Myocardial Perfusion Reserve and Strain-Encoded CMR for Evaluation of Cardiac Allograft Microvasculopathy

Developing and evaluating a chronic ischemic cardiomyopathy in swine model by rest and stress CMR

A large animal model of chronic coronary artery disease (CAD) is crucial for the understanding the underlying pathophysiological processes of chronic CAD and consequences for cardiac structure and function. The goal of this study was to develop a chronic model of CAD in a swine model and to evaluate the changes of myocardial structure, myocardial motility, and myocardial viability during coronary stenosis. A total of 30 swine (including 24 experimental animals and 6 controls) were enrolled. The chronic ischemia model was constructed by using Ameroid constrictor in experimental group. The 24 experimental animals were further divided into 4 groups (6 animals in each group) and were sacrificed at 1, 2, 3 and 4 weeks after operation for pathological examination, respectively. Cardiac magnetic resonance (CMR) was performed preoperatively and weekly postoperatively until sacrificed both in experimental and control group. CMR cine images, rest/adenosine triphosphate (ATP) stress myocardial contrast perfusion and LGE were performed and analyzed. The rest wall thickening (WT) score was calculated from rest cine images. The MPRI (myocardial perfusion reserve index) and MPR (myocardial perfusion reserve) were calculated based on rest and stress perfusion images. Pathology staining including triphenyltetrazolium chloride, HE and picrosirus red staining were performed after swine were sacrificed and collagen volume fraction (CVF) was calculated. The time to formation of ischemic, hibernating, and infarcted myocardium was recorded. In experimental group, from 1w to 4w after surgery, the rest WT score decreased gradually from 35.2 ± 2.0%, 32.0 ± 2.9% to 30.5 ± 3.0% and finally 29.06 ± 1.78%, p < 0.001. Left ventricular ejection fraction was gradually impaired after modeling (58.9 ± 12.6%, 56.3 ± 10.1%, 55.3 ± 9.0%, 53.8 ± 9.9%, respectively). And the MPR and MPRI also decreased stepwise with extent of surgery time (MPRI dropped from 2.1 ± 0.4, 2.0 ± 0.2 to 1.8 ± 0.3 and finally 1.7 ± 0.1, p = 0.004; MPR dropped from 2.3 ± 0.4, 2.1 ± 0.2 to 1.9 ± 0.4 and finally 1.8 ± 0.1, p < 0.001). Stronger associations between MPR, MPRI and CVF were paralleled lower wall thickening scores in fibrosis-affected areas. The ischemic myocardium was first appeared in the first week after surgery (involving ten segments), hibernated myocardium was first appeared in the second week after surgery (involving seventeen segments). LGE was first appeared in eight swine in the third weeks after surgery (16 segments). At 4w after surgery, average 9.6 g scar tissue was found among 6 swine. At the same time, histological analysis established the presence of fibrosis and ongoing apoptosis in the infarcted area. In conclusion, our study provided valuable insights into the pathophysiological processes of chronic CAD and its consequences for cardiac structure and function in a large animal model through combining myocardial motion and stress perfusion.

Cardiac magnetic resonance imaging in detection of progressive graft dysfunction in pediatric heart transplantation

BACKGROUND

Chronic graft failure (CGF) in pediatric heart transplant (PHT) is multifactorial and may present with findings of fibrosis and microvessel disease (MVD) on endomyocardial biopsy (EMB). There is no optimal CGF surveillance method. We evaluated associations between cardiac magnetic resonance imaging (CMR) and historical/EMB correlates of CGF to assess CMR's utility as a surveillance method.

METHODS

Retrospective analysis of PHT undergoing comprehensive CMR between September 2015 and January 2022 was performed. EMB within 6 months was graded for fibrosis (scale 0-5) and MVD (number of capillaries with stenotic wall thickening per field of view). Correlation analysis and logistic regression were performed.

RESULTS

Forty-seven PHT with median age at CMR of 15.7 years (11.6, 19.3) and time from transplant of 6.4 years (4.1, 11.0) were studied. Cardiac allograft vasculopathy (CAV) was present in 11/44 (22.0%) and historical rejection in 14/41 (34.2%). CAV was associated with higher global T2 (49.0 vs. 47.0 ms; p = 0.038) and peak T2 (57.0 vs. 53.0 ms; p = 0.013) on CMR. Historical rejection was associated with higher global T2 (49.0 vs. 47.0 ms; p = 0.007) and peak T2 (57.0 vs. 53.0 ms; p = 0.03) as well as global extracellular volume (31.0 vs. 26.3%; p = 0.03). Higher fibrosis score on EMB correlated with smaller indexed left ventricular mass (rho = -0.34; p = 0.019) and greater degree of MVD with lower indexed left ventricular end-diastolic volume (rho = -0.35; p = 0.017).

CONCLUSION

Adverse ventricular remodeling and abnormal myocardial characteristics on CMR are present in PHT with CAV, historical rejection, as well as greater fibrosis and MVD on EMB. CMR has the potential use for screening of CGF.

Multimodality Imaging in Advanced Heart Failure for Diagnosis, Management and Follow-Up: A Comprehensive Review

Advanced heart failure (AHF) presents a complex landscape with challenges spanning diagnosis, management, and patient outcomes. In response, the integration of multimodality imaging techniques has emerged as a pivotal approach. This comprehensive review delves into the profound significance of these imaging strategies within AHF scenarios. Multimodality imaging, encompassing echocardiography, cardiac magnetic resonance imaging (CMR), nuclear imaging and cardiac computed tomography (CCT), stands as a cornerstone in the care of patients with both short- and long-term mechanical support devices. These techniques facilitate precise device selection, placement, and vigilant monitoring, ensuring patient safety and optimal device functionality. In the context of orthotopic cardiac transplant (OTC), the role of multimodality imaging remains indispensable. Echocardiography offers invaluable insights into allograft function and potential complications. Advanced methods, like speckle tracking echocardiography (STE), empower the detection of acute cell rejection. Nuclear imaging, CMR and CCT further enhance diagnostic precision, especially concerning allograft rejection and cardiac allograft vasculopathy. This comprehensive imaging approach goes beyond diagnosis, shaping treatment strategies and risk assessment. By harmonizing diverse imaging modalities, clinicians gain a panoramic understanding of each patient's unique condition, facilitating well-informed decisions. The aim is to highlight the novelty and unique aspects of recently published papers in the field. Thus, this review underscores the irreplaceable role of multimodality imaging in elevating patient outcomes, refining treatment precision, and propelling advancements in the evolving landscape of advanced heart failure management.

Heart Transplantation: Indications, Surgical Techniques, and Complications

Heart transplantation has been increasingly performed for patients with end-stage heart failure most commonly related to ischemic and non-ischemic cardiomyopathies. The major complications are procedure-related complications, infection, acute rejection, cardiac allograft vasculopathy, and malignancy. Radiologists have an important role in the evaluation of transplant candidates and early detection of postoperative complications.

CT Coronary Angiography and Dynamic CT Myocardial Perfusion for Detection of Cardiac Allograft Vasculopathy

BACKGROUND

Cardiac allograft vasculopathy (CAV) is a major obstacle limiting long-term graft survival. Effective noninvasive surveillance modalities reflecting both coronary artery and microvascular components of CAV are needed.

OBJECTIVES

The authors evaluated the diagnostic performance of dynamic computed tomography-myocardial perfusion imaging (CT-MPI) and coronary computed tomography angiography (CCTA) for CAV.

METHODS

A total of 63 heart transplantation patients underwent combined CT-MPI and CCTA plus invasive coronary angiography (ICA) with intravascular ultrasonography (IVUS) between December 2018 and October 2021. The median interval between CT-MPI and heart transplantation was 4.3 years. Peak myocardial blood flow (MBF) of the whole myocardium (MBF_global) and minimum MBF (MBF_min) among the 16 segments according to the American Heart Association model, except the left ventricular apex, were calculated from CT-MPI. CCTA was assessed qualitatively, and the degree of coronary artery stenosis was recorded. CAV was diagnosed based on both ICA (ISHLT criteria) and IVUS. Patients were followed up for a median time of 2.3 years after CT-MPI and a median time of 5.7 years after transplantation.

RESULTS

Among the 63 recipients, 35 (55.6%) had diagnoses of CAV. The median MBF_global and MBF_min were significantly lower in patients with CAV (128.7 vs 150.4 mL/100 mL/min; P = 0.014; and 96.9 vs 122.8 mL/100 mL/min; P < 0.001, respectively). The combined use of coronary artery stenosis on CCTA and MBF_min showed the highest diagnostic performance with an area under the curve of 0.886 (sensitivity: 74.3%, specificity: 96.4%, positive predictive value: 96.3%, and negative predictive value: 75.0%).

CONCLUSIONS

The combination of CT-MPI and CCTA demonstrated excellent diagnostic performance for the detection of CAV. One-stop evaluation of the coronary artery and microvascular components involved in CAV using combined CCTA and CT-MPI may be a potent noninvasive screening method for early detection of CAV.

Case report: Coronary allograft vasculopathy: an accurate reflection of the histopathological findings on cardiovascular magnetic resonance imaging

Heart transplant recipients undergo extensive invasive and non-invasive postoperative screening to exclude complications, such as allograft rejection and vasculopathy. Cardiac magnetic resonance imaging is a non-invasive, non-irradiating, diagnostic tool for monitoring graft health and identifying possible tissue rejection or myocardial fibrosis. We describe the case of a 29-year-old female heart transplant recipient admitted to our care center with a worsening clinical condition. The patient underwent clinical evaluation, blood tests, including troponin I and N-terminal pro brain type natriuretic peptide, transthoracic echocardiography, invasive coronary angiography, and cardiovascular magnetic resonance imaging. Cardiovascular magnetic resonance imaging showed widespread sub-epicardial hyperintensity of the myocardial segments along the course of the coronary arteries. T2 mapping sequences showed an elevated value and the myocardial native T1 values and extracellular volume percentage were significantly increased. Late gadolinium enhancement demonstrated a diffuse sub-epicardial hypersignal along the lateral, free, and left ventricular walls. All the sequences evidenced widespread hyper-enhancement of epicardial fat along the course of the thickened main coronary artery walls. One month later, the recipient underwent re-transplantation due to progressive worsening of the clinical condition and refractoriness to intravenous medication. The anatomopathological findings of the explanted heart provided impressive visualization of structural and histopathological changes. These results could guide the tailoring of preventive therapeutic strategies and non-invasive monitoring of cardiac grafts.

Increased fibrosis and microvessel disease in allograft endomyocardial biopsies of children with chronic graft failure due to cardiac allograft vasculopathy

INTRODUCTION

Chronic graft failure (CGF) is the leading cause of mortality in pediatric heart transplant (PHT) patients and has multifactorial pathogenesis including cardiac allograft vasculopathy (CAV). CGF can present with microvessel disease (MVD) and myocardial fibrosis on endomyocardial biopsies (EMB). We investigated if CGF due to moderate- severe (M-S) CAV has histopathologic MVD and fibrosis prior to or at the time of CAV diagnosis.

METHOD

This retrospective case-control study included PHT with CGF secondary to M-S CAV. Control patients had no CAV or CGF. EMBs from CAV (3 sets: at 1-year post-transplant 1yrCAV, pre-CAV, and at the time of CAV diagnosis) and non-CAV cohorts were reviewed to grade the fibrosis and quantify MVD. Histopathologic changes were correlated and compared between CAV/non-CAV groups.

RESULTS

Each group had 8 patients. The median age at transplantation and time since transplant were similar between the two groups (P=.71 and P=.91, respectively). Fibrosis grade was 3.0 for CAV cohort compared to 1.0 for control (P= .003) and MVD score was 2.1 in CAV and 0.5 in non-CAV patients (P=.003). Similar degrees of fibrosis and MVD were present even before any evidence of CAV (1yrCAV fibrosis grade 2.5, pre-CAV fibrosis grade 2; 1yrCAV vs CAV P=.75, pre-CAV vs CAV P=.63; 1yrCAV MVD score 2, pre-CAV MVD score 2; 1yrCAV vs CAV P=1, pre-CAV vs CAV P=.91). The degree of MVD correlated with fibrosis (r=0.63, P<.0001) for all EMBs.

CONCLUSION

Simultaneous myocardial fibrosis and MVD are noted in CGF secondary to M-S CAV, changes that occur before angiographic CAV. EMBs can reveal significant changes in patients with subsequent development of CAV and may be used to modify the follow-up and treatment for these high-risk patients.

Cardiac Magnetic Resonance in the Evaluation of COVID-19

Cardiovascular involvement following COVID-19 is heterogeneous, prevalent and is often missed by echocardiography and serum biomarkers (such as troponin I and brain natriuretic peptide). Cardiac magnetic resonance (CMR) is the gold standard non-invasive imaging modality to phenotype unique populations after COVID-19, such as competitive athletes with a heightened risk of sudden cardiac death, patients with multisystem inflammatory syndrome, and people suspected of having COVID-19 vaccine-induced myocarditis. This review summarises the key attributes of CMR, reviews the literature that has emerged for using CMR for people who may have COVID-19-related complications after COVID-19, and offers expert opinion regarding future avenues of investigation and the importance of reporting findings.

Non-Invasive Imaging in the Evaluation of Cardiac Allograft Vasculopathy in Heart Transplantation: A Systematic Review

Cardiac allograft vasculopathy (CAV) is the leading cause of long-term graft dysfunction in patients with heart transplantation and is linked with significant morbidity and mortality. Currently, the gold standard for diagnosing CAV is coronary imaging with intravascular ultrasound (IVUS) during traditional invasive coronary angiography (ICA). Invasive imaging, however, carries increased procedural risk and expense to patients in addition to requiring an experienced interventionalist. With the improvements in non-invasive cardiac imaging modalities such as transthoracic echocardiography (TTE), computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET), an alternative non-invasive imaging approach for the early detection of CAV may be feasible. In this systematic review, we explored the literature to investigate the utility of non-invasive imaging in diagnosis of CAV in >3000 patients across 49 studies. We also discuss the strengths and weaknesses for each imaging modality. Overall, all four imaging modalities show good to excellent accuracy for identifying CAV with significant variations across studies. Majority of the studies compared non-invasive imaging with ICA without intravascular imaging. In summary, non-invasive imaging modalities offer an alternative approach to invasive coronary imaging for CAV. Future studies should investigate longitudinal non-invasive protocols in low-risk patients after heart transplantation.

Multiparametric Cardiac Magnetic Resonance Imaging Detects Altered Myocardial Tissue and Function in Heart Transplantation Recipients Monitored for Cardiac Allograft Vasculopathy

BACKGROUND

Cardiac allograft vasculopathy (CAV) is a complication beyond the first-year post-heart transplantation (HTx). We aimed to test the utility of cardiac magnetic resonance (CMR) to detect functional/structural changes in HTx recipients with CAV.

METHODS

Seventy-seven prospectively recruited HTx recipients beyond the first-year post-HTx and 18 healthy controls underwent CMR, including cine imaging of ventricular function and T1- and T2-mapping to assess myocardial tissue changes. Data analysis included quantification of global cardiac function and regional T2, T1 and extracellular volume based on the 16-segment model. International Society for Heart and Lung Transplantation criteria was used to adjudicate CAV grade (0–3) based on coronary angiography.

RESULTS

The majority of HTx recipients (73%) presented with CAV (1: n = 42, 2/3: n = 14, 0: n = 21). Global and segmental T2 (49.5 ± 3.4 ms vs 50.6 ± 3.4 ms, p < 0.001;16/16 segments) were significantly elevated in CAV-0 compared to controls. When comparing CAV-2/3 to CAV-1, global and segmental T2 were significantly increased (53.6 ± 3.2 ms vs. 50.6 ± 2.9 ms, p < 0.001; 16/16 segments) and left ventricular ejection fraction was significantly decreased (54 ± 9% vs. 59 ± 9%, p < 0.05). No global, structural, or functional differences were seen between CAV-0 and CAV-1.

CONCLUSIONS

Transplanted hearts display functional and structural alteration compared to native hearts, even in those without evidence of macrovasculopathy (CAV-0). In addition, CMR tissue parameters were sensitive to changes in CAV-1 vs. 2/3 (mild vs. moderate/severe). Further studies are warranted to evaluate the diagnostic value of CMR for the detection and classification of CAV.

Evaluation of cardiac allograft vasculopathy by positron emission tomography

Cardiac allograft vasculopathy (CAV) remains one of the most important late occurring complications in heart transplant (HT) recipients significantly effecting graft survival. Recently, there has been tremendous focus on the development of effective and safe non-invasive diagnostic strategies for the diagnosis of CAV employing a wide range of imaging technologies. During the past decade multiple studies have been published using positron emission tomography (PET) myocardial perfusion imaging, establishing the value of PET myocardial blood flow quantification for the evaluation of CAV. These independent investigations demonstrate that PET can be successfully used to establish the diagnosis of CAV, can be utilized for prognostication and may be used for serial monitoring of HT recipients. In addition, molecular imaging techniques have started to emerge as new tools to enhance our knowledge to better understand the pathophysiology of CAV.

Multi-parametric cardiovascular magnetic resonance with regadenoson stress perfusion is safe following pediatric heart transplantation and identifies history of rejection and cardiac allograft vasculopathy

BACKGROUND

The progressive risk of graft failure in pediatric heart transplantation (PHT) necessitates close surveillance for rejection and coronary allograft vasculopathy (CAV). The current gold standard of surveillance via invasive coronary angiography is costly, imperfect and associated with complications. Our goal was to assess the safety and feasibility of a comprehensive multi-parametric CMR protocol with regadenoson stress perfusion in PHT and evaluate for associations with clinical history of rejection and CAV.

METHODS

We performed a retrospective review of 26 PHT recipients who underwent stress CMR with tissue characterization and compared with 18 age-matched healthy controls. CMR protocol included myocardial T2, T1 and extracellular volume (ECV) mapping, late gadolinium enhancement (LGE), qualitative and semi-quantitative stress perfusion (myocardial perfusion reserve index; MPRI) and strain imaging. Clinical, demographics, rejection score and CAV history were recorded and correlated with CMR parameters.

RESULTS

Mean age at transplant was 9.3 ± 5.5 years and median duration since transplant was 5.1 years (IQR 7.5 years). One patient had active rejection at the time of CMR, 11/26 (42%) had CAV 1 and 1/26 (4%) had CAV 2. Biventricular volumes were smaller and cardiac output higher in PHT vs. healthy controls. Global T1 (1053 ± 42 ms vs 986 ± 42 ms; p < 0.001) and ECV (26.5 ± 4.0% vs 24.0 ± 2.7%; p = 0.017) were higher in PHT compared to helathy controls. Significant relationships between changes in myocardial tissue structure and function were noted in PHT: increased T2 correlated with reduced LVEF (r = - 0.57, p = 0.005), reduced global circumferential strain (r = - 0.73, p < 0.001) and reduced global longitudinal strain (r = - 0.49, p = 0.03). In addition, significant relationships were noted between higher rejection score and global T1 (r = 0.38, p = 0.05), T2 (r = 0.39, p = 0.058) and ECV (r = 0.68, p < 0.001). The presence of even low-grade CAV was associated with higher global T1, global ECV and maximum segmental T2. No major side effects were noted with stress testing. MPRI was analyzed with good interobserver reliability and was lower in PHT compared to healthy controls (0.69 ± - 0.21 vs 0.94 ± 0.22; p < 0.001).

CONCLUSION

In a PHT population with low incidence of rejection or high-grade CAV, CMR demonstrates important differences in myocardial structure, function and perfusion compared to age-matched healthy controls. Regadenoson stress perfusion CMR could be safely and reliably performed. Increasing T2 values were associated with worsening left ventricular function and increasing T1/ECV values were associated with rejection history and low-grade CAV. These findings warrant larger prospective studies to further define the role of CMR in PHT graft surveillance.

Cardiac allograft vasculopathy: current review and future research directions

Cardiac allograft vasculopathy (CAV) is a pathologic immune-mediated remodelling of the vasculature in transplanted hearts and, by impairing perfusion, is the major cause of late graft loss. Although best understood following cardiac transplantation, similar forms of allograft vasculopathy occur in other vascularized organ grafts and some features of CAV may be shared with other immune-mediated vasculopathies. Here, we describe the incidence and diagnosis, the nature of the vascular remodelling, immune and non-immune contributions to pathogenesis, current therapies, and future areas of research in CAV.

The role of non-invasive imaging modalities in cardiac allograft vasculopathy: an updated focus on current evidences

Cardiac allograft vasculopathy (CAV) is an obliterative and diffuse form of vasculopathy affecting almost 50% of patients after 10 years from heart transplant and represents the most common cause of long-term cardiovascular mortality among heart transplant recipients. The gold standard diagnostic technique is still invasive coronary angiography, which however holds potential for complications, especially contrast-related kidney injury and procedure-related vascular lesions. Non-invasive and contrast-sparing imaging techniques have been advocated and investigated over the past decades, in order to identify those that could replace coronary angiography or at least reach comparable accuracy in CAV detection. In addition, they could help the clinician in defining optimal timing for invasive testing. This review attempts to examine the currently available non-invasive imaging techniques that may be used in the follow-up of heart transplant patients, spanning from echocardiography to nuclear imaging, cardiac magnetic resonance and cardiac computed tomography angiography, weighting their advantages and disadvantages.

Feasibility and safety of quantitative adenosine stress perfusion cardiac magnetic resonance imaging in pediatric heart transplant patients with and without coronary allograft vasculopathy

BACKGROUND

Pediatric heart transplant patients require cardiac catheterization to monitor for coronary allograft vasculopathy. Cardiac catheterization has no safe and consistent method for measuring microvascular disease. Stress perfusion cardiac magnetic resonance imaging (MRI) assessing microvascular disease has been performed in adults.

OBJECTIVE

To investigate the feasibility and safety of performing cardiac MRI with quantitative adenosine stress perfusion testing in pediatric heart transplant patients with and without coronary allograft vasculopathy.

MATERIALS AND METHODS

All pediatric heart transplant patients with coronary vasculopathy at our institution were asked to participate. Age- and gender-matched pediatric heart transplant patients without vasculopathy were recruited for comparison. Patients underwent cardiac MRI with adenosine stress perfusion testing.

RESULTS

Sixteen pediatric heart transplant patients, ages 6-22 years, underwent testing. Nine patients had vasculopathy by angiography. No heart block or other complications occurred during the study. The myocardial perfusion reserve for patients with vasculopathy showed no significant difference with comparison patients (median: 1.43 vs. 1.48; P=0.49). Values for both groups were lower than expected values based on previous adult studies. The patients were also analyzed for time after transplant and the number of rejection episodes. Patients within 6 years of transplantation had a nonsignificant trend toward a higher myocardial perfusion reserve (median: 1.57) versus patients with older transplants (median: 1.47; P=0.46). Intra- and interobserver reproducibility were 97% and 92%, respectively.

CONCLUSION

Myocardial perfusion reserve is a safe and feasible method for estimating myocardial perfusion in pediatric heart transplant patients. There is no reliable way to monitor microvascular disease in pediatric patients. This method shows potential and deserves investigation in a larger cohort.

Imaging of Cardiac Transplantation: An Overview

Heart transplantation (HTx) remains the optimal treatment for selected patients with end-stage advanced heart failure. However, survival is limited early by acute rejection and long term by cardiac allograft vasculopathy (CAV). Even though the diagnosis of rejection is based on histology, cardiac imaging provides a pivotal role for early detection and severity assessment of these hazards. The present review focuses on the use and reliability of different invasive and non-invasive imaging modalities to detect and monitor CAV and rejection after HTx. Coronary angiography remains the corner stone in routine CAV surveillance. However, angiograms are invasive and underestimates the CAV severity especially in the early phase. Intravascular ultrasound and optical coherence tomography are invasive methods for intracoronary imaging that detects early CAV lesions not evident by angiograms. Non-invasive imaging can be divided into myocardial perfusion imaging, anatomical/structural imaging and myocardial functional imaging. The different non-invasive imaging modalities all provide clinical and prognostic information and may have a gatekeeper role for invasive monitoring. Acute rejection and CAV are still significant clinical problems after HTx. No imaging modality provides complete information on graft function, coronary anatomy and myocardial perfusion. However, a combination of invasive and non-invasive modalities at different stages following HTx should be considered for optimal personalized surveillance and risk stratification.

Detection of cardiac allograft vasculopathy by multi-layer left ventricular longitudinal strain in heart transplant recipients

Cardiac allograft vasculopathy (CAV) is an obliterative and diffuse type of coronaropathy that develops in the transplanted human heart, representing a major cause of graft failure and mortality. Nowadays the gold standard for the diagnosis of CAV is coronary angiography (CA). Non-invasive CAV detection, especially in the early stages of the disease, is still challenging. Our study aimed to investigate the role of speckle tracking echocardiography (STE), in particular three-layer STE, in predicting CAV at early stages, and if other traditional echocardiographic, clinical or biochemical parameters could relate to CAV. The study population was composed of a total of 33 heart transplanted patients, divided accordingly to the presence or absence of CAV (12 CAV+ , 22 CAV-). All subjects underwent a complete transthoracic echocardiographic examination on the same day of the CA, and all conventional parameters of myocardial function were obtained, including strain values assessed by STE. Strain values were significantly reduced in presence of CAV, at each myocardial layer but in particular the endocardial-epicardial gradient (- 4.15 ± 1.6 vs - 1.7 ± 0.4% < .0001) that was also highly predictive of CAV (AUC at ROC curve 0.97). Among diastolic parameters, the E wave deceleration time (DT) and the mean E/e' ratio were strongly positively associated with CAV. In our population, left ventricular global longitudinal strain (GLS), layer-specific GLS and the endocardial-epicardial LS gradient, E wave DT and E/e' ratio were the best independent non-invasive predictors of CAV.

Long-Term Prognosis of Patients With Coronary Microvascular Disease Using Stress Perfusion Cardiac Magnetic Resonance

OBJECTIVES

This study investigated the prognosis of coronary microvascular disease (CMD) as determined by stress perfusion cardiac magnetic resonance (CMR) in patients with ischemic symptoms but without significant coronary artery disease (CAD).

BACKGROUND

Patients with CMD have poorer prognosis with various cardiac diseases. The myocardial perfusion reserve index (MPRI) derived from noninvasive stress perfusion CMR has been established to diagnose microvascular angina with a threshold MPRI <1.4. The prognosis of CMD as determined by MPRI is unknown.

METHODS

Chest pain patients without epicardial CAD or myocardial disease from January 2009 to December 2017 were retrospectively included from 3 imaging centers in Hong Kong (HK). Stress perfusion CMR examinations were performed using either adenosine or adenosine triphosphate. Adequate stress was assessed by achieving splenic switch-off sign. Measurement of MPRI was performed in all stress perfusion CMR scans. Patients were followed for major adverse cardiovascular events defined as all-cause death, acute coronary syndrome (ACS), epicardial CAD development, heart failure hospitalization and non-fatal stroke.

RESULTS

A total of 218 patients were studied (mean age 59 ± 12 years; 49.5% male) and the average MPRI of that cohort was 1.56 ± 0.33. Females and a history of hyperlipidemia were predictors of lower MPRI. Major adverse cardiovascular events (MACE) occurred in 15.6% of patients during a median follow-up of 5.5 years (interquartile range: 4.6 to 6.8 years). The optimal cutoff value of MPRI in predicting MACE was found with a threshold MPRI ≤1.47. Patients with MPRI ≤1.47 had three-fold increased risk of MACE compared with those with MPRI >1.47 (hazard ratio [HR]: 3.14; 95% confidence interval [CI]: 1.58 to 6.25; p = 0.001). Multivariate Cox regression after adjusting for age and hypertension demonstrated that MPRI was an independent predictor of MACE (HR: 0.10; 95% CI: 0.03 to 0.34; p < 0.001).

CONCLUSIONS

Stress perfusion CMR-derived MPRI is an independent imaging marker that predicts MACE in patients with ischemic symptom and no overt CAD over the medium term.

Prognostic Value of Myocardial Extracellular Volume Fraction and T2-mapping in Heart Transplant Patients

OBJECTIVES

The purpose of this study was to examine prognostic value of T1- and T2-mapping techniques in heart transplant patients.

BACKGROUND

Myocardial characterization using T2 mapping (evaluation of edema/inflammation) and pre- and post-gadolinium contrast T1 mapping (calculation of extracellular volume fraction [ECV] for assessment of interstitial expansion/fibrosis) are emerging modalities that have been investigated in various cardiomyopathies.

METHODS

A total of 99 heart transplant patients underwent the magnetic resonance imaging (MRI) scans including T1- (n = 90) and T2-mapping (n = 79) techniques. Relevant clinical characteristics, MRI parameters including late gadolinium enhancement (LGE), and invasive hemodynamics were collected. Median clinical follow-up duration after the baseline scan was 2.4 to 3.5 years. Clinical outcomes include cardiac events (cardiac death, myocardial infarction, coronary revascularization, and heart failure hospitalization), noncardiac death and noncardiac hospitalization.

RESULTS

Overall, the global native T1, postcontrast T1, ECV, and T2 were 1,030 ± 56 ms, 458 ± 84 ms, 27 ± 4% and 50 ± 4 ms, respectively. Top-tercile-range ECV (ECV >29%) independently predicted adverse clinical outcomes compared with bottom-tercile-range ECV (ECV <25%) (hazard ratio [HR]: 2.87; 95% confidence interval [CI]: 1.07 to 7.68; p = 0.04) in a multivariable model with left ventricular end-systolic volume and LGE. Higher T2 (T2 ≥50.2 ms) independently predicted adverse clinical outcomes (HR: 3.01; 95% CI: 1.39 to 6.54; p = 0.005) after adjustment for left ventricular ejection fraction, left ventricular end-systolic volume, and LGE. Additionally, higher T2 (T2 ≥50.2 ms) also independently predicted cardiac events (HR: 4.92; CI: 1.60 to 15.14; p = 0.005) in a multivariable model with left ventricular ejection fraction.

CONCLUSIONS

MRI-derived myocardial ECV and T2 mapping in heart transplant patients were independently associated with cardiac and noncardiac outcomes. Our findings highlight the need for larger prospective studies.

Cardiovascular magnetic resonance-derived myocardial strain in asymptomatic heart transplanted patients and its correlation with late gadolinium enhancement

OBJECTIVES

To investigate whether cardiovascular magnetic resonance (CMR)-derived myocardial strains were abnormal in asymptomatic heart transplant (HT) patients with normal left ventricular ejection fraction (LVEF) and to detect the relationship between CMR-derived myocardial strain parameters and late gadolinium enhancement (LGE) in asymptomatic HT patients.

METHODS

A total of 72 HT patients and 35 healthy volunteers underwent 1.5-T MR scanning. The examination protocol included basic cine imaging and LGE. The deformation registration algorithm (DRA) and feature tracking (FT) software were used for the strain analyses. Myocardial strain measurements included left ventricular global longitudinal strain (LVGLS), LV global circumferential strain (LVGCS), LV global radial strain (LVGRS) and right ventricular longitudinal strain (RVLS).

RESULTS

Compared with healthy volunteers, HT patients had significantly decreased DRA- and FT- derived myocardial strain measurements (all p < 0.05). There was a significant correlation and high reproducibility between the DRA- and FT-derived strain parameters. Both CMR-derived LVGLS and LVGRS were significantly related to the presence of LGE, and multivariate logistic regression analyses showed that the LVGLS measurement obtained from both techniques was independently associated with the presence of LGE. The odds ratios (ORs) for DRA- and FT-LVGLS were 1.340 and 1.342, respectively.

CONCLUSIONS

Asymptomatic HT patients with preserved LVEF exhibited reduced myocardial strain parameters. The CMR-derived LVGLS was independently related to the presence of LGE in HT patients.

KEY POINTS

• Reduced myocardial strain parameters were found in asymptomatic heart transplanted (HT) patients with normal left ventricular ejection fraction (LVEF). • The deformation registration algorithm (DRA) and feature tracking (FT)-derived strains in asymptomatic HT patients had high reproducibility. • DRA- and FT-derived LVGLS had an independent relationship with late gadolinium enhancement (LGE) in asymptomatic HT patients.

Cardiac allograft vasculopathy: Insights on pathogenesis and therapy

Cardiac allograft vasculopathy (CAV) is a unique accelerated form of coronary vascular disease affecting heart transplant recipients. This complication is a significant contributor to medium- to long-term post-transplant morbidity and mortality. There is a high prevalence of CAV with approximately one in three patients developing CAV by 5 years post-transplant. Morphologically, CAV is characterized by concentric coronary intimal hyperplasia in both the epicardial arteries and intramural microvasculature. Although several immune and non-immune factors have been identified, their precise pathogenic mechanisms, interactions, and relative importance in the development of CAV are not well defined. The advent of improved imaging surveillance modalities has resulted in earlier detection during the disease process. However, overall management of CAV remains challenging due to paucity of treatment. This review aims to discuss key concepts on the pathogenesis of CAV and current management strategies, focusing on the use of mammalian target of rapamycin inhibitors.

Donor and Recipient Characteristics in Heart Transplantation Are Associated with Altered Myocardial Tissue Structure and Cardiac Function

PURPOSE

To use structure-function cardiac MRI in the evaluation of relationships between donor and heart transplantation (HTx) recipient characteristics and changes in cardiac tissue structure and function. HTx candidates and donor hearts are evaluated for donor-recipient matches to improve survival, but the impact of donor and recipient characteristics on changes in myocardial tissue and function in the transplanted heart is not fully understood.

MATERIALS AND METHODS

Cardiac MRI at 1.5 T was performed from August 2014 to June 2017 in 58 HTx recipients (mean age, 51.1 years ± 12.6 [standard deviation], 26 female patients) and included T2 mapping (to evaluate edematous and/or inflammatory changes), precontrast and postcontrast T1 mapping (allowing the calculation of extracellular volume fraction [ECV] to estimate interstitial expansion), and tissue phase mapping (allowing the calculation of myocardial velocities and twist). Donor and recipient demographics (age, sex, height, weight, and body mass index [BMI]) and comorbidities (hypertension, diabetes, and smoking history) were evaluated for relationships with cardiac MRI measures.

RESULTS

Sex-influenced cardiac MRI measures of myocardial tissue and function are as follows: Female HTx recipients demonstrated increased precontrast T1 (P = .002) and reduced systolic peak long-axis velocities (P = .015). Increased age of the donor heart was associated with elevated T2 (r = 0.32; P < .05) and ECV (r = 0.47; P < .01), indicating increased edema and interstitial expansion, as well as impaired diastolic peak long-axis velocities (r = 0.41; P < .01). Recipient-donor differences in age, weight, and BMI were significantly associated with elevated ECV (r = 0.36-0.48; P < .05). Hypertension in donors resulted in increased ECV (31.0% ± 4.2 vs 26.0% ± 3.3; P = .001).

CONCLUSION

Donor and HTx recipient characteristics were significantly associated with cardiac MRI-derived measures of myocardial tissue structure and function.© RSNA, 2019.

Multi-modal imaging of the pediatric heart transplant recipient

The assessment of pediatric patients after orthotropic heart transplantation (OHT) relies heavily on non-invasive imaging. Because of the potential risks associated with cardiac catheterization, expanding the role of non-invasive imaging is appealing. Echocardiography is fast, widely available, and can provide an accurate assessment of chamber sizes and function. Advanced echocardiographic methods, such as myocardial deformation, have potential to assess for acute rejection or cardiac allograft vasculopathy (CAV). While not currently part of routine care, cardiac magnetic resonance imaging (CMR) and computed tomography may potentially aid in the detection of graft complications following OHT. In particular, CMR tissue characterization holds promise for diagnosing rejection, while quantitative perfusion and myocardial late gadolinium enhancement may have a role in the detection of CAV. This review will evaluate standard and novel methods for non-invasive assessment of pediatric patients after OHT.

Cardiac Allograft Vasculopathy: The Enduring Enemy of Cardiac Transplantation

Cardiac allograft vasculopathy remains a major limiting factor in the long-term survival of the heart transplant recipient. Our understanding of its pathogenesis is continuously evolving as advances in imaging modalities have allowed a direct window into the natural history of the disease. Innovation in diagnostic modalities has spurred the proliferation of prognostic tools and biomarkers. And in parallel, pharmacological advances have emerged that have helped ameliorate the disease's progressive course.

Right atrial function in pediatric heart transplant patients by echocardiographic strain measurements

BACKGROUND

CAV is a major cause of mortality in PHTx patients. Research on echocardiographic indices to detect CAV focuses primarily on ventricular function and less is known about RAF. Thus, we primarily sought to evaluate RAF in PHTx patients with CAV. For secondary analysis, we compared RAF between PHTx patients and control patients and evaluated RAF with respect to rejection and surgical type.

METHODS

We retrospectively evaluated echocardiography derived RA strain indices in recipients <18 years old and >1 year from time of transplant. The RA strain phases included, reservoir (εs), conduit (εe), pump (εa), and respective strain rate indices (SRs, SRe, SRa).

RESULTS

There were 36 PHTx patients and 14 age-, sex-matched control patients. There was a significant reduction in εs, εe, SRs, and SRe (P < 0.001) in the PHTx patients when compared to controls. There was no difference between the CAV (+) and CAV (-) patients with respect to RAF indices. Furthermore, εs, εe, and SRe (P < 0.05) were lower in patients with acute rejection (n = 7) compared to those without (n = 26). Patients with a bi-atrial anastomosis (n = 14) had decreased εs, εa, SRs, SRa (P < 0.05), compared to bi-caval anastomosis (n = 24).

CONCLUSION

PHTx patients have decreased RAF compared to healthy children. RAF does not differentiate PHTx patients based on the presence of CAV. RAF is also decreased in PHTx patients with rejection and in those transplanted with a bi-atrial anastomosis.

Sensitization to endothelial cell antigens: Unraveling the cause or effect paradox

Anti-endothelial cell antibodies (AECAs) have been correlated with increased acute and chronic rejection across all organ types and early graft dysfunction in kidney and heart transplantation. Nevertheless, the lack of appropriate tools and clear criteria for defining injurious versus non-injurious AECAs prohibits their routine inclusion in clinical risk assessments and diagnostic algorithms for antibody mediated injury. Clinical characterization of AECAs is complicated due to the wide range of polymorphic and non-polymorphic antigens expressed across different vascular tissues and the diverse array of specificities observed between individuals. This complexity is also reflected in the broad spectrum of reported injury phenotypes. AECAs detected at time of allograft dysfunction may represent biomarkers of past vascular injury or active contributors to a current rejection process. New tools within the fields of proteomics, genomics, bioinformatics, and imaging are currently being validated and hold great promise for unraveling the AECA paradox.

Strain-encoded magnetic resonance: a method for the assessment of myocardial deformation

This study aims to assess the usefulness of strain‐encoded magnetic resonance (SENC) for the quantification of myocardial deformation (‘strain’) in healthy volunteers and for the diagnostic workup of patients with different cardiovascular pathologies. SENC was initially described in the year 2001. Since then, the SENC sequence has undergone several technical developments, aiming at the detection of strain during single‐heartbeat acquisitions (fast‐SENC). Experimental and clinical studies that used SENC and fast‐SENC or compared SENC with conventional cine or tagged magnetic resonance in phantoms, animals, healthy volunteers, or patients were systematically searched for in PubMed. Using ‘strain‐encoded magnetic resonance and SENC’ as keywords, three phantom and three animal studies were identified, along with 27 further clinical studies, involving 185 healthy subjects and 904 patients. SENC (i) enabled reproducible assessment of myocardial deformation in vitro, in animals and in healthy volunteers, (ii) showed high reproducibility and substantially lower time spent compared with conventional tagging, (iii) exhibited incremental value to standard cine imaging for the detection of inducible ischaemia and for the risk stratification of patients with ischaemic heart disease, and (iv) enabled the diagnostic classification of patients with transplant vasculopathy, cardiomyopathies, pulmonary hypertension, and diabetic heart disease. SENC has the potential to detect a wide range of myocardial diseases early, accurately, and without the need of contrast agent injection, possibly enabling the initiation of specific cardiac therapies during earlier disease stages. Its one‐heartbeat acquisition mode during free breathing results in shorter cardiovascular magnetic resonance protocols, making its implementation in the clinical realm promising.

Reduced Biventricular Volumes and Myocardial Dysfunction Long-term After Pediatric Heart Transplantation Assessed by CMR

BACKGROUND

Long-term cardiac remodeling after heart transplantation (HT) in children has been insufficiently characterized. The aim of our study was to evaluate ventricular size in HT patients using cardiovascular magnetic resonance (CMR) imaging, to find underlying factors related to potentially abnormal cardiac dimensions and to study its impact on functional class and ventricular function.

METHODS

Seventy-five pediatric HT recipients (age 14.0 ± 4.2 y) were assessed by using CMR 11.2 ± 5.4 years after HT. Right ventricular (RV) and left ventricular (LV) volumes and mass were derived from short-axis cine images and myocardial strain/strain rate was assessed using myocardial feature tracking technique. Results were compared with a healthy reference population (n = 79, age 13.7 ± 3.7 y).

RESULTS

LV end-diastolic ventricular volumes were smaller (64 ± 12 versus 84 ± 12 mL/m; P < 0.001) while mass-to-volume ratio (0.86 ± 0.18 versus 0.65 ± 0.11; P < 0.001) and heart rate (92 ± 14 versus 78 ± 13 beats/min; P < 0.001) were higher in HT patients. LV-ejection fraction (EF) was preserved (66% ± 8% versus 64% ± 6%; P = 0.18) but RV-EF (58 ± 7 versus 62% ± 4%, P = 0.004), LV systolic longitudinal strain (-12 ± 6 versus -15% ± 5%; P = 0.05), diastolic strain rate (1.2 ± 0.6 versus 1.5 ± 0.6 1/s; P = 0.03), and intra and interventricular synchrony were lower in the HT group. Smaller LV dimensions were primarily related to longer follow-up time since HT (β = -0.38; P < 0.001) and were associated with worse functional class and impaired ventricular systolic and diastolic performance.

CONCLUSIONS

Cardiac remodeling after pediatric HT is characterized by reduced biventricular size and increased mass-to-volume ratio. These adverse changes evolve gradually and are associated with impaired functional class and ventricular dysfunction suggesting chronic maladaptive processes affecting allograft health.

Myocardial perfusion reserve and global longitudinal strain as potential markers of coronary allograft vasculopathy in late-stage orthotopic heart transplantation

Coronary allograft vasculopathy (CAV) is a major cause of mortality in late-stage orthotopic heart transplantation (OHT) patients. Recent evidence has shown that myocardial perfusion reserve (MPR) derived from vasodilator cardiovascular magnetic resonance imaging (vCMR) and global longitudinal strain (GLS) from transthoracic echocardiography (TTE) are useful to detect CAV. However, previous studies have not comprehensively addressed whether these parameters are confounded by allograft rejection, myocardial scar/fibrosis, or allograft dysfunction. Our aim was to determine whether changes in late post-OHT MPR and GLS are due to CAV or other confounding factors. Twenty OHT patients (time from transplant to vCMR was 8.1 ± 4.1 years) and 30 controls (10 healthy volunteers and 20 with prior myocardial infarction to provide perspective with regards to the severity of any abnormalities seen in post-OHT patients) underwent vasodilator vCMR from which MPR index (MPRi), left ventricular ejection fraction (LVEF), and burden of late gadolinium enhancement (LGE) were quantified. TTE was used to measure GLS. The presence of CAV was determined from invasive coronary angiograms using thrombolysis in myocardial infarction (TIMI) frame counts and grading severity per guidelines. Previous endomyocardial biopsies were reviewed to assess association with episodes of rejection. We examined the correlations between MPRi and GLS with markers of CAV, allograft function, scar/fibrosis, and rejection. MPRi was abnormal in post-OHT patients compared to both healthy volunteers and MI controls. While there was no relationship between MPRi or GLS and LVEF, episodes of rejection, or LGE burden, both MPRi and GLS were associated with TIMI frame counts and presence and severity of CAV. Additionally, MPRi correlated with GLS (R = 0.68, P = 0.0002). In conclusion, MPRi and GLS are abnormal in late-stage OHT and associated with CAV, but not related to allograft rejection, myocardial scar/fibrosis, or allograft dysfunction. Non-invasive monitoring of MPRi and GLS may be a useful strategy to detect CAV.