Can we differentiate “Sarcomeric vs non Sarcomeric HCM” by Echocardiography ?

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Can we differentiate “Sarcomeric vs non Sarcomeric HCM” by Echocardiography ?

Echocardiography, the ultrasonic vision, with which we are able to directly visualize the heart is a monumental discovery ,gifted to us by Edler & Hertz in the 1950s. These high frequency sound interacts with myocytes in a variety of ways like penetration ,reflection, ab & adsorption, back scattering etc. It has further evolved , at the tissue level diagnostic like 3D speckle ,and strain etc .

With all all these advancements ,how good is echocardiography in ruling out (or in) reversible /treatable HCM mimickers or their molecular subsets.

Recognizing non-sarcomeric Hypertrophic Cardiomyopathy (HCM) by echocardiography is one such task .It can be challenging, but here are some clues to help:

  1. Unusual hypertrophy patterns: Non-sarcomeric HCM may exhibit atypical hypertrophy patterns, such as:
    • Mid-ventricular hypertrophy
    • Apical hypertrophy
    • Hypertrophy in the right ventricle
  2. Absence of systolic anterior motion (SAM): Unlike sarcomeric HCM, non-sarcomeric HCM may not exhibit SAM of the mitral valve.
  3. Normal or reduced left ventricular outflow tract (LVOT) gradient: Non-sarcomeric HCM may not have a significant LVOT obstruction.
  4. Presence of fibrosis or scar tissue: Look for signs of fibrosis or scar tissue on echocardiography, such as:
    • Bright or patchy appearance in the myocardium
    • Increased echogenicity
  5. Abnormal myocardial texture: Non-sarcomeric HCM may exhibit an abnormal myocardial texture, such as:
    • Speckled or “ground-glass” appearance
  6. Other structural abnormalities: Some non-sarcomeric HCM cases may exhibit other structural abnormalities, such as:
    • Mitral valve abnormalities
    • Tricuspid valve abnormalities
    • Right ventricular abnormalities

Ref : Sarcomeric versus Non-Sarcomeric HCM June 2023 Cardiogenetics 13(2):92-105

Some specific echocardiographic features of non-sarcomeric HCM include:

  • Fabry disease: Typically shows a “binary” appearance of the myocardium, with a bright and dark pattern.
  • Amyloidosis: Often exhibits a “granular sparkling” appearance of the myocardium.
  • Cardiac sarcoidosis: May show a “starry sky” appearance due to myocardial fibrosis.

Please keep in mind, that echocardiography should be complemented with clinical evaluation, genetic testing, and other diagnostic tools to confirm the diagnosis.

Amyloid -HCM coexistence

Medical pathology is never a pure science.It can make our assessment topsy turvy at any moment .One such rare phenomenon is amyloid getting deposited in a patient with classical inherited HOCM. (Boyangzi Li, Cardiac AA amyloidosis in a patient with obstructive hypertrophic cardiomyopathy,
Cardiovascular Pathology, Volume 48, 2020,
)

A comment on deep genetic profiling

Genetic studies in HOCM are academically exciting  and professionally gratifying. From the patient perspective, it provides  an opportunity to treat any reversible or treatable enzyme disorders(Ref 1 Migalastat for Fabry’s disease & Tifamidis and Patisiran in TTR Amyloidosis) .

But, the benefits of deep genetic testing has to be carefully harvested as there is a troubling trade off, due to the hitherto hidden prognostic anxiety, these genetic breakthroughs bring along.

Final message

Contrary to the belief , a carefully interpreted echocardiography along with clinical profile will be able to recognise sarcomeric HCM in most situations.But, it is still weak in ruling in a non- sarcomeric HCM.

Reference

1.McCafferty EH, Scott LJ. Migalastat: A Review in Fabry Disease. Drugs. 2019 Apr;79(5):543-554. doi: 10.1007/s40265-019-01090-4. Erratum in: Drugs. 2019 Aug;79(12):1363. doi: 10.1007/s40265-019-01166-1. PMID: 30875019; PMCID: PMC6647464.

2.The small interfering mRNA drug , is an interstitial protein excretory drug in TTR amyloid.



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