Appendix Valve Diameters

Table A1 lists mean "normal valve diameters: the first column for each valve comes from the data measured by Rowlatt and associates. The Great Ormond Street (GOS) group have found that these valve measurements tend to underestimate the true in vivo sizes. The data from

Rowlatt and coworkers (RRL data) were derived from a large series of normal hearts examined at autopsy. The Great Ormond Street group noted that there was a shrinkage factor due to formalin. Their angiographic estimates were correlated to fresh autopsy material and

Table A1. Mean Cardiac Valve Diameters (mm) Normalized to Body Surface Area.

Mitral Valve Tricuspid Valve Aortic Valve Pulmonary Valve

Table A1. Mean Cardiac Valve Diameters (mm) Normalized to Body Surface Area.

Mitral Valve Tricuspid Valve Aortic Valve Pulmonary Valve

BSA

RRLa

GOSb

RRL

GOS

RRL

GOS

RRL

GOS

0.25

11.2

16.0

13.4

19.2

7.2

10.3

8.4

12.0

0.30

12.6

18.0

14.9

21.3

8.1

11.6

9.3

13.3

0.35

13.6

19.4

16.2

23.2

8.9

12.7

10.1

14.4

0.40

14.4

20.6

17.3

24.7

9.5

13.6

10.7

15.3

0.45

15.2

21.7

18.2

26.0

10.1

14.4

11.3

16.2

0.50

15.8

22.6

19.2

27.5

10.7

15.3

11.9

17.0

0.60

16.9

24.2

20.7

29.6

11.5

16.4

12.8

18.3

0.70

17.9

25.6

21.9

31.3

12.3

17.6

13.5

19.3

0.80

18.8

26.9

23.0

32.9

13.0

18.6

14.2

20.3

0.90

19.7

28.2

24.0

34.3

13.4

19.2

14.8

21.2

1.0

20.2

28.9

24.9

35.6

14.0

20.0

15.3

21.9

1.2

21.4

30.6

26.2

37.5

14.8

21.2

16.2

23.2

1.4

22.3

31.9

27.7

39.6

15.5

22.2

17.0

24.3

1.5

23.1

33.0

28.9

41.3

16.1

23.0

17.6

25.2

1.8

23.8

34.0

29.1

41.6

16.6

23.6

18.0

25.7

2.0

24.2

34.6

30.0

42.9

17.2

24.6

18.2

26.0

Standard Deviations Mitral Valve

Standard Deviations Mitral Valve

Tricuspid Valve

Aortic Valve Pulmonary Valve

BSA < 0.3 = ±1.9 BSA > 0.3 = ±1.6 BSA < 1.0 = ±1.7 BSA > 1.0 = ±1.5 All BSA ± 1.0 All BSA ± 1.2

To convert to approximate predicted manufactured rigid prosthetic valve sizes, add 3-4 mm to measurement.

a RRL: data derived from Rowlatt and associates.b GOS = Great Ormond Street "normalized" diameters. Adapted from de Leval.

suggested that the atrioventricular valves were certainly under-estimated by the earlier techniques. The London (GOS) workers suggested that the RRL measurements should be multiplied by a factor of 1.43 to equal their fresh measurements (C. Bull, personal communication). Thus this table includes both the original data of Rowlatt and coworkers and the larger estimates of "normal."

The way we use this table relative to ventricular outflow valves is to consider the RRL valve diameters as the minimun acceptable diameter for a given body surface area and the GOS diameters as the mean to upper limits of achievable valve transplants. From a practical standpoint it means that we would try to place, for an "adult" sized freehand aortic valve implant, an allograft of 20 mm (internal diameter) for an individual with a body surface area (BSA) of 1m2 and a valve as large as 24.6 mm for a 2 m2 individual. Once a patient reaches approximately 20 kg in weight, an aortic valve of 17 mm or larger is usually implantable in the aortic position with the techniques described in the foregoing chapters, which is within the acceptable range.

The pulmonary outflow tract is optimally reconstructed with a 22 mm pulmonary valve for a 1 m2 individual and could be as large as a 26 mm for a 2 m2 individual adult. In most patients a valve between the upper and lower sizes is almost always achievable. On the right ventricular outflow tract side, a 14 mm (internal diameter) aortic valve can usually be place in a 5 kg child; once the child weighs more than 10kg, a right ventricular allograft conduit of 16mm or larger is implantable; and in children above 20 kg, it is almost always possible to place a 20 mm or larger conduit in the right ventricular outflow tract position. Mercer has argued that a more than 50% reduction in pulmonary valve orifice size is required before significant gradients occur. However, right-sided conduits have length as well as diameter, thus sizes below the RRL values are not recommended.

With use, we have found that this table has been best at predicting the aortic and pulmonary valve diameters. It is important to remember that the diameters in these tables refer to the internal diameters, not the external diameters.

Table A2. AV Valve Ring Diameter for Reconstruction.

Mitral Valve

Tricuspid Valve

BSA (m2)

(mm)

(mm)

1.0

26

32

1.2

28

34

1.4

29

36

1.5

30

37

1.8

31

38

The aortic and pulmonary valve columns are immediately translatable to homograft sizes which are also measured in internal diameter. For manufactured valves, at least 2-4mm needs to be added to correlate with the external sewing ring diameter as usually listed for rigid stented valves.Thus, a mechanical mitral valve choice for a 2.0 m2 BSA individual, would be preferably a size 27. For the aortic position, the smallest aortic prosthesis one would ever consider for a 2.0 m2 individual would be 17.2 plus 4.0mm which equals a 21, but the GOS value gives the preferred size of 25.

Manufactured valve sizes do not necessarily reflect either the predicted internal diameter of a natural valve for the patient or, in fact, even the measured external diameter of the prosthesis, but in fact are an approximation of those two values based upon manufacturing requirements. The mean diameters listed in Table I are actual internal diameters as would be measured by echocardiography from the hinge point of the base of the leaflets across the orifice of each valve. Thus they reflect the target values for reconstructions. They do not directly represent the prosthetic sewing ring valve size as is normally tabulated for manufactured valves. The mitral and tricuspid valve measurements have been correlated with empiric use of valve ring diameters used in reconstructions for patients between 1.0 and 2.0 BSA. These are listed in Table A2.

These "ring" estimates are target values based on BSA normalized valve measurements. They must be modified by specific measurements at surgery of available leaflet tissue for orifice coverage and the specific type and configuration of ring being used. We do not use rigid rings in smaller children to allow for growth.

0 0

Post a comment