Exercise-induced myocardial ischemia: can this be imaged with F-18-fluorodeoxyglucose?

Comparison of Tc-99m tetrofosmin myocardial perfusion scintigraphy and exercise F18-FDG imaging in detection of myocardial ischemia in patients with coronary artery disease

BACKGROUND

Direct ischemia imaging with F18-FDG can potentially overcome many limitations of SPECT-MPS inherent to "cold imaging". We compared SPECT-MPS with exercise F18-FDG PET in detection of ischemia in patients with suspected CAD.

METHODS

45 patients with clinical suspicion of CAD without the history of myocardial infarction were prospectively included. All patients underwent Tc-99m tetrofosmin SPECT-MPS and exercise F18-FDG PET imaging within 7 days of SPECT-MPS, and both modalities were compared with coronary angiography for detecting ischemia.

RESULTS

27 patients had an abnormal coronary angiography (at least one coronary artery with stenosis >50%). Exercise F18-FDG performed better than SPECT-MPS in LAD and LCX territory with comparably good performance in RCA territory. Exercise F18-FDG performed better in single-vessel disease and equally good in multi-vessel disease compared to SPECT-MPS. Performance of exercise 18F-FDG study was significantly better than SPECT-MPS (P = .0014) in the analysis of the 81 vascular territories in the 27 patients with abnormal coronary angiography. Performance of exercise F18-FDG was significantly better than SPECT-MPS in detecting ischemia in suspected CAD patients.

CONCLUSION

Exercise F18-FDG imaging is a potentially useful ischemia imaging modality which offers the advantages of direct ischemia imaging in CAD patients.

Direct myocardial ischemia imaging: a new cardiovascular nuclear imaging paradigm

Myocardial perfusion imaging (MPI), using radiotracers, has been in routine clinical use for over 40 years. This modality is used for the detection of coronary artery disease (CAD), risk stratification, optimizing therapy, and follow-up of patients with CAD. Molecular cardiovascular imaging using targeted radiotracers provides a unique opportunity for imaging biochemical and metabolic processes, and cell membrane transporter and receptor functions at a cellular and molecular level in experimental animal models as well as in humans. Cardiac imaging using radiolabeled free fatty acid analogues and glucose analogues enable us to image myocardial ischemia directly as an alternative to stress-rest MPI. Direct ischemia imaging techniques can avoid and overcome some of the limitations of standard stress-rest MPI. This article describes recent studies using (18) F-fluorodeoxyglucose ((18) FDG) for myocardial ischemia imaging.

Effect of duration of fasting and diet on the myocardial uptake of F-18-2-fluoro-2-deoxyglucose (F-18 FDG) at rest

CONTEXT

Patterns of myocardial fluoro-2-deoxyglucose (FDG) uptake with respect to duration of fasting and dietary modifications.

AIM

We observed the effect of duration of fasting and diet on the myocardial uptake pattern of F-18 FDG in patients routinely referred for oncological evaluation and no previous history of Coronary Artery Disease (CAD).

SETTINGS AND DESIGN

Prospective study.

SUBJECTS AND METHODS

A total of 153 patients (M: 81, F: 72; mean age: 47 ± 15 years; mean blood glucose level (mBG) 105 ± 23 mg/dl) were randomly divided in three groups. Group A: 4-6 h fasting; Group B: Overnight fasting (12-14 h); Group C: Low carbohydrate and fat rich diet for 2 days coupled with overnight fasting prior to the positron emission tomography (PET) scan. FDG uptake was classified as following: 1) homogeneous uptake, 2) heterogeneous uptake, and 3) 'no uptake' in the left ventricular (LV) myocardium. FDG PET study was performed as standard protocol for oncological conditions.

STATISTICAL ANALYSIS USED

Descriptive statistics, Chi-square test or Fisher's exact test, and Spearman's rank correlation tests were applied.

RESULTS

We observed the 'no uptake' pattern in five (10%), 28 (55%), and 39 (77%), 'heterogeneous' pattern in 20 (39%), 14 (28%), and seven (14%), and 'homogeneous' pattern in 26 (51%), nine (18%), and five (10%) patients in Group A, B, and C, respectively. There was statistically significant difference of myocardial uptake pattern between group A and B (P < 0.0001), between group A and C (P < 0.0001), and between Group B and C (P = 0.023). The mBG was 102, 105, and 111 mg/dl in 'no uptake', heterogeneous, and homogeneous uptake pattern, respectively, (P = 0.103). Also, within each group the mBG was not related to the uptake pattern.

CONCLUSION

Both restricted diet and duration of fasting play an important role in determining the pattern and suppression of myocardial F-18 FDG uptake. Overnight fasting and restricted diet together suppress myocardial FDG uptake more than overnight fasting alone, which suppresses uptake more than 4-h fasting.

Myocardial 18F-FDG uptake after exercise-induced myocardial ischemia in patients with coronary artery disease

We have recently demonstrated the potential of (18)F-FDG as an imaging marker of myocardial ischemia if injected at peak exercise. However, how long increased (18)F-FDG uptake can be observed after an episode of exercise-induced myocardial ischemia is not known. We performed the current study to determine whether increased regional myocardial (18)F-FDG uptake at exercise in patients with coronary artery disease (CAD) persists on rest imaging (24 h later), after an episode of exercise-induced myocardial ischemia.

METHODS

Twenty-four patients with suspected CAD underwent exercise (99m)Tc-sestamibi and (18)F-FDG imaging. Repeated (18)F-FDG imaging was performed 24 h after exercise imaging, after an injection of a second dose of (18)F-FDG at rest in 20 patients. Perfusion imaging with (99m)Tc-sestamibi was simultaneously performed with (18)F-FDG imaging. All patients underwent coronary angiography.

RESULTS

Eighteen patients had greater than or equal to 70% luminal narrowing of 1 or more coronary vessels. Fifteen patients (83%) showed increased regional (18)F-FDG uptake on exercise imaging, but only 11 patients (61%) had perfusion abnormalities. Of these 15 patients with increased regional (18)F-FDG uptake on exercise imaging, 8 (53%) had no discernible (18)F-FDG uptake, 5 (33%) had decreased (18)F-FDG uptake, and only 2 (13%) had persistent (18)F-FDG uptake on rest (18)F-FDG images. The summed (18)F-FDG uptake score significantly decreased, from 14.4 +/- 10.3 at exercise to 6.7 +/- 9.2 at rest (P = 0.01). Patients with persistent (18)F-FDG uptake at rest had more (18)F-FDG uptake and lower peak rate-pressure product at exercise, compared with patients with no residual (18)F-FDG uptake at rest.

CONCLUSION

Exercise-induced regional myocardial (18)F-FDG uptake is highly specific and sensitive for exercise-induced myocardial ischemia. Regional myocardial (18)F-FDG uptake may persist 24 h after an episode of exercise-induced myocardial ischemia in some patients.

Myocardial glucose metabolism assessed by positron emission tomography and the histopathologic findings of microvessels in syndrome X

BACKGROUND

Syndrome X has been recognized as a disease that is primarily reflected in the cardiac microvasculature. Myocardial metabolism in this condition has been studied, but not in relation to small vessel pathology.

METHODS AND RESULTS

In order to examine the relationship between myocardial metabolism and small vessel pathology, 24 consecutive patients with syndrome X (7 men, 17 women; mean age 58 years) were evaluated by the thallium exercise stress test, positron emission tomography using F-18 fluoro-deoxyglucose (FDG), and an endomyocardial biopsy. All patients showed either diffuse or focal increase in the myocardial uptake of FDG, but only 17 patients (71%) showed hypoperfused areas with partial or complete redistribution in the thallium study. Quantification of myocardial FDG uptake revealed that the value in syndrome X patients was 10-fold higher than in controls (p<0.0001). Histopathological examination revealed that in syndrome X there is an extensive increase in smooth muscle cells and thickening of the vascular wall, even in capillary vessels, and the small vessel lumen was markedly narrowed. There was a significant inverse correlation between FDG myocardial uptake and the microvessel luminal area.

CONCLUSIONS

In syndrome X patients, myocardial FDG uptake is increased extensively, which is strongly associated with narrowed myocardial microvasculature.

Direct imaging of exercise-induced myocardial ischemia with fluorine-18-labeled deoxyglucose and Tc-99m-sestamibi in coronary artery disease

BACKGROUND

Scintigraphic myocardial perfusion imaging is the most widely used noninvasive modality for the detection of coronary artery disease (CAD). A technique for direct imaging of exercise-induced myocardial ischemia is highly desirable and preferable over perfusion imaging but is presently unavailable. We evaluated the feasibility and diagnostic accuracy of direct imaging of exercise-induced myocardial ischemia with fluorine-18-2-deoxyglucose (18FDG).

METHODS AND RESULTS

Twenty-six patients with known or suspected CAD and no prior myocardial infarction underwent simultaneous myocardial perfusion and ischemia imaging after the intravenous injection of Tc-99m-sestamibi (99mTc-sestamibi) and 18FDG at peak exercise. Rest perfusion imaging was carried out separately. All patients underwent coronary angiography. Exercise 18FDG myocardial images were compared with exercise-rest 99mTc-sestamibi images and coronary angiography. Of 22 patients with > or =50% narrowing of > or =1 coronary arteries, 18 had perfusion abnormalities (sensitivity 82%) whereas 20 had abnormal myocardial 18FDG uptake (sensitivity 91%, P=NS). Perfusion abnormalities were seen in myocardial segments corresponding to 25 vascular territories of a total of 51 vessels with > or =50% luminal narrowing in 22 patients (sensitivity 49%), whereas increased 18FDG uptake was seen in 34 vascular territories (sensitivity 67%, P=0.008). 18FDG images were of high quality and easy to interpret but required simultaneous perfusion images for localizing abnormal myocardial 18FDG uptake.

CONCLUSIONS

Exercise-induced myocardial ischemia can be imaged directly with 18FDG. Combined exercise 18FDG-99mTc-sestamibi imaging provides a better assessment of exercise-induced myocardial ischemia compared with exercise-rest perfusion imaging. Direct ischemia imaging eliminates some of the limitations of presently used myocardial perfusion imaging. Large-scale clinical studies are warranted.