Are technetium-99m-labeled myocardial perfusion agents adequate for detection of myocardial viability?

Myocardial viability: what we knew and what is new. Cardiol Res Pract. 2012;2012:607486. [PMID: 22988540 PMCID: PMC3440854 DOI: 10.1155/2012/607486]

Some patients with chronic ischemic left ventricular dysfunction have shown significant improvements of contractility with favorable long-term prognosis after revascularization. Several imaging techniques are available for the assessment of viable myocardium, based on the detection of preserved perfusion, preserved glucose metabolism, intact cell membrane and mitochondria, and presence of contractile reserve. Nuclear cardiology techniques, dobutamine echocardiography and positron emission tomography are used to assess myocardial viability. In recent years, new advances have improved methods of detecting myocardial viability. This paper summarizes the pathophysiology, methods, and impact of detection of myocardial viability, concentrating on recent advances in such methods. We reviewed the literature using search engines MIDLINE, SCOUPS, and EMBASE from 1988 to February 2012. We used key words: myocardial viability, hibernation, stunning, and ischemic cardiomyopathy. Recent studies showed that the presence of viable myocardium was associated with a greater likelihood of survival in patients with coronary artery disease and LV dysfunction, but the assessment of myocardial viability did not identify patients with survival benefit from revascularization, as compared with medical therapy alone. This topic is still debatable and needs more evidence.

Preliminary clinical investigation of 99mTc-methoxyisobutylisonitrile washout rate in hypertrophic cardiomyopathy

OBJECTIVE

The aim of this study was to investigate the changes in early and late washout rates of 99mTc-methoxyisobutylisonitrile (MIBI) in hypertrophic cardiomyopathy (HCM), and to analyze the relationships between early and late washout rates and the hypertrophic thickness of left ventricular (LV) wall.

METHODS

The patients who were clinically diagnosed as positive for HCM underwent 99mTc-MIBI static planar and gated single-photon emission computed tomography (SPECT) imaging. Early (90 min after the intravenous injection) and late (4 h after the intravenous injection) washout rates of 99mTc-MIBI between HCM group and normal control group were compared. Linear correlation analysis was made between early and late washout rates and the hypertrophic thickness of LV wall measured by gated SPECT.

RESULTS

The early and late washout rates of 99mTc-MIBI in normal control group were (18.90+/-3.70) and (31.27+/-4.04)%, respectively; and the washout rates in HCM group were (27.77+/-2.60) and (42.66+/-3.30)%, respectively. Significant statistical differences were observed in the early and late washout rates of 99mTc-MIBI between HCM group and normal control group (t=-7.320 and t=-8.069, both P<0.01). Correlations between early and late washout rates and the maximal hypertrophic thickness of LV wall obtained by gated SPECT were excellent (r=0.611, P<0.05; r=0.873, P<0.01, respectively).

CONCLUSION

The early and late washout rates of 99mTc-MIBI in HCM group were significantly higher than those in normal control group, and both the early and late washout rates correlated well with the hypertrophic thickness of LV wall.

Myocardial uptake characteristics of three 99mTc-labeled tracers for myocardial perfusion imaging one hour after rest injection

OBJECTIVE

99mTc-tetrofosmin and 99mTc-sestamibi are approved tracers for myocardial perfusion studies. Recently, a 99mTc-MIBI preparation from a different manufacturer (99mTc-cardiospect-MIBI) has been introduced to the market. Therefore, the aim of this study was the evaluation of 99mTc-tetrofosmin as well as of two different 99mTc-labeled MIBI tracers with regard to differences in imaging quality under resting conditions.

METHODS

Sixty patients (mean age 63.8 years +/- 1.25) with known or suspected coronary artery disease but without evidence of rest-ischemia were included. Twenty patients in each group were examined by a two-day-rest-stress protocol using the three 99mTc-labeled tracers. Visual analysis of all images was performed by two experienced physicians blinded with regard to the applied tracer. Regions of interest (ROI) were defined over the heart, lung and whole body only in the rest imaging in order to calculate heart-to-lung, lung-to-whole body-, and heart-to-whole body-ratios.

RESULTS

The heart-to-lung ratio was statistically significant higher for 99mTc-cardiospect-MIBI as compared to 99mTc-sestamibi as well as to 99mTc-tetrofosmin. Furthermore, a significantly higher heart-to-lung ratio was found for 99mTc-sestamibi as compared to 99mTc-tetrofosmin. The heart-to-whole body-ratio and the lung-to-whole body-ratio were equivalent between all tracers. Visual analysis revealed only slight differences regarding image quality between all tracers.

CONCLUSIONS

ROI analysis surprisingly revealed a significant higher myocardial uptake and consequently a higher heart-to-lung ratio for 99mTc-cardiospect-MIBI. Whether this leads to a better visual image quality has to be evaluated in future studies with larger study populations as well as semiquantitative segmental analysis of the myocardial perfusion images.

Are there differences in breast tissue as a result of hormone replacement therapy? Can BEST imaging distinguish these differences?

Although it has been speculated that estrogen therapy may promote changes in breast tissue that could lead to cancer, no information exists as to differences in breast tissue for women who do and do not take hormone replacement (HRT) therapy. This study seeks to determine if there are differences in the tissue of women taking HRT in contrast to those who do not and if these differences are apparent in cases of breast cancer, cellular atypia, fibrocystic (FCD) disease and normal breasts. A total of 327 non-pregnant, non-lactating, pre-menopausal women were enrolled in the study, including 139 women who were actively taking HRT and 188 women who never had taken HRT. Using breast enhanced scintigraphy test (BEST) imaging, differentiation of breast tissue was determined. The groups were then analyzed to determine the effect of hormone therapy within each category of breast tissue. Differentiation between normal, FCD, cellular atypia, and breast cancer represent statistically significant differences (p.001) in metabolic activity and vascularity as demonstrated by differences in both average count activity (ACA) and maximal count activity (MCA). The distinction between cellular atypia and infiltrating breast cancer was statistically (p.05) different when looking at the maximal activity. Normal breast tissue and breasts with FCD appear more homogenous with no statistical differences in variability in breast tissue. Tissue variability is statistically greater when localized processes, such as cellular atypia and breast cancer, are present. Differentiation of cellular metabolic activity in breast tissue can be statistically determined when looking at the average and maximal metabolic activity. The final distinction between cellular atypia and cancer occurs when a focal region of breast tissue becomes metabolically more active than the surrounding breast tissue as shown by statistical increases in MCA. These findings are confirmed by the increased metabolic variability seen in regions of cellular atypia and cancer compared with the homogenous metabolic activity present in normal and fibrocystic breasts.

99mTc-Sestamibi SPECT is a useful technique for viability detection: results of a comparison with NH3/FDG PET

OBJECTIVE

Assessment of myocardial viability by 99mTc-Sestamibi Single Photon Emission Computerized Tomography (SPECT) has been suggested as a more readily available and cheaper alternative to Positron Emission Tomography (PET) with 13N-ammonia (NH3) and 18F-fluoro-deoxy-glucose (FDG). We hypothesized that a semi-quantitative evaluation by SPECT could delineate myocardial viability with an acceptable concordance to PET.

DESIGN

Fifty patients (age 57+/-7 years; ejection fraction 28 +/- 8%), with ischemic cardiomyopathy, underwent SPECT and PET imaging in random order. Viability by SPECT was defined as a defect size <50% of the segment area, or a defect representing > or =50% of the segment but with a mean activity > or =50% of peak activity. PET viability was defined as a perfusion score >2 and FDG score < or =2 (five-point scale, 0 = normal, 4 = absent activity).

RESULTS

By segmental comparison to PET. SPECT yielded a sensitivity and specificity of 87% and 82% for detection of viable myocardium. The positive and negative predictive values were 96% and 58%, respectively.

CONCLUSION

In patients with severe ischemic cardiomyopathy 99mTc-Sestamibi SPECT can delineate viable myocardium with an acceptable segmental concordance to NH3/FDG PET.

Clinical benefit of noninvasive viability studies of patients with severe ischemic left ventricular dysfunction

The population of patients who have congestive heart failure of ischemic origin is large and growing. It imposes a heavy burden on human suffering and economic costs such as the chronic use of costly medications, recurrent hospital admissions, and, eventually, death or the necessity of heart transplantation. Therefore, the development of methods for detecting viable myocardium may allow the accurate selection of those patients with coronary artery disease with severe left ventricular dysfunction who are most likely to benefit from revascularization, but also excludes patients who are unlikely to obtain any improvement with revascularization techniques. The presence of reversible dysfunctional myocardium that may improve after revascularization implies the concepts of stunned and hibernating myocardium. Recent evidence suggests that hibernation may not be a stable condition since it might evolve toward an irreversible dysfunction if it is not revascularized at the right moment. The techniques available for viability studies are single-photon emission computed tomography using thallium-201 or compounds labeled with technetium-99m, positron emission tomography, and dobutamine stress echocardiography. Newer and promising techniques are magnetic resonance imaging and contrast echocardiography, whose definitive roles are not clear yet. There is abundant evidence from several important studies showing that patients with a significant amount of viable myocardium have a poor outcome if they are treated medically. Conversely, if these patients are revascularized, their outcomes improve and their symptoms significantly decrease, with less necessity of medication, fewer admissions to the hospital, and even in some cases avoiding heart transplantation. On the other hand, patients with poor or no viability who are revascularized do not obtain significant benefit.

Impaired retention of technetium-99m tetrofosmin in hypertrophic cardiomyopathy

The purpose of this study was to determine whether myocardial imaging using technetium-99m tetrofosmin can noninvasively identify myocardial damage in hypertrophic cardiomyopathy (HC). The study consisted of 10 patients with apical HC, 10 with asymmetric septal HC (ASH) group, 5 with dilated cardiomyopathy (DC)-like group, and 20 healthy subjects. With use of a bull's-eye map of single-photon emission computed tomographic imaging, the total defect score of tetrofosmin and the washout rate were assessed in 5 segments (septum, and anterior, lateral, and inferior walls, and apex) of the left ventricle. A localized increase in defect score and washout rate was observed in the hypertrophied region in the group with apical HC. An increased washout rate was observed in the ASH group regardless of hypertrophy, suggesting that tetrofosmin retention by the mitochondria was impaired in the entire left ventricular wall. The washout rate was further increased at all segments in the DC-like group versus the ASH group. Tetrofosmin retention by mitochondria was impaired in the entire left ventricular wall in the ASH group and was increased further in the DC-like group. The dysfunction of myocardial cells was limited to the hypertrophied region in the apical HC group.

QTc interval and scintigraphically assessed myocardial perfusion in newly diagnosed and long-term type 1 diabetes mellitus

In diabetes mellitus, heart rate corrected QT interval (QTc) has been suggested to be related to ischemic heart disease and increased risk of sudden cardiac death. The aim of the study was to analyze the length of QTc interval with regard to global and regional myocardial perfusion in type 1 diabetic patients. Myocardial perfusion was investigated in 20 newly diagnosed and 40 long-term type 1 diabetic patients without clinical evidence for coronary artery disease by means of Tc-99-methoxyisobutylisonitrile (Tc-99m-MIBI)-scintigraphy (myocardial uptake (MU) score: 1-6). Five consecutive RR and QT intervals of resting electrocardiogram (ECG) tracing were measured and corrected for the previous cycle length. ECG-based cardiac autonomic neuropathy (CAN) was assessed with five cardiac reflex tests. Length of QTc interval was 423+/-29 ms in newly diagnosed and 433+/-26 ms in long-term type 1 diabetic patients. Nine (45%) newly diagnosed and 18 (45%) long-term diabetic patients demonstrated a prolonged QTc interval (>440 ms). Both newly diagnosed and long-term diabetic patients did not display significant global or regional myocardial perfusion defects (mean MU scores<3). In newly diagnosed diabetic patients, the length of QTc interval was related to global, posterior and septal Tc-99m-MIBI uptake (p<0.05, respectively). In long-term diabetic patients, the length of QTc interval was associated with apical Tc-99m-MIBI uptake (p<0.05). Two (10%) newly diagnosed and 19 (48%) long-term type 1 diabetic patients demonstrated ECG-based CAN. In long-term type 1 diabetic patients, global myocardial Tc-99m-MIBI uptake did not differ significantly between patients with and without CAN. QTc interval was not significantly different between diabetic patients with and without ECG-based CAN (433+/-19 ms vs. 428+/-17 ms). Long-term diabetic patients, of whom 10 (25%) patients had microalbuminuria and seven (18%) patients had macroalbuminuria, demonstrated an association between QTc interval and albuminuria (p<0.05). The results somewhat suggest an association between QTc interval and vascular factors in type 1 diabetes mellitus. Future investigations are required to analyze the role of QTc interval in the pathogenesis of abnormalities of myocardial perfusion.