Thallium-201 for assessment of myocardial viability: quantitative comparison of 24-hour redistribution imaging with imaging after reinjection at rest

Patient Selection and Clinical Indication for Chronic Total Occlusion Revascularization-A Workflow Focusing on Non-Invasive Cardiac Imaging

Percutaneous coronary intervention of chronic total occlusion (CTO PCI) is a challenging procedure with high complication rates and, as not yet fully understood long-term clinical benefits. Ischemic symptom relief in patients with high ischemic burden is to date the only established clinical indication to undergo CTO PCI, supported by randomized controlled trials. In this context, current guidelines suggest attempting CTO PCI only in non-invasively assessed viable CTO correspondent myocardial territories, with large ischemic areas. Hence, besides a comprehensive coronary angiography lesion evaluation, the information derived from non-invasive cardiac imaging techniques is crucial to selecting candidates who may benefit from the revascularization of the occluded vessel. Currently, there are no clear recommendations for a non-invasive myocardial evaluation or choice of imaging modality pre-CTO PCI. Therefore, selecting among available options is left to the physician's discretion. As CTO PCI is strongly recommended to be carried out explicitly in experienced centers, full access to non-invasive imaging for risk-benefit assessment as well as a systematic institutional evaluation process has to be encouraged. In this framework, we opted to review the current myocardial imaging tools and their use for indicating a CTO PCI. Furthermore, based on our experience, we propose a cost-effective systematic approach for myocardial assessment to help guide clinical decision-making for patients presenting with chronic total occlusions.

Revascularization in Patients With Severe Left Ventricular Dysfunction: Is the Assessment of Viability Still Viable?

Myocardial viability assessment is typically reserved for patients with coronary artery disease and significant left ventricular dysfunction. In this setting, there is myocardial adaptation to an altered physiological state that is potentially reversible. Imaging can characterize different parameters of cardiac function; however, despite previously published appraisals of different imaging modalities, there is still uncertainty regarding the role of these tests in clinical practice. The purpose of this review is to reflect on the physiological basis of myocardial viability, discuss the imaging tests available that characterize myocardial viability, and summarize the current published reports on the use of these tests in clinical practice.

Evaluation of myocardial viability with thallium-201 infusion MPSPECT after oral glucose application in patients with chronic coronary artery disease

AIM

The aim of this study was to evaluate the myocardial viability in nondiabetic patients with chronic coronary artery disease (CCAD) or past myocardial infarction (MI), using thallium-201 infusion myocardial perfusion single-photon emission computed tomography (MPSPECT) imaging after oral glucose application (Glu+Tl-infusion).

MATERIALS AND METHODS

In this study, 33 nondiabetic patients (three female, 30 male, mean age: 55.24+/-11 years, range: 33-77 years) with MI history or known CCAD were included. Rest/redistribution/24 h-late-MPSPECT imaging was performed for all patients. In all patients in whom fixed perfusion defect was observed on any wall of the left ventriculi, after 24 h-late-MPSPECT imaging, 75 g oral glucose was given. Thirty minutes later, 1 mCi thallium-201 in 100 ml of physiological saline solution was applied in a period of 20 min by slow infusion. After infusion at the 10th minute, MPSPECT imaging was performed. Perfusion was evaluated visually for a total of 3432 segments with the 26-segment 5-point scoring technique. Scoring measured perfusion as 0 = no perfusion defect, 1 = mildly reduced, 2 = moderately reduced, 3 = severely reduced, and 4 = absent uptake. Scores '0 and 1' were considered normal and scores '2-4' were considered abnormal.

RESULTS

For serum insulin levels measured after glucose application, a significant increase was determined, according to the period before glucose application (P<0.001). When compared with rest MPSPECT images, segmental perfusion improvement both in redistribution and in the 24 h-late-MPSPECT images were 16.3 and 18.3%, respectively. This ratio was found to be 27.2% for Glu+Tl-infusion images. The ratios of segments in which perfusion was worsening were calculated to be 9.4, 14.5, and 7.3%, respectively, for redistribution, 24 h-late-MPSPECT, and Glu+Tl-infusion images. When this evaluation was made for all three vessel areas, again the highest perfusion improvement and the lowest perfusion worsening were detected for Glu+Tl-infusion images. In addition, when this evaluation was made for the three vessel areas according to the coronary narrowing degree, again the highest perfusion improvement was detected for Glu+Tl-infusion images, in segments in the left anterior descending artery, and right coronary artery areas with >/=90% narrowing. In rest images, in segments with segmental scores of 3 and 4, when the total reversibility ratio was evaluated, this ratio was calculated to be 0.7% for redistribution images and 4.5% for 24 h-late-MPSPECT. The highest total reversibility ratio in these segments was detected with Glu+Tl-infusion images to be 10.3%. When we evaluated the patients with respect to the MI history time, the highest segmental perfusion improvement was detected in patients with 0-3 months of MI history.

CONCLUSION

We conclude that in nondiabetic patients who are known to have CCAD or past MI history, Glu+Tl-infusion is an easily applicable method that gives better results for the evaluation of myocardial viability.

Comparison of exercise-rest-reinjection Tl-201 imaging and rest sublingual isosorbide dinitrate Tc-99m MIBI imaging for the assessment of myocardial viability

PURPOSE

Nitrate administration has been proposed to enhance the detection of myocardial viability when performing myocardial perfusion imaging. In this study, we aimed to compare Tl-201 exercise-rest-reinjection protocol with rest isosorbide dinitrate (ISDN)-Tc99m MIBI study in the same population examined for the myocardial viability.

METHODS

Twenty-six patients with coronary artery disease who had fixed segmental defects on exercise-rest-Tl-201 imaging were studied. All of them underwent Tl-201 reinjection study. Within 1 week of Tl-201 imaging, rest-Tc99m MIBI imaging was performed after sublingual 5 mg ISDN administration (2-day protocol). For each study, tomograms were divided into 20 segments based on three short-axis slices, one vertical long-axis representing the totality of the left ventricle and regional tracer uptake was quantitatively analyzed. Regional tracer uptake was evaluated in 20 myocardial segments for all patients. Viability was defined as presence of tracer uptake >/=50% of peak activity on each study. A total 520 myocardial segments were assessed by semi quantitative analysis.

RESULT

On the baseline rest Tl-201 studies, 211 segments of the 520 segments that were analyzed had <50% of peak activity. Of these segments, 42 (20%) showed reversibility after reinjection Tl-201 imaging and 55 segments (27%) described as viable on the rest ISDN-Tc99m MIBI imaging. There was 89% concordance between the ISDN-Tc99m MIBI study and Tl-201 reinjection study regarding viable myocardial segments. Of the 23 segments with discordant results, 18 were irreversible on Tl-201 reinjection study, but showed >/=50% uptake on ISDN-Tc99m MIBI.

CONCLUSION

Observation of good agreement between Tl-201 reinjection and ISDN-Tc99m MIBI study studies led us to suggest the use of ISDN enhanced imaging in the evaluation of myocardial viability.

Diagnostic and imaging considerations: role of viability

Left ventricular systolic dysfunction is a recognised feature of heart failure. In developed nations, the leading cause of left ventricular systolic dysfunction is coronary artery disease. Revascularisation is a treatment strategy for patients with predominant symptoms of heart failure and significant left ventricular dysfunction. Presence or absence of myocardial viability has been shown to affect outcome after revascularisation. There are various techniques to assess myocardial viability. However, limitations of current literature, lack of completed randomised trials and high peri-procedural trials create significant uncertainty about the optimal strategy. This review focuses on the role of non-invasive testing for myocardial viability in patients with left ventricular systolic dysfunction and heart failure and also outlines the pros and cons of each technique.

The non-invasive assessment of hibernating myocardium in ischaemic cardiomyopathy--a myriad of techniques

Heart failure is placing an ever-increasing burden on society. Many subjects with heart failure and underlying coronary artery disease have a significant amount of akinetic but viable myocardium that is able to contract should myocardial perfusion improve (hibernating myocardium). Non-randomised studies have shown prognostic benefit in subjects with hibernating myocardium undergoing revascularisation. Several non-invasive techniques have been developed to assess the presence or absence of hibernating myocardium. This review will examine the epidemiology and underlying pathogenesis of hibernating myocardium; evaluate the non-invasive techniques for diagnosing hibernating myocardium, and look at therapeutic intervention in subjects with hibernating myocardium.

Exercise-induced ST-elevation is related to left ventricular dysfunction but not to myocardial viability in patients with healed myocardial infarction

BACKGROUND

Exercise-induced ST-segment elevation was proposed as a marker of myocardial viability after a recent myocardial infarction.

AIMS

The aim of this study was to evaluate whether exercise-induced ST segment elevation is related to viability or to left ventricular dysfunction in patients with history of old Q wave myocardial infarction.

METHODS

Fifty patients (43 men, age 57+/-11 years) were studied 31+/-49 months after a Q wave myocardial infarction. They all underwent stress, reinjection-redistribution, and late redistribution Tl-201 SPECT, completed by equilibrium radionuclide angiography. Viability was defined by defect reversibility or significant (>60%) persistent Tl-201 uptake in dyssinergic segments on late redistribution SPECT. Relative post-exercise and reinjection-redistribution LV volumes were calculated using validated software (QGS).

RESULTS

Twenty-one out of 50 patients (42%, G1) had significant stress-induced ST-elevation (>1 mm 80 ms after J point in at least 2 ECG leads with Q wave), and 29/50 (58%, G2) did not. Seventeen out of 50 patients (34%) demonstrated myocardial viability on late redistribution scan. The diagnostic accuracy of exercise-induced ST-elevation was only 52% for viability assessment. Significant LVEF reduction and increased relative LV volumes were observed in G1 compared to G2 (LVEF: 39+/-10% vs. 49+/-11%, P=0.003; post-stress LV volume: 134+/-98 ml vs. 81+/-41 ml, P<0.02; reinjection-redistribution LV volume: 123+/-86 ml vs. 79+/-40 ml; P<0.02). Perfusion defects were similar in G1 and G2 (post-exercise: 38+/-12% vs. 37+/-14%, ns; reinjection-redistribution: 31+/-11% vs. 30+/-11%, ns; late redistribution: 30+/-10% vs. 28+/-11%, ns).

CONCLUSION

These results suggest that, in patients with history of myocardial infarction, exercise-induced ST-segment elevation is not related to persistent myocardial viability but is associated to left ventricular dysfunction.

Value of linsidomin in assessing myocardial viability with thallium-201 SPECT

Myocardial viability can be assessed with rest/24 h redistribution (201)Tl myocardial single photon emission computed tomography (SPECT). The intravenous injection of vasodilators induces an early redistribution of (201)Tl and shortens the total examination time. The aim of this study was to compare the images after injection of linsidomin with the 24 h images. We studied 51 consecutive patients (38 males, 13 females), aged 66+/-11 years, referred for assessment of myocardial viability after acute myocardial infarction. SPECT acquisition at rest (30 projections over 180 degrees, 30 s per projection) was performed 20 min after injection of (201)Tl. A second acquisition (same parameters) was performed 2 min after intravenous injection of linsidomin (2 mg). A delayed acquisition was performed on the following day (50 s per step). Myocardial perfusion at rest was normal in 111 of 255 segments. For the 144 other segments, 24 h images were similar to the images acquired after the injection of linsidomin in 94% of cases (136 of 144 segments). The 24 h images showed partial redistribution that was not present after linsidomin in only eight segments (6%). Injection of linsidomin after rest acquisition can provide a reliable and more rapid assessment of myocardial viability. This very simple protocol (rest/linsidomin (201)Tl myocardial SPECT) can be performed in less than 1 h.

The clinical significance of reverse redistribution in Tl201 cardiac SPET

In an attempt to evaluate the clinical significance of reverse redistribution in Tl201 cardiac SPET, Tl201 SPET examinations included in the data base of our department have been retrospectively reviewed.

PATIENTS

Six hundred ninety eight patients demonstrated the pattern of reverse redistribution. For 237 of these patients' cardiac catheterization data were also available. One hundred and six patients of these had a history of myocardial infarction while the rest of them were referred for angina symptoms.

RESULTS

Catheterization showed that the infarction area was perfused by a stenosed but patent vessel in 79 of the 106 patients with a history of myocardial infarction (74.5%). Collateral circulation was evident in 21 of these 106 patients (19.8%). Only six patients (5.6%) showed a totally occluded vessel with no obvious evidence of collateral circulation. Of the 131 patients, with no myocardial infarction history, 14 (10.7%) had normal coronary vessels. The rest of the patients (89.3%) demonstrated stenotic vessels perfusing the same area where reverse redistribution was observed. Sixty-three of these patients have been reexamined after 9-36 months. On 15 of these patients (23.8%) the second scintigram showed ischemia in the same segments where reverse redistribution was initially detected. Another 17 of the above patients had a former scintigraphic examination that showed ischemia on the segments that currently demonstrated reverse redistribution.

CONCLUSION

The results of the present retrospective study indicate that, in patients with known coronary disease, the pattern of reverse redistribution frequently indicates the ischemic area.

Non-invasive investigations

The most commonly used techniques for imaging the effects of coronary artery disease (CAD) on the heart are myocardial perfusion scintigraphy (MPS) and echocardiography. Both tests have been validated during exercise and pharmacological stress and they are valuable for the diagnosis and aiding management decisions in patients with suspected or known CAD. In a proportion of these patients, repetitive episodes of myocardial ischaemia can lead to intracellular and extracellular changes so that myocytes, although viable, have insufficient energy to sustain contraction. This phenomenon is known as myocardial hibernation and it can be detected accurately by both MPS and stress echocardiography. The review that follows highlights the role of these techniques as powerful diagnostic and prognostic tools in clinical cardiology. In order to make the best use of them, attention to detail and planning are required to design the test to suit the clinical problem and to obtain the most accurate data possible.

Enhanced 99Tc(m)-MIBI SPECT detection of hibernating myocardium following the use of sub-lingual nitroglycerine

The purpose of this study was to assess the feasibility of detecting hibernating myocardium using 99Tc(m)-MIBI SPECT imaging following the use of sublingual glyceryl trinitrate (GTN). Thirty-eight subjects were studied, five asymptomatic and 33 with a history of myocardial ischaemia or myocardial infarction (MI). The study was conducted on two separate days, both at rest, one under controlled basal conditions and the other 20 min following the sublingual administration of GTN. A total of 190 cardiac segments were qualitatively analysed and 72 segments with fixed defects were compared to the study following the use of GTN for evidence of improved radionuclide uptake. Following GTN, 73.6% of fixed segment defects showed no change in uptake, 5.5% showed probable improvement whilst in 20.8% a definite enhanced uptake was demonstrated. In 3.7% of segments, worsening of radionuclide uptake was observed.

Immediate thallium re-injection after stress imaging for the detection of myocardial viability

Myocardial perfusion imaging with thallium is an established method to assess the presence of ischaemic and viable myocardium. Using planar imaging, images acquired 1 h after immediate thallium re-injection have been shown to be comparable to those of 3 h redistribution. The aim of this study was to clarify this using SPET. Twenty patients with chronic coronary artery disease with at least two perfusion defects on post-exercise images participated in this study. All patients received thallium re-injection after post-stress SPET and all had 1 h, 3 h and 24 h redistribution imaging. The thallium myocardial tomograms were divided into 14 segments for each patient. A total of 78 segments were studied. When the frequency of reversibility on 1 h, 3 h and 24 h redistribution images is compared, of the 78 SPET defects 18 (23.1%) showed reversibility by 1 h, 34 (43.6%) by combined 1 h and 3 h imaging (P < 0.05) and 50 (64.1%) by combined 1 h, 3 h and 24 h imaging (P < 0.05). Our results show that, compared to 3 h images, images acquired 1 h after immediate thallium re-injection underestimate the extent of viable myocardial segments and the incidence of late reversibility was not reduced by the immediate re-injection of thallium.

Prognostic implications of myocardial contractile reserve in patients with ischemic cardiomyopathy

The extent and degree of myocardial viability is an important parameter in the risk stratification of patients with significant left ventricular dysfunction due to coronary artery disease (CAD). Although several imaging modalities can identify viable myocardium, dobutamine stress echocardiography has gained considerable importance as an accurate, safe, and reliable method. In patients with significant left ventricular dysfunction secondary to CAD, identifying the presence and extent of contractile reserve and, therefore, viable myocardium, during low dose dobutamine infusion can predict recovery of left ventricular function postrevascularization, survival, and future cardiac events.

Comparing a High-dose Dipyridamole SPECT Imaging Protocol with Dobutamine and Exercise Stress Testing Protocols. Part III: Using Dobutamine to Determine Lung-to-Heart Ratios, Left Ventricular Dysfunction, and a Potential Viability Marker

Determination of the severity of coronary artery disease (CAD) by single photon emission computed tomography (SPECT) imaging has previously been shown to have greater sensitivity, specificity, and accuracy when performed with pharmacologic stress using dobutamine than by standard dose dipyridamole (SDD) or exercise stress testing (EST) prior to SPECT imaging. The use of lung to heart (L:H) ratios has been shown to be valuable in determining the presence or absence of left main (LM) or triple vessel (3V) CAD. No such work has been previously reported for dobutamine. Twenty-one patients were studied using dobutamine (n = 7) or EST (n = 14). These results were compared with results from Part II of this series of studies using high-dose dipyridamole (HDD) pharmacologic stress. In this study, patients underwent L:H ratio analysis following injection of 3 mCi of Tl-201, this provides sufficient time for thallium clearance from the blood pool. Results of the L:H ratios were compared with the results of coronary arteriographic (CA) evaluation. Patients who were "stressed" via EST demonstrated statistically greater (p </= 0.001) L:H ratios in patients with LM/3V CAD when compared with patients who had 0-2 significantly stenosed coronary arteries. Patients stressed with dobutamine demonstrated lower L:H ratios (p = NS) in patients with LM/3V CAD than was seen for patients with 0-2 V CAD. Patients stressed with dobutamine had statistically (p </= 0.05) lower L:H ratios than did similar patients stressed with EST. Increased L:H ratios following EST and HDD, as shown previously in Part II of this series, provide excellent markers for LM/3V CAD following Tl-201 injection. The presence of "normal" L:H ratios in patients with LM/3V CAD following dobutamine stress may suggest the presence of "stunned" or "hibernating" myocardium. The presence of "decreased" L:H ratios following dobutamine after HDD or EST has already shown an increased L:H ratio, might suggest a marker for myocardial viability that deserves further investigation.

Comparing a High-Dose Dipyridamole SPECT Imaging Protocol with Dobutamine and Exercise Stress Testing Protocols. Part II: Using High-Dose Dipyridamole to Determine Lung-to-Heart Ratios

Determination of the severity of coronary artery disease (CAD) by single photon emission computed tomography (SPECT) imaging has previously been shown to have greater sensitivity, specificity, and accuracy when performed with pharmacologic stress using high-dose dipyridamole (HDD), than by standard dose dipyridamole (SDD) or exercise stress (EST) prior to SPECT imaging. The use of lung-to-heart (L:H) ratios has been shown to be valuable in determining the presence or absence of left main (LM) or triple vessel (3V) CAD. Fifty-four patients were studied; HDD (n = 40) or EST (n = 14) was used for the study. These patients underwent L:H ratio analysis, in which anterior views were used 5-10 minutes after the injection of 3 mCi of T1-201. Results of the L:H ratios were compared with the diagnosis of epicardial CAD, as determined by coronary (CA) arteriography. Patients who were "stressed" using either HDD or EST demonstrated statistically greater (p < 0.001) L:H ratios if they had LM/3V CAD when compared with patients who had 0-2 significantly stenosed coronary arteries. Though L:H ratios were greater when HDD pharmacologic stress was used, there was no statistical (p = NS) differences between the two groups. Increased L:H ratios with HDD and EST provide excellent markers for LM/3V CAD using T1-201 imaging. Coupled with previously reported SPECT data, the use of HDD shows promise for increasing the diagnostic accuracy of SPECT imaging.

Assessment of myocardial viability by radionuclide imaging

The differentiation of viable from non viable myocardium is a key issue in the current era of revascularization. Several methods have been used to assess myocardial viability. The radionuclide detection of dysfunctional but viable myocardium depends upon the use of radiotracers whose uptake and trapping are related to presence and amount of living cells. The choice of the diagnostic technique to be applied in clinical practice depends on accuracy of the method and availability of resources. SPECT imaging with TI-201 and Tc-99m-myocardial perfusion tracers are widely available diagnostic tools. Several studies have documented their reliability to detect myocardial segments which may improve in both perfusion and function after revascularization. Positron emission tomography after injection of glucose analogues is a more sophisticated and accurate technology to detect viability, whose utilization is at present limited to few centers due to its high cost. Therefore an accurate selection of patients requiring viability studies is needed in order to identify the most appropriate diagnostic test.

Comparison of filled-in myocardial segments after early and late reinjection of thallium-201--influence of the timing of reinjection on fill-in

Thallium-201 (201Tl) late reinjection after stress-redistribution imaging improves the detection of viable myocardium. Recently, early reinjection of 201Tl immediately after stress imaging was proposed as a new method for distinguishing ischemic myocardium, hibernating myocardium, and myocardial scar. However, there are no data on the influence of the timing of reinjection on "fill-in." This study was designed to assess whether the reinjection time influences "fill-in" in chronic coronary artery disease. Thirty-three patients with chronic coronary artery disease were studied. All patients underwent exercise 201Tl tomography. Immediately after stress imaging, 37 MBq of thallium was reinjected earlier than usual and early reinjection delayed image (ERDI) was acquired 3 h later. With the same protocol, all patients also underwent a second study involving late reinjection of 201Tl within 1 week. An additional 37 MBq of thallium was reinjected 3 h after stress imaging, and late reinjection delayed image (LRDI) was obtained 10 min later. All images were analyzed qualitatively using a 4-point grading uptake score. Of the 72 hypoperfused segments on stress images, 66 segments showed fill-in and 6 showed persistent defects on ERDI, and of the same 72 segments 55 segments displayed fill-in and the remaining 17 showed persistent defects on LRDI (p<0.05). The delta uptake score (the uptake score of the delayed image minus that of stress image) in early reinjection was 1.60+/-0.80, which was significantly higher than that in late reinjection (1.24+/-0.94, p<0.01). A small dose of thallium reinjected immediately after stress imaging with delayed images obtained 3 h later is convenient and might provide another technique for determining myocardial viability.

Viability after myocardial infarction: can it be assessed within five minutes by low-dose dynamic iodine-123-iodophenylpentadecanoic acid imaging with a multicrystal gamma camera?

Although positron emission tomography (PET) assesses myocardial viability (V) accurately, a rapid, inexpensive substitute is needed. Therefore, the authors developed a low-dose (1 mCi) Iodine-123-Iodophenylpentadecanoic Acid (IPPA) myocardial viability scan requiring analysis of only the first three minutes of data acquired at rest with a standard multicrystal gamma camera. Twenty-one patients > 2 weeks after myocardial infarction (MI) (24 MIs, 10 anterior, 14 inferoposterior, 21 akinetic or dyskinetic) had cardiac catheterization and resting IPPA imaging. V was determined by either transmural myocardial biopsy during coronary bypass surgery (12 patients, 14 MIs) or reinjection tomographic thallium scan (9 patients, 10 MIs), and 50% of MIs were viable. The IPPA variables analyzed were: time to initial left ventricular (LV) uptake in the region of interest (ROI), the ratio of three-minute uptake in the ROI to three-minute LV uptake, three-minute clearing (counts/pixel) in the ROI (decrease in IPPA after initial uptake), and three-minute accumulation (increase in IPPA after initial uptake) in the ROI. Rules for detecting V were generated and applied to 10 healthy volunteers to determine normalcy. While three-minute uptake in nonviable MIs was only 67% of volunteers (P < 0.0001) and 75% of viable MIs, uptake alone identified only 50% of viable MIs and 75% of nonviable MIs. IPPA clearing, however, was > or = 13.5 counts/pixel in 10/12 (83%) of viable MIs, and IPPA accumulation > or = 6.75 counts/pixel identified one more viable MI, for a sensitivity for V of 11/12 (92%), with a specificity of 11/12 (92%), and a 100% normalcy rate. The authors conclude low-dose IPPA (five-minute acquisition with analysis of the first three minutes of data) has potential for providing rapid, inexpensive V data after MI. Since newer multicrystal cameras are mobile, IPPA scans can be done in emergency rooms or coronary care units generating information that might be useful in decisions regarding thrombolysis, angioplasty, or bypass surgery.

Determination of systolic thickening index with gated Tc-99m sestamibi SPECT. A new parameter of myocardial viability?

Myocardial perfusion imaging with Tc-99m MIBI SPECT may underestimate the amount of viable myocardium in patients with coronary artery disease and prior infarction. Electrocardiogram gating could potentially better correlate with the presence of jeopardized myocardium, since it allows the evaluation of systolic contractility parameters in addition to the assessment of perfusion. Using the diastolic and systolic bull's eyes of a rest Tc-99m MIBI-gated SPECT study to generate an index of systolic thickening, we clearly observed an impaired contractility in the anterior and septal walls in a patient with multiple vessel disease and a mild mid-left anterior descending stenosis, despite a normal tracer uptake. Confirmation of the index of systolic thickening findings was obtained by rest/redistribution TI-201 SPECT, showing decreased anteroseptal perfusion on the early images with almost complete perfusion. Gating myocardial perfusion imaging seems helpful to identify myocardium at risk. It can aid in the evaluation of the physiological significance of mild coronary artery disease, sometimes insufficient to result in perceptible flow disturbances but already responsible for contractility abnormalities, especially when a large arterial territory is involved.

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.

Myocardial viability: methods of assessment and clinical relevance

Myocardial hibernation is hypoperfused dysfunctional myocardium that has the potential to recover function after coronary revascularization. Although recovery of regional function after revascularization is the gold standard for assessing the diagnostic accuracy of various techniques, improvements of EF, symptoms, and survival are fundamental end points. Despite important differences in the markers of viability by positron-emission tomography, single-photon emission tomography, two-dimensional echocardiography, and magnetic resonance imaging, their positive and negative predictive values in nonrandomized studies are fairly comparable. Assessment of myocardial viability may be clinically important in many patients but especially in those with EF < 30% and congestive heart failure. The degree of improvement in EF after coronary revascularization depends on the extent of hibernation, the suitability of coronary structure for revascularization, the lack of perioperative infarction, the completeness of revascularization, and the long-term patency of grafts.

Clinical importance of viability assessment in chronic ischemic heart failure

BACKGROUND AND HYPOTHESIS

Revascularization has provided an effective treatment of depressed left ventricular function in patients with chronically ischemic or "viable" myocardium. Assessment of viable myocardium can be achieved by several noninvasive techniques including dobutamine stress echo or radionuclides such as flurodeoxyglucose (F18DG). F18DG uptake studies are based on the assumption that enhanced glucose uptake in areas of diminished blood flow provides evidence of viable myocardium. To determine the clinical utility of viability assessment in the management of chronic ischemic left ventricular dysfunction, we reviewed the findings and short-term treatment of a series of patients referred for heart failure evaluation who had subsequent F18DG uptake scans.

METHODS

We retrospectively reviewed 59 consecutive F18DG viability studies in a series of patients who had documented coronary artery disease and depressed left ventricular function. Single photon emission computerized tomography (SPECT) with F18DG was performed in the patients and these images were compared to SPECT images of resting myocardial perfusion using thallium, sestamibi, or teboroxime. Clinical decisions based on the results of these scans were obtained from chart review. Thirty-day mortality was determined from chart review or contact with the patient's physician. The patients were divided into those without and with F18DG uptake consistent with viable ischemic myocardium. Further analysis included subgroups of patients who were advised to undergo transplantation, revascularization, or to continue medical therapy.

RESULTS

Of 34 patients referred for cardiac transplantation, 18 had viable myocardium and 13 underwent revascularization. In the entire study group, 34 of 59 (58%) had evidence of viable myocardium and 29 had subsequent revascularization procedures. Thirty-day survival for all revascularization patients was 86%.

CONCLUSION

Assessment of myocardial viability with F18DG SPECT imaging in patients with ischemic left ventricular dysfunction led to a clinical decision for revascularization in approximately half the patients with severe coronary disease and left ventricular dysfunction who were evaluated for myocardial viability in our institution.

Clearance of thallium-201 from the peripheral blood: comparison of immediate and standard thallium-201 reinjection

As several reinjection procedures have shown encouraging results in terms of imaging, we investigated whether the kinetics of thallium-201 would differ between the standard stress-redistribution-reinjection approach and the stress-immediate reinjection approach. In 53 consecutive patients with undiagnosed chest pain, 75 MBq (2 mCi) 201Tl was injected at maximal exercise. In 26 of these patients (group I), 37 MBq (1 mCi) 201Tl was reinjected immediately after completing the exercise images (the immediate reinjection procedure) and in 27 patients (group II), 37 MBq (1 mCi) 201Tl was reinjected after completing 3-h redistribution images (the standard reinjection procedure). Mean peak 201Tl blood activity after exercise was 17.7+/-12.5 kBq/ml (4.8+/-3.4 mCi/ml) for group I versus 16.4+/-9.2 kBq/ml (4.4+/-2.5 mCi/ml) for group II (NS). The relative increase in 201Tl blood activity after reinjection of half the initial dose [37 MBq (1 mCi)] exceeded 50% of the initial peak in both groups. The relative amount of 201Tl delivered to the myocardium was assessed by the area under the curve after both exercise and reinjection, and was 117%+/-72% for group I and 112%+/-73% for group II (NS). Blood clearance of 201Tl was at least biexponential. Mean early decay constants (lambda 1) after exercise and reinjection were 0.30+/-0.18 min-1 and 0.22+/-0.046 min-1 respectively for group I (T 1/2 2.3 min and 3.2 min respectively, NS), and 0.30+/-0.12 min-1 and 0.24+/-0.07 min-1 respectively for group II (T1/2 2.3 min and 2.9 min respectively, NS). For both procedures no significant differences were found between lambda 1 after exercise and lambda 1 after injection. The mean late clearance (lambda 2) from the blood was 0.032+/-0.056 min-1 and 0.012+/-0.012 min-1 respectively for group I (T1/2 21.6 min and 57.7 min respectively, NS), and 0.036+/-0.030 min-1 and 0.014+/-0.014 min-1 respectively for group II (T1/2 19.3 min and 49.5 min respectively, NS). Also, no significant differences were found between lambda 2 after exercise for both groups and between lambda 2 after reinjection for both groups. We conclude that reinjection of 37 MBq (1 mCi) 201Tl (half the initial dose) results in a relative increase in the initial peak and a relative increase in the amount of 201Tl delivered to the myocardium of more than 50% for both the standard and the immediate reinjection procedure. The clearance of 201Tl from the blood was not influenced by exercise or by the time of reinjection. Based on 201Tl kinetics as measured in the peripheral blood, there is no reason to postpone reinjection until 3-4 h following exercise.

Comparative accuracy of various Tl-201 reinjection imaging protocols to detect myocardial viability

The conventional exercise-3 hours-redistribution thallium-201 [201Tl] imaging protocol has been recognized to be suboptimal for reliable detection of myocardial viability. Although 201Tl rest-injection after exercise has improved detection of viable myocardium, it is still underestimated in some patients. The present study was designed to compare detection of viable myocardium in five separate imaging steps: step 1: initial-exercise imaging, step 2: delayed-exercise imaging, step 3: Tl-201 reinjection imaging after delayed-exercise imaging, step 4: separate day rest-injection imaging, and step 5: separate day delayed-rest imaging. The study group consisted of 22 patients scheduled for coronary revascularization (either percutaneous transluminal coronary angioplasty or coronary bypass surgery). Pre- and postintervention echocardiographic wall motion and thickness served as independent markers of myocardial viability.

RESULTS

Accuracy in identifying myocardial viability gradually improved incrementally from 201Tl imaging step 1 to step 5. The positive predictive value, negative predictive value and overall accuracy were best for the separate day delayed-rest study (step 5) at 90%, 33% and 78%, respectively. Myocardial segments had fixed defects on separate day delayed-rest 201Tl imaging (step 5), but nevertheless echocardiographic evidence of myocardial viability indicated less severe defects than segments judged nonviable by echocardiography (p = 0.021). The overall accuracy of separate day delayed-rest imaging (step 5) in predicting viability improved to 88% when segments with moderate or mild defects were considered viable. In conclusion, the most reliable predictor of myocardial viability with 201Tl imaging is defect severity on separate day delayed-rest images.

Identification of hibernating myocardium by dobutamine stress echocardiography: comparison with thallium-201 reinjection imaging

The aim of this study was to determine the diagnostic value of dobutamine stress echocardiography (DSE) in the identification of hibernating myocardium and to compare its predictive accuracy with that of thallium-201 reinjection (RI) imaging. The subjects were 26 patients with wall motion abnormalities related to stenosed coronary arteries. DSE predicted postrevascularization improvement in 31 of 33 segments that were considered to be hibernating and identified 8 of 10 nonhibernating segments. In contrast, thallium-201 scintigraphy predicted all 33 hibernating segments when a post-RI myocardial thallium uptake in ischemic areas of > or = 50% of the maximum count in normal segments was used as a positive marker of myocardial viability. However, thallium studies predicted only 30 of 33 hibernating segments when thallium redistribution (RD) was used as a marker of viability in delayed or RI images. Among the 10 nonhibernating segments, an uptake of < 50% was observed in 4 segments and negative thallium-201 RD was observed in 5 segments. The sensitivity, specificity, and predictive values (PV) of DSE were 94%, 80%, positive PV 94%, and negative PV 80%, respectively. In contrast, the sensitivity, specificity, and PV of thallium-201 RI imaging were 100%, 40%, 85%, and 100% with uptake > or = 50% and 91%, 50% 86%, and 63% with RD, respectively. These results suggest that DSE may be useful for identifying hibernating myocardium and could therefore be helpful in selecting candidates for coronary revascularization.

Comparing a high-dose dipyridamole SPECT imaging protocol with dobutamine and exercise stress testing protocols

OBJECTIVE

To determine the safety, sensitivity, specificity, and accuracy of high-dose dipyridamole compared with treadmill and dobutamine stress imaging protocols.

BACKGROUND

Nuclear imaging studies using standard dose dipyridamole provide similar results to those obtained when treadmill stress is used. Recently dobutamine tomography and planar imaging with high-dose dipyridamole have been shown no improve nuclear imaging results.

METHODS

One hundred fifty-nine patients were imaged with thallium, teboroxime, or sestamibi per standard single photon emission computed tomography (SPECT) protocols. Pharmacologic stress was performed in 85 people with the remainder undergoing exercise testing by Bruce protocol. In this study, 0.852 mg dipyridamole was used per kilogram body weight and was infused over a four-minute period. Results from nuclear imaging were compared with those from coronary arteriograms.

RESULTS

The sensitivity and specificity of high-dose dipyridamole was 100% and 88.9%, respectively, which is statistically greater (P < 0.005) than that achieved when patients were stressed by treadmill. Side effects with the higher dose of dipyridamole were easily reversed with aminophylline. The sensitivity and specificity of intravenous dobutamine was 100%, but it was used in a limited number of subjects. When patients were stressed by Bruce protocol the sensitivity was 92.5% and specificity was 42.8%. The differences were not attributable to inadequate exercise duration.

CONCLUSIONS

High-dose dipyridamole is safe and easily reversed with intravenous aminophylline. The sensitivity and specificity of dipyridamole and dobutamine stress testing were statistically more accurate than results obtained with treadmill protocols when SPECT is used to image the heart. High-dose dipyridamole resulted in greater changes in heart rate and blood pressure response than seen with standard-dose dipyridamole. Associated side effects can be easily reversed with the administration of intravenous aminophylline without significant complications. The sensitivity, specificity, and accuracy of single photon emission computed tomography using high-dose dipyridamole are 100%, 88.9%, and 97.9%, respectively, for the overall presence or absence of disease when compared with coronary arteriography. This is significantly (P < 0.005) greater than that obtained by treadmill nuclear imaging protocols, independent imaging agent.

Residual 201Tl activity in irreversible defects as a marker of myocardial viability. Clinicopathological study

BACKGROUND

The objective of the present study was to characterize the relation between the residual 201Tl activity in irreversible perfusion defects and the extent of irreversible myocardial damage indicated by the volume fraction of myocardial interstitial fibrosis in patients with chronic coronary artery disease.

METHODS AND RESULTS

Stress planar 201Tl scintigraphy with tracer reinjection at rest was performed in 37 patients with > or = 75% stenosis of the left anterior descending coronary artery, and anteroseptal 201Tl activity was quantified by computer-assisted placement of regions of interest from the serial myocardial images. During coronary artery bypass grafting (performed within 6 +/- 3 weeks after scintigraphy), two transmural biopsy specimens were taken from the anterior wall of the left ventricle and the amount of interstitial fibrosis was assessed by use of light microscopic morphometry. A wide spectrum of interstitial fibrosis was obtained, ranging from 15 vol% to 60 vol%. Interstitial fibrosis was similar in patients with reversible (n = 11) or irreversible (n = 15) tracer defects in conventional stress-redistribution images. However, interstitial fibrosis was significantly lower in patients who had enhanced regional 201Tl activity after tracer reinjection compared with those who did not have enhancement of tracer activity after reinjection (28 +/- 8 vol%, n = 7, versus 41 +/- 12 vol%, n = 8; P = .031). The correlation between relative poststenotic 201Tl activity and interstitial fibrosis after tracer reinjection was significantly improved compared with conventional redistribution images (r = -.622 versus r = -.851, n = 15; P < .01).

CONCLUSIONS

The present data demonstrate that the level of regional 201Tl activity in redistribution and, in particular, reinjection images is significantly related to the mass of preserved viable myocytes in poststenotic left ventricular myocardium. Therefore, the residual 201Tl activity provides information about viability within irreversible perfusion defects and may itself serve as marker of myocardial viability.

The hibernating myocardium: implications for management of congestive heart failure

Left ventricular (LV) function is one of the most important determinants of long-term outcome in patients with coronary artery disease (CAD). Patients with normal or near-normal LV function have an excellent prognosis, whereas patients with impaired LV function are at substantial risk of death during medical therapy. It is now apparent that LV dysfunction is not always an irreversible process and that LV function may improve considerably, and even normalize, after myocardial revascularization in a large subset of patients. The identification of such patients with "hibernating" myocardium that is underperfused and dysfunctional, yet viable, has important implications in the selection of patients with LV dysfunction for revascularization procedures. Both nuclear cardiology techniques and 2-D echocardiography can be used for this purpose. The radionuclide techniques include positron emission tomography to assess blood flow and metabolism (using agents such as [18F]fluorodeoxyglucose) and thallium-201 (and possibly technetium-99m sestamibi) to assess blood flow and cell membrane integrity. Alternatively, echocardiographic imaging during low-dose infusions of dobutamine can be used to assess inotropic reserve. The data available to date suggest that patients with CAD in whom hibernating myocardium is largely the cause of impaired LV function constitute a subgroup of patients who may achieve a substantial improvement in LV function and in outcome if identified and treated with revascularization.

Prognostic significance of a fixed thallium defect one to six months after onset of acute myocardial infarction or unstable angina. Multicenter Myocardial Ischemia Research Group

In a large prospective study of myocardial ischemia, exercise thallium studies were performed in 896 patients 1 to 6 months after an acute coronary event (acute myocardial infarction, 70%; unstable angina, 30%). Thallium images were analyzed quantitatively and classified as normal or demonstrating either a reversible defect after 2 to 4 hours or having only a fixed defect. The effect of the thallium findings on the time to end point (cardiac death, nonfatal infarction, or unstable angina) were examined by Kaplan-Meier curves and compared using the log-rank statistic. Follow-up averaged 23 months. The likelihood of cardiac death, nonfatal infarction, and unstable angina was similar in patients who had a normal exercise thallium test result or showed only a fixed defect. Moreover, cardiac events were not related to the size of a fixed defect. In contrast, both cardiac death and nonfatal infarction were increased in patients with the largest areas of reversible defects, although the sensitivity for nonfatal myocardial infarction was suboptimal. The presence of a fixed defect on exercise thallium in patients who are stable an average of 2.6 months after an acute cardiac event is associated with a prognosis similar to that of a normal exercise thallium test.

Noninvasive testing in the diagnosis and management of unstable angina

Patients presenting with a clinical diagnosis of unstable angina comprise a heterogenous population and a wide spectrum of patients with varying degrees of underlying coronary artery disease, severity and prognosis are categorized in this syndrome. A very small number of patients with unstable angina who are refractory to adequate in-hospital medical therapy should undergo urgent coronary angiography and, if suitable, revascularization. The vast majority of patients do, however, stabilize on medical therapy and an invasive approach, such as a coronary angiography should not be performed routinely to all of these patients. Early recognition of clinical and non-invasive test variables indicating an adverse outcome is of paramount importance in unstable angina. This review focuses on the importance of baseline clinical markers and the usefulness of a non-invasive approach with exercise testing, myocardial perfusion imaging, stress echocardiography, and Holter monitoring in the diagnosis, risk stratification, and management of patients with unstable angina.

Comparison of persistent thallium perfusion defects by quantitative washout analysis with thallium reinjection in patients with coronary artery disease

Thallium reinjection can improve the detection of severely ischemic viable myocardium in patients with coronary artery disease. However, a disadvantage of this method is that it requires the acquisition of 3 separate sets of images and the administration of an additional dose of the radiotracer. Alternatively, quantitative analysis of the regional myocardial washout of thallium-201 can be easily obtained from the conventional postexercise and redistribution images without additional imaging time or radiation exposure to the patient. To determine whether this method can predict the results of thallium reinjection, this study analyzed thallium-201 images of 31 patients who had persistent perfusion defects in qualitative exercise/delayed redistribution single-photon emission computed tomographic thallium studies and who underwent thallium reinjection. The quantitative mean radioactive counts of each myocardial segment that had a persistent perfusion defect in the initial and delayed redistribution on 4-hour short-axis tomographic slices were measured to derive a delayed/initial ratio, and these values were compared with the results of thallium reinjection. The delayed/initial ratio was 1.06 +/- 0.22 in 39 segments that improved, versus 0.58 +/- 0.18 in 43 segments without improvement after reinjection (p < 0.001). Thirty-eight of the 39 segments that improved had a ratio of > or = 0.75, versus only 3 of the 43 segments that showed no improvement (sensitivity, 98%; specificity, 91%). The correlation between the delayed/initial ratio and reinjection results was equally high at any segment location or severity. It is concluded that quantitative regional thallium washout analysis predicts the results of thallium reinjection in segments with persistent thallium defects.(ABSTRACT TRUNCATED AT 250 WORDS)

Thallium 201 for detection of viable myocardium: comparison of different reinjection protocols

BACKGROUND

The finding fo false fixed 201Tl defects by the conventional stress-redistribution protocol is a well-known phenomenon. The aim of this study was to compare two different 201Tl reinjection protocols to identify viable myocardium in the same group of patients.

METHODS AND RESULTS

Twenty-seven patients with ischemic heart disease and at least one persistent defect on 201Tl uptake redistribution images 3 hours after stress were investigated. In the same-day protocol (R1) patients were reinjected with 1 mCi 201Tl immediately after redistribution images, with imaging starting 15 minutes later; in the different-day protocol the patients were reinjected with 2 mCi 48 to 96 hours later. Two sets of images were obtained, 30 (R2) and 180 (R3) minutes after reinjection. The comparison of redistribution and reinjection versus stress images showed a significant (p < 0.01) frequency distribution. The uptake of 201Tl of the 111 irreversible segments at redistribution was enhanced in 35.1% with R1, 43.2% with R2, and 49.5% with R3. The agreement among the three procedures in classifying the segmental defects was high between R2 and R3 (r = 0.81) and lower between the same- and different-day protocols. Of the 19 patients with a dominant scar pattern demonstrated by the conventional stress-redistribution study, 37%, 47%, and 53% were judged mainly ischemic after R1, R2, and R3, respectively. All but three of the 55 segments-showing an increased 201Tl uptake by R3 had an echocardiographic score of 2 or greater.

CONCLUSION

The best technique to differentiate scarred from viable myocardium seems to be the reinjection of a second dose of 201Tl on a different day followed by imaging 3 hours later.

Thallium-201 redistribution after early reinjection in patients with severe stress perfusion defects and ventricular dysfunction

Early poststress thallium-201 reinjection to obviate the need for two sets of redistribution images has been proposed as an alternative reinjection protocol although, in a preliminary study, it did not reduce the frequency of late redistribution. The efficacy of the early reinjection protocol was assessed in 102 patients with chronic ischemic heart disease and left ventricular dysfunction who showed severe thallium-201 defects on planar stress images. Thallium-201 was reinjected immediately after the poststress study, and redistribution images were acquired 4 and 24 hours later. By quantitative analysis, a further increase in thallium-201 uptake on 24-hour imaging was documented in only 48 (6%) of 740 segments still abnormal on 4-hour images, 26 (54%) of which were represented by partially reversible or not severe fixed defects. Overall, late thallium-201 uptake was less frequently observed in patients with depressed ejection fraction (p < 0.05). Clinically relevant late reversibility was found in only 3 (3%) of 94 patients. Scans were repeated after revascularization in 20 patients. Tracer uptake improved in 40 (34%) of 118 segments with 4-hour defect: the improvement mainly (85%) involved those segments already showing partial 4-hour reversibility or mild fixed defects on the preoperative study. Thus a negligible late tracer redistribution was found in patients with severe stress thallium-201 defects undergoing early reinjection and 4-hour imaging; no significant 24-hour improvement was observed in those patients with depressed ventricular function and fixed 4-hour defects. This simpler imaging protocol could obviate the need for additional late imaging to detect residual viability.

Myocardial uptake of thallium 201 and technetium 99m-labeled sestamibi after ischemia and reperfusion: comparison by quantitative dual-tracer autoradiography in rabbits

BACKGROUND

Myocardial scintigraphy with 99mTc-labeled sestamibi (99mTc-sestamibi) or 201Tl is used to assess regional perfusion in acute coronary syndromes associated with metabolic or functional abnormalities, such as acute coronary thrombosis with reperfusion and ischemia at rest. However, the initial uptake of these agents may be affected by a recent ischemic insult because the myocardial retention of these tracers depends on cellular metabolism.

METHODS AND RESULTS

Accordingly, 99mTc-sestamibi and 201Tl were injected simultaneously in rabbits after transient brief (10 to 15 minutes, group I) or prolonged (45 to 60 minutes, group II) coronary occlusion. Accumulated subendocardial and subepicardial 99mTc-sestamibi and corresponding 201Tl activity were determined from autoradiographs of 30 microns short-axis slices comounted with serial tissue standards. Circumferential 99mTc-sestamibi and 201Tl activity profiles closely overlapped in both groups. The initial global and segmental myocardial activity per unit blood flow within the ischemic zone did not differ from unity for either tracer regardless of the duration of the ischemic insult. The initial myocardial uptake of both 99mTc-sestamibi and 201Tl after an acute ischemic insult reflected predominantly coronary blood flow, independent of myocardial viability.

CONCLUSIONS

Thus this study supports the use of both 99mTc-sestamibi and 201Tl as perfusion probes in acute coronary syndromes characterized by acute occlusion and reperfusion.

The maze of myocardial perfusion imaging protocols in 1994

A confusing multitude of different myocardial perfusion imaging protocols have been proposed during the last few years. The impetus for this development was new insights in imaging with thallium 201 and the challenge to perform efficient imaging with the newly developed technetium 99m-labeled imaging agents. The practicing nuclear cardiologist is confronted with a true maze of options. This review describes in detail the various protocols, discusses advantages and disadvantages of each, and states, when appropriate, the personal preference of the author.

Value of thallium-201 early reinjection for assessment of myocardial viability

To assess the efficacy of early reinjection for predicting post intervention improvement in thallium-201 (T1) uptake and regional wall motion, we reinjected a small dose of T1 following post-stress imaging and obtained reinjection early images (10 min after early reinjection) and reinjection delayed images (3 hr afterwards) in 40 patients who were referred to us for revascularization (group I). Twenty-nine patients in group I also underwent conventional stress-redistribution T1 scintigraphy (group II). Conventional stress-redistribution T1 scintigraphy was repeated after intervention. Contrast left ventriculography was performed before and after intervention and changes in regional wall motion were assessed in 22 of 40 patients. In group I, the predictive value for improvement and no improvement (the accuracy) of reinjection early images in perfusion was 83%, while that of reinjection delayed images was 91%. Furthermore, the accuracy of reinjection early images in regional wall motion was 80%, while it was 91% for reinjection delayed images. In group II, the accuracy in perfusion was 78% and the value in regional wall motion was 70%. Both accuracy in perfusion and in regional wall motion obtained from reinjection delayed images were significantly higher than the values in group II (p < 0.05). These data suggest that early reinjection is useful for predicting postintervention thallium uptake and regional wall motion.

Myocardial viability in patients with chronic coronary artery disease. Comparison of 99mTc-sestamibi with thallium reinjection and [18F]fluorodeoxyglucose

BACKGROUND

99mTc-sestamibi and thallium imaging have similar accuracy when used for diagnostic purposes, but whether sestamibi provides accurate information regarding myocardial viability in patients with chronic coronary artery disease has not been established. Since there is minimal redistribution of sestamibi over time, it may overestimate nonviable myocardium in patients with left ventricular dysfunction, in whom blood flow may be reduced at rest.

METHODS AND RESULTS

We studied 54 patients with chronic coronary artery disease with a mean ejection fraction of 34 +/- 14%. Patients underwent stress/redistribution/reinjection thallium tomography and, within a mean of 5 days, same-day rest/stress sestamibi imaging using the same exercise protocol and with patients achieving the same exercise duration. Of the 111 reversible thallium defects on either the redistribution or reinjection study, 40 (36%) were determined to be irreversible on the rest/stress sestamibi study, whereas only 3 of 63 irreversible thallium defects despite reinjection (5%) were classified to be reversible by sestamibi imaging. The concordance regarding reversibility of myocardial defects between thallium stress/redistribution/reinjection and same day rest/stress sestamibi studies was 75%. A subgroup of 25 patients also underwent positron emission tomography (PET) studies with 15O-labeled water and [18F]fluorodeoxyglucose (FDG) at rest after an oral glucose load. As in the overall group of 54 patients, there was concordance between thallium and sestamibi imaging regarding defect reversibility in 51 of 73 regions (70%). In the remaining 22 discordant regions (30%), 18 (82%) appeared irreversible by sestamibi imaging but were reversible by thallium imaging. Myocardial viability was confirmed in 17 of 18 regions, as evidenced by normal FDG uptake (10 regions) or FDG/blood flow mismatch (7 regions) on PET. These regions were present in 16 of the 25 patients studied (64%). We then explored methods to improve the sestamibi results. First, when the 18 discordant regions with irreversible sestamibi defects were further analyzed according to the severity of defects, 14 (78%) demonstrated only mild-to-moderate reduction in sestamibi activity (51% to 85% of normal activity), suggestive of predominantly viable myocardium, and the overall concordance between thallium and sestamibi studies increased to 93%. Second, when an additional 4-hour redistribution image was acquired in 18 patients after the injection of sestamibi at rest, 6 of 16 discordant irreversible regions (38%) on the rest/stress sestamibi study became reversible, thereby increasing the concordance between thallium and sestamibi studies to 82%.

CONCLUSIONS

These data indicate that same-day rest/stress sestamibi imaging will incorrectly identify 36% of myocardial regions as being irreversibly impaired and nonviable compared with both thallium redistribution/reinjection and PET. However, the identification of reversible and viable myocardium can be greatly enhanced with sestamibi if an additional redistribution image is acquired after the rest sestamibi injection or if the severity of reduction in sestamibi activity within irreversible defects is considered.

Concordance and discordance between stress-redistribution-reinjection and rest-redistribution thallium imaging for assessing viable myocardium. Comparison with metabolic activity by positron emission tomography

BACKGROUND

Stress thallium scintigraphy provides important diagnostic and prognostic information in patients with coronary artery disease by demonstrating regional myocardial ischemia. However, if the clinical question being addressed is whether a region is viable and not whether there is inducible ischemia, then it may be more reasonable to perform rest-redistribution imaging rather than stress-redistribution imaging followed by either reinjection or late redistribution. Therefore, we determined whether stress-redistribution-reinjection and rest-redistribution imaging provide the same information regarding myocardial viability.

METHODS AND RESULTS

Both stress-redistribution-reinjection and rest-redistribution thallium single photon emission computed tomographic imaging was performed in 41 patients with chronic stable coronary artery disease, with quantitative analysis of regional thallium activity. Thallium reinjection was performed immediately after the 3- to 4-hour redistribution images were completed. Of the 155 myocardial regions with perfusion defects on the stress images, 91 (59%) were irreversible on conventional 3- to 4-hour redistribution images. When the outcomes of these irreversible regions were assessed after reinjection and compared with rest-redistribution images, there was concordance of data regarding myocardial viability (normal/reversible or irreversible) in 72 of the 91 (79%) irreversible defects. Twenty of the 41 patients also underwent positron emission tomography at rest with [18F]fluorodeoxyglucose and [15O]water. In these patients, stress-redistribution-reinjection and rest-redistribution imaging provided concordant information regarding myocardial viability in 427 (72%) of 594 myocardial regions and discordance in 167 regions. However, when irreversible thallium defects were further analyzed according to the severity of the thallium defect in these discordant regions, 149 of 167 (89%) demonstrated only mild-to-moderate reduction in thallium activity (51% to 85% of normal activity), and positron emission tomography verified 98% of these regions to be metabolically active and viable. Thus, when the severity of thallium activity was considered within irreversible thallium defects, the concordance between stress-redistribution-reinjection and rest-redistribution imaging regarding myocardial viability increased to 94%.

CONCLUSIONS

These data indicate that one of two imaging modalities, either stress-redistribution-reinjection or rest-redistribution imaging, may be used for identifying viable myocardium. However, if there are no contraindications to stress testing, stress-redistribution-reinjection imaging provides a more comprehensive assessment of the extent and severity of coronary artery disease by demonstrating regional myocardial ischemia without jeopardizing information on myocardial viability.