14.1 Dilated and Hypertrophic Cardiomyopathies, SAM, and LVOT Obstruction
Key Takeaways
- Describe a dilated or hypertrophic phenotype and its hemodynamic consequences before proposing etiology; echocardiography alone rarely distinguishes every genetic, ischemic, inflammatory, toxic, metabolic, or loading cause.
- For a dilated phenotype, quantify LV and RV size and function, regional motion, stroke volume, functional regurgitation, atrial remodeling, pressure estimates, and thrombus using reproducible chamber methods.
- For suspected HCM, report hypertrophy distribution and maximal end-diastolic wall thickness while excluding foreshortening, tangential cuts, papillary muscle, and right-ventricular structures from the measurement.
- Assess dynamic obstruction with 2-D anatomy, color and PW localization, correctly aligned CW at rest and with physiologic provocation, separating the LVOT envelope from MR and fixed obstruction.
Recognize the phenotype before naming the disease
CCI task D2 includes cardiomyopathy evaluation. A dilated cardiomyopathy phenotype has LV enlargement with systolic dysfunction that is not explained solely by abnormal loading. Measure biplane and, when feasible, 3-D end-diastolic and end-systolic volumes and EF from nonforeshortened views. Describe global versus regional dysfunction, GLS when technically valid, LV sphericity, wall thickness, stroke volume, spontaneous contrast or thrombus, and mechanical dyssynchrony. Use an ultrasound-enhancing agent when two or more contiguous segments or the apex are not adequately seen.
Extend the survey beyond the LV. Annular and papillary displacement can produce secondary MR; RV dysfunction and secondary TR may develop; atria enlarge as filling pressures rise. Record RV-focused dimensions and function, LA and RA volumes, IVC, pulmonary pressure, and other valve disease. A regional coronary pattern, scar, or aneurysm may favor ischemic injury, but advanced ischemic disease can look globally dilated. Myocarditis, genetic disease, tachycardia, alcohol or chemotherapy toxicity, pregnancy-associated disease, and endocrine or nutritional disorders can share the phenotype. Report what is observed and recommend interpreter-directed clinical, coronary, CMR, laboratory, or genetic correlation rather than assigning cause from LV shape alone.
| Feature | Dilated phenotype | Hypertrophic phenotype |
|---|---|---|
| LV cavity | Enlarged, often spherical | Usually nondilated; may be small or normal |
| Wall pattern | Normal or reduced relative thickness | Focal, asymmetric, apical, midventricular, or concentric increase |
| Systolic function | Commonly reduced EF and GLS | EF often normal/hyperdynamic; GLS may be reduced regionally |
| Valve effect | Tethering and annular dilation cause functional MR | SAM and leaflet/papillary anatomy can cause posterior MR |
| Hemodynamics | Low output and elevated filling pressure | Dynamic LVOT or midventricular obstruction, diastolic dysfunction |
Measure hypertrophy without manufacturing it
HCM is increased LV wall thickness not explained by another cardiac, systemic, syndromic, or metabolic cause. In an adult nondilated LV, maximal thickness at least 15 mm supports HCM; 13 mm can be diagnostic in an appropriate family or genetic context. These are clinical definitions, not permission to ignore hypertension, aortic stenosis, athlete remodeling, amyloidosis, Fabry disease, or other phenocopies. Describe the pattern and distribution rather than using “asymmetric septal hypertrophy” as a complete diagnosis.
Measure end-diastolic thickness in short-axis planes perpendicular to myocardium from base through apex, cross-checking long-axis views. Do not include RV trabeculation, moderator band, false tendon, papillary muscle, or epicardial fat. Tangential long-axis cuts overestimate septal thickness; apical foreshortening can hide apical HCM. Use contrast or CMR when borders, apex, maximal segment, apical aneurysm, or thrombus remain uncertain. Report LV mass, cavity volumes, EF, GLS when available, LA size, diastolic findings, RV involvement, and MR.
Connect SAM anatomy to dynamic obstruction
Inspect mitral leaflet length, coaptation position, papillary muscle number and displacement, chordal attachments, basal septal contour, and LVOT width. Systolic anterior motion (SAM) ranges from chordal motion to prolonged leaflet–septal contact. It can create a coaptation gap and often posteriorly directed MR. Central or anterior MR should prompt a search for intrinsic leaflet disease, although jet direction alone is not definitive. SAM is not specific to HCM; it also occurs with a small hyperdynamic LV, dehydration, sepsis, inotropes, vasodilation, Takotsubo syndrome, sigmoid septum, or after mitral or aortic intervention.
Use color to find systolic acceleration, then step a PW sample from the LV apex through the mid cavity and LVOT to localize its onset. Align CW through that site. Dynamic LVOT flow usually has a mid-to-late-systolic, concave or dagger-shaped envelope. Calculate peak instantaneous gradient with 4V². A resting or provoked peak gradient at least 30 mmHg defines obstruction; 50 mmHg or more is a management-relevant threshold in symptomatic patients, not a stand-alone treatment decision. Record BP, heart rate, rhythm, position, and loading conditions with every gradient.
Avoid tracing MR as LVOT flow. MR frequently begins earlier, lasts longer, has a rounder contour, and reaches a higher velocity; color and PW localization plus a cleaner apical long-axis alignment help separate overlapping signals. A fixed subaortic membrane or valvar AS generally accelerates earlier and has structural evidence. Very late cavity-obliteration flow can arise away from the LVOT in any hyperdynamic ventricle. Serial stenoses invalidate casual use of the simplified Bernoulli and continuity equations.
If the resting gradient is below the protocol target, acquire Valsalva strain and standing or squat-to-stand maneuvers when safe and authorized. Reduced preload or afterload and increased contractility intensify dynamic obstruction. In symptomatic patients without a rest or bedside-provoked gradient of 50 mmHg, physiologic exercise echocardiography is recommended; dobutamine is not the routine provocation because it creates nonphysiologic gradients even in normal hearts. Preserve the medication and exercise protocol, acquire the gradient at peak upright exercise when possible or immediately after, and document symptoms and BP.
A complete report distinguishes phenotype from etiology and states maximal wall thickness and segment, SAM structure and contact, obstruction level, rest and provoked peak gradients, MR mechanism/severity, LV/RV and atrial response, apical aneurysm or thrombus, and limitations. Communicate severe obstruction with hypotension, suspected thrombus, new systolic dysfunction, or dangerous stress findings promptly.
Preserve serial comparability
Compare chamber volumes, EF, GLS method, wall thickness, valve severity, and gradients with prior studies using the same border and provocation conventions. Reverse remodeling after therapy and new dilation or systolic decline are clinically important, but an apparent change should first trigger review of loading conditions, rhythm, image plane, and measurement reproducibility.
In suspected HCM, a clean late-peaking LVOT signal rises from 2.5 m/s at rest to 4.0 m/s during an effective Valsalva maneuver, with no fixed aortic-valve jet. Which interpretation is correct?
Which three actions belong in a complete evaluation of a hypertrophic phenotype with possible dynamic obstruction? Select three.
Select all that apply