The thickened heart: What sonographers need to know about echo assessment of hypertrophic cardiomyopathy
In this feature, Carrie L. Vanden Bussche, R.D.C.S., ACS, BS, FASE assistant supervisor echocardiography laboratory Rochester, MN highlights the practical echo findings that help sonographers recognize hypertrophic cardiomyopathy, avoid common Doppler pitfalls and know when provocation is needed.
Hypertrophic cardiomyopathy (HCM) — massive myocardial hypertrophy without another clear cause — affects roughly 1 in 500 people. Because echocardiography is central to identifying, characterizing and following these patients, a high-quality study depends not only on the interpreting cardiologist but also on the sonographer acquiring the images and Doppler data.
Three questions, one diagnosis
Diagnosis rests on three questions. What is needed? Left ventricular hypertrophy (LVH), typically a wall thickness of 15 mm or greater in adults, usually with a normal or small left ventricular (LV) cavity; any hypertrophy pattern can qualify. What is not needed? Obstruction: A gradient is not required to make the diagnosis. What must be excluded? Other causes of increased wall thickness, including hypertension, aortic or subvalvular stenosis, infiltrative disease, athlete's heart, and basal septal hypertrophy related to hypertension.
That last question carries the most weight. In one case, concentric LVH with a small, hyperdynamic cavity, systolic anterior motion of the mitral leaflet (SAM), and an 85 mm Hg resting gradient appeared to fit classic HCM. Biopsy ultimately showed amyloidosis.
Know the variants
Determine morphology from the parasternal long-axis or apical long-axis view. Common patterns include sigmoid septum (47%), reverse curvature (35%), apical hypertrophy (10%) and neutral septum (8%). Sigmoid morphology tends to be seen in older patients, reverse curvature more often in younger patients, and all four patterns can appear within the same family. Distribution does not predict outcome, but wall thickness 30 mm or more is associated with increased sudden-death risk.
Figure 1
Figure 2
Figure 3
Figure 4
A. Sigmoid septum. B. Reverse curvature. C. Neutral septum D. Apical hypertrophy
Image reproduced/adapted from: Binder J, et al. Mayo Clinic Proceedings. 2006;81:459 Physiology
Physiologically, patients fall into three groups: latent obstruction (40%), resting obstruction (30%) and nonobstructive disease (30%). A gradient of 30 mm Hg defines obstruction, while 50 mm Hg is the threshold generally used when considering septal reduction therapy in patients with symptoms.
It's a valve problem too
The mitral valve is often part of the story. Patients may have elongated leaflets, asymmetric leaflet enlargement, anteriorly displaced papillary muscles or direct papillary muscle insertion into the anterior leaflet. When coaptation shifts from the leaflet tips to the midbody, rapid ejection through a narrowed outflow tract can sweep the leaflet into the septum, producing SAM, obstruction and mitral regurgitation together in midsystole. Chest pain usually reflects supply-demand mismatch rather than coronary artery disease, and diastolic dysfunction is present in every variant.
The Doppler work
Color flow helps localize obstruction and characterize the mitral regurgitant (MR) jet. Pulsed wave (PW). Doppler helps identify the site of accelerated flow, but it should not be used to measure the peak gradient. Continuous wave (CW) Doppler is the workhorse: The dynamic left ventricular outflow tract (LVOT) obstruction signal is typically dagger shaped and late peaking. Applying the simplified Bernoulli equation, 4V², provides the peak dynamic gradient. In image G, a peak velocity of 4.6 m/s produces a peak gradient of approximately 85 mm Hg, consistent with severe left ventricular outflow tract obstruction.
E. (Figure 5)
F. (Figure 6)
E. Color flow showing the mosaic, turbulent jet at the level of the left ventricular outflow tract.
F. (Figure 7) PW Doppler at site of accelerated flow.
F. (Figure 7)
G. A late-peaking CW Doppler signal — the visual signature of dynamic obstruction.
A classic pitfall is mistaking Mitral Regurgitation for LVOT obstruction. MR velocity is higher because left atrial (LA) pressure is lower than aortic pressure. Timing helps distinguish the two signals: LVOT flow is limited to the ejection period, while MR is holosystolic and extends through isovolumic contraction time (IVCT) and isovolumic relaxation time (IVRT). Shown in image H
H. (Figure 8)
Provoke, or miss it
Gradients vary from hour to hour with dehydration, alcohol and heavy meals.
If the resting gradient is less than 50 mm Hg, the sonographer should instruct the patient to perform a Valsalva maneuver or use goal-directed Valsalva. If the gradient remains less than 50 mm Hg after Valsalva, additional provocation techniques may be considered, such as squat-to-stand or amyl nitrite. Once any technique demonstrates a gradient of 50 mm Hg or greater, no further provocation is required. In a 320-patient series, 75% had LVOT obstructionat rest or with provocation.
Speckle-tracking strain can add another layer of differentiation because HCM, athlete's heart and cardiac amyloid each tend to produce a distinct regional pattern. Figure 9 is suggestive of either reverse curvature or neutral HCM.
I. (Figure 9)
For suspected apical HCM, an ultrasound enhancement agent (UEA) should be given; the diagnosis of apical HCM can only be made from the apical windows. Without the use of a UEA, an apical aneurysm and/or thrombus may be missed. — 10%-31% harbor an apical aneurysm, with attendant risk of thrombus, arrhythmia, and sudden death.
J. (Figure 10)
Four cases worth remembering
A latent obstruction climbed from 10 mm Hg at rest to 36 mm Hg with Valsalva and 76 mm Hg with amyl nitrite — invisible on a resting study. A 96 mm Hg Valsalva gradient turned out not to be HCM at all, but rather a small cavity, thick basal septum and prominent chordae. A patient who had a myectomy still had a 60 mm Hg resting midcavity gradient and required a redo. Another post myectomy study revealed a small VSD, a rare complication associated with this procedure, caused by over resection — a reminder to interrogate the septum every time.
Bottom line
A complete HCM study defines the distribution of hypertrophy, evaluates the location and severity of obstruction, provokes when the resting gradient falls short, assesses SAM and MR, and uses strain to help exclude mimics. Obstructive and nonobstructive diseases are managed differently — which is why the Doppler work must be done carefully and completely.