Dilated-phase hypertrophic cardiomyopathy

Article written and reviewed by Dr Luca Moretti

Hypertrophic cardiomyopathy can evolve, in a minority of patients, toward reduced left ventricular systolic function. The conventional threshold is an ejection fraction below 50%, a value that in other conditions might appear only mildly reduced but in HCM signals a substantial loss relative to its usually hyperdynamic physiology. The more precise term is HCM with systolic dysfunction, because the cavity is not necessarily dilated and the expression “end-stage” incorrectly suggests a uniform and irreversible course.

The phenotype does not arise as a new dilated cardiomyopathy but as transformation of previously hypertrophied myocardium. Documentation from earlier echocardiograms, the distribution of residual hypertrophy, the fibrosis pattern and family history preserve the memory of the original disease. This phenotypic continuity is clinically decisive because arrhythmic risk, genetics and mechanical support issues do not coincide with those of common sporadic DCM.

The transition may include wall thinning, increased volumes, disappearance of previous obstruction and development of functional mitral regurgitation, but none of these features is mandatory. Some patients retain a relatively small cavity with low output, elevated filling pressures and restrictive physiology; others develop frankly dilated geometry. Speaking of a remodeling spectrum avoids forcing different presentations into a single anatomic sequence.

Reduced ejection fraction does not exhaust the assessment. Fibrosis, longitudinal function, output, the right ventricle, pulmonary pressure, arrhythmias and functional capacity may deteriorate before or independently of the global value. HCM with an apparently preserved but progressively declining ejection fraction therefore deserves attention, particularly when congestion, exercise intolerance or increasing extent of late gadolinium enhancement appears.

Management simultaneously belongs to cardiomyopathy medicine, advanced heart failure and arrhythmia care. The goal is not merely to normalize an echocardiographic number but to identify reversible components, reduce the risk of sudden death, preserve organs and determine early whether resynchronization, ventricular support or transplantation is needed. Timing of referral to an expert center often matters more than the choice of a single drug.

Mechanisms and trajectory of remodeling

The substrate of progression includes cardiomyocyte disarray, energetic abnormalities, microvascular ischemia, cell death and fibrous replacement. When loss of functioning myocardium exceeds the compensatory capacity of hypertrophy, global contractility declines and wall stress increases. Replacement fibrosis is not merely a marker: it interrupts force transmission, stiffens the ventricle and creates electrical heterogeneity favorable to arrhythmias.

Ischemia does not require epicardial coronary stenoses. Remodeled intramural arteries, reduced capillary density, systolic compression and the high demand of hypertrophied myocardium impair flow reserve. Repeated episodes of microvascular ischemia may produce microscopic necrosis and scar, especially in the most hypertrophied segments or those exposed to high intraventricular pressure.

Genetics modifies the probability and age of transition. In registries, pathogenic sarcomeric variants and the presence of multiple causal variants are associated with a more severe course but do not allow deterministic prediction in an individual. The sarcomeric genotype should be interpreted together with age at onset, the functional trajectory and family phenotype, avoiding attribution of prognostic value to a variant of uncertain significance that it does not possess.

Remodeling does not begin on the day ejection fraction falls to 49%. A serial decline relative to the individual baseline, worsening global longitudinal strain, increasing end-systolic volume and loss of previous hypercontractility may precede the threshold. This preclinical phase justifies comparison with previous examinations and makes an isolated reading classified only as normal or abnormal inadequate.

Previous obstruction may lessen as the ventricle loses force or enlarges, but its disappearance does not equal improvement. The patient may report fewer symptoms caused by the gradient while filling pressures and pump failure increase. Loss of the gradient should therefore be interpreted in the context of systolic function and not automatically celebrated as a therapeutic response.

Persistent atrial fibrillation, uncontrolled rate, frequent right ventricular pacing and bundle branch block may add a reversible or partially reversible component. Epicardial ischemia, valvular disease, uncontrolled hypertension and negative inotropic medications may also contribute. Searching for modifiable cofactors prevents every deterioration from being attributed to genetic progression and may allow clinically meaningful recovery.

The right ventricle enters the natural history through ventricular interdependence, pulmonary hypertension, tricuspid regurgitation and biventricular myocardial disease. Early right ventricular dysfunction may be concealed by treated congestion but becomes decisive in selection for mechanical support. Right ventricular reserve should therefore be assessed before renal or hepatic failure makes procedural risk prohibitive.

The clinical trajectory is heterogeneous. Some patients remain stabilized for years with heart failure therapy, others develop arrhythmias before congestion, and still others progress rapidly toward low output. The concept of longitudinal remodeling requires repeated measurements and updated decisions rather than a definitive prognosis formulated at the first reduction in ejection fraction.

Diagnosis, imaging and differential diagnosis

Diagnosis requires convincing evidence of previous or persistent HCM and reliable documentation of systolic dysfunction. Echocardiography measures volumes, ejection fraction, strain, regurgitation, right ventricular function and pulmonary pressure, searching for a residual gradient at rest or with provocation when appropriate. Serial comparison should use consistent methods because differences in quality or algorithm can simulate small changes.

Cardiac magnetic resonance defines geometry and function more accurately when echocardiographic windows are limited. Late gadolinium enhancement shows focal scar, whereas T1 mapping and extracellular volume describe diffuse abnormalities that relative LGE may underestimate in diffusely diseased myocardium. Tissue characterization contributes to prognosis and differential diagnosis but does not replace phenotypic history.

Genetic DCM may present with apparently thick walls because of edema, trabeculation or early remodeling, while hypertension and aortic stenosis may precede dysfunction from overload. Amyloidosis, Fabry, Danon, PRKAG2 and mitochondrial diseases produce hypertrophic phenotypes with specific evolution. Etiologic reassessment is necessary when the course, extracardiac findings or imaging do not match expected sarcomeric HCM.

Coronary artery disease should be excluded to a degree proportionate to age, symptoms and risk because an infarction may reduce function and modify the scar pattern. Coronary CT angiography or invasive coronary angiography is chosen according to pretest probability and clinical needs. The presence of stenosis does not, however, prove that it explains the entire phenotype; dual pathology is possible and requires segmental attribution of injury.

Electrocardiographic monitoring searches for atrial fibrillation, nonsustained ventricular tachycardia, pauses, conduction block and pacing burden. In device carriers, electrograms allow reconstruction of the temporal relationship between arrhythmia and functional decline. Arrhythmic burden, more than the simple presence of an episode, helps determine whether the arrhythmia is a cause, consequence or amplifier of deterioration.

Cardiopulmonary exercise testing quantifies oxygen consumption, ventilatory slope, blood pressure response and chronotropic limitation. A patient may minimize symptoms by unconsciously reducing activity, whereas an objective value reveals markedly impaired reserve. Cardiopulmonary capacity informs prognosis and transplant timing, provided it is interpreted with age, beta-blocker therapy, anemia and deconditioning.

Natriuretic peptides and high-sensitivity troponin describe stress and injury but are not specific. Renal function, sodium, iron, liver function, thyroid testing and blood count identify consequences or treatable aggravating factors. The laboratory profile also documents organ reserve before advanced procedures, preventing apparent stability from concealing chronic systemic congestion.

Right heart catheterization is not necessary in every patient but becomes essential when symptoms and imaging disagree, low output is suspected, or transplantation and mechanical support are being evaluated. Pressures, cardiac index, pulmonary vascular resistance and response to decongestion clarify physiology. Hemodynamic measurement should be performed under known clinical conditions because volume status and medications can profoundly alter its meaning.

Heart failure therapy and correction of reversible factors

When ejection fraction falls below 50%, pharmacologic strategy shifts toward systolic heart failure, adapting doses and sequence to blood pressure, renal function and congestion. Renin-angiotensin system inhibition or ARNI, an evidence-based beta-blocker, mineralocorticoid receptor antagonist and SGLT2 inhibitor constitute the pillars when tolerated. Foundational therapy should be started without waiting for marked dilation.

Specific randomized evidence in HCM with systolic dysfunction is limited, so many recommendations derive from the biology of heart failure with reduced ejection fraction and from consensus. This extrapolation is reasonable but requires caution in small ventricles, low blood pressure and possible residual obstruction. Individual titration is more important than automatic application of target doses that are not tolerated.

Loop diuretics control congestion and filling pressures without modifying the substrate by themselves. Excessive volume removal may reduce output, worsen renal function or reactivate a residual dynamic gradient. Euvolemic weight is therefore a clinical range pursued using symptoms, examination and laboratory testing rather than a rigid number.

Verapamil, diltiazem, disopyramide and myosin inhibitors are used in other HCM settings to reduce contractility or obstruction. In the presence of systolic dysfunction, their indication should be reassessed and myosin inhibitors discontinued according to product labeling and monitoring. Deprescribing negative inotropes may be as important as adding heart failure therapy.

Atrial fibrillation requires prompt rate control and rhythm assessment because loss of atrial systole is particularly poorly tolerated in a stiff ventricle. Cardioversion, antiarrhythmic drugs or ablation are selected considering duration, atrial size, comorbidities and the probability of maintaining rhythm. Rhythm control may recover a component of function when tachycardia has contributed to remodeling.

In HCM, clinical atrial fibrillation generally warrants anticoagulation regardless of the CHA2DS2-VASc score unless contraindicated. Intracavitary thrombosis or apical aneurysm introduces additional considerations but does not justify indiscriminate treatment without documented risk. Thromboembolic prevention should be coordinated with renal function, interactions and procedures.

A high percentage of right ventricular pacing or bundle branch block with dyssynchrony may worsen function. Device revision, biventricular resynchronization or physiologic pacing are assessed according to QRS, ejection fraction, symptoms and anatomy. Correction of dyssynchrony may improve efficiency without removing the fibrotic substrate, and response remains variable.

Anemia and iron deficiency, sleep apnea, obesity, diabetes, thyroid disease and renal insufficiency increase symptoms and vulnerability. Treating them does not replace cardiac therapy but broadens functional reserve and reduces precipitating factors. Management of comorbidities should avoid unproven supplements or interventions, distinguishing correction of a documented deficiency from generalized empirical treatment.

Physical activity is prescribed individually after stabilization, favoring moderate, progressive aerobic exercise. Congestion, uncontrolled arrhythmias, syncope or low output require reassessment before training. Cardiac rehabilitation may improve capacity and confidence but should not be confused with evidence that arrhythmic risk has disappeared.

Arrhythmias, devices and advanced heart failure

An ejection fraction below 50% is an important risk factor in HCM and supports discussion of a defibrillator for primary prevention. The decision integrates age, LGE, ventricular tachycardia, syncope, aneurysm, family history and competing risks. A preventive ICD protects against arrhythmic death but does not prevent hemodynamic progression and entails infections, inappropriate shocks and revisions over time.

Monitoring should identify slow arrhythmias as well as rapid ones. Fibrosis and genetic variants may produce conduction disease, while medications and procedures aggravate bradycardia. Selection of a pacing system considers anticipated pacing needs, possible resynchronization and the prospect of transplantation, not only the immediate problem.

Monomorphic ventricular tachycardias may reflect circuits within scar and cause recurrences despite an ICD. Antiarrhythmic drugs and ablation reduce burden and shocks, but access to the substrate may be complex because of thickness and intramural or epicardial location. Control of recurrences requires a center experienced in both HCM and ablation of structural cardiomyopathy.

Advanced heart failure is not defined by ejection fraction alone. Repeated hospitalizations, hypotension, increasing diuretic requirement, hyponatremia, worsening renal function, medication intolerance and low oxygen consumption are warning signs. The advanced profile should trigger assessment before the patient becomes dependent on inotropes or develops irreversible pulmonary hypertension.

Heart transplantation provides a solution to the myocardial substrate when medical therapy and devices do not control pump failure or arrhythmias. Candidacy includes nutritional status, adherence, social support, extracardiac function and pulmonary vascular resistance. Transplant assessment does not equal immediate listing but creates time to correct modifiable barriers.

Left ventricular assist support may be technically more difficult than in DCM because a small cavity, residual hypertrophy and right ventricular involvement favor inflow obstruction and right-sided failure. In patients with frankly dilated remodeling, support may be an effective bridge to transplantation. LVAD selection requires specific anatomic imaging and hemodynamic assessment without automatically transferring criteria developed for large ventricles.

Intravenous inotropes may temporarily support output in shock or as a bridge, but increase oxygen consumption and arrhythmic potential. Their chronic introduction signals a severe prognostic phase and should be linked to a defined goal. A therapeutic bridge without a destination instead exposes the patient to complications without changing the trajectory.

Palliative care is complementary to advanced therapies, not a late alternative reserved for the final days. Control of dyspnea, anxiety and pain, advance planning and discussion of shock deactivation improve quality and consistency of care. Shared planning remains appropriate even during transplant evaluation because prognosis and organ availability remain uncertain.

Follow-up, prognosis and family management

Follow-up is closer than in stable HCM and is modulated according to the rate of change, symptoms and therapy. Echocardiography, ECG, rhythm monitoring, laboratory testing and clinical assessment should answer defined questions, whereas CMR and cardiopulmonary testing are repeated when they can change decisions. Integrated surveillance avoids both excessive intervals and serial tests without operational consequences.

Prognosis is less favorable than in HCM with preserved function but is not uniformly terminal. Registries show a high burden of death, transplantation, mechanical support and heart failure, with wide individual variability. Prognostic communication should use updatable scenarios and indicators, avoiding aggregate percentages presented as personal destiny.

Partial recovery of ejection fraction does not authorize automatic treatment withdrawal. Scar and genotype persist, while arrhythmias, infections or medication discontinuation may provoke renewed dysfunction. Functional remission is therefore distinct from cure and maintains an indication for surveillance and, as a rule, continuation of tolerated treatments.

Pregnancy and the puerperium increase volume, heart rate and circulatory demand. A woman with systolic dysfunction requires multidisciplinary preconception counseling, review of teratogenic medications and a plan for delivery and postpartum care. Maternal risk depends on function, symptoms, arrhythmias and pulmonary pressure; severely reduced ejection fraction may make pregnancy high-risk or inadvisable.

In children and adolescents, systolic dysfunction may develop early and carries an important cumulative risk. Growth, medication dosing, sports, school and transition to adult care require dedicated pediatric expertise. The pediatric course cannot be modeled solely on adult data, although principles of imaging, genetics and early referral remain shared.

Development of the systolic phase in the proband does not mean that all relatives will follow the same trajectory. Clinical screening and cascade genetic testing, when a familial pathogenic variant exists, identify who requires surveillance. Family risk should be communicated by distinguishing variant transmission, phenotypic penetrance and the much less well-defined probability of progression.

In carrier relatives without hypertrophy, ECG and imaging are scheduled according to age, gene and family history. New symptoms, pregnancy or intense sports activity may bring reassessment forward. Surveillance of carriers should neither transform a predisposition into clinical disease nor ignore early electrical or structural signals.

An effective network connects a cardiomyopathy center, heart failure clinic, electrophysiology, genetics, rehabilitation and transplantation. The community physician maintains continuity for blood pressure, weight, adherence, vaccinations and comorbidities, while the center addresses high-complexity decisions. Shared care reduces the risk that the patient is followed in parallel pathways unable to recognize the overall trajectory.

Decision points and complex clinical scenarios

An ejection fraction still between fifty and sixty percent does not formally define the systolic phase but may represent an important decline in a patient whose baseline values were hyperdynamic. Comparison with previous examinations, strain and increasing volumes identifies a trajectory before the threshold is crossed. Relatively reduced function in HCM should not be interpreted using the same references as a normal heart.

Obstruction may lessen as the ventricle loses force and the cavity enlarges, but it does not disappear in every patient. If a gradient persists, indiscriminate reduction of preload or afterload may worsen symptoms, while continuing strongly negative inotropic drugs may aggravate dysfunction. The mixed hemodynamic phenotype requires measurements at rest and with provocation and close adjustment.

Atrial fibrillation may precipitate congestion through loss of atrial contraction, rapid response and mitral regurgitation, but may also result from chronically elevated pressures. Rhythm restoration is more likely to succeed if pursued before extreme atrial dilation. The causal role of the arrhythmia is estimated from timing and response, avoiding attribution of the entire decline to the myopathic substrate.

In a young patient, apparently modest deterioration may compromise decades of prognosis and justifies early assessment at an HCM and advanced heart failure center. In older patients, amyloidosis, hypertension, coronary disease and valvular disease may instead mimic or amplify the transition. Age-dependent interpretation modifies the differential diagnosis and threshold for additional investigations.

Pregnancy and the postpartum period increase volume and cardiac demand and may unmask reduced reserve. Planning considers function, arrhythmias, residual obstruction, teratogenic medications and maternal-fetal risk, with genetic counseling separated from hemodynamic risk. Preconception assessment allows controlled therapeutic changes and a plan for delivery and the puerperium.

Functional capacity may decline before reported symptoms appear severe because the patient unconsciously reduces activity. Serial cardiopulmonary testing objectively measures oxygen consumption, blood pressure response and ventilatory inefficiency and helps determine timing of advanced referral. Clinical-functional discordance is particularly relevant when ejection fraction alone appears stable.

The choice between mechanical support and transplantation is influenced by a small cavity, residual hypertrophy, right ventricular dysfunction and arrhythmias, which may make LVAD implantation more complex than in DCM. Late assessment may leave technically difficult support as the only option in a patient who already has multiorgan dysfunction. Planning for support should precede inotrope dependence or hemodynamic collapse.

The dilated phase does not represent a new independent disease but transformation of a substrate that retains its own genetic and arrhythmic implications. Documenting the entire trajectory makes it possible to distinguish progression, a second cardiomyopathy and reversible factors and to choose protection, therapy and advanced referral. The complete phenotypic history is therefore a diagnostic and therapeutic tool, not merely an archive of images.