Imaging-Guided Selection of Patients With Ischemic Heart Failure for High-Risk Revascularization Improves Identification of Those With the Highest Clinical Benefit

NUCLEAR IMAGING IN SUDDEN CARDIAC DEATH RISK ASSESSMENT

Sudden cardiac death is a cause of fatal outcomes in large proportion of cardiovascular patients. Left ventricle ejection fraction at the moment is the main criteria for sudden cardiac death risk stratification, however the parameter is not enough reliable. Nuclear imaging methods make it to visualize finer pathophysiological processes representing the probability of the life threatening ventricular arrhythmias development. The review is focused on recent data on nuclear imaging for cellular perfusion assessment, transient ischemia, vitality of myocardium and myocardial blood flow, metabolic disorders and sympathetic innervation.

N-Terminal Pro B-Type Natriuretic Peptide and High-Sensitivity Cardiac Troponin T Levels Are Related to the Extent of Hibernating Myocardium in Patients With Ischemic Heart Failure

BACKGROUND

Increased N-terminal pro b-type natriuretic peptide (NT-proBNP) and high-sensitivity cardiac troponin T (hs-cTnT) can identify patients with heart failure (HF) who are at increased risk of cardiac events. The relationship of these biomarkers to the extent of hibernating myocardium and scar has not been previously characterized in patients with ischemic left ventricular dysfunction and HF.

METHODS

Patients with ischemic HF meeting recruitment criteria and undergoing perfusion and fluorodeoxyglucose-positron emission tomography to define myocardial hibernation and scar were included in the study. A total of 39 patients (mean age 67 ± 8 years) with New York Heart Association class II-IV HF and ischemic cardiomyopathy (ejection fraction [EF], 27.9% ± 8.5%) were enrolled in the study.

RESULTS

Serum NT-proBNP and hs-cTnT levels were elevated in patients with ≥ 10% hibernating myocardium compared with those with < 10% (NT-pro-BNP, 7419.10 ± 7169.5 pg/mL vs 2894.6 ± 2967.4 pg/mL; hs-cTnT, 789.3 ± 1835.3 pg/mL vs 44.8 ± 78.9 pg/mL; P < 0.05). The overall receiver operating characteristic under the curve value for NT-proBNP and hs-cTnT to predict hibernating myocardium was 0.76 and 0.78, respectively (P < 0.05). The NT-proBNP (P = 0.02) and hs-cTnT (P < 0.0001) levels also correlated with hibernation, particularly in patients with ≥ 10% scar, independent of EF, age, and estimated glomerular filtration rate. No differences were noted in biomarker levels for patients with vs those without ≥ 10% scar.

CONCLUSIONS

NT-proBNP and hs-cTnT levels are elevated in patients with ischemic HF hibernation and are correlated with the degree of hibernation but not with the presence or extent of scar. Taken together, these data support the novel concept that NT-proBNP and hs-cTnT release in patients with ischemic HF reflects the presence and extent of hibernating myocardium.

The role of nuclear cardiac imaging in risk stratification of sudden cardiac death

Sudden cardiac death (SCD) represents a significant portion of all cardiac deaths. Current guidelines focus mainly on left ventricular ejection fraction (LVEF) as the main criterion for SCD risk stratification and management. However, LVEF alone lacks both sensitivity and specificity in stratifying patients. Recent research has provided interesting data which supports a greater role for advanced cardiac imaging in risk stratification and patient management. In this article, we will focus on nuclear cardiac imaging, including left ventricular function assessment, myocardial perfusion imaging, myocardial blood flow quantification, metabolic imaging, and neurohormonal imaging. We will discuss how these can be used to better understand SCD and better stratify patient with both ischemic and non-ischemic cardiomyopathy.

Long-Term Follow-Up of Outcomes With F-18-Fluorodeoxyglucose Positron Emission Tomography Imaging–Assisted Management of Patients With Severe Left Ventricular Dysfunction Secondary to Coronary Disease

Background—

Whether viability imaging can impact long-term patient outcomes is uncertain. The PARR-2 study (Positron Emission Tomography and Recovery Following Revascularization) showed a nonsignificant trend toward improved outcomes at 1 year using an F-18-fluorodeoxyglucose positron emission tomography (PET)–assisted strategy in patients with suspected ischemic cardiomyopathy. When patients adhered to F-18-fluorodeoxyglucose PET recommendations, outcome benefit was observed. Long-term outcomes of viability imaging–assisted management have not previously been evaluated in a randomized controlled trial.

Methods and Results—

PARR-2 randomized patients with severe left ventricular dysfunction and suspected CAD being considered for revascularization or transplantation to standard care (n= 195) versus PET-assisted management (n=197) at sites participating in long-term follow-up. The predefined primary outcome was time to composite event (cardiac death, myocardial infarction, or cardiac hospitalization). After 5 years, 105 (53%) patients in the PET arm and 111 (57%) in the standard care arm experienced the composite event (hazard ratio for time to composite event =0.82 [95% confidence interval 0.62–1.07]; P =0.15). When only patients who adhered to PET recommendations were included, the hazard ratio for the time to primary outcome was 0.73 (95% confidence interval 0.54–0.99; P =0.042).

Conclusions—

After a 5-year follow-up in patients with left ventricular dysfunction and suspected CAD, overall, PET-assisted management did not significantly reduce cardiac events compared with standard care. However, significant benefits were observed when there was adherence to PET recommendations. PET viability imaging may be best applied when there is likely to be adherence to imaging-based recommendations.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT00385242.

Severity of Remodeling, Myocardial Viability, and Survival in Ischemic LV Dysfunction After Surgical Revascularization

OBJECTIVES

This study sought to test the hypothesis that end-systolic volume (ESV), as a marker of severity of left ventricular (LV) remodeling, influences the relationship between myocardial viability and survival in patients with coronary artery disease and LV systolic dysfunction.

BACKGROUND

Retrospective studies of ischemic LV dysfunction suggest that the severity of LV remodeling determines whether myocardial viability predicts improved survival with surgical compared with medical therapy, with coronary artery bypass grafting (CABG) only benefitting patients with viable myocardium who have smaller ESV. However, this has not been tested prospectively.

METHODS

Interactions of end-systolic volume index (ESVI), myocardial viability, and treatment with respect to survival were assessed in patients in the prospective randomized STICH (Comparison of Surgical and Medical Treatment for Congestive Heart Failure and Coronary Artery Disease) trial of CABG versus medical therapy who underwent viability assessment (n = 601; age 61 ± 9 years; ejection fraction ≤35%), with a median follow-up of 5.1 years. Median ESVI was 84 ml/m(2). Viability was assessed by single-photon emission computed tomography or dobutamine echocardiography using pre-specified criteria.

RESULTS

Mortality was highest among patients with larger ESVI and nonviability (p < 0.001), but no interaction was observed between ESVI, viability status, and treatment assignment (p = 0.491). Specifically, the effect of CABG versus medical therapy in patients with viable myocardium and ESVI ≤84 ml/m(2) (hazard ratio [HR]: 0.85; 95% confidence interval [CI]: 0.56 to 1.29) was no different than in patients with viability and ESVI >84 ml/m(2) (HR: 0.87; 95% CI: 0.57 to 1.31). Other ESVI thresholds yielded similar results, including ESVI ≤60 ml/m(2) (HR: 0.87; 95% CI: 0.44 to 1.74). ESVI and viability assessed as continuous rather than dichotomous variables yielded similar results (p = 0.562).

CONCLUSIONS

Among patients with ischemic cardiomyopathy, those with greater LV ESVI and no substantial viability had worse prognosis. However, the effect of CABG relative to medical therapy was not differentially influenced by the combination of these 2 factors. Lower ESVI did not identify patients in whom myocardial viability predicted better outcome with CABG relative to medical therapy. (Comparison of Surgical and Medical Treatment for Congestive Heart Failure and Coronary Artery Disease [STICH]; NCT00023595).

Cardiac PET: metabolic and functional imaging of the myocardium

Cardiac PET has evolved over the past 30 years to gain wider acceptance as a valuable modality for a variety of cardiac conditions. Wider availability of scanners as well as changes in reimbursement policies in more recent years has further increased its use. Moreover, with the emergence of novel radionuclides as well as further advances in scanner technology, the use of cardiac PET can be expected to increase further in both clinical practice and the research arena. PET has demonstrated superior diagnostic accuracy for the diagnosis of coronary artery disease in comparison with single-photon emission tomography while it provides robust prognostic value. The addition of absolute flow quantification increases sensitivity for 3-vessel disease as well as providing incremental functional and prognostic information. Metabolic imaging using (18)F-fluorodeoxyglucose can be used to guide revascularization in the setting of heart failure and also to detect active inflammation in conditions such as cardiac sarcoidosis and within atherosclerotic plaque, improving our understanding of the processes that underlie these conditions. However, although the pace of new developments is rapid, there remains a gap in evidence for many of these advances and further studies are required.

An approach to the rational use of revascularization in heart failure patients

The most common cause of heart failure with reduced ejection fraction (HFrEF) is coronary artery disease. A multitude of factors come into play when deciding whether a patient with HFrEF and coronary artery disease should have coronary artery bypass graft (CABG) surgery, percutaneous coronary intervention, or medical therapy alone. For candidates for percutaneous coronary intervention and CABG, evidence from large registries would suggest that patients with 2-vessel coronary artery diseases and proximal left anterior descending disease and all patients with 3-vessel coronary artery disease do better with CABG. For patients that are candidates for medical therapy with or without CABG, the results of the Surgical Treatment for Ischemic Heart Failure (STICH) trial indicate that with CABG, the reduction of mortality is not statistically significant (hazard ratio [HR], 0.86; P = 0.12). However, CABG is superior in reducing cardiovascular deaths (HR, 0.81; P = 0.05), and the combination of cardiovascular deaths and cardiovascular hospitalizations (HR, 0.74; P < 0.001). Patients undergoing CABG have an upfront risk that is eliminated by 2 years and thereafter do better. The assessment of cardiac viability or reversible ischemia does not appear to be helpful in determining which individuals will improve more with CABG. Patients with severe mitral regurgitation who undergo CABG appear to benefit from simultaneous valve repair but not from the addition of surgical ventricular reconstruction of the left ventricle, although in specific patients this might be considered. The totality of evidence would thus suggest that patients with HFrEF should be evaluated for the possibility of coronary revascularization if they are candidates for CABG.

Alternative Imaging Modalities in Ischemic Heart Failure (AIMI-HF) IMAGE HF Project I-A: study protocol for a randomized controlled trial

BACKGROUND

Ischemic heart disease (IHD) is the most common cause of heart failure (HF); however, the role of revascularization in these patients is still unclear. Consensus on proper use of cardiac imaging to help determine which candidates should be considered for revascularization has been hindered by the absence of clinical studies that objectively and prospectively compare the prognostic information of each test obtained using both standard and advanced imaging.

METHODS/DESIGN

This paper describes the design and methods to be used in the Alternative Imaging Modalities in Ischemic Heart Failure (AIMI-HF) multi-center trial. The primary objective is to compare the effect of HF imaging strategies on the composite clinical endpoint of cardiac death, myocardial infarction (MI), cardiac arrest and re-hospitalization for cardiac causes.In AIMI-HF, patients with HF of ischemic etiology (n = 1,261) will follow HF imaging strategy algorithms according to the question(s) asked by the physicians (for example, Is there ischemia and/or viability?), in agreement with local practices. Patients will be randomized to either standard (SPECT, Single photon emission computed tomography) imaging modalities for ischemia and/or viability or advanced imaging modalities: cardiac magnetic resonance imaging (CMR) or positron emission tomography (PET). In addition, eligible and consenting patients who could not be randomized, but were allocated to standard or advanced imaging based on clinical decisions, will be included in a registry.

DISCUSSION

AIMI-HF will be the largest randomized trial evaluating the role of standard and advanced imaging modalities in the management of ischemic cardiomyopathy and heart failure. This trial will complement the results of the Surgical Treatment for Ischemic Heart Failure (STICH) viability substudy and the PET and Recovery Following Revascularization (PARR-2) trial. The results will provide policy makers with data to support (or not) further investment in and wider dissemination of alternative 'advanced' imaging technologies.

TRIAL REGISTRATION

NCT01288560.

Cardiac autonomic imaging with SPECT tracers

Radionuclide cardiac imaging has potential to assess underlying molecular, electrophysiologic, and pathophysiologic processes of cardiac disease. An area of current interest is cardiac autonomic innervation imaging with a radiotracer such as (123)I-meta-iodobenzylguanidine ((123)I-mIBG), a norepinephrine analogue. Cardiac (123)I-mIBG uptake can be assessed by planar and SPECT techniques, involving determination of global uptake by a heart-to-mediastinal ratio, tracer washout between early and delayed images, and focal defects on tomographic images. Cardiac (123)I-mIBG findings have consistently been shown to correlate strongly with heart failure severity, pre-disposition to cardiac arrhythmias, and poor prognosis independent of conventional clinical, laboratory, and image parameters. (123)I-mIBG imaging promises to help monitor a patient's clinical course and response to therapy, showing potential to help select patients for an ICD and other advanced therapies better than current methods. Autonomic imaging also appears to help diagnose ischemic heart disease and identify higher risk, as well as risk-stratify patients with diabetes. Although more investigations in larger populations are needed to strengthen prior findings and influence modifications of clinical guidelines, cardiac (123)I-mIBG imaging shows promise as an emerging technique for recognizing and following potentially life-threatening conditions, as well as improving our understanding of the pathophysiology of various diseases.

Nuclear perfusion imaging for functional evaluation of patients with known or suspected coronary artery disease: the future is now

Nuclear imaging, with both single-photon emission computed tomography and PET, has a well-established role in the assessment of patients with known or suspected coronary artery disease. There is a large body of evidence regarding the diagnostic accuracy and prognostic value of these modalities, however, they continue to evolve rapidly with advances in camera and tracer technology, as well as changes in imaging protocols to increase lab efficiency, improve image quality and to decrease radiation exposure to patients. Nuclear imaging also provides insights into atherogenesis at a molecular level and can be combined with other imaging modalities, providing both functional and structural data and complimentary information on the presence of coronary disease and its functional implications.