Common Atrium or Atrioventricular Septal Defect: What Is in a Name?

•Common atrium is characterized by complete/near-complete absence of IAS.•Common atrium frequently accompanies AVSD, although it can occur as an isolated entity.•Most AVSDs with an atrial communication have normal to near-normal atrial septal lengths.•Partial AVSD with near-complete absence of IAS is an uncommonly reported heart condition.•With many echo features present, it is difficult to apply one diagnostic label to complex CHD. IntroductionAtrioventricular septal defect (AVSD) is a well-described group of congenital heart conditions. The hallmark features for all types of AVSD are absence of atrioventricular (AV) septal structures and a common AV junction guarded by a common AV valve possessing five leaflets.1Rigby M. Atrioventricular septal defect: what is in a name?.J Cardiovasc Dev. 2021; 8: 19PubMed Google Scholar The most frequently observed form of an AVSD with two valve orifices is an isolated primum defect between the lower edge of the interatrial septum (IAS) and the AV valve leaflets (partial AVSD).1Rigby M. Atrioventricular septal defect: what is in a name?.J Cardiovasc Dev. 2021; 8: 19PubMed Google Scholar The term “common atrium” has been used to denote the condition characterized by complete or near-complete absence of the IAS, with or without AVSD.2Levy M.J. Salomon J. Vidne B.A. Correction of single and common atrium, with reference to simplified terminology.Chest. 1974; 66: 444-446Abstract Full Text Full Text PDF PubMed Scopus (16) Google Scholar,3Franklin R.C. Béland M.J. Colan S.D. Walters III, H.L. Aiello V.D. Anderson R.H. et al.Nomenclature for congenital and paediatric cardiac disease: the International Paediatric and Congenital Cardiac Code (IPCCC) and the Eleventh Iteration of the International Classification of Diseases (ICD-11).Cardiol Young. 2017; 27: 1872-1938Crossref PubMed Scopus (67) Google Scholar It is an uncommon disorder in humans that has been reported as individual case reports or as small case series. Common atrium and AVSDs are among the uncommonly reported congenital heart malformations in the domestic dog, but the rarity of reports of common atrium in dogs may simply be reflective of the inconsistent terminology used to describe this lesion. In humans, cases of common atrium are typically syndromic and have been reported in patients with heterotaxy, Ellis-van Creveld syndrome, and complete AVSD with and without concurrent Down syndrome.4Cetta F. Truong D. Minich L.L. Maleszewski J.J. O’Leary P. Dearani J.A. et al.Atrioventricular septal defect.in: Shaddy R.E. Penny D. Feltes T.F. Moss and Adams’ Heart Disease in Infant, Children, and Adolescents. 9th ed. Wolters Kluwer, London2016: 757-782Google Scholar Due to frequent occurrence of concurrent AV valve malformation, common atrium has been suggested to be a form of partial AVSD. However, the available literature in human patients suggests that it can occur as an isolated entity, without concurrent AVSD.2Levy M.J. Salomon J. Vidne B.A. Correction of single and common atrium, with reference to simplified terminology.Chest. 1974; 66: 444-446Abstract Full Text Full Text PDF PubMed Scopus (16) Google Scholar Here, we report a case of a young dog that presented for subclinical (asymptomatic) murmur evaluation, in which features of common atrium and partial AVSD were both observed using echocardiography. This case highlights that the constellation of congenital malformations that deviate from the usual morphology may pose challenges in assigning a single unambiguous term.Case PresentationA 1.5-year-old, intact, female Belgian Tervuren dog weighing 17.6 kg was presented to the Atlantic Veterinary College Teaching Hospital for evaluation of a heart murmur prior to undergoing general anesthesia for elective ovariohysterectomy. The dog did not have any history of weakness, exercise intolerance, collapse, or respiratory signs. However, the dog was reported to be underweight by the primary care veterinarian approximately 3 months before presentation. The dog had been receiving clomipramine hydrochloride for presumed generalized anxiety disorder. Physical examination revealed a grade 5/6 left basilar systolic and a grade 1-2/6 left basilar diastolic murmur and a split second heart sound. The dog was moderately underweight with moderate muscle loss. The rest of the physical examination was unremarkable. Results of a complete blood count and serum chemistry were within reference ranges.A transthoracic two-dimensional (2D) and Doppler echocardiographic study (Video 1) was performed with the patient unsedated. The IAS was not evident on several of the 2D imaging planes, suggesting a single atrial chamber (Figure 1). Upon careful interrogation, a small strand of tissue was noted in the dorsal wall of the common atrial chamber in some views, possibly representing a remnant of the IAS (Figure 1E). There was malformation of the AV valves (Video 1). Specifically, there was a common AV valve with septal leaflet (bridging leaflet) inserting at the same level on the crest of the interventricular septum (Figure 1A-B) and with the left-side portion of the AV valve being trifoliate in appearance (best visualized in the right parasternal short-axis left ventricle [LV]–right ventricle [RV] view; Video 1 and Figure 2A). These findings were consistent with the presence of a common AV annulus with two separate orifices (left and right AV orifices). The RV (end-diastolic diameter of 34 mm; Figure 1A–B, 2B-C) and main and branch pulmonary arteries were markedly dilated, suggesting marked right-sided volume overload (Video 1). The ratio of pulmonary (Qp) to systemic (Qs) flows was indirectly estimated by combining 2D echocardiography and pulsed-wave Doppler modes.5Serres F. Chetboul V. Tissier R. Gouni V. Desmyter A. Sampedrano C.C. et al.Quantification of pulmonary to systemic flow ratio by a Doppler echocardiographic method in the normal dog: repeatability, reproducibility, and reference ranges.J Vet Cardiol. 2009; 11: 23-29Crossref PubMed Scopus (17) Google Scholar The Qp/Qs ratio was 5.1:1, indicating marked pulmonary overcirculation due to left-to-right shunting (Table 1). The left ventricular (LV) end-diastolic (33 mm) and end-systolic (24 mm) dimensions, LV wall thickness, and systolic function (fractional shortening 27%) were normal when compared with published allometric weight-based normal reference ranges.6Cornell C.C. Kittleson M.D. Torre P.D. Häggström J. Lombard C.W. Pedersen H.D. et al.Allometric scaling of M-mode cardiac measurements in normal adult dogs.J Vet Intern Med. 2004; 18: 311-321Crossref PubMed Google ScholarTable 1Results of Doppler echocardiography for Qp/Qs estimationMain pulmonary arteryAortaDiameter measured at end systole, cm2.01.5Systolic flow velocity-time integral, cm36.212.5Flow volume, mL113.722.1Measurements reflect the mean of three cardiac cycles. Open table in a new tab Color Doppler imaging showed moderate left and right AV valve regurgitation (Video 1). The direction of shunting in the atrial chamber could not be accurately determined because of the turbulent jets of left and right AV valve regurgitation and the atrial chamber inflow. Interventricular communication was not noted. The aortic and pulmonic valves appeared normal. On the right parasternal four-chamber imaging planes tipped to accentuate the apical portion of the ventricles, a trivial amount of pericardial effusion was noted (Figure 2D), which was considered to be within the physiological amount. On continuous-wave spectral Doppler interrogation, the right AV valve regurgitation (Vmax = 3.6 m/sec) and pulmonic regurgitation (Vmax = 2.3 m/sec) jet velocities (in combination with the 2D features) suggested high probability for the presence of at least a moderate degree of pulmonary hypertension (PH).7Reinero C. Visser L.C. Kellihan H.B. Masseau I. Rozanski E. Clercx C. et al.ACVIM consensus statement guidelines for the diagnosis, classification, treatment, and monitoring of pulmonary hypertension in dogs.J Vet Intern Med. 2020; 34: 549-573Crossref PubMed Scopus (79) Google Scholar The left AV valve inflow pattern was normal. Mild pulmonic regurgitation was present.Figure 2Echocardiographic images illustrating abnormalities detected in a young dog with a large interatrial communication and common AV junction. (A) Right parasternal short-axis (RPS SAx) transventricular (LV-RV) view shows a common AV valve with a trifoliate left AV valve (red arrow). (B) RPS SAx LV-RV view showing marked right ventricular dilation. (C) M-mode obtained from RPS SAx LV-RV view showing marked right ventricular dilation and diastolic flattening of the interventricular septum (white arrow). (D) Scant amount of pericardial effusion (red arrow) is noted on the RPS long-axis imaging plane.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Two terms were considered to describe the echocardiographic findings in this dog: (1) partial AVSD with a large ostium primum atrial septal defect (ASD) and possibly a concurrent ostium secundum ASD and (2) common atrium with concurrent AVSD. These malformations resulted in secondary marked right-sided cardiac enlargement, pulmonary overcirculation, and PH.DiscussionThe present case report describes echocardiographic findings in a young dog, which comprised near-complete absence of the IAS or, at most, its representation by a small strand of tissue present in the cephalad wall of the atrial chamber, along with absence of interventricular communication and malformation of the AV valves (common AV valve with two orifices and a trifoliate left AV valve). This case illustrates the indispensable role that echocardiography plays in the diagnosis of congenital heart diseases (CHDs), highlights the inconsistencies in terminology and nomenclature of certain congenital heart malformations in the literature, and emphasizes that the constellation of congenital malformations that deviate from the usual morphology may pose challenges in assigning a single unambiguous diagnosis.In the literature, there is considerable nosologic confusion regarding the use of the terms “common atrium,” “single atrium,” and “AVSD.” The term “AVSD” is a generic name for a group of anomalies characterized by absence of AV septal structures and consequently possessing a common AV junction guarded by a common AV valve.8Silverman N.H. Zuberbuhler J.R. Anderson R.H. Atrioventricular septal defects: cross-sectional echocardiographic and morphologic comparisons.Int J Cardiol. 1986; 13: 309-331Abstract Full Text PDF PubMed Scopus (45) Google Scholar This common valve can have a single (common) orifice or can be divided into two orifices by a tongue of valve tissue joining the bridging leaflets.1Rigby M. Atrioventricular septal defect: what is in a name?.J Cardiovasc Dev. 2021; 8: 19PubMed Google Scholar The spectrum of AVSD can range from partial (shunting confined at either the atrial or the ventricular level with one common annulus and two separate AV orifices), intermediate (shunting at both atrial and ventricular levels with one common annulus and two separate orifices), or complete (shunting at both atrial and ventricular levels with one common AV annulus and one single AV orifice) AVSD.1Rigby M. Atrioventricular septal defect: what is in a name?.J Cardiovasc Dev. 2021; 8: 19PubMed Google Scholar,3Franklin R.C. Béland M.J. Colan S.D. Walters III, H.L. Aiello V.D. Anderson R.H. et al.Nomenclature for congenital and paediatric cardiac disease: the International Paediatric and Congenital Cardiac Code (IPCCC) and the Eleventh Iteration of the International Classification of Diseases (ICD-11).Cardiol Young. 2017; 27: 1872-1938Crossref PubMed Scopus (67) Google Scholar,9Calkoen E.E. Hazekamp M.G. Blom N.A. Elders B.B.L.J. Groot A.C.G. Hakk M.C. et al.Atrioventricular septal defect: from embryonic development to long-term follow-up.Int J Cardiol. 2016; 202: 784-795Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar An AVSD can occasionally exist in the absence of any ASD or interventricular communication.1Rigby M. Atrioventricular septal defect: what is in a name?.J Cardiovasc Dev. 2021; 8: 19PubMed Google Scholar Even this nomenclature and subdivision of the varying morphology of AVSDs, which is widely used, is felt by some researchers to lack specificity.Based on Rastelli et al‘s10Rastelli G. Rahimtoola S.H. Ongley P.A. McGoon D.C. Common atrium: anatomy, hemodynamics, and surgery.J Thorac Cardiovasc Sur. 1968; 55: 834-841Abstract Full Text PDF PubMed Google Scholar observations in 15 human patients and previous other reports stating that the complete absence of atrial septum always occurs with concurrent AV valve abnormalities, the common atrium was initially considered a form of AVSD. However, Levy et al,3Franklin R.C. Béland M.J. Colan S.D. Walters III, H.L. Aiello V.D. Anderson R.H. et al.Nomenclature for congenital and paediatric cardiac disease: the International Paediatric and Congenital Cardiac Code (IPCCC) and the Eleventh Iteration of the International Classification of Diseases (ICD-11).Cardiol Young. 2017; 27: 1872-1938Crossref PubMed Scopus (67) Google Scholar in 1974, followed by several other investigators, reported cases of complete absence of the atrial septum without malformation of the AV valves, indicating that this condition may exist alone as a specific entity without an AVSD. They recommended that the term “single atrium” be used to denote the condition characterized by (1) complete absence of the atrial septum, (2) absence of malformation of the AV valves, and (3) absence of interventricular communication. They suggested that the term “common atrium” should be used to denote the condition of complete absence of the atrial septum, accompanied by malformation of the AV valves, with or without interventricular communication. To standardize the nomenclature for CHD across the globe, the International Nomenclature Society linked its efforts with those of the World Health Organization to obtain a globally accepted nomenclature tree for CHD with the 11th iteration of the International Classification of Diseases. According to this publication,3Franklin R.C. Béland M.J. Colan S.D. Walters III, H.L. Aiello V.D. Anderson R.H. et al.Nomenclature for congenital and paediatric cardiac disease: the International Paediatric and Congenital Cardiac Code (IPCCC) and the Eleventh Iteration of the International Classification of Diseases (ICD-11).Cardiol Young. 2017; 27: 1872-1938Crossref PubMed Scopus (67) Google Scholar common atrium with separate AV junctions has been defined as “a congenital cardiovascular malformation in which there is complete or near-complete absence of the interatrial septum” and single atrium and atrium communis are denoted as synonyms. Common atrium with common AV junction has been defined as “a congenital cardiac malformation in which there is complete absence of the interatrial septum in the setting of a common atrioventricular junction (common atrioventricular canal).“3Franklin R.C. Béland M.J. Colan S.D. Walters III, H.L. Aiello V.D. Anderson R.H. et al.Nomenclature for congenital and paediatric cardiac disease: the International Paediatric and Congenital Cardiac Code (IPCCC) and the Eleventh Iteration of the International Classification of Diseases (ICD-11).Cardiol Young. 2017; 27: 1872-1938Crossref PubMed Scopus (67) Google Scholar The echocardiographic findings in the dog in this report have features that fit partially into both of these categories, that is, near-complete absence of the IAS but with a common AV junction.Atrioventricular septal defect is a rare CHD in domestic animals, with a reportedly higher occurrence in cats than in dogs.11Saponaro V. Staffieri F. Franchini D. Crovace A. Complete atrioventricular canal in a dog.J Vet Cardiol. 2010; 12: 135-140Crossref PubMed Scopus (4) Google Scholar,12Schrope D.P. Atrioventricular septal defects: natural and findings in Vet Cardiol. PubMed Scopus Google Scholar Common atrium is an reported CHD in However, this may simply be reflective of the inconsistent terminology used to describe this and may not be a representation of its both in the and in the that have been used or in the human and literature to describe AVSD or common atrium, there are at least two terms that could be to the echocardiographic findings observed in the dog of the present case (1) partial AVSD with a large ostium primum ASD and possibly a concurrent ostium secundum ASD for the lack of IAS and (2) common atrium with AVSD. in of the second term are human suggesting the AV septal and the presence of shunting at the atrial the atrial septum is a in the setting of M. Anderson R. echocardiographic of the of the atrial septum to the atrioventricular junction in atrioventricular septal PubMed Scopus Google Scholar in the case to AVSD in the many cats with AVSD appeared to have an atrial communication had normal to near-normal atrial septal D.P. Atrioventricular septal defects: natural and findings in Vet Cardiol. PubMed Scopus Google Scholar These findings are not because the shunting at the atrial level in partial AVSD has been to be due to the of the portion of the AV septum between the of the AV valve leaflets and the AV and not due to the of the IAS M. Anderson R. echocardiographic of the of the atrial septum to the atrioventricular junction in atrioventricular septal PubMed Scopus Google Scholar The dog in the present report has near-complete of the the echocardiographic findings in this dog are considered a form of partial AVSD, it have to be with a markedly large ostium primum concurrent ostium secundum or In this this case a form of partial AVSD in which the IAS is not a in to that D.P. Atrioventricular septal defects: natural and findings in Vet Cardiol. PubMed Scopus Google M. Anderson R. echocardiographic of the of the atrial septum to the atrioventricular junction in atrioventricular septal PubMed Scopus Google Scholar This case could be considered a form of partial AVSD with features that deviate from the usual and consistent nomenclature for CHD is for and communication between and is for and to the of are in and It from the the nomenclature of several that in patients with congenital heart malformation, we may not be to on individual for because of the presence of features or In these a complete and in the diagnosis may be than to fit a general The dog in this report can be as echocardiographic features of AVSD with a large interatrial communication. the interatrial communication in this dog a form of common atrium or a large ostium primum defect and concurrent ostium secundum defect is of the terminology to the findings in this dog, these congenital malformations resulted in secondary marked right-sided cardiac enlargement, pulmonary overcirculation, and in patients with common atrium or AVSD with atrial level communication are reported to be to those with large G. Rahimtoola S.H. Ongley P.A. McGoon D.C. Common atrium: anatomy, hemodynamics, and surgery.J Thorac Cardiovasc Sur. 1968; 55: 834-841Abstract Full Text PDF PubMed Google Scholar The amount of shunting that occurs across large on the of the two in the RV is approximately two to three as as the in the absence of other cardiac abnormalities, large in left-to-right M.D. congenital cardiovascular Kittleson M.D. Scholar In this the combination of AV valve regurgitation and atrial inflow within the atrial chamber it difficult to the direction of However, marked right-sided volume lack of shunting lack of and Qp/Qs ratio all left-to-right An study to the presence of shunting was not performed in this with common atrium frequently have abnormalities of systemic and pulmonary C. J. systemic common atrium, and partial atrioventricular a case report of Thorac Cardiovasc Full Text PDF PubMed Google Scholar In the previous case report of common atrium in a dog, left and systemic were M. Atrioventricular septal defect: what is in a name?.J Cardiovasc Dev. 2021; 8: 19PubMed Google Scholar In the present was not on the echocardiographic for and young with common atrium or AVSD of which is recommended in due to for development of pulmonary F. Truong D. Minich L.L. Maleszewski J.J. O’Leary P. Dearani J.A. et al.Atrioventricular septal defect.in: Shaddy R.E. Penny D. Feltes T.F. Moss and Adams’ Heart Disease in Infant, Children, and Adolescents. 9th ed. Wolters Kluwer, London2016: 757-782Google Scholar was not in this dog because of the lack of with Due to the lack of cardiac were echocardiographic examination months was recommended to and There were from the at the this report was atrium and AVSD are among rare in domestic large interatrial communication with concurrent AV valve malformation may occur in dogs with a murmur and without signs. The diagnosis can be on the of 2D and Doppler echocardiographic The present case report describes a constellation of echocardiographic findings of near-complete absence of the IAS, a common AV and absence of interventricular communication in a young These malformations resulted in secondary marked right-sided cardiac enlargement, pulmonary overcirculation, and These findings could be partial AVSD with a large interatrial communication or common atrium with AVSD. This case report is one a globally accepted nomenclature for patients with complex could be a to inconsistencies in IntroductionAtrioventricular septal defect (AVSD) is a well-described group of congenital heart conditions. The hallmark features for all types of AVSD are absence of atrioventricular (AV) septal structures and a common AV junction guarded by a common AV valve possessing five leaflets.1Rigby M. Atrioventricular septal defect: what is in a name?.J Cardiovasc Dev. 2021; 8: 19PubMed Google Scholar The most frequently observed form of an AVSD with two valve orifices is an isolated primum defect between the lower edge of the interatrial septum (IAS) and the AV valve leaflets (partial AVSD).1Rigby M. Atrioventricular septal defect: what is in a name?.J Cardiovasc Dev. 2021; 8: 19PubMed Google Scholar The term “common atrium” has been used to denote the condition characterized by complete or near-complete absence of the IAS, with or without AVSD.2Levy M.J. Salomon J. Vidne B.A. Correction of single and common atrium, with reference to simplified terminology.Chest. 1974; 66: 444-446Abstract Full Text Full Text PDF PubMed Scopus (16) Google Scholar,3Franklin R.C. Béland M.J. Colan S.D. Walters III, H.L. Aiello V.D. Anderson R.H. et al.Nomenclature for congenital and paediatric cardiac disease: the International Paediatric and Congenital Cardiac Code (IPCCC) and the Eleventh Iteration of the International Classification of Diseases (ICD-11).Cardiol Young. 2017; 27: 1872-1938Crossref PubMed Scopus (67) Google Scholar It is an uncommon disorder in humans that has been reported as individual case reports or as small case series. Common atrium and AVSDs are among the uncommonly reported congenital heart malformations in the domestic dog, but the rarity of reports of common atrium in dogs may simply be reflective of the inconsistent terminology used to describe this lesion. In humans, cases of common atrium are typically syndromic and have been reported in patients with heterotaxy, Ellis-van Creveld syndrome, and complete AVSD with and without concurrent Down syndrome.4Cetta F. Truong D. Minich L.L. Maleszewski J.J. O’Leary P. Dearani J.A. et al.Atrioventricular septal defect.in: Shaddy R.E. Penny D. Feltes T.F. Moss and Adams’ Heart Disease in Infant, Children, and Adolescents. 9th ed. Wolters Kluwer, London2016: 757-782Google Scholar Due to frequent occurrence of concurrent AV valve malformation, common atrium has been suggested to be a form of partial AVSD. However, the available literature in human patients suggests that it can occur as an isolated entity, without concurrent AVSD.2Levy M.J. Salomon J. Vidne B.A. Correction of single and common atrium, with reference to simplified terminology.Chest. 1974; 66: 444-446Abstract Full Text Full Text PDF PubMed Scopus (16) Google Scholar Here, we report a case of a young dog that presented for subclinical (asymptomatic) murmur evaluation, in which features of common atrium and partial AVSD were both observed using echocardiography. This case highlights that the constellation of congenital malformations that deviate from the usual morphology may pose challenges in assigning a single unambiguous

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