Preoperative positron emission tomographic viability assessment and perioperative and postoperative risk in patients with advanced ischemic heart disease

Quantitative clinical assessment of chronic anterior myocardial infarction with delayed enhancement magnetic resonance imaging and QRS scoring

BACKGROUND

Both the regional and global myocardial extent of chronic myocardial infarction (MI) are important prognostic factors for length and quality of life and also crucial for the choice of therapy in patients with ischemic heart disease. Our aim was to develop and validate techniques for comparison between regional and global size of remote anterior MI in the left ventricle quantified with both magnetic resonance imaging (MRI) and electrocardiogram (ECG).

METHODS

Delayed-enhancement (DE) MRI was used as a clinical "gold standard" for MI size to evaluate the extent of MI estimated with the commonly available standard 12-lead ECG. A method for comparing global and regional quantifications of MI with DE-MRI and ECG was developed. The Selvester QRS-scoring system was used for estimating MI size electrocardiographically.

RESULTS

Twenty-five patients with chronic single anterior MI, documented with DE-MRI, were studied. The best agreement for mean % MI per regional segment of the left ventricle was found in the middle third (26% vs 27%), whereas the most significant discrepancy was found in the apex (56% vs 30%). The global MI size of the left ventricle averaged 21 +/- 9% with DE-MRI and 22% +/- 12% with ECG, with a correlation of r = 0.40 (P <.05).

CONCLUSIONS

The current Selvester QRS scoring system performs well for quantifying anterior MI in the mid-regions of the left ventricle. The diagnostic performance of the Selvester QRS-scoring system for quantifying MI in the other regions, particularly the left ventricular apex, can potentially be improved, with DE-MRI as the gold standard.

Prognostic importance of the quantification of myocardial viability in revascularized patients with coronary artery disease and moderate-to-severe left ventricular dysfunction

The aim of this study was to assess the prognostic value of the amount of dysfunctional but viable myocardium in revascularized patients with coronary artery disease and left ventricular dysfunction. To quantify the amount of dysfunctional but viable myocardium, low-dose dobutamine echocardiography was performed. The wall motion was scored using a 16-segment model. The dysfunctional segments were defined as viable if they exhibited functional improvement of at least 1 grade with any dose of dobutamine, or only worsening with dobutamine infusion. Two hundred and twenty patients were revascularized and followed-up for a mean period of 33+/-23 months (range, 0-86) for cardiac-related death and hospitalization for heart failure. Standard follow-up echocardiography was performed 3-6 months after revascularization. Receiver operating characteristic curve analysis identified six dysfunctional but viable segments as the optimal cutoff value for discriminating patients with and without risk of cardiac events. Thirty-eight patients exhibited a large amount of dysfunctional but viable myocardium (>or=6 segments, group A), 103 patients had a small amount of dysfunctional but viable myocardium (2-5 segments, group B), and 79 patients were found to have dysfunctional myocardium irreversibly damaged (group C). Similar baseline left ventricular ejection fractions of 36+/-4, 34+/-5, 35+/-5% in groups A, B, and C increased to 46+/-6% (P<0.01 versus baseline and versus groups B and C), to 39+/-5% (P<0.01 versus baseline and group C), and to 36+/-7% (P<0.01 versus baseline), respectively, after revascularization. The greatest functional improvement after revascularization in group A patients was accompanied by a lower frequency of cardiac events during follow-up (1 vs. 27 in group B, P<0.01, and versus 18 in group C, P<0.01) and by a better cardiac event-free survival according to Kaplan-Meier survival analysis (P<0.01 versus groups B and C, respectively). In conclusion, in revascularized patients with coronary artery disease and moderate-to-severe left ventricular dysfunction, the presence of >or=6 dysfunctional but viable segments identifies patients with the best prognosis.

Individual prediction of functional recovery after coronary revascularization in patients with ischemic cardiomyopathy: the scar-to-biphasic model

Currently, the prediction of improvement of left ventricular (LV) ejection fraction (EF) after revascularization in patients with ischemic cardiomyopathy relies only on viable myocardium extent, whereas both the amount of viable and scar tissue may be important. A model was developed, based on the amount of viable and nonviable myocardium, to predict functional recovery. Viable and scarred myocardium was defined by dobutamine stress echocardiography (DSE) in 108 consecutive patients. LVEF before and 9 to 12 months after revascularization was assessed by radionuclide ventriculography; an improvement of > or =5% was considered significant. In the 1,089 dysfunctional segments (63%), DSE elicited biphasic response in 216 segments (20%), sustained improvement in 205 (19%), worsening in 43 (4%), and no change in 625 (57%). LVEF improved in 39 patients (36%). Only the numbers of biphasic and scar segments were predictors of improvement or no improvement of LVEF (odds ratio 1.5, 95% confidence interval 1.2 to 1.7, p <0.0001 for biphasic segments; odds ratio 0.8, 95% confidence interval 0.7 to 0.9, p <0.0005 for scarred segments). The sustained improvement and worsening pattern were not predictive of improvement or no improvement. A regression function, based on the number of scar and biphasic segments, showed that the likelihood of recovery was 85% in patients with extensive biphasic tissue and no scars and 11% in patients with extensive scars and no biphasic myocardium. Patients with a mixture of scar and biphasic tissue had an intermediate likelihood of improvement (50%). In patients with ischemic cardiomyopathy and a mixture of viable and nonviable tissue, both numbers of viable and nonviable segments should be considered to accurately predict functional recovery after revascularization.

Myocardial viability assessment using nuclear imaging

Myocardial assessment continues to be an issue in patients with coronary artery disease and left ventricular dysfunction. Nuclear imaging has long played an important role in this field. In particular, PET imaging using 18F-fluorodeoxyglucose is regarded as the metabolic gold standard of tissue viability, which has been supported by a wide clinical experience. Viability assessment using SPECT techniques has gained more wide-spread clinical acceptance than PET, because it is more widely available at lower cost. Moreover, technical advances in SPECT technology such as gated-SPECT further improve the diagnostic accuracy of the test. However, other imaging techniques such as dobutamine echocardiography have recently emerged as competitors to nuclear imaging. It is also important to note that they sometimes may work in a complementary fashion to nuclear imaging, indicating that an appropriate use of these techniques may significantly improve their overall accuracy. In keeping these circumstances in mind, further efforts are necessary to further improve the diagnostic performance of nuclear imaging as a reliable viability test.

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.

Coronary artery surgery for ischaemic heart failure: the surgeon's view

Recent advances in medical therapy have improved outcomes for patients with severe heart failure. However, overall survival remains poor. Transplantation is an established therapy for these patients but is limited by the large mismatch between demand and donor organ availability. Recently it has been recognised that not all ventricular dysfunction secondary to coronary artery disease is irreversible. Revascularisation in certain patients would appear to improve ventricular function. These patients are said to demonstrate myocardial "hibernation". Revascularisation in these patients may provide a further treatment option in the treatment of heart failure.

Positron emission tomography and recovery following revascularization (PARR-1): the importance of scar and the development of a prediction rule for the degree of recovery of left ventricular function

OBJECTIVES

The aim of this study was to determine whether the extent of viability or scar is important in the amount of recovery of left ventricular (LV) function, and to develop a model for predicting recovery after revascularization that could be tested in a randomized trial.

BACKGROUND

F-18-fluorodeoxyglucose (FDG) positron emission tomography (PET) is used to define viable myocardium in patients with coronary artery disease (CAD) and severe LV dysfunction and to guide revascularization decisions. Whether this approach improves clinical outcomes has not been tested in a randomized trial. Before doing so, an objective model for prediction of recovery is required.

METHODS

A total of 82 patients with CAD and an ejection fraction (EF) < or =35% had FDG PET perfusion imaging before revascularization. Complete follow-up was available on 70 patients (86%). Patients had radionuclide angiograms at baseline and three months post-revascularization.

RESULTS

Diabetes (p = 0.029), time to operation (p = 0.008), and scar score (p = 0.001) were significant independent predictors of the change in EF. Previous coronary artery bypass graft confounded the effect of age. There was a significant interaction between the perfusion tracer used and mismatch score (p = 0.02). The multivariable prediction model incorporating PET and clinical variables had a goodness of fit with p = 0.001. Across tertiles of scar scores (I, small: 0% to 16%; II, moderate: 16% to 27.5%; III, large: 27.5% to 47%), the changes in EFs were 9.0 +/- 1.9%, 3.7 +/- 1.6%, and 1.3 +/- 1.5% (p = 0.003: I vs. III), respectively.

CONCLUSIONS

In patients with severe LV dysfunction, the amount of scar was a significant independent predictor of LV function recovery after revascularization. A combination of PET and clinical parameters predicts the degree of recovery. This model is being applied in a large randomized controlled trial to determine the effectiveness of therapy guided by FDG PET.

Prognosis of hibernating myocardium is independent of recovery of function: evidence from a routine based follow-up study

Revascularization of hibernating segments improves both ventricular function (VF) and survival. In this study, we determined whether this relation is true in a routine based patients population with mildly reduced VF. Two to 6 years after undergoing 201Tl scintigraphy to detect hibernation, 153 patients were interviewed in order to collect medical information. This population was divided into four groups, according to the presence or absence of myocardial hibernation and of revascularization. Age, gender and left ventricular ejection fraction (LVEF) were similar in the four groups. Hard cardiac events (HEs) were noted in 14/33 (41%) patients with uncorrected hibernation, while in the other three groups HEs were recorded in fewer than 3% of patients. Univariate analysis indicated that the presence of hibernation, regardless of its extension, was the highest significant predictor of HEs. Multivariate analysis indicated that hibernation, stress ischaemia, age and absence of revascularization were significant predictors of HEs. These findings were not related to changes in LVEF or to New York Heart Association (NYHA) class during follow-up. In this routine based patient population, with mildly reduced VF, the rate of HEs seems to be related to uncorrected hibernation regardless of its extension. In these patients revascularization of hibernating segments is effective in reducing the risk of HEs while its role in improving VF or NYHA class is negligible.

Cost-effectiveness of preoperative positron emission tomography in ischemic heart disease

BACKGROUND

Revascularization of patients with ischemic heart disease and poor left ventricular function for surgical procedures is expensive and carries considerable risks, but may improve survival for patients with hibernating myocardium. Positron emission tomography can detect hibernating myocardium, and may be cost-effective if used to select patients for operation.

METHODS

An economic model was developed to compare the cost-effectiveness of three management strategies: (1) coronary artery bypass grafting for all patients; (2) using positron emission tomography to select candidates for coronary artery bypass grafting, those without hibernation remaining on medical therapy; and (3) medical therapy for all patients. The model used data from our hospital and the published literature. A sensitivity analysis was also undertaken.

RESULTS

Positron emission tomography was cost-effective in selecting patients for operation. In a hypothetical population of 1,000 patients, using positron emission tomography saved marginally more life-years and cost approximately Pound Sterling 3 million less. Using positron emission tomography before coronary artery bypass grafting instead of all patients receiving medical treatment saved lives but was more expensive. The incremental cost per life-year saved was Pound Sterling 77,000. The sensitivity analysis showed that the prevalence of hibernation and the survival rate of patients refused revascularization on the basis of the positron emission tomography scan were the areas most likely to influence cost-effectiveness.

CONCLUSIONS

Positron emission tomography may be cost-effective to select patients with poor left ventricular function for coronary artery bypass grafting.

Myocardial viability testing and impact of revascularization on prognosis in patients with coronary artery disease and left ventricular dysfunction: a meta-analysis

OBJECTIVES

This study pools data from published series examining late survival with revascularization versus medical therapy after myocardial viability testing in patients with severe coronary artery disease (CAD) and left ventricular (LV) dysfunction.

BACKGROUND

Previous observational studies have suggested survival benefit in such patients if they are revascularized when myocardial viability is detected on imaging tests.

METHODS

A MEDLINE database search returned 24 viability studies reporting patient survival using thallium perfusion imaging, F-18 fluorodeoxyglucose metabolic imaging or dobutamine echocardiography. Annual death rates were extracted, pooled and analyzed with a random effects model. The risk-adjusted relationship between severity of LV dysfunction, presence of viability and survival benefit associated with revascularization was assessed by meta-regression.

RESULTS

There were 3,088 patients (2,228 men), ejection fraction 32 +/- 8%, followed for 25 +/- 10 months. In patients with viability, revascularization was associated with 79.6% reduction in annual mortality (16% vs. 3.2%, chi-square = 147, p < 0.0001) compared with medical treatment. Patients without viability had intermediate mortality, trending to higher rates with revascularization versus medical therapy (7.7% vs. 6.2%, p = NS). Patients with viability showed a direct relationship between severity of LV dysfunction and magnitude of benefit with revascularization (p < 0.001). There was no measurable performance difference for predicting revascularization benefit between the three testing techniques.

CONCLUSIONS

This meta-analysis demonstrates a strong association between myocardial viability on noninvasive testing and improved survival after revascularization in patients with chronic CAD and LV dysfunction. Absence of viability was associated with no significant difference in outcomes, irrespective of treatment strategy.

Myocardial hibernation in coronary artery disease

Coronary artery disease (CAD) is very prevalent in Western societies and is a leading cause of mortality and morbidity. Despite decreases in mortality rates from CAD over the past 30 years, ischemic heart failure remains an important problem because people with CAD are now living longer. Hibernating myocardium may be defined as reversible left ventricular dysfunction due to chronic CAD that shows improvement in function after revascularization. Many patients with ischemic cardiomyopathy have areas of hibernating myocardium, and thus can potentially show improvement in left ventricular regional and global function if they are revascularized. Whether hibernating myocardium represents an adaptive response to hypoperfusion in the face of chronic ischemia or whether it is a degenerative process is not entirely clear. Clearly, ultrastructural changes of de-differentiation are seen, and include loss of sarcomeres and the appearance of small mitochondria and glycogen accumulation. Although the mechanisms underlying the changes in morphology and depressed contractility, and the factors governing recovery of function are not clear, changes in adrenergic receptor density, cytokine upregulation, and the degree of fibrosis may all play a role. Identification of viability is commonly performed with dobutamine echocardiography or nuclear imaging. Because patients with extensive CAD and poor left ventricular systolic function are high-risk candidates for coronary bypass surgery, the preoperative identification of viability provides important prognostic information. Patients with viable myocardium who are treated with revascularization rather than medical therapy have better outcomes in terms of survival, left ventricular function, symptoms, and exercise capacity.

Assessment of myocardial viability with contrast-enhanced magnetic resonance imaging: comparison with positron emission tomography

BACKGROUND

Recent studies indicate that MRI, after administration of gadolinium-diethylenetriamine pentaacetic acid, can identify nonviable areas in dysfunctional myocardium. We compared MRI hyperenhancement with PET as a gold standard for detection and quantification of myocardial scar tissue.

METHODS AND RESULTS

Thirty-one patients with ischemic heart failure (ejection fraction, 28+/-9%) were imaged with PET and MRI. Scar was defined as regionally increased MRI signal intensity 20 minutes after injection of 0.2 mmol/kg gadolinium-diethylenetriamine pentaacetic acid and as concordantly reduced perfusion and glucose metabolism as defined by PET. Sensitivity and specificity of MRI in identifying patients and segments (n=1023) with matched flow/metabolism defects was 0.96 of 1.0 and 0.86 of 0.94, respectively. Eleven percent of segments defined as viable by PET showed some degree of MRI hyperenhancement. Defect severity score based on visual analysis was 44.3+/-9.1 for PET and 47.6+/-11.1 for MRI (r=0.91, P<0.0001). Quantitatively assessed relative MRI infarct mass correlated well with PET infarct size (r=0.81, P<0.0001). Furthermore, MRI hyperenhancement was a better predictor of scar tissue than end-diastolic and end-systolic wall thickness or thickening.

CONCLUSIONS

In severe ischemic heart failure, MRI hyperenhancement as a marker of myocardial scar closely agrees with PET data. Although hyperenhancement correlated with areas of decreased flow and metabolism, it seems to identify scar tissue more frequently than PET, reflecting the higher spatial resolution. Additional functional studies after revascularization are required to define the significance of small islands of scar detected by MRI.

18F-deoxyglucose and the assessment of myocardial viability

The glucose analogue 18F-deoxyglucose allowed for the first time the ability to noninvasively probe and characterize the regional metabolism of glucose as a major fuel substrate of the human heart. Used with positron emission tomography, it became the tool for demonstrating the operation of metabolic processes, long before established in invasive or destructive experiments in animals, directly in the human myocardium. Clinical investigations with 18F-deoxy-glucose, combined with other radiotracers of the myocardium's substrate metabolism, showed the dependency of the heart's substrate selection on circulating levels of glucose, free fatty acid and insulin, and the operation of Randle's cycle in the human myocardium. Regional responses in substrate metabolism to the myocardial ischemia were now visualized entirely noninvasively as, for example, decreases in fatty acid usage and oxidation and oxygen consumption, but foremost as an increase in glucose use. Regional 18F-deoxyglucose uptake markedly in excess of myocardial blood flow in dysfunctional myocardium of patients after a myocardial infarction, with chronic coronary artery disease or with ischemic cardiomyopathy, soon became recognized as a hallmark of myocardial viability or potentially reversible contractile dysfunction. Defined as blood flow metabolism mismatch, this particular regional glucose uptake pattern identifies patients to be at high risk for cardiac events and, at the same time, to benefit most from surgical revascularization. The patterns predict a postrevascularization improvement in global left ventricular function and, even more important, in symptoms related to congestive heart failure and in long-term survival. 18F-deoxyglucose is now widely used with positron emission tomography and, more recently, with single photon emission computed tomography and radiotracers of myocardial perfursion for stratifying ischemic cardiomyopathy patients to the most efficacious treatment.

Anomalous origin of the left coronary artery from the pulmonary artery: Successful surgical strategy without assist devices

The objective of this review was to analyze a surgical strategy for children with anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA) where aortic implantation was successful without the use of extracorporeal membrane oxygenation (ECMO) or left ventricular assist device (LVAD). From 1989 through 1999, 16 consecutive children underwent aortic implantation for ALCAPA. Median age was 0.45 years. Surgical strategy included bicaval venous cannulation, LV vent, moderate systemic hypothermia (28 degrees C), antegrade cardioplegia with pulmonary artery (PA) occlusion, PA transection, aortic implantation with a large "button" of PA, PA reconstruction with pericardium, intraoperative transesophageal echocardiography, and inotropic support with dopamine, dobutamine, and milrinone. All patients survived. No patient was placed on ECMO or LVAD. Mean cardiopulmonary bypass (CPB) time was 152 +/- 41 minutes. Mean aortic cross-clamp time was 46 +/- 13 minutes. Mean time from cross-clamp removal to CPB off ("weaning" time) was 58 +/- 20 minutes. One patient had delayed sternal closure. Only 2 patients required more than 10 &mgr;g/kg/minute of dopamine and dobutamine. Mean hospital stay was 29 +/- 25 days. One patient required outpatient inotropic support for 5 months. Although ECMO or LVAD may be necessary for some ALCAPA patients, we describe a surgical strategy of aortic implantation that was successful without the use of assist devices. Copyright 2000 by W.B. Saunders Company

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.

Clinical importance of stunned and hibernating myocardium

Myocardial stunning and hibernation are states of potentially reversible myocardial dysfunction, which were first described more than 20 years ago (c.1980). Important advances have now been made in the ability to detect stunned and hibernating myocardium, as well as in the understanding of the impact of these conditions on patient outcomes. We discuss here the clinical importance of stunned and hibernating myocardium for patients with several common cardiac conditions.

Cardiac nuclear medicine in monitoring patients with coronary heart disease

Patient monitoring is a major indication for cardiac nuclear medicine procedures. Stress myocardial perfusion scintigraphy was initially used for diagnosis, but monitoring patients with coronary artery disease has become more common. Stress myocardial perfusion scintigraphy has been shown to provide a considerable amount of incremental prognostic information, which may be useful in selecting patients for therapy. In patients being considered for revascularization, fluorodeoxyglucose can be used to identify regions of dysfunctional but viable myocardium, even within regions that show fixed defects on stress perfusion imaging. It can be used to select a group of patients who will improve function with revascularization and who may have an improved outcome. Thus, cardiac nuclear medicine plays a pivotal role in monitoring patients with coronary artery disease.

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

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

Cardiac transplantation for cardiomyopathy and ischemic heart disease: differences in outcome up to 10 years

BACKGROUND

Ischemic heart disease (IHD) and cardiomyopathy (CM) are the most common indications for heart transplantation. The aim of this study was to investigate the difference in clinical outcome between these two groups.

METHODS

At our institution between 1987 and 1998 transplantation was performed in 133 patients with IHD and 87 with CM. Follow-up was complete for all patients (mean 87 months).

RESULTS

Mean age at time of surgery was 51 +/- 5 years for IHD versus 39 +/- 9 years for CM recipients (p = 0.02). There was no difference in donor age, donor gender, or pre-operative hemodynamics between the two groups. The operative mortality was 11.2% in IHD recipients and 10.6% in CM recipients (p = 0.9). No differences were observed in intra-cardiac pressures or incidence of renal dysfunction, infection, or malignancy between the two groups. The incidence of peripheral vascular incidents was significantly higher for IHD recipients (13% vs 3%, p = 0.02). At 10 years, the incidence of coronary artery disease was 35% and 9%, respectively (p = 0.02). Mean NYHA status was 2.0 +/- 0.3 and 1.1 +/- 0.2 for IHD and CM recipients, respectively (p = 0.013). The actuarial survival at 1, 5, and 10 years was 77%, 62%, and 39% for IHD recipients compared with 85%, 82%, and 80% for CM recipients (p = 0.7, p < 0.0001 and p < 0.0001, respectively).

CONCLUSION

After heart transplantation, medium- and long-term outcome is significantly better for CM than IHD recipients. In view of limited donor availability, it is appropriate to explore more vigorously alternative treatments for patients with severe ischemic left ventricular dysfunction.

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.

No difference in cardiac event-free survival between positron emission tomography-guided and single-photon emission computed tomography-guided patient management: a prospective, randomized comparison of patients with suspicion of jeopardized myocardium

OBJECTIVES

We sought to prospectively compare nitrogen-13 (13N)-ammonia/18fluorodeoxyglucose (18FDG) positron emission tomography (PET)-guided management with stress/rest technetium-99m (99mTc)-sestamibi single-photon emission computed tomography (SPECT)-guided management.

BACKGROUND

Patients with evidence of jeopardized (i.e., ischemic or viable) myocardium may benefit from revascularization, whereas patients without it should be treated with drugs. Both PET and SPECT imaging have been proven to delineate jeopardized myocardium. When patient management is based on identification of jeopardized myocardium, it is unknown which technique is most accurate for long-term prognosis.

METHODS

In a clinical setting, 103 patients considered for revascularization with left ventricular wall motion abnormalities and suspicion of jeopardized myocardium underwent both PET and SPECT imaging. The imaging results were used in a randomized fashion to determine management (percutaneous transluminal coronary angioplasty [PTCA], coronary artery bypass graft surgery [CABG] or drug treatment). Follow-up for cardiac events (cardiac death, myocardial infarction and revascularization) was recorded for 28 +/- 1 months. The study was designed to have a power of 80% to detect a 20% difference in the event rate between PET- and SPECT-based management.

RESULTS

Management decisions in 49 patients randomized to PET (12 who had PTCA, 14 CABG and 23 drug therapy) were comparable with 54 patients randomized to SPECT (15 who had PTCA, 13 CABG and 26 drug therapy). In terms of cardiac event-free survival, no differences between PET and SPECT were observed (11 vs. 13 cardiac events for PET and SPECT, respectively; p = NS by the Kaplan-Meier statistic).

CONCLUSIONS

No difference in patient management or cardiac event-free survival was demonstrated between management based on 13N-ammonia/18FDG PET and that based on stress/rest 99mTc-sestamibi SPECT imaging. Both techniques may be used for management of patients considered for revascularization with suspicion of jeopardized myocardium.

Positron emission tomography and low-dose dobutamine echocardiography in the prediction of postrevascularization improvement in left ventricular function and exercise parameters

BACKGROUND

We studied the value of low-dose dobutamine echocardiography (LDDE) and positron emission tomography (PET) in predicting improvement of left ventricular function and exercise parameters after revascularization.

METHODS

Forty-six consecutive patients with ischemic heart disease and an ejection fraction (EF) of 35% +/- 7% were included. Before revascularization, the patients underwent exercise testing and myocardial viability testing by LDDE and fluoride 18-fluoro-2-deoxyglucose PET. Six months after revascularization they underwent coronary angiography to study graft patency, and echocardiographic examination and the exercise test were repeated.

RESULTS

In the prediction of the presence or absence of improved postrevascularization function in left ventricular regions with patent grafts, PET was more sensitive than LDDE (42/52 regions [81%] vs 27/52 regions [51%], P <.01), whereas LDDE was more specific than PET (187/209 regions [89%] vs 118/209 regions [56%], P <.001). Improvement of regional myocardial dysfunction was found in 19 patients, but their global left ventricular function did not improve significantly (EF 34% +/- 6% and 36% +/- 7%). In the remaining 27 patients with irreversible dysfunction, EF decreased (EF 36% +/- 7% vs 32% +/- 8%, P <.05). Among patients with reversible myocardial dysfunction, the rate pressure product (RPP) increased after revascularization (19,522 +/- 5474 vs 26,190 +/- 5610 mm Hg/min, P <.01), whereas the RPP did not change in patients with irreversible myocardial dysfunction (21,546 +/- 5450 and 22,774 +/- 8249 mm Hg/min). The number of PET viable segments was a predictor of the postoperative increase in the RPP in univariate (P <.04) and multivariate analyses (P <.001). In contrast, LDDE did not bear any prognostic information about improvement in the RPP.

CONCLUSIONS

This study confirms earlier findings of higher sensitivity and lower specificity of PET compared with LDDE in predicting improvement of regional left ventricular function after revascularization. However, the feasibility of predicting postrevascularization improvement of exercise parameters seems unique for PET. The potential prognostic value of this finding needs further investigation.

The use of contrast-enhanced magnetic resonance imaging to identify reversible myocardial dysfunction

BACKGROUND

Recent studies indicate that magnetic resonance imaging (MRI) after the administration of contrast material can be used to distinguish between reversible and irreversible myocardial ischemic injury regardless of the extent of wall motion or the age of the infarct. We hypothesized that the results of contrast-enhanced MRI can be used to predict whether regions of abnormal ventricular contraction will improve after revascularization in patients with coronary artery disease.

METHODS

Gadolinium-enhanced MRI was performed in 50 patients with ventricular dysfunction before they underwent surgical or percutaneous revascularization. The transmural extent of hyperenhanced regions was postulated to represent the transmural extent of nonviable myocardium. The extent of regional contractility at the same locations was determined by cine MRI before and after revascularization in 41 patients.

RESULTS

Contrast-enhanced MRI showed hyperenhancement of myocardial tissue in 40 of 50 patients before revascularization. In all patients with hyperenhancement the difference in image intensity between hyperenhanced regions and regions without hyperenhancement was more than 6 SD. Before revascularization, 804 of the 2093 myocardial segments analyzed (38 percent) had abnormal contractility, and 694 segments (33 percent) had some areas of hyperenhancement. In an analysis of all 804 dysfunctional segments, the likelihood of improvement in regional contractility after revascularization decreased progressively as the transmural extent of hyperenhancement before revascularization increased (P<0.001). For instance, contractility increased in 256 of 329 segments (78 percent) with no hyperenhancement before revascularization, but in only 1 of 58 segments with hyperenhancement of more than 75 percent of tissue. The percentage of the left ventricle that was both dysfunctional and not hyperenhanced before revascularization was strongly related to the degree of improvement in the global mean wall-motion score (P<0.001) and the ejection fraction (P<0.001) after revascularization.

CONCLUSIONS

Reversible myocardial dysfunction can be identified by contrast-enhanced MRI before coronary revascularization.

Noninvasive characterization of stunned, hibernating, remodeled and nonviable myocardium in ischemic cardiomyopathy

OBJECTIVES

We evaluated a novel protocol of dual-isotope, gated single-photon emission computed tomographic (SPECT) imaging combined with low and high dose dobutamine as a single test for the characterization of various types of altered myocardial dysfunction.

BACKGROUND

Myocardial perfusion tomography and echocardiography have been used separately for the assessment of myocardial viability. However, it is possible to assess perfusion, function and contractile reserve using gated SPECT imaging.

METHODS

We studied 54 patients with ischemic cardiomyopathy using rest and 4 h redistribution thallium-201 imaging and dobutamine technetium-99m sestamibi SPECT imaging. The sestamibi images were acquired 1 h after infusion of the maximal tolerated dose of dobutamine and again during infusion of dobutamine at a low dose to estimate contractile reserve. Myocardial segments were defined as hibernating, stunned, remodeled or scarred.

RESULTS

Severe regional dysfunction was present in 584 (54%) of 1,080 segments. Based on the combination of function and perfusion characteristics in these 584 segments, 24% (n = 140) were labeled as hibernating; 23% (n = 136) as stunned; 30% (n = 177) as remodeled; and 22% (n = 131) as scarred. Contractile reserve, represented by improvement in wall motion/thickening by low dose dobutamine, was observed in 83% of stunned, 59% of hibernating, 35% of remodeled and 13% of scarred myocardial segments (p<0.05).

CONCLUSIONS

It is possible with this new imaging technique to characterize dysfunctional myocardium as stunned, hibernating, remodeled and nonviable. These subtypes often coexist in the same patient.

18-Fluorodeoxyglucose imaging with positron emission tomography and single photon emission computed tomography: cardiac applications

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 extensive viable myocardium, patients with predominantly scar tissue should be treated medically or evaluated for heart transplantation. Among the many viability tests, noninvasive assessment of cardiac glucose use (as a marker of viable tissue) with F18-fluorodeoxyglucose (FDG) is considered the most accurate technique to detect viable myocardium. Cardiac FDG uptake has traditionally been imaged with positron emission tomography (PET). Clinical studies have shown that FDG-PET can accurately identify patients with viable myocardium that are likely to benefit from revascularization procedures, in terms of improvement of left ventricular (LV) function, alleviation of heart failure symptoms, and improvement of long-term prognosis. However, the restricted availability of PET equipment cannot meet the increasing demand for viability studies. As a consequence, much effort has been invested over the past years in the development of 511-keV collimators, enabling FDG imaging with single-photon emission computed tomography (SPECT). Because SPECT cameras are widely available, this approach may allow a more widespread use of FDG for the assessment of myocardial viability. Initial studies have directly compared FDG-SPECT with FDG-PET and consistently reported a good agreement for the assessment of myocardial viability between these 2 techniques. Additional studies have shown that FDG-SPECT can also predict improvement of LV function and heart failure symptoms after revascularization. Finally, recent developments, including coincidence imaging and attenuation correction, may further optimize cardiac FDG imaging (for the assessment of viability) without PET systems.

Prognostic implications of Tc-99m sestamibi viability imaging and subsequent therapeutic strategy in patients with chronic coronary artery disease and left ventricular dysfunction

OBJECTIVES

The aim of the study was to verify the prognostic implications of viability detection using baseline-nitrate sestamibi imaging in patients with left ventricular (LV) dysfunction due to chronic coronary artery disease (CAD) submitted to different therapeutic strategies.

BACKGROUND

The prognostic meaning of preserved viability in these patients is still debated. Sestamibi is increasingly used for myocardial perfusion scintigraphy and is being accepted also as viability tracer, but no data are available about the relationship between viability in sestamibi imaging, subsequent treatment, and patient's outcome.

METHODS

Follow-up data were collected in 105 CAD patients with LV dysfunction who had undergone baseline-nitrate sestamibi perfusion imaging for viability assessment and had been later treated medically (group 1), or submitted to revascularization, which was either complete (group 2A) or incomplete (group 2B).

RESULTS

Eighteen hard events (cardiac death or nonfatal myocardial infarction) were registered during the follow-up. A significantly worse event-free survival curve was observed in the patients of group 1 (p < 0.0002) and group 2B (p < 0.03) compared to those of group 2A. Using a Cox proportional hazard model, the most powerful prognostic predictors of events were the number of nonrevascularized asynergic segments with viability in sestamibi imaging (p < 0.003, risk ratio [RR] = 1.4), and the severity of CAD (p < 0.02, RR = 1.28).

CONCLUSIONS

Viability detection in sestamibi imaging has important prognostic implications in CAD patients with LV dysfunction. Patients with preserved viability kept on medical therapy or submitted to incomplete revascularization represent high-risk groups.

F-18 fluoro deoxyglucose SPECT for assessment of myocardial viability

Identification of myocardial viability in hypokinetic segments is important in patients with ischemic cardiomyopathy because systolic dysfunction improves with revascularization. Positron emission tomography (PET) F-18 fluoro deoxyglucose (FDG) uptake has been demonstrated as an accurate indicator of metabolically active and thus viable myocardium. F-18 FDG single photon emission computed tomography (SPECT) has recently been introduced and offers a technically easier and less costly alternative to PET imaging for determination of myocardial viability. A body of literature demonstrates that F-18 FDG SPECT can reliably be performed with SPECT hardware equipped with 511-keV collimators, which provides an accurate assessment of myocardial viability. F-18 FDG SPECT offers data similar to those offered by F-18 FDG PET and compares favorably with other imaging modalities, including rest-redistribution and stress-reinjection thallium-201 myocardial perfusion imaging, gated technetium 99m SPECT, and low-dose dobutamine echocardiography.

Do the presence and amount of dysfunctional but viable myocardium affect the perioperative outcome of coronary artery bypass graft surgery?

The aim of our study was to assess the influence of the presence and amount of dysfunctional but viable myocardium on the perioperative outcomes in patients with coronary artery disease and moderate-to-severe left ventricular systolic dysfunction, who underwent coronary artery bypass graft surgery. Viability evaluation with low-dose dobutamine echocardiography was performed in 302 consecutive patients with coronary artery disease and left ventricular ejection fraction < or =40%, who were referred for coronary angiography and potential coronary revascularization. To quantify the amount of dysfunctional but viable myocardium, wall motion was scored using a 16-segment model. The dysfunctional segments were defined as viable if they exhibited improvement in their thickening by at least one grade. One hundred and twenty-seven patients underwent coronary artery bypass graft surgery. The perioperative outcomes were evaluated in 122 of them. Five patients were excluded because of inability to revascularize all vessels supplying dysfunctional but viable myocardial segments. Twenty-five patients exhibited a large amount of dysfunctional but viable myocardium (> or =6 segments, group A), 59 patients had a small amount of such myocardium (2-5 segments, group B), and 38 patients were found to have their dysfunctional myocardium irreversibly damaged (group C). The perioperative mortality in groups A, B, and C was 4, 10, and 11% (all P = NS), respectively. The rate of perioperative Q-wave myocardial infarction was 8, 10, and 3% (all P = NS), respectively. Similarly, there were no significant differences among the groups with respect to perioperative outcome variables including ventricular arrhythmias, duration and magnitude of catecholamine support, renal failure, pulmonary edema, and need for mechanical ventricular support or artificial ventilation. In patients with coronary artery disease and moderate-to-severe left ventricular dysfunction who underwent coronary artery bypass graft surgery, the presence and amount of dysfunctional but viable myocardium did not influence the perioperative outcome.

Failure to improve left ventricular function after coronary revascularization for ischemic cardiomyopathy is not associated with worse outcome

Background-Preoperative identification of viable myocardium in patients with ischemic cardiomyopathy is considered important because CABG can result in recovery of left ventricular (LV) function. However, the hypothesis that lack of improvement of LV function after CABG is associated with poorer patient outcome is untested. Methods and Results-Outcome was compared in patients with ischemic LV dysfunction (LVEF </=0.30) with and without improvement in LVEF after CABG. Of 135 consecutive patients, 128 (95%) survived CABG and 104 (77%) had pre- and post-CABG LVEF assessment. Of these 104 patients, 68 (65%) had >0.05 increase in LVEF (group A) and 36 (35%) had no significant change, or </=0.05 decrease in LVEF (group B) compared with pre-CABG LVEF. No significant differences existed in age, gender, comorbidities, baseline symptoms, baseline LVEF, or intraoperative variables between groups A and B. Group A increased LVEF from 0.24+/-0.05 to 0.39+/-0.1 (P<0.005). In Group B, LVEF did not change significantly postoperatively, 0.24+/-0.05 to 0.23+/-0.06 (P=NS). Postoperative improvement in angina and heart failure scores were similar between the 2 groups. Survival free of cardiac death was similar for both groups (93% in group A and 94% in group B, P=NS) at a mean follow-up of 32+/-23 months. Conclusions-Lack of improvement of global LVEF after CABG is not associated with poorer outcome compared with that of patients with improved LVEF, presumably because effective revascularization of ischemic myocardium, even without improvement in ventricular function, protects against future infarction and death.

Cardiological applications of nuclear medicine

Cardiovascular mortality is falling in most industrialised nations. Primarily responsible for this encouraging trend are preventive measures such as risk-factor modification but improved medical and surgical management have helped too. Clinical decision making in the patient with coronary heart disease demands techniques that not only describe coronary anatomy but also provide functional indices for early detection and to monitor the severity and extent of disease. Nuclear medicine methods can characterise non-invasively myocardial function, perfusion, and metabolism. Novel radiopharmaceuticals, improvements in imaging equipment, and extensive validation have contributed to the growing clinical acceptance of these techniques and to their cost-effective integration in the workup of patients with cardiovascular disease.

Dobutamine stress echocardiography and technetium-99m-tetrofosmin/fluorine 18-fluorodeoxyglucose single-photon emission computed tomography and influence of resting ejection fraction to assess myocardial viability in patients with severe left ventricular dysfunction and healed myocardial infarction

The purpose of this study was to compare 2 different techniques--dobutamine-atropine stress echocardiography (DSE) and dual-isotope simultaneous acquisition (technetium-99-m-tetrofosmin/fluorine 18-fluorodeoxyglucose) single-photon emission computed tomography (DISA-SPECT)--for assessment of viable myocardium. One hundred ten patients (mean age 55 +/- 9 years) with left ventricular (LV) dysfunction (mean LV ejection fraction 27 +/- 13%) underwent both DISA-SPECT and DSE. A 16-segment scoring model was adopted for both techniques. Four types of wall motion during DSE were assessed: (1) biphasic, improvement at low dose (10 microg/kg/min) with worsening at high dose; (2) worsening, deterioration without initial improvement; (3) sustained, persistent or late improvement; and (4) no change. Viability criteria were biphasic, worsening, and sustained improvement with DSE. Viability criteria with DISA-SPECT were normal perfusion and metabolism (normal), concordantly mildly reduced perfusion and metabolism (subendocardial scar), or severely reduced perfusion and increased metabolism (mismatch). Myocardium was considered nonviable with DSE in case of unchanged wall motion, or moderate reduction or absence in both technetium-99m-tetrofosmin perfusion and fluorodeoxyglucose uptake with DISA-SPECT. Of 1,756 of 1,760 analyzable LV segments, 1,373 (78%) had severe wall motion abnormalities at baseline (severe hypokinesia, akinesia, or dyskinesia). Of these abnormal segments, 282 (21%) were considered viable during DSE (63 [5%] with biphasic response, 47 [3%] with ischemia, and 172 [13%]) with sustained improvement, whereas 1,091 (79%) were considered nonviable. With DISA-SPECT, 396 (29%) segments were considered viable (312 [23%] with matched perfusion/metabolism and 84 [6%] with mismatch), whereas 977 segments (71%) were considered nonviable. Both techniques showed agreement for viability in 201 segments and 896 were concordantly classified as nonviable. Disagreement was present in 276 segments of which 195 (71%) were nonviable with DSE and viable with DISA-SPECT. Overall agreement between the 2 techniques was 81% (kappa 0.46) in a subgroup of patients with an ejection fraction <25% 78% (kappa 0.39). Thus, DSE and DISA-SPECT show good agreement for assessing viable myocardium not influenced by resting ejection fraction. DSE underestimated the amount of viable tissue compared with DISA-SPECT.

Improvement of left ventricular ejection fraction, heart failure symptoms and prognosis after revascularization in patients with chronic coronary artery disease and viable myocardium detected by dobutamine stress echocardiography

OBJECTIVES

This study was designed to address, in patients with severe ischemic left ventricular dysfunction, whether dobutamine stress echocardiography (DSE) can predict improvement of left ventricular ejection fraction (LVEF), functional status and long-term prognosis after revascularization.

BACKGROUND

Dobutamine stress echocardiography can predict improvement of wall motion after revascularization. The relation between viability, improvement of function, improvement of heart failure symptoms and long-term prognosis has not been studied.

METHODS

We studied 68 patients with DSE before revascularization; 62 patients underwent resting echocardiography/radionuclide ventriculography before and three months after revascularization. Long-term follow-up data (New York Heart Association [NYHA] functional class, Canadian Cardiovascular Society [CCS] classification and events) were acquired up to two years.

RESULTS

Patients with > or =4 viable segments on DSE (group A, n = 22) improved in LVEF at three months (from 27+/-6% to 33+/-7%, p < 0.01), in NYHA functional class (from 3.2+/-0.7 to 1.6+/-0.5, p < 0.01) and in CCS classification (from 2.9+/-0.3 to 1.2+/-0.4, p < 0.01); in patients with <4 viable segments (group B, n = 40) LVEF and NYHA functional class did not improve, whereas CCS classification improved significantly (from 3.0+/-0.8 to 1.3+/-0.5, p < 0.01). A higher event rate was observed at long-term follow-up in group B versus group A (47% vs. 17%, p < 0.05).

CONCLUSIONS

Patients with substantial viability on DSE demonstrated improvement in LVEF and NYHA functional class after revascularization; viability was also associated with a favorable prognosis after revascularization.

Concept and evaluation of hibernating myocardium

Hibernating myocardium is a state of persistently impaired myocardial and left ventricular function at rest due to reduced coronary blood flows. It can be defined as an exquisitely regulated tissue successfully adapting its activity to prevailing circumstances. It has been documented in patients with angina (chronic stable and/or unstable), acute myocardial infarction, heart failure and/or severe left ventricular dysfunction, and anomalous left coronary artery from the pulmonary artery. The diagnosis of hibernating myocardium involves (a) documenting left ventricular dysfunction at rest and (b) documenting that there is viable myocardium in the area of dysfunction. Tests commonly used for the latter are dobutamine echocardiography, 201Tl isotope studies, and positron image tomography. Revascularization, either by surgery or by interventional catheter techniques, has been shown to improve or normalize the abnormal left ventricular function at rest.

Prognostic utility of myocardial viability assessment

Myocardial viability assessment is useful in patients with severe coronary artery disease and severe left ventricular dysfunction. Whereas most studies have focused on recovery of regional function, there are emerging data on patient outcome. Review of these data suggests that patients with chronic ischemia, cardiomyopathy, and viable myocardium who are treated medically have a worse, outcome than those treated with coronary revascularization. However, there are no prospective randomized trials. We present perspectives for future studies.

Hibernating myocardium

Decreased myocardial contraction occurs as a consequence of a reduction in blood flow. The concept of hibernation implies a downregulation of contractile function as an adaptation to a reduction in myocardial blood flow that serves to maintain myocardial integrity and viability during persistent ischemia. Unequivocal evidence for this concept exists in scenarios of myocardial ischemia that lasts for several hours, and sustained perfusion-contraction matching, recovery of energy and substrate metabolism, the potential for recruitment of inotropic reserve at the expense of metabolic recovery, and lack of necrosis are established criteria of short-term hibernation. The mechanisms of short-term hibernation, apart from reduced calcium responsiveness, are not clear at present. Experimental studies with chronic coronary stenosis lasting more than several hours have failed to continuously monitor flow and function. Nevertheless, a number of studies in chronic animal models and patients have demonstrated regional myocardial dysfunction at reduced resting blood flow that recovered upon reperfusion, consistent with chronic hibernation. Further studies are required to distinguish chronic hibernation from cumulative stunning. With a better understanding of the mechanisms underlying short-term hibernation, it is hoped that these adaptive responses can be recruited and reinforced to minimize the consequences of acute myocardial ischemia and delay impending infarction. Patients with chronic hibernation must be identified and undergo adequate reperfusion therapy.

New concepts and paradigms in cardiovascular medicine: the noninvasive management of coronary artery disease

Coronary atherosclerosis is a diffuse heterogeneous process that occurs throughout the length of epicardial coronary arteries. Myocardial infarction and unstable coronary syndromes are caused most commonly by plaque rupture of lipid rich, less severe coronary artery stenoses. Vigorous cholesterol lowering by low fat food and lipid active drugs, control of hypertension, and smoking abstinence stabilize plaque and markedly reduce coronary events and angina pectoris with greater improvement in survival than reported for elective invasive revascularization procedures. The term "regression" or "reversal" of coronary artery disease (CAD) as used clinically incorporates the spectrum of beneficial changes in plaque composition and pathology, modest improvement in anatomic severity, endothelial healing, increased coronary flow and flow capacity, decreased symptoms, and improved survival. Standard coronary arteriography and standard noninvasive diagnostic tests (as commonly used) are inadequate for identifying or assessing severity of diffuse CAD. Newer technology or approaches using noninvasive positron emission tomography (PET), invasive intravascular ultrasound or pressure or flow velocity guide wires provide important new insights into the presence and severity of both segmental and diffuse CAD. Revascularization procedures may be beneficial in selected, restricted circumstances, primarily for 3-vessel disease and reduced left ventricular function and for "hibernating" or "stunned" myocardium. However, the benefits of revascularization procedures on survival in patients with good left ventricular function have not been convincingly documented, with substantive evidence that adverse outcomes outweigh the potential benefits. This collective new knowledge provides the basis for a shift in the management of CAD from an invasive, procedure-oriented viewpoint currently dominant in cardiology toward a noninvasive orientation that views the problem as a graded, continuous, heterogeneously diffuse disease process for which reversal treatment is optimal. Noninvasive management of CAD based on reversal treatment is a valid, safe, effective primary step, but it requires patient and physician knowledge. CAD should be treated immediately at the time of a firm diagnosis by simultaneous, vigorous risk factor management, low fat diet and a statin class drug. For control of high-density lipoprotein and triglycerides, other lipid active drugs should be added or substituted for statins if side effects prevent their use. Low fat food and weight control by appropriate caloric carbohydrate restriction are essential for reducing the highly atherogenic postprandial lipid surge that is not affected by statins. This vigorous reversal treatment, with aggressive anti-anginal and anti-platelet management as needed, should be used in every patient with diagnosed CAD before elective revascularization procedures are considered. In the author's experience, the majority of patients will pursue an effective reversal regimen when it is presented and managed appropriately with strong support by a knowledgeable participating physician providing sustained, intense guidance and pharmacologic control. For the minority of patients not responding to vigorous medical treatment or demonstrating progression, coronary arteriography and revascularization procedures are then appropriate.