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Figure 4 The pushing force of flow. Intraventricular flow relative to the mitral valve in the apical five-chamber view. In obstructive HCM the mitral leaflet coaptation point is closer to the septum than normal (1). The protruding leaflets extend into the edge of the flowstream and are swept by the pushing force of flow toward the septum. Flow pushes the underside of the leaflets (arrow) (6–9). Note that the midseptal bulge redirects flow so that it comes from a relatively lateral and posterior direction; on the five-chamber view, flow comes from "right field" or "one o’clock" direction. This contributes to the high angle of attack relative to the protruding leaflets. Also note that the posterior mitral leaflet is shielded and separated from outflow tract flow by the cowl of the anterior leaflet. Venturi flow in the outflow tract cannot be lifting the posterior leaflet because there is little or no area of this leaflet exposed to outflow tract flow. Venturi forces cannot be causing the anterior motion of the posterior leaflet.
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