Diagnostic and prognostic value of myocardial blood flow quantification as non-invasive indicator of cardiac allograft vasculopathy

Added prognostic value of visually estimated coronary artery calcium among heart transplant recipients

BACKGROUND

Cardiac hybrid positron emission tomography/computed tomography (PET/CT) has become a valid screening modality for cardiac allograft vasculopathy (CAV) following heart transplantation (HT). Visually estimated coronary artery calcium (VECAC) can be quantified from CT images obtained as part of PET/CT and has been shown to be associated with adverse cardiovascular outcomes in coronary artery disease. We investigated the prognostic value of VECAC following HT.

METHODS

A retrospective analysis of 430 consecutive adult HT patients who underwent 13N-ammonia cardiac PET/CT from 2016 to 2019 with follow-up through October 15, 2022, was performed. VECAC categories included: VECAC 0, VECAC 1-9, VECAC 10-99, and VECAC 100+. The association between VECAC categories and outcomes was assessed using univariable and multivariable proportional hazards regression. The primary outcome was death/retransplantation.

RESULTS

The cohort was 73% male, 33% had diabetes, 67% had estimated glomerular filtration rate <60 ml/min, median age was 61 years, and median time since HT was 7.5 years. VECAC alone was insufficiently sensitive to screen for CAV. During a median follow-up of 4.2 years ninety patients experienced death or retransplantation. Compared with those with VECAC 0, patients VECAC 10-99 (HR 2.25, 95% CI 1.23-4.14, p = 0.009) and VECAC 100+ (HR 3.42, 95% CI 1.96-5.99, p < 0.001) experienced an increased risk of death/retransplantation. The association was similar for cardiovascular death and cardiovascular hospitalization. After adjusting for other predictors of death/retransplantation, VECAC 10-99 (VECAC 10-99: aHR 1.95, 95% CI 1.03-3.71 p = 0.04) and VECAC 100+ (VECAC 100+: aHR 2.33, 95% CI 1.17-4.63, p = 0.02) remained independently associated with death/retransplantation.

CONCLUSIONS

VECAC is an independent prognostic marker of death/retransplantation following HT and merits inclusion as a part of post-HT surveillance PET/CT.

Longitudinal Change and Predictors of Myocardial Flow Reserve by Positron Emission Tomography for the Evaluation of Cardiac Allograft Vasculopathy Following Heart Transplantation

BACKGROUND

Positron emission tomography (PET) myocardial flow reserve (MFR) is a noninvasive method of detecting cardiac allograft vasculopathy in recipients of heart transplants (HTs). There are limited data on longitudinal change and predictors of MFR following HT.

METHODS

We conducted a retrospective analysis of HT recipients undergoing PET myocardial perfusion imaging at an academic center. Multivariable linear and Cox regression models were constructed to identify longitudinal trends, predictors and the prognostic value of MFR after HT.

RESULTS

Of HT recipients, 183 underwent 658 PET studies. The average MFR was 2.34 ± 0.70. MFR initially increased during the first 3 years following HT (+ 0.12 per year; P = 0.01) before beginning to decline at an annual rate of -0.06 per year (P < 0.001). MFR declines preceding acute rejection and improves after treatment. Treatment with mammalian target of rapamycin (mTOR) inhibitors (37.2%) slowed the rate of annual MFR decline (P = 0.03). Higher-intensity statin therapy was associated with improved MFR. Longer time post-transplant (P < 0.001), hypertension (P < 0.001), chronic kidney disease (P < 0.001), diabetes mellitus (P = 0.038), antibody-mediated rejection (P = 0.040), and cytomegalovirus infection (P = 0.034) were associated with reduced MFR. Reduced MFR (HR: 7.6, 95% CI: 4.4-13.4; P < 0.001) and PET-defined ischemia (HR: 2.3, 95% CI: 1.4-3.9; P < 0.001) were associated with a higher risk of the composite outcome of mortality, retransplantation, heart failure hospitalization, acute coronary syndrome, or revascularization.

CONCLUSION

MFR declines after the third post-transplant year and is prognostic for cardiovascular events. Cardiometabolic risk-factor modification and treatment with higher-intensity statin therapy and mechanistic target of rapamycin inhibitors are associated with a higher MFR.

Advances in Clinical Care with Contemporary Cardiac SPECT

State of the art of cardiac SPECT imaging continues to advance. Contemporary clinical applications of cardiac SPECT are reviewed and illustrated. Beyond traditional stress and rest myocardial perfusion imaging, the role of digital SPECT technology, ultra low dose imaging with efficient stress first / stress only if normal imaging, deep learning algorithms relative to coronary angiography and SPECT CT, sourceless emission attenuation correction, myocardial blood flow and blood flow reserve to assess ischemic jeopardy, culprit ischemic territories, and cardiac allograft vasculopathy, advanced methods of SPECT detection of amyloid cardiomyopathy, resting MPI to define pre-operative regional scar prior to operative ablation, parametric radionuclide ventriculography to quantify dyssynchrony and benefit of biventricular pacing, assessment of treatment response of RV and LV function in patients with pulmonary hypertension, dual isotope MIBG imaging to assess cardiac risk, and the value proposition of real world effectiveness of SPECT cardiac imaging are illustrated.

Cardiac PET Myocardial Blood Flow Quantification Assessment of Early Cardiac Allograft Vasculopathy

BACKGROUND

Positron emission tomography (PET) has demonstrated utility for diagnostic and prognostic assessment of cardiac allograft vasculopathy (CAV) but has not been evaluated in the first year after transplant.

OBJECTIVES

The authors sought to evaluate CAV at 1 year by PET myocardial blood flow (MBF) quantification.

METHODS

Adults at 2 institutions enrolled between January 2018 and March 2021 underwent prospective 3-month (baseline) and 12-month (follow-up) post-transplant PET, endomyocardial biopsy, and intravascular ultrasound examination. Epicardial CAV was assessed by intravascular ultrasound percent intimal volume (PIV) and microvascular CAV by endomyocardial biopsy.

RESULTS

A total of 136 PET studies from 74 patients were analyzed. At 12 months, median PIV increased 5.6% (95% CI: 3.6%-7.1%) with no change in microvascular CAV incidence (baseline: 31% vs follow-up: 38%; P = 0.406) and persistent microvascular disease in 13% of patients. Median capillary density increased 30 capillaries/mm2 (95% CI: -6 to 79 capillaries/mm2). PET myocardial flow reserve (2.5 ± 0.7 vs 2.9 ± 0.8; P = 0.001) and stress MBF (2.7 ± 0.6 vs 2.9 ± 0.6; P = 0.008) increased, and coronary vascular resistance (CVR) (49 ± 13 vs 47 ± 11; P = 0.214) was unchanged. At 12 months, PET and PIV had modest correlation (stress MBF: r = -0.35; CVR: r = 0.33), with lower stress MBF and higher CVR across increasing PIV tertiles (all P < 0.05). Receiver-operating characteristic curves for CAV defined by upper-tertile PIV showed areas under the curve of 0.74 for stress MBF and 0.73 for CVR.

CONCLUSIONS

The 1-year post-transplant PET MBF is associated with epicardial CAV, supporting potential use for early noninvasive CAV assessment. (Early Post Transplant Cardiac Allograft Vasculopahty [ECAV]; NCT03217786).

Frequency of screening for cardiac allograft vasculopathy: warranty period of initial low risk positron emission tomography

AIMS

The short-term risk of moderate-severe cardiac allograft vasculopathy (CAV) after a low-risk positron emission tomography/computed tomography (PET/CT) is unknown, and therefore, there is no guidance on how frequently to perform screening. The aim of this study was to assess the rate of progression to moderate-severe CAV as part of an annual screening programme.

METHODS AND RESULTS

Patients with no history of CAV 2/3 and a low-risk result on initial screening PET/CT (CAV 0/1) were enrolled in the study. The primary outcome was the progression to CAV 2/3 as part of an annual screening programme (within 6-18 months of initial scan). PET CAV results were graded according to a published and externally validated diagnostic criterion for CAV. Over the study period, 231 patients underwent an initial PET/CT and had a subsequent evaluation for CAV. In this cohort, 4.3% of patients progressed to CAV 2/3 at a median of 374 days (interquartile range 363-433). Initial PET CAV grade was the most significant patient characteristic associated with the progression of CAV, with 17% of patients with PET CAV 1 progressing to CAV 2/3 compared with 1.6% with PET CAV 0 (odds ratio 12.4, 95% confidence interval 3.06-50.3).

CONCLUSION

The rate of progression to moderate-severe CAV at 1 year after the lowest-risk PET/CT is low, but approximately 1/6 patients with PET CAV 1 progress to CAV 2/3. Annual screening with PET/CT for select patients with PET CAV 0 may not be warranted. The optimal screening interval awaits confirmation of our findings in multi-centre registries.

Role of Radiology in Assessment of Postoperative Complications of Heart Transplantation

Heart transplantation is a pivotal treatment of end-stage heart failure, and recent advancements have extended median posttransplant life expectancy. However, despite the progress in surgical techniques and medical treatment, heart transplant patients still face complications such as rejection, infections, and drug toxicity. CT is a reliable tool for detecting most of these complications, whereas MR imaging is particularly adept at identifying pericardial pathologies and signs of rejection. Awareness of these nuances by radiologists, cardiologists, and surgeons is desired to optimize care, reduce morbidities, and enhance survival.

Cytomegalovirus infection is associated with impaired myocardial flow reserve after heart transplantation

BACKGROUND

Cardiac allograft vasculopathy (CAV) limits long-term survival after heart transplantation (HT). This study evaluates the relationship between clinically significant cytomegalovirus infection (CS-CMVi) and CAV using cardiac positron emission tomography (PET).

METHODS

We retrospectively evaluated HT patients from 2005 to 2019 who underwent cardiac PET for CAV evaluation. Multivariable linear and logistic regression models were used to evaluate the association between CS-CMVi and myocardial flow reserve (MFR). Kaplan-Meier and Cox regression analyses were used to assess the relationship between CS-CMV, MFR, and clinical outcomes.

RESULTS

Thirty-two (31.1%) of 103 HT patients developed CS-CMVi at a median 9 months after HT. Patients with CS-CMVi had a significantly lower MFR at year 1 and 3, driven by reduction in stress myocardial blood flow. Patients with CS-CMVi had a faster rate of decline in MFR compared to those without infection (-0.10 vs -0.06 per year, p < 0.001). CS-CMVi was an independent predictor of abnormal MFR (<2.0) (odds ratio: 3.8, 95% confidence intervals (CI): 1.4-10.7, p = 0.001) and a lower MFR (β = -0.39, 95% CI: -0.63 to -0.16, p = 0.001) at year 3. In adjusted survival analyses, both abnormal MFR (log-rank p < 0.001; hazard ratio [HR]: 5.7, 95% CI: 4.2-7.2) and CS-CMVi (log-rank p = 0.028; HR: 3.3, 95% CI: 1.8-4.8) were significant predictors of the primary outcome of all-cause mortality, retransplantation, heart failure hospitalization, and acute coronary syndrome.

CONCLUSIONS

CS-CMVi is an independent predictor of reduced MFR following HT. These findings suggest that CMV infection is an important risk factor in the development and progression of CAV.

Chest Pain Evaluation: Diagnostic Testing

Chest pain/discomfort (CP) is a common symptom and can be a diagnostic dilemma for many clinicians. The misdiagnosis of an acute or progressive chronic cardiac etiology may carry a significant risk of morbidity and mortality. This review summarizes the different options and modalities for establishing the diagnosis and severity of coronary artery disease. An effective test selection algorithm should be individually tailored to each patient to maximize diagnostic accuracy in a timely fashion, determine short- and long-term prognosis, and permit implementation of evidence-based treatments in a cost-effective manner. Through collaboration, a decision algorithm was developed (www.chowmd.ca/cadtesting) that could be adopted widely into clinical practice.

The utilization of molecular microscope in management of heart transplant recipients in the era of noninvasive monitoring

INTRODUCTION

Monitoring for graft rejection is a fundamental tenet of post-transplant follow-up. In heart transplantation (HT) in particular, rejection has been traditionally assessed with endomyocardial biopsy (EMB). EMB has potential complications and noted limitations, including interobserver variability in interpretation. Additional tests, such as basic cardiac biomarkers, cardiac imaging, gene expression profiling (GEP) scores, donor-derived cell-free DNA (dd-cfDNA) and the novel molecular microscope diagnostic system (MMDx) have become critical tools in rejection surveillance beyond standard EMB.

METHODS

This paper describes an illustrative case followed by a review of MMDx within the context of other noninvasive screening modalities for rejection.

CONCLUSIONS

We suggest MMDx be used to assist with early detection of rejection in cases of discordance between EMB and other noninvasive studies.

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.

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.

Clinical Value of Positron Emission Tomography Myocardial Perfusion Imaging and Blood Flow Quantification

Myocardial blood flow (MBF) and flow reserve (MFR) measurements by PET/computed tomography provide incremental diagnostic and prognostic information over traditional quantification of ischemia and scar by myocardial perfusion imaging. A normal stress MBF and MFR (>2.0) have a very high negative predictive value for excluding high-risk obstructive coronary artery disease (CAD). These flow measurements are also used for surveillance of coronary allograft vasculopathy after heart transplantation. A global normal MFR (>2.0) identifies patients at lower clinical risk, whereas a severely reduced MFR (<1.5) identifies patients at high risk for adverse events, even among patients without regional perfusion abnormalities.

Negative Predictive Value and Prognostic Associations of Rb-82 PET/CT with Myocardial Blood Flow in CAV

BACKGROUND

Invasive coronary angiography (ICA) is the traditional screening modality for cardiac allograft vasculopathy (CAV). Positron emission tomography/computed tomography (PET/CT) scan with myocardial blood flow (MBF) quantification has emerged as a potential noninvasive alternative.

OBJECTIVES

The aim of the study was to validate the diagnostic and prognostic value of a previously published algorithm for diagnosing CAV via PET/CT scans with MBF in a larger population. The study also sought to assess the downstream use of ICA when using PET/CT scanning as a screening modality.

METHODS

Patients with heart transplantation without prior revascularization who underwent PET/CT scans with MBF were identified retrospectively. The accuracy of the algorithm was assessed in patients who underwent PET/CT scanning within 1 year of ICA. The prognostic value was assessed via a composite outcome of heart failure hospitalization, myocardial infarction, retransplantation, and all-cause mortality.

RESULTS

A total of 88 patients for the diagnostic portion and 401 patients for the prognostic portion were included. PET CAV 0 had high negative predictive value for moderate to severe CAV (97%) and PET CAV 2/3 had a high positive predictive value for moderate to severe CAV (68%) by ICA. The cohort was followed for a median of 1.2 (IQR: 1.0-1.8) years with 46 patients having an adverse event. The annualized event rates were 6.9%, 9.3%, and 30.8% for PET CAV 0, 1, and 2/3, respectively (P < 0.001).

CONCLUSIONS

An algorithm using PET/CT scanning with MBF demonstrates high a negative predictive value for CAV. PET CAV 2/3 is associated with a higher risk of adverse events and need for revascularization. PET/CT scanning with MBF is a reasonable alternative to ICA for screening for CAV.

PET Myocardial Blood Flow for Post-transplant Surveillance and Cardiac Allograft Vasculopathy in Heart Transplant Recipients

PURPOSE OF REVIEW

Cardiac allograft vasculopathy (CAV) is a late-occurring complication of heart transplantation significantly limiting overall graft survival. In the last few years, evidence has been growing about the use of positron emission tomography (PET) myocardial perfusion imaging with integrated myocardial blood flow (MBF) quantification in heart transplant recipients.

RECENT FINDINGS

Multiple studies have demonstrated that PET MBF assessment can be utilized to establish the diagnosis of CAV noninvasively and can be employed for prognostication. PET MBF quantification has also helped to define the link between transplant rejection and CAV. In addition, limited data suggests that PET MBF quantification can be used in heart transplant patients for serial monitoring of CAV. PET myocardial perfusion imaging integrating MBF quantification shows great promise for the evaluation of CAV with good diagnostic and prognostic performance.

Prognostic value of myocardial flow reserve obtained by 82-rubidium positron emission tomography in long-term follow-up after heart transplantation

BACKGROUND

Cardiac allograft vasculopathy (CAV) is a leading cause of death following heart transplantation (HTx) and non-invasive prognostic methods in long-term CAV surveillance are needed. We evaluated the prognostic value of myocardial flow reserve (MFR) obtained by 82-rubidium (82Rb) positron emission tomography (PET).

METHODS

Recipients undergoing dynamic rest-stress 82Rb PET between April 2013 and June 2017 were retrospectively evaluated in a single-center study. Evaluation by PET included quantitative myocardial blood flow and semiquantitative myocardial perfusion imaging. Patients were grouped by MFR (MFR ≤ 2.0 vs MFR > 2.0) and the primary outcome was all-cause mortality.

RESULTS

A total of 50 patients (68% men, median age 57 [IQR: 43 to 68]) were included. Median time from HTx to PET was 10.0 (6.7 to 16.0) years. In 58% of patients CAV was documented prior to PET. During a median follow-up of 3.6 (2.3 to 4.3) years 12 events occurred. Survival probability by Kaplan-Meier method was significantly higher in the high-MFR group (log-rank P = .02). Revascularization (n = 1), new CAV diagnosis (n = 1), and graft failure (n = 4) were more frequent in low-MFR patients. No retransplantation occurred.

CONCLUSIONS

Myocardial flow reserve appears to offer prognostic value in selected long-term HTx recipients and holds promise as a non-invasive method for CAV surveillance possibly guiding management strategy.

Cardiopulmonary transit time: A novel PET imaging biomarker of in vivo physiology for risk stratification of heart transplant recipients

BACKGROUND

Myocardial blood flow (MBF) can be quantified using dynamic PET studies. These studies also inherently contain tomographic images of early bolus displacement, which can provide cardiopulmonary transit times (CPTT) as measure of cardiopulmonary physiology. The aim of this study was to assess the incremental prognostic value of CPTT in heart transplant (OHT) recipients.

METHODS

94 patients (age 56 ± 16 years, 78% male) undergoing dynamic 13N-ammonia stress/rest studies were included, of which 68 underwent right-heart catherization. A recently validated cardiac allograft vasculopathy (CAV) score based on PET measures of regional perfusion, peak MBF and left-ventricular (LV) ejection fraction (LVEF) was used to identify patients with no, mild or moderate-severe CAV. Time-activity curves of the LV and right ventricular (RV) cavities were obtained and used to calculate the difference between the LV and RV bolus midpoint times, which represents the CPTT and is expressed in heartbeats. Patients were followed for a median of 2.5 years for the occurrence of major adverse cardiac events (MACE), including cardiovascular death, hospitalization for heart failure or acute coronary syndrome, or re-transplantation.

RESULTS

CPTT was significantly correlated with cardiac filling pressures (r = .434, P = .0002 and r = .439, P = .0002 for right atrial and pulmonary wedge pressure), cardiac output (r = - .315, P = .01) and LVEF (r = - .513, P < .0001). CPTT was prolonged in patients with MACE (19.4 ± 6.0 vs 14.5 ± 3.0 heartbeats, P < .001, N = 15) with CPTT ≥ 17.75 beats showing optimal discriminatory value in ROC analysis. CPTT ≥ 17.75 heartbeats was associated with a 10.1-fold increased risk (P < .001) of MACE and a 7.3-fold increased risk (P < .001) after adjusting for PET-CAV, age, sex and time since transplant.

CONCLUSION

Measurements of cardiopulmonary transit time provide incremental risk stratification in OHT recipients and enhance the value of multiparametric dynamic PET imaging, particularly in identifying high-risk patients.

Cardiac allograft vasculopathy: A review

BACKGROUND

Heart transplantation has become the standard of care for pediatric patients with end-stage heart disease, and outcomes have consistently improved over the last few decades. CAV, however, remains a leading cause of morbidity and mortality in heart transplantation and is the leading cause of death beyond 3 years post-transplantation. We sought out to provide an in-depth overview of CAV in the pediatric heart transplant population.

METHODS

Database searches were conducted in both Medline and Embase on the topic of cardiac vasculopathy in pediatric heart transplant recipients. The search used five broad concept terms: heart transplant; pediatric; CAV; diagnosis, prognosis, and risk factors; and guidelines and reviews. References were captured if there was at least one term in each of the concepts. The search was limited to articles in the English language.

RESULTS

A total of 148 articles were identified via the literature search with further articles identified via review of references. Pediatric data regarding the etiology and development of CAV remain limited although knowledge about the immune and non-immune factors playing a role are increasing. CAV continues to be difficult to detect with many invasive and non-invasive methods available, yet their effectiveness in the detection of CAV remains suboptimal. There remains no proven medical intervention to treat or reverse established CAV disease, and CAV is associated with high rates of graft loss once detected. However, several medications are used in hopes of preventing, slowing progression, or modifying the outcomes.

CONCLUSION

This review provides a comprehensive overview of CAV, discusses its clinical presentation, risk factors, diagnostic tools used to identify CAV in the pediatric population, and highlights the current therapeutic options and the need for ongoing research.

Coronary flow reserve and cardiovascular outcomes: a systematic review and meta-analysis

AIMS

This meta-analysis aims to quantify the association of reduced coronary flow with all-cause mortality and major adverse cardiovascular events (MACE) across a broad range of patient groups and pathologies.

METHODS AND RESULTS

We systematically identified all studies between 1 January 2000 and 1 August 2020, where coronary flow was measured and clinical outcomes were reported. The endpoints were all-cause mortality and MACE. Estimates of effect were calculated from published hazard ratios (HRs) using a random-effects model. Seventy-nine studies with a total of 59 740 subjects were included. Abnormal coronary flow reserve (CFR) was associated with a higher incidence of all-cause mortality [HR: 3.78, 95% confidence interval (CI): 2.39-5.97] and a higher incidence of MACE (HR 3.42, 95% CI: 2.92-3.99). Each 0.1 unit reduction in CFR was associated with a proportional increase in mortality (per 0.1 CFR unit HR: 1.16, 95% CI: 1.04-1.29) and MACE (per 0.1 CFR unit HR: 1.08, 95% CI: 1.04-1.11). In patients with isolated coronary microvascular dysfunction, an abnormal CFR was associated with a higher incidence of mortality (HR: 5.44, 95% CI: 3.78-7.83) and MACE (HR: 3.56, 95% CI: 2.14-5.90). Abnormal CFR was also associated with a higher incidence of MACE in patients with acute coronary syndromes (HR: 3.76, 95% CI: 2.35-6.00), heart failure (HR: 6.38, 95% CI: 1.95-20.90), heart transplant (HR: 3.32, 95% CI: 2.34-4.71), and diabetes mellitus (HR: 7.47, 95% CI: 3.37-16.55).

CONCLUSION

Reduced coronary flow is strongly associated with increased risk of all-cause mortality and MACE across a wide range of pathological processes. This finding supports recent recommendations that coronary flow should be measured more routinely in clinical practice, to target aggressive vascular risk modification for individuals at higher risk.

Prognostic utility of longitudinal quantification of PET myocardial blood flow early post heart transplantation

BACKGROUND

Myocardial blood flow (MBF) quantification by Rubidium-82 positron emission tomography (PET) has shown promise for cardiac allograft vasculopathy (CAV) surveillance and risk stratification post heart transplantation. The objective was to determine the prognostic value of serial PET performed early post transplantation.

METHODS AND RESULT

Heart transplant (HT) recipients at the University of Ottawa Heart Institute with 2 PET examinations (PET1 = baseline, PET2 = follow-up) within 6 years of transplant were included in the study. Evaluation of PET flow quantification included stress MBF, coronary vascular resistance (CVR), and myocardial flow reserve (MFR). The primary composite outcome was all-cause death, re-transplant, myocardial infarction, revascularization, allograft dysfunction, cardiac allograft vasculopathy (CAV), or heart failure hospitalization. A total of 121 patients were evaluated (79% male, mean age 56 ± 11 years) with consecutive scans performed at mean 1.4 ± 0.7 and 2.6 ± 1.0 years post HT for PET1 and PET2, respectively. Over a mean follow-up of 3.0 (IQR 1.8, 4.6) years, 26 (22%) patients developed the primary outcome: 1 death, 11 new or progressive angiographic CAV, 2 percutaneous coronary interventions, 12 allograft dysfunction. Unadjusted Cox analysis showed a significant reduction in event-free survival in patients with PET1 stress MBF < 2.1 (HR: 2.43, 95% CI 1.11-5.29 P = 0.047) and persistent abnormal PET1 to PET2 CVR > 76 (HR: 2.19, 95% CI 0.87-5.51 P = 0.045). There was no association between MFR and outcomes.

CONCLUSION

Low-stress MBF and persistent increased CVR on serial PET imaging early post HT are associated with adverse cardiovascular outcomes. Early post-transplant and longitudinal assessment by PET may identify at-risk patients for increased surveillance post HT.

Clinical Utility of SPECT in the Heart Transplant Population: Analysis From a Single Large-volume Center

BACKGROUND

Survival after heart transplant has greatly improved, with median survival now over 12 years. Cardiac allograft vasculopathy (CAV) has become a major source of long-term morbidity and mortality. Single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) is used for CAV surveillance, but there is limited data on its prognostic utility.

METHODS

We retrospectively identified patients undergoing SPECT MPI for CAV surveillance at a single, large-volume center. Images were assessed with semiquantitative visual scoring (summed stress score [SSS] and summed rest score) and quantitatively with total perfusion defect (TPD).

RESULTS

We studied 503 patients (mean age 62.5, 69.3% male) at a median of 9.0 years post-transplant. During mean follow-up of 5.1 ± 2.5 years, 114 (22.6%) patients died. The diagnostic accuracy for significant CAV (ISHLT grade 2 or 3) was highest for SSS with an area under the curve of 0.650 and stress TPD (area under the curve, 0.648), with no significant difference between SSS and stress TPD (P = 0.061). Stress TPD (adjusted hazard ratio, 1.07; P = 0.018) was independently associated with all-cause mortality, while SSS was not (P = 0.064). The prognostic accuracy of quantitative assessment of perfusion tended to be higher compared with semiquantitative assessment, with the highest accuracy for stress TPD (area under the receiver operating curve 0.584).

CONCLUSIONS

While SPECT MPI identified a cohort of higher risk patients, with quantitative analysis of perfusion demonstrating higher prognostic accuracy. However, the overall prognostic accuracy was modest and alternative noninvasive modalities may be more suitable for CAV surveillance.

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.

13N-ammonia positron emission tomography-derived left-ventricular strain in patients after heart transplantation validated using cardiovascular magnetic resonance feature tracking as reference

OBJECTIVE

Heart transplant rejection leads to cardiac allograft vasculopathy (CAV). 13N-ammonia positron emission tomography (PET) can be useful in detecting CAV, as it can evaluate both epicardial vessels and microvasculature. In this study, we evaluated the regional wall motion in heart transplant patients using our PET-specific feature-tracking (FT) algorithm for myocardial strain calculation and validated it using a cardiovascular magnetic resonance (CMR) FT strain as a reference.

METHODS

A total of 15 heart transplant patients who underwent both 13N-ammonia PET and CMR within 3 months were retrospectively enrolled. The same slice position of short-axis cine images of the middle slice of left ventricle (LV) and the same slice position of horizontal long-axis cine images were selected for the two modalities to measure the circumferential strain (CS) and longitudinal strain (LS), respectively. Based on the FT technique, time-strain curves were calculated by semi-automatic tracking of the endocardial contour on cine images throughout a cardiac cycle. The peak value in the time-strain curve was defined as the representative value. Correlations of CS and LS between PET and CMR were analyzed using Pearson correlation coefficients. The inter-modality error of strain measurements was evaluated using intraclass correlation coefficients (ICCs) with two-way random single measures.

RESULTS

Excellent correlations of CS and LS between PET and CMR were observed (CS: r = 0.80; p < 0.01; LS: r = 0.87; p < 0.01). Excellent ICCs were observed (0.89 and 0.85) in CS and LS derived from PET.

CONCLUSIONS

We propose the first PET strain showing an excellent agreement with the CMR strain and high reproducibility in measurement.

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.

Validation of multiparametric rubidium-82 PET myocardial blood flow quantification for cardiac allograft vasculopathy surveillance

BACKGROUND

We previously demonstrated high diagnostic accuracy of Rubidium-82 positron emission tomography (PET) myocardial blood flow (MBF) quantification for CAV. The purpose of this study was to validate multiparametric PET detection of CAV by combined rate-pressure-product-corrected myocardial flow reserve (cMFR), stress MBF, and coronary vascular resistance (CVR) assessment.

METHODS AND RESULTS

Diagnostic CAV cut-offs of cMFR < 2.9, stress MBF < 2.3, CVR > 55 determined in a previous study (derivation) were assessed in heart transplant recipients referred for coronary angiography and intravascular ultrasound (IVUS) (validation). CAV was defined as International Society of Heart and Lung Transplantation CAV1-3 on angiography; and maximal intimal thickness ≥ 0.5 mm on IVUS. Eighty patients (derivation n = 40, validation n = 40) were included: 80% male, mean age 54±14 years, 4.5±5.6 years post transplant. The prevalence of CAV was 44% on angiography and 78% on IVUS. Combined PET cMFR < 2.9, stress MBF < 2.3, CVR > 55 CAV assessment yielded high 88% (specificity 75%) and 83% (specificity 40%) sensitivity for ≥ 1 abnormal parameter and high 88% (sensitivity 59%) and 90% (sensitivity 43%) specificity for 3 abnormal parameters, in the derivation and validation cohorts, respectively.

CONCLUSION

We validate the diagnostic accuracy of multiparametric PET flow quantification by cMFR, stress MBF, and CVR for 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.

Diagnosis and management of cardiac allograft vasculopathy

One of the main causes of death beyond the first year after heart transplantation is cardiac allograft vasculopathy (CAV). This review summarises the current understanding of its complex pathophysiology, detection and treatment, including the available data on non-invasive imaging modalities used for screening and diagnosis. A better understanding of this entity is crucial to improving the long-term outcomes of the growing population of patients with a heart transplant.

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.

Donor-derived cell-free DNA is associated with cardiac allograft vasculopathy

BACKGROUND

The role of donor-derived cell-free DNA (dd-cfDNA) in screening for cardiac allograft vasculopathy (CAV) is unknown. We hypothesized that dd-cfDNA correlates with CAV, markers of inflammation, and angiogenesis in stable heart transplant (HT) recipients.

METHODS

Sixty-five HT recipients ≥2 years post-transplant, without recent rejection, were stratified by high (≥0.12%) versus low levels (<0.12%) of dd-cfDNA. A targeted amplification, next-generation sequencing assay (AlloSure^® ; CareDx, Inc.) was used to detect dd-cfDNA. Peripheral blood inflammatory and angiogenesis markers were assessed using a multiplex immunoassay system (Bioplex^® ).

RESULTS

Of 65 patients, 58 patients had a known CAV status and were included. Thirty had high levels of dd-cfDNA (≥0.12%), and 28 had low levels (<0.12%). CAV was present in 63% of patients with high dd-cfDNA vs. 35% with low dd-cfDNA (p = .047). Donor-specific antibodies were present in 25% of patients with high dd-cfDNA vs. 3.8% in those with low dd-cfDNA (p = .03). There were no differences in rejection episodes, inflammatory, or angiogenesis markers. Importantly, dd-cfDNA levels were not different when stratified by time post-transplant.

CONCLUSIONS

Higher dd-cfDNA levels were associated with CAV in stable chronic HT recipients. Further studies are warranted to investigate a possible association between dd-cfDNA levels and CAV severity and whether dd-cfDNA can predict CAV progression.

PET Assessment of Cardiac Allograft Vasculopathy

Heart transplantation is an effective and life-saving therapy for patients with end-stage heart disease. Cardiac allograft vasculopathy (CAV) is a frequent complication after heart transplantation and a leading cause of graft failure and death. The diffuse involvement of the coronary macro- and microvasculature in CAV poses significant challenges for noninvasive imaging surveillance techniques that depend on regional differences in myocardial perfusion or contractility to detect abnormalities. Recent imaging and transplantation guidelines recommend cardiac PET for CAV evaluation. Current evidence demonstrates high diagnostic accuracy of PET myocardial blood flow and myocardial flow reserve quantification for CAV as well as utility for post-transplant patient risk stratification. Multicenter prospective studies are needed to determine optimal PET measures and to define thresholds for diagnostic and prognostic assessment of CAV.

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.

Assessment of late-term progression of cardiac allograft vasculopathy in patients with orthotopic heart transplantation using quantitative cardiac 82Rb PET

The risk stratification and long-term survival of patients with orthotopic heart transplantation (OHT) is impacted by the complication of cardiac allograft vasculopathy (CAV). This study evaluates changes in myocardial blood flow (MBF) and myocardial coronary flow reserve (CFR) in a group of long-term OHT patients using quantitative cardiac ⁸²Rb-positron emission tomography (PET). Twenty patients (7 females and 13 males, mean age = 72.7 ± 12.2 years with CAV and 62.9 ± 7.2 years without CAV and post-OHT mean time = 13.9 years), were evaluated retrospectively using dynamic cardiac ⁸²Rb-PET at rest and regadenoson-induced stress. The patients also underwent selective coronary angiography (SCA) for diagnosis and risk stratification. CAV was diagnosed based on SCA findings and maximal intimal thickness greater than 0.5 mm, as defined by International Society of Heart and Lung Transplantation (ISHLT). Global and regional MBFs were estimated in three vascular territories using the standard 1-tissue compartment model for dynamic ⁸²Rb-PET. The myocardial CFR was also calculated as the ratio of peak stress MBF to rest MBF. Among twenty patients, seven had CAV in, at least, one major coronary artery (ISHLT CAV grade 1 or higher) while 13 patients did not have CAV (NonCAV). Mean rate-pressure products (RPP) at rest were significantly elevated in CAV patients compared to those without CAV (P = 0.002) but it was insignificant at stress (P = NS). There was no significant difference in the stress MBFs between CAV and NonCAV patients (P = NS). However, the difference in RPP-normalized stress MBFs was significant (P = 0.045), while RPP-normalized MBFs at rest was not significant (P = NS). Both CFR and RPP-normalized CFR were significantly lower in CAV compared to NonCAV patients (P < 0.001). There were significant correlations between MBFs and RPPs at rest for both CAV (ρ = 0.764, P = 0.047) and NonCAV patients (ρ = 0.641, P = 0.017), while there were no correlations at stress for CAV (ρ = 0.232, P = NS) and NonCAV patients (ρ = 0.068, P = NS). This study indicates that the resting MBF is higher in late-term post-OHT patients. The high resting MBF and reduced CFR suggest an unprecedented demand of blood flow and blunted response to stress due to impaired vasodilatory capacity that is exacerbated by the presence of CAV.

Canadian Cardiovascular Society/Canadian Cardiac Transplant Network Position Statement on Heart Transplantation: Patient Eligibility, Selection, and Post-Transplantation Care

Significant practice-changing developments have occurred in the care of heart transplantation candidates and recipients over the past decade. This Canadian Cardiovascular Society/Canadian Cardiac Transplant Network Position Statement provides evidence-based, expert panel recommendations with values and preferences, and practical tips on: (1) patient selection criteria; (2) selected patient populations; and (3) post transplantation surveillance. The recommendations were developed through systematic review of the literature and using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system. The evolving areas of importance addressed include transplant recipient age, frailty assessment, pulmonary hypertension evaluation, cannabis use, combined heart and other solid organ transplantation, adult congenital heart disease, cardiac amyloidosis, high sensitization, and post-transplantation management of antibodies to human leukocyte antigen, rejection, cardiac allograft vasculopathy, and long-term noncardiac care. Attention is also given to Canadian-specific management strategies including the prioritization of highly sensitized transplant candidates (status 4S) and heart organ allocation algorithms. The focus topics in this position statement highlight the increased complexity of patients who undergo evaluation for heart transplantation as well as improved patient selection, and advances in post-transplantation management and surveillance that have led to better long-term outcomes for heart transplant recipients.