Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy is common enough — affecting between 0.2% and 1.4% of the general population — that every echocardiographer will encounter it regularly, and the diagnosis rests more heavily on the echocardiogram than almost any other cardiomyopathy. See Introduction to Diseases of the Myocardium for how HCM fits into the broader phenotype classification this page builds on.

Definition and Genetics

HCM in adults is defined by wall thickness of 15 mm or more in one or more LV myocardial segments, not solely explained by loading conditions such as hypertension. In first-degree relatives of an affected patient — who carry a 50% risk of having inherited the causative gene — the diagnostic threshold is lower, at 13 mm or more, reflecting their genuinely different prior probability.

This is worth stating plainly: the definition is dimensional, not genetic. It deliberately covers a diverse group of diseases, both inherited and acquired, that happen to produce the same structural finding — which is exactly why the phenocopies discussed below matter so much. When HCM is caused by a sarcomeric gene variant, the pattern is autosomal dominant, with a disease-causing change found predominantly in MYBPC3 and MYH7 — in about a fifth of patients with a negative family history, and about half of those with a positive one. Genetic testing is rarely useful as a primary diagnostic tool in genuinely ambiguous cases, since a negative result remains likely even in confirmed disease; its real value is enabling pre-symptomatic screening of relatives once a disease-causing variant has been identified in the index case.

Age-related penetrance is a genuine feature of the disease: the proportion of gene carriers who go on to express the phenotype rises with age, and screening yield in first-degree relatives is correspondingly higher in families where disease onset has historically been early. Complications are reasonably common — in one multicenter longitudinal study, atrial fibrillation occurred in 20% of patients, sudden cardiac death or resuscitated cardiac arrest in 4%, and LV systolic dysfunction (EF under 50%) in 8%.

Measuring Wall Thickness Correctly

Because the diagnosis is dimensional, accurate measurement is genuinely foundational — ancillary features like LVOT obstruction don’t contribute to the diagnostic threshold itself.

• Measure in short-axis views, orthogonal to the endocardial and epicardial circumference, wherever the hypertrophy is maximal — at the basal (mitral valve level), mid-ventricular, and apical levels, across the anterior, septal, inferior, and lateral walls. The thickest segment may not be in the septum — a genuine reminder not to stop measuring once the septum looks impressive.
• Exclude the RV wall, papillary muscles, trabeculations, and the moderator band — including structures attached to but not truly incorporated into the septum, which overestimates thickness and risks a false diagnosis.
• State explicitly in the report if any LV segment couldn’t be visualized — commonly the basal anterior and anterolateral walls — and recommend cardiac MRI as an alternative when this happens.
• In apical HCM, where the normal tapering of the cavity and epicardium is lost, apical wall thickness can measure under 15 mm; one criterion defines apical HCM by an apical-to-basal wall thickness ratio exceeding 1.3:1. Sectioning the apex in all three apical views (four-, two-, and three-chamber) avoids the false impression of apical hypertrophy from foreshortening, and myocardial contrast can help when visualization is difficult.

Recognized Patterns of Hypertrophy

The distribution of LVH should be explicitly described, since the pattern itself carries diagnostic information — including, in one study, a genuine correlation with the likelihood of finding a disease-causing gene variant. A reverse-curvature septal contour had the highest genetic yield; a sigmoid septal contour had the lowest — worth knowing, since it means septal shape isn’t just descriptive.

• Asymmetric septal hypertrophy — the most common pattern, historically described by a septal-to-posterior wall thickness ratio exceeding 1.3:1, though the absolute thickness thresholds above are now the primary diagnostic criteria, with the ratio serving a supplementary, descriptive role.
• Concentric hypertrophy — diffuse, symmetric thickening; genuinely harder to distinguish from hypertensive heart disease or a storage/infiltrative phenocopy than the asymmetric pattern.
• Apical hypertrophy — confined to the LV apex, with the specific diagnostic ratio above; carries its own distinct risk of apical aneurysm formation (discussed below).
• Midventricular hypertrophy — can produce mid-cavity obstruction independent of, or alongside, classic LVOT obstruction.

RV hypertrophy accompanies LV hypertrophy in around 20% of HCM patients. It should still be reported, since it’s a feature of several phenocopies too — but its presence doesn’t independently increase the likelihood of finding a disease-causing mutation.

Papillary Muscle and Chordal Abnormalities Worth Recognizing

Hypertrophy can extend into the papillary muscles, contributing to mid-cavity obstruction in its own right. Additional morphologic abnormalities that can independently cause or worsen obstruction include antero-apical papillary muscle displacement, a double-bifid papillary muscle, and — genuinely distinctive — an anomalous papillary muscle that inserts directly into the mitral leaflet tissue, bypassing the chordae entirely. Discrete muscular bands running between the apex and the basal anteroseptal wall are also seen in HCM.

The Grey Zone: Athletes, Hypertension, and Ethnicity

Several factors genuinely overlap with the degree of hypertrophy seen in HCM, and the differential requires more nuance than a flat wall-thickness cutoff:

• Ethnicity matters for hypertensive LVH specifically: a wall thickness of 15–20 mm in a hypertensive patient of African or Afro-Caribbean descent can be an unremarkable consequence of hypertension, while the same thickness in a Caucasian hypertensive patient is more suggestive of HCM. Hypertensive and athletic hypertrophy both tend toward uniform, symmetric thickening — an asymmetric pattern favors HCM regardless of context.
• Athletic remodeling has its own ethnicity- and sex-specific limits: wall thickness doesn’t exceed 13 mm in Caucasian athletes or 15 mm in athletes of African/Afro-Caribbean descent, and is lower in female athletes than male athletes of the same background. A thickness over 16 mm in an athlete is essentially diagnostic of HCM; the genuine grey zone — 13–16 mm and concentric, with a relative wall thickness over 0.42 — occurs in only about 14% of athletes who turn out to have HCM, so true overlap is uncommon even though it gets disproportionate attention. LV cavity size (larger in athletic remodeling) has only modest discriminating value on its own.
• Resolving genuine uncertainty: reassessing wall thickness and LV mass after a sustained reduction in afterload — improved blood pressure control, weight loss, aortic valve replacement for severe aortic stenosis, or a period of deconditioning in an athlete — can clarify the diagnosis when the picture is otherwise ambiguous.

Recommended Reporting Language

Because the echocardiographic report itself so strongly shapes the clinical team’s next step, standardized language is genuinely worth using deliberately:

• Genuine uncertainty: “raises the possibility of HCM”
• Screening study with no evidence of LVH: “wall thickness is normal” — deliberately not “does not have HCM,” since a normal study doesn’t exclude early or non-penetrant disease
• Unequivocal findings (clear-cut apical HCM, gross hypertrophy in a young patient, definite LVH on a screening study): “consistent with HCM”

Phenocopies: When It Looks Like HCM but Isn’t

Because the definition is dimensional, a range of rarer conditions — genuinely different diseases with genuinely different management — can produce the same wall-thickness finding. These are termed phenocopies, and specific echocardiographic “red flags” should prompt consideration of one before defaulting to a sarcomeric HCM diagnosis. Avoid diagnosing HCM immediately after an acute cardiac injury such as myocarditis — the myocardium becomes edematous and thickened transiently, and these changes resolve with time rather than representing fixed disease.

Condition	Echocardiographic red flags
Cardiac amyloidosis	Thickened interatrial septum, mitral and tricuspid valves, and RV free wall; mild-moderate pericardial effusion; ground-glass myocardial texture; global hypokinesia (with or without LV dilation) in TTR amyloidosis specifically; markedly reduced longitudinal function with relative apical sparing of longitudinal strain; a mismatch between marked LVH on echo and low-voltage ECG
Fabry disease	Thickened mitral and tricuspid valves and RV free wall; concentric LVH; global hypokinesia (with or without LV dilation)
Myocarditis	Thickened RV free wall; mild-moderate pericardial effusion; global hypokinesia (with or without LV dilation)
Danon disease	Extreme concentric LVH; global hypokinesia (with or without LV dilation)
Pompe disease	Extreme concentric LVH
PRKAG2 mutations	Global hypokinesia (with or without LV dilation)
Glycogenosis	Concentric LVH
Mitochondrial disease	Global hypokinesia (with or without LV dilation)
Noonan syndrome and related disorders	RV outflow tract obstruction

Cardiac amyloidosis is the most recognizable phenocopy, and two findings are worth emphasizing specifically because they’re easy to miss if not actively sought: the apical-sparing pattern of longitudinal strain (severely reduced strain at the base and mid-ventricle with relative preservation at the apex — not pathognomonic on its own, but a genuinely distinctive pattern) and the mismatch between impressive wall thickening on echo and surprisingly low QRS voltage on ECG — the opposite of what true myocardial hypertrophy should produce electrically, and a strong clue that the “hypertrophy” is actually infiltration rather than myocyte growth. Since amyloidosis is also a leading infiltrative cause of restrictive cardiomyopathy, the same apical-sparing strain signature appears there too, framed from the restrictive-physiology side of the differential.

LVOT Obstruction

Mechanism

LVOT obstruction results from a reduced outflow tract cross-sectional area — from septal hypertrophy, mitral valve apparatus abnormalities, and, in most patients, a supranormal ejection that drags the anterior mitral valve leaflet anteriorly toward the basal septum. Obstruction isn’t confined to the outflow tract alone: it can also occur mid-cavity or at the apex (and, when the RV is involved, even there), from neighboring hypertrophied walls contracting toward one another during systole — accurately localizing the site matters for treatment planning.

A Formal, Three-Tier Definition

LVOT gradient	Classification
≥30 mmHg at rest	Basal or resting obstruction
Under 30 mmHg at rest, and under 30 mmHg after provocation	Non-obstructive
Under 30 mmHg at rest, but ≥30 mmHg with provocation	Labile, provocable, or dynamic obstruction

Provocation should be attempted at the bedside in every patient: re-image during a Valsalva maneuver, and in both seated and standing positions — not Valsalva alone. ≥50 mmHg, at rest or with provocation, is the threshold generally considered significant enough to warrant consideration of septal reduction therapy in patients with refractory symptoms despite medical management.

2D and M-Mode Signs

• Systolic anterior motion (SAM) — anterior displacement of the mitral leaflets and/or chordae toward the septum during systole, best confirmed with an on-axis M-mode cursor through the leaflet tips from the parasternal long-axis view.
• Mid-systolic aortic valve notching and coarse systolic fluttering — ancillary M-mode and 2D signs of LVOT obstruction, rather than the obstruction’s defining feature.
• “Contact plaque” — a specific, genuinely useful secondary sign: increased echogenicity in the basal anteroseptal wall from fibrosis at the point of repeated leaflet-septal contact during SAM, visible on parasternal long-axis and apical three-chamber views.

Mitral Regurgitation: Jet Direction Carries Real (Imperfect) Diagnostic Weight

MR in HCM most often results from disrupted leaflet coaptation as SAM pulls the anterior leaflet away from normal apposition. A posteriorly-directed jet in mid-to-late systole occurs in about 65% of SAM-related MR — but the same posterior direction also occurs in roughly a third of patients whose MR actually stems from genuinely intrinsic mitral valve disease. A central or anteriorly-directed jet points more specifically toward intrinsic valve pathology than toward SAM as the primary mechanism — a distinction that matters directly for septal reduction therapy selection below. See Mitral Regurgitation for the general approach to grading severity, which still applies here alongside this mechanism-specific reasoning.

Diastolic Function and Heart Failure Risk

Diastolic dysfunction is common in HCM, producing elevated filling pressures and left atrial enlargement — and grading it accurately is genuinely harder here than in most conditions, since LVOT obstruction and MR frequently coexist and distort the usual Doppler relationships. Integrating multiple parameters, rather than relying on any single one, is necessary. See LV Diastolic Function for the general framework this builds on.

A specific, high-risk phenotype worth actively identifying: preserved LV ejection fraction with a genuinely restrictive diastolic filling pattern, often accompanied by pulmonary hypertension. These patients have independently worse outcomes and warrant close observation for deterioration — heart transplantation becomes a consideration when heart-failure symptoms prove resistant to medical therapy.

Ejection fraction itself can be misleading as a systolic function measure in HCM — it’s frequently normal even when regional wall motion abnormalities and reduced global longitudinal strain (see below) indicate genuine systolic impairment. Even so, the absolute EF value carries prognostic meaning: outcomes are generally adverse once EF falls below 50%, and an EF of 50–60% identifies patients likely to progress to overt systolic dysfunction, while EF under 50% represents that dysfunction already being present — a distinction worth making explicitly in a report rather than treating “reduced EF” as one category. Below 50%, medical therapy escalation, heart transplant evaluation, and device therapy all become active considerations. See LV Systolic Function for the complementary tissue Doppler and visual radial function assessment that should accompany EF in this population.

Sudden Death Risk Stratification: What Echo Actually Contributes

The European Society of Cardiology’s risk calculator estimates five-year sudden death risk and categorizes patients into low, intermediate, and high-risk groups from seven parameters — three of which come directly from echocardiography: maximal wall thickness, LVOT gradient, and 2D parasternal long-axis left atrial size. Because this information needs to reach the referring clinician quickly, every report on a patient with suspected or confirmed HCM should state these three parameters explicitly in its conclusion.

Two further findings aren’t part of the calculator itself but still modify sudden death risk and belong in every conclusion: LV systolic impairment and apical aneurysm. Left atrial size specifically carries dual prognostic weight — beyond sudden death risk, it’s also an independent predictor of stroke and other thromboembolic events, making it worth measuring and reporting carefully rather than as an afterthought. New atrial fibrillation found on any study should be communicated directly to the referring team, given the anticoagulation implications.

Apical aneurysm formation deserves deliberate, active screening in every patient with apical hypertrophy, using myocardial contrast when needed — along with a specific look for associated apical thrombus.

Strain Imaging: A Targeted Tool, Not a Routine One

Global longitudinal strain by 2D speckle tracking is increasingly used, and reduced GLS with preserved EF is associated with adverse outcomes in HCM. Its routine use in every HCM patient has genuine practical limits, though: accurate strain curves require real expertise, tracking is difficult with gross or apical hypertrophy or apical papillary muscle insertion, inter-observer variability is likely higher than in dilated cardiomyopathy, and strain-based measures aren’t yet incorporated into clinical HCM management guidelines. The specific, targeted recommendation is to use GLS to help distinguish HCM from cardiac amyloidosis and from athletic remodeling — not as a blanket addition to every study.

3D and Transesophageal Echocardiography

3D echocardiography adds accurate LV and RV volume and EF quantification without 2D’s geometric assumptions, and directly characterizes mitral valve and LVOT morphology. TEE — often incorporating 3D — is specifically recommended when the transthoracic study suggests significant abnormality of the mitral valve apparatus, since this level of anatomic detail (and its causes) is often better resolved from the esophageal window, and is particularly valuable for planning septal reduction therapy.

Stress Echocardiography

Reserved for symptomatic patients whose resting study — even with bedside provocation — hasn’t shown an LVOT gradient at or above 50 mmHg, to unmask latent obstruction under physiologic load.

• Symptom-limited exercise on a bike or treadmill is used; treadmill exercise may provoke somewhat higher gradients than semi-supine bicycle exercise. Dobutamine is specifically avoided in HCM stress testing, because the infusion itself can induce LVOT obstruction in structurally normal hearts — a genuine false-positive risk unique to this population.
• Images are obtained within 60–90 seconds of peak exercise, since obstruction can appear before or after the patient reaches 85% of age-predicted maximum heart rate — and LVOT assessment should be performed before LV size and function assessment, since the gradient itself can be short-lived.
• A practical sequence, view by view: interrogate the LVOT or site of intracavitary obstruction first (CW, or PW with a high pulse-repetition-frequency, aimed with color as a guide — sampling throughout the LV cavity can pinpoint an unclear obstruction site); assess MR by color and CW, taking care to distinguish it from the LVOT jet; assess mitral inflow and SAM at both an intermediate stage (roughly 100–120 bpm) and at peak exercise; check for exercise-induced pulmonary hypertension via the TR jet; and assess LV size and function last, keeping in mind that a small, vigorously contracting LV cavity can itself make volumes difficult to measure at intermediate and peak stress.

Guiding Septal Reduction Therapy

For patients with obstruction who remain symptomatic despite medical therapy, echocardiography directly informs the choice between surgical myectomy and alcohol septal ablation — a genuinely specific decision, not simply “is the gradient high enough.”

Favors surgical myectomy	Aligns with alcohol septal ablation	Unfavorable for either
Septal thickness over 25 mm	Focal basal septal hypertrophy or a sigmoid septal contour	Apical hypertrophy
Central or anteriorly-directed MR from intrinsic valve disease	Posteriorly-directed MR from SAM	Mid-cavity obstruction
Abnormal mitral subvalvar apparatus contributing to obstruction
Concomitant aortic valve disease or coronary disease needing CABG

Surgery can address findings aligned with alcohol ablation, but the reverse isn’t true — alcohol ablation can’t correct an abnormal subvalvar apparatus or concomitant valve disease, which is why the echo findings favoring myectomy are the ones that matter most when the two approaches are both technically feasible.

Alcohol septal ablation itself is performed via a septal perforator branch of the LAD, targeting the hypertrophied basal septum adjacent to the point of SAM-septal contact — selective intracoronary contrast injection is essential to confirm the chosen branch supplies only the intended territory, without enhancement of the papillary muscles, inferior LV wall, or RV free wall, which would risk unintended remote infarction. Gradient reduction happens in two phases: an immediate drop from myocardial stunning, followed by a further, progressive reduction in both resting and provocable gradients over the next 3 to 6 months as the induced infarct matures into scar. Post-procedure imaging should track this expected trajectory rather than expecting the full effect immediately.

Clinical Importance

HCM is unusual among the cardiomyopathies in how directly the echocardiographic report itself steers management — the same three parameters (wall thickness, LVOT gradient, left atrial size) feed a formal sudden death risk score, jet direction alone reshapes the choice between two genuinely different procedures, and the language used to describe a borderline study can determine whether a patient is told they have a life-altering genetic diagnosis or a normal heart. Getting the technique right — measuring wherever hypertrophy is truly maximal, provoking obstruction deliberately rather than assuming its absence, and actively screening for the phenocopies that mimic sarcomeric HCM — is what makes that report trustworthy.