Prevalence of hibernating myocardium in patients with severely impaired ischaemic left ventricles

Gated metabolic myocardial imaging, a surrogate for dual perfusion-metabolism imaging by positron emission tomography

Objective

Perfusion-metabolism mismatch pattern on positron emission tomography (PET) predicts hibernating myocardium. We assess the ECG-gated metabolic PET as a surrogate for the perfusion-metabolism mismatch pattern on PET imaging.

Methods

¹³N-Ammonia (NH₃) and ¹⁸F-fluorodeoxyglucose (FDG) are respectively perfusion and metabolism PET tracers. We used ECG gating to acquire FDG-PET to collect wall thickening (mechanical) data. These allow detection of metabolic activity in regions with reduced contraction (metabolism-mechanical mismatch pattern). We had two data sets on each patient: perfusion-metabolism and metabolism-mechanical data sets. We tested the hypothesis that metabolism-mechanical pattern on PET could predict perfusion-metabolism mismatch pattern.

Results

We studied 55 patients (48 males), mean age 62 years. All were in sinus rhythm, and had impaired left ventricular contraction. Perfusion-metabolism mismatch pattern was found in 26 patients. Metabolism-mechanical mismatch pattern was found in 25 patients. The results were concordant in 52 patients (95%). As a surrogate for perfusion-metabolism mismatch pattern, demonstration of metabolism-mechanical mismatch pattern is highly sensitive (92%) and specific (97%). In this cohort, the positive and negative predictive accuracy of the new method are 96% and 93%, respectively.

Conclusion

Metabolism-mechanical mismatch pattern could predict perfusion-metabolism mismatch pattern in patients with myocardial viability criteria on PET. Prospective validation against the gold standard of improved myocardial contraction after revascularisation is needed.

Impact of Ischemic Heart Failure Etiology on Cardiac Recovery During Mechanical Unloading

BACKGROUND

Small-scale studies focused mainly on nonischemic cardiomyopathy (NICM) have shown that a subset of left ventricular assist device (LVAD) patients can achieve significant improvement of their native heart function, but the impact of ischemic cardiomyopathy (ICM) has not been specifically investigated. Many patients with acute myocardial infarction are discharged from their index hospitalization without heart failure (HF), only to return much later with overt HF syndrome, mainly caused by chronic remodeling of the noninfarcted region of the myocardium.

OBJECTIVES

This study sought to prospectively investigate the effect of ICM HF etiology on LVAD-associated improvement of cardiac structure and function using NICM as control.

METHODS

Consecutive patients (n = 154) with documented chronic and dilated cardiomyopathy (ICM, n = 61; NICM, n = 93) requiring durable support with continuous-flow LVAD were prospectively evaluated with serial echocardiograms and right heart catheterizations.

RESULTS

In patients supported with LVAD for at least 6 months, we found that 5% of subjects with ICM and 21% of subjects with NICM achieved left ventricular ejection fraction ≥40% (p = 0.034). LV end-diastolic and end-systolic volumes and diastolic function were significantly and similarly improved in patients with ICM and NICM.

CONCLUSIONS

LVAD-associated unloading for 6 months resulted in a substantial improvement in myocardial structure, and systolic and diastolic function in 1 in 20 ICM and 1 in 5 NICM patients. These specific incidence and timeline findings may provide guidance in clinical practice and research design for sequencing and prioritizing advanced HF and heart transplantation therapeutic options in patients with ICM and NICM.

Systematic review and modelling of the cost-effectiveness of cardiac magnetic resonance imaging compared with current existing testing pathways in ischaemic cardiomyopathy

BACKGROUND

Cardiac magnetic resonance imaging (CMR) is increasingly used to assess patients for myocardial viability prior to revascularisation. This is important to ensure that only those likely to benefit are subjected to the risk of revascularisation.

OBJECTIVES

To assess current evidence on the accuracy and cost-effectiveness of CMR to test patients prior to revascularisation in ischaemic cardiomyopathy; to develop an economic model to assess cost-effectiveness for different imaging strategies; and to identify areas for further primary research.

DATA SOURCES

Databases searched were: MEDLINE including MEDLINE In-Process & Other Non-Indexed Citations Initial searches were conducted in March 2011 in the following databases with dates: MEDLINE including MEDLINE In-Process & Other Non-Indexed Citations via Ovid (1946 to March 2011); Bioscience Information Service (BIOSIS) Previews via Web of Science (1969 to March 2011); EMBASE via Ovid (1974 to March 2011); Cochrane Database of Systematic Reviews via The Cochrane Library (1996 to March 2011); Cochrane Central Register of Controlled Trials via The Cochrane Library 1998 to March 2011; Database of Abstracts of Reviews of Effects via The Cochrane Library (1994 to March 2011); NHS Economic Evaluation Database via The Cochrane Library (1968 to March 2011); Health Technology Assessment Database via The Cochrane Library (1989 to March 2011); and the Science Citation Index via Web of Science (1900 to March 2011). Additional searches were conducted from October to November 2011 in the following databases with dates: MEDLINE including MEDLINE In-Process & Other Non-Indexed Citations via Ovid (1946 to November 2011); BIOSIS Previews via Web of Science (1969 to October 2011); EMBASE via Ovid (1974 to November 2011); Cochrane Database of Systematic Reviews via The Cochrane Library (1996 to November 2011); Cochrane Central Register of Controlled Trials via The Cochrane Library (1998 to November 2011); Database of Abstracts of Reviews of Effects via The Cochrane Library (1994 to November 2011); NHS Economic Evaluation Database via The Cochrane Library (1968 to November 2011); Health Technology Assessment Database via The Cochrane Library (1989 to November 2011); and the Science Citation Index via Web of Science (1900 to October 2011). Electronic databases were searched March-November 2011.

REVIEW METHODS

The systematic review selected studies that assessed the clinical effectiveness and cost-effectiveness of CMR to establish the role of CMR in viability assessment compared with other imaging techniques: stress echocardiography, single-photon emission computed tomography (SPECT) and positron emission tomography (PET). Studies had to have an appropriate reference standard and contain accuracy data or sufficient details so that accuracy data could be calculated. Data were extracted by two reviewers and discrepancies resolved by discussion. Quality of studies was assessed using the QUADAS II tool (University of Bristol, Bristol, UK). A rigorous diagnostic accuracy systematic review assessed clinical and cost-effectiveness of CMR in viability assessment. A health economic model estimated costs and quality-adjusted life-years (QALYs) accrued by diagnostic pathways for identifying patients with viable myocardium in ischaemic cardiomyopathy with a view to revascularisation. The pathways involved CMR, stress echocardiography, SPECT, PET alone or in combination. Strategies of no testing and revascularisation were included to determine the most cost-effective strategy.

RESULTS

Twenty-four studies met the inclusion criteria. All were prospective. Participant numbers ranged from 8 to 52. The mean left ventricular ejection fraction in studies reporting this outcome was 24-62%. CMR approaches included stress CMR and late gadolinium-enhanced cardiovascular magnetic resonance imaging (CE CMR). Recovery following revascularisation was the reference standard. Twelve studies assessed diagnostic accuracy of stress CMR and 14 studies assessed CE CMR. A bivariate regression model was used to calculate the sensitivity and specificity of CMR. Summary sensitivity and specificity for stress CMR was 82.2% [95% confidence interval (CI) 73.2% to 88.7%] and 87.1% (95% CI 80.4% to 91.7%) and for CE CMR was 95.5% (95% CI 94.1% to 96.7%) and 53% (95% CI 40.4% to 65.2%) respectively. The sensitivity and specificity of PET, SPECT and stress echocardiography were calculated using data from 10 studies and systematic reviews. The sensitivity of PET was 94.7% (95% CI 90.3% to 97.2%), of SPECT was 85.1% (95% CI 78.1% to 90.2%) and of stress echocardiography was 77.6% (95% CI 70.7% to 83.3%). The specificity of PET was 68.8% (95% CI 50% to 82.9%), of SPECT was 62.1% (95% CI 52.7% to 70.7%) and of stress echocardiography was 69.6% (95% CI 62.4% to 75.9%). All currently used diagnostic strategies were cost-effective compared with no testing at current National Institute for Health and Care Excellence thresholds. If the annual mortality rates for non-viable patients were assumed to be higher for revascularised patients, then testing with CE CMR was most cost-effective at a threshold of £20,000/QALY. The proportion of model runs in which each strategy was most cost-effective, at a threshold of £20,000/QALY, was 40% for CE CMR, 42% for PET and 16.5% for revascularising everyone. The expected value of perfect information at £20,000/QALY was £620 per patient. If all patients (viable or not) gained benefit from revascularisation, then it was most cost-effective to revascularise all patients.

LIMITATIONS

Definitions and techniques assessing viability were highly variable, making data extraction and comparisons difficult. Lack of evidence meant assumptions were made in the model leading to uncertainty; differing scenarios were generated around key assumptions.

CONCLUSIONS

All the diagnostic pathways are a cost-effective use of NHS resources. Given the uncertainty in the mortality rates, the cost-effectiveness analysis was performed using a set of scenarios. The cost-effectiveness analyses suggest that CE CMR and revascularising everyone were the optimal strategies. Future research should look at implementation costs for this type of imaging service, provide guidance on consistent reporting of diagnostic testing data for viability assessment, and focus on the impact of revascularisation or best medical therapy in this group of high-risk patients.

FUNDING

The National Institute of Health Technology Assessment programme.

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.

Prediction of cardiac events in patients with reduced left ventricular ejection fraction with dobutamine cardiovascular magnetic resonance assessment of wall motion score index

OBJECTIVES

The purpose of this study was to assess the utility of dobutamine cardiovascular magnetic resonance (DCMR) results for predicting cardiac events in individuals with reduced left ventricular ejection fraction (LVEF).

BACKGROUND

It is unknown whether DCMR results identify a poor cardiac prognosis when the resting LVEF is moderately to severely reduced.

METHODS

Two hundred consecutive patients ages 30 to 88 (average 64) years with an LVEF <or=55% that were poorly suited for stress echocardiography underwent DCMR in which left ventricular wall motion score index (WMSI), defined as the average wall motion of the number of segments scored, was assessed at rest, during low-dose, and after peak intravenous infusion of dobutamine/atropine. All participants were followed for an average of 5 years after DCMR to ascertain the post-testing occurrence of cardiac death, myocardial infarction (MI), and unstable angina or congestive heart failure warranting hospital stay.

RESULTS

After accounting for risk factors associated with coronary arteriosclerosis and MI, a stress-induced increase in WMSI during DCMR was associated with future cardiac events (p < 0.001). A DCMR stress-induced change in WMSI added significantly to predicting future cardiac events (p = 0.003), after accounting for resting LVEF, but this predictive value was confined primarily to those with an LVEF >40%.

CONCLUSIONS

In individuals with mild to moderate reductions in LVEF (40% to 55%), dobutamine-induced increases in WMSI forecast MI and cardiac death to a greater extent than an assessment of resting LVEF. In those with an LVEF <40%, a dobutamine-induced increase in WMSI does not predict MI and cardiac death beyond the assessment of resting LVEF.

The relationship between left ventricular ejection fraction and infarct size assessed by MRI

OBJECTIVES

We sought to study the relationship between left ventricular ejection fraction (LVEF) and infarct size in patients with ischemic heart disease (IHD) using magnetic resonance imaging (MRI), and to determine a dysfunction index based on the maximum possible LVEF in relation to infarct size.

DESIGN

In 149 patients with chronic IHD, LVEF and infarct size were quantified by MRI. Dysfunction index was defined as the maximum possible LVEF minus measured LVEF.

RESULTS

The maximum possible LVEF was found to be LVEF=72.2-[1.18*infarct size]. Dysfunction index for the study population was mean 20 (range -6 to 57), 74% of the study population had a dysfunction index >10 and 44% had a dysfunction index >20.

CONCLUSIONS

The present study suggests that infarct size by MRI can be used to estimate a maximum possible LVEF and a dysfunction index. The distribution of dysfunction index in the population suggests a considerable prevalence of dysfunctional but viable myocardium. Future studies are needed to assess if the dysfunction index can be useful to assess the potential for improvement in LVEF following revascularization.

Hospitalizations due to unstable angina pectoris in diastolic and systolic heart failure

Patients with diastolic heart failure (HF), i.e., clinical HF with normal or near normal left ventricular ejection fraction (LVEF), may develop unstable angina pectoris (UAP) due to epicardial atherosclerotic coronary artery disease and/or to subendocardial ischemia, even in the absence of coronary artery disease. However, the risk of UAP in ambulatory patients with diastolic HF has not been well studied. We examined incident hospitalizations due to UAP in 916 patients with diastolic HF (LVEF >45%) without significant valvular heart disease and 6,800 patients with systolic HF (LVEF <or=45%) in the Digitalis Investigation Group trial. During a 38-month median follow-up, 12% of patients (797 of 6,800) with systolic HF (incidence rate 435 per 10,000 person-years) and 15% of patients (138 of 916) with diastolic HF (incidence rate 536 per 10,000 person-years) were hospitalized for UAP (adjusted hazard ratio for diastolic HF 1.22, 95% confidence interval [CI] 1.02 to 1.47, p = 0.032). There was a graded increase in incident hospital admissions for UAP with increasing LVEF. Hospitalizations for UAP occurred in 11% (520 of 4,808, incidence rate 407 per 10,000 person-years), 14% (355 of 2,556, incidence rate 496 per 10,000 person-years), and 17% (60 of 352, incidence rate 613 per 10,000 person-years) of patients with HF, respectively, with LVEF values <35%, 35% to 55%, and >55%. Compared with patients with HF and an LVEF <35%, the adjusted hazard ratios for UAP hospitalization in those with LVEF values 35% to 55% and >55% were, respectively, 1.17 (95% CI 1.02 to 1.34, p = 0.028) and 1.57 (95% CI 1.20 to 2.07, p = 0.026). In conclusion, in ambulatory patients with chronic HF, a higher LVEF was associated with increased risk of hospitalizations due to UAP. As in patients with systolic HF, those with diastolic HF should be routinely evaluated for myocardial ischemia and managed accordingly.

Blood oxygen level-dependent (BOLD) magnetic resonance imaging in patients with dypiridamole induced ischaemia; a PET comparative study

BACKGROUND

Blood oxygen level-dependent (BOLD) MRI relies on changes in deoxyhaemoglobin level in tissues under stress for signal variation and may be used for detection of ischaemic myocardium.

METHODS

15 patients with stress induced myocardial ischaemia on PET scanning underwent rest and dypiridamole stress MRI using a double breath-hold T2-weighted, ECG gated sequence to produce BOLD contrast images and cine-MRI for wall thickening assessment. Signal change on BOLD MRI and wall thickening were compared between rest and stress images in ischaemic and non-ischaemic myocardial segments.

RESULTS

Using PET, 156 segments were identified with reversible ischaemia and 324 as non-ischaemic. The ischaemic segments were found on BOLD MRI to have an average signal change between rest and stress of -16.7% compared to -14% in the non-ischaemic segments (p=0.04). The average wall thickening was 7.8 mm in the ischaemic segments compared with 9.5 mm in the non-ischaemic segments (p<0.0001).

CONCLUSION

BOLD MRI with wall thickening assessment may differentiate ischaemic from non-ischaemic myocardium in patients with stress induced myocardial ischaemia. Larger studies with improved spatial resolution would help define a threshold for detection of ischaemia as well as determine this technique's sensitivity and specificity.

The heart failure challenge: optimizing medical and surgical management

The treatment of patients with coronary artery disease and left ventricular dysfunction has improved markedly over the past two decades. Nevertheless, the morbidity and mortality rates remain high in this population. In addition to pharmacological therapies to attenuate neurohumoral overactivation, the present challenge is to find additional therapeutic avenues. Percutaneous coronary intervention, although widely used in patients with coronary artery disease, is more challenging with multivessel disease and associated left ventricular dysfunction, and its optimal use in heart failure remains in question. Cardiac surgical revascularization and surgical ventricular restoration have also been advocated. To date, there are no prospective, randomized clinical studies to prove a benefit from these invasive interventions and to identify which patients may derive the most benefit compared with optimal medical therapy alone. The current management of patients with ischemic heart failure needs to be challenged and requires an objective evaluation of these invasive interventions. The ongoing Surgical Treatment for Ischemic Heart Failure (STICH) trial is the first randomized trial designed to determine the long-term benefits of surgical revascularization and surgical ventricular restoration compared with optimal medical therapy alone. The results of this study will provide additional evidence-based information to guide physicians in the rational allocation of health care resources. The role of percutaneous angioplasty in patients with ischemic heart failure also needs to be addressed objectively.

Clinical characteristics and referral pattern of patients with left ventricular dysfunction and significant coronary artery disease undergoing radionuclide imaging

BACKGROUND

Many observational studies that predict patient outcomes have examined the use of myocardial perfusion imaging results. However, a referral pattern for radionuclide testing could bias these analyses and should be determined. These patients may also differ with regard to the extent of coronary artery disease (CAD). All of these differences must be incorporated into proper outcomes examinations. We sought to identify the nuclear perfusion imaging referral pattern for patients with left ventricular (LV) dysfunction and significant CAD.

METHODS AND RESULTS

Patients with LV dysfunction and CAD (n = 2951) meeting our inclusion criteria were compared by receipt or absence of radionuclide perfusion testing within 6 months before or after angiography. Pearson chi2 and Kruskal-Wallis analyses were used to examine differences in baseline characteristics and catheterization results, whereas logistic regression modeling was applied to predict nuclear imaging referral before and after catheterization. Precatheterization nuclear cohort patients were more likely to be minority patients (odds ratio [OR], 1.34; P =.0083) with previous cardiac revascularization (OR, 2.27; P =.0001), Charlson comorbidity index greater than 1 (OR, 1.146; P =.0091), and heart failure symptoms (OR, 1.62; P =.0001) than those without imaging. They were less likely to have a myocardial infarction (OR, 0.464; P =.0001). After catheterization, the nuclear patients were more likely to have had congestive heart failure (OR, 1.452; P =.0019), a myocardial infarction (OR, 1.353; P =.0371), an ejection fraction lower than 30% (OR, 1.058; P =.0002), and prior revascularization (OR, 1.880; P =.0001). In addition, they had fewer diseased vessels (OR, 0.731; P =.0001).

CONCLUSIONS

Bias exists in nuclear referral for patients with LV dysfunction and significant CAD and must be considered when interpreting observational studies on this topic.

Revascularization in patients with coronary artery disease, left ventricular dysfunction, and viability: a meta-analysis

BACKGROUND

The effects of viability status and treatment allocation on long-term mortality in patients with left ventricular dysfunction and coronary artery disease have not been determined. Several observational studies with significant limitations have addressed this issue, and a recent meta-analysis has attempted to combine these results to increase statistical power. However, the analysis did not test for an interaction between viability status and treatment type, and included extraneous studies. We provide an alternate meta-analysis of this primary literature, utilizing interaction statistical methodology on relevant data and factoring in multiple limitations.

METHODS

We examined papers from this prior meta-analysis examining viable and nonviable patients undergoing surgical or medical therapy. We determined an interaction odds ratio for each study and used an empirical Bayes random-effects model to obtain a combined interaction odds ratio that was tested for statistical significance. We compared our results against an interaction odds ratio we estimated from the primary studies included in the previous meta-analysis.

RESULTS

Nine relevant studies with 1244 patients and 172 events were identified that utilized all 4 treatment/viability subsets. The interaction odds ratio was 2.76 (P =.0176, 95% CI 1.19-6.38), 2.5 times lower than our estimated interaction odds ratio of 7.27 for the prior meta-analysis.

CONCLUSIONS

We found a markedly reduced but statistically significant interaction between viability status and treatment allocation. However, numerous limitations in the primary studies and the application of meta-analysis along with significant improvements in medical therapies render a randomized controlled trial necessary to reach a definitive conclusion to this critical question.

Detection of scarred and viable myocardium using a new magnetic resonance imaging technique: blood oxygen level dependent (BOLD) MRI

BACKGROUND

The identification of viable myocardium in patients with impaired left ventricular contraction secondary to coronary heart disease is important clinically as such myocardium is likely to benefit from revascularisation. Blood oxygen level dependent (BOLD) magnetic resonance imaging (MRI) relies on changes in deoxyhaemoglobin concentration under stress for signal generation and could be used for the differentiation between scarred and viable myocardium.

AIM

To assess the signal change on BOLD MRI in viable and scarred myocardium as identified by positron emission tomography (PET).

METHOD

19 patients with impaired left ventricular contraction and at least one akinetic area were enrolled. They underwent rest and dipyridamole stress MRI, using a double breath hold T2* weighted, ECG gated sequence to produce BOLD contrast images, and cine-MRI for wall thickening assessment. Dynamic perfusion and metabolic PET images followed the MRI. Signal change on BOLD MRI and the wall thickening were compared between rest and stress images in hibernating and scarred segments identified by PET on two short axis slices of mid ventricle, with eight segments each.

RESULTS

Using PET, 68 segments were identified as hibernating and 42 as scarred. The hibernating segments were found on BOLD MRI to have an average signal change between rest and stress of -9.53%, compared with -2.15% in the scarred segments (p = 0.008). The average wall thickening was 8.7 mm in the hibernating segments compared with 5.9 mm in the scarred segments (p < 0.0001).

CONCLUSIONS

BOLD MRI with wall thickening may differentiate scarred and viable myocardium and help identify suitable patients for revascularisation. Further larger studies are needed to establish a threshold for detection, sensitivity, and specificity.

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

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

Heart failure etiology and response to milrinone in decompensated heart failure: results from the OPTIME-CHF study

OBJECTIVES

The goal of this study was to assess the interaction between heart failure (HF) etiology and response to milrinone in decompensated HF.

BACKGROUND

Etiology has prognostic and therapeutic implications in HF, but its relationship to response to inotropic therapy is unknown.

METHODS

The Outcomes of a Prospective Trial of Intravenous Milrinone for Exacerbations of Chronic Heart Failure (OPTIME-CHF) study randomized 949 patients with systolic dysfunction and decompensated HF to receive 48 to 72 h of intravenous milrinone or placebo. The primary end point was days hospitalized from cardiovascular causes within 60 days. In a post-hoc analysis, we evaluated the interaction between response to milrinone and etiology of HF.

RESULTS

The primary end point was 13.0 days for ischemic patients and 11.7 days for nonischemic patients (p = 0.2). Sixty-day mortality was 11.6% for the ischemic group and 7.5% for the nonischemic group (p = 0.03). After adjustment for baseline differences, there was a significant interaction between etiology and the effect of milrinone. Milrinone-treated patients with ischemic etiology tended to have worse outcomes than those treated with placebo in terms of the primary end point (13.6 days for milrinone vs. 12.4 days for placebo, p = 0.055 for interaction) and the composite of death or rehospitalization (42% vs. 36% for placebo, p = 0.01 for interaction). In contrast, outcomes in nonischemic patients treated with milrinone tended to be improved in terms of the primary end point (10.9 vs. 12.6 days placebo) and the composite of death or rehospitalization (28% vs. 35% placebo).

CONCLUSIONS

Milrinone may have a bidirectional effect based on etiology in decompensated HF. Milrinone may be deleterious in ischemic HF, but neutral to beneficial in nonischemic cardiomyopathy.

Prevalence of myocardial viability assessed by single photon emission computed tomography in patients with chronic ischaemic left ventricular dysfunction

OBJECTIVE

To assess the prevalence of myocardial viability by technetium-99m (Tc-99m)-tetrofosmin/fluorine-18-fluorodeoxyglucose (FDG) single photon emission computed tomography (SPECT) in patients with ischaemic cardiomyopathy.

DESIGN

A retrospective observational study.

SETTING

Thoraxcenter Rotterdam (a tertiary referral centre).

PATIENTS

104 patients with chronic coronary artery disease and severely depressed left ventricular function presenting with heart failure symptoms.

MAIN OUTCOME MEASURES

Prevalence of myocardial viability as evaluated by Tc-99m-tetrofosmin/FDG SPECT imaging. Two strategies for assessing viability in dysfunctional myocardium were used: perfusion imaging alone, and the combination of perfusion and metabolic imaging.

RESULTS

On perfusion imaging alone, 56 patients (54%) had a significant amount of viable myocardium, whereas 48 patients (46%) did not. Among the 48 patients with no significant viability by perfusion imaging alone, seven additional patients (15%) had significantly viable myocardium on combined perfusion and metabolic imaging. Thus with a combination of perfusion and metabolic imaging, 63 patients (61%) had viable myocardium and 41 (39%) did not.

CONCLUSIONS

On the basis of the presence of viable dysfunctional myocardium, 61% of patients with chronic coronary artery disease and depressed left ventricular ejection fraction presenting with heart failure symptoms may be considered for coronary revascularisation. The combination of perfusion and metabolic imaging identified more patients with significant viability than myocardial perfusion imaging alone.

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.

Echocardiographic and magnetic resonance methods for diagnosing hibernating myocardium

Hibernating myocardium refers to regions of impaired left ventricular function at rest due to coronary artery disease that is reversible with revascularization. The accurate identification and assessment of myocardial viability is a critical aspect of the management of the patient with coronary artery disease and left ventricular dysfunction. Several non-invasive methods exist to assist the clinician in distinguishing those patients with significant regions of hibernating myocardium from those who have non-viable scar. This is important not only to identify those patients who would most benefit from percutaneous intervention or surgery, but also to spare the latter group from the morbidity and mortality associated with a revascularization procedure that would provide little benefit. While nuclear medicine imaging is the most widely used means for evaluating myocardial viability, alternative modalities have emerged and have gained increasing acceptance in recent years. This article will review the echocardiographic and magnetic resonance imaging (MRI) methods that are currently available or under investigation to assess myocardial viability. These techniques include rest and stress echocardiography, myocardial contrast echocardiography, stress MRI, contrast-enhanced MRI and magnetic resonance spectroscopy (MRS).

Does the presence of hibernating myocardium in patients with impaired left ventricular contraction affect QT dispersion?

BACKGROUND

Hibernating myocardium is associated with increased cardiovascular events. Increased QT dispersion on the surface electrocardiogram is a marker for serious ventricular arrhythmias. In this study, we determine whether hibernating myocardium is associated with increased QT dispersion in patients with coronary artery disease and impaired left ventricular contraction.

METHODS

Positron emission tomography with (13)N-ammonia and (18)F-fluorodeoxyglucose determined the presence of metabolic-perfusion mismatch defect. QT dispersion was measured by means of a digitizing tablet with validated software. QT intervals were measured on two separate occasions by two investigators blinded to the result of the positron emission tomography scans.

RESULTS

Forty-two patients with impaired left ventricular contraction were studied. They were divided into two groups: group A was made up of patients with mismatch defects (n = 26) and group B was made up of patients with no mismatch defects (n = 16). The mean (SD) QT dispersion measurements were 61.7 +/- 29.8 ms and 70 +/- 24.6 ms for groups A and B, respectively (not significant). When the patients were divided according to the dominant viability status of the impaired myocardial segment, a similar result was found. The patients whose impaired myocardium was dominantly hibernating (n = 19) had a mean QT dispersion of 66.4 +/- 31.9 ms compared with 63.6 +/- 24.8 ms in the patients whose impaired myocardium was mainly scarred (not significant).

CONCLUSIONS

QT dispersion is not affected by the presence of hibernating myocardium and is therefore not clinically useful in identifying patients with this phenomenon. This is in contrast with recent reports by other groups and calls for further investigation of this dichotomy.

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.

Can the surface electrocardiogram be used to predict myocardial viability?

OBJECTIVE

To investigate whether QRS morphology on the surface ECG can be used to predict myocardial viability.

DESIGN

ECGs of 58 patients with left ventricular impairment undergoing positron emission tomography (PET) were studied. (13)N-Ammonia (NH(3)) and (18)F-fluorodeoxyglucose (FDG) were the perfusion and the metabolic markers, respectively. The myocardium is scarred when the uptake of both markers is reduced (matched defect). Reduced NH(3) uptake with persistent FDG uptake (mismatched defect) represents hibernating myocardium. First, the relation between pathological Q waves and myocardial scarring was investigated. Second, the significance of QR and QS complexes in predicting hibernating myocardium was determined.

RESULTS

As a marker of matched PET defects, Q waves were specific (79%) but not sensitive (41%), with a 77% positive predictive accuracy and a poor (43%) negative predictive accuracy. The mean size of the matched PET defect associated with Q waves was 20% of the left ventricle. This was not significantly different from the size of the matched PET defects associated with no Q waves (18%). Among the regions associated with Q waves on the ECG, there were 16 regions with QR pattern (group A) and 23 regions with QS pattern (group B). The incidence of mismatched PET defects was 19% of group A and 30% of group B (NS).

CONCLUSIONS

Q waves are specific but not sensitive markers of matched defects representing scarred myocardium. Q waves followed by R waves are not more likely to be associated with hibernating myocardium than QS complexes.