Rest technetium 99m-sestamibi tomoscintigraphy in hibernating myocardium

Noninvasive assessment myocardial viability: current status and future directions

Observations of reversibility of cardiac contractile dysfunction in patients with coronary artery disease and ischemia were first made more than 40 years ago. Since that time a wealth of basic science and clinical data has been gathered exploring the mechanisms of this phenomenon of myocardial viability and relevance to clinical care of patients. Advances in cardiac imaging techniques have contributed greatly to knowledge in the area, first with thallium-201 imaging, then later with Tc-99m-based tracers for SPECT imaging and metabolic tracers used in conjunction with positron emission tomography (PET), most commonly F-18 FDG in conjunction with blood flow imaging with N-13 ammonia or Rb-82 Cl. In parallel, stress echocardiography has made great progress also. Over time observational studies in patients using these techniques accumulated and were later summarized in several meta-analyses. More recently, cardiac magnetic resonance imaging (CMR) has contributed further information in combination with either late gadolinium enhancement imaging or dobutamine stress. This review discusses the tracer and CMR imaging techniques, the pooled observational data, the results of clinical trials, and ongoing investigation in the field. It also examines some of the current challenges and issues for researchers and explores the emerging potential of combined PET/CMR imaging for myocardial viability.

Prognostic role of single-photon emission computed tomography (SPECT) imaging in myocardial viability

PURPOSE OF REVIEW

Cardiac imaging is evolving rapidly. Appropriate use of this technology could reduce morbidity and mortality, but inappropriate use could have a significant financial burden. Single-photon emission computed tomography imaging is widely available. This review summarizes the clinical utility and limitations of the prognostic role of single-photon emission computed tomography imaging for myocardial viability in patients with coronary artery disease and left-ventricular dysfunction.

RECENT FINDINGS

201Tl single-photon emission computed tomography, 99mTc single-photon emission computed tomography with sestamibi or tetrofosmin, and 18F-fluorodeoxyglucose single-photon emission computed tomography are validated tools for assessing myocardial viability. These techniques have a very similar predictive value in determining regional and global response to revascularization. 201Tl single-photon emission computed tomography viability studies are predictive of reverse left-ventricular remodeling, symptom improvement, and patient outcome after revascularization. Combination imaging with dual-isotope simultaneous acquisition single-photon emission computed tomography or positron-emission tomography/single-photon emission computed tomography may improve the positive and negative predictive values of single-photon emission computed tomography-based viability studies.

SUMMARY

Single-photon emission computed tomography-based myocardial viability testing is an important diagnostic modality due to widespread availability and reasonably good sensitivity and specificity for detecting viable myocardium and predicting clinical and functional responses to revascularization. In the future single-photon emission computed tomography viability techniques may have a prognostic role in predicting responses to cardiac resynchronization therapy and evaluating myocardial stem-cell transplantation.

Myocardial Viability: Nuclear Assessment

There are an estimated 5 million patients with congestive heart failure (CHF) in the United States. The long-term outcome in these patients is poor with a 5-year mortality of 70%. There is evidence suggesting that revascularization in patients with viable myocardium can result in reduced event rate in these patients. The presence of viable myocardium best identifies patients who will improve with revascularization. Noninvasive imaging with radionuclide tracers has been used extensively to identify the presence and extent of viable myocardium. We have summarized the role of radionuclide myocardial perfusion and function evaluation in assessment of viable myocardium in this review.

Influence of infarct-zone viability detected by rest Tc-99m sestamibi gated SPECT on left ventricular remodeling after acute myocardial infarction treated by percutaneous transluminal coronary angioplasty in the acute phase

BACKGROUND

The purpose of this study was to assess the value of technetium 99m sestamibi gated single photon emission computed tomography (SPECT) in predicting the evolution of left ventricular volumes in patients treated successfully in the acute phase of a myocardial infarction (MI).

METHODS AND RESULTS

Twenty-nine patients with acute MI and early percutaneous transluminal coronary angioplasty (PTCA) were included in this study. A rest Tc-99m sestamibi electrocardiography (ECG)-gated SPECT study was performed 21 +/- 5 days after PTCA. The myocardial perfusion index was calculated by use of a semiautomatic sectorial analysis. All patients had contrast ventriculography performed during the acute phase and 6 months later. The patients were separated into two groups according to the absence (group I, n = 21) or presence (group II, n = 8) of end-systolic enlargement. The perfusion index in the infarct sectors was -2.29 +/- 2.90 SD in group I and -6.40 +/- 2.85 SD in group II ( P < .01). With a cutoff value of -2.46 SD, the sensitivity and specificity of Tc-99m sestamibi SPECT for the prediction of end-systolic volume enlargement were 100% and 62%, respectively. When the functional data from ECG-gated acquisitions were added, specificity increased to 86%.

CONCLUSIONS

Despite successful PTCA in the acute phase of MI, an increase in end-systolic volume was observed at 6 months in 28% of patients. Tc-99m sestamibi ECG-gated SPECT performed 3 weeks after the acute phase could predict this enlargement with a high accuracy.

Prognostic value of nitrate enhanced Tc99m MIBI SPECT study in detecting viable myocardium in patients with coronary artery disease

BACKGROUND

Assessing the viability in akinetic myocardium is vital for predicting functional recovery after therapeutic management in patients with chronic coronary artery disease (CAD) and depressed left ventricular (LV) function. The present study aimed to evaluate the efficacy of Tc99m MIBI SPECT enhanced with nitroglycerine infusion in detecting myocardial viability, as well as to asses the relationship between the myocardial viability and the subsequent treatment and outcome of patients.

METHODS AND RESULTS

Sixty-seven consecutive patients with CAD and LV dysfunction (LV ejection fraction 36.6 +/- 8.4%) underwent Tc99m MIBI imaging--at rest and during intravenous nitroglycerine infusion--for viability assessment. Fourteen patients were treated pharmacologically (Group I), and fifty-three (Group II) were submitted to coronary revascularization (PTCR or CABG). Fifteen major cardiac events were observed during 25 months of the follow-up. A significantly worse event-free survival was registered in the subjects of Group I than in Group II subjects. The prognostic predictors of cardiac events were: (1) the number of viable, non-revascularized segments in perfusion imaging (p < 0.001), (2) the severity of the disease assessed by coronary angiography (p < 0.05).

CONCLUSIONS

Viability detection in nitroglycerine infusion enhanced Tc99m MIBI imaging offers significant prognostic value in patients with CAD after myocardial infarction. Patients with preserved viability showed better prognosis after revascularization than those treated pharmacologically.

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.

Relevance of 99mTc-MIBI rest uptake, ejection fraction and location of contractile abnormality in predicting myocardial recovery after revascularization

The aim of this study was to analyse the influence of rest technetium-99m-methoxy-isobutyl-isonitrile (99mTc-MIBI) uptake, left ventricular ejection fraction (EF) and dysfunctional location in the prediction of myocardial viability. Rest 99mTc-MIBI single photon emission computed tomography (SPECT) was analysed in 82 patients (59+/-9 years, 70 men, 12 women) with one or more segments showing severe hypokinesia, akinesia or dyskinesia who had undergone coronary revascularization. Before and within 3-6 months after the revascularization, gated blood pool scintigraphy was performed. In the post-revascularization control, contractile recovery was observed in 48.7% (155/318) of the segments with severe hypokinesia, akinesia or dyskinesia. Significant increases in sensitivity (53%, 72% and 91%, P<0.0001) and negative predictive value (62%, 68% and 79%, P = 0.01) were observed with decreasing rest uptake 99mTc-MIBI levels of 50%, 40% and 30%, respectively. The decrease in specificity was also significant (67%, 53% and 32%, P<0.0001). The negative predictive value was higher than the positive predictive value mainly in patients with EF < or = 0.35 and with anterior dysfunction. In logistic regression analysis, uptake levels and EF were independent variables that influenced sensitivity and specificity. The negative predictive value was influenced by EF and the positive predictive value only by dysfunctional location. This study suggests that the negative predictive value of 99mTc-MIBI SPECT is higher than the positive predictive value, mainly in patients with EF < or = 0.35, and that the rest uptake level, EF and dysfunctional location are factors that must be considered when results of 99mTc-MIBI SPECT are analysed.

Use of 99Tcm-MIBI scintigraphy in the evaluation of perfusion improvement after myocardial revascularization with the use of the left internal thoracic artery

In spite of successful revascularization, in a significant group of patients myocardial ischaemia is present after surgery. The final effect of surgery depends on preoperative left ventricular function, initial coronary artery status, completeness of revascularization, the use of arterial or venous grafts, and many other factors. The aim of our 99Tcm-MIBI scintigraphy study was to examine the improvement of perfusion in the left anterior descending artery (LAD) vascular territory after revascularization with the use of the left internal thoracic artery (LITA), with respect to the LAD diameter and use of additional venous graft to diagonal artery. The study group consisted of 45 subjects (42 male, three female) aged 34-68 years (mean age 50.9+/-8.3 years) recruited from patients in whom LITA was grafted into LAD. The operation and postoperative period was uneventful in all patients. Two weeks before, and 3-4 months after surgery, dipyridamole-rest sestamibi SPECT were performed. The revascularization significantly improved both stress (deltaPI = 0.77+/-0.66; P < 0.001) and rest (deltaPI = 0.32+/-0.60; P < 0.001) perfusion of the LAD territory. The improvement was slightly better in patients who received two grafts (deltaPI = 1.42+/-0.91) for the LAD territory in comparison to the group revascularized only with LITA (deltaPI = 0.80+/-0.69; P = patients who received an arterial bypass to the LAD artery the perfusion was abnormal in all eight patients after anterior myocardial infarction and in 39% of patients without a history of infarction. The perfusion improvement was the best when the diameter of LAD was > or = 1.5 mm (deltaPI = 0.88+/-0.95). The independent predictors of perfusion improvement were the number of segments with reversible perfusion defect within the revascularized area (beta = 0.84, P < 0.001), the diameter of revascularized artery (beta = 0.17, P = 0.03) and the presence of pathological Q wave at preoperative ECG (beta = -0.20, P = 0.02). We conclude that the degree of perfusion improvement in the LAD territory after revascularization with the use of LITA depends on the diameter of bypassed coronary artery, completeness of revascularization and the reversibility of preoperative perfusion defect.

Quantitative thallium-201 and technetium 99m sestamibi tomography at rest in detection of myocardial viability in patients with chronic ischemic left ventricular dysfunction

BACKGROUND

This study was designed to determine the most effective quantitative threshold for thallium-201 and technetium 99m sestamibi uptake on tomographic imaging after rest injection for the detection of myocardial viability in patients with chronic myocardial infarction.

METHODS AND RESULTS

Thallium and sestamibi cardiac tomography at rest was performed in 43 patients with chronic myocardial infarction and impaired left ventricular (LV) function undergoing coronary revascularization. In all patients, echocardiography and radionuclide angiography were performed at baseline and repeated 12 months later to evaluate recovery of regional LV function and LV ejection fraction, respectively. Optimal threshold cutoff points to separate reversible from irreversible dysfunction were determined by receiver operating characteristic analysis. When all dysfunctional segments were considered, the best cutoff point in the identification of reversible LV dysfunction for both thallium and sestamibi activity was 67%. When only akinetic or dyskinetic segments were considered, the best cutoff point in the identification of reversible LV dysfunction was 58% for thallium and 55% for sestamibi. In these segments, the area under the receiving operating characteristic curves constructed for thallium and sestamibi activity were 0.74+/-0.05 and 0.75+/-0.04, respectively (P = not significant). LV ejection fraction was 33%+/-7% at baseline and increased to 37%+/-7% after revascularization (P<.0001). A significant relation between the number of akinetic or dyskinetic but viable myocardial segments and revascularization-induced changes in LV ejection fraction was observed for both thallium (r = 0.60, P<.0001) and sestamibi (r = 0.64, P<.0001) imaging.

CONCLUSIONS

In patients with chronic myocardial infarction, quantitative analysis of thallium and sestamibi activity on tomographic imaging at rest predicts recovery of regional and global LV dysfunction after revascularization procedures. The most effective quantitative threshold for detecting reversible LV dysfunction is comparable for thallium and sestamibi tomographic imaging. However, the optimal cutoff point is different for both tracers when all dysfunctional segments are considered or when the analysis is focused only on segments with more severe functional impairment (i.e., akinetic or dyskinetic segments).

Dobutamine magnetic resonance imaging as a predictor of myocardial functional recovery after revascularisation

OBJECTIVE

To assess the use of dobutamine magnetic resonance imaging (MRI) as a preoperative predictor of myocardial functional recovery after revascularisation, comparing wall motion and radial wall thickening analyses by observer and semi-automated edge detection.

PATIENTS

25 men with multivessel coronary disease and resting wall motion abnormalities were studied with preoperative rest and stress MRI.

MAIN OUTCOME MEASURES

Observer analysis for radial wall thickening was compared with a normal range, while wall motion analysis used a standard four point scale. Semi-automated analysis was performed using an edge detection algorithm. Segments displaying either improved or worsened thickening or motion with dobutamine were considered viable. Postoperative rest images were performed 3-6 months after coronary artery bypass grafting (CABG) for comparison.

RESULTS

For observer analysis the values for sensitivity and specificity were 50% and 72% for wall motion, with respective values of 50% and 68% for thickening. With semi-automated edge detection the figures for motion were 60% and 73%, with corresponding values of 79% and 58% for thickening. Combining thickening and motion for the semi-automated method to describe any change in segmental function yielded a sensitivity of 71% and specificity of 70%.

CONCLUSIONS

Dobutamine MRI is a reasonably good predictor of myocardial functional recovery after CABG. The use of semi-automated edge detection analysis improved results.

Effect of trimetazidine on 99Tcm-tetrofosmin uptake in patients with coronary artery disease

Myocardial uptake of 99Tcm-tetrofosmin in vivo is determined by a combination of flow and metabolic status of myocytes. The accumulation of tetrofosmin in the mitochondria is related to their ability to transduce metabolic energy into electronegative membrane potential. Trimetazidine (TMZ), an anti-ischaemic drug, appears to have a metabolic cytoprotective effect related to mitochondrial function, since it does not induce systemic or coronary haemodynamic changes. In this study, we evaluated the effects of TMZ on tetrofosmin uptake in hypoperfused myocardial regions in patients with coronary artery disease (CAD). Twenty-two patients, 14 with previous myocardial infarction (group A) and eight with a history of angina (group B), with angiographically documented CAD were studied. All patients underwent two tetrofosmin SPET studies at rest, before (baseline) and 1 week after TMZ administration (post-TMZ). On quantitative analysis, 131 segments showed less tetrofosmin uptake at baseline. In these segments, tetrofosmin uptake was 51 +/- 13% at baseline and 55 +/- 15% post-TMZ (P < 0.001 vs control). In the 86 hypoperfused segments of group A, tetrofosmin uptake was 48 +/- 14% at baseline and 52 +/- 17% post-TMZ (P < 0.001 vs control). In the 45 hypoperfused segments of group B, tetrofosmin uptake was 56 +/- 9% at baseline and 60 +/- 10% post-TMZ (P < 0.001 vs control). In the remaining 309 segments, no significant difference in tetrofosmin uptake before and after TMZ was observed. In conclusion, our results suggest that TMZ administration may increase myocardial uptake of tetrofosmin in hypoperfused regions at rest in patients with CAD, based on its metabolic effect.

Functional assessment with electrocardiographic gated single-photon emission computed tomography improves the ability of technetium-99m sestamibi myocardial perfusion imaging to predict myocardial viability in patients undergoing revascularization

This study evaluates the use of electrocardiographic (ECG) gated single-photon emission computed tomographic (SPECT) myocardial perfusion imaging for the prediction of viability in patients undergoing revascularization, who have coronary disease and left ventricular dysfunction. Fifty patients underwent technectium-99m (Tc-99m) sestamibi ECG gated SPECT imaging preoperatively at rest and 1 week after revascularization, whereas 36 (72%) also underwent imaging 6 weeks after revascularization. Images were interpreted by the consensus of 3 experienced readers without knowledge of patient identity or time of imaging (pre- or postrevascularization) for perfusion and wall motion using a 17-segment model. Results of perfusion alone were compared with perfusion and wall motion combined. One hundred five coronary artery territories were revascularized, 96 of which were viable and 9 nonviable. Perfusion alone predicted 87 to be viable and 18 nonviable (sensitivity 86%, specificity 55%, positive predictive value 95%, negative predictive value 28%, and overall accuracy 85%). Perfusion and wall motion combined identified 95 territories to be viable (sensitivity 95%; p <0.025; specificity 55%, positive predictive value 96%, negative predictive value 50%, and overall accuracy 91%; p <0.05). Thus, Tc-99m sestamibi ECG gated SPECT myocardial perfusion imaging at rest allows assessment of both perfusion and wall motion, which significantly improves the sensitivity and overall accuracy for determination of viability in comparison with perfusion alone.

Functional and ultrastructural evidence of myocardial stunning after acute carbon monoxide poisoning

OBJECTIVE

To study human myocardial ultrastructural changes after carbon monoxide (CO) poisoning inducing reversible cardiac failure.

DESIGN

CASE REPORT

clinical, functional and morphologic findings.

SETTINGS

Public university-affiliated hospital and electron microscopy laboratory.

PATIENT

A 25-yr-old woman with functional evidence of cardiac failure after acute CO poisoning.

INTERVENTIONS

Hyperbaric and intensive care treatment over 10 days. Scintigraphic and cardiac angiography with endomyocardial biopsy.

MEASUREMENTS AND MAIN RESULTS

Scintigraphy with 99mTc hexakis 2-methoxy-2-isobutyl isonitrile (sestaMIBI) showed an uptake defect in the left anterior descending artery territory. The cardiac angiography demonstrated a slight hypokinesis of the superior two thirds of the anterior wall and of the septal region with completely normal coronary angiograms. Electron microscopy of left ventricular biopsies showed slight ultrastructural changes in the myocytes. In addition, large glycogen deposits were mostly associated with swollen mitochondria. The patient was discharged in good clinical condition on day 10.

CONCLUSIONS

Presence of glycogen deposits associated with abnormal mitochondria may be signs of the incapability of myocardial cells in utilizing energy substrata. In the presence of normal myocardial perfusion, our findings are consistent with the presence of a stunned myocardium-like syndrome. Early recognition and treatment of this clinical syndrome allow the prevention of myocardial infarction.

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

The noninvasive assessment of myocardial viability in patients with coronary artery disease and depressed left ventricular function has proven clinically useful for identifying those patients with ischemic cardiomyopathy who benefit most from coronary revascularization. Thallium-201 (201Tl) imaging at rest has been the radionuclide imaging technique most often utilized for distinguishing viable myocardium from scar. However, new technetium-99m (99mTc) perfusion agents such as 99mTc-sestamibi and 99mTc-tetrofosmin have emerged as alternatives to 201Tl for imaging of regional myocardial perfusion. Whether these new agents, which have better physical properties for imaging with a gamma camera than 201Tl, are valid for use in assessing myocardial viability is still uncertain. Recent clinical studies have demonstrated that these agents, when imaged using quantitative SPECT, can identify patients with myocardial hibernation who exhibit improved regional systolic function following revascularization. Experimental laboratory studies have shown that the uptake of 99mTc-sestamibi and 99mTc-tetrofosmin in ischemic myocardium is only slightly lower than the uptake of 201Tl. These 99mTc-labeled agents remain bound intracellularly in mitochondria of viable myocytes under conditions of myocardial stunning and short-term hibernation, producing severe myocardial asynergy. With respect to determination of viability, the inferior wall region is at times problematic since attenuation of 99mTc-sestamibi and 99mTc-tetrofosmin is greatest in this area. Demonstration of preserved systolic thickening on ECG-gated SPECT images is indicative of viability in the instance of decreased regional 99mTc counts due to attenuation and not scar. Administration of nitrates prior to tracer injection improves the sensitivity for identifying viable myocardial segments using rest imaging with 99mTc-sestamibi or 99mTc-tetrofosmin. Thus, it appears that the new 99mTc perfusion imaging agents can be successfully employed for the determination of myocardial viability in the setting of severe regional dysfunction and chronic coronary artery disease. The greater the myocardial uptake of these agents in the resting state, the greater the probability of improved systolic function after coronary revascularization.

Accuracy of currently available techniques for prediction of functional recovery after revascularization in patients with left ventricular dysfunction due to chronic coronary artery disease: comparison of pooled data

OBJECTIVES

This study evaluated the relative merits of the most frequently used techniques for predicting improvement in regional contractile function after coronary revascularization in patients with left ventricular dysfunction due to chronic coronary artery disease.

BACKGROUND

Several techniques have been proposed for predicting improvement in regional contractile function after revascularization, including thallium-201 (Tl-201) stress-redistribution-reinjection, Tl-201 rest-redistribution, fluorine-18 fluorodeoxyglucose with positron emission tomography, technetium-99m sestamibi imaging and low dose dobutamine echocardiography (LDDE).

METHODS

A systematic review of all reports on prediction of functional recovery after revascularization in patients with chronic coronary artery disease (published between 1980 and March 1997) revealed 37 with sufficient details for calculating the sensitivity and specificity of each imaging modality. From the pooled data, 95% and 99% confidence intervals were also calculated.

RESULTS

Sensitivity for predicting regional functional recovery after revascularization was high for all techniques. The specificity of both Tl-201 protocols was significantly lower (p < 0.05) and LDDE significantly higher (p < 0.01) than that of the other techniques.

CONCLUSIONS

Pooled analysis of 37 studies showed that although all techniques accurately identify segments with improved contractile function after revascularization, the Tl-201 protocols may overestimate functional recovery. The evidence available thus far indicates that LDDE appears to have the highest predictive accuracy.

Comparable uptake of thallium-201 and technetium-99m MIBI in hibernating and "maimed" myocardium

Thallium-201 and technetium-99m-MIBI uptake are comparable in "maimed" (i.e., partially viable) and hibernating myocardium. The appreciation of myocardial viability should be based not only on the presence of a regional contractility improvement, but also on the evaluation of the initial level of contractility and of tracer uptake in the concerned area.

Is the addition of ECG gating to technetium-99m sestamibi SPET of value in the assessment of myocardial viability? An evaluation based on two-dimensional echocardiography following revascularization

The main goal of this study was to evaluate whether the addition of ECG gating to technetium-99m sestamibi single-photon emission tomographic (SPET) perfusion imaging assists the prediction of recovery of regional wall motion abnormalities after revascularization. Thirty-six patients with coronary artery disease were included in the study. All had wall motion abnormalities, and 31 (86%) had a clinical history of myocardial infarction. Coronary artery bypass surgery was performed in 18 patients and angioplasty in the remainder. All underwent ECG-gated and non-gated SPET at rest and after intravenous dipyridamole. Two-dimensional echocardiography was performed at a mean of 27 days before revascularization and at a mean of 69 days following revascularization to assess segmental wall motion changes. Perfusion prior to revascularization was analysed qualitatively and quantitatively on gated and non-gated SPET, and the results compared with those of echocardiography. Bullseye parameters were obtained from a normal database, generated from data in 40 normal volunteers, using dipyridamole ECG-gated and non-gated sestamibi SPET. There was good concordance between gated and non-gated qualitative analysis (79% with kappa=0.65) for normal, viable or necrotic segments. Gated SPET predicted functional recovery in 27 of 35 (77%) segments showing echocardiographic improvement while non-gated SPET did so in 30 of 39 (77%) such segments. Gated SPET predicted no functional recovery in 20 of 45 (44%) segments that did not show improved wall motion after revascularization, while with non-gated SPET the figure was 18 of 51 (35%). The positive predictive values of gated and non-gated SPET with regard to the recovery of wall motion following revascularization were 52% and 48%, while the negative predictive values were 71% and 67%, respectively. 99mTc-sestamibi had a low predictive value for recovery of function if visual assessment was used in the analysis of SPET data. Quantitative bullseye sestamibi parameters (defect extension and severity, reversibility and percentage change in extension), from gated or non-gated studies, appear best to distinguish which segments will display improved motility on the echocardiogram after revascularization. The addition of ECG gating does not significantly increase the predictive value of SPET imaging with regard to recovery of function.

Present assessment of myocardial viability by nuclear imaging

Prospective delineation of viable from nonviable myocardium in patients with coronary artery disease in an important factor in deciding whether a patient should be revascularized or treated medically. Two common techniques--single-photon emission computed tomography (SPECT) and positron-emission computed tomography (PET)--are used in nuclear medicine using various radiopharmaceuticals for the detection of myocardial viability in patients. Thallium-201 (201Tl) and technetium-99m (99mTc)-sestamibi are the common radiopharmaceuticals used in different protocols using SPECT, whereas fluoride-18 (18F)-fluorodeoxyglucose (FDG) and rubidium-82 (82Rb) are most widely used in PET. The SPECT protocols involve stress/redistribution, stress/redistribution/reinjection, and rest/redistribution imaging techniques. Many studies have compared the results of 201Tl and (99mTc)-sestamibi SPECT with those of FDG PET; in some studies, concordant results have been found between delayed thallium and FDG results, indicating that 201Tl, although considered a perfusion agent, shows myocardial viability. Discordant results in a number of studies have been found between sestamibi and FDG, suggesting that the efficacy of sestamibi as a viability marker has yet to be established. Radiolabeled fatty acids such as iodine-123 (123I)-para-iodophenylpentadecanoic acid and carbon-11 (11C)-palmitic acid have been used for the assessment of myocardial viability with limited success. 11C-labeled acetate is a good marker of oxidative metabolism in the heart and has been used to predict the reversibility of wall motion abnormalities. (18F)-FDG is considered the marker of choice for myocardial viability, although variable results are obtained under different physiological conditions. Detection of myocardial viability can be greatly improved by developing new equipment and radiopharmaceuticals of better quality.