Quantification of coronary flow reserve in patients with ischaemic and non-ischaemic cardiomyopathy and its association with clinical outcomes

Imaging of Cardiac Fibrosis: How Far Have We Moved From Extracellular to Cellular?

Cardiovascular disease is the leading cause of morbidity and mortality worldwide. Myocardial fibrosis plays an important role in adverse outcomes such as heart failure and arrhythmias. As the pathological response and degree of scarring, and therefore clinical presentation varies from patient to patient, early detection of fibrosis is crucial for identifying the appropriate treatment approach and forecasting the progression of a disease along with the likelihood of disease-related mortality. Current imaging modalities provides information about either decreased function or extracellular signs of fibrosis. Targeting activated fibroblasts represents a burgeoning approach that could offer insights prior to observable functional alterations, presenting a promising focus for potential anti-fibrotic therapeutic interventions at cellular level. In this article, we provide an overview of imaging cardiac fibrosis and discuss the role of different advanced imaging modalities with the focus on novel non-invasive imaging of activated fibroblasts.

Navigating the Landscape of Coronary Microvascular Research: Trends, Triumphs, and Challenges Ahead

Coronary microvascular dysfunction (CMD) refers to structural and functional abnormalities of the microcirculation that impair myocardial perfusion. CMD plays a pivotal role in numerous cardiovascular diseases, including myocardial ischemia with non-obstructive coronary arteries, heart failure, and acute coronary syndromes. This review summarizes recent advances in CMD pathophysiology, assessment, and treatment strategies, as well as ongoing challenges and future research directions. Signaling pathways implicated in CMD pathogenesis include adenosine monophosphate-activated protein kinase/Krüppel-like factor 2/endothelial nitric oxide synthase (AMPK/KLF2/eNOS), nuclear factor erythroid 2-related factor 2/antioxidant response element (Nrf2/ARE), Angiotensin II (Ang II), endothelin-1 (ET-1), RhoA/Rho kinase, and insulin signaling. Dysregulation of these pathways leads to endothelial dysfunction, the hallmark of CMD. Treatment strategies aim to reduce myocardial oxygen demand, improve microcirculatory function, and restore endothelial homeostasis through mechanisms including vasodilation, anti-inflammation, and antioxidant effects. Traditional Chinese medicine (TCM) compounds exhibit therapeutic potential through multi-targeted actions. Small molecules and regenerative approaches offer precision therapies. However, challenges remain in translating findings to clinical practice and developing effective pharmacotherapies. Integration of engineering with medicine through microfabrication, tissue engineering and AI presents opportunities to advance the diagnosis, prediction, and treatment of CMD.

PET myocardial perfusion imaging: Trends, challenges, and opportunities

Various non-invasive images are used in clinical practice for the diagnosis and prognostication of chronic coronary syndromes. Notably, quantitative myocardial perfusion imaging (MPI) through positron emission tomography (PET) has seen significant technical advancements and a substantial increase in its use over the past two decades. This progress has generated an unprecedented wealth of clinical information, which, when properly applied, can diagnose and fine-tune the management of patients with different types of ischemic syndromes. This state-of-art review focuses on quantitative PET MPI, its integration into clinical practice, and how it holds up at the eyes of modern cardiac imaging and revascularization clinical trials, along with future perspectives.

Risk Stratification Using Right Ventricular Longitudinal Strain Ratio Derived from 13N-Ammonia PET in Patients with Ischemic Heart Disease

Purpose To investigate whether right ventricular (RV) myocardial strain ratio (RVMSR) assessed using nitrogen 13 ammonia (13N-NH3) PET can predict cardiovascular events in patients with ischemic heart disease (IHD). Materials and Methods This retrospective study included 480 consecutive patients (mean age, 66 years ± 12 [SD]; 334 males and 146 females) with IHD who underwent 13N-NH3 PET. RVMSR was defined as the ratio of RV strain during stress to that at rest. The primary end point was major adverse cardiac events (MACEs), defined as cardiac death or heart failure hospitalization. The ability of RVMSR to predict MACE was assessed using receiver operating characteristic (ROC) curve and Kaplan-Meier analyses. Cox proportional hazards regression analysis was used to calculate hazard ratios (HRs) with 95% CIs. Results ROC curve analysis identified a sensitivity and specificity of 84% and 82%, respectively, for predicting MACE from RVMSR. Patients with reduced RVMSR (<110.2) displayed a significantly higher rate of MACE than those with a preserved RVMSR (34 of 240 vs four of 240; P < .001). Cox proportional hazards regression analysis of imaging parameters, including myocardial flow reserve, indicated that RVMSR was an independent predictor of MACE (HR, 0.94 [95% CI: 0.92, 0.97]; P < .001). Conclusion RVMSR was an independent predictor of MACE and has potential to aid in the risk stratification of patients with IHD. Keywords: Right Ventricular Myocardial Strain Ratio, Myocardial Flow Reserve, Ischemic Heart Disease, 13N-Ammonia Positron Emission Tomography Supplemental material is available for this article. © RSNA, 2024.

Economic and healthcare resource utilization assessments of PET imaging in Coronary Artery Disease diagnosis: a systematic review and discussion of opportunities for future economic evaluations

AIMS

This systematic literature review (SLR) consolidated economic and healthcare resource utilization (HCRU) evidence for positron emission tomography (PET) and single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) to inform future economic evaluations.

MATERIALS AND METHODS

An electronic search was conducted in MEDLINE, Embase, and Cochrane databases from 2012-2022. Economic and HCRU studies in adults who underwent PET- or SPECT-MPI for coronary artery disease (CAD) diagnosis were eligible. A qualitative methodological assessment of existing economic evaluations, HCRU, and downstream cardiac outcomes was completed. Exploratory meta-analyses of clinical outcomes were performed.

RESULTS

The search yielded 13,439 results, with 71 records included. Economic evaluations and comparative clinical trials were limited in number and outcome types (HCRU, downstream cardiac outcomes, and diagnostic performance) assessed. No studies included all outcome types and only one economic evaluation linked diagnostic performance to HCRU. The meta-analyses of comparative studies demonstrated significantly higher rates of early- and late-invasive coronary angiography and revascularization for PET- compared to SPECT-MPI; however, the rate of repeat testing was lower with PET-MPI. The rate of acute myocardial infarction was lower, albeit non-significant with PET- vs. SPECT-MPI.

LIMITATIONS AND CONCLUSIONS

This SLR identified economic and HCRU evaluations following PET- and SPECT-MPI for CAD diagnosis and determined that existing studies do not capture all pertinent outcome parameters or link diagnostic performance to downstream HCRU and cardiac outcomes, thus, resulting in simplified assessments of CAD burden. A limitation of this work relates to heterogeneity in study designs, patient populations, and follow-up times of existing studies. Resultingly, it was challenging to pool data in meta-analyses. Overall, this work provides a foundation for the development of comprehensive economic models for PET- and SPECT-MPI in CAD diagnosis, which should link diagnostic outcomes to HCRU and downstream cardiac events to capture the full CAD scope.

Characteristics of the phenotype of mixed cardiomyopathy in patients with implantable cardioverter-defibrillators

BACKGROUND OR PURPOSE

The prognosis of m ixed cardiomyopathy (CMP) in patients with implanted cardioverter-defibrillators (ICDs) has not been investigated. We aim to study the demographic, clinical, device therapies and survival characteristics of mixed CMP in a cohort of patients implanted with a defibrillator.

METHODS

The term mixed CMP was used to categorise patients with impaired left ventricular ejection fraction attributed to documented non-ischemic triggers with concomitant moderate coronary artery disease. This is a single center observational cohort of 526 patients with a mean follow-up of 8.7 ± 3.5 years.

RESULTS

There were 42.5% patients with ischemic cardiomyopathy (ICM), 26.9% with non-ischemic cardiomyopathy (NICM) and 30.6% with mixed CMP. Mixed CMP, compared to NICM, was associated with higher mean age (69.1 ± 9.6 years), atrial fibrillation (55.3%) and greater incidence of comorbidities. The proportion of patients with mixed CMP receiving device shocks was 23.6%, compared to 18.4% in NICM and 27% in ICM. The VT cycle length recorded in mixed CMP (281.6 ± 43.1 ms) was comparable with ICM (282.5 ± 44 ms; p = 0.9) and lesser than NICM (297.7 ± 48.7 ms; p = 0.1). All-cause mortality in mixed CMP (21.1%) was similar to ICM (20.1%; p = 0.8) and higher than NICM (15.6%; p = 0.2). The Kaplan-Meier curves revealed hazards of 1.57 (95% CI: 0.91, 2.68) for mixed CMP compared to NICM.

CONCLUSION

In a cohort of patients with ICD, the group with mixed CMP represents a phenotype predominantly comprised of the elderly with a higher incidence of comorbidities. Mixed CMP resembles ICM in terms of number of device shocks and VT cycle length. Trends of long-term prognosis of patients with mixed CMP are worse than NICM and similar to ICM.

Coronary perfusion pressure is associated with adverse outcomes in advanced heart failure

BACKGROUND

Myocardial perfusion is an important determinant of cardiac function. We hypothesized that low coronary perfusion pressure (CPP) would be associated with adverse outcomes in heart failure. Myocardial perfusion impacts the contractile efficiency thus a low CPP would signal low myocardial perfusion in the face of increased cardiac demand as a result of volume overload.

METHODS

We analyzed patients with complete hemodynamic data in the Evaluation Study of Congestive Heart Failure and Pulmonary Artery Catheterization Effectiveness trial using Cox Proportional Hazards regression for the primary outcome of the composite risk of death, heart transplantation, or left ventricular assist device [(LVAD). DT × LVAD] and the secondary outcome of the composite risk of DT × LVAD and heart failure hospitalization (DT × LVADHF). CPP was calculated as the difference between diastolic blood pressure and pulmonary artery wedge pressure. Heart failure categories (ischemic vs non-ischemic) were also stratified based on CPP strata.

RESULTS

The 158 patients (56.7 ± 13.6 years, 28.5% female) studied had a median CPP of 40 mmHg (IQR 35-52 mmHg). During 6 months of follow-up, 35 (22.2%) had the composite primary outcome and 109 (69.0%) had the composite secondary outcome. When these outcomes were then stratified based on the median, CPP was associated with these outcomes. Increasing CPP was associated with lower risk of both the primary outcome of DT × LVAD (HR 0.96, 95% CI 0.94-0.99 p = .002) and as well as the secondary outcome of DT × LVADHF (p = .0008) There was significant interaction between CPP and ischemic etiology (p = .04).

CONCLUSION

A low coronary artery perfusion pressure below (median) 40mmHg in patients with advanced heart failure undergoing invasive hemodynamic monitoring with a pulmonary artery catheter was associated with adverse outcomes. CPP could useful in guiding risk stratification of advanced heart failure patients and timely evaluation of advanced heart failure therapies.

Mitochondrial function and coronary flow reserve improvement after autologous myoblast patch transplantation for ischaemic cardiomyopathy: a case report

Background

Autologous myoblast patch (AMP) transplantation has resulted in good clinical outcomes for end-stage ischaemic cardiomyopathy, but the mechanisms behind them are unclear. Herein, we report the relationship between mitochondrial function and coronary flow reserve (CFR) before and after AMP transplantation.

Case summary

The patient was a 73-year-old man who underwent coronary artery bypass grafting (CABG). At that time, the left ventricular ejection fraction (LVEF) was 53%, but it declined to 25% after 6 years. He was diagnosed with ischaemic cardiomyopathy (ICM). Coronary flow reserve in NH3-positron emission tomography (NH3-PET) was impaired to 1.69. In Tc-99m MIBI scintigraphy, the washout rate (WR) was 17%, suggestive of impaired mitochondrial function. He was not a candidate for heart transplantation, and we performed AMP transplantation 6 years after CABG. One year after AMP transplantation, LVEF, CFR, and Tc-99m MIBI WR improved to 36%, 2.07, and 7%, respectively. The Tc-99m MIBI WR improved especially in the anterolateral region, and the CFR increased in almost all segments.

Discussion

In this case, AMP transplantation for ICM improved cardiac function, CFR, and mitochondrial function. The mitochondrial transfer from the transplanted myoblasts to the damaged myocardium may have contributed to the mitochondrial function improvement. This probably induced myocardial energy metabolism recovery and decreased oxygen demand. AMP transplantation also has the potential to improve microvascular dysfunction, due to angiogenesis induction. These effects can lead to improved prognoses of ICM after AMP transplantation, highlighting its potential to cure refractory heart failure.

Phenotyping heart failure by nuclear imaging of myocardial perfusion, metabolism, and molecular targets

Nuclear imaging techniques can detect and quantify pathophysiological processes underlying heart failure, complementing evaluation of cardiac structure and function with other imaging modalities. Combined imaging of myocardial perfusion and metabolism can identify left ventricle dysfunction caused by myocardial ischaemia that may be reversible after revascularization in the presence of viable myocardium. High sensitivity of nuclear imaging to detect targeted tracers has enabled assessment of various cellular and subcellular mechanisms of heart failure. Nuclear imaging of active inflammation and amyloid deposition is incorporated into clinical management algorithms of cardiac sarcoidosis and amyloidosis. Innervation imaging has well-documented prognostic value with respect to heart failure progression and arrhythmias. Emerging tracers specific for inflammation and myocardial fibrotic activity are in earlier stages of development but have demonstrated potential value in early characterization of the response to myocardial injury and prediction of adverse left ventricular remodelling. Early detection of disease activity is a key for transition from broad medical treatment of clinically overt heart failure towards a personalized approach aimed at supporting repair and preventing progressive failure. This review outlines the current status of nuclear imaging in phenotyping heart failure and combines it with discussion on novel developments.

Positron emission tomography myocardial perfusion imaging (PET MPI) findings predictive of post-liver transplant major adverse cardiac events

Positron emission tomography myocardial perfusion imaging (PET MPI) is a noninvasive diagnostic test capable of detecting coronary artery disease, structural heart disease, and myocardial flow reserve (MFR). We aimed to determine the prognostic utility of PET MPI to predict post-liver transplant (LT) major adverse cardiac events (MACE). Among the 215 LT candidates that completed PET MPI between 2015 and 2020, 84 underwent LT and had 4 biomarker variables of clinical interest on pre-LT PET MPI (summed stress and difference scores, resting left ventricular ejection fraction, global MFR). Post-LT MACE were defined as acute coronary syndrome, heart failure, sustained arrhythmia, or cardiac arrest within the first 12 months post-LT. Cox regression models were constructed to determine associations between PET MPI variable/s and post-LT MACE. The median LT recipient age was 58 years, 71% were male, 49% had NAFLD, 63% reported prior smoking, 51% had hypertension, and 38% had diabetes mellitus. A total of 20 MACE occurred in 16 patients (19%) at a median of 61.5 days post-LT. One-year survival of MACE patients was significantly lower than those without MACE (54% vs. 98%, p =0.001). On multivariate analysis, reduced global MFR ≤1.38 was associated with a higher risk of MACE [HR=3.42 (1.23-9.47), p =0.019], and every % reduction in left ventricular ejection fraction was associated with an 8.6% higher risk of MACE [HR=0.92 (0.86-0.98), p =0.012]. Nearly 20% of LT recipients experienced MACE within the first 12 months of LT. Reduced global MFR and reduced resting left ventricular ejection fraction on PET MPI among LT candidates were associated with increased risk of post-LT MACE. Awareness of these PET-MPI parameters may help improve cardiac risk stratification of LT candidates if confirmed in future studies.

Invasive Functional Assessment of Coronary Artery Disease in Patients with Severe Aortic Stenosis in the TAVI Era

Coronary artery disease (CAD) is a common finding in patients suffering from aortic valve stenosis (AS), with a prevalence of over 50% in patients 70 years of age or older. Transcatheter aortic valve intervention (TAVI) is the standard treatment option for patients with severe AS and at least 75 years of age. Current guidelines recommend percutaneous coronary intervention (PCI) in patients planned for TAVI with stenoses of >70% in the proximal segments of non-left main coronary arteries and in >50% of left main stenoses. While the guidelines on myocardial revascularization clearly recommend functional assessment of coronary artery stenoses of less than 90% in the absence of non-invasive ischemia testing, a statement regarding invasive functional testing in AS patients with concomitant CAD is lacking in the recently published guideline on the management of valvular heart disease. This review aims to provide an overview of the hemodynamic background in AS patients, discusses and summarizes the current evidence of invasive functional testing in patients with severe AS, and gives a future perspective on the ongoing trials on that topic.

Role of nuclear cardiology in diagnosis and risk stratification of coronary microvascular disease

Coronary flow reserve (CFR) with positron emission tomography/computed tomography (PET/CT) has an important role in the diagnosis of coronary microvascular disease (CMD), aids risk stratification and may be useful in monitoring therapy. CMD contributes to symptoms and a worse prognosis in patients with coronary artery disease (CAD), nonischemic cardiomyopathies, and heart failure. CFR measurements may improve our understanding of the role of CMD in symptoms and prognosis in CAD and other cardiovascular diseases. The clinical presentation of CAD has changed. The prevalence of nonobstructive CAD has increased to about 50% of patients with angina undergoing angiography. Ischemia with nonobstructive arteries (INOCA) is recognized as an important cause of symptoms and has an adverse prognosis. Patients with INOCA may have ischemia due to CMD, epicardial vasospasm or diffuse nonobstructive CAD. Reduced CFR in patients with INOCA identifies a high-risk group that may benefit from management strategies specific for CMD. Although measurement of CFR by PET/CT has excellent accuracy and repeatability, use is limited by cost and availability. CFR measurement with single-photon emission tomography (SPECT) is feasible, validated, and would increase availability and use of CFR. Patients with CMD can be identified by reduced CFR and selected for specific therapies.

Cardiac imaging for the prediction of sudden cardiac arrest in patients with heart failure

The identification of heart failure (HF) patients at risk for arrhythmic sudden cardiac arrest (SCA) is a major challenge in the cardiovascular field. In addition to optimal medical treatment for HF, implantable cardioverter defibrillator (ICD) is currently recommended to prevent SCA in patients with reduced left ventricular ejection fraction (LVEF). The indication for an ICD implantation, in addition to HF etiology, New York Health Association (NYHA) class and life expectancy, mainly depends on LVEF value at echocardiography. However, the actual role of LVEF in the prediction of SCA has recently been debated, while newer multimodality imaging techniques with increased prognostic accuracy have been developed. Speckle tracking imaging allows the quantification of mechanical dispersion, a marker of electrophysiological heterogeneity predisposing to malignant arrhythmias, while advanced cardiac magnetic resonance techniques such as myocardial T1-mapping and extracellular volume fraction assessment allow the evaluation of interstitial diffuse fibrosis. Nuclear imaging is helpful for the appraisal of sympathetic nervous system dysfunction, while newer computed tomography techniques assessing myocardial delayed enhancement allow the identification of focal myocardial scar. This review will focus on the most modern advances in the field of cardiovascular imaging along with its applications for the prediction of SCA in patients with HF. Modern artificial intelligence applications in cardiovascular imaging will also be discussed.

Microcirculatory Disease in Patients after Heart Transplantation

Although the treatment and prognosis of patients after heart transplantation have significantly improved, late graft dysfunction remains a critical problem. Two main subtypes of late graft dysfunction are currently described: acute allograft rejection and cardiac allograft vasculopathy, and microvascular dysfunction appears to be the first stage of both. Studies revealed that coronary microcirculation dysfunction, assessed by invasive methods in the early post-transplant period, correlates with a higher risk of late graft dysfunction and death during long-term follow-up. The index of microcirculatory resistance, measured early after heart transplantation, might identify the patients at higher risk of acute cellular rejection and major adverse cardiovascular events. It may also allow optimization and enhancement of post-transplantation management. Moreover, cardiac allograft vasculopathy is an independent prognostic factor for transplant rejection and survival rate. The studies showed that the index of microcirculatory resistance correlates with anatomic changes and reflects the deteriorating physiology of the epicardial arteries. In conclusion, invasive assessment of the coronary microcirculation, including the measurement of the microcirculatory resistance index, is a promising approach to predict graft dysfunction, especially the acute allograft rejection subtype, during the first year after heart transplantation. However, further advanced studies are needed to fully grasp the importance of microcirculatory dysfunction in patients after heart transplantation.

Coronary microvascular dysfunction in heart failure patients

Coronary microcirculation has multiple layers of autoregulatory function to maintain resting flow and augment hyperemic flow in response to myocardial demands. Functional or structural alterations in the coronary microvascular function are frequently observed in patients with heart failure with preserved or reduced ejection fraction, which may lead to myocardial ischemic injury and resultant worsening of clinical outcomes. In this review, we describe our current understanding of coronary microvascular dysfunction in the pathogenesis of heart failure with preserved and reduced ejection fraction.

Quantification of myocardial blood flow and myocardial flow reserve by 13N-NH3 PET/CT is not significantly affected by pixel size

PURPOSE

Myocardial blood flow (MBF) and myocardial flow reserve (MFR) are measurable by ¹³N-NH₃ positron emission tomography (PET). MFR, which is the ratio of MBF under adenosine stress to MBF at rest, is prognostically valuable. The ASNC imaging guidelines/SNMMI procedure standards recommend using 2-3 mm pixels, and pixel size does differ between institutions. We sought to evaluate the effects of pixel sizes on the quantitative values calculated from ¹³N-NH₃ PET images.

METHODS

Thirty consecutive patients with ischemic heart disease who underwent ¹³N-NH₃ PET were retrospectively enrolled. Dynamic images were quantified using PMOD's cardiac PET analysis tool (pixel sizes: 3.18, 2.03, and 1.59 mm). MBF under adenosine stress, MBF at rest, and MFR for the right coronary artery (RCA) region, left anterior descending artery region, and left circumflex coronary artery branch region innervation regions were calculated at each pixel size and compared.

RESULTS

Quantitative values did not significantly differ according to pixel size in any of the regions. However, MFR values for the RCA fluctuated the most. Ischemic and non-ischemic regions remained visually discernible in qualitative images, with no variation in quantitative values, regardless of pixel size.

CONCLUSIONS

Quantitative values were not significantly affected by pixel sizes within the recommended range of 2-3 mm. Values for the RCA region may have been overestimated, but this was true for all pixel sizes.

Prediction of cardiovascular events using myocardial strain ratio derived from 13N-ammonia positron emission tomography

OBJECTIVES

Myocardial flow reserve (MFR), derived from ammonia N-13 positron emission tomography (NH₃-PET), can predict the prognosis of patients with various heart diseases. We aimed to investigate whether myocardial strain ratio (MSR) was useful in predicting MACE and allowed for further risk stratification of cardiovascular events in patients with ischemic heart disease (IHD) in addition to MFR.

METHODS

Ninety-five patients underwent NH₃-PET because of IHD. MFR was determined as the ratio of hyperemic to resting myocardial blood flow (MBF). MSR was defined as the ratio of strains at stress and rest. The endpoint was major adverse cardiac events (MACE), including all-cause death, acute coronary syndrome, heart failure hospitalization, and revascularization. The ability to predict MACE was assessed using receiver operating characteristic (ROC) analysis, and the predictability of ME was analyzed using Kaplan-Meier analysis. The Cox proportional hazards regression model was used to calculate the hazard ratio (HR) with 95% confidence interval (CI).

RESULTS

The ROC curve analysis demonstrated a cutoff of 0.93 for MACE with MSR (sensitivity and specificity of 77% and 71%, respectively). Patients with MSR < 0.93 displayed a significantly higher MACE rate than those with MSR ≥ 0.93 (p = 0.0036). The Cox proportional hazards regression analysis indicated that MSR was an independent marker that could predict MACE in imaging and clinical parameters (HR, 7.32; 95% CI: 1.59-33.7, p = 0.011).

CONCLUSIONS

MSR was an independent predictor of MACE and was useful for further risk stratification in IHD. MSR has the potential for a new indicator of revascularization in patients with IHD.

KEY POINTS

• We hypothesized that combining myocardial flow reserve (MFR) with the myocardial strain ratio (MSR) obtained by applying the feature-tracking technique to ammonia N-13 PET would make it predictive of major adverse cardiac events (MACE) compared to MFR alone. • MSR was an independent predictor of MACE, allowing for further risk stratification in addition to MFR in patients with ischemic heart disease. • MSR is a potential new indicator of revascularization.

Emerging role of positron emission tomography (PET) imaging in cardiac surgery

Historically, structural and anatomical imaging has been the mainstay in the diagnosis and management of cardiovascular diseases. In recent years there has been a shift toward increased use of functional imaging studies, including positron emission tomography (PET). PET is a noninvasive nuclear medicine-imaging technique that uses radiotracers to generate images of a radionucleotide distribution by detecting the physiologic substrates that emit positron radionuclides. This article will focus on the applications of PET imaging for the cardiac surgeon and highlight the collaborative nature of using PET imaging for the management of complex heart disease. We present cases that demonstrate the value of using PET imaging in the diagnosis of coronary artery disease and management of complex endocarditis, and in targeted cardiovascular therapies.

Impairment in quantitative microvascular function in non-ischemic cardiomyopathy as demonstrated using cardiovascular magnetic resonance

Background

Microvascular dysfunction (MVD) is present in various cardiovascular diseases and portends worse outcomes. We assessed the prevalence of MVD in patients with non-ischemic cardiomyopathy (NICM) as compared to subjects with preserved ejection fraction (EF) using stress cardiovascular magnetic resonance (CMR).

Methods

We retrospectively studied consecutive patients with NICM and 58 subjects with preserved left ventricular (LV) EF who underwent stress CMR between 2011–2016. MVD was defined visually as presence of a subendocardial perfusion defect and semiquantitatively by myocardial perfusion reserve index (MPRI<1.51). MPRI was compared between groups using univariate analysis and multivariable linear regression.

Results

In total, 41 patients with NICM (mean age 51 ± 14, 59% male) and 58 subjects with preserved LVEF (mean age 51 ± 13, 31% male) were identified. In the NICM group, MVD was present in 23 (56%) and 11 (27%) by semiquantitative and visual evaluation respectively. Compared to those with preserved LVEF, NICM patients had lower rest slope (3.9 vs 4.9, p = 0.05) and stress perfusion slope (8.8 vs 11.7, p<0.001), and MPRI (1.41 vs 1.74, p = 0.02). MPRI remained associated with NICM after controlling for age, gender, hypertension, ethnicity, diabetes, and late gadolinium enhancement (log MPR, β coefficient = -0.19, p = 0.007).

Conclusions

MVD—as assessed using CMR—is highly prevalent in NICM as compared to subjects with preserved LVEF even after controlling for covariates. Semiquantitative is able to detect a greater number of incidences of MVD compared to visual methods alone. Further studies are needed to determine whether treatment of MVD is beneficial in NICM.

Prognostic Impact of Coronary Flow Reserve in Patients With Reduced Left Ventricular Ejection Fraction

Background

Intracoronary physiologic indexes such as coronary flow reserve (CFR) and left ventricular ejection fraction (LVEF) have been regarded as prognostic indicators in patients with coronary artery disease. The current study evaluated the association between intracoronary physiologic indexes and LVEF and their differential prognostic implications in patients with coronary artery disease.

Methods and Results

A total of 1889 patients with 2492 vessels with available CFR and LVEF were selected from an international multicenter prospective registry. Baseline physiologic indexes were measured by thermodilution or Doppler methods and LVEF was recorded at the index procedure. The primary outcome was target vessel failure, which was a composite of cardiac death, target vessel myocardial infarction, or clinically driven target vessel revascularization over 5 years of follow‐up. Patients with reduced LVEF <50% (162 patients [8.6%], 202 vessels [8.1%]) showed a similar degree of epicardial coronary artery disease but lower CFR values than those with preserved LVEF (2.4±1.2 versus 2.7±1.2, P<0.001), mainly driven by the increased resting coronary flow. Conversely, hyperemic coronary flow, fractional flow reserve, and the degree of microvascular dysfunction were similar between the 2 groups. Reduced CFR (≤2.0) was seen in 613 patients (32.5%) with 771 vessels (30.9%). Reduced CFR was an independent predictor for target vessel failure (hazard ratio, 2.081 [95% CI, 1.385–3.126], P<0.001), regardless of LVEF.

Conclusions

CFR was lower in patients with reduced LVEF because of increased resting coronary flow. Patients with reduced CFR showed a significantly higher risk of target vessel failure than did those with preserved CFR, regardless of LVEF.

Registration

URL: https://www.clinicaltrials.gov; Unique identifier: NCT04485234.

First Validation of Myocardial Flow Reserve Derived from Dynamic 99mTc-Sestamibi CZT-SPECT Camera Compared with 13N-Ammonia PET

¹³N-ammonia positron emission tomography (NH₃-PET) can evaluate myocardial blood flow (MBF) at rest, stress, and myocardial flow reserve (MFR) as well as the ratio of MBF at stress to that at rest. MFR is useful in predicting the prognoses of patients with various heart diseases. Cadmium-zinc-telluride single photon emission computed tomography (CZT-SPECT) enables us to acquire dynamic images of radiotracer kinetics and measure original MBF and MFR using ^99mTc-sestamibi. This study aimed to investigate the utility of CZT-SPECT for quantitative assessment of MBF compared to NH₃-PET. We validated the correlation of MBF and MFR between CZT-SPECT and NH₃-PET. Fourteen patients using one-day rest/stress CZT-SPECT, D-SPECT followed by NH₃-PET within 1 month were enrolled and analyzed prospectively. The reproducibility of the MBF and MFR obtained with these two methods was examined using Spearman's correlation coefficient and Bland-Altman plot analysis. The diagnostic value of D-SPECT for abnormal MFR defined using NH₃-PET results as MFR < 2.0 was assessed using receiver-operating characteristic (ROC) analysis. The median duration between D-SPECT and NH₃-PET was 20 days. Although MBF was overestimated by D-SPECT compared to NH₃-PET at high value (mean difference, 0.43 [0.34-0.53]), MBF and MFR were correlated with the two modalities (MBF: r = 0.71, P < 0.0001, MFR: r = 0.60, P < 0.0001). The ROC curve analysis demonstrated a cutoff of 1.6 for detecting abnormal MFR with D-SPECT (sensitivity, 68%; specificity, 91%; AUC, 0.75). MBF and MFR obtained using D-SPECT and NH₃-PET had a good correlation, suggesting that the quantitative MFR evaluation by CZT-SPECT may help understand the trend of NH₃-PET MFR.

Myocardial Flow Reserve in Coronary Artery Disease with Low Attenuation Plaque: Coronary CTA and 13N-ammonia PET Assessments

RATIONALE AND OBJECTIVES

Physiological measurements from coronary angiography show that coronary stenosis with necrotic core plaque reduces coronary flow reserve (CFR). Myocardial flow reserve (MFR) estimated by ¹³N-ammonia PET (NH₃-PET) is a different index from CFR. Low attenuation plaque (LAP) on coronary CTA (CCTA) contains necrotic core, but the link between LAP and MFR has not been elucidated. We aimed to investigate the influence of LAP on MFR in coronary artery disease (CAD).

MATERIALS AND METHODS

The study included 105 consecutive patients who underwent NH₃-PET and CCTA within 3 months. Nonevaluable coronary arteries due to severe calcification and stent implants were excluded. Finally, 290 major vessels were retrospectively analyzed. Coronary arteries were divided into mild (1%-49%), moderate (50%-69% stenosis), and severe (≥70% stenosis) groups. Coronary plaques were classified either LAP (including soft tissue CT value <30 HU) or completely classified plaques. MFR for the major vessels were calculated and MFR <2.0 was considered a significant decrease. Comparison of MFR between territories with and without LAP, and the effect of plaque characteristics on MFR was analyzed.

RESULTS

MFR was significantly lower for territories with LAP than with calcified plaques or no plaque (2.1 ± 0.7, 2.4 ± 0.7, and 2.3 ± 0.7; p < 0.05). There was no difference between calcified plaque and no plaque territories (p = 0.79). Multivariate logistic analysis for plaque characteristics and stenosis severity revealed that LAP and severe stenosis were independent predictors for territories with MFR <2.0 with odds ratios of 3.1 (95% confidence interval, 1.2-8.1) and 3.0 (95% confidence interval, 1.7-5.3).

CONCLUSION

LAP reduced MFR compared with calcified plaque or no plaque in CAD. LAP is an independent predictor of the territory with MFR <2.0.

Identification of MYH6 as the potential gene for human ischaemic cardiomyopathy

The present study aimed to explore the potential hub genes and pathways of ischaemic cardiomyopathy (ICM) and to investigate the possible associated mechanisms. Two microarray data sets (GSE5406 and GSE57338) were downloaded from the Gene Expression Omnibus (GEO) database. The limma package was used to analyse the differentially expressed genes (DEGs). Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment, Disease Ontology (DO) and Gene Ontology (GO) annotation analyses were performed. A protein‐protein interaction (PPI) network was set up using Cytoscape software. Significant modules and hub genes were identified by the Molecular Complex Detection (MCODE) app. Then, further functional validation of hub genes in other microarrays and survival analysis were performed to judge the prognosis. A total of 1065 genes were matched, with an adjusted p < 0.05, and 17 were upregulated and 25 were downregulated with|log₂ (fold change)|≥1.2. After removing the lengthy entries, GO identified 12 items, and 8 pathways were enriched at adjusted p < 0.05 (false discovery rate, FDR set at <0.05). Three modules with a score >8 after MCODE analysis and MYH6 were ultimately identified. When validated in GSE23561, MYH6 expression was lower in patients with CAD than in healthy controls (p < 0.05). GSE60993 data suggested that MYH6 expression was also lower in AMI patients (p < 0.05). In the GSE59867 data set, MYH6 expression was lower in CAD patients than in AMI patients and lower in heart failure (HF) patients than in non‐HF patients. However, there was no difference at different periods within half a year, and HF was increased when MYH6 expression was low (p < 0.05–0.01). We performed an integrated analysis and validation and found that MYH6 expression was closely related to ICM and HF. However, whether this marker can be used as a predictor in blood samples needs further experimental verification.

Relative Prognostic Significance of Positron Emission Tomography Myocardial Perfusion Imaging Markers in Cardiomyopathy

BACKGROUND

Rubidium-82 positron emission tomography myocardial perfusion imaging provides measurements of perfusion, myocardial blood flow and reserve (MBFR), and changes in left ventricular ejection fraction (LVEF) at rest and peak stress. Although all of these variables are known to provide prognostic information, they have not been well studied in patients with heart failure due to reduced LVEF.

METHODS

Between 2010 and 2016, 1255 consecutive unique patients with LVEF≤40% were included in this study who underwent rubidium-82 positron emission tomography myocardial perfusion imaging and did not have subsequent revascularization within 90 days. Perfusion assessment was scored semiquantitatively, and LVEF reserve (stress-rest LVEF) and global MBFR (stress/rest MBF) were quantified using automated software. Cox proportional hazards models adjusted for 14 clinical and 7 test characteristics were used to define the independent prognostic significance of MBFR on all-cause mortality.

RESULTS

Of 1255 patients followed for a mean of 3.2 years, 454 (36.2%) died. After adjusting for clinical variables, the magnitude of fixed and reversible perfusion defects was prognostic of death (P=0.02 and 0.01, respectively), while the rest LVEF was not (P=0.18). The addition of LVEF reserve did not add any incremental value, while the addition of MBFR revealed incremental prognostic value (hazard ratio per 0.1 unit decrease in MBFR=1.08 [95% CI, 1.05-1.11], P<0.001) with fixed and reversible defects becoming nonsignificant (P=0.07 and 0.29, respectively). There was no interaction between MBFR and cause of cardiomyopathy (ischemic versus nonischemic).

CONCLUSIONS

In patients with a known cardiomyopathy who did not require early revascularization, reduced MBFR as obtained by positron emission tomography myocardial perfusion imaging is associated with all-cause mortality while other positron emission tomography myocardial perfusion imaging measures were not.

Short-term repeatability of myocardial blood flow using 82Rb PET/CT: The effect of arterial input function position and motion correction

BACKGROUND

We tested the repeatability of myocardial blood flow (MBF) quantified using 82Rb with and without motion correction (MC) and with arterial input functions estimated from left ventricle (LV) and atrium (LA).

METHODS

Twenty-one patients referred for clinical 82Rb PET/CT underwent repeated rest scans in a single imaging session. Global MBF was quantified using three different assessments by two operators: (1) automatic processing without MC and LV arterial input function (AIF), (2) with MC and LV-AIF, and (3) with MC and LA-AIF. Inter-scan and inter-operator repeatability were tested using coefficient of variation (CV).

RESULTS

MC with LV-AIF did not change MBF (no MC: 1.01 ± 0.30 mL/min/g vs MC with LV-AIF: 1.01 ± 0.29, P = 0.70), whereas MC with LA-AIF showed significantly lower MBF assessments (0.95 ± 0.28 mL/min/g, P = 0.0006). We report significant improvement for test-retest reproducibility for global MBF following MC (CV; No MC: 16.0, MC (LV-AIF): 9.2, MC (LA-AIF): 8.8). Good inter-operator repeatability was observed for LV-AIF (CV = 4.7) and LA-AIF (CV = 5.6) for global MBF assessments.

CONCLUSIONS

MC significantly improved the test-retest repeatability between operators and between scans. MBF obtained after MC with LV-AIF were comparable, whereas MBFs after MC and LA-AIF were significantly reduced.

Risk stratification in coronary artery disease using NH3-PET myocardial flow reserve and CAD-RADS on coronary CT angiography

Myocardial flow reserve (MFR) derived from ¹³N-ammonia positron emission tomography (NH₃-PET) can predict the prognosis of patients with various heart diseases. Coronary computed tomography angiography (CCTA) is a non-invasive investigation for ischemic heart disease. The coronary artery disease reporting and data system (CAD-RADS) was established to standardize and facilitate the reporting of CCTA data regarding CAD. This study aimed to investigate the prognostic value of CAD-RADS and MFR. A total of 133 patients who underwent NH₃-PET and CCTA within 3 months were enrolled. Patients were divided into groups with CAD-RADS 0-2 and ≥ 3 and into groups with MFR ≥ 2.0 and < 2.0. The endpoint was major adverse cardiac events (MACE) comprising all-cause death, acute coronary syndrome, hospitalization due to heart failure, and cerebrovascular disease. The ability of CAD-RADS and MFR to predict MACE was analyzed using Kaplan-Meier analysis. There was no significant difference in MFR between patients with CAD-RADS 0-2 and ≥ 3 (2.3 ± 0.9 vs. 2.2 ± 0.7, p = 0.50). The MACE rate for patients with CAD-RADS 0-2 and ≥ 3 was equivalent (log-rank test, p = 0.64). Patients with MFR < 2.0 had a significantly higher MACE rate than those with MFR ≥ 2.0 (p = 0.017). In patients with CAD-RADS ≥ 3, patients with MFR < 2.0 had a significantly higher MACE rate than those with MFR ≥ 2.0 (p = 0.034). CAD-RADS did not contribute to MACE prediction. Conversely, MFR was useful in predicting MACE, allowing for further risk stratification in addition to CAD-RADS.

Machine learning and network medicine: a novel approach for precision medicine and personalized therapy in cardiomyopathies

The early identification of pathogenic mechanisms is essential to predict the incidence and progression of cardiomyopathies and to plan appropriate preventive interventions. Noninvasive cardiac imaging such as cardiac computed tomography, cardiac magnetic resonance, and nuclear imaging plays an important role in diagnosis and management of cardiomyopathies and provides useful prognostic information. Most molecular factors exert their functions by interacting with other cellular components, thus many diseases reflect perturbations of intracellular networks. Indeed, complex diseases and traits such as cardiomyopathies are caused by perturbations of biological networks. The network medicine approach, by integrating systems biology, aims to identify pathological interacting genes and proteins, revolutionizing the way to know cardiomyopathies and shifting the understanding of their pathogenic phenomena from a reductionist to a holistic approach. In addition, artificial intelligence tools, applied to morphological and functional imaging, could allow imaging scans to be automatically analyzed to extract new parameters and features for cardiomyopathy evaluation. The aim of this review is to discuss the tools of network medicine in cardiomyopathies that could reveal new candidate genes and artificial intelligence imaging-based features with the aim to translate into clinical practice as diagnostic, prognostic, and predictive biomarkers and shed new light on the clinical setting of cardiomyopathies. The integration and elaboration of clinical habits, molecular big data, and imaging into machine learning models could provide better disease phenotyping, outcome prediction, and novel drug targets, thus opening a new scenario for the implementation of precision medicine for cardiomyopathies.

Prognostic value of coronary flow reserve in patients with suspected or known coronary artery disease referred to PET myocardial perfusion imaging: A meta-analysis

BACKGROUND

We performed a meta-meta-analysis to evaluate the prognostic value of coronary flow reserve (CFR) assessed by cardiac positron emission tomography (PET) imaging in patients with suspected or known coronary artery disease (CAD).

METHODS

Studies published until April 2019 were identified by database search. We included studies if they evaluated CFR by PET providing data on adjusted hazard ratio (HR) for the occurrence of adverse events. Annualized event rates were calculated and the incidence rate ratios with 95% confidence interval (CI) were estimated to compare patients with impaired and preserved CFR.

RESULTS

We identified 13 eligible articles including 11,867 patients with a follow-up ranging from 0.6 to 7.1 years. The HR for the occurrence of major adverse cardiac events (MACE) was reported in 11 studies and pooled HR was 1.93 (95% CI 1.65-2.27). The HR for the occurrence of hard events was reported in 5 studies and pooled HR was 3.11 (95% CI 1.88-5.14). Six studies reported data useful to calculate separately the incidence rate of MACE in patients with preserved and impaired CFR and pooled IRR was 2.26 (CI 95% 1.79-2.85). Three studies reported data useful to calculate separately the incidence rate of hard events in patients with preserved and impaired CFR and pooled IRR was 4.12 (CI 95% 3.08-5.51). At meta-regression analysis, we found an association between HR for MACE and gender, diabetes and hypertension, while no significant association was found between HR for hard events and demographic and clinical variables.

CONCLUSION

In patients with suspected or known CAD, an impaired CFR is associated with adverse cardiovascular events. However, the large heterogeneity in study population underlines the need for further investigations to maximize the prognostic role of CFR.

Cardiac perfusion by positron emission tomography

Myocardial perfusion imaging (MPI) with positron emission tomography (PET) is an established tool for evaluation of obstructive coronary artery disease (CAD). The contemporary 3-dimensional scanner technology and the state-of-the-art MPI radionuclide tracers and pharmacological stress agents, as well as the cutting-edge image reconstruction techniques and data analysis software, have all enabled accurate, reliable and reproducible quantification of absolute myocardial blood flow (MBF), and henceforth calculation of myocardial flow reserve (MFR) in several clinical scenarios. In patients with suspected coronary artery disease, both absolute stress MBF and MFR can identify myocardial territories subtended by epicardial coronary arteries with haemodynamically significant stenosis, as defined by invasive coronary fractional flow reserve measurement. In particular, absolute stress MBF and MFR offered incremental prognostic information for predicting adverse cardiac outcome, and hence for better patient risk stratification, over those provided by traditional clinical risk predictors. This article reviews the available evidence to support the translation of the current techniques and technologies into a useful decision-making tool in real-world clinical practice.

Sweat the small stuff: The human microvasculature and heart disease

Traditionally thought of primarily as the predominant regulator of myocardial perfusion, it is becoming more accepted that the human coronary microvasculature also exerts a more direct influence on the surrounding myocardium. Coronary microvascular dysfunction (CMD) not only precedes large artery atherosclerosis, but is associated with other cardiovascular diseases such as heart failure with preserved ejection fraction and hypertrophic cardiomyopathy. It is also highly predictive of cardiovascular events in patients with or without atherosclerotic cardiovascular disease. This review focuses on this recent paradigm shift and delves into the clinical consequences of CMD. Concepts of how resistance arterioles contribute to disease will be discussed, highlighting how the microvasculature may serve as a potential target for novel therapies and interventions. Finally, both invasive and non-invasive methods with which to assess the coronary microvasculature both for diagnostic and risk stratification purposes will be reviewed.

Patient factors and outcomes associated with discordance between quantitative and qualitative cardiac PET ischemia information

BACKGROUND

Cardiac PET can provide quantitative myocardial blood flow (MBF) estimates. The frequency and clinical significance of discordant ischemia information between quantitative and qualitative parameters is unclear.

METHODS

This retrospective, cohort study analyzed 256 Rb-82 stress-rest PET/CT studies. Global MBF and myocardial flow reserve (MFR) were estimated in absolute units for quantitative results and sum-stress and difference scores were used for qualitative results. Four groups of patients were evaluated based on a specific definition of concordant and discordant quantitative and qualitative results.

RESULTS

31% of cases demonstrated discordance. Factors associated with microvascular disease were more common in the groups with abnormal quantitative results, regardless of the qualitative findings. Patients with concordant abnormal results had a significantly increased risk of myocardial infarction, heart failure, percutaneous intervention, and all-cause-mortality at 1 year compared to patients with concordant normal results. In patients with discordant results of abnormal quantitative and normal qualitative findings, there was a higher prevalence of heart failure than in controls (12.5% vs 0%, p = 0.01).

CONCLUSIONS

Discordance in qualitative and quantitative ischemia measures from PET is common, and further study is needed to clarify its prognostic implications. Moreover, quantitative estimation of MBF and MFR appears to add value to qualitative visual interpretation by supporting qualitative findings when results are concordant. Abnormal quantitative findings, regardless of concordance or discordance with qualitative findings, occurred in patients with risk factors associated with diffuse disease and with increased risk of heart failure admission.

Vascular effects of serelaxin in patients with stable coronary artery disease: a randomized placebo-controlled trial

AIMS

The effects of serelaxin, a recombinant form of human relaxin-2 peptide, on vascular function in the coronary microvascular and systemic macrovascular circulation remain largely unknown. This mechanistic, clinical study assessed the effects of serelaxin on myocardial perfusion, aortic stiffness, and safety in patients with stable coronary artery disease (CAD).

METHODS AND RESULTS

In this multicentre, double-blind, parallel-group, placebo-controlled study, 58 patients were randomized 1:1 to 48 h intravenous infusion of serelaxin (30 µg/kg/day) or matching placebo. The primary endpoints were change from baseline to 47 h post-initiation of the infusion in global myocardial perfusion reserve (MPR) assessed using adenosine stress perfusion cardiac magnetic resonance imaging, and applanation tonometry-derived augmentation index (AIx). Secondary endpoints were: change from baseline in AIx and pulse wave velocity, assessed at 47 h, Day 30, and Day 180; aortic distensibility at 47 h; pharmacokinetics and safety. Exploratory endpoints were the effect on cardiorenal biomarkers [N-terminal pro-brain natriuretic peptide (NT-proBNP), high-sensitivity troponin T (hsTnT), endothelin-1, and cystatin C]. Of 58 patients, 51 were included in the primary analysis (serelaxin, n = 25; placebo, n = 26). After 2 and 6 h of serelaxin infusion, mean placebo-corrected blood pressure reductions of -9.6 mmHg (P = 0.01) and -13.5 mmHg (P = 0.0003) for systolic blood pressure and -5.2 mmHg (P = 0.02) and -8.4 mmHg (P = 0.001) for diastolic blood pressure occurred. There were no between-group differences from baseline to 47 h in global MPR (-0.24 vs. -0.13, P = 0.44) or AIx (3.49% vs. 0.04%, P = 0.21) with serelaxin compared with placebo. Endothelin-1 and cystatin C levels decreased from baseline in the serelaxin group, and there were no clinically relevant changes observed with serelaxin for NT-proBNP or hsTnT. Similar numbers of serious adverse events were observed in both groups (serelaxin, n = 5; placebo, n = 7) to 180-day follow-up.

CONCLUSION

In patients with stable CAD, 48 h intravenous serelaxin reduced blood pressure but did not alter myocardial perfusion.

EANM procedural guidelines for PET/CT quantitative myocardial perfusion imaging

The use of cardiac PET, and in particular of quantitative myocardial perfusion PET, has been growing during the last years, because scanners are becoming widely available and because several studies have convincingly demonstrated the advantages of this imaging approach. Therefore, there is a need of determining the procedural modalities for performing high-quality studies and obtaining from this demanding technique the most in terms of both measurement reliability and clinical data. Although the field is rapidly evolving, with progresses in hardware and software, and the near perspective of new tracers, the EANM Cardiovascular Committee found it reasonable and useful to expose in an updated text the state of the art of quantitative myocardial perfusion PET, in order to establish an effective use of this modality and to help implementing it on a wider basis. Together with the many steps necessary for the correct execution of quantitative measurements, the importance of a multiparametric approach and of a comprehensive and clinically useful report have been stressed.

Coronary microvascular dysfunction in stable ischaemic heart disease (non-obstructive coronary artery disease and obstructive coronary artery disease)

Diffuse and focal epicardial coronary disease and coronary microvascular abnormalities may exist side-by-side. Identifying the contributions of each of these three players in the coronary circulation is a difficult task. Yet identifying coronary microvascular dysfunction (CMD) as an additional player in patients with coronary artery disease (CAD) may provide explanations of why symptoms may persist frequently following and why global coronary flow reserve may be more prognostically important than fractional flow reserve measured in a single vessel before percutaneous coronary intervention. This review focuses on the challenges of identifying the presence of CMD in the context of diffuse non-obstructive CAD and obstructive CAD. Furthermore, it is going to discuss the pathophysiology in this complex situation, examine the clinical context in which the interaction of the three components of disease takes place and finally look at non-invasive diagnostic methods relevant for addressing this question.

Prognostic Value of Stress CMR Perfusion Imaging in Patients With Reduced Left Ventricular Function

OBJECTIVES

The aim of this study was to investigate the prognostic value of stress cardiac magnetic resonance imaging (CMR) in patients with reduced left ventricular (LV) systolic function.

BACKGROUND

Patients with ischemic cardiomyopathy are at risk from both myocardial ischemia and heart failure. Invasive testing is often used as the first-line investigation, and there is limited evidence as to whether stress testing can effectively provide risk stratification.

METHODS

In this substudy of a multicenter registry from 13 U.S. centers, patients with reduced LV ejection fraction (<50%), referred for stress CMR for suspected myocardial ischemia, were included. The primary outcome was cardiovascular death or nonfatal myocardial infarction. The secondary outcome was a composite of cardiovascular death, nonfatal myocardial infarction, hospitalization for unstable angina or congestive heart failure, and unplanned late coronary artery bypass graft surgery.

RESULTS

Among 582 patients (mean age 62 ± 12 years, 34% women), 40% had a history of congestive heart failure, and the median LV ejection fraction was 39% (interquartile range: 28% to 45%). At median follow-up of 5.0 years, 97 patients had experienced the primary outcome, and 182 patients had experienced the secondary outcome. Patients with no CMR evidence of ischemia or late gadolinium enhancement (LGE) experienced an annual primary outcome event rate of 1.1%. The presence of ischemia, LGE, or both was associated with higher event rates. In a multivariate model adjusted for clinical covariates, ischemia and LGE were independent predictors of the primary (hazard ratio [HR]: 2.63; 95% confidence interval [CI]: 1.68 to 4.14; p < 0.001; and HR: 1.86; 95% CI: 1.05 to 3.29; p = 0.03) and secondary (HR: 2.14; 95% CI: 1.55 to 2.95; p < 0.001; and HR 1.70; 95% CI: 1.16 to 2.49; p = 0.007) outcomes. The addition of ischemia and LGE led to improved model discrimination for the primary outcome (change in C statistic from 0.715 to 0.765; p = 0.02). The presence and extent of ischemia were associated with higher rates of use of downstream coronary angiography, revascularization, and cost of care spent on ischemia testing.

CONCLUSIONS

Stress CMR was effective in risk-stratifying patients with reduced LV ejection fractions. (Stress CMR Perfusion Imaging in the United States [SPINS] Study; NCT03192891).

Coronary Microvascular Dysfunction

Many patients with chest pain undergoing coronary angiography do not show significant obstructive coronary lesions. A substantial proportion of these patients have abnormalities in the function and structure of coronary microcirculation due to endothelial and smooth muscle cell dysfunction. The coronary microcirculation has a fundamental role in the regulation of coronary blood flow in response to cardiac oxygen requirements. Impairment of this mechanism, defined as coronary microvascular dysfunction (CMD), carries an increased risk of adverse cardiovascular clinical outcomes. Coronary endothelial dysfunction accounts for approximately two-thirds of clinical conditions presenting with symptoms and signs of myocardial ischemia without obstructive coronary disease, termed "ischemia with non-obstructive coronary artery disease" (INOCA) and for a small proportion of "myocardial infarction with non-obstructive coronary artery disease" (MINOCA). More frequently, the clinical presentation of INOCA is microvascular angina due to CMD, while some patients present vasospastic angina due to epicardial spasm, and mixed epicardial and microvascular forms. CMD may be associated with focal and diffuse epicardial coronary atherosclerosis, which may reinforce each other. Both INOCA and MINOCA are more common in females. Clinical classification of CMD includes the association with conditions in which atherosclerosis has limited relevance, with non-obstructive atherosclerosis, and with obstructive atherosclerosis. Several studies already exist which support the evidence that CMD is part of systemic microvascular disease involving multiple organs, such as brain and kidney. Moreover, CMD is strongly associated with the development of heart failure with preserved ejection fraction (HFpEF), diabetes, hypertensive heart disease, and also chronic inflammatory and autoimmune diseases. Since coronary microcirculation is not visible on invasive angiography or computed tomographic coronary angiography (CTCA), the diagnosis of CMD is usually based on functional assessment of microcirculation, which can be performed by both invasive and non-invasive methods, including the assessment of delayed flow of contrast during angiography, measurement of coronary flow reserve (CFR) and index of microvascular resistance (IMR), evaluation of angina induced by intracoronary acetylcholine infusion, and assessment of myocardial perfusion by positron emission tomography (PET) and magnetic resonance (CMR).

Prognostic Value of Quantitative Metrics From Positron Emission Tomography in Ischemic Heart Failure

OBJECTIVES

The aim of this study was to investigate the prognostic and clinical value of quantitative positron emission tomographic (PET) metrics in patients with ischemic heart failure.

BACKGROUND

Although myocardial flow reserve (MFR) is a strong predictor of cardiac risk in patients without heart failure, it is unknown whether quantitative PET metrics improve risk stratification in patients with ischemic heart failure.

METHODS

The study included 254 patients referred for stress and rest myocardial perfusion imaging and viability testing using PET. Major adverse cardiac event(s) (MACE) consisted of death, resuscitated sudden cardiac death, heart transplantation, acute coronary syndrome, hospitalization for heart failure, and late revascularization.

RESULTS

MACE occurred in 170 patients (67%) during a median follow-up of 3.3 years. In a multivariate Cox proportional hazards model including multiple quantitative PET metrics, only MFR predicted MACE significantly (p = 0.013). Beyond age, symptom severity, diabetes mellitus, previous myocardial infarction or revascularization, 3-vessel disease, renal insufficiency, ejection fraction, as well as presence and burden of ischemia, scar, and hibernating myocardium, MFR was strongly associated with MACE (adjusted hazard ratio per increase in MFR by 1: 0.63; 95% confidence interval: 0.45 to 0.91). Incorporation of MFR into a risk assessment model incrementally improved the prediction of MACE (likelihood ratio chi-square test [16] = 48.61 vs. chi-square test [15] = 39.20; p = 0.002).

CONCLUSIONS

In this retrospective analysis of a single-center cohort, quantitative PET metrics of myocardial blood flow all improved risk stratification in patients with ischemic heart failure. However, in a hypothesis-generating analysis, MFR appears modestly superior to the other metrics as a prognostic index.

Multi-Modality Imaging in Dilated Cardiomyopathy: With a Focus on the Role of Cardiac Magnetic Resonance

Heart failure (HF) is recognized as a leading cause of morbidity and mortality worldwide. Dilated cardiomyopathy (DCM) is a common phenotype in patients presenting with HF. Timely diagnosis, appropriate identification of the underlying cause, individualized risk stratification, and prediction of clinical response to treatment have improved the prognosis of DCM over the last few decades. In this article, we reviewed the current evidence on available imaging techniques used for DCM patients. In this direction, we evaluated appropriate scenarios for the implementation of echocardiography, nuclear imaging, and cardiac computed tomography, and we focused on the primordial role that cardiac magnetic resonance (CMR) holds in the diagnosis, prognosis, and tailoring of therapeutic options in this population of special clinical interest. We explored the predictive value of CMR toward left ventricular reverse remodeling and prediction of sudden cardiac death, thus guiding the decisions for device therapy. Principles underpinning the use of state-of-the-art CMR techniques such as parametric mapping and feature-tracking strain analysis are also provided, along with expectations for the anticipated future advances in this field. We also attempted to correlate the evidence with clinical practice, with the intent to address questions on selecting the optimal imaging method for different indications and clinical needs. Overall, we recommend a comprehensive assessment of DCM patients at baseline and at follow-up intervals depending on the clinical status, with the addition of CMR as a second-line modality to other imaging techniques. We also provide an algorithm to guide the detailed imaging approach of the patient with DCM. We expect that future guidelines will upgrade their clinical recommendations for the utilization of CMR in DCM, which is expected to further improve the quality of care and the outcomes. This review provides an up-to-date perspective on the imaging of dilated cardiomyopathy patients and will be of clinical value to training doctors and physicians involved in the area of heart failure.

The role of resting myocardial blood flow and myocardial blood flow reserve as a predictor of major adverse cardiovascular outcomes

Cardiac perfusion PET is increasingly used to assess ischemia and cardiovascular risk and can also provide quantitative myocardial blood flow (MBF) and flow reserve (MBFR) values. These have been shown to be prognostic biomarkers of adverse outcomes, yet MBF and MBFR quantification remains underutilized in clinical settings. We compare MBFR to traditional cardiovascular risk factors in a large and diverse clinical population (60% African-American, 35.3% Caucasian) to rank its relative contribution to cardiovascular outcomes. Major adverse cardiovascular events (MACE), including unstable angina, non-ST and ST-elevation myocardial infarction, stroke, and death, were assessed for consecutive patients who underwent rest-dipyridamole stress 82Rb PET cardiac imaging from 2012–2015 at the Hospital of the University of Pennsylvania (n = 1283, mean follow-up 2.3 years). Resting MBF (1.1 ± 0.4 ml/min/g) was associated with adverse cardiovascular outcomes. MBFR (2.1 ± 0.8) was independently and inversely associated with MACE. Furthermore, MBFR was more strongly associated with MACE than both traditional cardiovascular risk factors and the presence of perfusion defects in regression analysis. Decision tree analysis identified MBFR as superior to established cardiovascular risk factors in predicting outcomes. Incorporating resting MBF and MBFR in CAD assessment may improve clinical decision making.