Discussion
HCM is a relatively common genetic cardiomyopathy that is believed to
affect 1:500 people worldwide and an estimated 600,000 people in the
United States [1]. HCM should be suspected in patients with maximal
LV wall thickness of >1.5cm by echocardiography, in the
absence of other compelling etiology [8]. The clinical presentation
can vary from an incidental finding to clinically significant
arrhythmias such as atrial fibrillation or sudden cardiac death, thereby
making accurate diagnosis imperative [9].
Various HCM geometrical phenotypes have been reported, including more
recently a rarely recognized spiral-variant, where there is segmental
hypertrophy that spirals in a counter-clockwise pattern from the basal
anterior septum towards the apex of the left ventricle [4, 10, 11].
Screening for HCM is traditionally accomplished with TTE with the
addition of genetic testing for guidance regarding a definitive
diagnosis as well as for screening recommendations for family members
[8, 12]. CMR is particularly helpful in the clarification of the
diagnosis for patients with suboptimal echocardiographic windows,
determining the HCM geometrical phenotype, and revealing the presence
and mechanism of LVOT obstruction [8, 13] and risk for SCD/VT as a
function of percent scar [7, 8]. It is clinically paramount to
evaluate HCM patients for LVOT obstruction (defined as peak
instantaneous gradient of ≥30 mm Hg), as it is associated with poor
prognosis and increased risk of sudden cardiac death [8].
While the benefits of CMR are clearly superior from a diagnostic and
prognostic aspect in this population, TTE remains the preferred initial
imaging modality for diagnosis of HCM [8]. The use of UEA in
echocardiography is a technique that is used to enhance endocardial
border delineation in studies with suboptimal left ventricular cavity
visualization. This allows for improved sensitivities and specificities
when comparing patients with poor echocardiographic windows to those
with well visualized windows, and in rare occasions it may reveal
previously occult yet ominous pathology [14-16]. Prior authors have
suggested that echocardiography with 3D processing is also useful in
visualizing the HCM geometric phenotype and pathophysiology of LVOT
obstruction [17].
In our patient, we utilized a multi-modal approach, and although CMR
provided a definitive diagnosis, the use of TTE with UEA allowed
adequate visualization of the spiral HCM geometry which, to our
knowledge we also represent as the first case diagnosed by TTE.
TTE findings of spiral variant HCM such as LVOT obstruction and systolic
anterior motion of the mitral valve have been associated with worse
clinical prognosis compared to non-spiral variants
[18,
19].
Higher rates of non-sustained ventricular tachycardia and sudden cardiac
death, as well as a higher incidence of heart failure and all-cause
mortality have been reported with the spiral pattern of HCM
[18].
In conclusion, the role of TTE has been to date restricted to screening
patients for HCM with reliance on CMR for diagnosis and characterization
of phenotype of HCM. In this case, we highlight that TTE with UEA may
prove to be a valuable tool in demonstrating the geometry of the rare
spiral variant HCM to the echocardiologist.