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J Thorac Cardiovasc Surg 1996;111:1107-1109
© 1996 Mosby, Inc.
LETTERS TO THE EDITOR |
Departments of Pathology and Cardiology
Children's Hospital
Departments of Pediatrics and Pathology
Harvard Medical School
Boston, MA 02115
Reply to the Editor:
Anderson, Uemura, and Devine begin by saying that we ignored all of their previous work on this subject. The purpose of our paper
1 was not to review the literature, but to present detailed morphologic anatomic data concerning the systemic and pulmonary venous connections in patients who have heterotaxy with asplenia, in order to facilitate their surgical management.
Anderson, Uemura, and Devine state that we are not following the morphologic method (that we helped to introduce) 2 because we are using the connections of the systemic and pulmonary veins to help to identify the atria. This is not true. Because the systemic veins (usually the right horn of the sinus venosus) and the pulmonary veins (the common pulmonary vein) normally are integral components of the morphologically right atrium and the morphologically left atrium, 2 respectively, these venous connections are part of the anatomic data that are used to make the diagnosis of morphologically right and left atrio. We never base the diagnosis of morphologically right or left atrium on the venous connections only. Although the pulmonary veins can be totally anomalous and may not connect at the atrial level, the systemic veins (sinus venosus) always connect with the atria. Moreover, the sinus venosus is always an integral part of the morphologically right atrium; this is not a variable.
To identify the atria morphologically, we use the following anatomic data 3,4: the atrial connections of the inferior vena cava and of the coronary sinus (if present); the size, shape, and location of the atrial appendages; and the atrial connections of the pulmonary veins. When all of the aforementioned morphologic data do not add up to a clear and confident diagnosis of morphologically right or left atrium, then we make the diagnosis of atrial situs ambiguus, indicating that we do not know what the atrial situs is.
Consequently, our use of the systemic and pulmonary venous connections in combination with all other available anatomic data is not a "contravention of the morphologic method," as Anderson, Uemura, and Devine allege. On the contrary, use of the venous connections in combination with all other relevant morphologic anatomic data is a good illustration of how the morphologic method is currently being used to identify the atria and the atrial situs in difficult situations that were previously regarded as undiagnosable—such as in the heterotaxy syndrome with asplenia and polysplenia.
Anderson, Uemura, and Devine say that it is unfortunate that neither of our two previous reports 3,4 concerning the diagnosis of the atrial situs in the heterotaxy syndrome was published in a peer-reviewed journal. Some of our most important work has been published in books 2 rather than in journals. The vehicle of publication (journal or book) does not determine scientific quality.
Anderson notes that we think that "isomerism of the atrial chambers is an erroneous concept." He is right about that. 5 Anderson's own understanding of the atria in the heterotaxy syndrome has undergone remarkable changes over the past 15 years: From 1980 to 1986, it was atrial isomerism. 6-8 From 1988 to early 1995, it was atrial appendage isomerism. 9,10 Now, Anderson, Uemura, and Devine have abandoned atrial appendage isomerism in favor of atrial appendage junction isomerism.
Concerning asplenia hearts, Anderson, Uemura, and Devine now say that "neither size nor shape of the appendages is sufficiently constant to permit their recognition." In other words, even the appearance of right atrial appendage isomerism—with reference to size and shape—often is not present in the asplenia syndrome. This is an anatomic fact with which we agree.
We shall not reiterate here all the reasons that the concept of atrial level isomerism in the heterotaxy syndrome is flawed both anatomically and logically. 5 Suffice it to say that because the atrial appendages often differ markedly in size and shape, so do their junctions with the main atrial chambers. These junctions are often not mirror images; that is, this is not isomerism. 5
From the diagnostic standpoint, the presence or absence of similar appearing atrial appendages ("isomerism") does not prevent the diagnosis of the atrial situs, which usually is possible in asplenia and almost always is possible in polysplenia. 3,4
Anderson, Uemura, and Devine seem never to have seen a normally formed coronary sinus in asplenia. We reported two such rare cases, one with solitus atria and the other with inversus atria. 1 We also have seen a postmortem-proved case of asplenia with interruption of the inferior vena cava, another rare finding (unreported data).
When the pulmonary veins connect with the atria in asplenia, we think that the pulmonary veins are normally connected. 11 Anderson, Uemura, and Devine disagree. We think that the atrial septum, that is, the septum primum, can be malpositioned, resulting in anomalous pulmonary venous drainage, even though the pulmonary venous connections are normal—relatively high (above the coronary sinus region) and between the right and left horns of the sinus venosus, that is, between the right and left superior venae cavae. When only one superior vena cava is present, the pulmonary veins connect to the left of the superior vena cava with solitus atria and to the right of the superior vena cava with inversus atria. 3,4,11
Anderson, Uemura, and Devine suggest that absence of septum secundum indicates that the pulmonary veins in asplenia must have an abnormality in "arrangement." We believe that this does not follow. It would be equally logical (or illogical) to say that the superior vena cava—which lies on the other side of the deficient or absent septum secundum—must also be abnormally arranged. We are aware of no anatomic data that would support either of these speculations. We agree that deficiency or absence of septum secundum favors anomalous pulmonary venous drainage, but it typically is not associated with anomalous pulmonary venous connection. For example, in left-sided juxtaposition of the atrial appendages, septum secundum is often very deficient or absent, but the pulmonary veins typically are normally connected. 12
We believe that the identification of the atrial situs in patients with heterotaxy and asplenia is of major importance, just as important as diagnosing the type of ventricular loop and the anatomic type of infundibulum and great arteries. Unless the atrial situs is diagnosed, complete segmental analysis of heterotaxy is impossible. Atrial situs inversus is prevalent in our experience: 31% in asplenia and 22% in polysplenia. 4 This is also true for the ventricles. L-loop ventricles were present in 38% of our patients with asplenia and 30% of our patients with polysplenia. 4 We hypothesize that when the etiology of visceral heterotaxy becomes better understood, it will prove to be related to the etiology of situs inversus.
In contrast, our patients with a documented history of any kind of trisomy (trisomy 9, 13, 18, or 21) never have had any visceral or cardiac segmental inversion. 13 Despite the fact that patients with trisomy often have common atrioventricular canal, just as patients with heterotaxy do, no individuals with trisomy have ever had visceral heterotaxy in our experience. 13
This realization has an important practical application. Because visceral heterotaxy can be diagnosed by fetal echocardiography, amniocentesis looking for fetal trisomy can be avoided as unnecessary: 14 individuals with trisomy never have heterotaxy and those with heterotaxy never have trisomy. To date, these entities have been mutually exclusive.
In conclusion, the realization that the concept of atrial level isomerism in patients who have heterotaxy with asplenia or polysplenia is wrong facilitates diagnosis of the atrial situs in such patients by application of the morphologic method. This new understanding will help to improve the surgical management of these difficult and complex cases and may also help to elucidate the etiology of the heterotaxy syndrome.
References
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