Diagnostic Utility of Cardiac Magnetic Resonance Imaging in Monozygotic Twins With Hypertrophic Cardiomyopathy and Identical Pattern of Left Ventricular Hypertrophy
Female, 18-year-old, monozygotic twins, had cardiac evaluations as a result of the suspicion of hypertrophic cardiomyopathy (HCM). Each was asymptomatic with active normal lifestyle. Both twins had normal 2-dimensional echocardiograms, which did not identify wall thickening in any segment of the left ventricular (LV) chamber (Figure). Mild systolic anterior motion of the mitral valve (associated with normal LV outflow tract velocities) and mitral regurgitation were present in both patients. LV end-diastolic cavity dimensions (40 and 34 mm, respectively) and left atrial dimension (20 and 28 mm, respectively) were similar. In each twin, 12-lead ECGs were abnormal but showed different patterns. Twin 1 had minor ST-T abnormalities and Twin 2 showed distinctively deep and narrow Q-waves in leads II, III, AVF, and V4–V6 (Figure).
Of note, cardiac magnetic resonance (CMR) imaging identified a virtually identical pattern of asymmetric LV wall thickening confined to the anterior free wall, undetected by echocardiography and measured at 16 mm in both twins (Figure). Therefore, because CMR imaging is more reliable than echocardiography in the definition of wall thickness in the anterolateral LV free wall,1 only CMR imaging permitted recognition of LV hypertrophy (ie, the HCM phenotype) and ultimately the correct diagnosis in these twins.
These images are notable on 2 points. First, monozygotic twins show identical LV morphology (ie, magnitude and distribution of hypertrophy). These findings support the view that genetic background represents the primary determinant of the HCM phenotype, and also suggest that environmental factors probably have limited impact on the morphological expression of this disease. Second, in contrast to 2-dimensional echocardiography, only CMR imaging has the diagnostic power to reliably identify segmental hypertrophy confined to the anterior LV free wall in patients with HCM.
The online-only Data Supplement, which consists of Movies I and II, is available with this article at http://circ.ahajournals.org/cgi/ content/full/115/24/e627/DC1.