Restrictive cardiomyopathy (RCM) is a phenotype of myocardial disease characterized predominantly by impaired ventricular filling, with increased myocardial stiffness, a rapid rise in diastolic pressures in response to small increases in filling volume, non-dilated ventricles and atrial dilatation. Systolic function, measured as left ventricular ejection fraction (LVEF), may be preserved in the early or intermediate stages, but this does not mean that the heart is functioning normally: cardiac output is often limited by the reduced filling capacity, atrial and venous pressures rise early, and the patient develops pulmonary congestion, systemic congestion or both, even in the absence of a dilated ventricular cavity.
Restrictive cardiomyopathy is the least frequent of the major cardiomyopathic phenotypes, but it is one of the most complex from a diagnostic perspective because it does not identify a single cause. It may be primary, idiopathic or genetic, or secondary to infiltrative, storage, inflammatory, endomyocardial, toxic, overload-related or systemic diseases. The most important causes include cardiac amyloidosis, cardiac sarcoidosis, hemochromatosis and iron overload, Fabry disease, endomyocardial fibrosis, hypereosinophilic syndromes, lysosomal storage disorders, desmin-related cardiomyopathies, familial sarcomeric forms and some post-radiation or post-surgical conditions. Its clinical relevance derives from the fact that many forms are recognized late, when congestion, atrial fibrillation, pulmonary hypertension, thromboembolic events or advanced heart failure are already present.
Restrictive cardiomyopathy must first be interpreted as a pathophysiological model and only then as an etiological diagnosis. The common feature is the loss of ventricular compliance, but the biological reasons for this stiffness vary considerably. In some forms, the problem is intrinsic to the cardiomyocyte, as in genetic variants that alter the sarcomere, cytoskeleton or intermediate proteins. In other forms, the myocardium becomes stiff because the interstitium is infiltrated by pathological material, such as amyloid fibrils, granulomas, iron or lysosomal storage products. In others, the primary injury involves the endocardium and subendocardial region, with fibrosis, apical obliteration, papillary muscle adhesion and deformation of the atrioventricular valve apparatuses.
Primary and familial forms are rare, but essential to recognize. They may result from pathogenic variants in sarcomeric genes, including TNNI3, TNNT2, MYH7, MYBPC3, ACTC1, MYL2 and MYL3, or from non-sarcomeric genes such as DES, FLNC, BAG3 and LMNA. Variants in TNNI3, which encodes cardiac troponin I, are among the most frequently described in familial restrictive forms and may produce severe diastolic dysfunction with absent or modest hypertrophy, markedly dilated atria and normal-sized ventricles. In these cases, the sarcomere does not necessarily produce a hypertrophic cavity as in hypertrophic cardiomyopathy, nor a dilated cavity as in dilated cardiomyopathy, but rather a stiff ventricle in which relaxation and distensibility are disproportionately impaired.
Infiltrative forms are dominated by the accumulation of substances in the interstitial space or within myocardial tissue. In cardiac amyloidosis, insoluble fibrils derived from immunoglobulin light chains in AL amyloidosis or from transthyretin in ATTR amyloidosis are deposited between cardiomyocytes, expand extracellular volume, separate fibers, compress the microcirculation and increase wall stiffness. In AL amyloidosis, there is also direct light-chain toxicity on cardiomyocytes, which may explain rapid progression, very high biomarkers and severe heart failure even when wall thickness is not extreme. In ATTR amyloidosis, whether wild-type or hereditary, accumulation is often slower, but it may become clinically important particularly in older adults, in patients with aortic stenosis, bilateral carpal tunnel syndrome, biceps tendon rupture, neuropathy or a compatible family history.
Storage and overload diseases can generate a restrictive phenotype through different mechanisms. In Fabry disease, alpha-galactosidase A deficiency causes accumulation of globotriaosylceramide and globotriaosylsphingosine in cardiomyocytes, endothelium, smooth muscle cells, the conduction system and other tissues; the result may be left ventricular hypertrophy, microvascular ischemia, inferolateral fibrosis, arrhythmias and diastolic dysfunction. In hereditary hemochromatosis or iron overload secondary to chronic transfusions, iron is deposited in the myocardium and causes oxidative stress, mitochondrial injury, calcium disturbance and cell death. Iron cardiomyopathy may begin with restrictive physiology, but it can evolve toward systolic dysfunction and dilation if the damage progresses.
Cardiac sarcoidosis produces restriction only in a subset of patients, but it must be considered because it may present with atrioventricular block, ventricular tachycardia, syncope, heart failure, septal abnormalities or suggestive cardiac magnetic resonance patterns. The mechanism is non-caseating granulomatous infiltration of the myocardium, followed by edema, necrosis, fibrosis and electrical discontinuity. When inflammation and scar predominate, the physiology may be restrictive, arrhythmogenic or dilated, or may combine several phenotypes. The disease may appear as isolated cardiac involvement or together with pulmonary, lymph node, cutaneous, ocular or neurological sarcoidosis.
Endomyocardial diseases represent another pathway to restriction. In tropical endomyocardial fibrosis and hypereosinophilic syndromes, the injury often begins with endocardial damage, eosinophilic degranulation, protein toxicity, mural thrombosis and subsequent fibrous organization. Fibrosis may obliterate the ventricular apices, incorporate papillary muscles, narrow the effective cavity, cause mitral or tricuspid regurgitation and lead to severe congestion. In the early stage, a necrotic-inflammatory component may predominate; in the thrombotic stage, intracavitary thrombi appear; in the fibrotic stage, restriction becomes stable and often difficult to reverse.
Risk factors and clinical modifiers depend on the cause. Advanced age, male sex, aortic stenosis, bilateral carpal tunnel syndrome, peripheral neuropathy, dysautonomia, proteinuria, macroglossia, periorbital ecchymoses, monoclonal gammopathy, a family history of amyloidosis or heart failure with non-dilated ventricles suggest amyloidosis. Origin from tropical or subtropical areas, nutritional poverty, environmental exposures, eosinophilia, parasitic diseases and a history of disproportionate ascites suggest endomyocardial fibrosis. Neuropathy, angiokeratomas, acroparesthetic pain, hypohidrosis, renal failure, stroke at a young age or unexplained hypertrophy suggest Fabry disease. Atrioventricular block, mediastinal lymphadenopathy, uveitis, skin lesions or an inflammatory pattern on magnetic resonance imaging suggest sarcoidosis.
The restrictive heart is hemodynamically characterized by a cavity that accepts little volume before pressure rises markedly. During early diastole, blood enters rapidly because atrial pressure is elevated and the atrioventricular gradient is significant; immediately afterward, however, filling stops because the stiff ventricle rapidly reaches the limit of distensibility. This produces the classic restrictive filling profile, with high E waves, short deceleration time and high filling pressures. Cardiac catheterization may show a “dip and plateau” profile, or square root sign, reflecting rapid early filling followed by a diastolic pressure plateau.
The earliest pathophysiological consequence is atrial dilatation. The atria work against stiff ventricles, sustain chronically elevated pressures and progressively dilate. Atrial dilatation is not a trivial secondary finding: it promotes atrial fibrillation, atrial flutter, atrial thrombosis, loss of the atrial contribution to filling and further hemodynamic deterioration. In a restrictive ventricle, atrial contraction is often decisive for maintaining adequate output; when atrial fibrillation occurs, even without an extreme rate, the patient may rapidly move from relative compensation to severe dyspnea, pulmonary congestion or low output.
Elevated left atrial pressure is transmitted to the pulmonary venous circulation and generates dyspnea, post-capillary pulmonary hypertension and, over time, right ventricular overload. If the right ventricle is also directly affected by the disease or secondarily damaged by chronically elevated pulmonary pressures, jugular venous distension, hepatomegaly, ascites, dependent edema and functional tricuspid regurgitation appear. Many patients with a restrictive phenotype come to medical attention precisely because of right-sided congestion that is disproportionate to the apparently preserved LVEF.
Systolic function may appear preserved because the percentage of blood ejected from a small or normal-sized cavity remains apparently normal. This finding can be misleading. Absolute stroke volume may be reduced because end-diastolic volume is low; reserve during exertion is limited because the ventricle cannot adequately increase filling; myocardial oxygen consumption may be high in infiltrative or hypertrophic forms; subendocardial perfusion may decrease because of increased diastolic pressure. Therefore, LVEF alone does not describe the severity of restrictive disease.
Final progression varies according to etiology. In pediatric or familial genetic forms, refractory heart failure with small ventricles and massively dilated atria may predominate. In AL amyloidosis, the trajectory may be rapid if light-chain production is not controlled. In ATTR amyloidosis, progression is often slower but cumulative, with increasing stiffness and conduction disturbances. In sarcoidosis, arrhythmic risk may dominate over congestion. In advanced endomyocardial fibrosis, endocardial and valvular deformation produces severe mechanical restriction. The pathophysiology is therefore common in its filling profile, but not in its pace, reversibility or therapeutic implications.
The clinical presentation of restrictive cardiomyopathy is often insidious because LVEF may be preserved and symptoms are initially attributed to age, chronic obstructive pulmonary disease, anemia, obesity, liver disease, renal failure or heart failure with preserved ejection fraction of undefined origin. Suspicion arises when dyspnea, congestion, atrial dilatation, arrhythmias, elevated biomarkers or systemic signs are not explained by hypertension, coronary artery disease, valvular disease or pericardial disease. The medical history must therefore search not only for cardiac symptoms, but also for extracardiac traces of the causal disease.
The most frequent symptom is exertional dyspnea. The patient reports progressive reduction in exercise tolerance, breathlessness when walking uphill, difficulty climbing stairs, the need to stop more often or shortness of breath during activities previously well tolerated. Dyspnea results from increased left-sided filling pressures and retrograde transmission to the pulmonary circulation. In more advanced stages, orthopnea, paroxysmal nocturnal dyspnea, congestion-related cough and, in acute cases, pulmonary edema occur. The characteristic feature is that these symptoms may coexist with non-dilated ventricles and an apparently normal LVEF.
Fatigue is equally important. It does not depend only on deconditioning, but on reduced absolute stroke volume, inability to increase output during exercise, autonomic dysfunction in some infiltrative forms, anemia or systemic involvement. In AL or ATTR amyloidosis, weight loss, marked asthenia, orthostatic hypotension, peripheral neuropathy, gastrointestinal disturbances or carpal tunnel syndrome may be associated. In Fabry disease, neuropathic pain, heat intolerance, hypohidrosis, renal disorders or a history of stroke may appear. In sarcoidosis, cough, pulmonary dyspnea, low-grade fever, uveitis, skin lesions or lymphadenopathy may be present.
Symptoms of right-sided congestion may dominate the picture. The patient may report ankle swelling, weight gain from fluid retention, abdominal tension, early satiety, nausea, pain or heaviness in the right upper quadrant, ascites, reduced diuresis and nocturia. In some forms, especially endomyocardial fibrosis predominantly affecting the right side or advanced amyloidosis, ascites may be disproportionate to pulmonary findings and may initially lead to hepatological evaluation. Chronic venous congestion may cause congestive hepatopathy, malabsorption, sarcopenia and worsening nutritional status.
Palpitations are frequent and often indicate atrial fibrillation, atrial flutter, supraventricular tachycardias or ventricular arrhythmias. In restrictive patients, atrial fibrillation is particularly poorly tolerated because it eliminates the atrial contribution to already impaired filling. Even a moderately elevated rate can reduce diastolic time and abruptly increase pulmonary venous pressure. The patient may present with sudden worsening of dyspnea, pulmonary edema, dizziness or syncope after onset of atrial arrhythmia.
Syncope and presyncope may result from low output, ventricular arrhythmias, atrioventricular block, autonomic dysfunction, orthostatic hypotension or severe restriction. Syncope is particularly concerning in the presence of cardiac sarcoidosis, amyloidosis with conduction disturbances, genetic forms involving the electrical system or extensive myocardial fibrosis. In these cases, assessment must distinguish hemodynamic syncope due to inability to increase output from arrhythmic syncope, because the implications for monitoring, pacemaker implantation or defibrillator use differ.
Chest pain may be present even without epicardial coronary artery disease. In amyloidosis, it may result from microvascular dysfunction, vascular infiltration and increased filling pressures; in Fabry disease, from microvascular ischemia and hypertrophy; in sarcoidosis, from myocardial inflammation; in iron overload, from myocardial injury and associated arrhythmias. However, coronary artery disease may coexist, especially in older adults, and must not be excluded solely because the phenotype is restrictive.
History-taking must specifically explore family history. Heart failure with preserved ejection fraction, early pacemaker implantation, sudden death, neuropathy, renal failure, amyloidosis, heart transplantation, undefined cardiomyopathy, muscle diseases, stroke at a young age or unexplained death may suggest a hereditary basis. In relatives of a patient with a TTR, GLA, TNNI3, DES, FLNC or other cardiomyopathy gene variant, even mild symptoms deserve attention because early diagnosis can modify surveillance and treatment.
On physical examination, blood pressure may be normal or low; in advanced amyloidosis and in forms with dysautonomia, orthostatic hypotension is common. The pulse may be irregular in atrial fibrillation, rapid during congestive phases or relatively slow in the presence of conduction disturbances. Jugular venous distension is a highly valuable finding because it reflects increased right-sided pressures; it may be associated with a prominent y descent, hepatojugular reflux and signs of systemic congestion. This finding may resemble constrictive pericarditis, which is why the differential diagnosis between myocardial restriction and pericardial constriction is a central point in subsequent assessment.
Cardiac auscultation may reveal a third heart sound, a fourth heart sound if sinus rhythm is maintained, murmurs from functional mitral or tricuspid regurgitation and signs of pulmonary hypertension. In infiltrative pictures, muffled heart sounds or signs of pericardial effusion may be present. Lung examination may show bibasal crackles or pleural effusion, but in patients with predominant right-sided congestion, the lungs may be relatively clear despite significant ascites and edema. Abdominal examination may reveal tender hepatomegaly, ascites and, in chronic cases, signs of persistent hepatic congestion.
The general examination must look for extracardiac clues. Macroglossia, periorbital ecchymoses, purpura, bilateral carpal tunnel syndrome, peripheral neuropathy or proteinuria suggest AL or ATTR amyloidosis depending on the context. Angiokeratomas, hypohidrosis, acroparesthetic pain, corneal changes, renal failure and an X-linked family history suggest Fabry disease. Lymphadenopathy, skin lesions, uveitis or respiratory signs suggest sarcoidosis. Hyperpigmentation, diabetes, hypogonadism, liver disease and arthropathy suggest hemochromatosis. Eosinophilia, thrombosis, rash, asthma, parasitosis or origin from endemic areas suggest eosinophilic disease or endomyocardial fibrosis.
The correct clinical sequence is therefore progressive: it begins with symptoms of congestion, low functional reserve, arrhythmia or syncope; it assesses whether the apparently preserved LVEF is consistent with high filling pressures and dilated atria; it searches for systemic signs indicating a specific cause; finally, it establishes the degree of urgency. A patient with rapidly progressive heart failure, very high biomarkers, hypotension, syncope, conduction block, ventricular arrhythmias or suspected AL amyloidosis requires an accelerated pathway, because some restrictive forms have an unfavorable prognosis if etiological treatment is delayed.
The diagnosis of restrictive cardiomyopathy is not based on a single examination, but on the integration of filling physiology, cardiac morphology, exclusion of constrictive pericarditis, recognition of the etiology and stratification of complications. The first error to avoid is generically diagnosing heart failure with preserved ejection fraction without explaining why the atria are dilated, why natriuretic peptides are elevated, why conduction disturbances are present or why the ventricle is not dilated despite severe congestion. The second error is stopping at the word “restrictive” without looking for amyloidosis, Fabry disease, iron, sarcoidosis, endomyocardial fibrosis or a primary genetic form.
According to the 2023 ESC guidelines and the contemporary definition proposed in the specialist literature, the phenotypic diagnosis of restrictive cardiomyopathy requires documentation of a persistent restrictive pathophysiology with non-dilated ventricles and atrial dilatation, independently of wall thickness and systolic function, and exclusion of extracardiac or pericardial conditions capable of producing the same hemodynamic profile. In practice, the following elements must be integrated:
The 12-lead electrocardiogram is often abnormal but not specific. It may show atrial fibrillation, atrial flutter, low voltages, pseudoinfarction patterns, atrioventricular block, bundle branch block, repolarization abnormalities, signs of hypertrophy or ventricular arrhythmias. The discordance between apparently thickened walls on echocardiography and low electrocardiographic voltages is a classic sign of amyloidosis, although it is not always present. Pre-excitation may suggest some storage diseases, while atrioventricular block or ventricular tachycardia in a relatively young patient should raise suspicion of sarcoidosis, laminopathies, desminopathies or infiltrative forms.
Laboratory testing must be organized on two levels. The first assesses heart failure, organ damage and comorbidities: N-terminal pro-B-type natriuretic peptide (NT-proBNP) or B-type natriuretic peptide (BNP), troponin, complete blood count, creatinine, estimated glomerular filtration rate, electrolytes, transaminases, bilirubin, albumin, iron profile, ferritin, transferrin saturation, glucose, glycated hemoglobin, thyroid-stimulating hormone (TSH), C-reactive protein and urinalysis. The second level searches for specific causes: serum and urine immunofixation, serum free light chains, transthyretin testing when indicated, alpha-galactosidase A and globotriaosylsphingosine for Fabry disease, targeted genetic testing, autoimmune markers, eosinophils, serologies and hematological evaluations according to context.
Transthoracic echocardiography is the most important initial examination. In restrictive forms, it shows non-dilated ventricles, dilated atria, preserved or reduced systolic function, impaired diastolic function, often elevated pulmonary pressure, a dilated inferior vena cava in congestive cases and functional mitral or tricuspid regurgitation. Transmitral Doppler may show a high E/A ratio, short deceleration time and signs of rapid early filling; tissue Doppler may show reduced e’ velocities, while the E/e’ ratio may support elevated filling pressures. Global longitudinal strain may reveal subclinical dysfunction; in amyloidosis, relative apical sparing compared with basal and mid segments is suggestive, although this finding is not pathognomonic.
Echocardiography must also assess the valve apparatuses and endocardium. In endomyocardial fibrosis, apical obliteration, organized thrombi, endocardial thickening, papillary muscle deformation and mitral or tricuspid regurgitation may appear. In amyloidosis, valvular thickening, thickened interatrial septum, mild pericardial effusion, increased wall thickness and dilated atria may be present. In sarcoidosis, findings may be more focal and include regional abnormalities, septal thinning or thickening, aneurysms and ventricular dysfunction disproportionate to symptoms.
Cardiac magnetic resonance (CMR) is central for tissue characterization and differential diagnosis. Late gadolinium enhancement (LGE) may show a diffuse subendocardial or transmural pattern in amyloidosis, an inferolateral pattern in Fabry disease, a patchy mid-wall or subepicardial pattern in sarcoidosis, and endocardial fibrosis and thrombi in endomyocardial fibrosis. T1 mapping and extracellular volume (ECV) are particularly useful: elevated native T1 and ECV values suggest amyloidosis or diffuse fibrosis, whereas low native T1 may suggest Fabry disease or iron overload. T2* sequences allow quantification of myocardial iron and are essential when cardiac hemosiderosis is suspected.
Nuclear medicine has a decisive role in transthyretin amyloidosis. Scintigraphy with bone tracers, such as 99mTc-pyrophosphate, 99mTc-3,3-diphosphono-1,2-propanodicarboxylic acid or 99mTc-hydroxymethylene diphosphonate, may allow non-invasive diagnosis of ATTR amyloidosis when cardiac uptake is high-grade and the search for a monoclonal component is negative. This step is crucial because positive uptake in the presence of monoclonal gammopathy does not automatically allow ATTR to be concluded: AL amyloidosis must be rigorously excluded, given its different treatment and more rapid prognosis. After diagnosis of ATTR amyloidosis, wild-type and hereditary forms must be distinguished through analysis of the TTR gene.
Fluorodeoxyglucose positron emission tomography (PET) may be useful in cardiac sarcoidosis to identify active inflammation, guide immunomodulatory therapy and monitor response, provided that metabolic preparation is correct. Computed tomography can assess pericardial calcifications, pericardial thickness, coronary anatomy, masses, lymphadenopathy and some extracardiac causes. Invasive coronary angiography or coronary computed tomography is indicated when age, chest pain, troponin, risk factors or regional abnormalities require exclusion of coronary artery disease.
Cardiac catheterization is now less commonly used as a first-line examination, but it remains decisive when imaging and clinical findings do not distinguish myocardial restriction from constrictive pericarditis. In restriction, elevated filling pressures and a dip and plateau profile are observed, but the differential diagnosis with constriction requires analysis of respiratory variation, ventricular interdependence and concordance or discordance between ventricular systolic pressures. In constrictive pericarditis, ventricular interdependence and respiratory discordance are more marked; in myocardial restriction, intrinsic myocardial stiffness predominates, with less dependence on respiratory variation. The distinction is essential because pericardiectomy may be curative in constriction, whereas it does not correct primary myocardial stiffness.
Endomyocardial biopsy is the definitive examination when the diagnosis remains uncertain or when the result changes treatment. It may demonstrate amyloid with Congo red staining and apple-green birefringence, type the protein with immunohistochemistry or mass spectrometry, and reveal sarcoid granulomas, iron accumulation, storage diseases, myocarditis, eosinophilic infiltrates or endomyocardial fibrosis. In patchy diseases, such as sarcoidosis, sensitivity may be limited if the sample does not reach the affected area; integration with imaging may increase diagnostic yield. Biopsy should not be used indiscriminately, but it must not be delayed when the specific diagnosis is essential.
Genetic testing is indicated when there is familial aggregation, young onset, a primary restrictive phenotype, suspected Fabry disease, hereditary ATTR amyloidosis, desmin-related cardiomyopathy, a sarcomeric form or a multisystemic picture. It must be preceded by genetic counseling, because a positive result may initiate cascade screening of relatives, whereas a variant of uncertain significance must not be transformed into a definite cause. In first-degree relatives, electrocardiogram, echocardiography, CMR and targeted genetic testing, when the familial variant is known, allow presymptomatic diagnosis and surveillance.
The differential diagnosis includes constrictive pericarditis, heart failure with preserved ejection fraction due to hypertension or aging, hypertrophic cardiomyopathy, dilated cardiomyopathy in a non-advanced phase, valvular disease, ischemic heart disease, primary pulmonary hypertension, liver disease with ascites, nephropathy with edema, chronic obstructive pulmonary disease and anemia. The key is not to confuse the clinical consequence, namely congestion and exercise intolerance, with the cause. A patient with ascites and jugular venous distension may appear to have liver disease, but the combination of dilated atria, non-dilated ventricles, high filling pressures and systemic signs must bring the reasoning back to the heart.
Treatment of restrictive cardiomyopathy must be built on two levels: control of congestion and treatment of the cause. Symptomatic treatment of heart failure alone is often insufficient, because some etiologies have specific pathways that modify the natural history. AL amyloidosis requires timely hematological treatment; ATTR amyloidosis may benefit from transthyretin stabilization or reduction according to specific indications; Fabry disease has enzyme therapies or chaperone therapy in selected patients; iron overload requires iron removal or chelation; sarcoidosis requires control of inflammation; advanced endomyocardial fibrosis may require surgery. When the cause remains idiopathic or genetic without specific treatment, management focuses on congestion, rhythm, thromboembolic events, devices and early evaluation for transplantation in progressive cases.
Fluid control is the symptomatic cornerstone. Loop diuretics reduce pulmonary congestion, edema, ascites and jugular venous distension, but they must be used precisely because the restrictive heart depends on preload to maintain output. Excessive diuresis may cause hypotension, worsening renal function, syncope and low output; insufficient diuresis maintains elevated venous pressures, hepatic congestion, effusions and dyspnea. In patients with significant ascites or resistant congestion, diuretic combinations, close monitoring of electrolytes and renal function, education on body weight and frequent reassessment may be necessary.
Standard therapies for heart failure with reduced ejection fraction do not have the same role when LVEF is preserved and the dominant problem is restriction. Renin-angiotensin-aldosterone system inhibitors, beta-blockers, mineralocorticoid receptor antagonists (MRA) and sodium-glucose cotransporter 2 inhibitors (SGLT2i) may be indicated for comorbidities, hypertension, nephropathy, diabetes, heart failure or reduced LVEF, but they do not replace etiological treatment. Beta-blockers and calcium-channel blockers must be used cautiously in advanced amyloid forms or in the presence of conduction disturbances, because they may worsen low output, bradycardia or hypotension.
Atrial fibrillation requires aggressive management. Maintenance of sinus rhythm may be hemodynamically important because atrial contraction contributes to ventricular filling. Cardioversion, selected antiarrhythmics or ablation may be considered according to arrhythmia duration, atrial size, underlying cause and procedural risk. Rate control must avoid both tachycardia, which shortens diastole, and excessive bradycardia, which may reduce output in patients with fixed stroke volume. Anticoagulation is often necessary in the presence of atrial fibrillation, thrombi, amyloidosis with high atrial risk or endomyocardial fibrosis with intracavitary thrombosis, according to clinical evaluation and bleeding risk.
In AL amyloidosis, treatment is urgent and must be coordinated with expert hematology. The goal is to rapidly suppress the plasma cell clone responsible for light-chain production, using anti-plasma cell regimens and, in selected patients, autologous hematopoietic stem cell transplantation. Prognosis depends strongly on cardiac stage, NT-proBNP and troponin levels, hematological response and the speed with which light-chain production is reduced. Cardiology support requires particular attention because hypotension, dysautonomia, nephropathy and frailty limit many common heart failure therapies.
In ATTR amyloidosis, treatment aims to stabilize transthyretin or reduce its production, according to phenotype, availability, regulatory indications and patient characteristics. Tafamidis has demonstrated benefit in patients with ATTR cardiomyopathy, reducing mortality and cardiovascular hospitalizations in controlled studies. Other strategies that reduce hepatic transthyretin production or stabilize its structure have taken on an increasing role in selected contexts. After diagnosis of ATTR amyloidosis, it is essential to distinguish wild-type from hereditary forms, because hereditary disease requires genetic counseling and family screening.
In Fabry disease, treatment should be started before myocardial fibrosis and organ damage are advanced. Enzyme replacement therapy and, for amenable variants, chaperone therapy can reduce lysosomal burden and slow progression, but cardiac benefit is greater in the early stages, before replacement fibrosis becomes extensive. Cardiology treatment includes management of arrhythmias, hypertrophy, microvascular ischemia, renal failure, stroke and conduction disturbances. Family evaluation is essential because X-linked transmission does not protect women from clinically relevant cardiac manifestations.
In iron overload, iron removal is the causal therapy. In hereditary hemochromatosis, therapeutic phlebotomy is effective especially before advanced cardiac damage appears; in transfusional forms or when phlebotomy is not feasible, chelation strategies are used under hematological expertise. CMR with T2* allows myocardial iron monitoring and guides treatment intensity. Cardiac recovery is possible if damage is detected before irreversible fibrosis or advanced dysfunction develops.
In cardiac sarcoidosis, treatment aims to control granulomatous inflammation, prevent scar formation and reduce arrhythmic events. Corticosteroids represent the initial basis in many patients with active inflammation, often associated with or followed by steroid-sparing immunomodulation when necessary. Therapy must be guided by clinical findings, CMR, PET, ventricular function, conduction disturbances and arrhythmias. Pacemakers, implantable cardioverter-defibrillators (ICD) or ablation may be necessary when atrioventricular block, ventricular tachycardia or arrhythmogenic scar dominate the picture.
In hypereosinophilic syndromes and endomyocardial fibrosis, treatment depends on the stage. In the inflammatory or active eosinophilic phase, controlling the hematological, immunological, parasitic or clonal cause may prevent progression. When intracavitary thrombi are present, anticoagulation may be required. In the advanced fibrotic phase, medical therapy improves congestion but does not remove the endocardial mechanical obstacle; in selected patients, endocardiectomy, endocardial decortication and valve repair or replacement may improve symptoms, but they carry high risk and require experienced centers.
Devices are used according to the dominant problem. The pacemaker is indicated in symptomatic or advanced atrioventricular block, frequent in amyloidosis and sarcoidosis. ICD is indicated for secondary prevention after major ventricular arrhythmias and may be considered for primary prevention in selected patients with sarcoidosis, ventricular dysfunction, extensive scar, arrhythmic syncope or other high-risk conditions. In advanced amyloid forms, the decision on ICD must be individualized because death may also result from electromechanical dissociation or progressive heart failure, not only from defibrillatable tachyarrhythmias.
Heart transplantation is an option for selected patients with advanced and refractory restrictive heart failure, but candidacy depends on etiology, age, extracardiac involvement, pulmonary hypertension, renal function, nutritional status and control of systemic disease. In AL amyloidosis, adequate hematological control must be achieved; in genetic or idiopathic forms, familial risk and extracardiac involvement must be assessed; in systemic infiltrative diseases, it must be established whether the heart is the limiting organ or part of a disease that is too extensive. Referral to an advanced center must be early, because delaying until cachexia, severe renal failure or fixed pulmonary hypertension may close the therapeutic window.
Prognosis is highly variable. Pediatric idiopathic forms and some genetic forms may have a severe course, with need for transplantation. Untreated AL amyloidosis has an unfavorable prognosis when the heart is involved, but a deep hematological response markedly improves outcomes. ATTR amyloidosis has a slower course, but produces progressive functional loss if not recognized. Sarcoidosis can be controlled in many cases, but arrhythmias and conduction block remain prognostic determinants. Advanced endomyocardial fibrosis has a limited prognosis when diagnosis and surgery occur late. In all forms, prognosis is worsened by refractory congestion, hypotension, renal failure, hyponatremia, elevated NT-proBNP, persistent troponin, atrial fibrillation, pulmonary hypertension, right-sided involvement, extensive LGE, low output and failure to identify the cause.
The most frequent complication of restrictive cardiomyopathy is heart failure with congestion. Ventricular stiffness increases filling pressures, the atria dilate, the pulmonary and systemic venous circulations are exposed to high pressures, and the patient develops dyspnea, orthopnea, edema, ascites and exercise intolerance. Unlike dilated cardiomyopathy, the ventricular cavity may remain normal or small; for this reason, clinical severity may be underestimated if only LVEF is considered. Chronic congestion damages the kidneys, liver, intestine, skeletal muscle and nutritional status.
Atrial fibrillation is a central complication because it affects a system that depends heavily on atrial function. Atrial dilatation, high pressure, fibrosis and infiltration promote atrial arrhythmias; when sinus rhythm is lost, ventricular filling immediately worsens. This may cause acute dyspnea, pulmonary edema, hypotension or worsening right-sided congestion. Atrial fibrillation also increases thromboembolic risk, which is particularly relevant in amyloidosis, markedly dilated atria and endomyocardial fibrosis.
Thromboembolic events may affect the brain, limbs, kidneys, spleen, mesenteric circulation or lungs according to site and mechanism. Atrial stasis, atrial fibrillation, intracavitary thrombi, apical obliteration, fibrotic endocardium and some hematological or inflammatory conditions increase risk. In endomyocardial fibrosis and eosinophilic syndromes, the thrombotic phase is part of the natural history; in amyloidosis, risk may be high even when the arrhythmia is intermittent or not yet stably documented. Prevention requires rhythm surveillance, accurate imaging of the chambers and anticoagulation when indicated.
Pulmonary hypertension is a consequence of chronically elevated left atrial pressure. Initially it is post-capillary and potentially reversible; over time, pulmonary vascular remodeling, increased vascular resistance and right ventricular overload may develop. When the right ventricle fails, edema, ascites, congestive hepatopathy and a marked worsening of prognosis appear. Advanced pulmonary hypertension may limit the possibility of heart transplantation if it becomes irreversible.
Right ventricular involvement may be primary or secondary. In amyloidosis, sarcoidosis and endomyocardial fibrosis, the right ventricle may be directly infiltrated, inflamed or fibrotic; in other cases, it is overloaded by increased pulmonary pressures. Right ventricular dysfunction reduces flow to the left ventricle, worsens low output, promotes systemic congestion and makes diuretic management more difficult. The appearance of refractory ascites or persistent jugular venous distension is often a sign of an advanced stage.
Ventricular arrhythmias and sudden death have different weight according to the cause. In cardiac sarcoidosis, granulomatous scar and active inflammation may generate ventricular tachycardia and advanced block. In genetic forms involving desmin, filamin C, lamin A/C or other structural proteins, electrical risk may be high even with non-dilated cavities. In advanced amyloidosis, tachyarrhythmias, bradyarrhythmias, block and electromechanical dissociation may occur. Risk stratification must therefore be etiological, not based only on the LVEF value.
Conduction disturbances are frequent in infiltrative and inflammatory forms. Atrioventricular block, bundle branch block, pauses, symptomatic bradycardia and need for pacemaker implantation may be manifestations of amyloidosis, sarcoidosis, Fabry disease, desminopathies or laminopathies. These disturbances may cause syncope, falls, low output and worsening heart failure. In patients with associated ventricular arrhythmic risk, the choice between a pacemaker and a device with defibrillation function must be weighed before implantation.
Renal dysfunction is common and may result from hypoperfusion, renal venous congestion, diuretics, renal amyloidosis, Fabry disease, diabetes, hypertension or hematological disease. Worsening renal function limits congestion control, increases the risk of electrolyte imbalance, complicates anticoagulation and reduces tolerance to specific therapies. The liver may also be affected by chronic congestion, with cholestasis, increased transaminases, coagulopathy, ascites and congestive fibrosis. These organ injuries are not simple comorbidities, but direct consequences of restrictive hemodynamics.
Cardiac cachexia and frailty appear in advanced stages. Intestinal congestion, early satiety, inflammation, dysautonomia, malabsorption, low output, reduced physical activity and systemic disease reduce muscle mass and nutritional reserves. This worsens exercise tolerance, increases hospitalizations, reduces eligibility for advanced procedures and worsens surgical or transplant outcomes. Nutritional and rehabilitation assessment must therefore be introduced early in follow-up.
Valvular complications derive mainly from atrial dilatation, endocardial deformation, infiltration or tethering of the subvalvular apparatuses. Functional tricuspid regurgitation worsens right-sided congestion; mitral regurgitation increases pulmonary pressures and dyspnea; in endomyocardial fibrosis, papillary muscle entrapment may make regurgitation a structural part of the disease. When the valve defect is secondary to restriction, correcting only the valve without addressing the myocardial substrate may not improve the overall picture.
Cause-specific complications must always be sought. In AL amyloidosis, nephrosis, neuropathy, bleeding, macroglossia, dysautonomia and multiorgan involvement may occur. In ATTR amyloidosis, neuropathy, lumbar stenosis, carpal tunnel syndrome and slow but disabling functional progression are frequent. Fabry disease is associated with renal failure, stroke, neuropathic pain and conduction system disturbances. In sarcoidosis, inflammatory relapses and pulmonary, ocular or neurological involvement may occur. In iron overload, diabetes, liver disease, hypogonadism and arrhythmias may progress together with cardiac damage.
Treatment-related complications include hypotension and renal failure from excessive diuresis, bradycardia from negative chronotropic medications, bleeding from anticoagulation, device infections or malfunction, systemic effects of immunomodulation, toxicity of hematological treatments, surgical complications in endomyocardial fibrosis and recurrence or progression after transplantation in some systemic diseases. These risks do not justify therapeutic inertia, but they require a specialist, multidisciplinary pathway calibrated to the etiology.