Cardiac amyloidosis

Article written and reviewed by Dr Luca Moretti

Cardiac amyloidosis is a disease in which misfolded proteins organize into insoluble fibrils and deposit in the extracellular space of the heart. The deposits increase stiffness and apparent wall thickness, alter the microcirculation, infiltrate the atria, valves and conduction system, and progressively reduce filling and pumping capacity. The term amyloid cardiomyopathy describes organ damage, but a therapeutically useful diagnosis must identify the protein that forms the fibrils.

More than 98% of currently diagnosed cardiac forms derive from monoclonal immunoglobulin light chains, AL amyloidosis, or from transthyretin, ATTR amyloidosis. The latter may result from a normal TTR sequence that becomes unstable with age, ATTRwt, or from a germline pathogenic variant, ATTRv. Other proteins can deposit in the heart but are exceptional. The AL-ATTR dichotomy dominates the initial pathway because the timing, specialists and treatments of the two diseases are radically different.

AL is a hematologic emergency: even a small plasma-cell clone can produce highly amyloidogenic and cardiotoxic light chains, with rapid progression and early mortality in advanced-stage disease. ATTR tends, on average, to follow a slower trajectory, but it is not benign and causes heart failure, fibrillation, block and disability. The biological pace requires immediate exclusion of a monoclonal component whenever cardiac suspicion is concrete, without waiting for completion of all imaging.

Recognition has increased thanks to scintigraphy, magnetic resonance and disease-modifying therapies. ATTRwt is identified in a proportion of older adults with heart failure with preserved ejection fraction, thickened walls or aortic stenosis, but percentages from screening studies cannot be applied indiscriminately to the general population. Contextual prevalence depends on age, sex, setting and criteria, whereas AL remains rare and should not be sought by unselected screening but promptly suspected in consistent phenotypes.

From misfolded protein to cardiac damage

Amyloidogenic proteins lose their native conformation, form oligomers and ultimately fibrils rich in beta sheets that resist degradation. The fibrils bind matrix components, including serum amyloid P component, and accumulate between cardiomyocytes and around small vessels. Interstitial expansion increases extracellular volume, separates fibers and makes the wall stiff before ejection fraction falls.

In AL, light chains and their oligomers also exert direct toxicity through oxidative stress, lysosomal dysfunction and alterations in proteostasis. This helps explain why, at an apparently similar wall thickness or burden, AL may present with higher biomarkers and more rapid progression than ATTR. Precursor toxicity makes an early hematologic response a vital goal even if the deposit has not yet regressed.

Transthyretin is a tetrameric protein produced mainly by the liver that transports thyroxine and retinol-binding protein. Dissociation of the tetramer into monomers is a rate-limiting step in amyloidogenesis; age or TTR variants destabilize the structure and promote aggregation. Stabilizers and silencers act at different points in this transthyretin cascade, slowing new formation without instantly removing material already present.

Atrial involvement reduces contractility and reservoir function, promoting fibrillation, thrombi and atrioventricular valve regurgitation. The conduction system develops block and bradycardia, while the infiltrated microcirculation can generate angina and ischemia without epicardial stenoses. Pan-cardiac disease explains why the phenotype cannot be reduced to left ventricular diastolic dysfunction alone.

With progression, longitudinal strain and output decrease, right ventricular function worsens and ejection fraction may fall. Blood pressure often declines from previous values and previously tolerated antihypertensive drugs cause hypotension, especially when dysautonomia coexists. The systolic transition represents an advanced phase but is not necessary to define clinically severe cardiomyopathy.

Red flags and presentations that should not be separated

Dyspnea, edema, ascites and fatigue are common but nonspecific. Suspicion increases when heart failure with preserved ejection fraction is associated with unexplained thickened walls, enlarged atria, reduced right ventricular function, a small effusion, block or fibrillation, or when blood pressure falls in a previously hypertensive patient. The clinical mismatch between an apparently hypertrophied heart and low pressure reserve is often more useful than a single cutoff.

In ATTRwt, bilateral carpal tunnel syndrome, lumbar spinal stenosis, biceps tendon rupture and orthopedic surgery may precede cardiac disease by years because transthyretin deposits in ligaments and tenosynovium. These findings are common in older adults and do not prove disease, but their combination with heart failure changes the probability. The extracardiac chronology can sometimes reveal an otherwise early cardiac phase.

ATTRv may present with sensorimotor neuropathy, neuropathic pain, dysautonomia, gastrointestinal disturbances, weight loss, carpal tunnel syndrome, nephropathy or cardiomyopathy, with expression depending on the variant and geographic area. A negative family history does not exclude hereditary disease because of penetrance, missed diagnoses and small families. Universal TTR testing after confirmation of ATTR distinguishes variant from wild-type disease even in older adults.

In AL, proteinuria, nephrotic edema, macroglossia, periorbital purpura, hepatomegaly, neuropathy, dysautonomia and weight loss are classic but not mandatory clues. A monoclonal component may be small and absence of myeloma criteria does not exclude amyloidogenic production. Clone size does not necessarily reflect organ severity, because the toxic quality of the light chain matters more than tumor burden.

Syncope may result from block, tachyarrhythmia, dysautonomia or inability to increase output; angina may reflect microvasculopathy; stroke may precede documented fibrillation in severe atrial disease. The multiplicity of mechanisms requires rhythm documentation, hemodynamic assessment and a search for thrombi, avoiding automatic attribution of every event to a single cause.

ECG, echocardiography and biomarkers

The ECG may show low limb-lead voltage, a pseudo-infarction pattern, axis deviation, bundle-branch or atrioventricular block and fibrillation. Low voltage is not present in all patients, particularly in ATTR, and concomitant hypertension may preserve high voltages. The mass-voltage mismatch between thick walls and small signals is a useful clue, but its absence does not justify exclusion.

Echocardiography may show increased biventricular wall thickness, nondilated cavities, enlarged atria, thickened valves and interatrial septum, effusion, reduced right ventricular function and a restrictive pattern. The term granular sparkling is not sufficiently specific with modern harmonic imaging and should not be used as a criterion. Infiltrative geometry emerges from the combination of structures and mechanics, not from subjective image texture.

Global longitudinal strain falls early and may show relative apical sparing compared with basal and mid segments. This apical sparing increases suspicion in an appropriate context, but also occurs in other conditions and may be absent in specific stages or types. The strain map is a recognition and prognostic tool, not a test capable of distinguishing AL from ATTR.

NT-proBNP and troponin are often persistently elevated and are used in staging systems, but must be interpreted with renal function, fibrillation, age and treatment. In AL, the difference between involved and uninvolved light chains, dFLC, completes Mayo staging; in ATTR, NT-proBNP and eGFR form the NAC system. Disease-specific staging compares patients with the same disease and is not interchangeable between the two precursors.

Serial biomarker changes may reflect decongestion, causal response, renal function or progression. In AL, hematologic response often precedes cardiac response and a rapid fall in light chains is central; in ATTR, the course is slower and no single biomarker is validated as a universal surrogate of efficacy. Longitudinal interpretation therefore requires therapeutic context and functional measurements.

Magnetic resonance and evidence of cardiac involvement

Magnetic resonance measures volumes, function and mass and characterizes tissue with LGE, native T1 and ECV. Gadolinium distributes into a greatly expanded interstitium and is rapidly cleared from blood, producing difficulty with nulling and diffuse subendocardial or transmural patterns. Contrast kinetics are characteristic of marked extracellular expansion but do not identify the deposited protein.

Native T1 is generally elevated and can be useful when contrast is contraindicated, whereas ECV quantifies the extracellular fraction and correlates with burden and prognosis. Absolute values depend on field strength, sequence and center and should not be transferred without local references; anemia and edema can influence them. ECV quantification allows serial comparisons when acquisition and analysis are standardized.

LGE and mapping are sensitive to cardiac involvement and help distinguish amyloidosis from HCM, hypertension and Fabry disease, but overlap prevents reliable AL-ATTR typing. A suggestive magnetic resonance study does not replace monoclonal screening, and an inconclusive study does not negate strong suspicion. Post-MRI probability determines the next test; it does not automatically close the pathway.

Magnetic resonance also provides prognostic information: transmural LGE and high ECV are associated with worse outcomes in AL and ATTR cohorts. However, individual risk depends on precursor, stage, renal function, class and therapy and cannot be communicated as a deterministic consequence of an image. Multiparametric stratification integrates tissue with biomarkers and clinical status.

Diagnostic algorithm: monoclonal component first

When cardiac amyloidosis is suspected, the first decision point excludes a monoclonal protein with serum immunofixation, urine immunofixation and free light chains. Serum electrophoresis alone is not sufficiently sensitive, and an abnormal ratio must be interpreted in light of reduced renal clearance. The complete monoclonal triad has high sensitivity for an AL clone and must be ordered without omissions.

If all monoclonal tests are negative, scintigraphy with DPD, PYP or HMDP is interpreted using planar images and SPECT or SPECT/CT. Perugini grade 2 or 3 cardiac uptake in a compatible phenotype permits a nonbiopsy diagnosis of ATTR; SPECT confirms that activity is in the myocardium rather than blood pool or ribs. The noninvasive ATTR pathway depends on the entire combination, not on the heart-to-contralateral ratio in isolation.

Negative scintigraphy does not exclude AL and may be negative in some TTR variants or early stages. Mild grade 1 uptake is indeterminate and does not meet nonbiopsy criteria; moreover, recent infarction, calcifications, residual blood pool and specific rare amyloidoses can create misleading interpretations. Scintigraphic quality requires appropriate timing, tracer and three-dimensional interpretation.

If at least one monoclonal test is abnormal and scintigraphy is positive, there are three possibilities: AL, ATTR with incidental monoclonal gammopathy, or rare coexistence. In this setting, tissue with typing is required, often endomyocardial biopsy if an extracardiac sample does not definitively demonstrate and identify the deposit responsible for cardiac involvement. Concomitant gammopathy is one of the most dangerous pitfalls in older adults.

If monoclonal screening is positive but scintigraphy does not show diagnostic uptake, AL remains the priority and requires rapid hematologic involvement and biopsy of the most appropriate site. Periumbilical fat and bone marrow may be less invasive but have variable sensitivity; a negative result does not exclude cardiac disease. AL diagnostic urgency justifies an accelerated pathway toward tissue demonstration when organ suspicion is high.

Biopsy and fibril typing

Congo red demonstrates the deposit, and apple-green birefringence under polarized light is the classic histologic property. The amount of amyloid in a small sample does not necessarily measure the entire cardiac burden, and a negative extracardiac site does not exclude myocardial deposition. Histologic diagnosis requires adequate sampling and expert interpretation, especially when deposition is scant.

Typing by mass spectrometry after laser microdissection identifies deposit proteins more reliably than nonoptimized immunohistochemistry. Antibodies may react nonspecifically and circulating proteins may contaminate the sample; therefore, a result inconsistent with the clinical picture should be reviewed. The proteomic signature is the reference standard when therapeutic choice depends on distinguishing AL, ATTR or rare forms.

Demonstrating a clonal plasma cell in bone marrow does not prove that the deposit is AL, just as finding a TTR variant does not prove that the heart is infiltrated. The complete causal chain links precursor, fibril and organ: a typed AL deposit with a concordant clone, or nonbiopsy/tissue ATTR criteria with subsequent genetic assessment. Causal coherence prevents confusion between a risk factor and manifest disease.

After an ATTR diagnosis, TTR sequencing is recommended regardless of age or apparent absence of neuropathy because it distinguishes ATTRv from ATTRwt and opens family screening. After AL, clone characterization includes bone marrow, FISH and gammopathy assessment according to hematology practice. The post-typing phase defines origin, organs involved and strategy; it is not a minor step after the cardiac diagnosis.

Rare forms, dual pathology and causal attribution

AL and ATTR explain the great majority of clinically recognized cardiac amyloidosis, but not every deposit. Apolipoproteins AI and AII, gelsolin, fibrinogen A-alpha, lysozyme and other proteins can produce hereditary amyloidoses with different organ distributions; AA amyloid from chronic inflammation mainly affects the kidney and only rarely the heart as the dominant organ. Precursor rarity does not justify labeling a deposit ATTR merely because AL has been excluded.

Mass spectrometry becomes decisive when family history, scintigraphy and immunofixation do not converge. Some rare amyloidoses may show uptake with bone tracers and some ATTR forms may have modest uptake; in parallel, monoclonal gammopathy in older adults may be incidental. Discordance between platforms is an indication to obtain well-typed tissue, not to choose the most convenient result.

Two processes can coexist in the same heart. ATTR may accompany aortic stenosis, hypertension, coronary disease or HCM; more rarely, deposits of two proteins or independent cardiotoxicity are documented. To attribute symptoms and prognosis, the contribution of each mechanism must be estimated, because correcting a valve does not remove infiltration and an anti-amyloid drug does not treat ischemia. Proportional causality replaces a single label with a therapeutic hierarchy.

The differential diagnosis of thickened walls includes hypertensive heart disease, sarcomeric HCM, Fabry, Danon, PRKAG2, mitochondrial disease and myocardial edema. Valve disease, kidney disease, pre-excitation, weakness, age and LGE pattern narrow the field; low native T1 points toward lipid or iron accumulation rather than amyloid, albeit with technical exceptions. Comparison among phenocopies prevents a sensitive sign from being converted into a specific diagnosis.

Atria, microcirculation and thrombosis

The atrium is not merely a chamber dilated because of ventricular pressure. Wall infiltration reduces reservoir function, conduction and contraction, creating an atrial myopathy that can precede or amplify fibrillation. A poorly contractile atrium creates stasis even in sinus rhythm, especially with severe diastolic dysfunction. Amyloid atrial myopathy helps explain thrombi disproportionate to scores developed in the general population.

Before cardioversion, transesophageal echocardiography is often indicated despite apparently adequate anticoagulation because thrombi or spontaneous echo contrast are more frequent. Outside atrial fibrillation, however, systematic anticoagulation in all patients in sinus rhythm lacks definitive evidence; the decision considers documented thrombus, atrial function, bleeding and other factors. Thromboembolic prevention should be aggressive when risk is demonstrated, but not dogmatic where evidence is lacking.

Perivascular deposition and endothelial dysfunction impair coronary reserve. Angina, exertional dyspnea and persistently elevated troponin may occur without significant epicardial stenoses; in AL, direct light-chain toxicity adds to this. Amyloid microangiopathy explains part of the subendocardial injury and prevents dismissing every pain episode as noncardiac after a negative coronary angiogram.

Ischemic assessment should nevertheless be calibrated to atherosclerotic risk because amyloidosis and coronary disease can coexist. Functional tests may be difficult to interpret in the presence of low flow and diffuse abnormalities, whereas CT or angiography answers the anatomical question. Dual coronary pathophysiology requires distinguishing a treatable lesion from the microvascular deficit that will remain after revascularization.

Situations that alter biomarkers

NT-proBNP is central to staging but depends on renal function, fibrillation, age, filling pressure and drugs; BNP and NT-proBNP are not interchangeable, and sacubitril/valsartan mainly alters the former. Troponin reflects chronic injury but also increases with ischemia, tachycardia or renal failure. Biomarker contextualization requires trends, sampling conditions and consistency with volume status and rhythm.

In AL, the difference between the involved and uninvolved light chain, or dFLC, measures clonal production but loses precision when both rise because of reduced clearance. The ratio can be distorted by renal disease and immune suppression; immunofixation and bone marrow complete the interpretation. Hematologic response cannot be inferred from the absolute value of a single chain alone in a patient with advanced nephropathy.

In ATTR, there is no circulating biomarker that directly quantifies amyloid mass and is validated to choose a change in drug therapy. A reduction in transthyretin during silencing documents the pharmacodynamic effect but does not by itself measure cardiac benefit; retinol and retinol-binding protein change through the same mechanism. Pharmacodynamic-clinical separation prevents escalation based on a biologically expected number.

Weight and creatinine may move in apparently contradictory directions during decongestion. A modest rise in creatinine with marked improvement in volume signs does not necessarily equal structural injury, whereas a stable value in severe congestion does not guarantee adequate perfusion. Dynamic renal function is interpreted with diuresis, blood pressure, electrolytes and the clinical trajectory.

Common cardiac management and limitations of drugs

Congestion is treated mainly with loop diuretics, often combined with a mineralocorticoid antagonist if blood pressure, potassium and renal function allow. The margin between overload and hypovolemia is narrow because stroke volume is small and preload dependent; weight, blood pressure and renal function guide adjustments. Monitored euvolemia improves symptoms without attempting to normalize pressures in an infiltrated ventricle.

Beta-blockers, ACE inhibitors, ARBs and ARNIs may be poorly tolerated because of hypotension, low output and dysautonomia, but should not be considered universally prohibited. The 2026 ESC consensus on ATTR distinguishes scenarios and emphasizes the scarcity of randomized trials of nonspecific therapies; observational data suggest possible benefits from mineralocorticoid antagonists and low-dose beta-blockers in subgroups. Hemodynamic personalization replaces absolute rules of withdrawal or prescription.

Atrial fibrillation is frequent and often poorly tolerated. Rhythm control may be pursued, but recurrences are common; digoxin and nondihydropyridine calcium-channel blockers require caution because of toxicity, amyloid binding and hemodynamic depression. Anticoagulation is generally indicated in fibrillation regardless of the traditional score, after bleeding assessment. Thrombogenic atrial disease warrants attention even before cardioversion and in sinus rhythm when thrombus is strongly suspected.

Blocks and bradycardia require a pacemaker according to standard indications, while resynchronization may be considered with a high pacing burden and dysfunction. An ICD may be indicated for selected secondary prevention, but evidence for primary prevention is limited because some deaths result from electromechanical dissociation or non-shockable heart failure. Device selection integrates documented arrhythmias, stage, life expectancy and patient goals.

Aortic stenosis and ATTR can coexist; a diagnosis of amyloidosis does not automatically exclude valve replacement. TAVI may provide benefit in selected patients, considering frailty, output, function and systemic prognosis. The dual valvular-infiltrative burden requires estimating how much of the symptoms is reversible and avoiding both futility and denial of a useful therapy.

Causal therapy, follow-up and prognosis

In AL, therapy aims to rapidly eliminate light-chain production through clone-directed regimens, now often based on daratumumab and bortezomib, adapted to cardiac stage. In ATTR, stabilizer or silencer drugs reduce new amyloidogenesis and have demonstrated clinical benefits in trials. Source-directed therapy is always precursor specific and should begin as early as possible, but does not replace day-to-day management of heart failure.

AL follow-up assesses light chains very promptly and cardiac and renal response over subsequent months; ATTR follow-up integrates functional status, hospitalizations, biomarkers, rhythm and imaging at reasonable intervals. Changes in NT-proBNP may result from volume, kidney function or fibrillation and should not be interpreted in isolation as failure. Multidomain response distinguishes precursor control, clinical stability and tissue regression.

Mayo 2012 staging in AL uses troponin, NT-proBNP and dFLC, whereas NAC staging in ATTR combines NT-proBNP and glomerular filtration rate. These systems stratify cohorts and support prognostic discussions, but modern therapy, age and comorbidities modify outcomes compared with the original cohorts. Updated prognosis must include response and trajectory rather than stopping at initial stage.

Heart transplantation is possible in selected candidates. In AL, it requires a plan to control the clone and absence of incompatible extracardiac disease; in ATTR, it considers neuropathy, age and TTR therapies, while liver transplantation now has a more limited role than in the past. The transplant strategy is decided by centers integrating cardiology, hematology, neurology and genetics.

Early diagnosis changes the natural history because intervention occurs before a small cavity, right-sided failure and multiorgan damage reduce therapeutic tolerance. However, benefit is not immediate and advanced disease remains high risk even after a biological response. Realistic communication combines concrete possibilities for slowing disease with the need for long-term management of congestion, arrhythmias and quality of life.