Radionuclide detection of myocardial ischemia and myocardial viability: is the glass half empty of half full?

Scintigraphic prediction of left ventricular functional recovery early after primary coronary angioplasty using single-injection quantitative electrocardiographic gated SPECT

OBJECTIVE

The clinical usefulness of characterizing reperfused myocardium by perfusion/thickening assessment using electrocardiographic gated single photon emission computed tomography (SPECT) has not been investigated. We evaluated whether single-injection gated SPECT with 99mTc tetrofosmin early after primary percutaneous coronary intervention (PCI) can predict left ventricular (LV) functional recovery.

METHODS

Gated SPECT was performed 3 days after primary PCI in 45 patients with acute myocardial infarction and revascularized segments were classified into perfusion/thickening mismatched segments, matched normal and matched abnormal segments. Gated SPECT was repeated 3 months later to evaluate the changes in LV ejection fraction (deltaLVEF).

RESULTS

Among 332 revascularized segments, there were 83 mismatched segments, 163 matched abnormal segments and 86 matched normal segments. In all the patients, LVEF increased significantly from 3 days to 3 months after primary PCI (52+/-13 to 57+/-14%, P<0.0001). Patients were divided into two groups according to deltaLVEF: 24 patients with LV functional recovery (deltaLVEF > or = 5%) and 21 patients without LV functional recovery. The number of mismatched segments in patients with LV functional recovery was significantly greater than that in patients without (2.7+/-1.7 vs. 0.8+/-1.4, P<0.0003) despite no differences in the number of matched abnormal and matched normal segments. There was a significant correlation between deltaLVEF and the number of mismatched segments (r=0.56, P<0.0001) and LVEF at 3 months after primary PCI was related to the number of matched abnormal segments (r=-0.78, P<0.0001).

CONCLUSION

Single-injection gated SPECT early after primary PCI can predict LV functional recovery.

Attenuation-corrected 99mTc-tetrofosmin single-photon emission computed tomography in the detection of viable myocardium: comparison with positron emission tomography using 18F-fluorodeoxyglucose

OBJECTIVES

The purpose of this study was to assess the efficacy of attenuation-corrected (AC) technetium-99m (99mTc)-tetrofosmin single-photon emission computed tomography (SPECT) in detecting viable myocardium compared to 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET).

BACKGROUND

The role of 99mTc-labeled perfusion tracers in the assessment of myocardial viability remains controversial. Attenuation artifacts affect the diagnostic accuracy of SPECT images.

METHODS

Twenty-four patients with coronary artery disease (mean left ventricular ejection fraction 30%) underwent resting 99mTc-tetrofosmin SPECT and FDG PET imaging. Both AC and non-attenuation-corrected (NC) SPECT images were generated.

RESULTS

Using a 50% threshold for viability by FDG PET, the percentage of concordant segments of viability between 99mTc-tetrofosmin and FDG on the patient basis increased from 79.8%+/-14.0% (mean+/-SD) on the NC images to 90.8%+/-10.6% on the AC images (p=0.002). The percentage of 99mTc-tetrofosmin defect segments within PET-viable segments, an estimate for the degree of underestimation of viability, decreased from 19.8%+/-15.2% on the NC images to 9.7%+/-12.6% on the AC images (p=0.01). Similar results were obtained when a 60% threshold was used to define viability by FDG PET. When the anterior-lateral and inferior-septal regions were separately analyzed, the effect of attenuation correction was significant only in the inferior-septal region.

CONCLUSIONS

The results indicate that AC 99mTc-tetrofosmin SPECT improves the detection of viable myocardium mainly by decreasing the underestimation of viability particularly in the inferior-septal region, although some underestimation/overestimation of viability may still occur even with attenuation correction.

Assessment of myocardial viability in chronic coronary artery disease using technetium-99m sestamibi SPECT. Correlation with histologic and positron emission tomographic studies and functional follow-up

OBJECTIVES

The value of 99mTc-sestamibi (2-methoxy-isobutyl isonitrile [MIBI]) as a viability tracer was investigated in patients undergoing coronary artery bypass graft surgery.

BACKGROUND

Initial studies claim that rest MIBI single-photon emission computed tomographic (SPECT) studies can be used to assess myocardial viability.

METHODS

Thirty patients with a severely stenosed left anterior descending coronary artery and wall motion abnormalities were prospectively included. The patients underwent a MIBI rest study, a positron emission tomographic (PET) flow (13NH3) and metabolism (18F-deoxyglucose) study and nuclear angiography before undergoing bypass surgery. A preoperative transmural biopsy specimen was taken from the left ventricular anterior wall. Morphometry was performed to assess percent fibrosis. After 3 months, radionuclide angiography was repeated.

RESULTS

Statistically significant higher MIBI values were found in the group with myocardial viability as assessed by PET than in the group with PET-assessed nonviability (p < 0.01). Significantly higher MIBI values were found in the group with enhanced contractility at 3 months (76 +/- 13% vs. 53 +/- 22%, p < 0.01). A linear relation was found between MIBI uptake and percent fibrosis in the biopsy specimen (r = 0.78, p < 0.00001). When maximizing the threshold for assessment of viability with MIBI by using functional improvement as the reference standard, a cutoff value of 50% was found, with positive and negative predictive values of 82% and 78%, respectively.

CONCLUSIONS

99mTc MIBI uptake was significantly higher in PET-assessed viable areas and in regions with enhanced contractility at 3 months. A linear relation was found between percent fibrosis and MIBI uptake. An optimal threshold of 50% was found for prediction of functional recovery.