a Department of Pathology, University of Bologna, Azienda Ospedaliera S. Orsola-Malpighi of Bologna, via Massarenti 9, 40138 Bologna, Italy
b Institute of Cardiology, University of Bologna, Azienda Ospedaliera S. Orsola-Malpighi of Bologna, Italy
c Department of Cardiovascular Surgery, University of Bologna, Azienda Ospedaliera S. Orsola-Malpighi of Bologna, Italy
Received December 2, 2003;
revised March 21, 2004;
accepted April 2, 2004
* Corresponding author. Tel.: +39-05-163-64511; fax: +39-05-163-64571
E-mail address: oleone{at}orsola-malpighi.med.unibo.it
See page 1185 for the editorial comment on this article1
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Abstract |
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Methods and results One hundred and twenty-eight atrial appendages (66 left and 62 right), obtained from 72 patients with rheumatic valve disease and chronic AF undergoing cardiac surgery for valve replacement or repair and AF treatment were histologically evaluated for the presence of amyloid deposits. One hundred and four specimens of left and right auricles from 52 patients in sinus rhythm with severe chronic heart failure undergoing heart transplant were also analyzed (controls). Amyloid was found in 33 (46%) valvular patients with chronic persistent AF and in 6 (12%) controls. Amyloid was related to the presence and duration of AF, was more frequently found in left atrial samples and was independent of age. On stepwise logistic regression analysis, AF duration and female gender were independently related to amyloid deposition.
Conclusions Patients with long-standing AF and rheumatic heart disease have a very high prevalence of atrial amyloidosis. Amyloid deposition is more frequent in left than in right atrial appendage and correlates with AF duration and female gender. Amyloid deposition could constitute an additional histological feature in the structural remodeling of atria during long-standing AF, at least in rheumatic valve disease. Persistence of AF might play a pivotal role in promoting amyloid deposition.
Key Words: Amyloid Atrial fibrillation Atrial remodelling Rheumatic heart disease Cardiac surgery
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Introduction |
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In a large group of patients affected by persistent atrial fibrillation, secondary to mitral valvular heart disease, we systematically investigated the presence and extent of amyloid deposition in both auricles.
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Methods |
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During surgery, both right and left atrial appendages were removed from 56 patients (112 specimens) and only one auricle from 16 patients (6 right and 10 left atrial appendages). Histological studies were carried out on two entire cross-sections of each of the 128 atrial appendage specimens (66 from left and 62 from right atrial appendages), fixed in 10% buffered formalin and embedded in paraffin. De-paraffined sections were stained with haematoxylin and eosin and Azan Mallory trichrome. Amyloid deposits were identified by the presence of green birifrangence from alkaline alcoholic Congo red stain under polarised light. The site (interstitial, endocardial and/or vascular) and pattern (multifocal, diffuse) of amyloid deposition were assessed. The size of deposits were evaluated using a micrometric ocular. Other myocardial and interstitial changes, such as the presence of inflammation, were also histologically studied.
Ultrastructural studies were also carried out in 93 auricular specimens (73%), examining ultra-thin sections stained with uranyl acetate and lead citrate, taken from pieces of myocardium fixed in 2.0% glutaraldehyde, post-fixed in 1.0% osmium tetroxide, dehydrated, and embedded in Epon.
A control group of 52 patients (7 women and 45 men, mean age 54.3±8.7 years) in stable sinus rhythm requiring orthotopic heart transplant due to severe chronic heart failure was also included in the study (36 of these patients were NYHA class III, and 16 were class IV; the aetiology was dilated cardiomyopathy in 24 patients and ischaemic heart disease in 28). At cross-sectional echocardiogram, the left ventricular ejection fraction was 23.2±4.2% (range 1431%) and left atrial diameter (parasternal view) was 4.9±4.2 mm (range 3.66.4 mm). Samples from both right and left atrial appendages were examined histologically in all cases following transplantation (104 samples); no ultra-structural examination was made in these control specimens.
Statistical analysis
Statistical analysis was performed using SPSS 11.0 statistical software (SPSS Inc, Chicago, IL, USA). Continuous variables are expressed as the mean±1 SD or 1 SE as specified; categorical variables are expressed as percentages. Relevant clinical, echocardiographic, and haemodynamic variables were first analysed using univariate analysis by the MannWhitney U two-tailed test, the test or Fisher's exact test, as appropriate in order to determine which single factors could have influenced the presence of amyloid deposits.
values less than 0.05 were considered statistically significant.
Variables achieving in the univariate analysis were then included in a forward stepwise logistic regression analysis to evaluate independent predictors of amyloid deposition. The level of significance used for inclusion into the final model was
; that for removal was
.
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Results |
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Among the 56 patients with valvular heart disease, from whom both right and left auricles were available, amyloid was found in 25/56 (45%) left appendages and in 17/56 (30%) right appendages (). Among the positive specimens, a diffuse pattern was recorded in 9/25 (36%) of the left appendages and in 2/17 (12%) of the right appendages. In the control group, deposits were present in 6/52 (12%) patients (in 1 patient amyloid was present in both appendages, and in 5 patients only in the left).
In the main study group (valvular heart disease), amyloid deposits were localised in the myocardial interstitium in all specimens as thin filaments, or streaks, along the sarcolemma of myocytes. These streaks varied in size from 10 to 300 (Fig. 1(a)); only in 25% of cases was the endocardium focally involved. The depositions were patchy in 22 cases (74%) and diffuse in 11 (26%). No amyloid deposit was found in small vessel walls. Light microscopy identification of amyloid deposits was confirmed by electron microscopy as accumulations of non-branching straight fibrils, approximately 10 nm in width.
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Clinically, at univariate analysis, the patients with amyloid deposits in the main study group were more likely to be female (), more frequently had disease affecting multiple valves (
), and had chronic AF of longer duration (
) (Fig. 2(a)); no difference was found regarding age or the other clinical and functional parameters shown in Table 1. Patients with amyloid deposits showing a diffuse pattern tended to have a longer duration of AF than those with a multi-focal pattern (Fig. 2(b)). Logistic regression analysis showed that the presence of amyloid deposits were significantly associated with AF duration (with an odds ratio (OR) of 1.021 per month, 95% confidence interval (CI) 1.0061.036;
) and female gender (OR 8.8, CI 1.5351.4,
).
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Discussion |
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Intra-auricular deposition of amyloid was identified in 46% of our patients with permanent valvular atrial fibrillation. Unsurprisingly, this prevalence is somewhat higher than that reported in the two other available studies7,10 regarding patients with persistent atrial fibrillation (37% in the study by Röcken et al., and 23% in that of Looi et al.), both of which investigated only right auricular histology. Indeed, in our patients, amyloidosis turned out to be more frequent in the left atrial appendage (45%) than in the right, where the prevalence (30%) was in line with that of the two other series.
Our study has shown that the female gender wash independently associated with amyloid deposition. This finding confirms a previous report by Röcken et al.,7 derived from a population of patients characterised by various underlying pathologies (many of the patients were undergoing coronary by-pass surgery due to ischaemic heart disease).
Pathogenesis of atrial amyloidosis
Our study does not provide information on the immuno-histochemical type of the amyloid deposits. This is a limitation of the present study and could be the object of future research. In the study by Röcken et al.,7 the deposits of the right auricle were all immuno-reactive for atrial natriuretic peptide (ANP) and, in addition, four cases showed transthyretin positive deposits; these were thus interpreted as `isolated atrial amyloidosis'. In the absence of immuno-histochemical characterisation, it is reasonable to assume is that the amyloid deposits in our series were probably ANP-related. Indeed, none of our patients had evidence of haematological disorders causing immunoglobulin light chain amyloidosis or familial polyneuropathy. Considering the long time interval since the acute phase, it seems highly unlikely that the amyloidosis could have been "reactive post-inflammatory", that is secondary to rheumatic disease per se.
What can provoke an overproduction and increased atrial deposition of ANP? In theory, this may be due to either a time factor (i.e., the age of the patient), to increased atrial pressure, or to chronic AF itself.11 In our patient population, duration of AF correlated with both the prevalence of amyloid deposits and with histological severity of amyloidosis. Furthermore, the prevalence of amyloidosis was significantly higher in the study group of patients with valvular AF with respect to the controls (hearts explanted during transplantation from patients in sinus rhythm with end-stage heart failure) despite their more severe haemodynamic impairment. All these observations support the hypothesis that chronic AF itself could be the main cause of an enhanced turnover of ANP leading to intra-atrial amyloid deposition. To address this point directly, a comparison of atrial histological findings from patients in sinus rhythm with long standing AF and with no valvular heart disease could be useful.
Clinical and therapeutic implications
The results of our study extend the previous observations by Röcken et al.,7 which related to a differently characterised patient population in terms of underlying heart disease. Our data support the hypothesis that not only fibrosis12 but also amyloidosis is responsible for the atrial histological remodelling that follows persistent AF. No clinically validated pharmacological intervention to remove or reabsorb amyloid deposits from affected tissues is yet available. However, research in this field is encouraging; a new anthracycline, -iodo-
-deoxydoxorubicin (I-DOX), has been shown to interfere and reverse the process of deposition of amyloid A protein, amyloid immunoglobulin light chain (AL) and transthyretin fibrils, due to its ability to bind the fibrils and alter their final conformation. However, the clinical applications of I-DOX are limited by its toxicity and by the observation that the most striking therapeutic responses have occurred in patients with soft-tissue amyloid deposits.13 Hrncic et al.14 induced resolution of AL deposits by passive administration of an amyloid-reactive antibody in mice being injected with amyloid proteins extracted from patients with AL amyloidosis. A competitive inhibitor of serum amyloid P component (SAP) is currently under clinical investigation. Administration of the drug results in rapid circulatory depletion of SAP and its prompt elimination by the liver, leading to a shift in the balance between the plasma and amyloid pools. Since SAP stabilises amyloid fibrils in vitro and protects them from degradation, its removal could reduce the stability of amyloid deposits and promote their regression, and possibly also delay new amyloid deposition.15
It will be interesting to see whether interventions aimed at reabsorption of atrial deposits could play a role in the therapeutic approach to the treatment and prevention of AF.
Conclusions
Atrial amyloidosis is a very frequent histological finding in patients with long-standing valvular AF. Amyloid deposition is more frequent in the left, rather than in the right, atrial appendage and correlates with AF duration and female gender. These observations reinforce the hypothesis that amyloidosis has a pivotal role in the atrial remodelling which characterises long-standing AF, at least in patients with rheumatic valvular disease. They also seem to underline the multi-factorial origin of the so-called `atrial myopathy' of AF. Amyloidosis could become a target of therapeutic interventions aimed at halting or reabsorbing atrial deposits.
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Footnotes |
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References |
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