Clinical significance of reduced regional myocardial glucose uptake in regions with normal blood flow in patients with chronic coronary artery disease

Clinical significance of quantitative assessment of glucose utilization in patients with ischemic cardiomyopathy

BACKGROUND

The aim of this study was to prospectively quantify the rate of myocardial glucose uptake (MRGlu) in myocardium with different perfusion-metabolism patterns and determine its prognostic value in patients with ischemic cardiomyopathy.

METHODS AND RESULTS

79 patients with ischemic cardiomyopathy were prospectively enrolled for dynamic cardiac FDG PET, and then followed for at least 6 months. Perfusion-metabolism patterns were determined based on visual score analysis of 201Tl SPECT and FDG PET. MRGlu was analyzed using the Patlak kinetic model. The primary end-point was cardiovascular mortality. Significantly higher MRGlu was observed in viable compared with non-viable areas. Negative correlations were found between MRGlu in transmural match and a history of hyperlipidemia, statin usage, and triglyceride levels. Diabetic patients receiving dipeptidyl peptidase-4 inhibitors (DPP4i) had a significantly lower MRGlu in transmural match, mismatch, and reverse mismatch. Patients with MRGlu in transmural match ≥ 23.40 or reverse mismatch ≥ 36.90 had a worse outcome.

CONCLUSIONS

Myocardial glucose utilization was influenced by substrates and medications, including statins and DPP4i. MRGlu could discriminate between viable and non-viable myocardium, and MRGlu in transmural match and reverse mismatch may be prognostic predictors of cardiovascular death in patients with ischemic cardiomyopathy.

Functional and metabolic improvement after coronary intervention for non-viable myocardium detected by 18F fluorodeoxyglucose positron emission tomography

We report a case of a 64-year-old man suspected of myocardial infarction two months previously. Coronary angiography revealed total occlusion of the left anterior descending (LAD), and left ventriculography (LVG) showed remarkably reduced cardiac function and anterior dyskinesis. Electrocardiogram-gated thallium-201 Single Photon Emission Tomography (TL-SPECT) and ¹⁸F fluorodeoxyglucose positron emission tomography (FDG) were performed separately, and revealed large anterior myocardial infarction with markedly reduced tracer uptake, suggestive of non-viable myocardium. Percutaneous coronary intervention (PCI) was performed and stent was implanted successfully. Six months after PCI, LVG showed remarkable recovery in global function. Significant wall motion improvement and recovered glucose metabolism were observed in the infarcted myocardium despite having previously been diagnosed as lacking viability. <Learning Objectives: In patients with left ventricular dysfunction, revascularized myocardium can contribute to improve cardiac function and prognosis. This evidence was established for old, or chronic status of myocardial infarction which is defined as over one month from onset of acute myocardial infarction. In this case report, we suggest that it can be premature to determine myocardial viability using FDG for the patient with under pre-chronic status after myocardial infarction due to underestimation on myocardial FDG uptake.>.

Status of F-18 fluorodeoxyglucose uptake in normal and hibernating myocardium after glucose and insulin loading

Objective

F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) has been increasingly used in myocardial viability imaging. In routine PET viability studies, oral glucose and intravenous insulin loading is commonly utilized. In an optimal study, glucose and insulin loading is expected to cause FDG uptake both in hibernating and normal myocardium. However, in routine studies it is not uncommon to see absent or reduced FDG uptake in normal myocardium. In this retrospective study we further analyzed our PET viability images to evaluate FDG uptake status in myocardium under the oral glucose and intravenous insulin loading protocol that we use in our hospital.

Methods

Patients who had both myocardial perfusion single photon emission computed tomography (SPECT) and FDG PET cardiac viability studies were selected for analysis. FDG uptake status in normal and abnormal myocardial segments on perfusion SPECT was evaluated. Based on SPECT and PET findings, patients were divided into two main groups and four subgroups. Group 1 included PET viable studies and Group 2 included PET-nonviable studies. Subgroups based on FDG uptake in normal myocardium were 1a and 2a (normal uptake) and 1b and 2b (absent or significantly reduced uptake).

Results

Seventy-one patients met the inclusion criteria. Forty-two patients were PET-viable and 29 were PET-nonviable. In 33 of 71 patients (46.4%) there was absent or significantly reduced FDG uptake in one or more normal myocardial segments, which was identified more in PET-viable than PET-nonviable patients (59.5% vs. 27.5%, p = 0.008). This finding was also more frequent in diabetic than nondiabetic patients (53% vs. 31.8%), but the difference was not significant (p = 0.160).

Conclusions

In nearly half of our patients, one or more normal myocardial segments showed absent or significantly reduced FDG uptake. This finding, particularly if it is diffuse, could be from suboptimal study, inadequacy of current glucose and insulin loading protocols, or various other patient-related causes affecting FDG uptake both in the normal and hibernating myocardium. In cases with significantly reduced FDG uptake in normal myocardium, PET images should be interpreted cautiously to prevent false-negative results for viability.

Takotsubo cardiomyopathy systematic review: Pathophysiologic process, clinical presentation and diagnostic approach to Takotsubo cardiomyopathy

Takotsubo cardiomyopathy (TTC) is characterized by transient left ventricular apical ballooning with the absence of coronary occlusion, which typically occurs in older women after emotional or physical stress. The pathophysiology of TTC is not well established, though several possible causes such as catecholamine cardiotoxicity, metabolic disturbance, coronary microvascular impairment and multivessel epicardial coronary artery spasm have been proposed. A number of diagnostic criteria have been suggested in the world and not unified as single, but the most common accepted one is Mayo Clinic proposed criteria. Since the clinical presentation of TTC is usually similar to acute coronary syndrome, differential diagnosis is essential to exclude other diseases and also for its treatment. Imaging modality including echocardiogram, angio CT and cardiac MRI, and lab tests for catecholamine, troponin T, creatine kinase MB and B-type natriuretic peptide can be useful to differentiate TTC from other diseases. Prognosis is generally favorable and in-hospital mortality is from 0% to within 10%.

Altered myocardial glucose utilization and the reverse mismatch pattern on rubidium-82 perfusion/F-18-FDG PET during the sub-acute phase following reperfusion of acute anterior myocardial infarction

BACKGROUND

Reperfused myocardium post-acute myocardial infarction (AMI) may have altered metabolism with implications for therapy response and function recovery. We explored glucose utilization and the "reverse mismatch" (RMM) pattern (decreased F-18-fluorodeoxyglucose (FDG) uptake relative to perfusion) in patients who underwent mechanical reperfusion with percutaneous coronary intervention (PCI) for AMI.

METHODS AND RESULTS

Thirty-one patients with anterior wall AMI treated with acute reperfusion, with left ventricular ejection fraction ≤45%, underwent rest rubidium-82 (Rb-82) and FDG PET 2-10 days post-AMI. Resting echocardiograms were used to assess wall motion abnormalities. Significant RMM occurred in 15 (48%) patients and was associated with a shorter time to PCI of 2.9 hours (2.2, 13.3 hours) compared to patients without significant RMM: 11.4 hours (3.9, 22.4 hours) (P = .03). Within the peri-infarct regions, segments with significant RMM were more likely to have wall motion abnormalities (OR = 2.3 (1.1, 4.7), P = .02) compared to segments without significant RMM.

CONCLUSIONS

RMM is a common pattern on perfusion/FDG PET during the sub-acute phase following reperfusion of AMI and is associated with shorter times to PCI. Within the peri-infarct region, RMM occurs frequently and is more often associated with wall motion abnormalities than segments without RMM. Whether this represents a myocardial metabolic shift during the sub-acute phase of recovery warrants further study.

Transient left ventricular dysfunction syndrome: patho-physiological bases through nuclear medicine imaging

BACKGROUND

Takotsubo cardiomyopathy (TTC) is a novel heart disease, mimicking acute myocardial infarction. The term "transient left ventricular dysfunction syndrome" (TLVDS) seems to be more appropriate since variant forms of TTC sparing apical segments (mid-ventricular ballooning syndrome (MVBS) and inverted TTC) have been described. Patho-physiological bases of TLVDS remain poorly understood and its optimal management is until now empirical. Our aim was to characterize patho-physiological mechanisms of TLVDS by means of nuclear medicine procedures and to discuss the clinical usefulness of isotopic imaging for a non-invasive diagnosis of TLVDS.

METHODS AND RESULTS

During the sub acute phase, eighteen patients with TLVDS (13 TTC and 5 MVBS) underwent myocardial (99m)Tc-tetrofosmin or (201)Thallium Gated Single Photon Emission Computed Tomography (G-SPECT) (n=11), (123)I-mIBG SPECT (n=8) and (18)F-FDG Gated Positron Emission Tomography (G-PET) (n=15), assessing respectively LV perfusion, sympathetic innervation and glucose metabolism. Hypocontractile LV segments were characterized by normal perfusion but reduced uptake of (18)F-FDG and (123)I-mIBG. Topography and extent of metabolic defects and innervation abnormalities were largely overlapping. Follow-up (123)I-mIBG SPECT and (18)F-FDG G-PET were performed in selected patients showing rapid normalization of LV motion and progressive improvement of both glucose metabolism and sympathetic innervation.

DISCUSSION

With the hypothesis of neurogenic stunned myocardium as the central causative mechanism of TLVDS, (123)I-mIBG SPECT seems to be the most specific diagnostic technique. Sympathetic function and glucose metabolism seem to be strictly correlated in the hypocontractile LV segments. Finally, our results underline the role of nuclear imaging in the setting of patho-physiological mechanisms of TLVDS.

Reverse perfusion-metabolism mismatch predicts good prognosis in patients undergoing cardiac resynchronization therapy: a pilot study

BACKGROUND

Cardiac resynchronization therapy (CRT) improves glucose metabolism in the septum of patients with heart failure, so in the present study the predictive value of combined fluorodeoxyglucose (FDG)-positron emission tomography (PET) and metoxy-isobutyl isonitrile (MIBI)-single photon emission computed tomography (SPECT) for the prognosis of patients undergoing CRT was investigated.

METHODS AND RESULTS

Fourteen patients (70.3+/-8.2 years) who underwent FDG-PET and MIBI-SPECT before implantation of a biventricular pacemaker were enrolled. The total number of matches, mismatches, reverse mismatches, summed difference score (SDS: sum total of FDG - MIBI scores) and SDS per segment (%SDS) in each of 5 areas of myocardium (septum, anterior, lateral, inferior area, apex) was calculated and compared between the survival groups (all survival: survival group; survival without ischemic heart disease (IHD): non-IHD survival group) and non-survival group. Both the number of reverse mismatch segments and the %SDS in the septum in the non-IHD survival group were significantly greater than in the non-survival group (3.2+/-1.6 vs 0.5+/-0.6, p<0.05; 0.62+/-0.61 vs -0.11+/-0.19, p<0.05). The receiver-operating characteristics curves for prognosis showed that the area under the curve for the number of reverse mismatch segments in the septum (0.93; confidence interval 0.61-0.98) was significantly greater.

CONCLUSION

A reverse mismatch pattern in the septum can predict a good prognosis for patients treated with CRT.

Positron emission tomography for assessment of viability

PURPOSE OF REVIEW

The recent success of magnetic resonance imaging for viability assessment has raised questions about the future role of positron emission tomography and older imaging modalities in the assessment of viability. Recent information, however, indicates that positron emission tomography will remain a valuable tool.

RECENT FINDINGS

The primary positron emission tomography tracer used for assessment of viability is 18F-fluorodeoxyglucose, a glucose analogue that exhibits enhanced uptake in ischemic tissue. The finding of enhanced 18F-fluorodeoxyglucose uptake and a relative reduction in perfusion is considered the positron emission tomography correlate of myocardial hibernation. The mismatch pattern has been shown to identify patients with improvement in systolic function, heart failure symptoms, and prognosis with revascularization. Mismatch identifies a subset of patients with vulnerable myocardium who have a higher likelihood of a cardiac event compared with those without significant mismatch. Delay in revascularization may pose extra risk for those with mismatch. Positron emission tomography and magnetic resonance imaging demonstrate a close correlation in the detection of viable myocardium. The development of combined positron emission tomography/computed tomography scanners can reduce imaging time and improve functional-anatomic correlations.

SUMMARY

Positron emission tomography imaging utilizing 18F-fluorodeoxyglucose and perfusion tracers provides valuable diagnostic and prognostic information in patients with ischemic left ventricular dysfunction and has comparable accuracy to competing technologies for detection of viability.

Acute impairment of regional myocardial glucose uptake in the apical ballooning (takotsubo) syndrome

BACKGROUND

Apical ballooning syndrome (ABS) is a poorly understood clinical entity characterized by acute, transient systolic dysfunction of the left ventricular (LV) apex in the absence of epicardial coronary artery disease and commonly associated with acute emotional stress. We report abnormal regional myocardial perfusion and glucose uptake in 4 consecutive ABS patients studied using positron emission tomography with 13N-ammonia and 18F-fluorodeoxyglucose within 72 hours of presentation with ABS.

METHODS

All patients were postmenopausal females, 3 of whom had a major recent life stress event. Coronary angiography revealed no or minimal obstructive epicardial coronary artery disease. All patients exhibited reduced glucose uptake in the mid-LV and apical myocardial segments, which was out of proportion to perfusion abnormalities in half of the cases.

CONCLUSION

In all 4 patients, affected regions subsequently recovered regional LV systolic function within 6 weeks.

Acute impairment of regional myocardial glucose uptake in the apical ballooning (takotsubo) syndrome

BACKGROUND

Apical ballooning syndrome (ABS) is a poorly understood clinical entity characterized by acute, transient systolic dysfunction of the left ventricular (LV) apex in the absence of epicardial coronary artery disease and commonly associated with acute emotional stress. We report abnormal regional myocardial perfusion and glucose uptake in 4 consecutive ABS patients studied using positron emission tomography with 13N-ammonia and 18F-fluorodeoxyglucose within 72 hours of presentation with ABS.

METHODS

All patients were postmenopausal females, 3 of whom had a major recent life stress event. Coronary angiography revealed no or minimal obstructive epicardial coronary artery disease. All patients exhibited reduced glucose uptake in the mid-LV and apical myocardial segments, which was out of proportion to perfusion abnormalities in half of the cases.

CONCLUSION

In all 4 patients, affected regions subsequently recovered regional LV systolic function within 6 weeks.

Comparative assessment of18F-fluorodeoxyglucose PET and99mTc-tetrofosmin SPECT for the prediction of functional recovery in patients with reperfused acute myocardial infarction

PURPOSE

Although preserved glucose metabolism is considered to be a marker of myocardial viability in the chronic stage, it has not been fully elucidated whether this is also true with regard to reperfused acute myocardial infarction (AMI). The aim of this study was to compare the diagnostic performance of(99m)Tc-tetrofosmin SPECT and(18)F-fluorodeoxyglucose (FDG) PET for the prediction of functional recovery in reperfused AMI.

METHODS

The study population comprised 28 patients. Both tetrofosmin SPECT and FDG PET were performed in all 28 patients at ca. 2 weeks and in 23 at 6 months. The tetrofosmin and FDG findings in infarct-related segments were compared with the regional wall motion score assessed by left ventriculography over 6 months to determine the predictive value for functional recovery.

RESULTS

Of 120 infarct-related segments, 83 had preserved flow (tetrofosmin uptake >/=50%) and 81 had preserved glucose metabolism (FDG uptake >/=40%). The sensitivity and specificity of tetrofosmin SPECT for the prediction of functional recovery tended to be superior to those of FDG PET (90.0% and 72.5% vs 85.0% and 67.5%, respectively). Thirteen segments with preserved flow and decreased glucose metabolism demonstrated marked recovery of contractile function from 2.5+/-1.0 to 1.4+/-1.4 (p<0.01), with restoration of glucose metabolism at 6 months. In contrast, 11 segments with decreased flow and preserved glucose metabolism demonstrated incomplete functional improvement from 3.0+/-0.8 to 2.2+/-1.2.

CONCLUSION

In the subacute phase, preserved myocardial blood flow is more reliable than glucose metabolism in predicting functional recovery in reperfused myocardium.

Incidence of stunned, hibernating and scarred myocardium in ischaemic cardiomyopathy

PURPOSE

Different criteria to identify residual viability in chronically dysfunctioning myocardium in patients with coronary artery disease (CAD) can be derived by the combined assessment of myocardial blood flow (MBF) and glucose utilisation (MRG) using positron emission tomography (PET). The aim of this study was to evaluate, in a large number of patients, the prevalence of these different patterns by purely quantitative means.

METHODS

One hundred and sixteen consecutive patients with ischaemic cardiomyopathy (LVEF < or =40%) underwent resting 2D echocardiography to assess regional contractile function (16-segment model). PET with 15O-labelled water (H2 15O) and 18F-fluorodeoxyglucose (FDG) was used to quantify MBF and MRG during hyperinsulinaemic euglycaemic clamp. Dysfunctional segments with normal MBF (> or =0.6 ml min(-1) g(-1)) were classified as stunned, and segments with reduced MBF (<0.6 ml min(-1) g(-1)) as hibernating if MRG was > or =0.25 micromol min(-1) g(-1). Segments with reduced MBF and MRG <0.20 micromol min(-1) g(-1) were classified as transmural scars and segments with reduced MBF and MRG between 0.20 and 0.25 micromol min(-1) g(-1) as non-transmural scars.

RESULTS

Eight hundred and thirty-four (46%) segments were dysfunctional. Of these, 601 (72%) were chronically stunned, with 368 (61%) having normal MRG (0.47+/-0.20 micromol min(-1) g(-1)) and 233 (39%) reduced MRG (0.16+/-0.05 micromol min(-1) g(-1)). Seventy-four (9%) segments with reduced MBF had preserved MRG (0.40+/-0.18 micromol min(-1) g(-1)) and were classified as hibernating myocardium. In addition, 15% of segments were classified as transmural and 4% as non-transmural scar. The mean MBF was highest in stunned myocardium (0.95+/-0.32 ml min(-1) g(-1)), intermediate in hibernating myocardium and non-transmural scars (0.47+/-0.09 ml min(-1) g(-1) and 0.48+/-0.08 ml min(-1) g(-1), respectively), and lowest in transmural scars (0.40+/-0.14 ml min(-1) g(-1), P<0.01). MRG was comparable in hibernating and stunned myocardium with preserved MRG (0.40+/-0.19 micromol min(-1) g(-1) vs 0.46+/-0.20 micromol min(-1) g(-1), NS), and lowest in stunned myocardium with reduced MRG and transmural scars.

CONCLUSION

Chronic stunning is more prevalent than expected. The degree of MRG reduction in stunned myocardium may disclose segments at higher risk of permanent damage.

Case Report: Unstable angina with flow-fatty acid metabolism mismatch and reverse flow-glucose metabolism mismatch patterns

A 79-year-old man with unstable angina underwent an emergency coronary angiography, and percutaneous balloon angioplasty was performed for LCX. Left ventriculography showed hypokinesis in the posterior wall, inferior and apical wall immediately after the PCI therapy. The defects on 123I-BMIPP SPECT seen in the inferior, posterior and lateral wall were more extensive than those observed on 99mTc-MIBI SPECT, and a flow-fatty acid metabolism mismatch pattern was observed. The 18F-FDG PET showed reduced uptake in the lateral segment, although 13N-NH3 PET showed normal perfusion, and a reverse flow-glucose metabolism mismatch pattern was observed. Left ventriculography showed significant improve to normal contraction on the 3-month follow up, and there was not significantly reduced uptake in 99mTc-MIBI SPECT, 123I-BMIPP SPECT, 13N-NH3 PET or 18F-FDG PET.

Ischemically compromised myocardium displays different time-courses of functional recovery: correlation with morphological alterations?

OBJECTIVE

It has been demonstrated that positron emission tomography (PET) predicts the functional recovery of viable but ischemically compromised myocardium. Reversible contractile dysfunction after revascularization has been reported for 'hibernating myocardium' and stunned myocardium, however, there are little data concerning the time-course and the extent of improvement of the two different pathophysiological conditions.

METHODS

Twenty-nine patients with advanced coronary artery disease and severely reduced left ventricular function (EF 18--35%) who were referred for isolated coronary artery bypass grafting underwent preoperative PET viability assessment and were functionally assessed by two-dimensional echocardiography preoperatively at 11 days, 14 weeks, and more than 12 months after surgical revascularization. Intraoperative biopsies were taken from dysfunctional areas defined by PET as segments of normal perfusion and normal metabolism (stunned myocardium) and from areas with a 'mismatch' between perfusion and metabolism (hibernating myocardium). The degree of morphological alterations was evaluated by electron microscopy.

RESULTS

In 70% of the 240 dysfunctional segments, 'stunned myocardium' was present whereas 'hibernating myocardium' could be detected in only 24% (P < 0.01). Hibernating myocardium was associated with more severe preoperative wall motion abnormalities and incomplete postoperative recovery. After 1 year, 31% of 'stunned' segments vs. only 18% of 'hibernating' segments showed complete functional restoration (P < 0.05). This incomplete improvement was associated with more severe morphological alterations including depletion of sarcomeres, accumulation of glycogen, loss of sarcoplasmatic reticulum, and cellular sequestration.

CONCLUSIONS

These data indicate that in patients with severe ischemic left ventricular dysfunction 'stunned myocardium' is more prevalent than 'hibernation'. Functional normalization is more frequent in 'stunned' segments, whereas areas of 'hibernation' showed more severe tissue injury and protracted recovery. Different degrees of myocardial injury coexist in most patients, which determines the time-course and the extent of improvement after revascularization.

Time course and extent of improvement of dysfunctioning myocardium in patients with coronary artery disease and severely depressed left ventricular function after revascularization: correlation with positron emission tomographic findings

OBJECTIVES

This study was performed to evaluate the prevalence, time course of recovery and extent of improvement of segments with a positron emission tomographic (PET) flow-metabolism mismatch and match pattern, as well as of PET segments with normal perfusion but with impaired myocardial function.

BACKGROUND

Previous studies have shown that scintigraphic techniques evaluating myocardial viability provide predictive information about the improvement of regional wall motion. However, there are little data concerning the time course and extent of improvement of segments according to preoperative scintigraphic patterns.

METHODS

Twenty-nine patients with ischemic cardiomyopathy (ejection fraction 18% to 35%) underwent preoperative PET viability assessment and were functionally assessed by two-dimensional echocardiography preoperatively and at 11 days, 14 weeks and >12 months after coronary artery bypass graft surgery.

RESULTS

In 168 (70%) of 240 dysfunctional segments, a "normal" scintigraphic pattern was present, whereas a "mismatch" pattern was observed in 24% (p<0.01). Mismatch areas were associated with more severe preoperative wall motion abnormalities and incomplete postoperative recovery. After one year, 31% of normal scintigraphic segments, compared with only 18% of mismatch segments, showed complete functional restoration (p<0.05).

CONCLUSIONS

These data suggest that in patients with severe left ventricular dysfunction, a scintigraphic pattern of normal perfusion and normal metabolism is more prevalent than a flow-metabolism mismatch pattern. Functional recovery is more frequent in normal scintigraphic segments, whereas in mismatch segments, postoperative recovery remains incomplete even after one year.

A reverse flow-metabolism mismatch pattern: a new marker of viable myocardium with greater contractility during dobutamine stress than myocardium with a flow-metabolism mismatch pattern

Few studies have investigated the contractility of myocardium with a reverse flow-metabolism pattern; that is, greater uptake of nitrogen- 13-ammonia (NH3) than fluorine- 18-fluorodeoxyglucose (FDG) on positron emission tomography (PET). This study examined the contraction thickening represented by count increase in ECG-gated FDG-PET of myocardium with a reverse flow-metabolism pattern during low-dose dobutamine stress. Fifty-four patients with myocardial infarction were studied. Relative NH3 and FDG uptake (%NH3, %FDG) and %count increase were measured in 216 apical and 216 lateral segments on ECG-gated FDG-PET. The %count increase during low-dose dobutamine stress was greater in myocardium with a reverse flow-metabolism mismatch pattern than in myocardium with a flow-metabolism mismatch pattern (35.9+/-25.7% vs 24.6+/-15.9%, p=0.0221 in apical segments, and 38.4+/-22.6% vs 27.6+/-18.4%, p=0.0040 in lateral segments) despite smaller %FDG. A reverse flow-metabolism mismatch pattern should be noted as a new marker of viable myocardium with greater contractility during dobutamine stress than myocardium with a flow-metabolism mismatch pattern.

Comparison of dobutamine echocardiography, dobutamine sestamibi, and rest-redistribution thallium-201 single-photon emission computed tomography for determining contractile reserve and myocardial ischemia in ischemic cardiomyopathy

Both dobutamine stress echocardiography (DSE) and myocardial perfusion scintigraphy are used to assess myocardial viability. Few studies have compared the data on myocardial viability and ischemia by low and peak dose DSE and myocardial perfusion imaging in the same patients. Fifty-four patients (45 men and 9 women aged 65 +/- 9 years) with ischemic cardiomyopathy (mean ejection fraction 24 +/- 9%) underwent rest 4-hour redistribution thallium-201 single-photon emission computed tomography (SPECT), low and peak dose DSE, and dobutamine sestamibi SPECT. A total of 864 segments were analyzed (16 segments/patient). Wall motion abnormality was present in 796 segments (92%), and contractile reserve during dobutamine infusion was seen in 400 of these segments (50%). Contractile reserve was seen in 331 of 509 hypokinetic segments (65%) and 69 of 287 akinetic/dyskinetic segments (24%) (p <0.001). Contractile reserve was more frequent in segments with normal thallium uptake (64%), reversible thallium defects (42%), or mild to moderate fixed thallium defects (48%) than severely fixed defects (22%) (p <0.05 each). Concordant information about viability by thallium imaging and DSE was obtained in 62% of segments. Dobutamine sestamibi ischemia was seen in 518 of 796 segments (65%) compared with 265 segments (33%) by DSE (p <0.001). Scintigraphic ischemia was noted in 126 of 195 segments (65%) demonstrating biphasic response, 129 of 205 segments (63%) showing sustained improvement, 42 of 70 segments (60%) deteriorating during dobutamine infusion, and 221 of 326 (68%) demonstrating no change (p = NS). Thus, in patients with ischemic cardiomyopathy, contractile reserve is more frequent in hypokinetic segments than akinetic/dyskinetic segments. The number of segments with normal or near-normal thallium uptake or with scintigraphic ischemia is significantly greater than the number of those capable of increasing contractile function or demonstrating an ischemic response during dobutamine echocardiography.

Thallium scintigraphy compared with 18F-fluorodeoxyglucose positron emission tomography for assessing myocardial viability in patients with moderate versus severe left ventricular dysfunction

Thallium-201 reinjection imaging and positron emission tomography provide concordant information regarding myocardial viability in many patients with coronary artery disease and left ventricular (LV) dysfunction. It is unclear whether this concordance applies to patients with severe, as well as those with moderate, LV dysfunction. We studied 44 patients with chronic coronary artery disease and LV dysfunction, subgrouped on the basis of severity of dysfunction: 23 patients had moderate and 21 had severe dysfunction (ejection fractions 34 +/- 6% and 19 +/- 6%). Patients underwent exercise thallium single-photon emission computed tomography (SPECT) with 3- to 4-hour redistribution and reinjection imaging, as well as positron emission tomography (PET) imaging with 18fluorodeoxyglucose and 15O-water. Data were analyzed quantitatively in aligned transaxial PET and SPECT tomograms. A myocardial region was considered nonviable by PET if 18fluorodeoxyglucose activity was <50% of that in a normal region, associated with proportional reduction in blood flow. Similarly, regions were considered nonviable by thallium if activity was <50% of activity in normal regions on redistribution and reinjection studies. Thallium SPECT and PET data were concordant regarding viability in 98% and 93% of myocardial regions, respectively, in patients with moderate and with severe LV dysfunction. Lower concordance was observed only when regions with severe irreversible thallium perfusion defects on redistribution images were considered in both groups: 86% and 78%, respectively (p <0.01). Thus, thallium SPECT with reinjection yields information regarding regional myocardial viability that is similar to that provided by PET in patients with severe as well as moderate LV dysfunction. However, there is discordance in >20% of regions manifesting severe irreversible thallium defects in patients with severely reduced LV function.

Cardiac positron emission tomography

Positron emission tomography (PET) is an intrinsically quantitative tool that provides a unique and unparalleled approach for clinicians and researchers to interrogate the heart noninvasively. The ability to label substances of physiological interest with positron-emitting radioisotopes has permitted insight into normal blood flow and metabolism and the alterations that occur with disease states. The efficacies of interventional therapies also have been demonstrated with cardiac PET. PET is unequaled in establishing the presence or absence of coronary artery disease (CAD) as well as for assessment of myocardial viability. Using mathematically and physiologically appropriate models, myocardial blood flow, metabolism, and ligand density and flux can be measured noninvasively, providing physicians and researchers with an exceptional window to the heart. Future advances in both instrumentation as well as radiochemistry and image processing will improve our understanding of the heart under normal conditions as well as with disease and should provide therapeutic approaches to enhancing the treatment of patients with heart disease of diverse etiologies.

Relation between contractile reserve and positron emission tomographic patterns of perfusion and glucose utilization in chronic ischemic left ventricular dysfunction: implications for identification of myocardial viability

OBJECTIVES

This study sought to determine the incidence and extent of dobutamine-induced contractile reserve in myocardial regions characterized by classical and new positron emission tomographic (PET) patterns in patients with chronic ischemic left ventricular dysfunction.

BACKGROUND

PET is considered the most accurate method for assessment of myocardial viability, which is traditionally identified by perfusion-metabolism mismatch.

METHODS

In 23 patients, segmental wall thickening expressed by four echocardiographic scores at rest and during low dose (5 and 10 microg/kg body weight per min) dobutamine infusion and regional myocardial uptake of potassium-38 and fluorine-18 fluorodeoxyglucose (F-18 FDG) during glucose clamp were compared in 16 corresponding segments.

RESULTS

Of a total of 368 segments, data analysis focused on 214 (58%) dyssynergic segments at baseline. Contractile reserve was identified with increasing incidence according to the six following PET patterns: 1) diminished perfusion and moderate reduction of F-18 FDG uptake (3 [11%] of 28 segments); 2) proportional reduction of perfusion and F-18 FDG uptake (10 [23%] of 43 segments); 3) perfusion-metabolism mismatch (19 [46%] of 41 segments); 4) preserved perfusion but moderate reduction of F-18 FDG uptake (13 [46%] of 27 segments); 5) preserved perfusion and F-18 FDG uptake (37 [59%] of 63 segments) compared with our normal database; and 6) normal perfusion but absolute increased F-18 FDG uptake (8 [73%] of 11 segments). In the latter category, only 7 of 24 segments had normal rest function. In dyssynergic segments with F-18 FDG uptake > or = 50% supplied by vessels with > or = 75% stenosis, improvement in contractility during dobutamine correlated with the presence of collateral channels.

CONCLUSIONS

Myocardial regions with the traditional mismatch pattern of viability show contractile reserve in slightly < 50%. In segments with moderate reduction of F-18 FDG uptake, the contractile response to dobutamine is linked to the level of rest perfusion. Most segments with preserved perfusion and increased F-18 FDG uptake have impaired rest function, but contractile reserve is still present. These data suggest that in chronic ischemic left ventricular dysfunction, myocardial hibernation is a heterogeneous condition.

Hibernating myocardium has reduced blood flow at rest that increases with low-dose dobutamine

The study of Sun and coworkers is important because (1) it provides additional data that HM has an inotropic and an attenuated coronary vasodilator reserve. They also provided data that support the conclusion that with dobutamine, the improvement of abnormal LV wall motion is real in many patients. (2) It emphasizes the possibility of a deleterious effect (infarction) of dobutamine in HM and thus the need for appropriate caution during its use. (3) It provides additional data that confirm that areas of perfusion-metabolism mismatch on PET imaging (HM) are associated with a reduced MBF at rest. However, their conclusions about areas of LV dysfunction with "normal" MBF in coronary artery disease are problematic; therefore, one must be extremely cautious about these conclusions on the basis of the data that are presented.

Assessment of myocardial viability in patients with chronic coronary artery disease. Rest-4-hour-24-hour 201Tl tomography versus dobutamine echocardiography

BACKGROUND

To date, late redistribution after resting 201Tl injection has not been evaluated. In addition, the concordance between resting 201Tl imaging and dobutamine echocardiography in identifying viable myocardium has not been assessed.

METHODS AND RESULTS

Forty patients with coronary artery disease underwent rest-4-hour-24-hour 201Tl tomography and dobutamine echocardiography (5 to 10 micrograms.kg-1.min-1). Late redistribution occurred in 46 (21%) of 219 persistent defects at 4 hours. Systolic function and contractile reserve were similar among persistent defects at 4 hours with and without late redistribution. Contractile reserve was more frequent in segments with normal 201Tl uptake (59%), completely reversible defects (53%), or mild to moderate defects at 4 hours (56%) compared with severe defects (14%; P < .02 versus all). Of 105 hypokinetic segments, 99 (94%) were viable by 201Tl, and 88 (84%) showed contractile reserve. In contrast, of 155 akinetic segments, 119 (77%) were viable by 201Tl, but only 34 (22%) had contractile reserve. Concordance between 201Tl and dobutamine was 82% in hypokinetic segments but 43% in akinetic segments. In 109 revascularized segments, positive accuracy for functional recovery was 72% for 201Tl and 92% for dobutamine, whereas negative accuracy was 100% and 65%, respectively. Sensitivity was 100% for 201Tl and 79% for dobutamine.

CONCLUSIONS

Late redistribution occurs in one fifth of persistent defects at 4 hours, and it does not correlate to systolic function or contractile reserve. Dobutamine and 201Tl yield concordant information in the majority of hypokinetic segments, whereas concordance is low in akinetic segments. Dobutamine demonstrates higher positive accuracy and sensitivity in predicting recovery of dysfunctional myocardium, whereas 201Tl shows higher negative predictive accuracy but reduced positive accuracy.

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.

Pathophysiology of chronic left ventricular dysfunction. New insights from the measurement of absolute myocardial blood flow and glucose utilization

BACKGROUND

Chronically dysfunctional myocardium may improve after coronary revascularization. This condition was thought to be due to a chronically reduced myocardial blood flow (MBF). Recently, however, it has been shown that in patients without previous infarction but with chronic left ventricular dysfunction, baseline MBF was normal.

METHODS AND RESULTS

To study the pathophysiology of chronic left ventricular dysfunction in patients with previous infarction, regional MBF (milliliter per minute per gram of water-perfusable tissue) and glucose utilization (MRG; micromoles per minute per gram) during hyperinsulinemic euglycemic clamp were measured with positron emission tomography in 30 patients before bypass. At baseline, 133 myocardial segments were normal, and 107 were dysfunctional. After revascularization, 59 of 107 segments improved, while 48 of 107 were unchanged. MBF was 0.92 +/- 0.25 mL.min-1.g-1 in normal segments, 0.87 +/- 0.31 mL.min-1.g-1 in improved segments (P = NS versus normal), and 0.82 +/- 0.40 mL.min-1.g-1 in unchanged segments (P < .05 versus normal). In 90% of the dysfunctional segments, MBF was > 0.42 mL.min-1.g-1, a cutoff value corresponding to the mean MBF minus 2 SD in normal segments. The MRG was 0.71 +/- 0.14 mumol.min-1.g-1 in 9 age-matched normal subjects, 0.45 +/- 0.19 mumol.min-1.g-1 (P < .01) in normal segments, 0.44 +/- 0.14 mumol.min-1.g-1 in improved segments (P = NS versus normal), and 0.34 +/- 0.17 mumol.min-1.g-1 in unchanged segments (P < .01 versus normal and improved).

CONCLUSIONS

The results suggest that resting MBF measured with 15O-labeled water in chronically dysfunctional segments is not reduced and that the myocardium of these patients is less sensitive to insulin than that of normal subjects.

Dobutamine echocardiography predicts improvement of hypoperfused dysfunctional myocardium after revascularization in patients with coronary artery disease

BACKGROUND

In patients with coronary artery disease, dysfunctional hypoperfused myocardium at rest may represent either necrotic or viable hibernating myocardium. The accuracy of inotropic stimulation in identifying hypoperfused, reversibly dysfunctional myocardium has not been extensively investigated.

METHODS AND RESULTS

Eighteen patients with stable chronic coronary artery disease underwent, while off drugs, quantitative 201Tl single-photon emission computed tomography after rest injection (2 to 3 mCi), two-dimensional echocardiography at rest and during dobutamine (5 to 10 micrograms/kg per minute i.v.), and radionuclide angiography. Single-photon emission computed tomography and echocardiography at rest were repeated 34 +/- 10 days after coronary revascularization, and radionuclide angiography was repeated 45 +/- 13 days after revascularization. Resting hypoperfusion was defined as 201Tl uptake < 80% of maximal activity. Systolic function was scored from 1 (normal) to 4 (dyskinesia), and functional improvement was defined as a score change > 1 grade. Of 79 dysfunctional hypoperfused segments, 48 (61%) improved function after revascularization. In 42 (88%) of these latter segments, function had improved during dobutamine. Conversely, systolic function after revascularization did not improve in 31 segments, and in 27 (87%), it had not improved during dobutamine. Functional improvement after revascularization was observed in 42 (91%) of 46 segments manifesting an improvement during dobutamine as opposed to 6 (18%) of 33 segments that did not improve during dobutamine. Resting 201Tl uptake (% of maximal activity) before revascularization (65 +/- 9%) significantly increased at follow-up in segments where function improved (70 +/- 12%, P < .005), whereas it did not change significantly in segments with unchanged systolic function after revascularization (from 57 +/- 13% to 60 +/- 17%, P = NS). In 10 patients with prerevascularization ejection fraction < 45%, left ventricular ejection fraction significantly increased from 36 +/- 7% before revascularization to 42 +/- 7% at follow-up (P < .05).

CONCLUSIONS

Inotropic stimulation using dobutamine echocardiography identifies hypoperfused reversibly dysfunctional myocardium. Functional improvement during dobutamine is highly predictive of improvement after revascularization.