Submitted:
21 March 2024
Posted:
23 March 2024
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Abstract
Duct-dependent lesions are classically divided into duct dependent pulmonary circulation which involves severe right sided obstructive lesions such as pulmonary atresia or critical stenosis, and duct dependent systemic circulation which is characterized by malformation of the left side of the heart, and whose severest spectrum is hypoplastic left heart syndrome. Dextro-transposition of the great arteries remains in gray zone between being included in some old classifications as a duct dependent pulmonary circulation lesion or a new category of duct-dependent or independent mixing lesion. We hypothesize that re-classifying duct dependent congenital defects into duct dependent perfusion and oxygenation offers a model to fit D-TGA into the same category of right sided obstructive lesions and reflects the clinical spectrum in a more comprehensive way.
Keywords:
Nomenclature of duct dependent lesions
; Duct-dependent perfusion and oxygenation
Background:
Congenital heart defects (CHDs) represent a spectrum of structural abnormalities affecting the heart's development, ranging from minor defects to complex, life-threatening conditions. Critical CHD, defined as lesions requiring surgery or catheter-based intervention in the first year of life accounts for approximately 25 percent of CHD. Most patients suffering with critical CHD’s present with either hypoplastic left ventricle (LV) and/ or severe obstructive lesions in the valves or great arteries in the right or left heart system. The important hemodynamic change which occurs after birth is the transition from fetal circulation to postnatal circulation and during this transition, newborns with CHD’s are vulnerable thereby increasing their dependence on central shunts mainly patent ductus arteriosus (PDA) to ensure ample blood flow between the systemic and pulmonary circulation. These lesions are collectively known as “Ductal-dependent lesions”.[1]
In a normal heart, PDA typically closes shortly after birth as a part of normal physiological changes due to the transition from fetal to neonatal circulation. However, since obstructive lesions heavily rely on the blood flow through the PDA for adequate circulation between the systems, patients present with severe cyanosis, shock or collapse. Hence, duct-dependent lesions stand out among critical CHD’s as it requires immediate clinical attention and intervention.[2,3]
Patients with congenital heart defects (CHDs) are classified as duct-dependent lesions may have either systemic or pulmonary duct-dependent lesions.
Lesions characterized where the systemic output is reliant on the pulmonary artery system via the patent ductus arteriosus (PDA), with flow occurring from the main pulmonary artery to the aorta are known as Duct Dependent Systemic Lesions. Disruption of this delicate balance can result in compromised perfusion of vital organs. As the PDA constricts or closes after birth, these conditions may lead to systemic hypotension, shock, or collapse. This group includes a range of left-sided obstructive lesions, such as hypoplastic left heart syndrome (HLHS), severe aortic valve stenosis, coarctation of the aorta, interruption of the aortic arch, and complex lesions with systemic outflow obstruction.[4]
Lesions which are characterized by various kinds of ride-sided obstructive lesions or right to left shunt lesions such as tetralogy of Fallot, ventricular septal defect (VSD), pulmonary atresia, pulmonary valve stenosis or pulmonary atresia with intact ventricular septum are commonly called as Duct Dependent Pulmonary lesions. Such defects mainly rely on duct dependent pulmonary flow in which pulmonary blood flow for oxygenation is dependent on the systemic output with the flow arising from the aorta to the pulmonary artery. Typically, these conditions lead to poor oxygenation of blood causing cyanosis as the PDA closes after birth.[5]
D-TGA a special case:
Cyanosis, also results from another duct-dependent lesion which is Dextro-Transposition of the great arteries (D-TGA), where the ventriculoarterial connections are "misplaced" or "transposed" across the interventricular septum. As a result, the pulmonary artery arises from the morphologic left ventricle and the aorta from the morphologic right ventricle. Because the pulmonary and systemic circulations in this particular case are parallel, the deoxygenated systemic venous blood travels to the aorta via the morphologic right ventricle and the oxygenated pulmonary venous blood returns to the pulmonary circulation through the morphologic left ventricle. Blood mixing between these two circulations, which takes place via PDA, atrial septal defect (ASD) or Patent foramen ovale (PFO), or VSD, is essential for survival in neonates with TGA. There is conflicting literature on the classification of D-TGA, some of the literature classify as a duct0-dependent pulmonary circulation, some others as an independent entity, in the presence of a significant PFO or VSD, it is being classified as a duct independent mixing lesion alongside total anomalous pulmonary venous return and truncus arteriosus. [6]
The binary distinction between "pulmonary" and "systemic" fails to fully capture the complex interplay between oxygenation, perfusion, and associated anatomical abnormalities present in many congenital heart defects. For example, ttransposition of the great arteries (TGA) presents a unique challenge within the spectrum of congenital heart defects. In TGA, the aorta and pulmonary artery are anatomically switched, resulting in two separate parallel circulations: one where deoxygenated blood circulates systemically and another where oxygenated blood circulates to the lungs.
Based on its impact on circulation, TGA in the literature has been classified most of the time as “duct-dependent pulmonary”, and some papers classify it as a separate entity: duct dependent mixing lesion. However, this classification overlooks the complex physiology and clinical management considerations inherent in TGA.[5,7,8]
Suggestions:
The term “Duct dependent systemic and pulmonary lesions” incorporates the involvement of PDA in maintaining systemic and pulmonary blood flow. However, changing to an alternative nomenclature, “duct dependent oxygenation and perfusion” shifts the focus on physiological functions that are essential to life. Oxygenating blood in the lungs and perfusion of oxygenated blood in the body are two processes which are fundamental to the cardiovascular system.
Conclusion:
In conclusion, the transition from "duct-dependent pulmonary and systemic lesions" to "duct-dependent oxygenation and perfusion" signifies a progressive step in medical terminology. By understanding a more comprehensive and physiological perspective of congenital heart defects. This change in nomenclature recognizes the broader meaning which facilitates a more integrated approach to diagnosis, management, and treatment options. Moreover, enhancing communication between healthcare professionals and patients. Using terms such as "duct-dependent oxygenation and perfusion" could promote clearer explanations to patients and their families, developing a more informed and engaged healthcare experience. The current terminology limit the broader implications of duct-dependent lesions. This shift reflects a deeper understanding for cardiovascular physiology and the critical role of the ductus arteriosus in sustaining adequate oxygenation and perfusion.
List of Abbreviations:
CCHD: Critical congenital heart diseases
HLHS: hypoplastic left heart syndrome.
PDA: patent ductus arteriosus
D-TGA: Dextro-Transposition of the great arteries
VSD: Ventricular septal defect
Author Contributions
Conceptualization, AA; Methodology, AA, AG, DM, FA, SP; software, AA, AG, DM, FA, SP; investigation, AA, AG, DM, FA, SP; resources, AA, AG, DM, FA, SP, data curation, AA, AG, DM, FA, SP; writing—original draft preparation, AA, AG, DM, FA, SP; writing—review and editing, AA, AG, DM, FA, SP; supervision, AA, AG, DM, FA, SP; project administration, AA, AG, DM, FA, SP; funding acquisition, (none). All authors have read and agreed to the published version of the manuscript.
Institutional Review Board Statement
Not applicable as this study is a hypothesis/view point.
Informed Consent Statement
Not applicable as this study is a viewpoint/editorial.
Data Availability Statement
All data is made available within the manuscript.
Acknowledgments
I wanted, as a first author, to dedicate this work to anyone who is considered as a “black sheep” in his workplace, college or school environment, just because he is beautifully different. We all, through different stages of our life, have gone through similar, difficult times, where we felt alone and non-appreciated, but you should know that your personal worth is unrelated to others’ perception.
Conflicts of Interest
The authors declare no conflict of interest.
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