Background
Approximately 1.5 million of the 44 million individuals of African descent in the United States are carriers of the p.V142I variant in transthyretin (TTR). This is the most common cause of variant amyloid cardiomyopathy (ATTR-CM) worldwide which leads to heart failure (HF) and premature death. Despite promising new treatments, ATTR-CM is often diagnosed at an advanced stage and conventional diagnostic tools lack specificity to detect early disease. Thus, the overall objectives of the Variant Imaging of Subclinical Transthyretin Amyloidosis (VISTA) study are to determine imaging and biomarker evidence of subclinical ATTR-CM that indicates amyloid progression in p.V142I TTR carriers.
Methods and Results
In a multisite nested case-control study, contrast-enhanced cardiac resonance imaging (CMRI) and amyloid-specific blood biomarker measurements will be used to compare metrics associated with cardiac amyloid infiltration between a cohort of p.V142I TTR carriers without HF with age-, sex-, and race-matched non-carrier controls. A sub-sample of participants will undergo novel exercise CMRI to measure and compare cardiac systolic and diastolic reserve.
Conclusions
Completion of VISTA will establish evidence of subclinical variant ATTR-CM in p.V142I TTR carriers, will change how we think about ATTR-CM, and will justify future research in screening and treatment strategies for disease prevention.
Transthyretin Amyloid Cardiomyopathy (ATTR-CM) is a restrictive cardiomyopathy caused by the genesis of misfolded transthyretin protein that can infiltrate the myocardium. It currently affects <1/100,000 individuals worldwide and it is an underrecognized cause of heart failure in older adults. ATTR-CM is typically classified by the sequence variations in the TTR gene. It is considered wild type (wt-ATTR) if no variant is present and hereditary (ATTRv) if a TTR destabilizing variant is present. The most common ATTRv mutation that causes cardiac amyloidosis in the United States and worldwide is the valine to isoleucine substitution at position 142 in the TTR precursor protein (NP_000362.1: p.Val142Ile; rs76992529). It is found in 3-4% of individuals of African descent and estimates suggest there may be 1.6 million carriers in the United States. ,,,,,, ATTRv is inherited in an autosomal dominant fashion, and although the disease penetrance is not well understood, it is thought to be higher in men. ,, Furthermore, the extent of the symptoms is also uncertain due to variable expressivity of the genotype. Not all carriers develop symptomatic disease even though some estimates suggest that pathologic cardiac amyloid deposition may be present in all p.V142I TTR carriers without clinical evidence of ATTR-CM. ,,
Several epidemiological studies have demonstrated that p.V142I TTR carriers in the general population have a higher incidence of heart failure and all-cause mortality in comparison with noncarrier controls, especially after the age of 65. ,,,,, Presumably, these events are related to cardiac amyloidosis which is indirectly suggested by subtle differences in cardiac phenotype as measured by echocardiography and noncontrast enhanced cardiac MRI.
Among p.V142I carriers with heart failure, only a minority have a formal ATTR-CM diagnosis documented, indicating substantial under-recognition of amyloidosis. , When left untreated, outcomes are poor. The median survival is approximately 31 months from diagnosis, compared with 57 months in ATTRwt-CM and 69 months in non p.V142I ATTR-CM individuals. Consistent with this, trial data from the Transthyretin Amyloidosis Cardiomyopathy Clinical Trial (ATTR-ACT) and HELIOS-B- a cardiovascular outcomes trial of vutrisiran in ATTR-CM,suggest greater benefit when TTR- specific therapy is initiated earlier in the disease course. ,
Recognition of p.V142I ATTRv-CM has increased, particularly as a cause of heart failure with preserved ejection fraction in the elderly. This recognition reflects not only advances in epidemiologic understanding but also a growing appreciation of the underlying biology and the availability of disease modifying therapies. These scientific advances have led to the development of several safe, well-tolerated, and highly efficacious targeted therapies for ATTR-CM.
Tafamidis, a non-nonsteroidal anti-inflammatory benzoxazole derivative, is a once daily, oral bioavailable kinetic stabilizer of TTR that decreases all-cause mortality and rates of cardiovascular related hospitalizations in patients with ATTR-CM. Acoramidis, similar in mechanism, is also a TTR stabilizer but differs from tafamidis in that it binds with higher affinity and provides enhanced stabilization of both wild-type and variant forms of TTR. Acoramidis was designed to mimic the protective p.T139M TTR mutation, which naturally enhances tetramer stability and slows amyloid formation. Vutrisiran, an RNA silencer, decreases hepatic production of both mutant and wild-type TTR by targeting TTR mRNA. It has been shown to improve neuropathy, cardiac biomarkers, and quality of life in patients with ATTR polyneuropathy and cardiomyopathy. , These therapies act upstream by lowering circulating TTR levels and by offering an alternative to TTR stabilizers; additional therapeutic options are currently in phase 3 clinical trials.
In parallel, advances in noninvasive imaging have transformed diagnostic recognition. Cardiac amyloid radionuclide imaging, typically performed using technetium-99m-labeled pyrophosphate, hydroxymethylene diphosphonate, or 3,3-diphosphono-1,2-propanodicarboxylic acid, now enables a nonbiopsy diagnosis of ATTR-CM when there is grade 2-3 myocardial uptake and no evidence of a monoclonal protein, sparing many patients endomyocardial biopsy. Cardiac magnetic resonance is also valuable and can detect deposition of amyloid with sensitivity and specificity approaching 90%. , Despite these advances, ATTR-CM is still frequently recognized at advanced stages, diminishing therapeutic benefit and highlighting the need for earlier diagnosis.
Herein, we report the design and rationale of the VISTA study. This study will test the hypothesis that ATTR-CM has a long latency period in p.V142I TTR carriers that will be detected through subclinical amyloidosis imaging, exercise testing, and biomarker phenotyping. We hypothesize that p.V142I carrier status will be independently associated with greater evidence of cardiac amyloid infiltration, amyloidogenesis in the blood, and that exercise will be able to unmask abnormal pathophysiology attributable to amyloid. Accordingly, we are leveraging a multidisciplinary collaborative research team and existing data from p.V142I TTR carriers in the Dallas Heart Study, Dallas Biobank, and cascade genetic screening from these carriers supplemented with family members of p.V142I ATTR-CM patients at UT Southwestern (UTSW), Cleveland Clinic, and Columbia University. Completion of this study will help characterize potential subclinical features of ATTR-CM among p.V142I TTR carriers. By identifying pathophysiologic evidence of cardiac amyloid progression prior to ATTR-CM onset, this study will refine our understanding of the disease and justify future research on screening and treatment strategies to prevent ATTR-CM. Together, these efforts aim to reduce HF morbidity and mortality through earlier recognition and therapy.
Study Design and Methods
Objective
The primary goal of this study is to determine the presence of subclinical ATTR-CM and to identify circulating biomarkers that indicate amyloid progression in p.V142I TTR carriers without HF.
Design
This will be a cross-sectional, nested case-control study. We will enroll three groups of participants: 1) p.V142I TTR carriers without heart failure; 2) matched noncarrier controls; and 3) individuals with symptomatic p.V142I ATTR-CM. p.V142I TTR carriers without heart failure will be identified from the Dallas Heart Study (DHS) or the Dallas Biobank (DBB) and will also be recruited and enrolled from the three clinical sites: UTSW, Columbia, or Cleveland Clinic. Recruitment and enrollment started in the Fall of 2022. Both carriers without HF and noncarrier controls will undergo detailed imaging and biomarker assessments while symptomatic p.V142I ATTR-CM patients will undergo biomarker assessments only. The p.V142I TTR carriers without HF will be matched by age, sex, and race/ethnicity to noncarrier controls identified with TTR gene sequencing completed as part of the DHS.
Overview of Study Registries
The DHS, located at UT Southwestern, is a large multiethnic cohort of Dallas County residents designed to determine the prevalence of cardiovascular diseases and risk factors predisposing to cardiovascular disease. At study entry in 2000-2002, a detailed clinical evaluation was performed for 2,772 participants (median age 45 years; 49% Black). Participants underwent genotyping and comprehensive cardiac and biomarker phenotyping. Beginning in 2007, DHS participants were reexamined using a similar testing protocol; supplemented with spouses and unrelated family members, providing a sample size of 2,888 (median age 50 years; 49% Black). Participants have been actively followed since study entry.
Similarly, the DBB study, also located at UT Southwestern, is a large multiethnic repository of DNA samples collected from over 25,000 individuals: approximately 10,000 Caucasians, 8,000 Blacks, and 6,000 Hispanic/Latino Americans. This registry was designed to allow researchers to study the relationships between genetics and disease in different ethnic groups in North Texas.
Study population
p.V142I TTR carriers without heart failure
Key inclusion and exclusion criteria are listed in Table 1 . In summary, to be eligible for inclusion in this study, p.V142I TTR carriers must be between 30 and 80 years of age, have the pathogenic valine-to-isoleucine substitution at position p.142 identified by TTR gene sequencing (either heterozygous or homozygous), and have no clinical history of heart failure. A history of heart failure is defined as being hospitalized for the management of HF within the previous 12 months, having an elevated B-type natriuretic peptide level of ≥100 pg/mL or NTproBNP ≥360 pg/mL within the previous 12 months, or having a clinical diagnosis of HF from a treating clinician. Exclusion criteria include: having isolated or concomitant missense variants (pathogenic, likely pathogenic, or variant of unknown significance) in TTR , a self-reported history of clinical HF, other known causes of cardiomyopathy, having a history of systemic light-chain cardiac amyloidosis, prior Type I non ST-elevation myocardial infarction (NSTEMI) or ST-elevation myocardial infarction (STEMI), history of cardiac transplantation, body weight that prohibits CMR imaging, eGFR of ≤30 mL/min/1.73 m2, and inability to safely undergo MRI.
Table 1
Inclusion and exclusion criteria
| Inclusion criteria | Exclusion criteria |
|---|---|
|
General (all participants):
Age 30–80 years |
Other TTR variants (pathogenic, likely pathogenic, or VUS)
History of heart failure (self-reported or clinical) Other known causes of cardiomyopathy Systemic AL amyloidosis Prior NSTEMI/STEMI History of cardiac or liver transplantation Use of a TTR stabilizer within 14 d before enrollment Prior treatment with a TTR silencer Enrollment in another ATTR-CM clinical trial Body weight prohibiting CMR eGFR <30 mL/min/1.73 m² Inability to safely undergo MRI |
|
p.V142I carriers
Confirmed p.V142I TTR variant by gene sequencing No clinical history of HF (no hospitalization in prior 12 months, BNP ≥100 pg/mL or NT-proBNP ≥360 pg/mL, or clinician diagnosis) |
|
|
Matched noncarrier controls
No pathogenic or stabilizing TTR variants (e.g., p.T139M, p.R124H) No clinical heart failure (as above) |
|
|
Symptomatic p.V142I ATTR-CM cohort
Biopsy proven amyloid (Congo red or equivalent with typing) ORPositive 99mTc-pyrophosphate/bisphosphonate scan with AL amyloidosis excluded Clinical history of HF (≥1 hospitalizations in prior 12 months, BNP ≥100 pg/mL or NT-proBNP ≥360 pg/mL, or clinician diagnosis) |
Non-carrier controls
Age-, sex-, and race- matched noncarrier controls must be free of any TTR pathogenic mutations or the p.T139M or p.R124H stabilizing mutations. They must also have no history of heart failure by the same criteria used for the p.V142I TTR carrier group. Exclusion criteria are also identical to the p.V142I TTR carrier group.
Participants with symptomatic p.V142I ATTR-CM
Participants with symptomatic p.V142I ATTR-CM must be 30-80 years of age, have a clinical history of heart failure, and an established diagnosis of ATTR-CM to be included in this study. Diagnosis may be confirmed through at least one of the following pathways: (a) tissue biopsy confirmed by Congo red (or equivalent) staining and typing by immunohistochemistry, mass spectrometry, and/or immunoelectron microscopy, and/or (b) by a positive technetium-99m pyrophosphate, hydroxymethylene diphosphonate, or 3,3-diphosphono-1,2-propanodicarboxylic acid scan, combined with laboratory findings that rule out light-chain amyloidosis (absence of an abnormal M-protein).
TTR gene sequencing must also confirm the presence of p.V142I mutation. Exclusion criteria include any other known cause of cardiomyopathy, a history of systemic light-chain cardiac amyloidosis, prior cardiac or liver transplantation, use of a TTR stabilizer within 14 days of enrollment, enrollment into a clinical trial testing a novel treatment for ATTR-CM, prior treatment with a TTR silencer, or an estimated glomerular filtration rate (eGFR) ≤30 mL/min/1.73 m².
Clinical Assessments
After consent is obtained, all participants will undergo an extensive history, physical examination, and electrocardiogram (EKG). The history will include a detailed medication list, family, medical, cardiac, and surgical history. It will also capture any musculoskeletal signs that may predate amyloidosis (e.g. carpal tunnel syndrome, atraumatic biceps tendon rupture, lumbar canal stenosis). Additionally, the Norfolk-QOL-DN and COMPASS-31 questionnaires will be administered to evaluate symptoms of neuropathy and autonomic dysfunction, respectively. These questionnaires are validated assessments of neuropathy progression and dysautonomia in amyloidosis. ,
Study Procedures
Cardiac magnetic resonance
All participants will undergo a cardiac magnetic resonance imaging (CMRI) assessment using a 3T clinical scanner (Philips Achieva at UT Southwestern, General Electric 750 W at Columbia University, and Siemens MAGNETOM Cima.X at the Cleveland Clinic with a dedicated cardiac coil). After localization, imaging will be performed during end-expiratory breath holding with ECG gating. The protocol will include the following imaging sequences and endpoints ( Fig. 1 ) , with specific sequence parameters included in Table 1 . Image acquisition will be performed by certified technicians experienced in CMRI, under the direct oversight of study personnel.
Representative cardiac MRI. (A) High resolution steady-state free precession cine images in the short axis, beginning with basal slice (S1) and progressing through the apex of the left ventricle (S9). Long axis cine images acquired in the horizontal and vertical long axis orientation (HLA and VLA, respectively), and left ventricular outflow tract view (LVOT). (B) Three evenly spaced short axis tissue tagging images spanning the left ventricle. (C) Three evenly spaces short axis and HLA native and post-contrast T1 maps. (D) Three evenly spaced short axis T2 maps. (E) Inversion time scout (Look Locker) at the mid-ventricular level (TI: Inversion Time, time in msec). (F) Phase and magnitude images at the level of the mitral valve in early diastole. (G) Phase-sensitive inversion recovery images to identify presence of late gadolinium enhancement.
CMRI evaluations will include multiplanar cine (morphology & function), MR tissue tagging (tissue deformation), phase contrast imaging, inversion time scout, native T1 and T2 mapping, and post contrast imaging detailed below.
Multiplanar cine imaging will assess cardiac morphology and function by acquiring balanced steady-state free precession (bSSFP) images in standard long-axis (2-, 3-, and 4-chamber) views and a contiguous stack of short-axis slices spanning the ventricular base to apex.
Tissue tagging will be used to quantify myocardial (circumferential) strain and deformation patterns with spatial modulation of magnetization (SPAMM) tagging performed in three short-axis slices (basal, midventricular, and apical levels). Phase contrast imaging will measure mitral inflow velocities across the mitral valve during diastole, providing complementary information about diastolic filling and relaxation. Native T1 and T2 mapping will characterize myocardial tissue properties with Modified Look-Locker Inversion recovery (MOLLI) sequences acquired in 3 short-axis slices (basal, midventricular, and apical levels) and a horizontal long-axis (4 chamber) image. In addition, native T2 maps will be obtained using a T2-prepared bSSFP sequence in a midventricular short-axis slice to quantify myocardial edema and interstitial expansion
Postcontrast imaging
A macrocyclic gadolinium-based contrast agent (Gadovist [gadobutrol]) will be administered intravenously at a dose of 0.1 mmol/kg body weight. An Inversion Time (Look-Locker) scout sequence in a midventricular short-axis slice will be performed 7 minutes postcontrast administration to determine the inversion time for nulling the myocardium. At 10 minutes, the TI scout will be repeated, followed by T1 mapping (3 short-axis slices and a horizontal long-axis image). Phase-sensitive inversion recovery (PSIR) imaging in the long- and short-axis views will then be performed immediately after T1 mapping, to assess myocardial scar and fibrosis.
Exercise cardiac MRI
To complement conventional diagnostic approaches, assessment of cardiac performance under stress may provide additional insight into early dysfunction. A subgroup of participants, enrolled at UT Southwestern, will undergo exercise CMR before resting CMR images are obtained. We aim to enroll 100 of the p.V142I TTR carriers and 100 of the controls. Participants will exercise within the bore of the magnet using an MR compatible ergometer with adjustable electronic resistance (Ergospect Cardio-Stepper, Ergospect) performing workloads of 30, 60, and 90W. The maximal workload will be determined by each individual’s tolerance to exercise, with participants encouraged to continue to volitional exhaustion. Each stage of the imaging protocol will last approximately 5 minutes (2 min to achieve physiologic steady state, followed by 3 minutes of imaging).
cMRI image analysis
All imaging data will be analyzed by an experienced (15+ years) core laboratory at UT Arlington, using dedicated analysis software. ,,, Briefly, left ventricular (LV) and right ventricular volumes and ejection fraction (EF), LV mass and thickness, circumferential and longitudinal strain (by feature tracking), mitral inflow patterns, T1 (pre and postcontrast) and T2 time, and inversion recovery dynamics (i.e. myocardium null time), will be quantified using commercially available software (CVI 42 version 6.1.3, Circle Cardiovascular Imaging, Calgary, AB). Myocardial tissue tagging images will be processed using in-house software to measure LV circumferential strain and strain rate, twist, and torsion.
A typical Look-Locker pattern will be defined as myocardial nulling, occurring prior to blood pool nulling on the TI scout sequence. Extracellular volume will be derived using the patient’s hematocrit and the T1 values pre and postcontrast using previously defined methods. Every effort will be made to control for postural changes in hematocrit caused by extravascular fluid shifts. All efforts will be made to have blood drawn from the catheter used for contrast administration before the scan, following at least 20 minutes of supine rest, or immediately after the MRI before the participant transitions from the exam table (in supine position). In addition, LGE will be qualitatively assessed, with a typical pattern being defined as subendocardial or transmural enhancement within hypertrophied myocardium with either circumferential or involving > 6 myocardial segments.
Primary and Secondary Imaging Outcomes
Table 2 shows a summary of the study endpoints. The primary imaging endpoint will be evidence of amyloid infiltration, measured by ECV and changes in stroke volume index from rest to peak stress among participants in the exercise CMR substudy. ECV expansion can represent interstitial expansion from amyloid infiltration and greater levels can distinguish amyloidosis from other hypertrophic cardiomyopathies and correlate with cardiac amyloidosis disease severity. In patients with ATTR-CM, ECV is associated with mortality independent of age, NT-proBNP levels, ejection fraction, severity of diastolic function (e.g. E/e’), LV mass, and late gadolinium enhancement (LGE).
Table 2
Primary and secondary outcomes
| Primary outcomes (CMR) | Secondary outcomes (CMR) |
|---|---|
|
Extracellular Volume Fraction (%)
Stroke Volume Index (rest to peak stress in exercise CMR sub-study)-ml/m2 |
Presence or absence of LGE
Extent of LGE, ≥6 SD above mean myocardial signal (%) LV and RV mass index (g/m²) Global systolic function (%) Mass-to-Volume Longitudinal strain (%) Long. e’ SR (s-1) Circumferential Strain (%) Circ. e’ SR (s-1) E/e’SR Native T1 relaxation time (ms) Native T2 relaxation time (ms) Post-gadolinium T1 signal intensity(ms) Left and right ventricular end diastolic volume index (mL/m²) Left and right ventricular end systolic volume index (mL/m²) Magnetic Resonance tissue tagging Mitral inflow velocities (cm/s) Peak circumferential strain (%) Peak ejection rate (mL/s) Peak filling rate (mL/s) |
Secondary endpoints will include the following: presence and extent of LGE, native T1 and T2 parameters to evaluate for the presence of diffuse interstitial expansion or edema respectively, post gadolinium myocardial and blood null time, LV and RV end-diastolic and end-systolic volume, stroke volume and ejection fraction, LV mass and wall thickness, LV regional tissue deformation (i.e. circumferential and longitudinal strain), and diastolic function (i.e. mitral inflow velocities [E and A], diastolic strain rates [e’ and a’]). For participants undergoing exercise CMRI, end-diastolic volume index, end-systolic volume index, stroke index, ejection fraction, cardiac index and heart rate reserve will be assessed.
Overview of Biomarker Assessments
All participants will undergo detailed biomarker assessments. Venous blood samples using phlebotomy will be obtained from all groups: p.V142I TTR carriers, noncarrier controls, and participants with symptomatic p.V142I ATTR-CM. These biomarker assessments will include circulating TTR and retinal binding protein 4 (RBP4) levels, TTR kinetic stability, and presence of nonnative TTR. These data will serve as a rich biorepository and remaining blood samples will be banked for future assessments.
Transthyretin (TTR)
TTR is a liver-secreted tetrameric protein composed of 4 identical 127- amino acid monomers. , TTR becomes amyloidogenic when the tetramer destabilizes and dissociates into individual monomer. , Lower plasma TTR concentrations are associated with decreased tetramer stability and increased amyloidogenic potential. Prior studies, including data from the Dallas Heart Study, have shown that p.V142I TTR carriers have significantly lower circulating TTR levels compared to matched noncarriers. , Therefore, in this study, TTR levels will be measured to serve as a surrogate marker for tetramer stability. Total TTR concentration will be quantified by ELISA at the Cleveland Clinic. ,
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
