Ethan J. Halpern MD, Presenter: Research grant, Koninklijke Philips Electronics NV Research grant, Lantheus Medical Imaging, Inc Equipment support, Toshiba Corporation

David J. Halpern, Abstract Co-Author: Nothing to Disclose

David H Wiener MD, Abstract Co-Author: Nothing to Disclose

A diagnosis of left ventricular outflow tract (LVOT) obstruction is suggested in the setting of a normal aortic valve with an elevated gradient in the left ventricular outflow tract. LVOT obstruction is classically associated with left ventricular hypertrophy (LVH) and dynamic ventricular function. We recently encountered a symptomatic adult patient with LVOT obstruction based upon a Doppler gradient, but without LVH. Echocardiographic visualization of the LVOT was limited. Cardiac CT demonstrated an LVOT area of 2.2sq cm by planimetry (diameters: 2.1 x 1.5cm) with associated systolic anterior motion of the mitral leaflets. However, normal values of LVOT area were not available in the literature to validate that our patient had subaortic obstruction on the basis of a small LVOT. This study was performed to establish a normal range for LVOT diameters and area.

A retrospective review was performed of 100 cardiac CT angiography studies performed for the evaluation of chest pain (iCT scanner; Philips Medical Systems). All patients had a normal aortic valve with no history of aortic stenosis. Short axis views of the LVOT were obtained at end systole (40% of the R-R interval) by identifying the LVOT on a standard three chamber long axis view and rotating the volume 90°. Measurements of the transverse and antero-posterior diameter of the LVOT were obtained along with planimetry of the LVOT area.

The LVOT was clearly visualized on all CT studies. The adult LVOT measured during systole is oval in shape, with a larger transverse diameter (2.8cm ± 0.20) as compared to the antero-posterior diameter (2.1cm ± 0.25), p<0.001. The mean normal LVOT area by planimetry measured 4.6sq cm ± 0.86. Thus, the LVOT measurements of our patient with subaortic stenosis were approximately 3 standard deviations below the mean (see figure: patient on top row; normal control below).

The LVOT is well visualized and easily defined on ECG-gated cardiac CT. Our study provides normal values for LVOT diameters and area.

A small LVOT may be useful to explain dynamic LVOT obstruction in patients who present with an LVOT gradient.

Halpern, E, Halpern, D, Wiener, D, Normal Measurements of the Left Ventricular Outflow Tract by ECG-gated Cardiac CT.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11001653.html