Click on image to view larger version.

Figure 4 Schematic representation of the relationship between the increase in transmitral pressure gradient (TMP) (the instantaneous difference between left ventricular and left atrial pressure) and the decrease in effective regurgitant orifice area (EROA). During OFF (top panel), left ventricular (LV) contractility is low and results in a slow rise in the LV pressure curve and TMP with a relatively late systolic maximum. Due to the slow LV pressure rise with delayed development of an effective transmitral closing force (approximately TMP), EROA remains large for a relatively long period until it finally reaches its minimal value. In contrast, during cardiac resynchronization therapy (CRT) (bottom panel), LV contractility improves, TMP rises faster and to a higher maximal value, which is also reached earlier. Consequently, the reduction in EROA occurs earlier, EROA reaches lower values and for a prolonged period of time. The shaded area represents the time in systole during which EROA is below 50% of its initial value. Note that, in the chosen example, the reduction in the height of the V-wave after a decrease in the initial mitral regurgitation will contribute to a preserved TMP during the latter half of systole. Solid line = left atrial (LA) and LV pressure; dotted line = EROA. Adapted from Hung et al. (15).