iodophenyl)-3(R, S)-methylpentadecanoic acid (BMIPP) and thallium-201 SPET scans were performed early after coronary reperfusion. A severity score was determined from the extent of the imaging defect with each tracer. Left ventricular wall motion score (WMS) and ejection fraction (EF) were obtained at admission and at 4 weeks after the onset of infarction. In 32 of the 37 patients, discordance in defect sizes delineated with the two SPET studies was found during the acute stage. The severity score for BMIPP was larger than that for²⁰¹Tl during the acute stage (7.7±2.4 vs 4.4±2.5,P <0.001). There was a fair correlation between the severity score for BMIPP and WMS (r=0.82,P <0.0001), but a poor correlation between that for²⁰¹Tl and WMS. The extent of discordance in severity scores between BMIPP and²⁰¹Tl during the acute stage correlated well with the extent of the improvement in WMS (r=0.86,P <0.0001) and that of EF (r=0.85,P <0.0001). We conclude that the discordance in defect size on BMIPP and²⁰¹TI SPET images during the acute stage of infarction is an early predictor of the viability of the myocardium at risk of infarction.     

Clinical results with β-methyl-p-(<Superscript>123</Superscript>I)iodophenylpentadecanoic acid,single-photon emission computed tomography in cardiac disease

This study was undertaken to evaluate the relationships between myocardial perfusion and metabolism. Simultaneous β-methyl-p-(¹²³I)iodophenylpentadecanoic acid (¹²³I-BMIPP) and thallium 201 myocardial single-photon emission computed tomography (SPECT) were performed in 25 patients with myocardial infarction (group A) and 16 patients with hypertrophic cardiomyopathy (group B). The severity scores of¹²³I-BMIPP and²⁰¹Tl myocardial SPECT images were evaluated semiquantitatively by segmental analysis. In Group A, dissociations between thallium- and¹²³I-BMIPP-imaged defects were frequently observed in patients with successful reperfusion compared with those with no reperfusion and those with reinfarction. In four patients with successful reperfusion, repeated¹²³I-BMIPP and²⁰¹Tl myocardial SPECT showed gradual improvement of the¹²³I-BMIPP severity score compared with the thallium severity score. In group B, dissociations between thallium- and¹²³I-BMIPP-imaged defects were also demonstrated in hypertrophic myocardium. In addition, nonhypertrophic myocardium also had decreased¹²³I-BMIPP uptake. In groups A and B,¹²³I-BMIPP severity scores correlated well with left ventricular function compared with thallium severity scores. These findings indicate that¹²³I-BMIPP is a suitable agent for the assessment of functional integrity, because left ventricular wall motion is energy dependent and¹²³I-BMIPP may reflect an aspect of myocardial energy production. This agent may be useful for the early detection and patient management of various heart diseases as an alternative to positron emission tomographic study.     

A comparison of rest sestamibi and rest-redistribution thallium single photon emission tomography: Possible implications for myocardial viability detection in infarcted patients

Thirty patients (26 men, 4 women, mean age 61 ± 8 years) who had suffered myocardial infarction 15 ± 6 months previously, were submitted to (1) standard stress-redistribution thallium-201 single photon emission tomography (SPET), (2) rest-redistribution²⁰¹Tl SPET and (3) stress-rest technetium-99m sestamibi SPET. Uptake modifications in relation to exercise-induced defects were evaluated in a total of 390 myocardial segments. Tracer uptake was scored as normal (=0), mildly reduced (=1), apparently reduced (=2), severely reduced (=3) or absent (=4). Comparison of stress studies failed to show any statistical difference (58% segmental abnormalities with sestamibi vs 61% with thallium). Uptake abnormalities (score 1–4) were detected in 55% of the segments wiliest sestamibi, 55% with standard thallium redistribution, 55% with early imaging after thallium injection at rest and 54% with 3-h delayed rest imaging (P = NS). Absence of tracer uptake (score = 4) under resting conditions was recorded in 75 (19%) segments with standard²⁰¹Tl redistribution, 75 (19%) with rest sestamibi, 70 (18%) with rest²⁰¹Tl imaging and 62 (16%) with rst-rdistruion²⁰¹Tl (P<0.05 vs other imaging modalities). Thus, 3-h delayed rest thallium imaging detected reversibility of uptake defects in a significantly higher number of myocardial segments. This finding might have important implications for both tracer and technique selection when myocardial viability is the main clinical issue.     

A case of myocardial infarction with ventricular tachycardia, which had discrepancy of defect size between 123I-MIBG and 201TlCl myocardial imaging

123I-MIBG and 201TaCl myocardial imaging were carried out in 69 years-old man who had anterior myocardial infarction with ventricular tachycardia. In planar and SPECT imaging, the defect size of 123I-MIBG was larger compared to that of 201TlCl. The zone of fractionated activity was corresponded with the defect of 123I-MIBG. Thus, the denervated but viable myocardium could be detected by 123I-MIBG and 201TlCl myocardial imaging. 123I-MIBG may give a useful clinical information, since denervation may play a role in causing ventricular arrhythmia after myocardial infarction.     

Left ventricular postmyocardial infarction remodeling studied by combining MR-tagging with delayed MR contrast enhancement

OBJECTIVES: We sought to monitor the evolution of noninfarcted and infarcted myocardium function in the process of left ventricular (LV) remodeling after a reperfused myocardial infarction. MATERIAL AND METHODS: Pigs (n = 8) were subjected to reperfused infarction. Magnetic resonance imaging (MRI) was performed at 3 days and 8 weeks after infarction. Regional circumferential shortening (Ecc) and principal strain L1 in the infarcted, peri-infarcted, and remote myocardium were evaluated by tagged cine MRI combined with matched late enhancement data (Gadolinium-DOTA-enhanced IR-GRE) Global LV function was evaluated by cine MRI. Animals were euthanized after the second imaging session and tissue samples from the different myocardial regions were obtained for histopathologic study. RESULTS: There was a significant deterioration in Ecc between the 3-day and 8-week studies in the peri-infarcted myocardium at apex (-9.9% +/- 4.5% to -6.5 +/- 3.9; P = 0.046) whereas it remained stable for all other regions at all levels. A trend toward improvement in Ecc existed in the infarcted myocardium when infarction transmurality was less than 50% of the LV wall (-7.5% +/- 0.8% to -12.2% +/- 2.9% P = 0.06). Ecc in infarcted myocardium was significantly inferior (P < 0.002) to that in remote and peri-infarcted myocardium at the apical level (2.7% +/- 2.6% vs. -14.4% +/- 3.3% and -9.9% +/- 4.5%, respectively). Global LV function substantially deteriorated after infarction and was associated with a significant LV dilation. CONCLUSION: These results confirm the hypothesis that scarred myocardium imposes additional functional burden to the peri-infarcted myocardium.     

Utility of reinjection method in stress Tl-201 myocardial scintigraphy to assess viability of the infarcted myocardium

To assess viability of the infarcted myocardium, we performed stress Tl-201 myocardial scintigraphy using reinjection method in 37 patients with old myocardial infarction, and in 13 patients of them, Tl myocardial imagings were performed in resting state on the other day within 4 weeks after this examination. In this method, 111 MBq (3 mCi) of thallium was injected at the peak of exercise and initial and delayed images were acquired, then additionally 37 MBq (1 mCi) of thallium was injected after delayed scanning (reinjection) and we obtained post-reinjection images. Delayed images showed redistribution in 15 patients (41%), and no redistribution in 22 patients (59%). In post-reinjection images, 7 (19%) of 15 patients with redistribution and 3 (8%) of 22 patients without redistribution showed improvement of thallium uptake, in total 10 patients (27%) had additional thallium uptake in infarcted regions. And the degree of thallium uptake in post-reinjection images were almost equal to that in resting images. In conclusion, myocardial imaging using thallium reinjection method may be useful for the assessment of viability of the infarcted myocardium.     

Thallium and indium antimyosin dual-isotope single-photon emission tomography in acute myocardial infarction to identify patients at further ischaemic risk

Dual-isotope single-photon emission tomography (SPET) with indium-111 antimyosin and thallium-201 chloride was performed in 54 patients with acute myocardial infarction (AMI) to detect the location and extent of myocardial necrosis (antimyosin) and viable myocardium (²⁰¹T1). All patients underwent intravenous thrombolytic therapy with either streptokinase (1.5 million units/90 min) or tissue plasminogen activator (80 mg/90 min). Sensitivity in detecting MI was 91% (49/54 patients). With regard to dual-isotope SPET patterns, patients were devided into three groups: match, i.e. antimyosin uptake in segments with thallium defect (n = 8); mismatch, i.e. no uptake of either of the nuclides in corresponding segments (presence of perfusion abnormalities in the absence of antimyosin uptake) (n = 5); and overlap, i.e. thallium uptake in segments with uptake of antimyosin (n = 41). Coronary angiography and thallium exercise tests were performed in 40 and 45 patients, respectively, 5–14 days after MI. Exercise-induced ischaemia occurred in 66% of patients with overlap, 14% with match and 0% with mismatch (P <0.05 for overlap vs other groups). If, however, major in-hospital complications (sudden cardiac death, severe arrhythmias; five overlap, three overlap in addition to match/mismatch, two match, two mismatch) were included in the statistical analysis, there was no significant difference between the three groups (P = NS). Thus, although the dual-isotope pattern overlap identifies a subgroup of patients with a substantial amount of residual viable tissue after MI and a high probability of exercise-induced ischaemia, this criterion is of limited value in assessing short-term prognosis. Nevertheless, in cases of doubt it may help to decide which patients should undergo coronary revascularization.     

Quantitation of myocardial iodine-123 MIBG uptake in SPET studies: a new approach using the left ventricular cavity and a blood sample as a reference

In patients with chronic heart failure increased sympathetic activity is related to unfavourable prognosis. Since myocardial iodine-123 metaiodobenzylguanidine ([¹²³I]MIBG) uptake is related to myocardial noradrenaline content, i.e. cardiac sympathetic activity, measurement of myocardial [¹²³I]MIBG uptake may be of clinical use in determining prognosis or the effect of pharmacological intervention in these patients. The aim of the present study was to evaluate a new method to quantitate myocardial [¹²³I]MIBG uptake with respect to reproducibility and accuracy. Eighteen [¹²³I]MIBG planar and single-photon emission tomography (SPET) studies of patients with chronic heart failure were evaluated. Myocardial uptake was calculated from the myocardial (MYO) to left ventricular cavity (C) count density ratio and the¹²³I activity in a blood sample. This was performed employing planar LAO images, a single-slice SPET method using the midventricular myocardial short-axis slice, and finally a multi-slice SPET method analysing semi-automatically drawn volumes of interest (VOIs). The accuracy of the multi-slice SPET method was verified using a cardiac phantom. The planar method was found to be reproducible [intra- and interobserver coefficients of variation (IACV and IRCV) were 0.025 and 0.012 respectively] but the mean MYO/C count density ratio was only 1.31±0.16 as a consequence of overprojection. For the single-slice SPET method IACV was 0.2 and IRCV was 0.13, representing poor reproducibility. For the multi-slice SPET method IACV was 0.051, IRCV was 0.047 and the mean MYO/C count density ratio was 5.4±2.42. Accuracy was 81% at a true MYO/C count density ratio of 6 in the phantom. It is concluded that the multi-slice SPET method using the left ventricular cavity VOI and a blood sample as a reference is a reproducible and accurate method for assessing myocardial [¹²³I]MIBG uptake.     

Nitrate administration to enhance the detection of myocardial viability by technetium-99m tetrofosmin single-photon emission tomography

A comparison was performed between technetium-99m tetrofosmin myocardial perfusion tomography at baseline and after nitrate administration, using a 2-day protocol, and rest-reinjection thallium-201 single-photon emission tomography (SPET) studies in order to assess whether nitrates enhance the detection of viable myocardium with^99mTc-tetrofosmin. Fifteen patients with coronary artery disease, previous myocardial infarction and a left ventricular ejection fraction <40% underwent²⁰¹T1 rest-injection and^99mTc-tetrofosmin. baseline-postnitroglycerin (0.4 mg sublingually) SPET studies, within 48 h. Tomograms based on the three spatial planes were divided into 15 segments and regional tracer uptake was quantitatively analysed. Viability was defined as presence of tracer uptake >50% of peak activity on baseline studies or after reversibility. The percentage of peak activity of^99mTc-tetrofosmin at baseline correlated with that of 201T1 (r=0.82,P <0.001). On baseline^99mTc-tetrofosmin studies, 73 of the 225 segments that were analysed had <50% of peal. activity. Fifteen percent of these segments showed reversibility after nitrate administration, with an increase in^99mTc-tetrofosmin uptake from 40%±9% to 57%±9% of peak activity (P=0.003). All reversible segments after nitrate administration had viability criteria on²⁰¹Tl studies, but 20 segments that were non-viable on^99mTc-tetrofosmin. studies were viable on²⁰¹Tl studies. Using a threshold value of >40% of peak activity, only seven segments remained non-viable on^99mTc-tetrofosmin studies. Overall agreement between^99mTc-tetrofosmin with nitrates and²⁰¹Tl-reinjection regarding the presence of myocardial viability was 90%. Detection of myocardial viability with^99mTc-tetrofosmin. was enhanced after nitrate administration, correlating with viability criteria observed on thallium studies.     

Relationship between quantitative cardiac neuronal imaging with 123I-meta-iodobenzylguanidine and hospitalization in patients with heart failure

Purpose

Hospitalization in patients with systolic heart failure is associated with morbidity, mortality, and cost. Myocardial sympathetic innervation, imaged by ¹²³I-meta-iodobenzylguanidine (¹²³I-mIBG), has been associated with cardiac events in a recent multicenter study. The present analysis explored the relationship between ¹²³I-mIBG imaging findings and hospitalization.

Methods

Source documents from the ADMIRE-HF trial were reviewed to identify hospitalization events in patients with systolic heart failure following cardiac neuronal imaging using ¹²³I-mIBG. Time to hospitalization was analyzed with the Kaplan-Meier method and compared to the mIBG heart-to-mediastinum (H/M) ratio using multiple-failure Cox regression.

Results

During 1.4 years of median follow-up, 362 end-point hospitalizations occurred in 207 of 961 subjects, 79 % of whom had H/M ratio <1.6. Among subjects hospitalized for any cause, 88 % had H/M ratio <1.6 and subjects with H/M ratio <1.6 experienced hospitalization earlier than subjects with higher H/M ratios (log-rank p?=?0.003). After adjusting for elevated brain natriuretic peptide (BNP) and time since heart failure diagnosis, a low mIBG H/M ratio was associated with cardiac-related hospitalization (HR 1.48, 95 % CI 1.05 – 2.0; p?=?0.02).

Conclusion

The mIBG H/M ratio may risk-stratify patients with heart failure for cardiac-related hospitalization, especially when used in conjunction with BNP. Further studies are warranted to examine these relationships.     

I-123 labeled hexadecenoic acid in comparison with Thallium-201 for myocardial imaging in coronary heart disease

The imaging properties of ¹²³I-16-iodo-9-hexadecenoic acid (¹²³I-HA), a terminally iodinated 17-carbon atom fatty acid analogue, were compared with Thallium-201 (²⁰¹Tl). Because of its shorter half-life, favourable photon-energy and rapid myocardial turnover rate, ¹²³I-HA possesses potential advantages in the study of regional myocardial perfusion and metabolism. Twelve patients with documented coronary artery disease (CAD) were studied; eight patients sustained an acute myocardial infarction, four patients suffered from unstable angina. Visually assessed, a similar distribution pattern and comparable imaging quality was demonstrated with both radionuclides. The scintigraphic results were also correlated with coronary arteriographic findings. A good relationship was found between the perfusion defects and the location of the coronary artery lesions in the patients with acute myocardial infarction.We conclude that ¹²³I-HA is comparable to ²⁰¹Tl in detecting areas of reduced myocardial perfusion in patients with CAD with the advantage of studying myocardial metabolism.     

The determination of myocardial viability using Gd-DTPA in a canine model of acute myocardial ischemia and reperfusion

The partition coefficient of Gd-DTPA was thought to vary with the amount of cellular membrane damage after an acute myocardial infarction. The relationship between the partition coefficient of Gd-DTPA (λ) and the uptake of ²⁰¹TI (as a marker of tissue viability) was studied 2 h to 3 weeks after reperfusion of a 2-h occlusion to the left anterior descending coronary artery in a canine model. Gd-DTPA was infused as a bolus followed by a prolonged constant infusion, and this infusion protocol was optimized such that the concentration of Gd-DTPA was directly related to λ. After this infusion, MR images of excised hearts showed regions of increased signal intensity corresponding to increased Gd-DTPA concentration. At all time points, λ and ²⁰¹TI uptake were strongly negatively correlated indicating that λ is an accurate indicator of myocardial viability. Furthermore, λ in the infarcted regions was increased relative to normal regions after 2 h of reperfusion and stayed elevated up to 3 weeks. At all time points, λ in the infarcted and normal regions were significantly different. As well, this data showed a trend that λ in infarcted regions decreased monotonically from 1 day to 3 weeks. This trend was confirmed with MR imaging by examining the change in signal intensity of in vivo images from 4 days to 3 weeks in two animals. These results suggest that MRI with Gd-DTPA could be used to measure the extent of myocardial damage after an acute myocardial infarction.     

Metabolic myocardial imaging with 123I-labeled heptadecanoic acid in patients with angina pectoris

The potential value of ¹²³I-heptadecanoic acid (¹²³I-H^oA) in myocardial scintigraphy has recently been assessed in patients with acute myocardial infarction (AMI) by studying regional myocardial metabolism (Van der Wall et al. 1981 a). To determine the metabolic behavior of ¹²³I-H^oA in patients with stable angina pectoris (AP) as well, 30 patients with AP were included in this study: 18 patients were exercised and 12 patients were studied at rest.Regional myocardial metabolism was evaluated by generating background subtracted time-activity curves, acquired by external detection over normally perfused and ischemic regions during a 30-min period after intravenous injection of ¹²³I-H^oA. Following monoexponential curve-fitting, clearance rates were measured representing turnover rate (T_1/2) of ¹²³I-H^oA.The exercise group showed prolonged T1/2 values of 46.7±7.1 min (mean±SD) in ischemic regions and 28.7±3.6 min in normally perfused regions. The group at rest did not reveal any scintigraphic abnormalities and showed normal T1/2 values in all myocardial regions (29.1±4.7 min).Our observations of prolonged turnover rates in ischemic areas differ from the results of our recent study in patients with AMI, which demonstrated fast turnover rates in infarcted tissue. These data imply that ¹²³I-H^oA permits the study of myocardial metabolism in patients with AP and the discrimination of normally perfused, reversibly ischemic (AP) and irreversibly ischemic (AMI) myocardium.     

Low-dose dobutamine gated single-photon emission tomography: comparison with stress echocardiography

Perfusion scintigraphy provides important information regarding the presence of viable tissue after myocardial infarction. Defects of moderate severity, however, may represent viable myocardium, necrotic tissue or a mixture of both. In this study the presence or absence of inotropic response in the infarcted area was assessed by low-dose dobutamine tetrofosmin gated single-photon emission tomography (LDD gated SPET). Results were compared with those obtained with stress echocardiography (SE). Twenty-five patients with acute myocardial infarction were studied. Gated SPET myocardial perfusion imaging was performed 60 min after the injection of technetium-99m tetrofosmin (925 MBq) at rest using a triple-headed camera equipped with focussing collimators (Cardiofocal). Two consecutive acquisitions were performed according to a ”fast” gated SPET protocol (3×20 stops, 9 s/stop, 64×64 pixel matrix, zoom 1.23) with the subjects remaining in the same position. The first acquisition was obtained at rest; the second acquisition was obtained under infusion of 10 μg kg^–1 min^–1 dobutamine. The severity of regional dysfunction, wall thickening severity (WT_sev), was assessed and quantified using a method based on circumferential profile analysis. SE was performed at rest and during infusion of 5 and 10 μg kg^–1 min^–1 dobutamine. Two patients could not be analysed because of disturbing gastro-intestinal activity on the perfusion study. Under dobutamine 11 patients presented a significant change in WT_sev (three showed normalisation, five an improvement and three a deterioration), while in 12 patients the WT_sev score remained unchanged. The overall concordance between LDD gated SPET and SE was 83%. In patients with perfusion defects of moderate severity the concordance was 90% (9/10). It may be concluded that functional changes in infarcted areas induced by dobutamine can be detected with gated SPET. Good agreement was observed between LDD gated SPET and SE for the identification of inotropic reserve in infarcted areas. Received 5 September and in revised form 22 November 1999     

Prognostic value of iodine-123 labelled BMIPP fatty acid analogue imaging in patients with myocardial infarction

This study was undertaken to evaluate the prognostic value of iodine-123 labelled 15-iodophenyl3-R,S-methyl pentadecanoic acid (BMIPP) imaging in patients with myocardial infarction. BMIPP is an iodinated methyl branched fatty acid analogue which is trapped in the myocardium with little washout, thereby reflecting fatty acid utilization in the myocardium. We previously reported that in patients with myocardial infarction, regions are often observed where reduced BMIPP uptake is seen relative to thallium-201 perfusion at rest. However, the clinical significance of such discordant BMIPP uptake remains unknown. Fifty consecutive patients with chronic myocardial infarction referred for stress thallium scan and coronary arteriography underwent BMIPP imaging at rest. Each patient was in a stable condition at the time of the radionuclide study. Follow-up was performed at a mean interval of 23 months to investigate the prognostic implications of the radionuclide studies. Nine patients had cardiac events during the follow-up period. Univariate analysis showed that the number of discordant BMIPP versus²⁰¹TL uptake segments was the best predictor of future cardiac events (P=0.0245), followed by the presence of discordant BMIPP uptake (P=0.0388) and the number of²⁰¹TL redistribution segments (P=0.0444). When all the clinical and radionuclide variables were analysed by Cox regression analysis, the presence of discordant BMIPP uptake was the best, and an independent, predictor of future cardiac events (²=8.5) followed by the number of coronary stenoses on angiography (²=3.9). These preliminary data suggest that decreased BMIPP uptake relative to²⁰¹TL is a valuable predictor of future cardiac events in patients with myocardial infarction. Areas with such discordant BMIPP uptake may contain jeopardized myocardium where fatty acid utilization has been severely suppressed relative to myocardial perfusion.Presented in part at the 40th Annual Meeting of Society of Nuclear Medicine at Orlando, Florida, June 1994     

Usefulness of resting thallium-201 delayed imaging for detecting myocardial viability in patients with previous myocardial infarction

To test the feasibility of resting thallium-201 (²⁰¹Tl) initial and delayed scintigraphy for detecting the area of viable myocardium, we performed single photon emission computed tomography (SPECT) in 57 patients with previous myocardial infarction (MI). All had received coronary arteriography (CAG) and left ventriculography (LVG). Initial and delayed myocardial imagings were carried out 10 min and 2 hours, respectively, after the injection of²⁰¹Tl at rest. Redistribution was judged by visual interpretation and/or the circumferential profile curve, and found in the infarcted or its adjacent area in 40 of the 57 cases (70.2%). A negative washout (net increase of²⁰¹Tl uptake in delayed image) was detected in 17 of these 40 cases. In 10 of the 57 patients, both exercise and rest-injected²⁰¹Tl myocardial images were obtained at exercise and rest, and compared visually. The areas of abnormal perfusion were smaller in the resting delayed images than those seen after exercise in 9 of the 10 cases, and were equal in one case. Thus, resting²⁰¹Tl delayed myocardial scintigraphy appears to reduce the underestimation of the size of the viable myocardium by the usual²⁰¹Tl images obtained after exercise or by single initial images obtained at rest in patients with previous MI.