Pushing the Limits of Balance in Atrioventricular Septal Defect and Complex Techniques for Valve Re-repair in Atrioventricular Septal Defect

Management of the bad atrioventricular valve in Fontan…time for a change

Congenital heart malformations are the most common type of defects found at birth. About 1% of infants are born with one or more heart defect on a yearly basis. Congenital Heart Disease (CHD) causes more deaths in the first year of life than any other congenital abnormality, and each year, nearly twice as many children die in the United States from CHD as from all forms of childhood cancers combined. Atrioventricular septal defects (AVSD) are congenital heart malformations affecting approximately 1 in 2000 live births. Babies born with an AVSD often require surgical intervention shortly after birth. However, even after successful surgery, these individuals typically have to deal with lifelong complications with the most common being a leaky mitral valve. In recent years the understanding of the molecular etiology and morphological mechanisms associated with the pathogenesis of AVSDs has significantly changed. Specifically, these studies have linked abnormal development of the Dorsal Mesenchymal Protrusion (DMP), a Second Heart Field-derived structure, to the development of this congenital defect. In this review we will be discuss some of the latest insights into the role of the DMP in the normal formation of the atrioventricular septal complex and in the pathogenesis of AVSDs.

Double orifice mitral valve (DOMV) is a rare congenital malformation described as division of mitral orifice into two anatomically distinct orifices separated by an accessory bridge of fibrous tissue. In 85% of cases, both orifices are unequal in size. It is usually associated with other congenital defects such as atrioventricular septal defect and complex congenital heart disease. Most of cases could be diagnosed by two-dimensional echocardiography (2DE). The real-time three-dimensional echocardiography (RT3DE) helped in more detailed structure and function. Presented here RT3DE used for orientation of DOMV that allowed detailed and comprehensive assessment incremental to that obtained by 2DE.

The myocardium constitutes the bulk of the atrial and ventricular tissues. Cardiomyocytes exhibit the electrical properties of excitability and current conduction and the mechanical properties of contraction, active relaxation, passive elongation, and stiffness. Myocardial diseases affect cardiomyocytes, cell junctions and supporting tissues. Heart muscle diseases include congenital malformations of the cardiac septa. Ventricular septal defects are most common in horses; atrial septal defects and complex atrioventricular (AV) septal defects occur sporadically. Myocardial hypertrophy occurs as an adaptive response to a sustained increase in workload. Most myocardial diseases involve the left ventricular (LV) myocardium. The underlying pathophysiology leading to clinical signs usually relates to systolic dysfunction, from reduced myocardial contractility. Recurrent ventricular premature complexes (VPCs) or ventricular tachycardias are common with myocardial disease. Toxins that can injure the myocardium include ionophore antibiotic feed additives, poisonous plants, cantharidin (blister beetle), snake venoms, and heavy metals such as cobalt.

Commentary: Atrioventricular valve insufficiency: Achilles' heel in single-ventricle physiology

Failure to form the septal structures that separate the left and right cardiac chambers results in defects that allow shunting of blood from one side of the heart to the other, leading to the mixing of oxygenated and de-oxygenated blood. The atrioventricular (AV) mesenchymal complex, consisting of the AV cushions, the Dorsal Mesenchymal Protrusion (DMP), and the mesenchymal cap, plays a crucial role in AV septation. Cells found in these structures derive from different cell lineages. In this study we have investigated the role of the transcription factor Sox9 in the Second Heart Field (SHF) with the emphasis on the formation of the atrioventricular septal complex. Using a mouse model in which Sox9 is conditionally deleted from the SHF we demonstrate that in this model virtually all mouse embryos develop septal abnormalities, including complete atrioventricular septal defects (cAVSDs) and isolated ventricular septal defects. Our morphological analyses indicate that perturbation of the development of the mesenchymal cap appears to play a crucial role in the pathogenesis of the atrial septal defects observed in the AVSDs and suggests that this component of the AV mesenchymal complex might play a more important role in AV septation than previously appreciated.