Extracellular volume quantification by dynamic equilibrium cardiac computed tomography in cardiac amyloidosis

Myocardial Extracellular Volume Quantification by Cardiovascular Magnetic Resonance and Computed Tomography

PURPOSE OF REVIEW

This review article discusses the evolution of extracellular volume (ECV) quantification using both cardiovascular magnetic resonance (CMR) and computed tomography (CT).

RECENT FINDINGS

Visualizing diffuse myocardial fibrosis is challenging and until recently, was restricted to the domain of the pathologist. CMR and CT both use extravascular, extracellular contrast agents, permitting ECV measurement. The evidence base around ECV quantification by CMR is growing rapidly and just starting in CT. In conditions with high ECV (amyloid, oedema and fibrosis), this technique is already being used clinically and as a surrogate endpoint. Non-invasive diffuse fibrosis quantification is also generating new biological insights into key cardiac diseases. CMR and CT can estimate ECV and in turn diffuse myocardial fibrosis, obviating the need for invasive endomyocardial biopsy. CT is an attractive alternative to CMR particularly in those individuals with contraindications to the latter. Further studies are needed, particularly in CT.

Cardiac amyloidosis is prevalent in older patients with aortic stenosis and carries worse prognosis

BACKGROUND

Non-invasive cardiac imaging allows detection of cardiac amyloidosis (CA) in patients with aortic stenosis (AS). Our objective was to estimate the prevalence of clinically suspected CA in patients with moderate and severe AS referred for cardiovascular magnetic resonance (CMR) in age and gender categories, and assess associations between AS-CA and all-cause mortality.

METHODS

We retrospectively identified consecutive AS patients defined by echocardiography referred for further CMR assessment of valvular, myocardial, and aortic disease. CMR identified CA based on typical late-gadolinium enhancement (LGE) patterns, and ancillary clinical evaluation identified suspected CA. Survival analysis with the Log rank test and Cox regression compared associations between CA and mortality.

RESULTS

There were 113 patients (median age 74 years, Q1-Q3: 62-82 years), 96 (85%) with severe AS. Suspected CA was present in 9 patients (8%) all > 80 years. Among those over the median age of 74 years, the prevalence of CA was 9/57 (16%), and excluding women, the prevalence was 8/25 (32%). Low-flow, low-gradient physiology was very common in CA (7/9 patients or 78%). Over a median follow-up of 18 months, 40 deaths (35%) occurred. Mortality in AS + CA patients was higher than AS alone (56% vs. 20% at 1-year, log rank 15.0, P < 0.0001). Adjusting for aortic valve replacement modeled as a time-dependent covariate, Society of Thoracic Surgery predicted risk of mortality, left ventricular ejection fraction, CA remained associated with all-cause mortality (HR = 2.92, 95% CI = 1.09-7.86, P = 0.03).

CONCLUSIONS

Suspected CA appears prevalent among older male patients with AS, especially with low flow, low gradient AS, and associates with all-cause mortality. The importance of screening for CA in older AS patients and optimal treatment strategies in those with CA warrant further investigation, especially in the era of transcatheter aortic valve implantation.

Measurement of liver and spleen interstitial volume in patients with systemic amyloid light-chain amyloidosis using equilibrium contrast CT

OBJECTIVES

To investigate equilibrium contrast-enhanced CT (EQ-CT) measurement of extracellular volume fraction (ECV) in patients with systemic amyloid light-chain (AL) amyloidosis, testing the hypothesis that ECV becomes elevated in the liver and spleen and ECV correlates with other estimates of organ amyloid burden.

METHODS

26 patients with AL amyloidosis underwent EQ-CT, and ECV was measured in the liver and spleen. Patients also underwent serum amyloid P (SAP) component scintigraphy with grading of liver and spleen involvement. Mann-Whitney U test was used to test for a difference between patients with amyloid deposition (SAP grade 1-3) and those without (SAP grade 0). Variation in ECV across SAP grades was assessed using the Kruskal-Wallis test and association between ECV and SAP grades with Spearman correlation.

RESULTS

Mean ECV in the spleen and liver was significantly greater (p < 0.0005) in amyloidotic organs (SAP grade 1-3) [spleen, liver: 0.430, 0.375] compared with healthy tissues [spleen, liver: 0.304, 0.269]. ECV increased with increasing amyloid burden, showing positive correlation with SAP grade in both the liver (r = 0.758) and spleen (r = 0.867).

CONCLUSION

In patients with systemic AL amyloidosis, EQ-CT can demonstrate increased spleen and liver ECV, which is associated with amyloid disease burden.

Recent Advances in Cardiovascular Imaging Relevant to the Management of Patients with Suspected Cardiac Amyloidosis

Cardiac amyloidosis is a form of infiltrative cardiomyopathy typically presenting with progressive heart failure. The clinical presentation and morphological findings often overlap with other cardiovascular diseases, and frequently results in misdiagnosis and consequent under-reporting. Cardiovascular imaging is playing an increasingly important diagnostic and prognostic role in this referral population, and is reducing the reliance on endomyocardial biopsy as a confirmatory testing. Advancements across multiple cardiac imaging modalities, including echocardiography, magnetic resonance imaging, nuclear imaging, and computed tomography, are improving diagnostic accuracy and offering novel approaches to sub-type differentiation and prognostication. This review explores recent advancements in cardiac imaging for the diagnosis, typing, and staging of cardiac amyloidosis, with a focus on new and evolving techniques. Emphasis is also placed on the promise of non-invasive cardiac imaging to provide value across the spectrum of this clinical disease, from early disease identification (prior to the development of increased wall thickness) through to markers of advanced disease associated with early mortality.

Aortic Stenosis, a Left Ventricular Disease: Insights from Advanced Imaging

Aortic stenosis (AS) is the most common primary valve disorder in the elderly with an increasing prevalence. It is increasingly clear that it is also a disease of the left ventricle (LV) rather than purely the aortic valve. The transition from left ventricular hypertrophy to fibrosis results in the eventual adverse effects on systolic and diastolic function. Appropriate selection of patients for aortic valve intervention is crucial, and current guidelines recommend aortic valve replacement in severe AS with symptoms or in asymptomatic patients with left ventricular ejection fraction (LVEF) <50 %. LVEF is not a sensitive marker and there are other parameters used in multimodality imaging techniques, including longitudinal strain, exercise stress echo and cardiac MRI that may assist in detecting subclinical and subtle LV dysfunction. These findings offer potentially better ways to evaluate patients, time surgery, predict recovery and potentially offer targets for specific therapies. This article outlines the pathophysiology behind the LV response to aortic stenosis and the role of advanced multimodality imaging in describing it.

Computed tomography of cardiomyopathies

Cardiac computed tomography (CT) is increasingly used in the evaluation of cardiomyopathies, particularly in patients who are not able to undergo other non-invasive imaging tests such as magnetic resonance imaging (MRI) due to the presence of MRI-incompatible pacemakers/defibrillators or other contraindications or due to extensive artifacts from indwelling metallic devices. Advances in scanner technology enable acquisition of CT images with high spatial resolution, good temporal resolution, wide field of view and multi-planar reconstruction capabilities. CT is useful in cardiomyopathies in several ways, particularly in the evaluation of coronary arteries, characterization of cardiomyopathy phenotype, quantification of cardiac volumes and function, treatment-planning, and post-treatment evaluation. In this article, we review the imaging techniques and specific applications of CT in the evaluation of cardiomyopathies.

Myocardial iodine concentration measurement using dual-energy computed tomography for the diagnosis of cardiac amyloidosis: a pilot study

OBJECTIVE

To measure myocardium iodine concentration (MIC) in patients with cardiac amyloidosis (CA) using dual-energy computed tomography (DECT).

METHODS

Twenty-two patients with CA, 13 with non-amyloid hypertrophic cardiomyopathies (CH) and 10 control patients were explored with pre-contrast, arterial and 5-minute DECT acquisition (Iomeprol; 1.5 mL/kg). Inter-ventricular septum (IVS) thickness, blood pool iodine concentration (BPIC), MIC (mg/mL), iodine ratio and extra-cellular volume (ECV) were calculated.

RESULTS

IVS thickness was significantly (p < 0.001) higher in CA (17 ± 4 mm) and CH (15 ± 3 mm) patients than in control patients (10 ± 1 mm). CA patients exhibited significantly (p < 0.001) higher 5-minute MIC [2.6 (2.3-3.1) mg/mL], 5-minute iodine ratio (0.88 ± 0.12) and ECV (0.56 ± 0.07) than CH [1.7 (1.4-2.2) mg/mL, 0.57 ± 0.07 and 0.36 ± 0.05, respectively] and control patients [1.9 (1.7-2.4) mg/mL, 0.58 ± 0.07 and 0.35 ± 0.04, respectively). CH and control patients exhibited similar values (p = 0.9). The area under the curve of 5-minute iodine ratio for the differential diagnosis of CA from CH patients was 0.99 (0.73-1.0; p = 0.001). With a threshold of 0.65, the sensitivity and specificity of 5-minute iodine ratio were 100% and 92%, respectively.

CONCLUSION

Five-minute MIC and iodine ratio were increased in CA patients and exhibited best diagnosis performance to diagnose CA in comparison to other parameters.

KEY POINT

• Dual-energy computed tomography can be used to detect cardiac amyloidosis • Five-minute myocardial iodine concentration and iodine ratio increase in cardiac amyloidosis • Among iodine parameters, 5-minute iodine ratio has the best diagnosis performance.

Myocardial Extracellular Volume Is Not Associated With Malignant Ventricular Arrhythmias in High-risk Hypertrophic Cardiomyopathy

INTRODUCTION AND OBJECTIVES

Myocardial interstitial fibrosis, a hallmark of hypertrophic cardiomyopathy (HCM), has been proposed as an arrhythmic substrate. Fibrosis is associated with increased extracellular volume (ECV), which can be quantified by computed tomography (CT). We aimed to analyze the association between CT-determined ECV and malignant ventricular arrhythmias.

METHODS

A retrospective case-control observational study was conducted in HCM patients with implantable cardioverter-defibrillator, undergoing a CT-protocol with continuous iodine contrast infusion to determine equilibrium ECV. Left ventricular septal and lateral CT-determined ECV was compared between prespecified cases (malignant arrhythmia any time before CT scan) and controls (no prior malignant arrhythmias) and among ECV tertiles.

RESULTS

A total of 78 implantable cardioverter-defibrillator HCM patients were included; 24 were women, with a mean age of 52.1 ± 15.6 years. Mean ECV ± standard deviation in the septal left ventricular wall and was 29.8% ± 6.3% in cases (n = 24) vs 31.9% ± 8.5% in controls (n = 54); P = .282. Mean ECV in the lateral wall was 24.5% ± 6.8% in cases vs 28.2% ± 7.4% in controls; P = .043. On comparison of the entire population according to septal ECV tertiles, no significant differences were found in the number of patients receiving appropriate shocks. Conversely, we found a trend (P = .056) for a higher number of patients receiving appropriate shocks in the lateral ECV lowest tertile.

CONCLUSIONS

Extracellular volume was not increased in implantable cardioverter-defibrillator HCM patients with malignant ventricular arrhythmias vs those without arrhythmias. Our findings do not support the use of ECV (a surrogate of diffuse fibrosis) as a predictor of arrhythmias in high-risk HCM patients.

Automatic quantification of the myocardial extracellular volume by cardiac computed tomography: Synthetic ECV by CCT

BACKGROUND

The quantification of extracellular volume fraction (ECV) by Cardiac Computed Tomography (CCT) can identify changes in the myocardial interstitium due to fibrosis or infiltration. Current methodologies require laboratory blood hematocrit (Hct) measurement - which complicates the technique. The attenuation of blood (HU_blood) is known to change with anemia. We hypothesized that the relationship between Hct and HU_blood could be calibrated to rapidly generate a synthetic ECV without formally measuring Hct.

METHODS

The association between Hct and HU_blood was derived from forty non-contrast thoracic CT scans using regression analysis. Synthetic Hct was then used to calculate synthetic ECV, and in turn compared with ECV using blood Hct in a validation cohort with mild interstitial expansion due to fibrosis (aortic stenosis, n = 28, ECV_CT = 28 ± 4%) and severe interstitial expansion due to amyloidosis (n = 27; ECV_CT = 54 ± 11%, p < 0.001). For histological validation, synthetic ECV was correlated with collagen volume fraction (CVF) in a separate cohort with aortic stenosis (n = 18). All CT scans were performed at 120 kV and 160 mAs.

RESULTS

HU_blood was a good predictor of Hct (R² = 0.47; p < 0.01), with the regression model (Hct = [0.51 * HU_blood] + 17.4) describing the association. Synthetic ECV correlated well with conventional ECV (R² = 0.96; p < 0.01) with minimal bias and 2SD difference of 5.7%. Synthetic ECV correlated as well as conventional ECV with histological CVF (both R² = 0.50, p < 0.01). Finally, we implemented an automatic ECV plug-in for offline analysis.

CONCLUSION

Synthetic ECV by CCT provides instantaneous quantification of the myocardial extracellular space without the need for blood sampling.

Myocardial T1-mapping at 3T using saturation-recovery: reference values, precision and comparison with MOLLI

BACKGROUND

Myocardial T1-mapping recently emerged as a promising quantitative method for non-invasive tissue characterization in numerous cardiomyopathies. Commonly performed with an inversion-recovery (IR) magnetization preparation at 1.5T, the application at 3T has gained due to increased quantification precision. Alternatively, saturation-recovery (SR) T1-mapping has recently been introduced at 1.5T for improved accuracy. Thus, the purpose of this study is to investigate the robustness and precision of SR T1-mapping at 3T and to establish accurate reference values for native T1-times and extracellular volume fraction (ECV) of healthy myocardium.

METHODS

Balanced Steady-State Free-Precession (bSSFP) Saturation-Pulse Prepared Heart-rate independent Inversion-REcovery (SAPPHIRE) and Saturation-recovery Single-SHot Acquisition (SASHA) T1-mapping were compared with the Modified Look-Locker inversion recovery (MOLLI) sequence at 3T. Accuracy and precision were studied in phantom. Native and post-contrast T1-times and regional ECV were determined in 20 healthy subjects (10 men, 27 ± 5 years). Subjective image quality, susceptibility artifact rating, in-vivo precision and reproducibility were analyzed.

RESULTS

SR T1-mapping showed <4 % deviation from the spin-echo reference in phantom in the range of T1 = 100-2300 ms. The average quality and artifact scores of the T1-mapping methods were: MOLLI:3.4/3.6, SAPPHIRE:3.1/3.4, SASHA:2.9/3.2; (1: poor - 4: excellent/1: strong - 4: none). SAPPHIRE and SASHA yielded significantly higher T1-times (SAPPHIRE: 1578 ± 42 ms, SASHA: 1523 ± 46 ms), in-vivo T1-time variation (SAPPHIRE: 60.1 ± 8.7 ms, SASHA: 70.0 ± 9.3 ms) and lower ECV-values (SAPPHIRE: 0.20 ± 0.02, SASHA: 0.21 ± 0.03) compared with MOLLI (T1: 1181 ± 47 ms, ECV: 0.26 ± 0.03, Precision: 53.7 ± 8.1 ms). No significant difference was found in the inter-subject variability of T1-times or ECV-values (T1: p = 0.90, ECV: p = 0.78), the observer agreement (inter: p > 0.19; intra: p > 0.09) or consistency (inter: p > 0.07; intra: p > 0.17) between the three methods.

CONCLUSIONS

Saturation-recovery T1-mapping at 3T yields higher accuracy, comparable inter-subject, inter- and intra-observer variability and less than 30 % precision-loss compared to MOLLI.

Sudden cardiac death from structural heart diseases in adults: imaging findings with cardiovascular computed tomography and magnetic resonance

Sudden cardiac death (SCD) is defined as the unexpected natural death from a cardiac cause within an hour of the onset of symptoms in the absence of any other cause. Although such a rapid course of death is mainly attributed to a cardiac arrhythmia, identification of structural heart disease by cardiovascular computed tomography (CCT) and cardiovascular magnetic resonance (CMR) imaging is important to predict the long-term risk of SCD. In adults, SCD most commonly results from coronary artery diseases, coronary artery anomalies, inherited cardiomyopathies, valvular heart diseases, myocarditis, and aortic dissection with coronary artery involvement or acute aortic regurgitation. This review describes the CCT and CMR findings of structural heart diseases related to SCD, which are essential for radiologists to diagnose or predict.

Beyond the plasma cell: emerging therapies for immunoglobulin light chain amyloidosis

Systemic immunoglobulin light chain (LC) amyloidosis (AL) is a potentially fatal disease caused by immunoglobulin LC produced by clonal plasma cells. These LC form both toxic oligomers and amyloid deposits disrupting vital organ function. Despite reduction of LC by chemotherapy, the restoration of organ function is highly variable and often incomplete. Organ damage remains the major source of mortality and morbidity in AL. This review focuses on the challenges posed by emerging therapies that may limit the toxicity of LC and improve organ function by accelerating the resorption of amyloid deposits.

Cardiac Amyloid - An Update

Cardiac amyloidosis is a condition characterised by rapidly progressive heart failure and poor prognosis. The two main subtypes, immunoglobulin light chains (AL) and transthyretin (ATTR), have been investigated extensively in recent years. Cardiac imaging has advanced with the widespread use of cardiac MRI with late gadolinium enhancement imaging and newer techniques including T1 mapping to quantify amyloid burden. Nuclear imaging has developed as a highly accurate method to confirm cardiac amyloid deposits non-invasively with very high sensitivity in ATTR amyloidosis. Despite advances in imaging, cardiac biopsy remains the gold standard diagnostic test to confirm and type amyloidosis. Hereditary ATTR amyloidosis of V122I type has been the focus of important studies in the past year, due to the high prevalence of the amyloidogenic allele in patients of African descent. Recent research concluded a significant number of Afro-Caribbean heart failure patients are likely to have undiagnosed cardiac amyloidosis. Misdiagnosis may lead to inappropriate treatment with potentially harmful 'standard' heart failure medications with no evidence base in amyloidosis. Treatment options have, until recently, been limited but cardiac amyloidosis is the focus of novel therapeutic regimes. New insights into the pathophysiological mechanisms resulting in disease have suggested exciting targets for drug therapy.