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LETTERS

Re: Development of the Outflow Tract

To the Editor: The discussion by Noden et al. (1995)’ in the March/April issue is timely and im- portant. The authors are also wise when they recommend caution in applying re- sults in animal models to the human population. Might I add a further note of caution, namely the need also to take cognisance of topographical relation- ships? In my opinion, the full signifi- cance of development of the outflow tract will not become clear until note is taken of the discrepancy between the anatomic ventriculo-arterial junction, formed in the definitive heart by the union of the walls of the arterial trunks with the supporting ventricular struc- tures, and the haemodynamic junction, the latter marked by the semilunar at- tachments of the leaflets of the arterial valves (Anderson 1990). It is this discor- dance in anatomic and haemodynamic junctions which produces the important interleaflet triangles, an area often for- gotten in anatomic discussions of the outflow tracts (Sutton et al. 1993). I am aware Figure 4 is designed to be dia-

grammatic, but it contains several pit- falls for the unwary. First, it is unlikely that the aorticopulmonary septum would be represented in a parietal struc- ture. Second, I have never seen the ori- fice of a coronary artery arising quite so close to the attachment of the leaflet of an arterial valve. In this respect, the re- search of one of the authors cited in the review (Bogers et al. 1993) stressed the frequent high origin of the coronary ar- teries in hearts with common arterial trunk, so it is a feature of which they are well aware. Third, are the truncal cush- ions really found within the outflow component of the heart? Having been careful elsewhere to distinguish outflow tract from arterial segment, the authors rather spoil the effect when labelling in- tracardiac components as “truncus” in Figures 4 and 5. The advances made in understanding molecular and cellular events over the past few years have been truly spectacular, and the authors of this timely review are rightly acknowledged as leaders in this revolution. It will be disappointing if these advances are not

matched by equal attention to the time- honored field of topographical anatomy.

Robert H. Anderson Department of Pediatrics

National Heart and Lung Institute Dovehouse Street,

London SW3 6LY, UK

SSDI 1050-1738(95)00076-L

References

Noden DM, Poelmann RR, Gittenbexgerde Groat AC: 1995. Cell origins and tissue boundaries during outflow tract develop- ment. Trends Cardiovasc Med 5:69-75.

Anderson RI-Ll990. Editorial note: The ana- tomy of arterial valvar stenosis. Int J Car- diol26:355-359.

Sutton JP III, Ho SY, Anderson RI-L 1995. The forgotten interleaflet triangles: A review of the surgical anatomy of the aortic valve. Am Thorac Surg 59419-427.

Bogers ASSC, Bartelings MM, Bakenkamp R et al: 1993. Common arterial trunk uncom- mon arterial anatomy. J Thorac Cardiovasc Surg 106:1133-1137. TCM

Reply from D. Noden et al. to RH. Anderson’s Letter to Trends We fully support Anderson’s argument that detailed knowledge of topographi- cal relationships is essential to under-

‘All figures referred to herein are from Noden et al. 1995.

stand the development of the outflow spatiotemporal map suitable for special- tract fully. Our schematic diagram [see ists. Refined topographical descriptions Figure 3t; Noden et al. (1995)] showing emphasizing three-dimensional rela- the intracardiac and extracardiac ori- tions and morphogenetic changes in gins and relative contributions of mes- aorticopuhnonary mesenchyme, and enchymal components of the outflow particularly its extensions into intracar- tract deliberately emphasizes cell lin- diac endocardial outflow tract ridges, eages and fates, issues of importance to are available (for example, Bartelings a wide spectrum of investigators and cli- and Gittenberger-de Groot (1988 and nicians, and is not intended as a precise 1989)].

TCM Vol. 5, No. 5, 1995 91995, Elsevier Science Inc.. lOSO-1738/95/$9.50 173