Infiltrative cardiomyopathies

Article written and reviewed by Dr Luca Moretti

Infiltrative cardiomyopathies include diseases in which a substance, a protein organized into fibrils, inflammatory cells or granulomas alter cardiac tissue. The result is not uniform: some apparently increase wall thickness and produce restriction, others cause blocks and arrhythmias with preserved function, and still others progress toward dilation and systolic failure. The term infiltrative describes a general pathological mechanism and must always be completed by the name of the material and its distribution.

Cardiac amyloidosis is the paradigm of extracellular expansion, but even within it AL amyloidosis and ATTR amyloidosis differ in precursor, urgency and causal therapy. Hemochromatosis cardiomyopathy, by contrast, results mainly from intracellular iron accumulation and oxidative stress, whereas sarcoidosis replaces foci of granulomatous inflammation with scar. The biology of the deposit determines testing, therapy and potential reversibility.

In practice, the terms infiltrative, deposit and storage are sometimes overlapped, but they are not perfect synonyms. Amyloid deposits in the extracellular space; iron and lipids may accumulate in cardiomyocytes; glycogen and lysosomal material belong to metabolic diseases; granulomas are cellular infiltrates. A mechanistic nomenclature prevents an echocardiographic analogy from erasing differences with immediate therapeutic consequences.

The modern pathway combines clinical clues, ECG, echocardiography, magnetic resonance, biomarkers, nuclear medicine, genetics and tissue. No modality resolves every etiology, and the same findings change meaning with age and pretest probability. Multimodality reasoning builds a diagnosis by convergence and reserves biopsy for cases in which noninvasive typing is unsafe or the result will change treatment.

What happens in cardiac tissue

In amyloidosis, misfolded proteins form insoluble fibrils that accumulate in the interstitium, separate cardiomyocytes, involve microvessels, valves and conduction tissue, and expand extracellular volume. In AL, circulating light chains also have direct toxic effects, contributing to rapid injury that does not depend only on the amount of deposit. The pathological extracellular matrix therefore alters mechanics, perfusion and electrical behavior.

In sarcoidosis, aggregates of macrophages and lymphocytes form noncaseating granulomas, often patchily distributed in the basal septum, free wall or right ventricle. The inflammatory phase can cause edema, block and arrhythmias; fibrotic healing creates reentry circuits and dysfunction. The focal distribution explains why unguided endomyocardial biopsy may be negative even in clinically important disease.

Free iron catalyzes oxidative reactions, damages membranes and mitochondria and alters ion channels. Accumulation may initially produce diastolic dysfunction and arrhythmias and then progress to dilation and systolic dysfunction; a restrictive phenotype is therefore neither mandatory nor permanent. Iron toxicity can regress with timely removal, whereas ferritin does not directly measure myocardial burden.

In storage diseases, metabolites or enlarged organelles alter cell volume and enzyme function. Fabry disease accumulates globotriaosylceramide and derivatives, PRKAG2 alters energy regulation and promotes glycogen storage and pre-excitation, and Pompe disease involves the lysosome. These processes generate a distinct pseudohypertrophy and are covered among metabolic cardiomyopathies because their biology differs from extracellular infiltration.

The cardiac response depends on the region involved. Diffuse ventricular involvement increases filling pressures; septal involvement interrupts conduction; subepicardial foci promote tachycardia; atrial infiltration causes fibrillation and stasis. Tissue topography is therefore as important as total deposit volume and links imaging, ECG and clinical risk.

Cardiac and extracardiac red flags

Unexplained thickened walls, heart failure with preserved ejection fraction, progressive intolerance of antihypertensive drugs, disproportionately low voltage, a pseudo-infarction pattern and conduction block suggest amyloidosis. None, however, is required: normal voltages and modest wall thickness occur in early stages. Discordance between data, more than a single classic sign, should trigger an etiologic pathway.

Bilateral carpal tunnel syndrome, lumbar stenosis, atraumatic biceps rupture and joint replacement sometimes precede cardiac ATTR by years; neuropathy, dysautonomia and family history suggest variant forms. Macroglossia, periorbital purpura, proteinuria, weight loss and gammopathy point toward AL. Multisystem constellations increase specificity when chronology and combination are coherent.

High-grade atrioventricular block, ventricular tachycardia, aneurysms and patchy LGE in a young adult raise consideration of sarcoidosis, particularly with lymphadenopathy, uveitis, skin or lung lesions. The absence of overt extracardiac sarcoidosis does not exclude an isolated form, and a positive PET can be confounded by inadequate metabolic preparation. Inflammatory probability comes from anatomy, activity and context, not from uptake alone.

Bronze skin, diabetes, liver disease, arthropathy and hypogonadism point toward hemochromatosis, whereas transfusion dependence suggests secondary overload. In young patients, pre-excitation, elevated CK, weakness, angiokeratomas, neuropathic pain or renal failure open the metabolic investigation. The extracardiac phenotype selects high-yield tests and limits costly panels without a clinical question.

An oncologic history changes the spectrum: radiotherapy may produce myopericardial fibrosis, whereas hematologic malignancies and gammopathies increase suspicion of AL. Cardiac metastases are neoplastic infiltration but are not generally classified as primary cardiomyopathy. The treatment history should include radiation fields and doses, chemotherapies and elapsed time because late effects can add to age-related diseases.

ECG and echocardiography as the gateway

The ECG may show low voltage, poor R-wave progression, pseudo-necrotic Q waves, blocks and fibrillation in amyloidosis; block and ventricular arrhythmias often dominate in sarcoidosis; tachyarrhythmias and nonspecific abnormalities occur with iron overload. The relationship between echocardiographic thickness and voltage provides a clue, but sensitivity and specificity are limited. The electrophenotype guides etiology only when read with age, imaging and systemic manifestations.

Echocardiography defines wall thickness, cavities, function, atria, valves, effusion, pulmonary pressure and strain. Advanced amyloidosis may show thickened walls and interatrial septum, a small cavity, thick valves and effusion; relative apical sparing of strain is suggestive but not exclusive. Composite morphology is more informative than a wall-thickness cutoff and should not be confused with HCM solely because of a concentric appearance.

Sarcoidosis may cause basal septal thinning, noncoronary regional abnormalities, aneurysms, right ventricular dysfunction or effusion, but echocardiography may be normal in early stages. In hemochromatosis, the phenotype progresses from diastolic to dilated without a specific echocardiographic signature. The echocardiographic limitation is poor tissue typing, which requires magnetic resonance or dedicated techniques when probability remains high.

Natriuretic peptides and troponin quantify stress and injury and have prognostic value in amyloidosis, but are influenced by kidney function, rhythm and treatment. Persistently elevated troponin with preserved function may reflect microvasculopathy or AL toxicity, whereas active sarcoidosis may have normal biomarkers. Circulating biology complements imaging without replacing the search for the precursor.

Magnetic resonance, nuclear medicine and specific measurements

Magnetic resonance shows LGE distribution and measures native T1, T2 and ECV. In amyloidosis, diffuse subendocardial or transmural LGE, abnormal gadolinium kinetics, and high T1 and ECV reflect extracellular expansion; in sarcoidosis, multifocal LGE, often subepicardial or intramyocardial, identifies scar but does not prove activity. The magnetic resonance signature changes probability and prognosis but rarely types the protein by itself.

Scintigraphy with 99mTc-DPD, PYP or HMDP can diagnose cardiac ATTR without biopsy when myocardial uptake is grade 2 or 3, is confirmed by SPECT, and the entire monoclonal screen is negative. If a monoclonal protein is present, AL, ATTR with MGUS or their rare coexistence remain possible and typed tissue is required. The nonbiopsy criterion is a complete algorithm, not simply a positive planar image.

FDG PET assesses inflammatory metabolism in sarcoidosis and requires preparation that suppresses physiologic myocardial glucose use. Focal uptake combined with perfusion defects supports activity, whereas LGE mainly represents damage and scar; the two modalities answer complementary questions. Separation of activity from scar guides immunosuppression and stratification without attributing absolute precision to a single test.

Cardiac T2* decreases with iron and allows reproducible measurement of myocardial burden, particularly important in transfused patients. Elevated ferritin may result from inflammation or liver disease and high saturation describes systemic risk but not the amount in the heart. The T2 star metric also allows response to chelation to be followed before ejection fraction changes.

Tissue, typing and diagnostic pitfalls

Extracardiac biopsy may demonstrate amyloid in periumbilical fat, bone marrow, kidney or another organ, but sensitivity varies by type and a negative result does not exclude cardiac deposition. Endomyocardial biopsy has high sensitivity if adequately sampled, and Congo red with green birefringence confirms amyloid. The presence of the deposit is only the first step: its precursor must be identified.

Mass spectrometry based on laser microdissection is the reference for typing when available because immunohistochemistry may be limited by antibodies, background and contamination. An older patient may have ATTR and MGUS simultaneously, so attributing the deposit to a light chain without proof is dangerous. Proteomic typing prevents a hematologic coincidence from leading to inappropriate chemotherapy.

In sarcoidosis, biopsy of an accessible extracardiac site is preferred when it can confirm granulomas at lower risk, whereas cardiac biopsy can be guided by imaging or electroanatomic mapping to increase yield. Noncaseating granulomas require exclusion of infection and other causes. Histologic specificity depends on microbiological and clinical context, not on granuloma shape alone.

In iron overload, liver biopsy can assess damage and systemic deposition, but magnetic resonance has reduced the need for cardiac tissue. In storage diseases, biopsy or enzymatic/genetic tests can define the defect, with attention to pseudodeficiencies and variants. The etiology-specific method avoids the idea that every infiltrative cardiomyopathy requires biopsy of the same organ.

Causal therapy and cardiology management

Therapy for amyloidosis reduces production of or stabilizes the precursor: in AL it urgently suppresses the plasma-cell clone, while in ATTR transthyretin stabilizers and silencers slow progression according to indications. Existing deposits may regress slowly or persist, so a hematologic response does not immediately equal cardiac recovery. The speed of causal control is particularly critical in AL, where circulating toxicity contributes to early mortality.

Active sarcoidosis is treated with corticosteroids and, when necessary, steroid-sparing immunosuppressants, whereas arrhythmias, blocks and sudden-death risk may require ICDs and ablation. Suppressed inflammation does not automatically eliminate arrhythmogenic scar. The dual target of activity and substrate requires immunology and electrophysiology to proceed together.

In hereditary iron overload, phlebotomy removes iron when hemoglobin and clinical conditions permit; in transfusional forms, chelators are used. Iron-related cardiac dysfunction can improve substantially with intensive treatment, but the choice depends on burden, organs, hematopoiesis and urgency. Iron reversibility makes early cardiac measurement essential before overt heart failure develops.

Diuretics, anticoagulation, rhythm control and devices are adapted to physiology and cause. Dysautonomia in amyloidosis limits vasodilators; sarcoidosis may require defibrillation despite relatively preserved function; iron overload and some metabolic diseases may recover after therapy. Supportive cardiology is not interchangeable among different infiltrative diseases and must be coordinated with the causal strategy.

Heart transplantation is possible in selected patients, but systemic disease and persistent precursor production must be controlled. In AL, depth of clonal response and organ involvement are assessed; in ATTR, neuropathy and pharmacologic strategy are considered; in sarcoidosis, extracardiac activity and recurrence. Transplant selection integrates noncardiac prognosis and the possibility of controlling the cause, not ventricular function alone.

Tissue distribution and phenotypic overlap

The same substance can produce different phenotypes according to duration, quantity and site. Predominantly ventricular deposition generates restriction and low output, atrial involvement promotes stasis and thrombosis, conduction-system involvement causes bradycardia and blocks, while microvascular involvement may cause angina and elevated troponin without epicardial coronary stenoses. The regional phenotype explains why two patients with the same etiology may present with heart failure, syncope or arrhythmia, respectively.

Phase also changes the image. In amyloidosis, increased wall thickness may be absent at onset and become evident after years; in iron overload, diastolic dysfunction may precede dilation; in sarcoidosis, edema and focal thickening during the active phase may leave thinning and scar aneurysm. Temporal interpretation prevents tests performed at different biological times from being considered incompatible.

Phenotypes may also overlap with common conditions. Hypertension and aortic stenosis do not exclude ATTR, coronary disease may coexist with sarcoidosis, and fatty liver does not automatically explain elevated ferritin. Determining which process drives limitation requires comparing severity, distribution and proportionality of findings. Pathological coexistence is more common than the reassuring idea of one diagnosis per patient.

Age guides but does not decide. Wild-type ATTR is typical of older adults, whereas TTR variants, lysosomal diseases and genetic forms may emerge earlier; AL may present in middle or advanced age and sarcoidosis spans a wide range. An age-based prior serves to rank hypotheses, not to erase a constellation of signs incompatible with the most common cause.

When tissue is necessary

The decision to biopsy arises from the expected incremental value. If validated criteria permit noninvasive ATTR diagnosis and monoclonal screening is truly negative, cardiac biopsy is not routine; if a monoclonal component appears, scintigraphy is discordant or the phenotype is atypical, knowing the fibril type radically changes therapy. A decision-oriented biopsy answers a concrete fork in the pathway rather than simple morphological curiosity.

The site is chosen by comparing yield and risk. Abdominal fat, bone marrow, kidney, liver, skin, lymph node or lung may provide material in systemic diseases, but negativity at a low-sensitivity site does not close the case. Endomyocardial biopsy becomes appropriate when the heart is the only convincing organ or when alternatives require mutually incompatible treatments. A representative sample matters as much as staining quality.

The report should include methods and limitations. Congo red and birefringence identify amyloid but not its type; granulomas require a search for microorganisms and differential diagnosis; siderosis must be interpreted with distribution and context; negative staining does not exclude focal infiltration. Integrated pathology compares slide, imaging, laboratory tests and history before converting a finding into an etiologic diagnosis.

Previous samples can be re-evaluated. Tissue obtained for carpal tunnel syndrome, spinal stenosis, prosthetic surgery, renal biopsy or lymph-node biopsy may contain decisive information if retrieved and typed with appropriate methods. This strategy may avoid a new procedure but requires verification of quantity, preservation and representativeness. Diagnostic reuse of tissue is particularly useful when clinical probability has changed after years.

Monitoring response and progression

Following an infiltrative cardiomyopathy means measuring two distinct processes: activity of the cause and cardiac consequence. Light chains, transthyretin production, inflammatory uptake or iron burden may change before pressures, strain and functional capacity; conversely, congestion or arrhythmia may worsen despite biological control. The two-level response prevents declaring failure or cure on the basis of a single indicator.

The common core includes symptoms, supine and standing blood pressure, weight, volume signs, ECG, rhythm, renal function, electrolytes, natriuretic peptides and echocardiography. Frequency depends on instability and therapy: weeks during high-risk phases or after major changes, months in routine control, and longer intervals in carriers without phenotype. A proportionate schedule concentrates resources when a change can alter treatment.

Specific measurements remain etiologic. In AL, the speed of hematologic response is crucial; in ATTR, cardiac and neurologic trajectories are integrated; in sarcoidosis, inflammatory activity is distinguished from scar; in iron overload, T2* documents myocardial removal. The appropriate metric must have a demonstrated relationship with the process intended to be modified.

Serial imaging does not mean indiscriminately repeating every test. Echocardiography and strain are accessible but depend on loading and rhythm; magnetic resonance and ECV characterize tissue but have costs, contraindications and variability; PET requires preparation and a question about activity; bone scintigraphy is not a routine quantitative ATTR response test. Purposeful repetition avoids radiation and spurious interpretation of minimal changes.

Outcomes that matter to the patient include dyspnea, syncope, hospitalizations, independence, neuropathy, orthostatic tolerance and quality of life. A favorable biomarker does not compensate for toxicity that eliminates ambulation, whereas functional stability may represent success in a naturally progressive disease. The overall clinical trajectory links biological efficacy, safety and individual goals.

From clue to appropriate pathway

The pathway begins with a precise clinical question: unexplained thickened wall, block, arrhythmia, restriction or heart failure. Age, systemic history and ECG define probability; echocardiography and magnetic resonance localize and characterize damage; laboratory tests and nuclear medicine test specific hypotheses. The probabilistic sequence reduces delays without turning every patient with HFpEF into a recipient of the same panel.

Suspected amyloid requires immediate complete monoclonal screening because the priority is not to miss AL. If negative, scintigraphy can confirm ATTR in the appropriate context; if positive or discordant, typed biopsy resolves the fork. Suspected sarcoid requires inflammatory imaging and a search for extracardiac sites; suspected iron requires T2*. Etiologic branching is more efficient than an identical sequence for all cardiomyopathies.

The diagnostic conclusion should state cause, certainty, extent of cardiac involvement, activity, function, arrhythmias and organs involved. Saying only infiltrative cardiomyopathy is insufficient for prescribing therapy or communicating prognosis. An operational diagnosis makes clear what is proven, what remains probable and which result could change the strategy.

Care links cardiology, imaging, hematology, neurology, pulmonology, rheumatology, genetics and metabolism according to the disease. Follow-up simultaneously verifies causal response and cardiac consequences because one may precede the other and an isolated biomarker may mislead. Structured multidisciplinarity is not a sum of consultations but a single plan with shared goals and timing.