Unclassified cardiomyopathies

The designation unclassified cardiomyopathies does not identify a single disease, a common pathogenetic mechanism or a definitive clinical diagnosis. It is mainly a historical category, used in previous taxonomies to collect myocardial abnormalities that did not meet the morphofunctional definitions available at the time.
In contemporary practice the term may still appear in old reports, registries, coding systems or as a provisional label during the diagnostic work-up, but it should not become a permanent container for rare, systemic, toxic or genetic forms that now have a precise identity.
The 2023 European Society of Cardiology guidelines replaced this residual grouping with an approach that starts from the observable phenotype, integrates morphology, function, tissue characterization and electrical profile, and proceeds to investigation of the genetic or acquired cause.

The change is substantial because it separates description of the heart from the name of the disease. A ventricle may be dilated, hypertrophied, stiff, scarred without dilation, or predominantly involved on the right; each configuration represents an entry point into reasoning, not necessarily its conclusion.
The final diagnosis should specify, whenever possible, phenotype, etiology, familial distribution, extracardiac manifestations and determinants of risk. In this model, a pathogenic DSP variant with subepicardial left ventricular scar is no longer relegated to unclassifiable forms, but described as desmoplakin-related non-dilated left ventricular cardiomyopathy; likewise, Fabry disease, amyloidosis, laminopathy or anthracycline cardiomyopathy should be named for what they are.

No reliable prevalence can be assigned to the category. The included populations have changed together with classifications, imaging criteria have undergone major revisions, and many entities historically included in the group were subsequently relocated.
Estimates derived from previous case series therefore describe the behavior of different nosologic systems, not the frequency of a homogeneous disease. The clinically useful epidemiology is that of the modern phenotype and the specific cause once identified.
The current value of this page is therefore to clarify how to interpret a historical label and how to transform an initially indeterminate case into an integrated diagnosis, avoiding both false precision and premature abandonment of etiologic investigation.

Early classifications of cardiomyopathies were developed when echocardiography, magnetic resonance, molecular genetics and immunohistochemical characterization of myocardium were absent or limited.
Nosology therefore had to rely mainly on chamber geometry, hemodynamics and pathology. The 1995 World Health Organization/International Society and Federation of Cardiology report, published in 1996, recognized dilated, hypertrophic, restrictive and arrhythmogenic right ventricular cardiomyopathy, together with unclassified forms.
The residual category had a pragmatic function: it acknowledged that some heart muscle diseases could not be placed in the major groups without forcing them. It did not, however, imply a common etiology or authorize all collected entities to be treated as a single disease.

The 2006 American Heart Association scientific statement adopted a different taxonomy, distinguishing primary cardiomyopathies, in which the heart was the predominantly involved organ, from secondary forms embedded in generalized systemic disorders.
Primary forms were further divided into genetic, mixed and acquired; left ventricular noncompaction was placed among genetic forms and stress cardiomyopathy among acquired forms. This approach foregrounded biological origin, but sometimes made it difficult to classify diseases in which cardiac and systemic involvement overlapped or in which the genetic component had not yet been demonstrated.
The difference from the European model was not merely a terminological dispute: it showed the still-present tension between classification based on the shape of the heart and classification based on cause.

The 2008 ESC position chose a clinical phenotype-centered model. Cardiomyopathies were initially recognized as hypertrophic, dilated, arrhythmogenic right ventricular, restrictive or unclassified, and each phenotype was then distinguished as familial or genetic and non-familial or non-genetic.
Among the unclassified forms, the document discussed mainly left ventricular noncompaction and Takotsubo cardiomyopathy. That choice was consistent with knowledge at the time, but subsequent spread of magnetic resonance and population studies showed that prominent trabeculae can also occur as an isolated or adaptive trait, whereas Takotsubo is an acute syndrome with usually transient dysfunction.
The category thus began to lose cohesion precisely in the two entities that had made it recognizable.

The MOGE(S) system, proposed in 2013 and supported by the World Heart Federation, sought to describe complexity rather than reduce it to a single label.
The nomenclature codes morphofunctional phenotype, involvement of other organs, inheritance pattern, genetic or non-genetic etiology, and functional status. Its conceptual value lies in showing that two patients apparently belonging to the same morphological category may have radically different causes, risks and family needs.
The complexity of the notation has limited everyday use, but the principle of multidimensional description has entered modern practice and helped make the term unclassified progressively less useful.

The ESC 2023 guidelines recognize five cardiomyopathy phenotypes: hypertrophic cardiomyopathy, dilated cardiomyopathy, non-dilated left ventricular cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy and restrictive cardiomyopathy.
The main innovation is explicit inclusion of tissue characterization. Non-ischemic scar or fatty replacement of the left ventricle may be the dominant sign of disease even when there is no dilation or severe systolic dysfunction.
This observation made it possible to recognize NDLVC, non-dilated left ventricular cardiomyopathy, preventing patients with scarred or hypokinetic non-dilated phenotypes from being dispersed among incomplete dilated cardiomyopathy, left arrhythmogenic cardiomyopathy and residual categories.

NDLVC is defined by the presence of non-ischemic scar or fatty replacement of the left ventricle in the absence of dilation, with or without global or regional wall-motion abnormalities, or by isolated global left ventricular hypokinesia without scar.
It is not equivalent to a single genetic disease: it may reflect variants in DSP, FLNC, LMNA, DES, PLN and other genes, or acquired sequelae and phenocopies. Identification therefore requires a second etiologic step.
Its clinical importance lies in the fact that a normal or mildly reduced ejection fraction does not neutralize the risk associated with scar, ventricular arrhythmias, conduction disturbances or specific genotypes.

Left ventricular hypertrabeculation is now considered a morphological trait, not a cardiomyopathy in a general sense. It may be isolated, associated with dilated or hypertrophic cardiomyopathy, present in genetic and congenital diseases, or become more prominent in states of increased preload such as pregnancy and intense athletic activity.
The term noncompaction suggests an embryologic arrest that has not been demonstrated as a universal explanation in humans; for this reason, the ESC task force prefers hypertrabeculation, especially for transient or clearly acquired phenomena in adulthood.
Diagnosis cannot depend on a single morphometric ratio: it must integrate function, dilation, scar, symptoms, arrhythmias, family history and the underlying cause.

Takotsubo syndrome is often called stress cardiomyopathy, but the ESC 2023 guidelines do not recommend classifying it among cardiomyopathies because of the transient nature of the phenomenon.
The syndrome retains its own clinical identity, international diagnostic criteria and important acute risks, including shock, dynamic obstruction, arrhythmias and thrombosis. Excluding it from cardiomyopathy taxonomy does not mean considering it benign or irrelevant; it means distinguishing reversible regional dysfunction from a persistent structural or functional disease of the heart muscle.
It should therefore be discussed in a dedicated monograph, not as a subtype of a residual category.

In practice, a patient may remain temporarily unclassified when the phenotype is very early, imaging is discordant, features of several categories coexist, the disease is evolving, or genetic and family data are missing.
This state of uncertainty should be documented precisely, specifying which elements are present and which hypotheses remain open. It is preferable, for example, to write non-dilated non-ischemic scar phenotype with ventricular arrhythmias under etiologic investigation rather than apply a generic label without operational content.
Longitudinal reclassification is not a diagnostic failure: it is an expected component of cardiomyopathy medicine, characterized by age-dependent penetrance, variable expressivity and progressive remodeling.

Because the category does not define a unitary disease, there is no common etiology. The first task is to distinguish true cardiomyopathy from loading conditions or injury sufficient to explain the abnormality, such as coronary artery disease, hypertension, valvular disease and congenital heart disease.
These conditions may coexist with cardiomyopathy and their presence does not automatically exclude myocardial disease; it is necessary to determine whether severity and distribution of the finding are proportionate. Extensive subepicardial scar, early ventricular arrhythmias or a positive family history are not explained by modest hypertension merely because it is present.
Etiology should be investigated using a probabilistic model linking age, phenotype, exposures, extracardiac manifestations, pedigree and imaging pattern.

Genetic causes affect proteins with very different functions. Variants in sarcomeric genes modify force generation and transmission; variants in titin and other cytoskeletal proteins alter elasticity, stability and mechanosensitivity; laminopathies and desminopathies impair the nuclear envelope and intermediate filament network; desmosomal defects weaken adhesion at intercalated discs; abnormalities of phospholamban and other regulators disturb calcium homeostasis.
The consequence is not mechanically and immutably determined by the gene. The same variant may produce dilation, non-dilated scar, conduction disturbances or arrhythmic predominance in different family members, while different variants may converge on the same phenotype.
Incomplete penetrance, age, sex, modifier variants, physical activity, pregnancy, inflammation, alcohol and other exposures contribute to genotype-phenotype heterogeneity.

In the sarcomere, reduced ability to develop force or an excessive energetic cost of contraction activates compensatory responses that initially support output but over time promote hypertrophy, dilation or contractile failure.
Abnormal calcium handling alters excitation-contraction coupling, diastolic relaxation and electrical stability. Increased wall stress and neurohormonal activation stimulate the renin-angiotensin-aldosterone system, sympathetic tone and profibrotic signals; the immediate hemodynamic benefit is paid for by salt and water retention, increased oxygen consumption, apoptosis and remodeling.
The transition from molecular lesion to clinical phenotype therefore occurs through a network of compensations that becomes progressively maladaptive.

In forms involving intercalated discs and the cytoskeleton, repeated mechanical stress may cause cardiomyocyte loss and fibrous or fibrofatty replacement. Scar disrupts uniform electrical propagation, creates areas of slow conduction and facilitates re-entry circuits responsible for ventricular tachycardia.
This explains why some patients develop important arrhythmias before a marked reduction in ejection fraction. In DSP-related forms, myocarditis-like episodes with pain, elevated troponin and edema may occur and be followed by subepicardial scar; in laminopathies, conduction disturbances and atrial arrhythmias may precede dilation.
Electrical pathophysiology is therefore not simply a late complication of heart failure, but may be a primary manifestation of disease.

Acquired causes include immune-mediated or infectious myocarditis, autoimmune diseases, sarcoidosis, eosinophilia, toxic exposures, cardiotoxic drugs, persistent tachyarrhythmias and peripartum conditions. Some produce direct cardiomyocyte injury, whereas others act through the microcirculation, immunity, mitochondria or catecholaminergic overload.
The acute phase may be dominated by necrosis, edema and dysfunction; the chronic phase by cell loss, fibrosis and remodeling. When inflammation subsides but a non-ischemic scar persists without dilation, the patient may present as NDLVC; if dilation and hypokinesia predominate, the phenotype will be dilated.
Distinguishing active disease from scar sequelae is decisive because only the former may benefit, in selected and documented conditions, from etiologic immunologic treatment.

Infiltrative and storage diseases should not be called unclassified simply because they mimic common phenotypes. Amyloidosis, Fabry disease, hemochromatosis, glycogen storage diseases, Danon disease and other metabolic disorders have specific mechanisms and, in several cases, targeted therapies.
Extracellular deposition of amyloid fibrils, lysosomal accumulation of glycosphingolipids, iron overload or impaired autophagy increase apparent mass, stiffness, oxidative stress and vulnerability of the conduction system. The result may mimic hypertrophic or restrictive cardiomyopathy, but biology, extracardiac distribution and prognosis differ.
Recognizing the phenocopy prevents treatments and risk estimates derived from sarcomeric cardiomyopathy from being applied to a completely different disease.

Mitochondrial dysfunction is another convergence point. The myocardium depends on oxidative phosphorylation to produce ATP and maintain contraction, relaxation and ion gradients; defects of mitochondrial or nuclear DNA, toxicity and oxidative stress reduce energy reserve.
When demand exceeds production capacity, reactive oxygen species, membrane abnormalities, opening of permeability pores and cell death increase. The response may manifest as hypertrophy, dilation, hypertrabeculation, arrhythmias or conduction disturbances, often together with deafness, myopathy, neuropathy, diabetes or other systemic manifestations.
The multiplicity of phenotypes does not justify a residual label: it indicates the need for appropriate metabolic and genetic diagnosis.

Fibrosis is the principal cross-cutting pathophysiologic denominator, but it is not specific. It may result from necrosis, inflammation, mechanical stress, microvascular ischemia, infiltration or chronic activation of fibroblasts and transforming growth factor beta pathways.
Extracellular matrix deposition increases stiffness and filling pressures, reduces contractile efficiency, electrically uncouples myocytes and promotes arrhythmias. Scar distribution provides clues: a subendocardial or transmural pattern typically follows an ischemic territory, whereas mid-wall, subepicardial, ring-like or focal patterns suggest non-ischemic etiologies, without being pathognomonic by themselves.
Magnetic resonance should therefore be interpreted together with the clinical context and not as an automatic diagnosis generator.

Hypertrabeculation illustrates how morphology and pathogenesis can be confused. Prominent trabeculae and deep recesses may accompany genetic cardiomyopathy, but may also become more evident in a healthy heart exposed to increased preload.
Attributing every finding to presumed arrest of embryonic compaction produces overdiagnosis, because the adult myocardium does not build new structures during pregnancy or training: an architecture already present becomes more visible. Pathological significance increases when dysfunction, dilation, scar, arrhythmias, family events or a convincing causal variant coexist.
In the absence of these elements, the isolated trait does not demonstrate cardiomyopathy and does not automatically justify anticoagulation, sports restriction or extensive genetic screening.

Finally, many cardiomyopathies follow a multiple-hit model. A genetic predisposition may remain silent until pregnancy, chemotherapy, alcohol, infection, rapid arrhythmia or hemodynamic stress reduces myocardial reserve.
Conversely, an apparently sufficient exposure does not exclude an inherited basis, especially when injury is disproportionate, recurs in the family or persists after the cause is removed. Cause and effect should be argued rather than merely presumed from temporal coexistence.
This interaction explains why a rigid separation between genetic and acquired is often insufficient and why an integrated diagnosis should include both levels.

A patient with a phenotype that cannot immediately be classified may be asymptomatic, present with heart failure symptoms, come to attention because of an arrhythmia, or be identified after a family event. The assessment should begin from the concrete reason for presentation and reconstruct the temporal sequence without being conditioned by the label in a previous report.
Dyspnea, chest pain, palpitations and syncope are the most frequent modes of presentation in cardiomyopathies, but their association with age, exertion, fever, stress, pregnancy, drugs or systemic symptoms radically changes their meaning.
An incidental ECG or imaging finding may be the first expression of familial disease, whereas a clinically severe presentation may result from a reversible acquired cause: symptom intensity and nature of the etiology are not equivalent.

The history of dyspnea should specify onset, progression, exercise threshold, orthopnea, paroxysmal nocturnal dyspnea, weight gain and edema. Rapid onset suggests acute heart failure, arrhythmia, ischemia, inflammation or Takotsubo syndrome; slow deterioration suggests chronic remodeling, restriction, storage or neuromuscular disease.
Reduced exercise capacity may precede overt congestion and result from diastolic dysfunction, chronotropic incompetence, dynamic obstruction, reduced output or extracardiac muscular and respiratory involvement.
Fatigue should not automatically be attributed to the heart when anemia, thyroid dysfunction, myopathy, mitochondrial disease or drug therapy coexist.

Chest pain requires rigorous reconstruction of quality, duration, radiation, relationship to exertion and breathing, and associated symptoms. Acute coronary syndrome, aortic dissection and pulmonary embolism should be excluded according to clinical probability before invoking a rare cardiomyopathy.
Pain with elevated troponin and non-obstructed coronary arteries may result from myocarditis, Takotsubo, vasospasm, coronary embolism or other causes of myocardial infarction with non-obstructive coronary arteries. Recurrent myocarditis-like episodes, especially in young people with subepicardial scar or family history, may be a red flag for genetic diseases such as those related to desmoplakin.
Pain is therefore nonspecific, but its chronology can link an inflammatory event to subsequent development of a scar phenotype.

Palpitations should be distinguished as perception of isolated beats, regular or irregular tachycardia, sustained episodes, and association with presyncope, pain or dyspnea. Absence of palpitations does not exclude clinically important arrhythmias, especially in conduction disease or nonsustained tachycardias.
Syncope during exertion, in the supine position, without prodromes or accompanied by palpitations requires urgent arrhythmic assessment; typical vasovagal syncope remains possible but should not be accepted without comparison with ECG, family history and structural substrate.
Early-onset atrial fibrillation, atrioventricular block, frequent ventricular ectopy or ventricular tachycardia may precede dysfunction and provide stronger etiologic clues than ejection fraction.

Personal history should explore hypertension, valvular disease, coronary artery disease, congenital heart disease, infections, autoimmune disease, cancer and oncologic treatments, endocrinopathies, pregnancy and puerperium, and renal and liver disease.
Medication and toxicologic history should quantify cumulative exposure, dose, duration and temporal relationship for anthracyclines, anti-HER2 therapies, immune checkpoint inhibitors, antimalarials, alcohol, cocaine, amphetamines, anabolic androgenic steroids and other relevant substances.
A generic question about medication use is not sufficient: the patient may not recognize supplements, recreational substances or previous therapies as potentially cardiotoxic.

Family history should be transformed into a three- or four-generation pedigree. The search should include not only explicit diagnoses of cardiomyopathy, but also unexplained heart failure, transplantation, sudden death, drowning, unexplained road crashes, sudden infant death, pacemaker or defibrillator at a young age, early stroke and muscle weakness.
Apparent absence of family history does not exclude inheritance because of incomplete penetrance, de novo variants, small families, sex and age of relatives, or missing information. Male-to-male transmission makes an X-linked model unlikely, whereas an exclusively maternal line suggests mitochondrial DNA; these patterns guide but do not replace testing.
Relatives' reports should be verified when possible because labels recalled from memory may be inaccurate.

Extracardiac manifestations are often decisive. Weakness, contractures, respiratory difficulty, persistently elevated CK and gait disturbance suggest neuromuscular disease; deafness, diabetes, ptosis, ophthalmoplegia, short stature, neuropathy or metabolic crises point toward mitochondrial disease.
Proteinuria, renal failure, angiokeratomas, acroparesthesias and hypohidrosis may indicate Fabry disease; bilateral carpal tunnel syndrome, lumbar stenosis, biceps tendon rupture and neuropathy point toward transthyretin amyloidosis; rash, arthritis, asthma, eosinophilia and neuropathy suggest an immunologic or eosinophilic cause.
Each extracardiac red flag should be linked to the cardiac phenotype through targeted verification, not automatically turned into a diagnosis.

Physical examination proceeds from general condition and vital signs to hemodynamic signs. Pulse rate and regularity, blood pressure in both arms when indicated, oxygen saturation, peripheral perfusion and respiratory status identify instability, congestion or low output.
Inspection may show dysmorphism, short stature, weakness, cyanosis or skin signs; jugular venous pressure, hepatojugular reflux, edema and ascites document systemic congestion. A displaced apical impulse, third or fourth heart sound, murmurs of functional regurgitation and signs of dynamic obstruction orient the phenotype, while pulmonary crackles and effusions complete assessment of congestion.
A normal physical examination does not exclude scarred or arrhythmogenic cardiomyopathy in early stages.

Pediatric presentation requires particular attention to growth, feeding, sweating, tachypnea, recurrent infections, hypotonia, regression of milestones, dysmorphic features and consanguinity. In neonates and young children, metabolic, syndromic and mitochondrial causes are proportionally more represented and may deteriorate rapidly.
In adolescents, exertional syncope, pain, palpitations, declining athletic performance or family history should be interpreted without trivialization. Even in childhood the phenotype may be incomplete and a negative genetic test does not exclude an inherited cause.
Early involvement of pediatric cardiology, clinical genetics and metabolic or neuromuscular specialists is required when red flags are present.

Finally, the clinical course itself is informative. Complete recovery after an acute event supports a transient syndrome but does not eliminate the need to confirm the diagnosis; progression from isolated scar to dysfunction suggests phenotypic evolution; onset of block or arrhythmias in a previously normal relative may clarify inheritance.
The next visit should not merely repeat the previous one. New symptoms, pregnancies, exposures, diagnoses in relatives, variant reclassification and new images should be reintegrated into the reasoning.
The longitudinal history is often the test that transforms an apparently unclassifiable cardiomyopathy into a specific diagnosis.

There are no official international diagnostic criteria for a contemporary category called unclassified cardiomyopathies. Using the expression as though it had an echocardiographic threshold, a score or a pathognomonic combination would be scientifically incorrect.
According to the ESC 2023 guidelines, suspected cardiomyopathy requires systematic multiparametric assessment including clinical evaluation, pedigree, ECG, Holter monitoring, laboratory testing and multimodality imaging; the purpose is to demonstrate and characterize a phenotype and identify its etiology.
The provisional diagnosis should state the degree of uncertainty and be replaced, as soon as possible, by a more precise phenotypic and etiologic description.

In the acute patient, the priority is to recognize emergencies. Pain, ST-segment elevation, elevated troponin, shock or arrhythmias require prompt exclusion of acute coronary syndrome, aortic dissection, pulmonary embolism, complicated myocarditis, Takotsubo and immediately correctable metabolic or toxic causes.
Coronary assessment may use invasive angiography or computed tomography according to presentation, age and pre-test probability; absence of stenosis does not end the pathway, but opens the differential diagnosis of non-obstructive myocardial injury.
Hemodynamic stabilization and treatment of arrhythmias take precedence over final nosologic characterization, which is completed as soon as conditions permit.

The first level begins with a 12-lead ECG. Voltages, axis deviation, non-ischemic Q waves, repolarization abnormalities, QRS fragmentation, pre-excitation, PR interval, QRS duration, blocks and distribution of ectopy may suggest phenotype and cause.
A normal ECG does not exclude cardiomyopathy, but a markedly abnormal ECG with an almost normal echocardiogram should increase suspicion of early electrical or scar disease. Ambulatory monitoring quantifies ectopy, nonsustained ventricular tachycardia, atrial fibrillation, pauses and blocks; duration and frequency of monitoring depend on symptoms and risk.
Exercise testing and cardiopulmonary exercise testing assess provoked arrhythmias, functional capacity, blood pressure response, ischemia when relevant and the mechanism of limitation, without being used as the sole proof of diagnosis.

Transthoracic echocardiography is the principal initial imaging test. It should measure dimensions and volumes of both ventricles, wall thickness, global and regional systolic function, diastolic function, atrial dimensions, valvular apparatuses, pulmonary pressures, pericardium and possible dynamic obstructions.
Global longitudinal strain may reveal subclinical dysfunction and suggestive patterns, but is not specific; echocardiographic contrast improves endocardial definition, helps assess the apex and hypertrabeculation, and facilitates exclusion of thrombi. Values should be indexed and interpreted according to age, sex, body surface area and training status.
A single ratio between trabeculated and compacted layers is not enough to diagnose cardiomyopathy.

Cardiac magnetic resonance has a central role when the phenotype is uncertain because it combines morphofunctional measurements with tissue characterization. Cine sequences describe volumes, function and wall motion; T2-weighted sequences and T2 mapping assess edema; native T1 and extracellular volume help recognize diffuse fibrosis, infiltration or storage; late gadolinium enhancement identifies focal scar and defines its distribution and extent.
A subendocardial or transmural ischemic pattern follows a coronary territory, whereas mid-wall, subepicardial or ring-like patterns suggest a non-ischemic origin. No pattern is absolutely specific, and technical quality, timing of the examination and associated conditions should be considered.
CMR is also superior to echocardiography for many assessments of the right ventricle, apex and equivocal thrombi.

Recognition of non-ischemic scar or fatty replacement of the left ventricle without dilation, with or without wall-motion abnormalities, points toward NDLVC; isolated global hypokinesia without scar may also meet the definition.
The diagnosis does not end there: genetic causes, previous or active myocarditis, sarcoidosis and other phenocopies should be distinguished. Location and distribution of LGE, myocarditis-like episodes, ECG, arrhythmias, extracardiac signs and pedigree guide the second level.
Absence of LGE does not exclude cardiomyopathy because disease may be early, diffuse below resolution, or dominated by dysfunction without focal scar.

First-line blood tests assess etiology, severity and organ injury simultaneously. Blood count, electrolytes, renal and hepatic function, glucose, thyroid function, CK, troponin and natriuretic peptides are selected and interpreted in context; iron, ferritin and transferrin saturation are useful in relevant phenotypes.
In hypertrophic or restrictive presentations, serum and urine immunofixation and free light chains search for a monoclonal component, while bone-tracer scintigraphy is used within a rigorous algorithm for transthyretin amyloidosis. Alpha-galactosidase A and lyso-Gb3, especially in males, may point toward Fabry disease; lactate, pyruvate, acylcarnitine profile, amino acids and organic acids belong to specialist metabolic pathways.
Autoantibodies, serologies, eosinophils and infectious disease investigations should not be requested indiscriminately, but on the basis of a precise pre-test hypothesis.

Cardiac computed tomography is useful for coronary anatomy, calcification, pericardium and patients who cannot undergo CMR. Nuclear medicine answers selected questions: scintigraphy for transthyretin amyloidosis and 18F-FDG PET, with appropriate metabolic preparation, for inflammatory activity compatible with sarcoidosis.
An isolated uptake is not automatically diagnostic and should be correlated with extracardiac distribution, CMR and clinical probability. Right and left heart catheterization clarifies hemodynamics when symptoms and imaging do not agree, distinguishes restriction from constriction and supports assessment of advanced heart failure.
Every second-line test should address a question capable of changing diagnosis, prognosis or therapy.

Genetic testing is indicated when it can confirm etiology, guide risk and treatment, or enable cascade screening. The pathway should include pre-test counseling, informed consent, selection of a panel of genes with demonstrated validity and post-test disclosure by competent professionals.
A pathogenic or likely pathogenic variant consistent with the phenotype may establish the cause and allow targeted testing in relatives. A variant of uncertain significance does not prove causality, should not be used to exclude or confirm disease in relatives, and alone does not justify device implantation, reproductive restrictions or other irreversible decisions.
Familial segregation, new evidence and periodic reassessment may change variant classification, so the genetic report and phenotype should be reviewed over time.

A negative test does not exclude inherited cardiomyopathy. Panel limitations, uncovered regions, structural variants, mosaicism, genes not yet validated and oligogenic or polygenic architectures may leave the cause unresolved.
Clinical screening of first-degree relatives with history, ECG and imaging therefore remains necessary when the familial phenotype is convincing, even if testing of the proband does not identify a causal variant. If a familial pathogenic variant is known, relatives who do not carry it can generally be discharged from specific follow-up, except for justified clinical or genetic exceptions.
In carriers without phenotype, surveillance and counseling are adapted to gene, age and family history.

Endomyocardial biopsy is not a routine test for every uncertain cardiomyopathy. It is appropriate when the result can concretely change diagnosis or treatment, such as suspected giant cell myocarditis, eosinophilic myocarditis, sarcoidosis, vasculitis, drug-related immune inflammation or specific infiltrative and storage diseases unresolved by non-invasive methods.
Histology, immunohistochemistry, electron microscopy and molecular analyses should be selected according to the question; biopsy location may be guided by CMR, PET or electroanatomic mapping in focal processes. A negative sample does not always exclude disease because of sampling error.
Risks and benefits require an expert center and should not be justified by the unclassified label alone.

The differential diagnosis includes athletic remodeling, hypertension, obesity, valvular disease, congenital heart disease, coronary artery disease, constrictive pericarditis, tachycardiomyopathy, pacing-related dysfunction, Takotsubo, myocarditis and systemic conditions.
Deconditioning may be useful only in selected cases and does not replace comprehensive assessment of the athlete; indiscriminate restriction can cause harm. Constrictive pericarditis may mimic restrictive physiology but shows ventricular interdependence and pericardial signs; tachycardiomyopathy is supported by a temporal relationship and recovery after rhythm control, without ignoring that arrhythmia may result from a pre-existing cardiomyopathy.
Correct diagnosis requires comparison among alternative hypotheses, not an unstructured accumulation of tests.

The conclusion should formulate an integrated diagnosis. Phenotype, severity, ventricular function, scar distribution, arrhythmias, etiology, genotype, clinical stage and extracardiac involvement are reported coherently.
When the cause remains unknown, it is appropriate to use idiopathic only after an investigation proportionate to red flags and to state what has been excluded; when the phenotype is also incomplete, the observed traits are described and reassessment is planned. It is not appropriate to present uncertainty as certainty or to stop follow-up of a high-risk patient or family because the first assessment is inconclusive.
Modern diagnosis does not eliminate uncertainty, but makes it explicit, verifiable and updatable.

There is no treatment for unclassified cardiomyopathies because there is no single disease. The strategy combines phenotype-directed therapy, prevention of complications and etiologic treatment while assessment continues.
A provisional diagnosis does not justify passive waiting when congestion, arrhythmias, thrombi or instability are present; at the same time, it does not authorize unproven specific therapies such as empirical immunosuppression, anticoagulation for hypertrabeculation alone, or a defibrillator based solely on diagnostic anxiety.
Every intervention should be linked to a demonstrated clinical target and reassessed when the phenotype is reclassified.

In patients with heart failure and reduced ejection fraction, foundational drug therapy recommended by the ESC 2026 guidelines is applied unless contraindications or etiologic features dictate otherwise: an evidence-based beta-blocker, ACE inhibitor, ARNI or angiotensin receptor blocker as indicated, a mineralocorticoid receptor antagonist and an SGLT2 inhibitor.
Diuretics correct congestion but do not replace prognostic therapy. Titration, blood pressure, renal function, potassium and tolerance should be monitored; recovery of ejection fraction does not automatically imply withdrawal because it may represent remission under treatment rather than biological cure.
In restrictive, obstructive or preserved-function phenotypes, hemodynamic management requires adaptation and cannot be mechanically transferred from the dilated model.

Atrial fibrillation is treated with control of concomitant factors, a rate or rhythm strategy, and thromboembolic prevention according to guidelines and the specific phenotype. In hypertrophic cardiomyopathy, the threshold for anticoagulation in the presence of atrial fibrillation differs from that in the general population; in other phenotypes, the decision integrates scores, function, atrial size and thromboembolic history.
Cardioversion and ablation may be appropriate, but recurrence and atrial substrate should be discussed. A documented ventricular thrombus requires anticoagulation and imaging follow-up; the mere presence of prominent trabeculae, in the absence of thrombus, atrial fibrillation, previous embolism or relevant dysfunction, is not an automatic indication.
Bleeding risk should be reassessed together with benefit.

Ventricular arrhythmias require correction of reversible factors, definition of the substrate and assessment of sudden death risk. An implantable cardioverter-defibrillator is indicated for appropriate secondary prevention, whereas primary prevention should consider the reclassified phenotype, ejection fraction, syncope, nonsustained ventricular tachycardia, scar extent, right ventricular function, family history and genotype.
In some genetic cardiomyopathies, arrhythmic risk may be significant before ejection fraction reaches conventional thresholds; in other cases an early device would expose the patient to complications without demonstrated benefit. Ablation, antiarrhythmic drugs and pacing are chosen in context and do not necessarily eliminate the need for protection from sudden death.
The decision should be shared, documenting uncertainty, expected longevity and the psychological and technical consequences of the device.

Conduction disturbances are treated according to symptoms, site and severity, but they may also provide etiologic information. A pacemaker corrects bradycardia and block, not the myocardial process; when ventricular risk or dysfunction coexist, the choice among pacemaker, ICD and resynchronization should anticipate plausible evolution.
A high burden of right ventricular pacing may worsen dyssynchrony and function, so physiologic strategies or resynchronization are considered in appropriate patients. In laminopathies, desminopathies, neuromuscular diseases and some infiltrative forms, conduction disease may progress rapidly.
Rhythm monitoring continues even after implantation because the device does not replace overall stratification.

Etiologic therapy can radically modify prognosis. Withdrawal of alcohol, stimulants or cardiotoxic drugs, treatment of thyrotoxicosis or deficiencies, control of a tachyarrhythmia, therapy for amyloidosis, enzyme replacement or chaperone therapy in selected Fabry disease, and chelation or phlebotomy in hemochromatosis address different mechanisms.
Immunosuppression and anti-inflammatory therapies should be reserved for conditions in which etiology and activity are sufficiently documented, following specific guidelines; an inactive post-inflammatory scar is not reversed by empirical immunosuppression. In genetic forms that currently lack causal therapy, counseling, control of modifiers and early surveillance of relatives remain substantial interventions.
Diagnostic precision therefore becomes part of treatment.

Physical activity is prescribed individually. Moderate exercise may improve functional capacity and well-being in many stable patients, whereas high-intensity or competitive activity may increase risk in specific arrhythmogenic cardiomyopathies or in the presence of arrhythmias, dysfunction or significant scar.
It is not appropriate to impose the same restriction on an asymptomatic carrier, a patient with isolated hypertrabeculation and a person with DSP-related NDLVC and tachycardias. The program considers symptoms, monitoring, exercise testing, genotype and preferences, with reassessment over time.
Occupational activity, driving, proarrhythmic drugs and alcohol consumption should also be discussed when risk requires it.

Pregnancy and puerperium may reveal or worsen a predisposition and require preconception counseling in patients with cardiomyopathy or a causal variant. Maternal risk, teratogenic drugs, transmission, monitoring needs and delivery planning are assessed by a cardio-obstetric team.
Development of hypertrabeculation during pregnancy alone does not demonstrate cardiomyopathy, whereas dysfunction, symptoms, biomarkers or family history require further assessment. Postpartum clinical recovery does not exclude a genetic predisposition, especially in peripartum forms with family history or persistent phenotype.
Anesthesia and major procedures require similar planning in obstructive, restrictive, arrhythmic or multisystem phenotypes.

Follow-up should be organized according to risk rather than the generic nature of the label. In stable patients with cardiomyopathy, clinical assessment, ECG and imaging are repeated periodically; Holter monitoring and CMR intervals are adapted to phenotype, symptoms, genotype, previous scar and clinical changes.
The ESC guidelines indicate that serial CMR every two to five years may help assess progression according to severity and course, whereas closer follow-up is necessary after events, new arrhythmias or therapeutic changes. Family history and variant classification should also be updated.
Follow-up serves to detect progression and to reclassify, not merely to confirm what was already known.

In advanced heart failure, early evaluation at a dedicated center allows ventricular assist devices and transplantation to be considered before right ventricular dysfunction, renal or hepatic failure, or cachexia make risk prohibitive. Etiology and extracardiac involvement influence candidacy and choice of support.
A patient with progressive systemic disease is not equivalent to one with a defect confined to the heart; conversely, some severe genetic diseases may benefit from transplantation when other organs are preserved. Palliative care and shared planning are part of management when advanced therapies are not appropriate.
Late referral is an avoidable complication of diagnostic uncertainty.

Prognosis cannot be stated for the unclassified category. It depends on cause, reversibility, ventricular function, extent and location of scar, arrhythmic burden, syncope, conduction disease, therapeutic response and involved extracardiac organs.
A preserved ejection fraction does not guarantee low risk in the presence of scar and arrhythmogenic genotypes; a reduced fraction may instead improve after removal of a toxin or control of tachycardia. Isolated hypertrabeculation with normal function does not automatically share the prognosis of genetic cardiomyopathy with hypertrabeculation.
Prognostic estimation should be updated with every new piece of information and communicated without turning group probabilities into individual destiny.

Complications derive from the underlying phenotype and etiology, not from the unclassified label. Heart failure is the most common cross-cutting manifestation and may develop through systolic dysfunction, diastolic stiffness, obstruction, arrhythmia, functional valvular regurgitation or right ventricular involvement.
Elevated filling pressures produce pulmonary and systemic congestion; neurohormonal activation temporarily maintains perfusion but promotes retention, vasoconstriction and further remodeling. Acute episodes may be triggered by infections, arrhythmias, pregnancy, drugs, ischemia or resumption of toxic exposures.
Prevention requires appropriate therapy and early recognition of signs of deterioration.

Cardiogenic shock may complicate severe dysfunction, fulminant myocarditis, Takotsubo, sustained arrhythmias or end-stage heart failure. The mechanism should be defined rapidly because low contractility, dynamic obstruction, right ventricular failure and tamponade require different strategies.
Vasopressors, inotropes and mechanical support may be lifesaving but can increase harm in specific settings if used without hemodynamic understanding. Nosologic uncertainty should not delay urgent echocardiography, catheterization when necessary and referral to a shock center.
Etiologic diagnosis is refined in parallel with stabilization.

Ventricular arrhythmias and sudden cardiac death are among the most feared complications. Fibrosis and fatty replacement create conduction heterogeneity, while calcium abnormalities, ischemia, catecholamines and QT-prolonging drugs favor triggered activity.
Risk may precede advanced dysfunction in NDLVC and in some genotypes, making a strategy based only on ejection fraction insufficient. Syncope, nonsustained ventricular tachycardia, LGE extent, family history and the specific variant modify assessment.
The defibrillator terminates lethal arrhythmias but does not prevent substrate progression, heart failure or atrial arrhythmias.

Atrial fibrillation and flutter result from atrial dilation, elevated pressures, fibrosis and inflammation. Loss of atrial contraction may be particularly poorly tolerated in hypertrophic and restrictive phenotypes, in which ventricular filling depends more heavily on the atrial contribution.
Tachycardia and irregularity worsen output and congestion; atrial stasis increases embolic risk. Frequent recurrences may make it difficult to distinguish whether arrhythmia is the cause of tachycardiomyopathy, a consequence of the substrate, or both.
Monitoring function after rhythm control helps reconstruct the causal relationship.

Conduction disturbances include sinus node disease, atrioventricular block and intraventricular delays. They may result from fibrosis, infiltration or genetic involvement of the conduction system and may precede overt cardiomyopathy by years.
Syncope, bradycardia, chronotropic incompetence and pauses cause hypoperfusion; chronic non-physiologic pacing may itself induce dyssynchrony and worsen function. Early block in an uncertain cardiomyopathy should reopen the search for laminopathy, neuromuscular disease, sarcoidosis, amyloidosis and other relevant causes.
Treating bradycardia without identifying its origin may miss opportunities for arrhythmic protection and family screening.

Thromboembolism may arise from atrial fibrillation, severe ventricular dysfunction, aneurysms, regional akinesia or intracavitary thrombi. Endocardial injury and stasis contribute to thrombus formation, which may embolize to the brain, kidneys, spleen, mesentery or limbs.
Extensive apical Takotsubo and some eosinophilic diseases have specific risks, but they should be diagnosed by name. Isolated hypertrabeculation does not by itself demonstrate clinically sufficient stasis and should not be converted into a universal indication for anticoagulation.
Contrast echocardiography or CMR resolves doubts between trabeculae and thrombus and allows the therapeutic response to be documented.

Fibrotic progression transforms an initial lesion into a permanent mechanical and electrical substrate. Stiffness, dysfunction, arrhythmias and loss of contractile reserve increase; repeated inflammatory episodes may enlarge the scar even when ejection fraction appears stable between events.
Serial CMR may show evolution, but clinical decisions should integrate symptoms, rhythm and function. The absence of a treatment capable of removing scar makes it essential to act on an active cause before damage becomes irreversible.
Late diagnosis reduces the margin for etiologic therapy and increases dependence on devices and advanced therapies.

Functional mitral and tricuspid regurgitation result from annular dilation, leaflet tethering, papillary muscle abnormalities and ventricular geometry; they worsen volume overload and congestion. Chronic elevation of left-sided pressures causes pulmonary hypertension and right ventricular overload.
When right ventricular dysfunction appears, exercise tolerance, renal and hepatic perfusion and prognosis worsen. Percutaneous or surgical valve correction should be considered after optimizing the phenotype and therapy because valvular disease may be a consequence rather than the primary cause.
In restrictive forms the hemodynamic margin is particularly narrow.

Extracardiac complications depend on the cause: respiratory failure in neuromuscular diseases, neuropathy and endocrinopathies in mitochondrial forms, renal failure in Fabry disease or amyloidosis, liver disease from congestion or toxicity, and hematologic progression in light-chain forms.
They limit medications, anticoagulation, transplant candidacy and rehabilitation capacity. For this reason, a cardiomyopathy team includes genetics, imaging, electrophysiology and, when necessary, neurology, nephrology, hematology, rheumatology, metabolic medicine and cardio-oncology.
Fragmented care may produce incompatible prescriptions or lose the relationship among organs.

Therapeutic interventions also generate complications. Heart failure drugs may cause hypotension, renal failure or hyperkalemia; antiarrhythmics may be proarrhythmic or toxic; anticoagulants expose patients to bleeding; pacemakers and ICDs may become infected, develop lead fractures or deliver inappropriate shocks.
Unnecessary immunosuppression exposes patients to infection and toxicity without correcting inactive scar. Prevention requires sound indications, monitoring and reassessment of the benefit-risk ratio, not abandonment of effective therapies.
In young patients, the horizon of multiple device replacements should be included in shared decision-making.

The most frequent conceptual complication is misclassification. Overdiagnosis turns anatomical variants into disease, producing anxiety, sports restrictions, treatments and unnecessary family screening; underdiagnosis leaves patients with scar, arrhythmias or early genetic disease unprotected.
Calling a form unclassified when it is now recognizable may delay causal therapy, whereas forcing an incomplete phenotype into a specific category may create false certainty. The solution is not to choose one simplification over the other, but to describe data accurately, state uncertainty and plan reassessment.
A provisional diagnosis is safe only when accompanied by a plan.

Psychological and family consequences also deserve attention. Uncertainty about the risk of sudden death, transmission to children and ability to participate in sport may cause anxiety, hypervigilance and decision conflict; a variant of uncertain significance communicated as a mutation causes concrete harm.
Genetic counseling, explanation of the probabilistic meaning of results and psychological support help avoid fatalism and false reassurance. New information may concern relatives not yet assessed, but sharing should respect consent, confidentiality and applicable law.
Quality of communication is as much a part of preventing complications as imaging and pharmacotherapy.