Hypertrophic cardiomyopathy with extreme outflow tract obstruction

Hypertrophic cardiomyopathy (HCM) is the most common heritable cardiomyopathy, with 75% of patients demonstrating dynamic left ventricular outflow tract (LVOT) obstruction (LVOTO).1,2 Left ventricular outflow tract obstruction results from narrowing of the LVOT by left ventricular hypertrophy and mitral apparatus systolic anterior motion (SAM). Left ventricular outflow tract obstruction is associated with worse outcomes3 and is the primary therapeutic target in obstructive HCM. A maximum instantaneous gradient of >30 mmHg at rest or >50 mmHg with provocation is considered significant obstruction. A 73-year-old woman without hypertension presented with intermittent angina despite minimal coronary atherosclerosis and New York Heart Association Class II–III exertional dyspnoea and fatigue. Transthoracic echocardiography demonstrated HCM with maximal wall thickness 18 mm (A) and dynamic LVOTO with moderate SAM-mediated mitral regurgitation (B). Despite combination metoprolol tartrate and diltiazem therapy, resting LVOTO gradient was extremely high (216 mmHg, C), disproportionate to her relatively mild hypertrophy. Extreme obstruction was attributed to small habitus (BMI 19.2 kg/m2), sigmoid septal contour, ventricular-aortic angulation, and elongated mitral leaflets. Intraoperative left ventricular and aorta needle pressure measurement at transaortic myectomy confirmed LVOTO gradient 230 mmHg (D). Direct LVOT visualization demonstrated focal narrowing with a fibrotic basal SAM-septal contact lesion (E). Extended septal myectomy resulted in a widely patent LVOT (F) with needle confirmation of elimination of obstruction (G). Discharge echocardiogram demonstrated LVOT enlargement without SAM (H) and >10-fold LVOT gradient reduction (I), with anemia-associated flow acceleration accounting for residual Doppler findings. Extreme LVOTO may present in HCM despite relatively mild left ventricular hypertrophy and can be effectively relieved with septal myectomy.