CHAPTER 10 ANTERIOR LEAFLET AREA 10-1

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CHAPTER 10 ANTERIOR LEAFLET AREA 10-1

MITRAL VALVE MECHANICS by Neil B. Ingels, Jr. and Matts Karlsson

CHAPTER 10 ANTERIOR LEAFLET AREA

Anterior leaflet area was calculated using the Matlab algorithm given in Appendix C. For each frame in each heart, this algorithm fits a surface to all the anterior leaflet markers shown in Figure 1.2, tiles this surface with a fine mesh of rectangular elements with dimensions dx by dy, computes the area of each element as dx*dy, then sums all these areas to arrive at the total leaflet surface area. Tests of this algorithm showed that it is capable of measuring the surface area of a half sphere to within 1%.

Figure 10.1 shows the anterior leaflet areas for each frame throughout three consecutive cardiac cycles in each of the six hearts. Note, in Figure 10.1, that:

• In each heart, leaflet area vs. time (frame) morphology is virtually identical from beat-to-beat. This suggests very little biological and computational randomness for this variable. The data in Table 10.1 support this point.

• Leaflet areas change very little during the entire time the mitral valve is closed. This is of particular interest because LVP changes considerably during IVR, but leaflet area remains relatively unaffected. Table 10.1 quantifies this change from the MVC+1 frame to the MVO-1 frame. During this interval, mean LVP falls from 69 to 22 mmHg, yet mean leaflet area changes only -1%. Further, this area change ranges from -7% to +4% in these six hearts, decreasing in some hearts, increasing in others. This is not the behavior of a simple tense elastic membrane responding to changes in pressure loading. These small area changes also set limits on leaflet strains, a subject that will be explored in the next chapter.

• The small leaflet area change during ejection is consistent with the concept, emphasized in previous chapters, that the anterior leaflet serves as a stable structural boundary for the LV outflow tract throughout systole.

• As will be discussed in a subsequent chapter, the dynamics of anterior leaflet area are not correlated with the dynamics of mitral annular area through the cardiac cycle, showing, once again, the independence of the anterior leaflet from other components of the mitral valvular complex.

• Finally, computing leaflet area during diastole is subject to considerable noise. We know the coordinates of the leaflet markers to within roughly 0.1 mm through the cardiac cycle, and hold the best-fit leaflet plane in a constant position in each frame, yet Figure 10.1 still demonstrates that the leaflet area calculation is very noisy during diastole. The reason this is such a noisy calculation during diastole is that the local curvature of the leaflet becomes so great (the leaflet even folds back on itself during some diastolic excursions) that it becomes impossible to define leaflet area with the markers spaced as they are in this study. If our arrays employed thousands of markers, perhaps much of this steep curvature could be measured, but even then it would be difficult to fit a spatial curve to regions that were folding back on themselves. It is important to understand how noisy the measurement of leaflet area is in diastole, because this is a

measurement that is studied in a clinical context. Unlike diastole, however, leaflet shape is quite stable during systole and thus is thus amenable to reasonably accurate and reproducible area measurement.

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CHAPTER 10 ANTERIOR LEAFLET AREA 10-2

MITRAL VALVE MECHANICS by Neil B. Ingels, Jr. and Matts Karlsson

Figure 10.1 H1-H6 anterior leaflet areas (mm2) throughout three cardiac cycles. LVP=Left Ventricular

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CHAPTER 10 ANTERIOR LEAFLET AREA 10-3

MITRAL VALVE MECHANICS by Neil B. Ingels, Jr. and Matts Karlsson

TABLE 10.1

HEART BEAT FRAME F1 MVC+1 FRAME F2 MVO-1 AREA A1 AT F1 (mm2) AREA A2 AT F2 (mm2) % CHANGE 100*(A2-A1) /A1 LVP AT F1 mmHg LVP AT F2 mmHg H1 B1 22 40 625 601 -4 83 28 nac03r04 B2 58 76 625 593 -5 82 28 B3 94 112 623 599 -4 82 23 H2 B1 24 41 510 490 -4 68 24 nam14r01 B2 60 77 519 487 -6 70 23 B3 96 113 521 483 -7 72 22 H3 B1 30 51 610 599 -2 74 19 nam18r03 B2 78 99 619 602 -3 73 21 B3 126 147 617 600 -3 72 23 H4 B1 17 37 483 488 1 55 29 nsa12r01 B2 60 80 482 489 1 76 19 B3 102 122 486 493 1 75 19 H5 B1 23 44 592 583 -2 46 29 nac09r03 B2 63 84 587 590 1 57 24 B3 102 123 591 583 -1 48 28 H6 B1 18 42 780 811 4 70 11 nas07r03 B2 63 87 779 809 4 70 11 B3 108 132 780 809 4 70 11 LOW 482 483 -7 46 11 HIGH 780 811 4 83 29 MEAN 602 595 -1 69 22 MEDIAN 601 592 -2 71 23

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