Histological alterations in chronically hypoperfused myocardium. Correlation with PET findings

Heat shock protein upregulation protects against pacing-induced myolysis in HL-1 atrial myocytes and in human atrial fibrillation

Atrial fibrillation (AF) causes myocyte stress by inducing structural changes, predominantly myolysis, which is related to the progression of AF. As heat shock proteins (Hsp) protect against cellular stress, their efficacy in preventing myolysis was investigated in a tachy-paced cell model for AF and in patients with AF. HL-1 atrial myocytes were subjected to tachy-pacing, which induced myolysis. Hsp overexpression was accomplished by a mild heat shock or by the drug geranylgeranylacetone (GGA). Hsp-gene-transfection studies were carried out to investigate roles of individual Hsp. In left and/or right atrial appendages from patients with paroxysmal (n=14), persistent (n=17) AF and controls (n=13) in sinus rhythm (SR), Hsp levels (Westerns) and localization (confocal microscopy) were determined. Heat shock and GGA administered prior to tachy-pacing resulted in almost complete protection against tachy-pacing-induced myolysis. Overexpression of Hsp27, but not of Hsp70, also provided complete protection against pacing-induced myolysis. In patients with paroxysmal AF, Hsp27 expression was significantly increased compared to SR and persistent AF. No changes in Hsp40, Hsc70, Hsp70 and Hsp90 expression levels were observed. Hsp27 levels correlated inversely with the duration of paroxysmal and persistent AF and the extent of myolysis. Furthermore, Hsp27 was localized on myofibrils in tachy-paced HL-1 myocytes and in human cardiomyocytes. These data demonstrate that upregulation of Hsp, especially Hsp27, protects tachy-paced atrial myocytes from myolysis. Therefore, the observed elevated Hsp27 expression in patients with paroxysmal AF might serve to protect myocytes from myolysis and limit the progression to persistent AF. Pharmacological induction of Hsp, with drugs such as GGA, may represent a novel therapeutic approach in AF.

Relationship between atrial histopathology and atrial fibrillation after coronary bypass surgery

BACKGROUND

Postoperative atrial fibrillation is common after coronary surgery. The cellular condition of atrial myocytes might play a part in the postoperative development of atrial fibrillation. Our study aimed to investigate whether patients in whom postoperative atrial fibrillation develops show pre-existent alterations in histopathology of the right atrium and how such changes are expressed in relation to the use of cardiopulmonary bypass.

METHODS

Seventy patients undergoing elective coronary revascularization were prospectively randomized to on-pump conventional surgery (conventional coronary artery bypass grafting, n = 35) or off-pump surgery on the beating heart (off-pump coronary artery bypass grafting, n = 35). Samples from the right atrial appendage were immediately collected after opening the pericardium. In the on-pump group samples were also taken after weaning from cardiopulmonary bypass. Focusing on degenerative alterations, histology was studied by means of light microscopy and for confirmation of particular findings by means of electronic microscopy.

RESULTS

Twenty-two (31%) patients had postoperative atrial fibrillation, with the rate not being different between the off-pump coronary artery bypass grafting and conventional coronary artery bypass grafting groups (P = .797). Left atrial enlargement and inotropic requirement were related to atrial fibrillation. Interstitial fibrosis, vacuolization, and nuclear derangement of myocytes were the histologic abnormalities associated with the development of postoperative atrial fibrillation. However, in multivariate analysis fibrosis was confounded by myocyte vacuolization (P = .002) and nuclear derangement (P = .016), representing independent atrial fibrillation predictors. As expected, the conventional coronary artery bypass grafting and off-pump coronary artery bypass grafting groups showed similar histology, but more importantly, no atrial changes were detected in relation to cardiopulmonary bypass exposure in the conventional coronary artery bypass grafting group. Atrial histology showed degenerative changes that correlated with advanced age and left atrial enlargement.

CONCLUSIONS

Our study supports the contention that atrial fibrillation after coronary surgery is associated with pre-existing histopathologic changes of the right atrium. Patients randomly allocated to off-pump coronary artery bypass grafting procedures showed a similar rate of atrial fibrillation and a similar relationship to atrial histology as did those exposed to cardiopulmonary bypass. Cardiopulmonary bypass did not cause additional changes in tested histology variables.

Imaging techniques in nuclear cardiology for the assessment of myocardial viability

The assessment of myocardial viability has become an important aspect of the diagnostic and prognostic work-up of patients with ischemic cardiomyopathy. Although revascularization may be considered in patients with sufficient viable myocardium, patients with predominantly scar tissue should be treated medically. Patients with left ventricular dysfunction who have viable myocardium are the patients at highest risk because of the potential for ischemia but at the same time benefit most from revascularization. It is important to identify viable myocardium in these patients, and radionuclide myocardial scintigraphy is an excellent tool for this. Single-photon emission computed tomography perfusion scintigraphy (SPECT), whether using (201)thallium, (99m)Tc-sestamibi, or (99m)Tc-tetrofosmin, in stress and/or rest protocols, has consistently been shown to be an effective modality for identifying myocardial viability and guiding appropriate management. Metabolic and perfusion imaging with positron emission tomography (PET) radiotracers frequently adds additional information and is a powerful tool for predicting which patients will have an improved outcome from revascularization. New techniques in the nuclear cardiology field, like attenuation corrected SPECT, dual isotope simultaneous acquisition (DISA) SPECT and gated FDG PET are promising and will further improve the detection of myocardial viability. Also the combination of multislice computed tomography scanners with PET opens possibilities of adding coronary calcium scoring and non-invasive coronary angiography to myocardial perfusion imaging and quantification. Evaluation of the clinical role of these creative new possibilities warrants investigation.

Role of F-18 FDG positron emission tomography (PET) in the assessment of myocardial viability

Positron emission tomography (PET) is a functional imaging technique with important clinical applications in cardiology, oncology, and neurology. In cardiac imaging, its role has been extensively evaluated in the noninvasive diagnosis of coronary artery disease and in the determination of prognosis. Additionally, cardiac PET with F-18 fluorodeoxyglucose (FDG) is very helpful in selection of patients with coronary artery disease and left ventricular dysfunction who would benefit from coronary artery revascularization. Cardiac PET is arguably considered by many as a gold standard in this particular application. F-18, unlike other positron emitters, has a reasonably long physical half-life, which permits its distribution through commercial radiopharmacies. This is further facilitated by increasing popularity of FDG PET in oncology, which makes cardiac FDG PET a practical option for hospitals and outpatient centers equipped with PET scanners. In addition, gamma camera single photon emission computed tomography (SPECT) systems, routinely used in nuclear medicine departments, can be equipped with coincidence circuit or high-energy 511 KeV collimators, providing a cost-effective means of FDG cardiac imaging. Myocardial utilization of glucose as a substrate is variable, depending, among other factors, on serum levels of glucose and insulin. Therefore, patient preparation is important in obtaining good-quality images and in turn allowing for accurate interpretation of myocardial viability. There are various protocols to choose from that provide diagnostic image quality in both diabetic and nondiabetic patients. Mismatch between blood flow and FDG metabolism, an indicator of viable, jeopardized myocardium, can predict postrevascularization improvement in left ventricular function, symptomatic relief, and long-term survival.

The influence of myocardial blood flow and volume of distribution on late Gd-DTPA kinetics in ischemic heart failure

PURPOSE

To determine the mechanism of enhancement of contrast-enhanced MRI (ceMRI) in chronic ischemic myocardium. While ceMRI can identify scar tissue in chronic ischemic myocardium, the mechanism of enhancement is not completely understood.

MATERIALS AND METHODS

A total of 11 patients with ischemic heart failure (ejection fraction [EF] 28 +/- 9%) were imaged with ceMRI and positron emission tomography (PET) to measure myocardial blood flow (MBF). Longitudinal relaxation rate (T1) of blood, normal tissue, and scar tissue defined by ceMRI was determined before and two to 50 minutes after contrast (Look Locker technique), and the partition coefficient (lambda) and volume of distribution (VD) were calculated.

RESULTS

In scar and viable tissue, T1 was significantly different over the whole period after contrast, but not before contrast. However, T1 of scar and blood were similar five to 15 minutes post contrast, making the detection of subendocardial defects difficult. lambda reached an initial steady state in viable tissue, but was delayed (20 minutes) in scar tissue. VD in scar was double that of viable tissue (0.54 +/- 0.01 vs. 0.29 +/- 0.02, respectively) indicating an increased interstitial space. Contrast wash-in kinetics correlated moderately with MBF (r = -0.36), but well with the combination of MBF and VD (r = 0.59).

CONCLUSION

Late myocardial contrast kinetics depend on both MBF and VD; however the increased VD seems to be the main mechanism for the late enhancement effect.

Assessment of Myocardial Viability with Dobutamine Stress Echocardiography in Patients with Ischemic Left Ventricular Dysfunction

The noninvasive assessment of myocardial viability has proved clinically useful for distinguishing hibernating and/or stunned myocardium from irreversibly injured myocardium in patients with chronic ischemic heart disease or recent myocardial infarction, with marked regional and/or global left ventricular (LV) dysfunction. Noninvasive techniques utilized for the detection of viability in asynergic myocardial regions include positron emission tomographic imaging of residual metabolic activity, single photon emission tomography (SPECT) of radioisotope uptake with thallium-201, low-dose dobutamine echocardiography assessment of inotropic reserve and myocardial contrast echocardiography for evaluation of microvascular integrity. Of these techniques, dobutamine stress echocardiography is a safe, widely available and relatively inexpensive modality for the identification of myocardial viability for risk stratification and prognosis. Low-dose dobutamine response can accurately predict improvement of dysfunctional yet viable myocardial regions, and thus identify a subset of patients whose LV function will improve following successful coronary revascularization.

Impaired mitochondrial response to simulated ischemic injury as a predictor of the development of atrial fibrillation after cardiac surgery: In vitro study in human myocardium

OBJECTIVE

Atrial fibrillation occurs in 20% to 40% of patients after cardiac surgery, but its pathophysiology remains unclear. Recent studies demonstrated preexisting histologic markers that portend the development of postoperative atrial fibrillation. In this prospective study, we focused on mitochondrial dysfunction in response to ischemic stress as a potential predictor for postoperative atrial fibrillation.

METHODS

Slices of right atrial trabeculae from 50 patients undergoing elective cardiac surgery were surperfused with oxygenated glucose-containing phosphate-buffered saline solution. After 30 minutes of stabilization, the sections were exposed to 90 minutes of simulated ischemia (nitrogenated phosphate-buffered saline solution without glucose) followed by 90 minutes of reoxygenation (reintroduction of the oxygenated solution). Mitochondrial viability and response were measured by staining with 3-[4.5 dimethylthiazol 2-yl]-2,5-diphenyltetrazolium bromide. The magnitudes of mitochondrial recovery after simulated ischemia and 28 possible risk factors for postoperative atrial fibrillation were entered into univariate and multivariate models.

RESULTS

There were no deaths in this group of patients. Nineteen patients (38%) had postoperative atrial fibrillation. Interestingly, no difference in baseline (before simulated ischemia) mitochondrial function was documented between patients who had postoperative atrial fibrillation and those who did not. An independent predictor for postoperative atrial fibrillation was the degree of mitochondrial dysfunction in response to simulated ischemia, as measured by the intensity of the staining.

CONCLUSION

This study has identified for the first time an association between mitochondrial dysfunction in response to ischemia and postoperative atrial fibrillation. This finding improves our understanding of the pathophysiology of postoperative atrial fibrillation and may eventually lead us to identify candidates for selective preoperative or early postoperative prophylactic treatment.

Functional and clinical repercussions of myocyte apoptosis in the multifaceted damage by ischemia/reperfusion injury: old and new concepts after 10 years of contributions

Ten years ago, the first finding of apoptotic cell death on the 'crime scene' of cardiac ischemia/reperfusion injury profoundly dismayed the scientific community. This observation jarred with the deeply rooted conviction that cardiac myocytes stoically 'break, but do not bend' in the fight against ischemia, instead of spontaneously accepting a peaceful demise for the greater good. Ten years later, a number of studies not only proved right the coexistence of necrosis and apoptosis on the ischemic battle field, but also implicated myocyte apoptosis in the pathogenesis of all the shapes and shades that cardiac ischemic injury can take on.

Myocardial hibernation: a delicate balance

The pathophysiology of myocardial hibernation is characterized as a situation of reduced regional contractile function distal to a coronary artery stenosis that recovers after removal of the coronary stenosis. A subacute "downregulation" of contractile function in response to reduced regional myocardial blood flow exists, which normalizes regional energy and substrate metabolism but does not persist for more than 12-24 h. Chronic hibernation develops in response to one or more episodes of myocardial ischemia-reperfusion, possibly progressing from repetitive stunning with normal blood flow to hibernation with reduced blood flow. An upregulation of a protective gene program is seen in hibernating myocardium, putting it into the context of preconditioning. The morphology of hibernating myocardium is characterized by both adaptive and degenerative features.

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.

Extent of myocardial scarring on nonstress delayed-contrast-enhancement cardiac magnetic resonance imaging correlates directly with degrees of resting regional dysfunction in chronic ischemic heart disease

BACKGROUND

Hyper-enhancement on delayed-enhancement magnetic resonance imaging (DE-MRI) is a marker of irreversible myocardial injury. Both reversible and irreversible ischemically injured regions of myocardium develop reductions in systolic function compared with unaffected regions. This study evaluated whether there is a relationship between myocardial hyper-enhancement from remote scarring on DE-MRI and the degree of myocardial circumferential shortening (%CS) as determined with dynamic MRI tissue tagging (TAG-MRI) in the setting of chronic ischemic heart disease (CIHD).

METHODS

Thirty-five patients with CIHD and 8 control patients underwent nonstress, resting DE-MRI and TAG-MRI. A total of 168 CIHD and 96 control segments from the basal- and middle-thirds of the left ventricle (LV) were selected to achieve a balanced test set. With a 16-segment model, segmental myocardial scarring was graded on the basis of the amount of hyper-enhancement on DE-MRI. With TAG-MRI images, segmental %CS was calculated.

RESULTS

Patients with CIHD had lower LV ejection fraction compared with the control patients (28% vs 67%). The %CS of normal segments was notably different from %CS of CIHD segments, regardless of the presence or absence of myocardial hyper-enhancement on DE-MRI. Among the CIHD segments, however, %CS correlated inversely with the amount of myocardial hyper-enhancement from scarring (P <.0001, r = -0.38).

CONCLUSIONS

On cardiac MRI for CIHD, myocardial hyper-enhancement correlates inversely with %CS, supporting the direct relationship between the amount of remote myocardial scarring determined with nonstress DE-MRI and baseline resting functional impairment.

Ultrastructural evidence of increased tolerance of hibernating myocardium to cardioplegic ischemia-reperfusion injury

OBJECTIVES

The goal of this study was to investigate the effects of ischemia-reperfusion on myocardial ultrastructure in patients with and without hibernating myocardium.

BACKGROUND

It is generally accepted that chronically dysfunctional, hibernating myocardium may remain nonetheless viable for a long time. It has been postulated that hibernating myocytes may survive, despite being subtended by a severe coronary artery stenosis, as they might be less susceptible to ischemic insults. However, whether hibernating myocardium is indeed more resistant to ischemia has never been investigated.

METHODS

Myocardial biopsies were taken before cardiac arrest and after reperfusion from the anterior wall of the left ventricle in patients undergoing coronary artery bypass surgery, divided according to presence (n = 7) or absence (n = 7) of hibernating myocardium. Ultrastructural changes were studied by electron microscopy. Because ischemia-reperfusion injury is related to oxidative stress, we also evaluated coronary sinus concentration of the antioxidants alpha-tocopherol, beta-carotene, and ubiquinol, and of lipid peroxidation products pre-ischemia and after reperfusion.

RESULTS

Both groups were similar with respect to length of ischemia and changes in the various indexes of oxidative stress. In normally contracting myocardium, ischemia/reperfusion induced moderate overall ultrastructural changes, and marked alterations at the mitochondrial level. In contrast, post-reperfusion biopsies of hibernating myocardium displayed only minor overall ultrastructural changes, and scored significantly better on mitochondrial damage.

CONCLUSIONS

Despite similar severity of ischemia/reperfusion, hibernating myocardium showed significantly less ultrastructural evidence of cell injury compared with normally contracting myocardium. These data indicate that human hibernating myocardium is intrinsically more resistant to ischemia/reperfusion injury.

Relation between left ventricular contractile reserve during low dose dobutamine echocardiography and plasma concentrations of natriuretic peptides

BACKGROUND

In ischaemic cardiomyopathy, raised plasma concentrations of natriuretic peptides are associated with a poor long term prognosis, while the presence of contractile reserve is a favourable sign.

OBJECTIVE

To assess the relation between plasma natriuretic peptides and contractile reserve.

DESIGN

Prospective observational study.

SETTING

Tertiary referral centre.

PATIENTS

66 consecutive patients undergoing low dose dobutamine stress echocardiography to evaluate contractile reserve in regions with contractile dysfunction at rest, divided into two groups: group 1, 31 patients with ischaemic cardiomyopathy (left ventricular ejection fraction < or = 40%) and heart failure symptoms; group 2, 35 patients with normal left ventricular function.

MAIN OUTCOME MEASURES

Plasma atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), measured using immunoradiometric assays. Contractile reserve was defined as an improvement in segmental wall motion score during infusion of low dose dobutamine.

RESULTS

Plasma ANP and BNP concentrations were higher in group 1 than in group 2 (mean (SD): ANP, 17.8 (32.8) v 7.2 (9.7), p < 0.005; BNP, 24.4 (69.0) v 5.0 (14.3) pmol/l, respectively; p < 0.001). In group 1, the presence of contractile reserve was inversely related to ANP and BNP levels; however, patients with contractile reserve had lower ANP and BNP concentrations than patients without contractile reserve (ANP, 14.2 (9.1) v 24.2 (44.2), p < 0.05; BNP, 20.2 (25.5) v 37.5 (93.8) pmol/l, respectively; p < 0.05).

CONCLUSIONS

Plasma natriuretic peptide concentrations are raised in patients with left ventricular dysfunction, but in the presence of preserved myocardial contractile reserve, relatively low levels of ANP and BNP are present.

Myocardial positron emission computed tomographic images obtained with fluorine-18 fluoro-2-deoxyglucose predict the response of idiopathic dilated cardiomyopathy patients to beta-blockers

OBJECTIVES

The aim of this study was to elucidate whether the response of idiopathic dilated cardiomyopathy (DCM) patients to beta-blockers can be predicted by positron emission tomography with fluorine-18 fluoro-2-deoxyglucose (FDG-PET).

BACKGROUND

Patients with DCM often have a poor prognosis, and it is important to predict their response to beta-blocker therapy, which may be effective in DCM. However, no accurate methods of predicting their response have been available.

METHOD

In 22 DCM patients with reduced left ventricular (LV) systolic function, FDG-PET was performed. Uptake in the LV after glucose loading was evaluated based on the average global percent uptake of the injected dose (G%ID) and the coefficient of variance (CV) in 24 segments of the LV. Uptake during fasting was evaluated semiquantitatively on the basis of the total uptake score. The beta-blocker was administered, and LV function was monitored by echocardiography. The histologic findings were assessed in the 18 patients who underwent endomyocardial biopsy.

RESULTS

The beta-blocker was effective in the majority of patients whose G%ID after glucose loading was >0.7%, and the sensitivity and specificity of G%ID as a predictor of beta-blocker efficacy were 83.3% and 90.0%, respectively. Percent CV did not predict efficacy. Four groups, defined on the basis of the FDG uptake score during fasting and G%ID after glucose loading, had distinctive histologic findings and outcomes.

CONCLUSIONS

It has been shown that FDG-PET is a good predictor for the effectiveness of beta-blockers.

Baseline/post-nitrate Tc-99m tetrofosmin mismatch for the assessment of myocardial viability in patients with severe left ventricular dysfunction: comparison with baseline Tc-99m tetrofosmin scintigraphy/FDG PET imaging

BACKGROUND

Positron emission tomography (PET) flow/metabolic mismatch is considered the nuclear medicine gold standard for the assessment of myocardial viability. The aim of this study was to investigate whether baseline/nitrate technetium 99m tetrofosmin single photon emission computed tomography (SPECT) mismatch may provide equivalent clinical information.

METHODS AND RESULTS

We studied 23 patients (aged 62 +/- 10 years, 19 men) with previous myocardial infarction (16 anterior, 4 inferior, and 3 anterior plus inferior) and postischemic heart failure (gated SPECT [G-SPECT] ejection fraction, 26% +/- 8%). All patients underwent Tc-99m tetrofosmin G-SPECT at rest and after nitrates (intravenous isosorbide dinitrate, 0.2 mg/mL, 10 mL/h) as well as a fluorine 18 fluoro-2-deoxy-d-glucose (FDG) PET scan. Regional wall motion analysis was performed with quantitative G-SPECT (QGS). Myocardial dysfunction was defined as a regional QGS score of 2 or greater. Regional perfusion was assessed by quantitative perfusion score (QPS) providing percent Tc-99m tetrofosmin uptake in a 20-segment model. Semiquantitative analysis of FDG uptake was performed by use of polar maps generated by Siemens ECAT HR + software. In areas with a perfusion rate lower than 80%, PET viability was identified by a normalized FDG percent uptake/baseline Tc-99m tetrofosmin percent uptake ratio greater than 1.2. We analyzed 460 segments; 298 (64%) were dysfunctional by QGS analysis. Of these, 170 were viable by PET imaging whereas 128 were nonviable. Regional Tc-99m tetrofosmin uptake was higher in viable than in nonviable segments both at rest (60% +/- 24% vs 42% +/- 12%, P <.01) and after nitrates (67% +/- 20% vs 41% +/- 18%, P <.01). According to receiver operating characteristic curve analysis, a cutoff value of 63% for resting as well as post-nitrate G-SPECT provided the highest diagnostic accuracy for the detection of myocardial viability (67% and 72% at rest and after nitrates, respectively). When the same algorithm used for the comparison with PET (normalized nitrate percent uptake/baseline percent uptake) was applied to G-SPECT, we obtained the highest agreement with PET (accuracy, 93%; sensitivity, 95%; specificity, 92%).

CONCLUSIONS

In patients with severe left ventricular dysfunction, perfusion data alone, both at rest and after nitrates, do not allow an accurate estimate of myocardial viability. In dysfunctioning segments, the analysis of rest/post-nitrate Tc-99m tetrofosmin mismatch provides results similar to those obtained by PET flow/metabolic mismatch.

Late post-repair ventricular function in patients with origin of the left main coronary artery from the pulmonary trunk

This study investigated ventricular function in postoperative patients with abnormal origin of the the left main coronary artery from the pulmonary trunk using ultrasound-based deformation imaging. Although radial left ventricular deformation parameters were completely normalized, longitudinal deformation remained abnormal.

Coronary revascularization in ischemic cardiomyopathy

This article first discusses coronary artery disease, including left-ventricular dysfunction, hibernating myocardium, the relationship between stunning, hibernation, and heart failure, and molecular mechanisms underlying myocardial hibernation. Left ventricular function and the prognosis and pathophysiology of left-ventricular dysfunction are then examined. Selection of patients for revascularization is discussed, to include which coronary patients should be investigated for myocardial viability, and other surgical considerations are outlined. The outcome following revascularization in the heart failure patient, the results of revascularization, and the time course of functional recovery after coronary artery bypass graft are also covered.

Changes in the response of hibernated myocardium to inotropic stimulation after angioplasty: a Doppler myocardial imaging study

BACKGROUND

Angioplasty of an infarct related artery (IRA) performed several weeks or months after myocardial infarction (MI) may improve myocardial function.

HYPOTHESIS

We hypothesized that, as Doppler myocardial imaging (DMI) allows for the quantitative assessment of the systolic movement of myocardial segments, it may be a sensitive method for assessing changes in regional myocardial contraction and contractile reserve pre and post angioplasty of the IRA.

METHODS

In all, 39 patients (30 men, mean age 53.4 +/- 8.3 years), 1 to 6 months after MI, who qualified for IRA angioplasty on the basis of myocardial viability in the infarcted zone as demonstrated by dobutamine stress echocardiography, were included in the study. Peak regional myocardial systolic velocities (S wave) of the infarcted segments were measured at rest and during low-dose dobutamine infusion (15 microg/kg/min) 1 day before angioplasty (Exam 1), 2 to 5 days (Exam 2), and 30 days (Exam 3) after successful angioplasty. The long-axis movement of the mitral annulus and of the basal and medial segments of the posterior (20 patients), anterior (17 patients), and lateral walls (2 patients) was evaluated.

RESULTS

At rest, S-wave velocity of the infarcted segments increased between Exams 1 and 2, without further improvement between Exams 2 and 3 (4.9 +/- 1.2 vs. 5.6 +/- 1.3 cm/s, p < 0.05 and 5.6 +/- 1.3 vs. 5.5 +/- 1.3 cm/s, NS, respectively). However, S-wave velocities measured during low-dose dobutamine infusion differed significantly both between Exams 1 and 2, and 2 and 3 (7.0 +/- 1.5 vs. 7.8 +/- 1.8 cm/s; p < 0.01; 7.8 +/- 1.8 vs. 8.5 +/- 1.6 cm/s; p < 0.05).

CONCLUSIONS

Resting contractility at an infarct zone demonstrated rapid initial improvement after angioplasty of the IRA with no further change, whereas contractile reserve improved not only immediately after angioplasty but also during the next month.

Pathophysiology and diagnosis of hibernating myocardium in patients with post-ischemic heart failure: the contribution of PET

Identification and treatment of hibernating myocardium (HM) lead to improvement in LV function and prognosis in patients with post-ischemic heart failure. Different techniques are used to diagnose HM: echocardiography, MRI, SPECT and PET and, in patients with moderate LV impairment, their predictive values are similar. There are few data on patients with severe LV dysfunction and heart failure in whom the greatest benefits are apparent after revascularization. Quantification of FDG uptake with PET during hyperinsulinemic euglycemic clamp is accurate in these patients with the greatest mortality risk in whom other techniques may give high false negative rates. The debate on whether resting myocardial blood flow to HM is reduced or not has stimulated new research on heart failure in patients with coronary artery disease. PET with H2(15)O or 13NH3 has been used for the absolute quantification of regional blood flow in human HM. When HM is properly identified, resting blood flow is not different from that in healthy volunteers although a reduction of approximately 20% can be demonstrated in a minority of cases. PET studies have shown that the main feature of HM is a severe impairment of coronary vasodilator reserve that improves after revascularization in parallel with LV function. Thus, the pathophysiology of HM is more complex than initially postulated. The recent evidence that repetitive ischemia in patients can be cumulative and lead to more severe and prolonged stunning, lends further support to the hypothesis that, at least initially, stunning and HM are two facets of the same coin.

Clinical value of gallium-67 scintigraphy in assessment of disease activity in Wegener's granulomatosis

BACKGROUND

Diagnosis of active pulmonary and paranasal involvement in patients with Wegener's granulomatosis (WG) can be difficult. The diagnostic value of gallium-67 scintigraphy in WG is unclear.

OBJECTIVE

To evaluate the added diagnostic value of gallium-67 scintigraphy in patients with WG with suspected granulomatous inflammation in the paranasal and chest regions.

METHODS

Retrospectively, the diagnostic contribution of chest and head planar gallium scans in 40 episodes of suspected vasculitis disease activity in 28 patients with WG was evaluated. Scans were grouped into normal or increased uptake for each region. Histological proof or response to treatment was the "gold standard" for the presence of WG activity.

RESULTS

WG activity was confirmed in 8 (20%) episodes, with pulmonary locations in three, paranasal in four, and both in one (n=7 patients); all these gallium scans showed increased gallium uptake (sensitivity 100%). Gallium scans were negative for the pulmonary area in 23/36 scans (specificity 64%), and negative for paranasal activity in 13/16 scans (specificity 81%) in episodes without WG activity. Positive predictive value of WG activity for lungs and paranasal region was 24% and 63%, respectively, negative predictive value was 100% for both regions. False positive findings were caused by bacterial or viral infections.

CONCLUSION

Gallium scans are clinically helpful as a negative scan virtually excludes active WG. Gallium scintigraphy of chest and nasal region has a high sensitivity for the detection of disease activity in WG. However, because of positive scans in cases of bacterial or viral infections, specificity was lower.

Myocardial viability in chronic ischemic heart disease: comparison of contrast-enhanced magnetic resonance imaging with (18)F-fluorodeoxyglucose positron emission tomography

OBJECTIVES

We sought to compare contrast-enhanced magnetic resonance imaging (ceMRI) with nuclear metabolic imaging for the assessment of myocardial viability in patients with chronic ischemic heart disease and left ventricular (LV) dysfunction.

BACKGROUND

Contrast-enhanced MRI has been shown to identify scar tissue in ischemically damaged myocardium.

METHODS

Twenty-six patients with chronic coronary artery disease and LV dysfunction (mean ejection fraction 31 +/- 11%) underwent (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET), technetium-99m tetrofosmin single-photon emission computed tomography (SPECT), and ceMRI. In a 17-segment model, the segmental extent of hyperenhancement (SEH) by ceMRI, defined as the relative amount of contrast-enhanced tissue per myocardial segment, was compared with segmental FDG and tetrofosmin uptake by PET and SPECT.

RESULTS

In severely dysfunctional segments (n = 165), SEH was 9 +/- 14%, 33 +/- 25% (p < 0.05), and 80 +/- 23% (p < 0.05) in segments with normal metabolism/perfusion, metabolism/perfusion mismatch, and matched defects, respectively. Segmental glucose uptake by PET was inversely correlated to SEH (r = -0.86, p < 0.001). By receiver operator characteristic curve analysis, the area under the curve was 0.95 for the differentiation between viable and non-viable segments. At a cutoff value of 37%, SEH optimally differentiated viable from non-viable segments defined by PET. Using this threshold, the sensitivity and specificity of ceMRI to detect non-viable myocardium as defined by PET were 96% and 84%, respectively.

CONCLUSIONS

Contrast-enhanced MRI allows assessment of myocardial viability with a high accuracy, compared with FDG-PET, in patients with chronic ischemic heart disease and LV dysfunction.

Autologous skeletal myoblast transplantation for severe postinfarction left ventricular dysfunction

OBJECTIVES

This phase I trial was designed to assess the feasibility and safety of autologous skeletal myoblast transplantation in patients with severe ischemic cardiomyopathy.

BACKGROUND

Experimentally, myoblast grafting into postinfarction myocardial scars improves left ventricular function.

METHODS

Ten patients were included on the basis of the following criteria: 1) severe left ventricular dysfunction (ejection fraction < or = 35%); 2) the presence of a postinfarction akinetic and nonviable scar, as assessed by dobutamine echocardiography and 18-fluorodeoxyglucose positron emission tomography; and 3) an indication of coronary bypass in remote areas. Skeletal myoblasts were grown from a biopsy taken at the thigh.

RESULTS

An average of 871 x 10(6) cells (86% of myoblasts) were obtained after a mean period of 16 days and implanted uneventfully across the scar at the time of bypass. Except for one patient whose early death was unrelated to the cell transplantation, all patients had an uncomplicated postoperative course. Four patients showed delayed episodes of sustained ventricular tachycardia and were implanted with an internal defibrillator. At an average follow-up of 10.9 months, the mean New York Heart Association functional class improved from 2.7 +/- 0.2 preoperatively to 1.6 +/- 0.1 postoperatively (p < 0.0001), and the ejection fraction increased from 24 +/- 1% to 32 +/- 1% (p < 0.02). A blinded echocardiographic analysis showed that 63% of the cell-implanted scars (14 of 22) demonstrated improved systolic thickening. One noncardiac death occurred 17.5 months after transplantation.

CONCLUSIONS

These preliminary data suggest the feasibility and safety of autologous skeletal myoblast transplantation in severe ischemic cardiomyopathy, with the caveat of an arrhythmogenic potential. New-onset contraction of akinetic and nonviable segments suggests a functional efficacy that requires confirmation by randomized studies.

Nuclear imaging is more sensitive for the detection of viable myocardium than dobutamine echocardiography

Intact perfusion, preserved metabolism of free fatty acids and glucose, and the presence of contractile reserve have been used as markers of viable myocardium. However, not all viable myocardium may exhibit all these characteristics. Accordingly, these features were evaluated in patients with chronic coronary artery disease and left ventricular dysfunction. Fourteen patients with chronic ischaemic heart disease and depressed left ventricular function (LVEF 34+/-10%) perfusion was evaluated by early resting 201Tl single photon emission computed tomography (SPECT), fatty acid utilization by 15-p-[123I]iodophenyl-3-(R,S)-methylpentadecanoic acid SPECT, glucose utilization by 2-[18F]fluoro-2-deoxy-D-glucose SPECT and contractile reserve (CR) by dobutamine echocardiography. The comparison of the different modalities was restricted to akinetic or dyskinetic myocardium as assessed by resting 2-dimensional echocardiography. For all techniques a 13-segment model was used. Sixty-four of 182 segments (35%) showed akinesia or dyskinesia. Intact perfusion was found in 33/64 (52%) segments. Fatty acid utilization was maintained in 38/64 (59%) segments and glucose utilization was maintained in 38/64 (59%) segments. CR was present in significantly fewer segments: 21 of 64 (33%) (P<0.01 vs glucose and fatty acid utilization). In the 21 segments with preserved CR, perfusion was intact in 16/21 (76%) segments, fatty acid utilization in 19/21 (90%) segments and glucose utilization was preserved in all (100%) segments. Conversely, in the 43 segments without CR, 17 segments (40%) showed intact perfusion, 19 segments (44%) preserved fatty acid utilization and 17 (40%) still showed preserved glucose utilization. Disagreement in segments between the viability markers was caused mainly by segments without CR but preserved perfusion, fatty acid or glucose utilization. The substantial number of segments with preserved glucose and fatty acid utilization but without contractile reserve, suggests an underestimation of myocardial viability by dobutamine echocardiography.

Myocardial perfusion and viability by positron emission tomography in infants and children with coronary abnormalities: correlation with echocardiography, coronary angiography, and histopathology

OBJECTIVES

This study was designed to assess the feasibility and accuracy of positron emission tomography (PET) imaging in infants and children.

BACKGROUND

Positron emission tomography is employed in adults for the evaluation of myocardial perfusion and the detection of myocardial viability.

METHODS

Perfusion and metabolism findings on PET in infants and children with suspected coronary abnormalities (age 14 days to 12 years old, mean 3.3 +/- 4.0 years) were correlated with findings on coronary angiography, echocardiography, and myocardial histopathology. The segmental myocardial uptake of the flow tracer (13)N-ammonia and of the glucose tracer (18)F-deoxyglucose ((18)FDG) was graded on a five-point scale and compared with the angiographic perfusion score, with regional wall motion, and the presence of fibrosis.

RESULTS

There was an agreement of r = 0.72 (p < 0.05) between regional myocardial perfusion and angiography. The correlation of histopathologic changes with normal, moderately, and severely reduced segmental (13)N-ammonia uptake was 87%, 60%, and 75%, respectively. Segmental myocardial (18)FDG uptake and histopathologic findings were concordant in 48 (79%) of 64 segments without fibrosis; absence of viability by perfusion and metabolism imaging correlated with the presence of fibrosis in 21 (84%) of 25 segments.

CONCLUSIONS

The observed agreements between the findings on PET perfusion and metabolism imaging with those on coronary angiography, echocardiography, and histopathology support the utility and accuracy of PET for characterizing myocardial perfusion abnormalities and viability in pediatric patients.

MR imaging of myocardial perfusion and viability

CMR is a rapidly developing new modality with applications in clinical cardiology for detection and assessment of myocardial ischemia and viability. CMR perfusion results for the detection of ischemia in comparison with stress echocardiography and scintigraphic techniques are reasonable, but all the studies reported to date have been conduced in selected patients. Larger studies in patient populations reflecting a broader spectrum of disease are necessary before perfusion CMR can be envisaged as a clinically reliable and robust diagnostic tool. Other CMR techniques provide a variety of novel methods of obtaining information on postischemic viability. Signs of viability that can be observed by CMR are the absence of late gadolinium-based contrast enhancement in a myocardial region involved in a recent infarct, any sign of wall thickening at rest (which is detectable with high accuracy by CMR), wall thickening after stimulation by low-dose dobutamine, and preserved wall thickness. Conversely, myocardial necrosis is characterized by signal enhancement of the infarct area after injection of Gd-DTPA, reduced wall thickness in chronic infarcts, and absence of a contractile reserve during dobutamine stimulation. Dobutamine CMR and late enhancement contrast-enhanced CMR predict contractile improvement after revascularization.

New surgical treatments for heart failure

Medical therapy for heart failure is quickly advancing, but long-term survival unfortunately remains poor. New surgical techniques seek to halt and reverse the progression of heart failure. Positron emission tomography has refined patient selection techniques for coronary artery bypass grafting in the failing heart. Left ventricular (LV) remodeling surgery and new devices change the shape of the LV and decrease LV wall stress. Passive restraint devices improve systolic function by preventing ventricular dilatation. LV assist devices have proven to be effective and provide a significantly higher 1-year survival rate when compared with maximal medical therapy. New ideas and devices are defining a new role for surgical treatment of the aging population of the United States and may provide the answer to long-term management of heart failure.

Ischemic cardiomyopathy in pigs with two-vessel occlusion and viable, chronically dysfunctional myocardium

A chronic left anterior descending coronary artery (LAD) stenosis leads to the development of hibernating myocardium with severe regional hypokinesis but normal global ventricular function after 3 mo. We hypothesized that two-vessel occlusion would accelerate the progression to hibernating myocardium and lead to global left ventricular (LV) dysfunction and heart failure. Pigs were instrumented with a fixed 1.5-mm constrictor on the proximal LAD and circumflex arteries. After 2 mo, there were no overt signs of right-heart failure and triphenyl tetrazolium chloride infarction was trivial (1.4 +/- 0.1% of the LV). Compared with shams, regional function [myocardial systolic excursion (DeltaWT); 2.1 +/- 0.3 vs. 4.6 +/- 0.4 mm, P < 0.05] and resting perfusion (0.90 +/- 0.13 vs. 1.32 +/- 0.09 ml small middle dot min(-1) small middle dot g(-1), P < 0.05) were reduced, consistent with hibernating myocardium. Pulmonary systolic (45.9 +/- 3.3 vs. 36.5 +/- 2.2 mmHg, P < 0.05) and wedge pressures (19.1 +/- 1.6 vs. 11.2 +/- 0.9 mmHg, P < 0.05) were increased with global ventricular dysfunction (ejection fraction 43 +/- 2 vs. 50 +/- 2%, P < 0.05). Early LV remodeling was present with increased cavity size and mass. Reductions in sarcoplasmic reticulum Ca(2+)-ATPase and phospholamban were confined to the dysfunctional LAD region with no change in calsequestrin. Thus combined stenoses of the LAD and circumflex arteries accelerate the development of hibernating myocardium and result in compensated heart failure.

Assessment of myocardial viability by positron emission tomography

Accurate assessment of myocardial viability is critical for identifying patients likely to benefit from coronary revascularization. Positron emission tomography (PET) has several advantages over single photon emission computed tomography (SPECT), including higher sensitivity and specificity, as well as the ability to measure myocardial blood flow and myocardial metabolism in absolute terms, which is important in understanding the pathophysiology of ischemic cardiomyopathy. The most commonly used PET tracer is [18F]2-fluoro-2deoxy-D-glucose (FDG). The dependence of ischemic myocardium on glucose metabolism makes FDG an ideal tracer in this setting. Studies have shown positive and negative predictive values for the detection of viable myocardium in the range of 48-94%, and 73-96%, respectively. FDG is superior to SPECT using thallium or technetium myocardial perfusion agents, as well as echocardiography with dobutamine infusion. FDG PET also provides important prognostic information. Patients with evidence of myocardial viability by FDG PET have fewer cardiac events and survive longer if revascularized compared to patients who are treated medically. This article will review myocardial metabolism, PET procedures and interpretive criteria, as well as problems and limitations. Data from the literature regarding diagnostic and prognostic information will also be summarized.

The histology of viable and hibernating myocardium in relation to imaging characteristics

OBJECTIVES

This study characterizes the histology of myocardium predicted to be hibernating using three different imaging techniques to explain the discordance among them.

BACKGROUND

Both radionuclide and functional imaging techniques were used to assess myocardial hibernation. The former have high sensitivity and the latter high specificity for predicting functional recovery.

METHODS

Nineteen patients underwent thallium-201 and 99m-technetium tetrofosmin myocardial perfusion imaging, and dobutamine magnetic resonance imaging (MRI), prior to coronary bypass grafting. Criteria for predicted hibernation for each technique were defined before operation. Postoperative criteria for scar and true hibernation were also defined. Biopsies were analyzed for myocyte volume fraction (MVF), glycogen deposition and pathologic cell features.

RESULTS

Thallium was most sensitive in predicting hibernation (88%) and MRI most specific (84%); and, although there was good agreement between thallium and tetrofosmin (85%), agreement between MRI and thallium (59%) or tetrofosmin (59%) was poor. For each technique, MVF was higher in segments predicted to be hibernating rather than scar (p < 0.05). The MVF was higher where both thallium and MRI predicted hibernation (0.77+/-0.07) than in segments predicted by thallium alone (0.69+/-0.13, p < 0.05). Proven hibernating segments had a higher MVF than scar (0.72+/-0.11 vs. 0.6+/-0.26, p < 0.05).

CONCLUSIONS

Preservation of myocyte fraction is an important determinant of functional recovery after revascularization. A higher myocyte fraction is required to maintain contractile reserve than to achieve significant tracer uptake. This explains the higher sensitivity of radionuclide imaging compared with dobutamine MRI in the identification of myocardial hibernation.

Histologic atrial myolysis is associated with atrial fibrillation after cardiac operation

BACKGROUND

Postoperative atrial fibrillation after cardiac operation is common. Despite the identification of risk factors associated with postoperative atrial fibrillation, the pathophysiologic mechanisms remain unclear. Myolysis has been recently described to be associated with maintenance of atrial fibrillation in experimental animals. In this study, we attempted to identify histopathologic changes in atria that might predict the development of postoperative atrial fibrillation, and specifically address its association with myolysis.

METHODS

Right appendicular atrial tissue was sampled before and after cardiopulmonary bypass from 60 patients in sinus rhythm who underwent elective coronary artery bypass grafting.

RESULTS

Fifteen patients (25%) developed postoperative atrial fibrillation. Histopathologic abnormalities were found in most patients (52 of 60). However, only myolysis and lipofuscin levels were found to be an independent histologic finding associated with the development of postoperative atrial fibrillation. Electron microscopy showed that myolytic vacuoles were not membrane bound, and were associated with lipofuscin deposits. Neither mitochondrial pathology nor apoptosis was detected in the atria before or after operation.

CONCLUSIONS

Abnormalities in biopsies before cardiopulmonary bypass can indicate the susceptibility to develop postoperative atrial fibrillation. This implies that the status of the atrium before cardiopulmonary bypass is a major determinant in the development of this common complication.

Clinical pathophysiology of hibernating myocardium

Our current knowledge of the pathophysiology of chronic hibernating myocardium is mainly based on results from clinical studies, because of the absence of appropriate and validated animal models. These clinical observations have given rise to two major controversies: the role of reduced blood flow and that of histological changes in the hibernating segments. In this review, these two subjects will be briefly discussed, and put into the perspective of findings emerging from recently developed animal models.

Stability of hibernating myocardium in pigs with a chronic left anterior descending coronary artery stenosis: absence of progressive fibrosis in the setting of stable reductions in flow, function and coronary flow reserve

OBJECTIVES

This study was performed to determine whether hibernating myocardium is adaptive or is destined to undergo progressive irreversible injury.

BACKGROUND

Previous studies have suggested that hibernating myocardium eventually results in progressive dysfunction. Since serial studies cannot be performed in humans, the temporal progression of physiologic and structural adaptations was evaluated in pigs with hibernating myocardium.

METHODS

Pigs were instrumented with a left anterior descending coronary artery (LAD) stenosis (1.5 mm) and underwent physiologic studies three to five months later to quantify regional function, perfusion and 18F-2-deoxyglucose (FDG) uptake. Viability was confirmed by histology and contractile reserve.

RESULTS

Hibernating myocardium was characterized by severe regional dysfunction (centerline score, -1.9+/-0.1), reduced resting subendocardial flow (LAD: 0.85+/-0.03 vs. normal: 1.02+/-0.03 ml/min/g, p < 0.01), critically reduced subendocardial flow reserve (adenosine flow: 1.04+/-0.09 ml/min/g, p = NS vs. rest; epinephrine flow: 0.88+/-0.07 ml/min/g, p = NS vs. rest) and increased FDG uptake (0.022+/-0.002 vs. 0.014+/-0.001 ml/g/min, p < 0.01). Physiologic parameters were not different among animals studied at three (93+/-1 days, n = 27), four (118+/-2 days, n = 26) or five months (150+/-6 days, n = 9). Pathology revealed a small increase in LAD connective tissue (6.4+/-0.4% vs. 4.0+/-0.2%, p < 0.001), with no change over this time frame.

CONCLUSIONS

Thus, physiologic and structural features of hibernating myocardium remain constant for at least two months. The absence of functional deterioration or progressive fibrosis suggests that hibernation is adaptive rather than an unstable physiology destined to progress to irreversible injury. The stability of this model appears ideally suited for interventions targeted to improve flow and function in chronically dysfunctional myocardium.

[Regional diastolic function is more preserved in viable than non-viable myocardium. Demonstration by pulsed-wave Doppler tissue imaging in basal conditions]

INTRODUCTION AND OBJECTIVES

The aim of this study was to analyze the differences in regional diastolic function between viable and non-viable myocardium when assessed by pulsed-wave Doppler tissue imaging performed in basal conditions.

PATIENTS AND METHODS

The study population included 21 patients with three-vessel disease and regional systolic dysfunction. These patients underwent transthoracic echocardiographic study and pulsed-wave Doppler tissue imaging in basal conditions and, in addition, stress echocardiography with dobutamine performed by a different investigator.

RESULTS

Three-hundred and twenty-two segments were studied, 140 of which (43%) had systolic dysfunction. Of the 140 segments with systolic dysfunction, 52 (37%) were considered hypokinetic by transthoracic echocardiography, 80 (57%) akinetic and 8 (6%) dyskinetic. As assessed by dobutamine echocardiography, 67 segments (48%) were considered viable and 73 (52%) non-viable. Viable segments had a higher peak velocity of the early diastolic wave e (5.5 +/- 1.9 vs. 4.7 +/- 2.0 cm/s; p = 0.03). An e/a ratio < 1 was more frequent in non-viable versus non-viable segments (52 vs. 70%; p < 0.05). There were no differences in relation to regional isovolumetric relaxation time and peak velocity of a wave. Although peak velocity of s wave was lower in non-viable segments, differences were not statistically significant.

CONCLUSION

Compared with non-viable segments, viable myocardial segments have less impaired regional diastolic function as assessed by pulsed-wave Doppler tissue imaging.

Significance of both negative T waves and stress-induced normalization of the repolarization phase in infarcted patients: a positron-emission-tomography assessment of regulation of myocardial blood flow and viability of myocardium

BACKGROUND

The clinical correlation of stress-induced normalization of previously negative T waves (NNTW) to regulation of regional myocardial blood flow (MBF) and tissue viability is still being debated.

OBJECTIVE

To clarify its meaning.

METHODS

We studied 25 patients, who had previously suffered anterior myocardial infarction and for whom negative T waves were recorded on baseline electrocardiographic precordial leads, by means of positron emission tomography. We obtained MBF in the infarcted myocardial regions under resting conditions for all patients, during infusion of dipyridamole (17 patients) and dobutamine (20 patients), using [13N]-ammonia as a flow tracer.

RESULTS

During stress tests, 13 patients exhibited NNTW (group 1) whereas the remaining 12 presented persistent negative T waves (group 2). NNTW was observed in 18 stress studies (for 10 and eight patients during administration of dobutamine and dipyridamole, respectively) whereas persistent negative T waves occurred 19 times (for 10 patients during infusion of dobutamine and nine patients during administration of dipyridamole). A complete concordance of the modifications of the repolarization phase was observed for patients who were subjected both to dipyridamole and to dobutamine studies. Furthermore, we assessed viability of myocardium in 20 of 25 patients using [18F]-fluorodeoxyglucose. For the remaining five patients not subjected to metabolic imaging, a coronary reserve of 1.65 was considered a cut-off of viability. Resting MBF for patients in groups 1 and 2 were similar (0.53 +/- 0.20 versus 0.47 +/- 0.17 ml/min per g, respectively, NS) whereas during pharmacological stress, MBF of patients in group 1 was significantly higher than that for patients in group 2 (0.99 +/- 0.41 versus 0.56 +/- 0.26 ml/min per g, respectively, P < 0.0001). Coronary vasodilating capability, expressed as stress/resting MBF ratio, turned out to be 1.88 +/- 0.49 and 1.16 +/- 0.37 for patients in groups 1 and 2, respectively (P < 0.0001). We observed no difference in mean exercise work load (9.6 +/- 2.80 versus 8.46 +/- 2.18 min, NS) and rate- pressure product (24230 +/- 6425 versus 24207 +/- 8146 mmHg beats/ min, NS) at peak for the two categories of patients. All 13 patients in group 1 (100%) had viable myocardium in the anterior infarcted areas whereas only one of 12 patients in group 2 did (9%, P< 0.0001 versus group 1). Finally, a subanalysis for the specific pharmacological agent used was performed and it gave similar results.

CONCLUSION

Regardless of the specific stress test able to elicit the electrocardiographic sign, infarcted dysfunctional areas with stress-induced NNTW were demonstrated to have a higher coronary vasodilating capability and a greater probability of viability of myocardium than had persistent negative T wave regions. Therefore, detection of NNTW appears to be a cheap first-line method for the identification both of a better preserved coronary microcirculatory function and of the persistence of viability of myocardium in the infarcted areas.

The contribution of positron emission tomography to the study of ischemic heart failure

Cardiac imaging with positron emission tomography offers unrivaled sensitivity and specificity to probe cardiovascular physiology in health and disease. The use of positron emission tomography to noninvasively measure regional myocardial blood flow and assess myocardial viability in patients with ventricular dysfunction and coronary artery disease has contributed greatly to our understanding of the pathophysiology of ischemic heart failure. The advances and the need for further studies to establish both the natural history of such ventricular dysfunction and the role of coronary revascularization are discussed.

Coronary artery surgery for ischemic heart failure: risks, benefits, and the importance of assessment of myocardial viability

Heart failure and left ventricular dysfunction are common and are most often caused by myocardial ischemia/infarction secondary to occlusive coronary artery disease. Although recent refinements in medical therapy have resulted in improved survival, morbidity and mortality remain high in patients with advanced heart failure. Heart transplantation remains an option for selected patients, and implantable left ventricular assist devices may soon provide another treatment strategy for such patients. However, patients with established postischemic heart failure, significant myocardial viability, and coronary artery anatomy amenable to surgical revascularization can derive significant functional and survival benefit after coronary artery surgery, albeit with an increased perioperative risk. We discuss the role of coronary artery surgery in ischemic heart failure and review the evidence for such an approach.

The pathophysiology of myocardial hibernation: current controversies and future directions

It is now widely accepted that patients with chronic coronary artery disease can experience prolonged regional ischemic dysfunction that does not necessarily arise from irreversible tissue damage and, to some extent, can be reversed by restoration of blood flow. Recent clinical and experimental data suggest that this form of chronic but reversible left ventricular dysfunction represents a complex, progressive, and dynamic phenomenon. The initial stages of dysfunction are probably caused by chronic stunning. They are characterized by normal resting perfusion but reduced flow reserve, mild myocyte alterations, maintained membrane integrity (allowing the transport of both thallium and glucose), preserved capacity to respond to an inotropic stimulus, and no or little tissue fibrosis. After revascularization, functional recovery will probably be rapid and complete. On the other hand, the more advanced stages of dysfunction likely correspond to chronic hibernation. They usually are associated with reduced rest perfusion; increased tissue fibrosis; more severe myocyte alterations (degeneration[?], apoptosis); and a decreased ability to respond to inotropic stimuli. Nonetheless, membrane function and glucose metabolism may long remain preserved. After revascularization, functional recovery, if any, will probably be quite delayed and mostly incomplete.

The identification of myocardial hibernation in patients with ischemic heart failure by echocardiography and radionuclide studies

Dobutamine echocardiography and myocardial radionuclide tomography are widely used to assess viability in patients with ischemic cardiomyopathy and left ventricular dysfunction. The main goal of viability evaluation has been the identification of reversible regional dysfunction in the attempt to identify patients in whom revascularization may determine an improvement of global left ventricular ejection fraction. In this application, echocardiographic and radionuclide techniques are used to characterize different pathophysiologic aspects of viable myocardium, ie, integrity of cell membrane and contractile reserve. This explains why the information of the 2 techniques are often divergent and why radionuclide techniques have the highest sensitivity but reduced specificity compared with echocardiography for predicting recovery of regional dysfunction. The identification of residual viable myocardium by either technique is strongly associated with adverse prognosis if the patients are not revascularized, and this substantially contributes to the decision-making process in individual patients. Although it has been assumed that prognostic advantages of revascularization are linked to an increase of ejection fraction, pathophysiologic and clinical observations challenge us with the possibility that benefits of revascularization may also ensue independently on the recovery of ejection fraction through alternative pathophysiologic mechanisms. Therefore, clinical application of viability tests should be evaluated against relevant endpoints, mainly represented by prolongation of life and improvement of life quality, and not by surrogate endpoints as represented by recovery of global ejection fraction. Future studies are needed to assess whether a more clinically oriented approach will provide a better selection of patient candidates for revascularization.

Early assessment of regional myocardial blood flow and metabolism in thrombolysis in myocardial infarction flow grade 3 reperfused myocardial infarction using carbon-11-acetate

OBJECTIVES

The aim of this study was to investigate the prognostic value of carbon-11-acetate (acetate) positron emission tomography (PET) after successful reperfusion of myocardial infarction (MI).

BACKGROUND

Acetate PET allows the measurement of both myocardial flow and oxidative metabolism. The prognostic value of acetate measurements performed early (within 24 h) after Thrombolysis In Myocardial Infarction (TIMI) flow grade 3 reperfused MI is unknown.

METHODS

In 18 patients with TIMI flow grade 3 reperfusion of their first MI, a dynamic acetate study was performed within 24 h of the acute event. At five days, nitrogen-13-NH3 (NH3) and fluorine-18-labeled fluorodeoxyglucose (FDG) PET studies were performed. Infarct-related areas were classified as "PET viable" or "PET nonviable," as assessed with NH3 and FDG, according to previously established criteria. At five days and three months, radionuclide angiography was performed for evaluation of left ventricular (LV) function.

RESULTS

In infarct-related regions, myocardial blood flow, FDG uptake and oxygen consumption were decreased, compared with remote regions. However, oxygen consumption values, as measured with acetate in both PET-viable and PET-nonviable areas, as assessed with NH3 and FDG, were not significantly different (p = NS). A significant linear correlation was observed between global LV ejection fraction at three months and oxidative metabolism in the infarct-related area (r = 0.8, p < 0.0001). Multivariate analysis revealed that oxidative metabolism measurements in reperfused myocardium was the only significant predictor for recovery of LV function at three months (p < 0.05).

CONCLUSIONS

Measurement of oxidative metabolism early after TIMI flow grade 3 reperfusion of MI offers important prognostic value concerning LV function at follow-up.