Neuromuscular cardiomyopathies

Article written and reviewed by Dr Luca Moretti

Neuromuscular cardiomyopathies include myocardial and electrical-system injury accompanying a heterogeneous group of muscular dystrophies, myopathies and inherited multisystem diseases. They are not a single biological entity: defects of the sarcolemma, nuclear envelope, RNA regulation or mitochondrial homeostasis produce different phenotypes. The common denominator is coordinated, but not necessarily simultaneous, vulnerability of skeletal muscle and the heart. This organ dissociation requires independent cardiology surveillance even when mobility and strength appear stable.

The term cardiomyopathy describes only part of the problem. In some diseases, ventricular fibrosis with subsequent systolic dysfunction predominates; in others, the first manifestation is sinus-node disease, atrioventricular block or an atrial arrhythmia while wall thickness and ejection fraction initially remain normal. Still others develop hypertrophy and reduced diastolic reserve. Electrical disease may therefore precede, accompany or remain relatively independent of mechanical impairment.

Reduced motor capacity makes assessment particularly difficult. A patient who does not walk or performs little exertion may never reach the workload needed to provoke heart-failure dyspnea, while fatigue, orthopnea and tachycardia may be attributed to hypoventilation, weakness or deconditioning. Absence of symptoms therefore does not equal absence of injury. This masked clinical picture explains why ECG, imaging and rhythm monitoring should begin according to the neuromuscular diagnosis rather than after heart failure appears.

Dystrophinopathies illustrate how the same gene can produce different disease rates: cardiomyopathy in Duchenne muscular dystrophy often follows an early progressive course, whereas cardiomyopathy in Becker muscular dystrophy has more variable expressivity and may be disproportionate to weakness. In Emery-Dreifuss cardiomyopathy, by contrast, gene and substrate determine the relative contribution of conduction disease, atrial arrhythmias, ventricular tachyarrhythmias and dysfunction. Molecular diagnosis thus becomes a concrete cardiovascular variable.

Cardiomyopathy in myotonic dystrophy requires particular attention to progression of conduction disease and arrhythmias, which cannot be inferred from peripheral myotonia. In Friedreich ataxia with cardiac involvement, frataxin deficiency more often leads to hypertrophic remodeling and energetic dysfunction, with a trajectory distinct from that of dystrophies. Grouping these conditions in the same chapter is useful only if comparison preserves their differences and builds a cross-cutting method for recognition, stratification and care.

Clinical scope and etiologic classification

The most informative classification starts from the protein and cellular compartment involved. Dystrophinopathies and some limb-girdle dystrophies impair the link between cytoskeleton, membrane and extracellular matrix; laminopathies and emerinopathies alter the nuclear envelope; myotonic dystrophies result from nucleotide expansions that sequester splicing regulators; Friedreich ataxia reduces frataxin and disrupts iron-sulfur clusters and mitochondrial metabolism. The primary mechanism guides the form of injury without determining it absolutely.

Not every neuromuscular disease carries the same cardiac risk. Some limb-girdle dystrophies associated with sarcoglycans or FKRP can cause major cardiomyopathy, whereas in other myopathies the heart is rarely involved. Facioscapulohumeral dystrophy and motor neuron disease should not automatically be assimilated to dystrophinopathies; mitochondrial myopathies and Pompe disease belong to etiologic pathways that overlap only partly. A pragmatic taxonomy should distinguish frequency, age and type of complication rather than use weakness as the sole inclusion criterion.

The word cardiomyopathy also requires precision. The phenotype may be dilated, hypokinetic nondilated, hypertrophic, restrictive or mixed, but the conduction system and atria may be the dominant targets. In nuclear-envelope diseases, for example, only moderately reduced ejection fraction does not exclude relevant arrhythmic risk; in emerinopathies, atrial and conduction disease may deteriorate before ventricular disease. Phenotypic description should therefore include mechanics, tissue and rhythm.

The boundary with isolated genetic cardiomyopathy is porous. LMNA variants may cause Emery-Dreifuss muscular dystrophy, limb-girdle muscular dystrophy, dilated cardiomyopathy with conduction disease or overlapping phenotypes within the same family. A person may first receive a cardiac diagnosis and later show contractures or mild weakness; the reverse occurs in neuromuscular services. Phenotypic continuity makes integration between cardiologist and neurologist more useful than defending categories based on the first symptomatic organ.

From the molecular defect to myocardial fibrosis

Dystrophin stabilizes the sarcolemma during contraction and organizes a complex that transmits force and signals. When absent or dysfunctional, repeated cycles of mechanical stress increase membrane permeability, calcium influx, necrosis and fibro-adipose replacement. The process in the heart is not simply a consequence of immobility because it begins within the cardiomyocyte itself and may appear while global function is still preserved. Replacement fibrosis progressively creates both contractile failure and electrical heterogeneity.

In laminopathies, the nucleus loses part of its mechanical resistance and regulation of signaling, chromatin and stress responses changes. Cardiomyocytes and conduction-system cells, subjected to continuous deformation, develop cell death and fibrosis; however, propensity to ventricular arrhythmias is not explained solely by the amount of visible scar. Variant, sex, conduction disturbances, nonsustained ventricular tachycardia and ventricular function contribute to risk. Nuclear vulnerability therefore links biomechanics and electrical instability.

In myotonic dystrophy, CTG expansion in DMPK or CCTG expansion in CNBP generates toxic RNA and alters splicing of numerous proteins. The heart develops fibrosis, conduction-system disorganization and arrhythmias with variable expressivity that cannot be reduced to repeat length measured in blood. Somatic mosaicism, age and modifiers contribute to discordance among relatives and organs. RNA toxicity explains why a dynamic mutation produces progressive multisystem disease.

In Friedreich ataxia, frataxin deficiency impairs iron-sulfur cluster enzymes, the respiratory chain and oxidative control. The high-energy-demand cardiomyocyte responds with growth, disorganization and fibrosis; hypertrophy is not equivalent to sarcomeric hypertrophy and may progress to thinning and failure. Diabetes and other systemic determinants modify the load but do not exhaust the mechanism. Bioenergetic reserve is central to the cardiac phenotype here.

These mechanisms converge on inflammation, oxidative stress, cell death and remodeling, but convergence does not justify uniform treatment. A strategy plausible in a membrane disease may be irrelevant to a splicing defect, while the same heart-failure drug class may have different timing and tolerability. The pathologic substrate must remain explicit when interpreting a common measure such as ejection fraction, strain or LGE.

Expressivity, age and organ dissociation

Age at onset and rate of progression are not interchangeable. A normal heart in childhood may belong to a disease with high adult risk, whereas early fibrosis may precede dysfunction by years. Surveillance recommendations therefore define a starting point linked to diagnosis and intervals that shorten with age or findings. The individual trajectory matters more than an occasional comparison with a normality threshold.

Peripheral strength does not reliably predict the heart because isoforms, mechanical load, modifiers and tissue mosaicism differ. In Becker muscular dystrophy, severe cardiomyopathy may occur with relatively limited weakness; in women with a DMD variant, random X inactivation may cause cardiac injury without an overt muscle phenotype. In laminopathies, modest contractures may coexist with disproportionate electrical risk. Heart-muscle discordance is not a diagnostic exception but a property of the group.

Longer survival changes the observed natural history. Noninvasive ventilation, cough assistance, glucocorticoids and better orthopedic management have reduced early complications in some dystrophies, leaving more time for cardiomyopathy to emerge. Historical cohorts therefore do not automatically represent contemporary patients, and causes of death change with care. Conditional prognosis should be updated according to the therapeutic era and quality of care.

Sex modifies penetrance and expression but should not become automatic reassurance. Female carriers of a dystrophinopathy may develop fibrosis or dysfunction; LMNA variants have risk associations that include male sex, but a woman is not thereby protected; Friedreich ataxia is autosomal recessive and follows different rules. The sex variable should be interpreted within the genetic model, not used as a substitute for imaging and family history.

Clinical recognition and cardiovascular red flags

Palpitations, presyncope and syncope require careful temporal reconstruction. A fall may result from weakness, but sudden loss of consciousness without prodrome in a laminopathy or myotonic dystrophy should be considered potentially arrhythmic until adequately assessed. Chest pain and troponin elevation may reflect nonischemic myocardial injury while still requiring exclusion of common emergencies. Unexplained syncope is a red flag, not a symptom to attribute by exclusion to neurologic disease.

Signs of heart failure are often attenuated or confounded. Edema may be affected by immobility, orthopnea and fragmented sleep by hypoventilation, weight loss by dysphagia, and reduced exercise tolerance by myopathy. Assessment seeks change from usual level, congestion, perfusion, rhythm and respiratory function at the same time. An integrated interpretation prevents both missed heart failure and treatment of every dependent swelling as congestion.

An ECG with prolonged PR, wide QRS, fascicular blocks, nonischemic Q waves or atrial arrhythmia changes the level of concern. In myotonic dystrophy, progressively abnormal intervals signal conduction-system involvement; in dystrophinopathies, inferolateral Q waves and repolarization abnormalities may accompany injury; in nuclear-envelope diseases, bradycardia, atrial paralysis and block are characteristic. Serial abnormalities are more informative than a single tracing generically labeled abnormal.

Family history should include apparently unrelated events: pacemaker implantation before age fifty, early atrial fibrillation, nocturnal death, transplantation, cardiomyopathy in a man with little weakness or sudden loss of independence. The maternal side and female carriers should also be represented. A pedigree recording only neuromuscular diagnoses loses half the information. The cardioneurologic family helps identify incomplete penetrance and initially isolated presentations.

Presymptomatic surveillance and diagnostic pathway

Baseline cardiology assessment should follow recognition of a disease associated with cardiac risk without waiting for symptoms. It includes targeted history, examination, ECG and echocardiography; ambulatory monitoring and magnetic resonance are added according to diagnosis, age and acoustic-window quality. The initial result serves to define an individual reference rather than merely certify normality. A complete baseline permits measurement of small but coherent changes over time.

There is no single interval applicable to the whole group. In dystrophinopathies surveillance becomes regular from pediatric age; in myotonic dystrophy and laminopathies rhythm may require closer checks when intervals or symptoms change; in Friedreich ataxia imaging and clinical assessment are adapted to the cardiac phenotype. Pathogenic variant, previous findings, family history and therapy modify frequency. Dynamic frequency replaces a rigid schedule independent of risk.

A normal examination does not end surveillance because many manifestations are age-dependent. Conversely, an isolated finding does not necessarily demonstrate progression: heart rate, hydration, growth, image quality and laboratory differences may alter measurements. Comparing images, using reproducible methods and evaluating trend reduces false alarms. Longitudinal data gain value only when technique and context are comparable.

Neuromuscular assessment enters cardiac reasoning. Respiratory function, scoliosis, transfer ability, cough, dysphagia and independence determine symptoms, test feasibility and procedural safety. Likewise, the cardiologist should communicate hemodynamic and arrhythmic limits to rehabilitation without imposing unjustified inactivity. The coordinated pathway avoids duplication and makes each measurement interpretable in relation to global function.

Electrocardiography and arrhythmic risk

A 12-lead ECG provides information on rhythm, atrioventricular and intraventricular conduction, voltages, apparent electrical necrosis and repolarization. In progressive diseases, preserving tracings and comparing PR, QRS and axes is essential. A threshold may prompt further investigation, but rate of change may be equally relevant. Electrical phenotyping is not exhausted by automated reporting or by whether an arrhythmia is present at the time of examination.

Ambulatory monitoring documents pauses, intermittent blocks, ectopy, nonsustained ventricular tachycardia and often asymptomatic atrial arrhythmias. Duration should be selected according to the expected event frequency: a short Holter may suffice for a daily burden, while rare symptoms require longer devices or a loop recorder. A negative result applies only to the observed window. The monitoring strategy should therefore start from the clinical question rather than the available device.

Electrophysiologic study has a selective role, particularly when myotonic dystrophy presents with conduction abnormalities or unexplained symptoms. The HV interval may reveal infra-Hisian disease and support a pacing decision, but does not replace overall ventricular-risk assessment. Inducibility, function and genotype have different meanings in different conditions. Invasive physiology is useful when it answers a concrete decision rather than as universal screening.

The choice between pacemaker and defibrillator is crucial in diseases with progressive conduction abnormalities and ventricular substrate. A pacemaker prevents bradycardia and asystole but does not treat ventricular tachycardia or fibrillation; in some genotypes, especially LMNA, a pacing indication should prompt simultaneous assessment of malignant arrhythmic risk. The profile may differ in emerinopathies. Appropriate protection depends on etiology, not merely on the presence of a pacing indication.

Atrial arrhythmias are not a minor problem. Fibrillation, flutter, tachycardias and atrial paralysis can reduce output, promote thrombi and precede ventricular disease while symptoms remain modest in less active people. Anticoagulation and rhythm control follow general principles adapted to risk, anatomy and procedures, but absence of palpitations does not exclude a high burden. Atrial surveillance protects against both thromboembolism and hemodynamic deterioration.

Echocardiography, magnetic resonance and biomarkers

Echocardiography measures geometry, volumes, ejection fraction, right ventricular function, valves and pressures but encounters specific limitations. Scoliosis, chest-wall deformity and reduced mobility may restrict acoustic windows and make volumes or comparisons imprecise. Consistent use of the same method and, when possible, three-dimensional imaging improves reproducibility. Technical quality should be reported because an apparently normal ejection fraction from incomplete images is not solid reassurance.

Longitudinal strain may detect regional or global dysfunction before an obvious decline in ejection fraction, but depends on quality, software, age and loading conditions. No universal threshold alone defines therapy in every neuromuscular disease. Its strength lies in serial assessment and concordance with CMR, ECG and biomarkers. A subclinical signal becomes clinically useful when it changes probability and leads to proportionate follow-up or intervention.

Cardiac magnetic resonance quantifies volumes without depending on the chest window and characterizes tissue using LGE and mapping. In dystrophinopathies, subepicardial or midwall inferolateral fibrosis may precede global dysfunction; in other genotypes, distribution and significance differ. LGE indicates expansion of extracellular space and scar but does not by itself identify the cause. The fibrotic map integrates the phenotype but must be interpreted with the mutation and disease stage.

Sedation, inability to maintain position, contractures, ventilation and devices may limit magnetic resonance. Gadolinium risk is assessed with renal function and device compatibility should be verified without assuming that every implant prevents scanning. When CMR is not feasible, optimized echocardiography and other serial information become central. Accessible imaging is imaging that produces reliable data without imposing disproportionate risk.

Troponin and natriuretic peptides may support assessment but do not replace imaging and clinical evaluation. Persistently or intermittently elevated troponin may reflect myocardial injury, whereas CK and transaminases often derive from skeletal muscle and should not be interpreted as specific cardiac markers. BNP or NT-proBNP are influenced by rhythm, renal function, age and body mass. A contextualized biomarker is useful for a trajectory, not for automatically attributing every abnormality to the heart.

Cardioprotection and heart-failure treatment

Principles of therapy for heart failure with reduced ejection fraction remain the reference, but the evidence base in individual neuromuscular diseases is more limited. Renin-angiotensin system inhibition, beta-blockade and mineralocorticoid antagonism are used according to phenotype, blood pressure, renal function and heart rate. In dystrophinopathies, data and consensus support early cardioprotection, whereas it is incorrect to transfer the same timing automatically to every genotype. Early therapy requires disease-specific justification.

Blood pressure sometimes tends to be low because of reduced muscle mass, dysautonomia or deconditioning, limiting conventional doses. A dose below that used in general trials does not necessarily mean futility, but symptoms, perfusion, creatinine and potassium should guide titration. Beta-blockers and other rate-slowing drugs also require caution when conduction is fragile. Individual tolerance matters more than mechanically reaching a target not validated in that population.

For sacubitril/valsartan and SGLT2 inhibitors, efficacy in general heart failure is established, but disease-specific experience in rare neuromuscular disorders remains less robust. They may be considered according to cardiac indications and patient characteristics, explicitly acknowledging extrapolation, hypotension risk, nutritional status and vulnerability to fasting or infections. Plausible benefit should not be presented as genotype-specific evidence when dedicated trials do not exist.

Diuretics treat congestion but not the primary disease and may worsen hypotension or dehydration. Weight loss is an ambiguous indicator with dysphagia and sarcopenia; examination, usual weight, edema, renal function and respiratory symptoms should therefore be interpreted together. Arrhythmia management may also improve function when tachycardia or loss of synchrony contributes to deterioration. The hemodynamic phenotype avoids automatic prescribing based on the cardiomyopathy diagnosis alone.

Molecular therapies targeting neuromuscular disease may modify survival and skeletal function without equivalent cardiac effects because of tissue distribution or duration of available data. Exon skipping, gene transfer and RNA correction should not be considered cardioprotective without dedicated evidence. At the same time, prolonging life changes exposure to cardiac risk. Independent cardiac assessment should accompany every innovation and measure benefits or unexpected myocardial signals.

Devices and advanced therapies

Pacemaker implantation follows symptoms, degree of block and disease-specific features, often with a lower tolerance for foreseeable progression. Before the procedure, venous access, anatomy, ventilation, anesthetic risk and future need for defibrillation or resynchronization are assessed. A strategy that solves the present event but precludes near-future options may be insufficient. Device planning considers the entire trajectory rather than only the day's tracing.

Primary prevention with an ICD cannot rely solely on ejection fraction in every genotype. Laminopathies may develop ventricular arrhythmias with nonsevere dysfunction, whereas in other diseases the relationship among fibrosis, ectopy and sudden death is less defined. Variant, sex, conduction, nonsustained ventricular tachycardia, LGE and family history contribute with different weights. Genotype-specific stratification integrates general guidelines without turning every variant into an automatic indication.

Resynchronization may be appropriate when dyssynchrony, function and symptoms meet criteria, but procedural difficulties and overall status must be considered. Chronic right ventricular pacing may worsen vulnerable function, making it important to anticipate the expected pacing burden. Physiologic pacing techniques are promising, but data specific to individual neuromyopathies remain limited. Ventricular synchrony is part of preventing iatrogenic injury, not only therapy for advanced disease.

Ventricular assistance and transplantation are not excluded by a neuromuscular diagnosis in itself. Selection evaluates neurologic progression, respiratory function, rehabilitation capacity, nutrition, infections, support and ability to manage the device. Some people with stable muscle involvement and severe cardiomyopathy may benefit from advanced therapies, whereas in others overall risk predominates. Multidimensional assessment replaces both categorical exclusion and an indication based on the heart alone.

Respiration, independence and perioperative risk

Heart and ventilation influence each other in both directions. Nocturnal hypoventilation, hypoxemia and infections increase hemodynamic and arrhythmic load; pulmonary congestion worsens already reduced respiratory reserve. Blood-gas analysis, adapted spirometry, sleep studies and cough assessment may be needed to interpret dyspnea or sleepiness. Cardiopulmonary physiology prevents attributing every symptom to one organ and overlooking a correctable cause.

Effective noninvasive ventilation can reduce respiratory stress and improve sleep, but pressures, preload and tolerance should be considered in heart failure. During an acute episode, oxygen alone may correct saturation without treating hypoventilation and delay recognition of hypercapnia. Cardiologist and pulmonologist should share goals and warning signs. Ventilatory support is part of cardiovascular management when it modifies gases, work of breathing and rhythm stability.

Procedures, anesthesia and sedation require planning before entering the operating room. Respiratory weakness, airway difficulties, dysphagia, cardiomyopathy, blocks and drug sensitivity vary among diseases; myotonic dystrophy poses different problems from a dystrophinopathy. Labeling all myopathies with the same anesthetic risk is inaccurate. Preoperative assessment should identify diagnosis, ventilatory function, rhythm, device and the individual postoperative plan.

Reduced mobility and contractures affect transfers, vascular access, positioning and recovery. A technically indicated test or implant may require aids, caregivers and additional time to be truly safe. Exercise should also be prescribed together with rehabilitation: avoiding harmful overload does not mean imposing inactivity, which worsens deconditioning and metabolic risk. Clinical accessibility turns a theoretical recommendation into feasible care.

Genetics, family members and continuity of care

Genetic testing confirms etiology when variant and phenotype are coherent, clarifies inheritance and directs relatives, but a variant of uncertain significance should not guide implants or predictive testing. DMD requires techniques capable of detecting deletions, duplications and sequence variants; DMPK and CNBP expansions are not detected by every panel; FXN requires appropriate GAA expansion analysis. The appropriate method is part of diagnosis, not a laboratory detail.

Cascade screening preferably uses the familial pathogenic or likely pathogenic variant and adds cardiology assessment when risk is actionable. A relative negative for the causal variant can be released from disease-specific surveillance, whereas an asymptomatic positive relative enters a program based on age and genotype. In women with a DMD variant, follow-up does not depend on weakness. Family prevention turns an individual diagnosis into anticipatory protection.

Reproductive counseling should explain X-linked, autosomal dominant, recessive inheritance and anticipation without reducing the information to a percentage. In dynamic expansions, size and transmission may modify onset; in X-linked disease, sex and X inactivation affect expression; in recessive disease, risk depends on partner status. Nondirective counseling links probabilities, predictive limitations and options to family preferences.

Transition from pediatric to adult care is a clinical phase, not an administrative one. The record should report the variant, ECG and imaging trajectory, therapies and tolerability, respiratory function, devices, anesthetic risks, independence and center contacts. Loss to follow-up at this stage often coincides with the age when cardiac risk rises. Documented continuity avoids reconstructing an already available history too late.

Prognosis, communication and multidisciplinary model

Prognosis cannot be communicated as the average for a category. Gene, variant, sex, age, ventricular function, LGE, conduction, arrhythmias, ventilation and response to treatment define different risks. Muscle stability does not guarantee cardiac stability and scar does not inevitably imply an immediate event. A stratified prognosis describes what is known, residual uncertainty and which assessments can reduce it.

Relevant outcomes do not always coincide with ejection fraction. Avoided syncope, prevention of block, lower arrhythmic burden, fewer hospitalizations, better sleep and the ability to remain at home may have great value. Trials and registries need standardized cardiac measures together with function, survival and quality of life. A person-centered outcome prevents a technically elegant parameter from replacing experienced benefit.

Decisions about devices, advanced therapies and end-of-life care require early discussion, especially when cardiac and neuromuscular progression occur at different rates. Preferences regarding shocks, resuscitation, ventilation and hospitalization may change and should be revisited without assuming that disability equals poor quality of life. Shared decision-making provides realistic information and preserves the person's control over proportionate choices.

The most effective model brings cardiology, electrophysiology, neurology, pulmonology, genetics, rehabilitation, anesthesia and primary care together around a single plan. Each specialist retains their expertise but interprets data in the context of other organs. Well-characterized registries and experienced centers are essential for rare diseases provided they do not distance routine care from the local setting. Integrated neurocardiology reduces late diagnoses, therapeutic contradictions and unsustainable procedures.

The purpose of surveillance is not to multiply tests but to identify the point at which a change is still treatable. A compared ECG, well-indicated magnetic resonance study or identified relative may precede heart failure by years; a device chosen according to genotype may prevent an event that ejection fraction alone would not have predicted. Cardiology prevention in neuromuscular diseases arises from knowledge of the trajectory and the ability to act before often-masked symptoms become irreversible.