Hypertrophic cardiomyopathy (HCM) is a myocardial disease characterized by left ventricular hypertrophy that is not explained by loading conditions sufficient to justify its extent, such as severe arterial hypertension, aortic stenosis, congenital heart disease, or physiological adaptation to training. In the classic form, the ventricle is not dilated, left ventricular ejection fraction (LVEF) is normal or increased in the early stages, but the heart is functionally abnormal because hypertrophy is associated with cardiomyocyte disarray, fibrosis, microvascular ischemia, diastolic dysfunction, electrical instability and, in a significant proportion of patients, dynamic obstruction of the left ventricular outflow tract.
Hypertrophic cardiomyopathy is one of the most common genetic cardiomyopathies. The estimated clinical prevalence in the adult population is around 1:500, but the widespread use of cardiovascular imaging, genetic testing and family screening suggests that the number of individuals carrying a phenotype or genetic predisposition may be higher. The disease may appear in childhood, adolescence, adulthood or old age, with variable penetrance and marked clinical heterogeneity even within the same family. Many patients remain asymptomatic for years and have a life expectancy close to that of the general population when they are correctly recognized, stratified and treated; a minority develop limiting dyspnea, chest pain, atrial fibrillation, cardioembolic stroke, heart failure, sudden cardiac death or progression toward a phase with systolic dysfunction.
The most typical cause of nonsyndromic hypertrophic cardiomyopathy is genetic. In most recognized familial cases, transmission is autosomal dominant and involves genes encoding cardiac sarcomere proteins. The most frequently implicated genes are MYBPC3, which encodes cardiac myosin-binding protein C, and MYH7, which encodes the beta-myosin heavy chain. Other genes with an established relationship include TNNT2, TNNI3, TPM1, MYL2, MYL3, ACTC1 and, in specific contexts, CSRP3 and ALPK3. Not all variants have the same biological weight: some cause highly penetrant disease with severe hypertrophy and early onset, while others generate late-onset, incomplete phenotypes or phenotypes modulated by sex, age, blood pressure, physical activity, metabolic comorbidities and other genetic modifiers.
The certain etiological causes, when referring to sarcomeric hypertrophic cardiomyopathy, are pathogenic or likely pathogenic variants capable of altering fundamental contractile proteins. The sarcomere becomes mechanically inefficient: to produce a given amount of work it consumes more energy, develops tension abnormally and modifies calcium sensitivity. The cardiomyocyte perceives this imbalance as chronic stress and activates growth, remodeling and survival signals. The resulting hypertrophy is not simply an adaptation to an external load, but a primary response of the cardiac muscle to an internal defect of the contractile machinery. For this reason, the wall may thicken even in the absence of hypertension, valvular stenosis or evident hemodynamic overload.
Non-sarcomeric disease must be precisely distinguished from phenocopies. Some genetic, metabolic, mitochondrial, lysosomal or infiltrative conditions may produce left ventricular hypertrophy and simulate hypertrophic cardiomyopathy, but they have different pathogenesis, prognosis and treatment. These include Fabry disease, Danon disease, PRKAG2 mutation syndrome, Pompe disease, Friedreich ataxia, RASopathies such as Noonan syndrome, cardiac amyloidosis, mitochondrial diseases and some glycogen storage disorders. In these cases, hypertrophy may derive from intracellular accumulation, extracellular infiltration, energy alterations, lysosomal defects or extracardiac growth signals. Improperly defining these conditions as sarcomeric HCM represents a clinical error, because some have specific therapies or require targeted extracardiac surveillance.
Risk factors are not equivalent to genetic causes, but they modify phenotypic expression. A family history of hypertrophic cardiomyopathy, sudden death, unexplained syncope, implantable defibrillator, heart failure or early atrial fibrillation increases the probability of an inherited basis. Male sex, age, arterial hypertension, obesity, obstructive sleep apnea, diabetes mellitus, intense competitive physical activity, dehydration, vasodilation and tachycardia may accentuate symptoms, dynamic gradients, ischemia or arrhythmias. Hypertension may coexist with HCM and make interpretation of hypertrophy more difficult; its presence does not exclude the diagnosis if wall thickness, hypertrophy distribution, family history, magnetic resonance imaging pattern or genetic testing indicate a primary myocardial disease.
The first pathogenetic event in sarcomeric HCM is contractile dysfunction at the microscopic level. Alterations in myosin, myosin-binding protein C, troponin or other sarcomere components modify the actin-myosin cross-bridge cycle, the availability of myosin heads, myofilament calcium sensitivity and the energetic cost of contraction. The cardiomyocyte tends to work in a state of excessive activation, with consumption of adenosine triphosphate (ATP) disproportionate to the mechanical work produced. This energetic imbalance reduces metabolic reserve, promotes oxidative stress, alters diastolic relaxation and stimulates hypertrophic signaling pathways, including calcineurin, mitogen-activated protein kinases and mechanosensitive signals.
Macroscopic hypertrophy is only the visible part of a much more complex disease. Typical histological findings include myocyte disarray, myofibrillar disorganization, cardiomyocyte hypertrophy, thickening of intramural arterioles and interstitial or replacement fibrosis. Disarray creates electrically heterogeneous tissue in which the impulse propagates less uniformly. Myocardial fibrosis interrupts fiber continuity, stiffens the ventricle and provides a substrate for re-entry circuits. Microvascular ischemia results from disproportion between increased myocardial mass and an insufficient capillary network, intramural compression during systole, arteriolar remodeling and increased filling pressure. The result is a hypertrophic but vulnerable myocardium, able to maintain an apparently normal LVEF despite reduced coronary and diastolic reserve.
Diastolic dysfunction is an early and often dominant consequence. The hypertrophic ventricle is stiff, relaxes slowly, fills at higher pressures and depends more heavily on atrial contraction. Even when LVEF is normal, stroke volume may be limited because the ventricular cavity is small and filling is inefficient. During exercise, tachycardia or atrial fibrillation, diastolic time shortens and loss of atrial systole may cause an abrupt rise in filling pressures, dyspnea, pulmonary edema or hypotension. This dependence on atrial systole is one of the reasons why atrial fibrillation is often poorly tolerated in patients with HCM.
Dynamic obstruction of the left ventricular outflow tract is a distinctive feature of the obstructive form. It is not a fixed stenosis like aortic valve stenosis, but a variable phenomenon that depends on contractility, preload, afterload, heart rate, septal anatomy, cavity shape, papillary muscle position and mitral valve morphology. During systole, the anterior mitral leaflet may move toward the interventricular septum, a phenomenon called systolic anterior motion (SAM). This narrows the outflow tract, generates a dynamic pressure gradient and often produces secondary mitral regurgitation. The gradient increases when the ventricle is smaller and hyperdynamic, as during dehydration, the Valsalva maneuver, standing, vasodilation or exercise, and may decrease with increased preload, reduced contractility or slower heart rate.
The mitral valve is not merely a bystander. Many patients with obstructive HCM have elongated mitral leaflets, anteriorly displaced papillary muscles, abnormal insertions, accessory chordae or abnormalities of the subvalvular apparatus. These features bring the mitral valve closer to the outflow tract and make systolic anterior motion more likely. The resulting mitral regurgitation is usually late systolic and posteriorly directed, consistent with displacement of the anterior leaflet toward the septum; when the jet is central or anterior, an associated primary mitral valve disease should be suspected. This distinction is essential because a patient with obstruction and significant mitral abnormality may require a surgical strategy different from simple septal reduction.
Non-obstructive forms and forms with mid-ventricular obstruction also exist. In non-obstructive HCM, the dominant problem is often the combination of diastolic stiffness, microvascular ischemia, fibrosis, increased filling pressures and reduced functional reserve. In mid-ventricular obstruction, narrowing occurs in the mid portion of the ventricle and may be associated with an intracavitary gradient, high apical pressure and development of an apical aneurysm. Apical aneurysm is important because it favors thrombosis, ventricular arrhythmias and localized transmural scar, even when the rest of the ventricle preserves systolic function.
The arrhythmic pathophysiology arises from the interaction between substrate and triggers. The substrate consists of disarray, fibrosis, hypertrophy, ischemia, calcium alterations and conduction heterogeneity. Triggers may include ventricular premature beats, ischemia, tachycardia, electrolyte imbalances, dehydration, adrenergic activation or intense exercise. Ventricular arrhythmias account for a proportion of sudden cardiac deaths, especially in young people, but the absolute risk varies greatly among patients. Atrial fibrillation, by contrast, arises from atrial dilation and fibrosis, chronic elevation of filling pressures, mitral regurgitation and aging; once it appears, it may markedly worsen symptoms and embolic risk.
Progression toward a phase with systolic dysfunction is a less frequent but serious evolution. In this phase, LVEF falls below 50%, hypertrophy may regress or be replaced by dilation and fibrosis, the clinical picture resembles advanced heart failure and the risk of events increases. This is not an obligatory transformation of HCM, but a possible outcome when fibrosis, ischemia, remodeling and cardiomyocyte loss exceed compensatory capacity. The presence of multiple sarcomeric variants, extensive fibrosis, atrial fibrillation, declining LVEF, apical aneurysm or unfavorable family history suggests an aggressive evolutionary trajectory.
Hypertrophic cardiomyopathy may be discovered incidentally or present with major symptoms. In clinical practice, suspicion often arises from a systolic murmur, an abnormal electrocardiogram, a family history, syncope, a sports evaluation, an episode of atrial fibrillation, chest pain with unobstructed coronary arteries or an echocardiogram requested because of dyspnea. The correct sequence of clinical assessment starts with history-taking, because HCM symptoms depend on different mechanisms and their interpretation guides the entire diagnostic pathway.
The most frequent symptom is exertional dyspnea. The patient may report breathlessness when climbing stairs, reduced exercise tolerance, the need to slow down compared with peers or slower recovery after physical activity. The cause may be diastolic, obstructive, ischemic, arrhythmic or mixed. A stiff ventricle rapidly increases filling pressures during exercise; a dynamic gradient may reduce forward output; SAM-related mitral regurgitation increases left atrial pressure; microvascular ischemia limits myocardial reserve. For this reason, two patients with similar wall thickness may have very different symptoms.
Chest pain is common and may simulate angina. It often appears during exertion, but may also occur at rest. Coronary angiography may be normal, because the pain derives from microvascular ischemia, increased myocardial mass, compression of small vessels, increased wall stress and reduced subendocardial perfusion. The presence of pain does not, however, justify excluding coronary artery disease, especially in older patients or those with cardiovascular risk factors. HCM and coronary artery disease may coexist, and their simultaneous recognition is essential to avoid overly rapid diagnostic attribution.
Palpitations may derive from premature beats, supraventricular tachycardias, atrial fibrillation or ventricular arrhythmias. Atrial fibrillation may present with irregular palpitations, sudden dyspnea, worsening functional capacity, chest pain, dizziness or heart failure. In patients with HCM, loss of the atrial contribution to ventricular filling is particularly relevant, because the hypertrophic ventricle depends on atrial systole more than a normal ventricle. The onset of atrial fibrillation must therefore be considered a major clinical event, not a simple electrocardiographic finding.
Syncope and presyncope require rigorous evaluation. They may result from severe dynamic obstruction, abnormal blood pressure response to exercise, ventricular tachycardia, bradyarrhythmia, rapid atrial fibrillation, hypovolemia, vasodilation or neurally mediated causes. Recent unexplained syncope, especially if it occurred during exertion, in the supine position or without prodromes, increases concern about arrhythmic risk. Presyncope during standing or dehydration may be related to an increased dynamic gradient, but it should not be dismissed as benign without correlation with imaging, rhythm monitoring and family history.
Some patients report symptoms specifically related to outflow tract obstruction. Dyspnea, a sensation of emptiness, chest pain or lightheadedness may worsen after large meals, alcohol, hot showers, fever, dehydration, vasodilators or sudden exertion. These contexts reduce preload or afterload, increase contractility or modify heart rate, making the provocable dynamic gradient more evident. History-taking must therefore explore not only the presence of symptoms, but also the circumstances in which they occur.
In children and adolescents, presentation may be different. The diagnosis may emerge from family screening, a murmur, syncope, exertional chest pain, dyspnea, poor growth, arrhythmias or cardiac arrest. In neonates and infants, especially when hypertrophy is marked or associated with extracardiac signs, syndromic, metabolic or storage diseases must be considered. Early age at onset, severity of hypertrophy, family history and the presence of extracardiac manifestations influence prognosis and the diagnostic pathway.
Family history must be collected systematically. It is necessary to look for cases of HCM, ventricular hypertrophy, sudden death, resuscitated cardiac arrest, unexplained syncope, unclear road accidents or drownings, defibrillator, pacemaker, early atrial fibrillation, juvenile stroke, heart failure, heart transplantation, death during sleep or during sports activity. Signs compatible with phenocopies should also be sought, such as neuropathy, renal failure, angiokeratomas, hypohidrosis, neuropathic pain, hearing loss, muscle weakness, cognitive delay, short stature, syndromic facies, multiple lentigines or ataxia. These elements may shift suspicion from sarcomeric HCM toward a different diagnosis.
Physical examination is normal in many patients. When dynamic obstruction is present, the most typical finding is an ejection systolic murmur at the left sternal border or apex, often variable with maneuvers. The murmur increases with Valsalva, standing or reduced preload, whereas it may decrease with squatting or increased venous return. This variability helps distinguish it from many fixed valvular stenoses. If SAM-related mitral regurgitation coexists, an apical holosystolic or late systolic murmur may appear. Murmur intensity does not precisely measure risk, but it signals the need to assess the gradient at rest and with provocation.
Cardiovascular examination may show a sustained apical impulse, a fourth heart sound from atrial contraction against a stiff ventricle, a bifid or brisk pulse in obstructive patients, signs of congestion in advanced cases and rhythm irregularity in atrial fibrillation. Blood pressure may be normal, elevated or show an abnormal response to exertion. In patients with advanced heart failure, edema, pulmonary crackles, jugular venous distension, hepatomegaly and signs of low output may appear, but these findings are less frequent than dyspnea due to diastolic dysfunction or obstruction.
The clinical assessment must conclude with a synthesis that separates asymptomatic from symptomatic patients, obstructive from non-obstructive patients, subjects at arrhythmic risk from those at apparently low risk and probably sarcomeric forms from phenocopies. This initial classification does not replace investigations, but it avoids a common error: treating all patients with HCM as though they had the same disease. HCM is simultaneously an anatomical, genetic, hemodynamic and electrical diagnosis, and clinical evaluation must prepare the integrated interpretation of all these levels.
The diagnostic pathway for hypertrophic cardiomyopathy must establish whether hypertrophy is real, whether it is primary or secondary, whether it is obstructive or non-obstructive, whether there is a genetic cause or a phenocopy, and what the individual risk of complications is. The most frequent error is stopping at wall thickness without interpreting its context, distribution, physiology, tissue pattern and family history. A thick septum is not enough to diagnose HCM; it is necessary to demonstrate that hypertrophy is not explained by sufficient loading conditions and that the overall picture is consistent with a primary myocardial disease.
International guidelines share diagnostic criteria based on cardiac imaging and exclusion of alternative causes of hypertrophy. The practical formulation of the diagnostic criteria is as follows:
The 12-lead electrocardiogram is a first-line examination and may be abnormal even when echocardiographic hypertrophy is mild. It may show criteria for left ventricular hypertrophy, pseudo-infarction Q waves, repolarization abnormalities, deep T-wave inversion in apical forms, left atrial enlargement, pre-excitation in phenocopies, conduction disturbances or arrhythmias. A markedly abnormal electrocardiogram with mild hypertrophy should raise suspicion of phenocopies or genetically relevant forms; an almost normal electrocardiogram does not exclude HCM, but reduces the probability of an advanced phenotype.
Transthoracic echocardiography is the main initial examination. It must measure maximum thickness in all segments, not only in the basal septum, and evaluate ventricular cavity, LVEF, diastolic function, left atrium, mitral apparatus, papillary muscles, mitral regurgitation, right ventricle and outflow tract gradient. The distribution of hypertrophy may be asymmetric septal, apical, concentric, lateral, mid-ventricular or rarer. Echocardiography must look for SAM, mitral-septal contact, resting obstruction, provocable obstruction and the pattern of mitral regurgitation. Measurement of thickness alone is not sufficient, because two patients with an 18 mm septum may have completely different risks and treatments if one has severe obstruction and the other has a non-obstructive apical form with aneurysm.
Gradient assessment is an essential part of the examination. A maximum left ventricular outflow tract gradient ≥30 mmHg at rest or with provocation defines the presence of hemodynamically recognizable obstruction; a gradient ≥50 mmHg, associated with attributable symptoms, is the threshold usually used to consider specific therapies for obstruction, including advanced therapy or septal reduction in appropriate patients. If the gradient is not present at rest, echocardiography must include the Valsalva maneuver, standing and, when necessary, exercise echocardiography. Pharmacological provocation with dobutamine is not suitable for physiologically reproducing HCM obstruction and may overestimate phenomena that are not clinically relevant.
Cardiac magnetic resonance (CMR) is essential when echocardiography is incomplete, when hypertrophy distribution is atypical, when apical form, aneurysm or phenocopy is suspected, or when tissue characterization is needed. CMR measures wall thickness and volumes with high accuracy, visualizes the apex better than echocardiography, and identifies crypts, papillary abnormalities, aneurysms and fibrosis. Late gadolinium enhancement (LGE) indicates replacement fibrosis and has prognostic value, especially when extensive. T1 and T2 mapping and extracellular volume (ECV) help distinguish sarcomeric HCM, amyloidosis, Fabry disease, myocarditis, diffuse fibrosis and other conditions.
Laboratory tests do not diagnose sarcomeric HCM, but they are indispensable for differential diagnosis, comorbidities and phenocopies. B-type natriuretic peptide (BNP) or N-terminal pro-B-type natriuretic peptide (NT-proBNP) may reflect filling pressures, obstruction, diastolic dysfunction or heart failure. Troponin may be chronically mildly elevated in some patients because of microvascular ischemia or myocardial stress. Creatinine, electrolytes, liver function, blood count, iron status, thyroid-stimulating hormone (TSH), glucose, glycated hemoglobin and lipid profile help with overall management. Alpha-galactosidase A, lyso-globotriaosylceramide, targeted genetic studies, immunofixation, free light chains, bone scintigraphy for transthyretin amyloidosis and other tests are used only when the clinical picture suggests a specific alternative diagnosis.
Rhythm monitoring is necessary for functional diagnosis and risk stratification. Electrocardiographic Holter monitoring, prolonged monitoring or selected implantable recorders may document silent atrial fibrillation, non-sustained ventricular tachycardia, pauses, bradyarrhythmias or premature beat burden. Detection of atrial fibrillation is particularly important in patients with a dilated left atrium, palpitations, stroke, older age or intermittent symptoms. Non-sustained ventricular tachycardia does not automatically equal an indication for a defibrillator, but it enters the overall assessment together with age, maximum thickness, syncope, family history, LGE, apical aneurysm and systolic function.
Exercise testing has several functions. It allows assessment of real functional capacity, blood pressure response, symptoms, arrhythmias, ischemia and exercise-induced gradient. In patients with symptoms disproportionate to resting findings, exercise echocardiography may demonstrate latent obstruction. Cardiopulmonary exercise testing (CPET) quantifies oxygen consumption, ventilatory efficiency and functional reserve, and is useful when assessing advanced heart failure, exercise eligibility, therapeutic response or candidacy for invasive therapies.
Genetic testing must be preceded by genetic counseling. It is indicated especially when the clinical diagnosis is clear, when there is family history, when the patient is young, when screening of relatives may benefit from a molecular result, or when a phenocopy with specific treatment is suspected. A positive result allows cascade testing in relatives and may help with prognosis; a negative result does not exclude HCM; a variant of uncertain significance must not be used to diagnose or exclude the disease in relatives. First-degree relatives must receive clinical evaluation with electrocardiogram and echocardiogram, repeated over time according to age, family phenotype and genetic result.
The differential diagnosis with athlete’s heart requires caution. Sports adaptation may produce increased wall thickness, but it is usually associated with a larger ventricular cavity, normal or supranormal diastolic function, absence of pathological LGE, absence of family history and partial regression after detraining. HCM may, however, coexist with intense training, and a genetically predisposed athlete may have a phenotype that is more difficult to interpret. The distinction requires integration of wall thickness, cavity dimensions, electrocardiogram, CMR, family history, genetic testing and evolution over time.
The differential diagnosis with hypertension and aortic stenosis is equally important. Hypertension tends to produce concentric hypertrophy proportionate to pressure load, but it may overlap with HCM and mask it. Aortic stenosis generates fixed pressure overload and requires complete valvular assessment. Amyloidosis and Fabry disease may simulate HCM in adults: low voltages or mass-voltage discordance, valvular thickening, carpal tunnel syndrome, neuropathy, proteinuria, diffuse CMR pattern or reduced native T1 in Fabry disease point toward alternative diagnoses. In children, marked hypertrophy, hypotonia, developmental delay, dysmorphic features or multiorgan involvement must prompt investigation for metabolic and syndromic diseases before concluding that isolated sarcomeric HCM is present.
The treatment of hypertrophic cardiomyopathy depends on the clinical profile. The first distinction is between asymptomatic and symptomatic patients, then between obstructive and non-obstructive forms, and finally between low and high arrhythmic risk. The objectives are to reduce symptoms and gradient when present, prevent sudden death in at-risk subjects, treat atrial fibrillation and heart failure, recognize treatable phenocopies, guide physical activity and pregnancy, and protect relatives through screening and genetic counseling. A uniform approach is not appropriate, because HCM may be an almost silent condition or a complex hemodynamic, arrhythmic and familial disease.
In asymptomatic patients without significant obstruction and without high-risk markers, treatment mainly consists of clinical, echocardiographic, rhythm and family surveillance. Therapy intended only to reduce stable wall thickness is not indicated in the absence of symptoms or specific risk. Dehydration, alcohol abuse, stimulants and self-medication that may increase tachycardia, vasodilation or preload reduction should be avoided. Mild or moderate recreational physical exercise is generally encouraged in stable patients, whereas participation in competitive activity requires specialist assessment and shared decision-making, considering phenotype, arrhythmic risk, family history, LGE, symptoms and patient preferences.
In symptomatic obstructive HCM, initial therapy aims to reduce heart rate, contractility and dynamic gradient, improving filling time and reducing SAM and mitral regurgitation. Non-vasodilating beta-blockers are often the first choice, especially in patients with dyspnea, chest pain or exertional symptoms. If not tolerated or ineffective, non-dihydropyridine calcium channel blockers such as verapamil or diltiazem may be used in selected patients, avoiding excessive caution but also improper use in settings with hypotension, very severe obstruction, advanced congestion or elevated filling pressure. Disopyramide may reduce contractility and gradient, usually in combination with a beta-blocker or calcium channel blocker, but requires attention to QT interval, anticholinergic effects, renal function and proarrhythmic risk.
Cardiac myosin inhibitors have changed the treatment of symptomatic obstructive HCM. Mavacamten reduces excessive actin-myosin interaction, attenuates sarcomeric hypercontractility and may reduce gradient, symptoms and the need for septal reduction therapy in selected patients with obstructive HCM. Its use requires echocardiographic monitoring of LVEF, because excessive reduction in contractility may induce systolic dysfunction. Aficamten, another myosin inhibitor in advanced clinical development, has shown benefit in trials of patients with symptomatic obstructive HCM, but its regulatory positioning and definitive integration into clinical pathways depend on approvals and recommendations in individual healthcare settings. These therapies do not replace correct diagnosis of the obstructive mechanism and must not be used for phenocopies or non-indicated forms.
When obstructive symptoms persist despite optimized therapy and the gradient remains significant, septal reduction therapy is considered. Surgical septal myectomy is the reference treatment in expert centers, especially when complex anatomy, elongated mitral leaflets, papillary abnormalities, mitral regurgitation not exclusively secondary to SAM or the need for associated valvular correction are present. Alcohol septal ablation is an alternative for selected patients, often older or with high surgical risk, when septal coronary anatomy is suitable and the center has experience. Both procedures require rigorous indication, because benefit depends on correct attribution of symptoms to obstruction and on the technical quality of the intervention.
In symptomatic non-obstructive HCM, treatment is more complex because there is no gradient to abolish. Beta-blockers or non-dihydropyridine calcium channel blockers may improve heart rate, relaxation and chest pain in some patients. Diuretics may be used cautiously for congestive symptoms, avoiding excessive preload depletion. If LVEF <50% appears, the patient enters a phase of systolic dysfunction and must be treated according to the principles of heart failure with reduced ejection fraction, adapting angiotensin receptor-neprilysin inhibitor (ARNI), angiotensin-converting enzyme inhibitors (ACEi), angiotensin II receptor blockers (ARB), beta-blockers, mineralocorticoid receptor antagonists (MRA), sodium-glucose cotransporter 2 inhibitors (SGLT2i) and diuretics to hemodynamic tolerance. In advanced cases, heart transplantation or mechanical support must be considered early.
Prevention of sudden cardiac death is one of the cornerstones of management. An implantable cardioverter-defibrillator (ICD) is indicated for secondary prevention after cardiac arrest, ventricular fibrillation or hemodynamically significant sustained ventricular tachycardia not attributable to a reversible cause. In primary prevention, the decision must integrate multiple markers: family sudden death, recent unexplained syncope, very high maximum wall thickness, non-sustained ventricular tachycardia, reduced LVEF, apical aneurysm, extensive LGE, age, clinical history and validated risk models. The choice must be neither automatic nor delayed when risk is evident, because the ICD protects against fatal arrhythmia but carries possible complications, inappropriate shocks and psychological impact.
Atrial fibrillation requires aggressive management of embolic risk. In patients with HCM, the onset of atrial fibrillation entails significant thromboembolic risk and oral anticoagulation is recommended regardless of scores used in the general population, unless contraindicated. Rhythm control is often preferable when the arrhythmia is symptomatic or poorly tolerated, using cardioversion, selected antiarrhythmic therapies or transcatheter ablation in appropriate cases. Rate control must avoid persistent tachycardia and worsening of filling. Dilated left atrium, atrial fibrosis and chronic obstruction make recurrence common, so follow-up must be continuous.
Treatment of phenocopies must be specific. In Fabry disease, enzyme replacement therapy or chaperone therapies in selected patients may modify the systemic and cardiac course. In transthyretin amyloidosis, transthyretin stabilizers and other targeted strategies have a completely different rationale from sarcomeric HCM therapy. In glycogen storage disorders, mitochondrial diseases or RASopathies, management requires a multidisciplinary team. Identifying these conditions is not an academic detail, because it changes treatment, prognosis, family screening and extracardiac surveillance.
Pregnancy is generally tolerated by many women with stable HCM, but it requires preconception assessment when symptoms, significant obstruction, arrhythmias, reduced LVEF, antiarrhythmic therapy, ICD or complex family history are present. During pregnancy, plasma volume, heart rate and hemodynamic demand increase; these changes may worsen gradient, dyspnea or arrhythmias. Management must coordinate cardiology, obstetrics and anesthesia, avoiding dehydration, tachycardia, hypotension and inappropriate treatment discontinuation.
The prognosis of HCM is now much better than the historical perception of the disease. Most patients, if correctly diagnosed and followed, can have long survival and good quality of life. However, individual prognosis remains heterogeneous. Unexplained syncope, family sudden death, extreme hypertrophy, extensive LGE, apical aneurysm, LVEF <50%, atrial fibrillation, stroke, persistent severe obstruction, refractory symptoms, frequent or rapid non-sustained ventricular tachycardia, progression toward heart failure and genetic variants associated with early onset or more aggressive disease are unfavorable. Periodic risk reassessment is therefore essential, because risk is not static and may change with age, onset of arrhythmias, remodeling, fibrosis and new family information.
Sudden cardiac death is the most feared complication of hypertrophic cardiomyopathy, although it is not the most frequent in absolute terms. It predominantly results from ventricular tachycardia or ventricular fibrillation on a substrate of disarray, fibrosis, microvascular ischemia, severe hypertrophy and electrical abnormalities. It may be the first manifestation of the disease, especially in young people, but risk is highly variable. Effective prevention requires recognition of major markers, appropriate use of the ICD and dynamic follow-up, because a patient initially at low risk may change category after syncope, onset of extensive LGE, non-sustained ventricular tachycardia or deterioration of systolic function.
Atrial fibrillation is one of the most common and clinically relevant complications. It arises from chronic elevation of filling pressures, left atrial dilation, atrial fibrosis, mitral regurgitation and aging. In patients with HCM, it may cause abrupt worsening of symptoms because the stiff ventricle loses the contribution of atrial contraction. The most serious complication is cardioembolic stroke, which may occur even in patients who, according to general scores, would appear not to be at high risk. For this reason, atrial fibrillation in HCM immediately changes anticoagulant management and requires closer surveillance.
Heart failure may appear through different mechanisms. In obstructive forms it derives from dynamic gradient, mitral regurgitation, increased left atrial pressure and diastolic dysfunction. In non-obstructive forms it derives mainly from ventricular stiffness, microvascular ischemia, fibrosis and inability to increase output during exercise. In the advanced phase with LVEF <50%, heart failure assumes systolic features, with remodeling, relative dilation, extensive fibrosis and worse prognosis. This distinction is important because an obstructive patient may improve markedly after gradient reduction, whereas a patient with advanced systolic phase requires an advanced heart failure pathway.
Left ventricular outflow tract obstruction may produce functional limitation, syncope, ischemia, mitral regurgitation and atrial remodeling. The mechanism is dynamic and may worsen intermittently, which is why some patients report symptoms that vary from day to day. Dehydration, fever, vasodilation, alcohol, large meals, tachycardia and exertion may increase the gradient. An indirect complication of chronic obstruction is progressive left atrial dilation, which favors atrial fibrillation and therefore embolic risk.
Mitral regurgitation secondary to SAM is frequent in obstructive forms. The anterior mitral leaflet is displaced toward the septum, loses coaptation with the posterior leaflet and generates a jet that is often posterior. SAM-related mitral regurgitation increases left atrial pressure, worsens dyspnea and amplifies hemodynamic instability during exercise. If regurgitation depends exclusively on SAM, it may decrease with therapy that attenuates the gradient or with effective myectomy. If, instead, primary mitral disease or complex papillary abnormality exists, persistence of regurgitation after simple septal reduction becomes a predictable complication if not recognized before intervention.
Myocardial ischemia and chest pain may occur even in the absence of epicardial coronary stenosis. Increased myocardial mass requires more oxygen, while the microcirculation is relatively insufficient and intramural arterioles are thickened. Increased ventricular diastolic pressure reduces the subendocardial perfusion gradient, especially during tachycardia. Repeated microvascular ischemia favors fibrosis, arrhythmias, worsening diastolic function and, in some forms, progression toward systolic dysfunction. Coexisting atherosclerotic coronary disease further worsens the picture and must be sought in appropriate patients.
Apical aneurysm is a less frequent complication but has high clinical significance. It may develop especially in forms with mid-ventricular obstruction, where elevated apical pressure and local ischemia favor thinning and scar formation. An apical aneurysm may harbor thrombi, cause systemic embolism and provide a substrate for ventricular tachycardias. Cardiac magnetic resonance is often superior to echocardiography in recognizing it, especially when the apex is poorly visualized. Its presence modifies risk stratification and may influence decisions on anticoagulation and ICD.
Thromboembolic complications derive mainly from atrial fibrillation, but may also appear in the presence of apical aneurysm or severe systolic dysfunction. Stroke is the most feared manifestation and may be disabling. Prevention requires timely recognition of atrial arrhythmias, appropriate anticoagulation, apical assessment when indicated and control of factors favoring stasis and atrial dilation. In patients with embolic episodes without documented atrial fibrillation, the search for silent arrhythmias must be intensified.
Progression toward a phase with systolic dysfunction is a relatively rare but serious complication. When LVEF falls below 50%, the patient must not be considered only “mildly reduced” as in other heart diseases, because in HCM a lower-than-normal LVEF signals significant loss of contractile reserve. The transition may be accompanied by apparent reduction in wall thickness, dilation, extensive fibrosis, functional mitral regurgitation, arrhythmias and advanced heart failure. In this phase, follow-up must include heart failure therapy, ICD assessment, possible resynchronization if indicated, transplantation in refractory cases and review of family history.
Psychological and familial complications are relevant. A diagnosis of HCM may generate anxiety about sudden death, uncertainty regarding physical activity, reproductive concerns and insurance or work-related difficulties. In relatives, finding a pathogenic variant may create tension between prevention and the perception of disease in the absence of symptoms. Genetic counseling also serves to avoid incorrect interpretations: being a carrier does not necessarily mean being ill at that moment, while a negative genetic test in the absence of the known familial variant may reduce the need for specific cardiological surveillance.
Treatment-related complications must be considered without weakening the indication when the benefit is clear. Beta-blockers may cause bradycardia, fatigue or hypotension; verapamil and diltiazem may worsen congestion in selected patients; disopyramide may cause anticholinergic effects and QT prolongation; myosin inhibitors may excessively reduce LVEF and require structured monitoring. Myectomy may involve conduction blocks, ventricular septal defects, aortic insufficiency or surgical complications; alcohol septal ablation may cause atrioventricular block and the need for a pacemaker. The ICD protects against sudden death but may cause infections, inappropriate shocks, lead fracture and psychological impact. Modern HCM management also consists of minimizing these risks through correct indication and expert centers.