Author + information
- Received September 17, 2013
- Revision received November 6, 2013
- Accepted November 7, 2013
- Published online April 1, 2014.
- Selma F. Mohammed, MBBS∗,†,
- Sultan A. Mirzoyev‡,
- William D. Edwards, MD§,
- Ahmet Dogan, MD, PhD‖,
- Donna R. Grogan, MD¶,
- Shannon M. Dunlay, MD∗,
- Veronique L. Roger, MD∗,#,
- Morie A. Gertz, MD‖,
- Angela Dispenzieri, MD‖,
- Steven R. Zeldenrust, MD, PhD‖ and
- Margaret M. Redfield, MD∗∗ ()
- ∗Division of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota
- †Mayo Graduate School, Mayo Clinic, Rochester, Minnesota
- ‡Mayo Medical School, Mayo Clinic, Rochester, Minnesota
- §Division of Anatomic Pathology, Mayo Clinic, Rochester, Minnesota
- ‖Division of Hematology, Mayo Clinic, Rochester, Minnesota
- ¶Clementia Pharmaceuticals, Montreal, Canada
- #Department of Health Science Research, Mayo Clinic, Rochester, Minnesota
- ↵∗Reprint requests and correspondence:
Dr. Margaret M. Redfield, Mayo Clinic and Foundation, CV Research, Guggenheim 9, Mayo Clinic, 200 First Street SW, Rochester, Minnesota 55905.
Objectives This study sought to determine the frequency of left ventricular amyloid in heart failure with preserved ejection fraction (HFpEF).
Background Left ventricular amyloid deposition can cause diastolic dysfunction and HFpEF.
Methods Autopsy of left ventricular specimens from patients with antemortem diagnosis of HFpEF without clinically apparent amyloid (n = 109) and from control subjects (n = 131) were screened with sulfated Alcian blue and subsequent Congo red staining with microdissection for mass spectrometry–based proteomics to determine amyloid type. Fibrosis was assessed with quantitative whole-field digital microscopy.
Results The presence of wild-type transthyretin (wtTTR) amyloid was associated with age at death and male sex, but the age- and sex-adjusted prevalence of wtTTR amyloid was higher in HFpEF patients than in control subjects (odds ratio: 3.8, 95% confidence interval: 1.5 to 11.3; p = 0.03). Among HFpEF patients, moderate or severe interstitial wtTTR deposition, consistent with senile systemic amyloidosis as the primary etiology of HFpEF, was present in 5 (5%) patients (80% men), with mild interstitial and/or variable severity of intramural coronary vascular deposition in 13 (12%) patients. While, wtTTR deposition was often mild, adjusting for age and presence of HFpEF, wtTTR amyloid was associated with more fibrosis (p = 0.005) and lower age, sex, and body size–adjusted heart weight (p = 0.04).
Conclusions Given the age- and sex-independent association of HFpEF and wtTTR deposition and an emerging understanding of the pathophysiology of the amyloidoses, the current findings support further investigation of the role of wtTTR in the pathophysiology of HFpEF.
- heart failure with preserved ejection fraction
- mass spectrometry-based proteomics
Cardiac amyloid deposition can cause heart failure with preserved ejection fraction (HFpEF). While approximately 30 proteins have been linked to cardiac amyloidosis, monoclonal immunoglobulin from clonal plasma cells (AL amyloid) and transthyretin (TTR amyloid) are the most common forms.
Transthyretin is a hepatic-derived, homotetrameric transporter protein that exists in equilibrium with TTR monomers. A number of genetic variations in the TTR gene cause hereditary amyloidosis, affecting the nerves, heart, or both. Cardiac amyloidosis (senile systemic amyloidosis [SSA]) due to deposition of amyloid derived from wild-type TTR (wtTTR) in the myocardial interstitium and intramural coronary vessels is associated with left ventricular (LV) wall thickening, diastolic dysfunction, and HFpEF (1–4).
While marked amyloid deposition is present in clinically diagnosed SSA, emerging evidence suggests that cell damage in TTR amyloid is due to deposition of lower molecular weight non-amyloid TTR species that precede detectable TTR amyloid fibril deposition (5–10). Variant TTR is structurally less stable and more prone to amyloid fibril formation (7), but the factors leading to wtTTR amyloid deposition have yet to be fully elucidated. In vitro studies suggest that oxidative modification of wtTTR increases its amyloidogenicity (7). As aging is associated with increased oxidative stress, oxidative modification of wtTTR may account for the association of the SSA with age.
HFpEF accounts for one-half of HF patients, and its prevalence increases dramatically with age and female sex (11). Clinical suspicion of amyloid in HFpEF patients may be low, as they often have alternative explanations, such as chronic hypertension, for LV wall thickening and diastolic dysfunction.
Development of novel compounds that may attenuate TTR amyloid cardiac deposition has heightened interest in the significance of TTR amyloid as a cause of HF (12–14). While autopsy rates in older HF patients are low (15), autopsy specimens provide the optimal opportunity to assess the prevalence of unsuspected amyloid deposition in HFpEF, as endomyocardial biopsy is infrequent in older HFpEF patients (16) and fat aspirate has limited sensitivity for detection of wtTTR amyloid (17–19).
Accordingly, we sought to determine the frequency, extent, and type of cardiac amyloid deposition in patients with an antemortem diagnosis of HFpEF (but not of amyloid) who subsequently underwent autopsy, as compared with age-appropriate control autopsy subjects.
The study was approved by Mayo Clinic Institutional Review Board and the Mayo Biospecimens Committee. Only autopsy specimens with consent for use of specimens for research purposes were used.
Identification of HFpEF cases with autopsy
HFpEF subjects were identified using cohorts previously assimilated from administrative datasets. Consecutive patients admitted to Mayo Clinic hospitals in Rochester, Minnesota, between January 1, 1986, and December 31, 2001, with a discharge diagnosis of HF confirmed by both the International Classification of Diseases-, Ninth Revision-, Clinical Modification (ICD-9-CM) code 428 and the diagnosis related-group code 127 for HF (n = 6,440), were identified as previously described (20,21).
This patient list was crossed to the MTR (Mayo Tissue Registry) (15,22) to identify patients who had undergone autopsy (n = 441, 6.8%) (23). Characteristics, including EF distribution, of patients with and without autopsy were similar except for a slightly higher rate of hypertension and coronary disease in patients with autopsy (Online Table 1). Many autopsies were restricted in extent (neurologic only). Thus, of the 441 patients with autopsy, 331 had EF measured at HF diagnosis and of these, 75 had EF >40% at HF diagnosis.
To supplement this cohort, additional patients hospitalized with HF (ICD-9-CM code 428) at Mayo hospitals from 2003 to 2010 were identified and crossed with the MTR, yielding 25 additional cases with EF >40% at HF diagnosis and cardiac autopsy. Additionally, outpatients with HF (ICD-9-CM code 428) diagnosed between March 1980 and July 2009 who were residents of Olmsted County, Minnesota, and who had HF confirmed by medical record review (Framingham criteria) (24) were crossed with the MTR, yielding an additional 12 cases with EF >40% at HF diagnosis and autopsy, for a total of 112 cases with antemortem diagnosis of HFpEF and cardiac specimens from autopsy.
Medical records of these subjects were reviewed and any mention of definitive or probable cardiac amyloid in the clinical notes or reference to echocardiographic features of amyloid or cardiac biopsy findings suggestive of amyloid was considered antemortem suspicion. Three HFpEF cases had antemortem diagnosis of amyloidosis. Importantly, in all 3 patients, the amyloid was light chain type. Thus, exclusion of these patients does not affect estimates of the prevalence of wtTTR amyloid in HFpEF. As antemortem suspicion of cardiac amyloidosis could influence the decision to perform an autopsy, these 3 patients were excluded, leaving 109 patients with HFpEF and no clinical suspicion of cardiac amyloidosis prior to death and autopsy.
Identification of control subjects
After reviewing the distribution of age at death and sex of the HFpEF autopsy cases, a minimum of 20 subjects per age at death decade, ≥40 years of age without antemortem HF diagnosis and who died of noncardiovascular causes and had undergone autopsy between January 3, 1971, and October 12, 2010, were identified from the MTR database (n = 131) to serve as age- and sex-appropriate control subjects. Though not formally age-matched in a 1:1 ratio (where equal numbers of control and HFpEF patients of the same age would be studied, due to the small number of HFpEF patients in some age groups), appropriate numbers of control subjects were selected to allow statistical assessment of age dependence of findings. Medical record review was performed to define clinical characteristics and exclude antemortem diagnosis of amyloid in control subjects.
Autopsy data and tissue processing
Finalized autopsy reports were reviewed and included assessment of absolute and percent of expected heart weight (percent of normative values on the basis of age, sex, and body size (22)), severity of coronary artery disease (semiquantitative ordinal scale [0 to 4] reflecting no  to critical  atherosclerosis) and gross and microscopic hypertrophy, fibrosis, or infarction. A sum coronary artery score was calculated by adding the individual artery scores (left main, left anterior descending, circumflex, and right coronary arteries).
For this study, all histologic analysis was performed by a highly experienced cardiovascular pathologist (W.D.E.) who was blinded to clinical information. Hematoxylin and eosin–stained samples from the LV inferior wall were reviewed to determine the quality of the specimen. If an infarct involved >50% of the inferior LV section, an adjacent noninfarcted section was chosen. Sections were then stained with sulfated Alcian blue (SAB) and counterstained with Van Gieson stain (25) to screen for the presence of amyloid. Amyloid-positive slides were then stained with Congo red for confirmation and mass spectroscopy–based proteomics for determining the type of amyloid. Extent of interstitial amyloid deposition (green with SAB) was assessed semiquantitatively as mild, moderate, or severe, corresponding to <25%, 25% to 50%, and >50% of myocardial surface area, with vascular involvement similarly graded and corresponding to <33%, 33% to 67%, and >67% of vascular circumference (26).
Microdissection and mass spectroscopy–based proteomic analysis
Amyloid deposits were isolated with laser microdissection of 10-μm thick Congo red stained slides (performed by A.D.), subjected to trypsin digestion, and analyzed by liquid chromatography electrospray ionization tandem mass spectrometry (27). For protein sequence identification, raw data were analyzed using 3 algorithms (SEQUEST, Scripps Research Institute, La Jolla, California; Mascot, Matrix Science, Boston, Massachusetts; and X!Tandem, Global Proteome Machine Organization), which collectively provided coverage for known TTR amyloid mutations. Subsequently, amyloid type and genotype were determined according to spectral matching as previously described (27). Mass spectroscopy (versus immunohistochemistry) was used as it allows screening for multiple proteins simultaneously (both known and unknown). We previously validated mass spectrometry in comparison to immunohistochemistry and the gold standard clinicopathologic criteria (27). When tissue quantity was adequate, mass spectrometry was superior to immunohistochemistry in identifying amyloid type with sensitivity and specificity over 98% (27). Of note, previous reports had shown lower sensitivity of mass spectrometry due to inadequate tissue specimen rather than misclassification (28).
Quantitative assessment of fibrosis
Because stains used to assess fibrosis in standard autopsy procedures can cause difficulty distinguishing between collagen and amyloid fibrils, SAB-stained sections (amyloid stains green and collagen stains red) were scanned using whole-field digital microscopy (WFDM) and the entire slide analyzed (blinded to group and patient characteristics) with an automated quantitative analysis software system (Definiens, Munich, Germany) using a custom designed rule set to quantify fibrosis (red) as a percent of total tissue area (see the supplemental methods in the Online Appendix).
All available electrocardiograms closest to death were reviewed and the voltages were measured manually (S.F.M.). LV hypertrophy (determined by Cornell and Sokolow criteria) and low voltage (all limb lead voltages <5 mm or all precordial voltages <10 mm ) were assessed. Ventricular-paced QRS complexes were excluded from voltage analysis.
Data are presented as mean ± SD or percentage of frequency. Group comparisons were performed using unpaired Student t test for continuous variables or chi-square test for categorical variables. Multivariable nominal logistic regression was used to elucidate the association of wtTTR (present or absent) with group (HFpEF vs control) adjusting for age or sex. Multivariable standard least-squares linear regression was used to elucidate the association between extent of fibrosis or heart weight and wtTTR presence, adjusting for pertinent covariates (HF presence, age). All statistical analyses were 2-tailed and performed using JMP software (version 9.0.1, SAS Institute, Cary, North Carolina). A p value <0.05 was considered statistically significant.
Consistent with previous community-based reports, HFpEF subjects were elderly and predominantly women (Table 1). There was no difference in sex distribution between the HFpEF and control groups. HFpEF subjects had more cardiovascular comorbidities. As control subjects were not formally age-matched (equal numbers of patients of comparable age), as a group, control subjects were younger due to larger numbers of patients in their 40s and 50s (Fig. 1). Compared with women with HFpEF, men with HFpEF were slightly but not significantly younger and had more coronary artery disease (Online Table 2).
At autopsy, HFpEF patients had higher BMI than control subjects (Table 1). HFpEF subjects had more cardiac hypertrophy (by heart weight and microscopic analysis), chamber dilation, coronary disease, and evidence of old or new infarction. HFpEF patients had more gross and microscopic fibrosis as assessed by standard autopsy procedures and by quantitative analysis (WFDM) of SAB-stained sections. Compared with women, men with HFpEF were larger, had higher heart weight but similar percentage of expected heart weight, a higher prevalence of old infarction on gross and microscopic inspection, and severer cases of coronary artery disease (Online Table 2).
Prevalence and type of left ventricular amyloid in control and HFpEF
Overall, 7 (5%) of the 131 control subjects and 21 (19%) of the 109 HFpEF patients without antemortem suspicion of amyloid had LV amyloid deposition at autopsy. Notably, control subjects were 7 years younger than HFpEF patients were. Adjusting for age at death and sex, amyloid (any type) was more common in patients with HFpEF than in control subjects (Table 2).
All 7 control subjects with amyloid had wtTTR amyloid. Two (2%) of the 83 women and 5 (10%) of the 48 men had wtTTR amyloid.
Among the HFpEF patients, 2 (2%) patients had unknown amyloid type due to inadequate specimens for microdissection, 1 (1%) had light chain amyloid, and 18 (17%) had wtTTR amyloid, involving 9 (15%) of the 62 women and 9 (19%) of the 47 men. The 2 patients with inadequate specimens for microdissection had mild interstitial or mild focal nonobstructive vascular deposition of amyloid.
wtTTR amyloid: deposition site and severity in control and HFpEF
Representative examples of mild, moderate, and severe interstitial or coronary vascular amyloid deposition are shown in Figure 2. Of the 7 control subjects with wtTTR amyloid, deposition was vascular-only in 4 (57%), interstitial-only in 2 (29%), and both vascular and interstitial in 1 (14%) (Fig. 3). The worst severity of deposition was mild in 5 (71%) patients and moderate to severe in 2 (29%) patients (1 vascular and 1 interstitial). Only 1 control subject (man) had more than mild interstitial amyloid deposition.
Of the 18 HFpEF patients with wtTTR amyloid, deposition was vascular-only in 6 (33%), interstitial-only in 8 (44%), and both vascular and interstitial in 4 (22%) (Fig. 3). The worst severity of deposition was mild in 9 (50%) patients and moderate to severe in 9 (50%) patients. Thus, only 5 (5%; 4 men and 1 woman) HFpEF patients had moderate or severe interstitial amyloid deposition consistent with HF due to SSA.
wtTTR amyloid: association with fibrosis and hypertrophy
Representative examples of SAB-stained LV sections from HFpEF patients with mild (<5%), moderate (5% to 10%), and severe (>15%) myocardial fibrosis along with the corresponding definition of fibrosis versus myocardial tissue by the Definiens analysis program are shown in Figure 4. In the entire study group, adjusting for age and the presence of HFpEF, patients with wtTTR amyloid had more fibrosis as assessed by WFDM than those without amyloid. Adjusting for the presence of HFpEF, patients with wtTTR amyloid had lower age-, sex-, and body size–adjusted heart weight (percentage of expected heart weight) than patients without wtTTR amyloid (Table 3).
In sensitivity analysis, when analysis was confined to the HFpEF groups only, wtTTR was associated with more fibrosis (2.9%; SE: 1.1%; p = 0.02) and lower percent of expected heart weight (–14.8%; SE: 6.4%; p = 0.02) compared with no TTR amyloid.
wtTTR amyloid: impact of age at onset of HFpEF on prevalence of wtTTR amyloid
Left ventricular wtTTR amyloid deposition was not observed at autopsy in patients diagnosed with HFpEF before 65 years of age, but it was very common at autopsy in those who were ≥80 years of age at the time of HFpEF diagnosis (Fig. 5). Adjusting for sex, wtTTR amyloid was associated with age at HFpEF onset (p < 0.001).
HFpEF subjects with and without wtTTR cardiac amyloid
Compared with those without wtTTR, HFpEF subjects with wtTTR amyloid were older at HF diagnosis and death, but they had similar sex distribution and comorbidities (Table 4). HFpEF patients with wtTTR amyloid had smaller weight hearts, more fibrosis by WFDM, and more microscopic infarcts than HFpEF patients without wtTTR amyloid. When available, the electrocardiogram closest to death showed no difference in the prevalence of low voltage in HFpEF patients with or without wtTTR amyloid, with only 8% of wtTTR amyloid HFpEF patients showing low voltage.
To our knowledge, this is the first study to examine the age- and sex-adjusted prevalence of LV amyloid deposition in HFpEF, and it was made possible by the unique resources afforded by Mayo Clinic HFpEF databases and the MTR. Rigorous methodology was used with blinded systematic review of control and HFpEF LV specimens by a highly experienced cardiovascular pathologist, state-of-the-art pathology methodologies to determine amyloid type and fibrosis severity, and statistical analysis of age- and sex-specific prevalence rates. Significant (moderate or severe) interstitial wtTTR amyloid deposition consistent with a diagnosis of SSA as the major cause of HFpEF was uncommon (5%) with the expected male (80%) predominance. However, the age- and sex-adjusted prevalence of wtTTR LV amyloid deposition was higher in HFpEF patients than in control subjects due to the identification of mild interstitial and/or variable severities of coronary vascular wtTTR deposition. Furthermore, adjusting for age and the presence of HFpEF, wtTTR amyloid deposition, though often mild, was associated with more fibrosis and lower age-, sex-, and body size–adjusted heart weights.
The higher prevalence of wtTTR amyloid in HFpEF patients indicates a form of ascertainment bias whereby the HFpEF autopsy group is enriched for the presence of amyloid. This ascertainment bias could be due to bias toward obtaining autopsy due to antemortem clinical suspicion of amyloid, amyloid deposition predisposing to HFpEF, or HFpEF predisposing to amyloid deposition. Given the potent age association of both HFpEF and wtTTR amyloid, the age- and sex-independent association of HFpEF and wtTTR deposition, and the emerging understanding of the pathophysiology of the amyloidoses, the current findings support the need for further investigation of the role of wtTTR in HFpEF.
Prevalence of amyloid in previous autopsy studies
Previous autopsy studies investigating the prevalence of cardiac amyloid have used varying patient selection criteria—and often distinction of location, extent, and type of amyloid have been lacking—with variable methods for determining the type of amyloid.
A Finnish population-based autopsy study of persons dying at age >84 (n = 256) found LV TTR amyloid deposition (mostly mild) in 25% (33% of men and 23% of women), where TTR amyloid was confirmed by immunohistochemistry and genetic analysis for 1 TTR variant (2). TTR amyloid deposition was associated with age but not significantly with sex, although male subjects had more severe deposition. Although clinically recognized SSA is well known to display a male predominance (17,30–32), in autopsy studies where detection of milder TTR deposition is possible, the association of TTR amyloid deposition with sex has varied (2,4,33). We found that TTR amyloid was more common in men in both the control and HFpEF populations after adjusting for age. However, both men and women HFpEF patients had higher prevalence of TTR amyloid than control subjects.
Hodkinson et al. (4) screened for cardiac (atrial and LV) amyloid deposits at autopsy in an unselected series of 244 hospitalized patients over 60 years of age who died of any cause and underwent autopsy. Amyloid deposition (screening with SAB and confirmation by Congo red staining) was characterized as atrial-only or LV in location. Any (atrial or LV) amyloid was more common in women (56%) than in men (38%). LV amyloid was present in 14 of 96 (14.5%) men and was moderate or severe in 11 (11.5%). LV amyloid was present in 24 of 148 (16.2%) women, with moderate or severe LV amyloid present in 10 (6.7%). The presence of any amyloid was associated with clinical HF or atrial fibrillation during the hospital stay but amyloid type and type of HF (HFpEF vs. HF with reduced EF) were not specified.
Lie et al. (33) examined consecutive cardiac autopsy specimens from persons dying from any cause (48% cardiovascular death) at age ≥90 years. Details on the severity of LV or coronary deposition, amyloid type, or association with HF were not provided. Cardiac amyloid was detected in 66% of men and 65% of women, but it was restricted to the atria in two-thirds of patients, suggesting a prevalence of LV amyloid in approximately 22% of patients, which was lower than observed in HFpEF patients in their 90s in the current study.
A study of 52,370 clinically reported autopsies showed a prevalence of presumed SSA (age >60 years, primarily cardiac involvement) of 0.42% in non-Hispanic whites and 1.6% in blacks (23,34). Immunohistochemistry for TTR with deoxyribonucleic acid analysis in a subset of SSA patients was performed and showed that the increased prevalence of SSA in blacks was actually related to late onset hereditary amyloidosis due to the V122I TTR variant, rather than to wtTTR. The prevalence of milder amyloid deposition was not reported. The current study used MS characterization of the TTR amyloid to confirm wtTTR, and the patients were all white.
Potential for bias to obtain autopsy in amyloid positive HFpEF patients
The higher prevalence of wtTTR amyloid in HFpEF patients could be due to bias toward obtaining autopsy in patients in whom the presence of amyloid was suspected antemortem or due to more rigorous review for amyloid in HFpEF specimens. This is unlikely because: review of medical records was specifically performed to determine whether amyloid was suspected prior to death, the clinical characteristics of autopsied and nonautopsied HF patients were similar; the electrocardiogram changes were not suggestive of amyloid in HFpEF patients and the extent of amyloid was mild or limited to the intramural coronary vessels in a majority of patients, making it less likely to be suspected clinically on the basis of echocardiography. Screening of control and HFpEF specimens for amyloid was performed blinded to clinical information and, as outlined, the prevalence of amyloid in control specimens was consistent with previous studies.
wtTTR amyloid deposition as a potential contributor to development of HFpEF
The pathophysiology of HFpEF is complex, but hypertrophic and fibrotic LV remodeling, diastolic dysfunction, subtle systolic dysfunction, vascular dysfunction, adverse ventricular-vascular coupling, and impaired cardiovascular reserve function are thought to contribute prominently to the pathophysiology of HFpEF (35). Structural and functional changes within aging myocytes, which negatively affect cellular plasticity, have yet to be explored in detail. Comorbidities (hypertension, diabetes, vascular disease, and atrial fibrillation) are common in patients with HFpEF.
Cardiac SSA is conventionally diagnosed when marked deposition producing wall thickening is present, and it has been assumed that such marked deposition is required to produce cardiac dysfunction (1,36). However, emerging evidence from in vitro and in vivo studies supports cytotoxic effects by lower molecular weight species that may be intermediates in the pathway of amyloid fibril deposition (5–10). These adverse effects occur before tissue deposition ensues and are associated with inflammation and cell death (6,10). These cytotoxic effects were observed with mutant and wild-type TTR in human cardiomyocyte cell culture studies (6). Oxidized or carbonylated wtTTR has a higher propensity to form aggregates and fibrils and was cytotoxic in human cardiomyocytes (7). Further, in a murine model of human wtTTR overexpression, up-regulation of genes encoding for inflammatory and immune response pathways was observed in the heart prior to detectable amyloid deposition (10).
In asymptomatic carriers for familial amyloid polyneuropathy, aggregated, nonfibrillar, Congo red birefringence-negative TTR deposition was reported in association with early nerve damage as evidenced by inflammatory markers (8). In the current study, the presence of wtTTR amyloid was associated with more fibrosis and less hypertrophy, and these findings may support the presence of inflammation and cell death prior to marked amyloid deposition. Amyloid fibrils were also present in intramural coronary vessels. Coronary vascular dysfunction can contribute to diastolic dysfunction and/or ischemic injury and contribute to HFpEF pathophysiology (35).
HFpEF as a potential cause of wtTTR deposition
Alternatively, the increased prevalence of amyloid deposition in failing hearts may reflect a pro-oxidative state related to the neurohumoral activation and metabolic derangements seen in older HFpEF patients, as oxidative modification of wtTTR increases its cytotoxicity and alters its kinetic stability and amyloidogenicity (7). Both advanced age and the HF state are associated with increased oxidative stress, as are several of the comorbidities (chronic kidney disease, hypertension, and vascular disease) commonly associated with HFpEF (37). Oxidative stress and associated redox changes has been implicated in the pathophysiology of HF (38).
Using a transgenic model of human wtTTR overexpression, Buxbaum et al. (10) found that failure of hepatic proteostatic capacity enhanced age-related deposition of wtTTR in the heart. These data suggest that increased production and abnormal hepatic function may contribute to wtTTR amyloid deposition in the heart. Whether chronic hepatic congestion due to HF can alter hepatic proteostatic function is unclear.
Diagnostic and therapeutic implications
Currently, in older subjects presenting with HFpEF symptoms, the diagnosis of TTR amyloidosis is seldom entertained and HF is usually attributed to the underlying comorbidities. The variable yield of abdominal fat pad or rectal biopsies (17–19) limit the ability to diagnose wtTTR amyloid noninvasively, and the lack of effective therapy discourages use of endomyocardial biopsy. However, novel TTR proteostatic compounds and TTR gene silencing therapeutics offer the hope of specific preventative or disease-slowing therapy for TTR amyloidoses (12–14,39). As use of such therapeutics only in patients with advanced, clinically recognized SSA may have a minimal impact, the current findings underscore the need for a better understanding of the natural history of wtTTR deposition and its impact on cardiac structure and function.
Sample size was reduced by requirement for consent to use specimens for research. The autopsy rate observed among HF patients (Online Table 1) is lower than that reported nationally (∼7%), but both advanced age and HF diagnosis are known to be associated with reduced autopsy rates (15). The present study is largely descriptive and cannot establish whether amyloid deposition is a contributor to or a result of HFpEF pathophysiology. The clinical significance of amyloid deposits in older HFpEF subjects should be interpreted in the context of an autopsy study and may not be generalizable to younger HFpEF patients. Due to the limited statistical power, we were unable to adjust for comorbidities and other confounders that may influence amyloid deposition. The relationship between HFpEF and amyloid deposition could be explained by these confounders. We are unable to characterize the relative prevalence of wtTTR versus variant TTR amyloid in HFpEF patients of other ethnic groups.
While marked wtTTR amyloid deposition consistent with a diagnosis of SSA was an infrequent cause of HFpEF in this autopsy series, overall, the age- and sex-adjusted prevalence of wtTTR amyloid deposition in the LV and/or intramural coronary vessels was greater in HFpEF patients than in control subjects and was associated with more fibrosis and lower cardiac mass, as adjusted for age, sex, and body size. Although this study cannot establish whether amyloid deposition is a contributor to or a result of HFpEF pathophysiology, the findings and the emergence of disease-modifying drugs for TTR amyloid suggest the need for further investigation of the natural history of wtTTR amyloid and its role in the pathophysiology of HFpEF.
The authors dedicate this manuscript to the memory of Dr. David C. Utz.
For supplemental methods and tables, please see the online version of this article.
The National Institutes of Health and the Mayo Clinic supported this study (grants #HL 72435, #HL 55502 and UL1 TR000135) and/or the investigators (grants #U01HL 84907 and #PO1HL 76611 to Dr. Redfield; T32-HL07111 to Dr. Mohammed). Dr. Mohammed is a heart failure clinical research network skills development fellow (U01HL 84907). A grant from FoldRx, a fully owned subsidiary of Pfizer, provided funds for technician support and mass spectrometry–based proteomics characterization. Dr. Grogan is an employee of FoldRx and has stock options. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose. Dr. Mohammed and Mr. Mirzoyev contributed equally to this work.
- Abbreviations and Acronyms
- ejection fraction
- heart failure
- heart failure with preserved ejection fraction
- International Classification of Diseases
- left ventricle
- sulfated Alcian blue
- senile systemic amyloidosis
- whole-field digital microscopy
- wild-type transthyretin
- Received September 17, 2013.
- Revision received November 6, 2013.
- Accepted November 7, 2013.
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