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.