Echocardiographic Assessment of Left Ventricular and Mitral Valve Geometry in Cats with Hypertrophic Cardiomyopathy
ACVIM 2008
K.E. Schober; A. Todd
Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University
Columbus, OH, USA

Hypertrophic cardiomyopathy (HCM) is the most common cardiac disease in the domestic cat. Obstruction of the left ventricular outflow tract (LVOT) is frequently observed in HCM (referred to as HOCM) and is usually due to systolic anterior motion and mid-to-late systolic contact of the mitral valve with the interventricular septum (IVS). Altered LV geometry secondary to abnormal myocardial growth as well as intrinsic mitral valve abnormalities secondary to congenital mitral valve malformations may both favor obstruction of the LVOT but may both be associated with a different outcome and a different response to treatment. This study addresses the hypothesis that abnormalities of the LVOT and the mitral valve are common in cats with HOCM and can be detected by two-dimensional (2D) transthoracic echocardiography.

A total of 102 cats (30 normal control cats, 43 cats with HCM without obstruction, and 29 cats with HOCM) underwent a comprehensive transthoracic 2D echocardiographic examination including the assessment of chamber size, wall thickness, and anatomy of the mitral valve apparatus and the LVOT using an ultrasonographic unit (Vivid 7, GE, Milwaukee, WI) and a transducer array of 7 to 10 MHz nominal frequency. A total of 20 variables were assessed, including the size of the left atrium (2 variables), anatomy of the left ventricle (8 variables) and the LVOT (2 variables), and morphology of the mitral valve (8 variables). All cats were imaged in lateral recumbency with the transducer from underneath. Normal control cats, cats with HCM, and cats with HOCM were compared using analysis of variance on ranks for unpaired observations and the Holm-Sidak test or Dunn's test for post-hoc analyses.

Cats with HOCM had increased (P<0.05) LV wall thickness, LV myocardial area, number of papillary muscles and papillary muscle area, and increased length of the anterior mitral valve leaflet compared to cats without obstruction. There was no difference (P>0.05) between groups with regard to age, body weight, sex, IVS thickness, chordae tendinae length, mitral annulus dimension, distance of the mitral valve leaflet coaptation point to the LV free wall, inter-papillary muscle distance, position of the papillary muscles in the LV cavity, and the IVS-to-aortic root angle.

Abnormalities of LV geometry, anatomy of the papillary muscles, and length of the anterior mitral valve leaflet are common in cats with HOCM suggesting a possible role of such abnormalities in the genesis of the obstruction. Additional imaging and post-mortem studies are needed to validate our echocardiographic findings.

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Karsten Schober, DVM, PhD, DECVIM
The Ohio State University
Columbus, OH

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