Coronary revascularisation for postischaemic heart failure: how myocardial viability affects survival

Clinical value of dark-blood late gadolinium enhancement cardiovascular magnetic resonance without additional magnetization preparation

BACKGROUND

For two decades, bright-blood late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) has been considered the reference standard for the non-invasive assessment of myocardial viability. While bright-blood LGE can clearly distinguish areas of myocardial infarction from viable myocardium, it often suffers from poor scar-to-blood contrast, making subendocardial scar difficult to detect. Recently, we proposed a novel dark-blood LGE approach that increases scar-to-blood contrast and thereby improves subendocardial scar conspicuity. In the present study we sought to assess the clinical value of this novel approach in a large patient cohort with various non-congenital ischemic and non-ischemic cardiomyopathies on both 1.5 T and 3 T CMR scanners of different vendors.

METHODS

Three hundred consecutive patients referred for clinical CMR were randomly assigned to a 1.5 T or 3 T scanner. An entire short-axis stack and multiple long-axis views were acquired using conventional phase sensitive inversion recovery (PSIR) LGE with TI set to null myocardium (bright-blood) and proposed PSIR LGE with TI set to null blood (dark-blood), in a randomized order. The bright-blood LGE and dark-blood LGE images were separated, anonymized, and interpreted in a random order at different time points by one of five independent observers. Each case was analyzed for the type of scar, per-segment transmurality, papillary muscle enhancement, overall image quality, observer confidence, and presence of right ventricular scar and intraventricular thrombus.

RESULTS

Dark-blood LGE detected significantly more cases with ischemic scar compared to conventional bright-blood LGE (97 vs 89, p = 0.008), on both 1.5 T and 3 T, and led to a significantly increased total scar burden (3.3 ± 2.4 vs 3.0 ± 2.3 standard AHA segments, p = 0.015). Overall image quality significantly improved using dark-blood LGE compared to bright-blood LGE (81.3% vs 74.0% of all segments were of highest diagnostic quality, p = 0.006). Furthermore, dark-blood LGE led to significantly higher observer confidence (confident in 84.2% vs 78.4%, p = 0.033).

CONCLUSIONS

The improved detection of ischemic scar makes the proposed dark-blood LGE method a valuable diagnostic tool in the non-invasive assessment of myocardial scar. The applicability in routine clinical practice is further strengthened, as the present approach, in contrast to other recently proposed dark- and black-blood LGE techniques, is readily available without the need for scanner adjustments, extensive optimizations, or additional training.

Dark-blood late gadolinium enhancement without additional magnetization preparation

BACKGROUND

This study evaluates a novel dark-blood late gadolinium enhancement (LGE) cardiovascular magnetic resonance imaging (CMR) method, without using additional magnetization preparation, and compares it to conventional bright-blood LGE, for the detection of ischaemic myocardial scar. LGE is able to clearly depict myocardial infarction and macroscopic scarring from viable myocardium. However, due to the bright signal of adjacent left ventricular blood, the apparent volume of scar tissue can be significantly reduced, or even completely obscured. In addition, blood pool signal can mimic scar tissue and lead to false positive observations. Simply nulling the blood magnetization by choosing shorter inversion times, leads to a negative viable myocardium signal that appears equally as bright as scar due to the magnitude image reconstruction. However, by combining blood magnetization nulling with the extended grayscale range of phase-sensitive inversion-recovery (PSIR), a darker blood signal can be achieved whilst a dark myocardium and bright scar signal is preserved.

METHODS

LGE was performed in nine male patients (63 ± 11y) using a PSIR pulse sequence, with both conventional viable myocardium nulling and left ventricular blood nulling, in a randomized order. Regions of interest were drawn in the left ventricular blood, viable myocardium, and scar tissue, to assess contrast-to-noise ratios. Maximum scar transmurality, scar size, circumferential scar angle, and a confidence score for scar detection and maximum transmurality were also assessed. Bloch simulations were performed to simulate the magnetization levels of the left ventricular blood, viable myocardium, and scar tissue.

RESULTS

Average scar-to-blood contrast was significantly (p < 0.001) increased by 99% when nulling left ventricular blood instead of viable myocardium, while scar-to-myocardium contrast was maintained. Nulling left ventricular blood also led to significantly (p = 0.038) higher expert confidence in scar detection and maximum transmurality. No significant changes were found in scar transmurality (p = 0.317), normalized scar size (p = 0.054), and circumferential scar angle (p = 0.117).

CONCLUSIONS

Nulling left ventricular blood magnetization for PSIR LGE leads to improved scar-to-blood contrast and increased expert confidence in scar detection and scar transmurality. As no additional magnetization preparation is used, clinical application on current MR systems is readily available without the need for extensive optimizations, software modifications, and/or additional training.

Hibernating myocardium in heart failure

Ischemic left ventricular systolic dysfunction may result from myocardial necrosis or from hypocontractile areas of viable myocardium. In some cases, recovery of contractility may occur on revascularization--this reversibly dysfunctional tissue is commonly referred to as hibernating myocardium. Observational data suggest that revascularization of patients with ischemic left ventricular systolic dysfunction and known viable myocardium provides a survival benefit over medical therapy. Identification of viable, dysfunctional myocardium may be especially worthwhile in deciding which patients with ischemic left ventricular systolic dysfunction will benefit from revascularization procedures. Randomized, prospective trials evaluating this are currently ongoing. This review will provide an overview of the complex pathophysiology of viable, dysfunctional myocardium, and will discuss outcomes after revascularization. Of the techniques used to determine the presence of hibernating myocardium, functional methods such as stress echocardiography and cardiac magnetic resonance appear more specific, but less sensitive, than the nuclear modalities, which assess perfusion and metabolic activity. Currently, the availability of all methods is variable.

Dual inversion-recovery mr imaging sequence for reduced blood signal on late gadolinium-enhanced images of myocardial scar

PURPOSE

To investigate whether a dual inversion-recovery (IR) prepulse improves scar-to-blood contrast and expert confidence and consistency at late gadolinium-enhanced magnetic resonance (MR) imaging of myocardial scar compared with the standard IR technique at 3.0 T.

MATERIALS AND METHODS

The study was approved by the local ethics committee, and all patients provided written informed consent. Twelve men (mean age±standard deviation, 63 years±8) with known myocardial scar underwent MR imaging 10, 20, and 30 minutes after administration of 0.2 mmol/kg gadobutrol with a standard and dual IR sequence. Contrast-to-noise ratios (CNRs) were measured by using region-of-interest analysis, and data were compared with the analysis of variance test. Two experts measured scar size and transmurality, and data were compared with the Student t test and Bland-Altman test. Experts assigned confidence scores for scar detection and transmurality, which were compared with a Wilcoxon matched-pairs signed rank test.

RESULTS

Patient data showed improved scar-to-blood CNR for the dual IR technique compared with the standard IR technique at all time points (P<.05). For images obtained 20 minutes after contrast material administration, the dual IR sequence provided higher confidence scores for scar detection and transmurality assessment (P<.05) and resulted in more consistent assessment of scar size and transmurality between readers compared with the IR sequence (P<.05).

CONCLUSION

In this preliminary patient study, the dual IR prepulse improved contrast, scar visualization, and expert confidence and reduced expert differences in transmurality and scar size assessment compared with the standard IR technique.

PET and PET/CT in cardiovascular disease

The present review provides an overview of the role of cardiac positron emission tomography in the diagnosis and management of cardiovascular disease. It expands on the relative advantages and disadvantages over other imaging modalities as well as the available evidence supporting its value in the diagnosis and management of patients with coronary artery disease, the assessment of myocardial viability, and evaluation of the cardiac sympathetic nervous system. Furthermore, the recent developments, such as the implementation of high-end computed tomography devices to form hybrid systems, and the advances of molecular imaging probes in experimental applications are briefly discussed.

Radionuclide Imaging of Viable Myocardium: Is it Underutilized?

Coronary artery disease is the major cause of heart failure in North America. Viability assessment is important as it aims to identify patients who stand to benefit from coronary revascularization. Radionuclide modalities currently used in the assessment of viability include (201)Tl SPECT, (99m)Tc-based SPECT imaging, and (18)F-fluorodexoyglucose ((18)F-FDG)-PET imaging. Different advances have been made in the last year to improve the sensitivity and specificity of these modalities. In addition, the optimum amount of viable (yet dysfunctional) myocardium is important to identify in patients, as a risk-benefit ratio must be considered. Patients with predominantly viable/hibernating myocardium can benefit from revascularization from a mortality and morbidity standpoint. However, in patients with minimal viability (predominantly scarred myocardium), revascularization risk may certainly be too high to justify revascularization without expected benefit. Understanding different radionuclide modalities and new developments in the assessment of viability in ischemic heart failure patients is the focus of this discussion.

Hibernating myocardium: diagnosis and patient outcomes

Approximately 50% of the patients with chronic obstructive coronary artery disease resulting in chronic contractile dysfunction have hibernating myocardium and may benefit from revascularization. This pooled analysis describes the relative merits of dobutamine echocardiography, thallium-201 and technetium-99m scintigraphy, positron emission tomography, and magnetic resonance imaging, for the diagnosis of hibernating myocardium and prediction of patient outcomes.

Metabolic imaging using PET

INTRODUCTION

There is growing evidence that myocardial metabolism plays a key role not only in ischaemic heart disease but also in a variety of diseases which involve myocardium globally, such as heart failure and diabetes mellitus. Understanding myocardial metabolism in such diseases helps to elucidate the pathophysiology and assists in making therapeutic decisions.

MEASUREMENT

As well as providing information on regional changes, PET can deliver quantitative information about both regional and global changes in metabolism. This capability of quantitative measurement is one of the major advantages of PET along with physiological positron tracers, especially relevant in evaluating diseases which involve the whole myocardium.

DISCUSSION

This review discusses major PET tracers for metabolic imaging and their clinical applications and contributions to research regarding ischaemic heart disease and other diseases such as heart failure and diabetic heart disease. Future applications of positron metabolic tracers for the detection of vulnerable plaque are also highlighted briefly.

Diagnostic and clinical perspectives of fusion imaging in cardiology: is the total greater than the sum of its parts?

Positron emission tomography, cardiovascular magnetic resonance and multislice computed tomography have contributed to changing our pathophysiological understanding of many conditions. Clinically, they have provided new tools for the identification of preclinical disease and a better understanding of how disease progresses. The application of these imaging modalities to preclinical disease and the use of these techniques in patients with overt cardiovascular disease are reviewed.

The use of stress echocardiography for prognostication in coronary artery disease: an overview

PURPOSE OF REVIEW

Stress echocardiography has a high accuracy for the detection of coronary artery disease. Additionally, it provides clinically useful prognostic information, such as resting left ventricular function, myocardial viability, stress-induced ischemia, vascular extent of wall motion abnormalities, and changes in end-systolic volume and ejection fraction with stress.

RECENT DEVELOPMENTS

The timing, extent, and severity of the stress-induced wall motion abnormalities are important determinants of long-term prognosis. Previous studies have shown the efficacy of stress echocardiography in predicting long-term cardiac events in mixed patient groups and the value of this test in selected patient subsets.

SUMMARY

This review attempts to define the role of stress echocardiography for prognostication in coronary artery disease, pointing out the ability of this technique to identify low-risk and high-risk subsets among patients with known or suspected coronary artery disease and thus guide patient management decisions.

Myocardial infarct: depiction with contrast-enhanced MR imaging--comparison of gadopentetate and gadobenate

Institutional review board approval and patient written informed consent were obtained. On two separate occasions, 24 hours apart, contrast-enhanced cardiac magnetic resonance (MR) imaging was performed prospectively at 1, 3, 5, 10, and 20 minutes after injection of gadopentetate dimeglumine and gadobenate dimeglumine in 15 patients (11 men, four women) with history of myocardial infarction. Both agents allowed detection of infarcted myocardium. T1 values at all times were significantly (P < .05) lower for gadobenate, compared with values for gadopentetate, in both infarcted and noninfarcted myocardium. At 1 minute after administration of both agents, T1 values in left ventricular cavity (LVC) were not different; at 3-20 minutes after injection, values were significantly (P < .05) lower for gadobenate. Differences between contrast-to-noise ratio (CNR) values of infarcted and noninfarcted myocardium were significantly higher on gadobenate-enhanced images (P < .05). CNR values between infarcted myocardium and LVC were significantly higher on gadopentetate-enhanced images (P < .05). Gadopentetate might permit better delineation of infarcts, especially subendocardial infarcts.

Coronary recanalisation, myocardial viability, and ventricular remodelling after infarction

It is important to identify the mechanisms that determine the progression to left ventricular remodelling after an acute myocardial infarction, in order that patients can be treated before the development of overt heart failure.

The relation between viable segments and left ventricular ejection fraction improvement

For patients with coronary artery disease and left ventricular dysfunction who undergo revascularization, it is important to estimate the left ventricular ejection fraction (LVEF) improvement after revascularization, as this is a strong indicator of the long-term outcome. Identification of viable segments from echocardiography has been considered a predictive sign of LVEF improvement. However, a quantitative relation between segmental function recovery and global ejection fraction improvement has not been established. There is a clinical need to determine parameters that are predictive to LVEF improvement. A cylindrical left ventricular model is proposed to establish the relation between segmental myocardial function and LVEF based on a 12-segment echocardiograph model. Model results show that LVEF improvement is directly related to the contraction ratio in normal segments and a weighted sum of the number of viable segments that recover to normal or hypokinetic, which is equal to a weighted sum of the change in wall motion scores. This new combined parameter is a better predictor of the amount of LVEF improvement than the total number of viable segments or preoperative ejection fraction. The predictive value of the model was illustrated in a group of four patients with coronary artery disease who underwent revascularization.

An echocardiogram-based 16-segment model for predicting left ventricular ejection fraction improvement

An important goal of cardiac revascularization is to improve the left ventricular ejection fraction, which is an important clinical determinant of the long-term outcome for patients with coronary artery disease. Regional myocardium function improvement may be expected from revascularization when viable myocardium is detected using non-invasive cardiac imaging. However, the quantitative relation between regional myocardial function recovery and global heart function improvement has not been determined and there is no tool to predict the amount of ejection fraction improvement prior to revascularization. A 16 segment biomechanical model of the left ventricle is proposed to establish the relationship between the ejection fraction improvement and the viable segments detected by echocardiography. With the assumption that the viable segments would potentially improve contractility after revascularization, the ejection fraction improvement is estimated for all possible wall motion score improvement in viable segments. The model shows that the ejection fraction improvement is linearly related to the contractility in the normal segments and a weighted sum of the numbers of viable segments that recover to normal or hypokinetic contractility. The predictive value of the model is illustrated for a group of patients reported in the literature. The model predictions of the post-revascularization ejection fraction are very close to the follow-up data with a very strong correlation (R2 = 0.92). By predicting the ejection fraction improvement, the model may provide a tool for evaluating the efficacy of revascularization and for selecting patients who would benefit from revascularization.

Does resting two-dimensional echocardiography identify patients with ischemic cardiomyopathy and low likelihood of functional recovery after coronary revascularization?

OBJECTIVE

To evaluate the potential of a simple and widely available technique as two-dimensional (2D) echocardiography to identify patients with ischemic cardiomyopathy and low likelihood of functional recovery after coronary revascularization.

METHODS

Two-dimensional echocardiography and radionuclide ventriculography (RNV) were performed before coronary revascularization in 94 patients with ischemic cardiomyopathy. Left ventricular ejection fraction (LVEF) was measured by RNV. Regional wall motion abnormalities, wall motion score index, end-diastolic wall thickness (EDWT), left ventricular (LV) volumes and LV sphericity index were assessed in the echocardiographic images. RNV was repeated 9-12 months after revascularization to assess LVEF change; an improvement >or=5% was considered clinically significant.

RESULTS

Nine hundred and ninety-nine segments were severely dysfunctional; 149 out of 999 (15%) had an EDWT <or=6 mm. A severe enlargement of the end-diastolic volume index (EDVI) (>or=100 ml/ml) and of the end-systolic volume index (>or=80 ml) was present in 32 (34%) and 21 (22%) patients, respectively. A spherical shape of the LV was observed in 35 (37%) patients. LVEF after revascularization increased in 30 out of 94 patients (32%) from 30+/-8% to 39+/-9% (P<0.0001). On multivariate analysis, the EDVI was the only predictor of no recovery in LVEF [odds ratio, 1.06, confidence interval (CI), 1.04-1.1, P<0.0001]. The cut-off value of EDVI >or=90 ml/ml accurately identified patients that virtually never recover. Post-operatively, LVEF increased in three out of 42 (7%, 95% CI 0-15%) patients with EDVI >or=90 ml/ml as compared to 27 out of 52 (52%) patients with EDVI<90 ml/ml (P<0.0001).

CONCLUSIONS

In patients with ischemic cardiomyopathy and severe LV enlargement, improvement of LVEF after revascularization is unlikely to occur. Conversely, in patients with relatively preserved LV size, a higher likelihood of functional recovery may be anticipated.

The contribution of hibernation to heart failure

For many years the functional sequelae of chronic coronary artery disease (CAD) were considered irreversible. Evidence accrued over the past three decades proves that this concept is not necessarily true. Non-randomised studies demonstrated that coronary revascularisation (CR) confers symptomatic and prognostic benefits to patients with CAD and heart failure. Based on available studies, one can assume that the beneficial effect of CR in heart failure derives primarily from recovery of contractile function in 'hibernating myocardium' (HM), i.e., chronically dysfunctional, but viable, myocardium subtended by stenosed coronary arteries which recovers after CR. Cardiac imaging with echocardiography, single photon and positron emission tomography (PET) and magnetic resonance allows the identification of HM. These techniques have comparable predictive values in patients with moderate left ventricular impairment. PET studies have shown that resting myocardial blood flow is preserved in most cases of HM while its main feature is a severe impairment of coronary flow reserve. Thus, the pathophysiology of HM is more complex than initially postulated. Recent evidence that repetitive ischaemia 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.

Early versus delayed revascularization in patients with ischemic cardiomyopathy and substantial viability: impact on outcome

BACKGROUND

Patients with ischemic cardiomyopathy and viable myocardium may improve in function and prognosis following revascularization. Delayed revascularization may result in less favorable outcome, and therefore the impact of timing of revascularization on long-term outcome was evaluated.

METHODS AND RESULTS

Patients (n=85) with ischemic cardiomyopathy and substantial viability (>or=25% of the left ventricle) on dobutamine stress echocardiography underwent surgical revascularization. Based on the waiting time for revascularization, patients were divided into 2 groups: early (<or=1 month) and late (>1 month) revascularization. Left ventricular ejection fraction (LVEF) was assessed before and 9 to 12 months after revascularization; follow-up data were acquired up to 2 years after revascularization. Hence, 40 patients underwent early (20+/-12 days) and 45 late (85+/-47 days) revascularization. Baseline characteristics of the two groups were comparable. Preoperative deaths were 0 in the early and 2 in the late group. Patients with early revascularization remained shorter time in the intensive care unit (2.4+/-1.5 days versus 5.9+/-2.1 days for the late group, P<0.05). Low output syndrome was observed more frequently in the late group (8% versus 22%, P=0.06). On long-term follow-up, mortality (5% versus 20%, P<0.05) and re-hospitalization for heart failure (10% versus 24%, NS) were higher in the late group. LVEF improved from 28+/-9% to 40+/-12% (P<0.05) in the early group and remained unchanged in the late group (27+/-10% versus 25+/-7%, NS).

CONCLUSIONS

Patients with ischemic cardiomyopathy and viable myocardium benefit from early revascularization (with improvement in LVEF and favorable prognosis), whereas delayed revascularization of these patients is associated with worse outcome.

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.

The heart failure revascularisation trial (HEART): rationale, design and methodology

BACKGROUND

Most patients with heart failure due to left ventricular systolic dysfunction (LVSD) secondary to coronary artery disease (CAD) have evidence of myocardium in jeopardy (reversible ischaemia and/or stunning hibernation). It is not known whether revascularisation in such cases is safe or beneficial.

AIMS

To determine whether revascularisation will improve the survival of patients with LVSD and heart failure secondary to CAD and myocardium in jeopardy.

METHODS

This is a randomised controlled trial comparing revascularisation or not, in addition to optimal medical therapy with ACE inhibitors, beta-blockers, aldosterone antagonists and an anti-thrombotic agent. Patients must have heart failure requiring treatment with diuretics, a left ventricular ejection fraction <35% and evidence of coronary disease. Myocardial viability and ischaemia are assessed by a broad range of techniques including stress echocardiography and nuclear imaging. All imaging tests are reviewed in core laboratories to ensure uniform reporting. Any conventional revascularisation technique is permitted. The primary outcome measure is all cause mortality. Symptoms, quality of life and health economic issues will also be explored. Assuming an annual mortality of 10% in the control group and allowing for substantial cross-over rates, a study of 800 patients followed for 5 years has 80% power with an alpha of 0.05 (two-sided) to show a 25% reduction in mortality with revascularisation.

RESULTS

At the time of writing 180 patients have been screened for inclusion, 111 have consented to participate and 70 have been randomised. The results of viability testing are awaited in 22 patients. Twenty-six patients had been investigated for myocardial viability and/or by angiography prior to consent, as part of the routine practice in that cardiology department. Of 68 patients who have completed assessment only after consent, 47 (69%) were included. The principal reason for drop-out between consent and randomisation was lack of evidence of myocardial ischaemia or hibernation.

CONCLUSION

The HEART trial will help to determine whether investigation of myocardial ischaemia and/or viability with a view to revascularisation should become part of the routine care of patients with heart failure due to LVSD and CAD.

Radionuclide viability testing: should it affect treatment strategy in patients with cardiomyopathy and significant coronary artery disease?

BACKGROUND

Ischemic heart failure is a significant source of morbidity and mortality, yet it has an unclear treatment strategy. The assessment of viable myocardium by nuclear imaging studies has shown promise in predicting improvements in ejection fraction and symptoms. However, the relationship of viability to long-term mortality has not been fully established.

METHODS

A number of studies have addressed long-term mortality with nuclear viability imaging in patients with impaired left ventricular function and significant coronary artery disease. These studies were analyzed to determine differences in design, results, trends, and limitations. They were then evaluated by use of qualitative criteria established for prognostic studies.

RESULTS

Fourteen studies met our criteria. Although the conclusions differed, it appears that patients with viability who undergo revascularization have the highest survival rate, whereas patients with viability who are treated medically have a much lower survival rate. Patients without viability have an intermediate survival rate, regardless of treatment. Several limitations were identified, including a lack of randomization, small sample size, inadequate follow-up, and extensive study protocol and design differences.

CONCLUSIONS

The use of viability testing in patients with heart failure and significant coronary artery disease has shown promise in predicting the long-term mortality rate with treatment allocation. However, there is a need for further study involving larger cohorts with a randomized design, longer periods of follow-up, improved study designs, and identification of referral bias and viability prevalence.

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.

Hibernation and congestive heart failure

The most common cause of heart failure is coronary artery disease, and whilst intensive treatment of acute coronary syndromes and myocardial infarction continue to reduce the mortality associated with these conditions, many survivors develop heart failure. In general, heart failure secondary to ischaemic heart disease results from: (i) irreversible myocyte loss due to infarction with scar formation; (ii) chronic left ventricular dysfunction which may recover after revascularisation (hibernating myocardium); (iii) changes in remote myocardium (adverse remodelling). A number of studies suggest that patients with post-ischaemic heart failure may derive symptomatic and prognostic benefit from coronary revascularisation and most of this benefit is thought to derive from functional improvement of hibernating myocardium. Although the mechanisms of hibernation remain poorly understood, studies with positron emission tomography have shown that blood flow to hibernating myocardium is usually within or only slightly below the normal range whilst the coronary vasodilator reserve is always severely reduced and the concept that stunning and hibernation may be causally related has gained support in recent years. There is increasing consensus amongst clinicians regarding the importance of identifying and treating hibernating myocardium in patients with coronary artery disease and heart failure, and a randomised study comparing optimum medical treatment to optimum medical treatment with complete revascularisation has just commenced in the United Kingdom (HEART-UK) and will provide guidance regarding diagnosis and treatment of these patients.

Usefulness of quantitative echocardiographic techniques to predict recovery of regional and global left ventricular function after acute myocardial infarction

The left ventricular response to dobutamine may be quantified using tissue Doppler measurement of myocardial velocity or displacement or 3-dimensional echocardiography to measure ventricular volume and ejection fraction. This study sought to explore the accuracy of these methods for predicting segmental and global responses to therapy. Standard dobutamine and 3-dimensional echocardiography were performed in 92 consecutive patients with abnormal left ventricular function at rest. Recovery of function was defined by comparison with follow-up echocardiography at rest 5 months later. Segments that showed improved regional function at follow-up showed a higher increment in peak tissue Doppler velocity with dobutamine therapy than in nonviable segments (1.2 +/- 0.4 vs 0.3 +/- 0.2 cm/s, p = 0.001). Similarly, patients who showed a >5% improvement of ejection fraction at follow-up showed a greater displacement response to dobutamine (6.9 +/- 3.2 vs 2.1 +/- 2.3 mm, p = 0.001), as well as a higher rate of ejection fraction response to dobutamine (9 +/- 3% vs 2 +/- 2%, p = 0.001). The optimal cutoff values for predicting subsequent recovery of function at rest were an increment of peak velocity >1 cm/s, >5 mm of displacement, and a >5% improvement of ejection fraction with low-dose dobutamine.

Imaging time after Gd-DTPA injection is critical in using delayed enhancement to determine infarct size accurately with magnetic resonance imaging

BACKGROUND

In patients with acute myocardial infarction (MI), delayed enhancement is seen in MRI 5 to 7 minutes after gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) injection, and the enhancement occurs in regions that later show recovery of function. However, in a canine model of acute MI, delayed enhancement 20 to 30 minutes after injection only occurs in necrotic regions and not in surrounding, reversibly injured myocardium. The objective of the present study was to determine (1) if the size of the enhanced region varies with time after Gd-DTPA injection and (2) if and when the size of the enhanced region corresponds to the true infarct size.

METHODS AND RESULTS

The left coronary artery was occluded in 15 Lewis rats for 30 minutes (n=9) or 2 hours (n=6); this was followed by reperfusion. MRI scans were performed 48+/-2 hours after-MI. Midventricular short-axis images were obtained continuously for 40 minutes after Gd-DTPA injection (0.3 mmol/kg). The sizes of enhanced regions at each time were determined by threshold analysis and compared with triphenyltetrazolium chloride-stained sections of the excised rat heart. In all animals, the enhanced region overestimated infarct size (28+/-5%) immediately after the injection of Gd-DTPA, although it then gradually receded to match the size of the infarct. The time required for enhancement to accurately determine infarct size was significantly different between 2-hour infarcts (16+/-2 minutes) and 30-minute (26+/-4 minutes) infarcts (P<0.05).

CONCLUSIONS

In reperfused acute MI, accurate determination of infarct size by delayed enhancement MRI requires imaging at specific times after Gd-DTPA injection, and this time varies with the duration of occlusion.

Quantitative prediction of improvement in cardiac function after revascularization with MR imaging and modeling: initial results

PURPOSE

To evaluate a model that can be used quantitatively to predict changes in postrevascularization left ventricular function based on classification of myocardial tissue as hibernating, scarred, or normal with cine magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Eleven patients with chronic left ventricular dysfunction were studied before and after revascularization with cine MR imaging. Regional myocardial contractility and wall thickness were used in the model to predict postrevascularization ejection fraction (EF). The actual EF from the postrevascularization MR images was compared with the EF from the prerevascularization images predicted with the model by using regression analysis and Bland-Altman analysis.

RESULTS

Correlation between the actual EF after revascularization and the EF predicted by using the model yielded an R value of 0.98, with a standard error of 1.3 EF percentage points. Predicting changes in function in a myocardial segment was less successful because only 55% of segments classified as hibernating actually improved resting function after revascularization. In nonimproved segments, 78% were either adjacent to infarcted segments or had nontransmural wall thinning.

CONCLUSION

A simple mathematical model combined with functional information provided by MR imaging was used to predict improvements in global EF resulting from revascularization.

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.

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.