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CLINICAL STUDY: HYPERTROPHIC CARDIOMYOPATHY

Impact of left ventricular outflow tract area on systolic outflow velocity in hypertrophic cardiomyopathy

A real-time three-dimensional echocardiographic study

^* Department of Cardiology, the Cleveland Clinic Foundation, Cleveland, Ohio, USA

Manuscript received May 18, 2001; revised manuscript received September 4, 2001, accepted October 17, 2001.

^* Reprint requests and correspondence: Dr. Takahiro Shiota, Department of Cardiology, Desk F15, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, Ohio 44195, USA.
shiotat{at}ccf.org

OBJECTIVES: The aim of this study was to use real-time three-dimensional echocardiography (3DE) to investigate the quantitative relation between minimal left ventricular (LV) outflow tract area (A_LVOT) and maximal LV outflow tract (LVOT) velocity in patients with hypertrophic obstructive cardiomyopathy (HCM).

BACKGROUND: In patients with HCM, LVOT velocity should change inversely with minimal A_LVOT unless LVOT obstruction reduces the pumping capacity of the ventricle.

METHODS: A total of 25 patients with HCM with systolic anterior motion (SAM) of the mitral valve leaflets underwent real-time 3DE. The smallest A_LVOT during systole was measured using anatomically oriented two-dimensional "C-planes" within the pyramidal 3DE volume. Maximal velocity across LVOT was evaluated by two-dimensional Doppler echocardiography (2DE). For comparison with 3DE A_LVOT, the SAM-septal distance was determined by 2DE.

RESULTS: Real-time 3DE provided unique information about the dynamic SAM-septal relation during systole, with A_LVOT ranging from 0.6 to 5.2 cm² (mean: 2.2 ± 1.4 cm²). Maximal velocity (v) correlated inversely with A_LVOT (v = 496 A_LVOT^–0.80, r = –0.95, p < 0.001), but the exponent (–0.80) was significantly different from –1.0 (95% confidence interval: –0.67 to –0.92), indicating a significant impact of small A_LVOT on the peak LVOT flow rate. By comparison, the best correlation between velocity and 2DE SAM-septal distance was significantly (p < 0.01) poorer at –0.83, indicating the superiority of 3DE for assessing A_LVOT.

CONCLUSIONS: Three-dimensional echocardiography-measured A_LVOT provides an assessment of HCM geometry that is superior to 2DE methods. These data indicate that the peak LVOT flow rate appears to be significantly decreased by reduced A_LVOT. Real-time 3DE is a potentially valuable clinical tool for assessing patients with HCM.

Abbreviations and Acronyms   ALVOT   area of left ventricular outflow tract   CI   confidence interval   HCM   hypertrophic cardiomyopathy   IVS   interventricular septum   LV   left ventricle or left ventricular   LVOT   left ventricular outflow tract   MR   mitral regurgitant   PG   pressure gradient   PWT   posterior wall thickness   Qmax   peak cardiac outflow   SAM   systolic anterior motion of mitral valve leaflets   v   peak velocity   2DE   two-dimensional echocardiography   3DE   three-dimensional echocardiography

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