Fig: Dextrocardia
Picture from Developmental Anatomy. Leslie Brainerd Arey. 1966, p. 391.
Like other congenital malformations, heart defects presumably result from a disturbance of normal developmental mechanisms. Neither the cause nor the origin of most heart defects are attributed to single-gene mutations, chromosomal aberrations, or exposure to specific teratogens. An error in almost any step of heart formation can result in a cardiac defect.
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Dextrocardia
This disease results when the primitive heart tube folds to the right instead
of to the left. Most people with this malformation exhibit a general reversal
in the handedness of many organs. This is a condition known as situs inversus.
It is believed that situs inversus is caused by the absence of or a defective
protein which is critical to the body's ability to adopt the correct handedness.
Oliwenstein, Lori. The gene that knows left from right.
Discover. August 1993: 14:20-21.
Summary: This article is about the gene that was discovered
in mice, that when mutated, causes sinus venosus in mice. This gene determines
which side of the body to place internal organs.
Yokoyama, Takahiko, Neal G. Copeland, et.al. Reversal of left-right
asymmetry: a situs inversus mutation. Science, April 30, 1993: 260:679-683.
Summary: This article is about the research of symmetry and
the anatomy of vertebrates.
Spigelman, Allan D. Situs inversus. The New England Journal
of Medicine. March 3, 1994: 330:606.
Summary: This article is about the abnormalities of the heart.
Cooke, Jonathan. Vertebrate embryo handedness. Nature. April
20, 1995: 374:681.
Summary: This article is about research in developmental biology
using bird
Atrial Septal Defects
At birth, the septum primum and septum secundum are pressed together. An
atrial septal defect develops when the septum secundum is to short to completely
cover the ostium secundum. Thus, causing a hole in the muscular wall between
the heart chambers. This allows blood to pass between the chambers in an
irregular fashion. This defect is associated with almost all autosomal and
sex chromosome aberrations. Usually throughout childhood there are no noticeable
symptoms from this defect. Because of this the patient goes on undiagnosed
for much of their life. However, the life expectancy in these patients is
significantly reduced.
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Mangion, Judy R., Roberto M. Lang, and Richard H. Marcus.
Ostium secundum atrial septal defect. The New England Journal of Medicine.
May 18, 1995: 332:1336-1339.
Geggel, Robert L., and Eugene J. Mark. A 48-year-old woman
with an atrial septal defect and pulmonary hypertension. The New England
Journal of Medicine. Sept. 16, 1993: 329:864- 873.
Summary: This article is the story of a 48-year-old woman
who was misdiagnosed at age eleven as having a heart murmur. At age 39,
she was retested by a coronary angiography and magnetic resonance imaging
(MRI). These tests found the atrial septal defect in her heart. The defect
was then corrected through open-heart surgery.
Perloff, Joseph K. Surgical closure of atrial septal defect
in adults. The New England Journal of Medicine. August 24, 1995: 333:513-515.
Summary: This article deals with the treatment of atrial septal
defects. According to the article, surgery appears to be more effective
than drugs in the treatment of this defect.
Konstantinides, Stavros, Annette Geibel, et. al. A comparison
of surgical and medical therapy for atrial septal defect in adults. The
New England Journal of Medicine. August 24, 1995: 333:469 -474.
Summary: This article also discusses the advantages to surgery
over medical therapy. However, both surgery and medical therapy were equally
effective in reducing the risk of arrhythmias, heart attacks, and strokes.
Ventricular Septal Defects
These defects are the most common of all congenital heart malformations.
A ventricular septal defect can arise from several causes:
(1) deficient development of the proximal truncoconal swellings,
(2) failure of the muscular and membranous ventricular septa to fuse,
(3) failure of the superior and inferior endocardial cushions to
fuse, and
(4) excessive perforation of the interventricular muscular septum
during development.
Whatever the origin of a ventricular septal defect, its most serious consequence
is massive left-to-right shunting of blood and consequent pulmonary hypertension
after birth. Surgical repair of the defect in children is common, and they
are able to return back to normal fairly rapidly.
Beyar, Rafael, Sheng-Jing Dong, et. al. Ventricular interaction
and septal deformation: a model compared with experimental data. The American
Journal of Physiology. Dec. 1993: 265:2044- 2057.
Summary: This article investigates the physiological aspects
of ventricular septal defects by understanding the heart ventricles and
pulmonary artery better. By studying model of the heart they are able to
better understand the defects that the heart deals with.
Stewart, Julian M., Thomas H. Hintze, et. al. Nature of heart
failure in patients with ventricular septal defect. The American Journal
of Physiology. Oct. 1995: 269:473-481.
Summary: This article deals with the research of heart failure.
Especially on heart septum abnormalities. They have found that the myocardial
contractility index is substantially reduced in failing hearts.
Tricuspid and Mitral Valve
Defects
These defects arise from errors in the process by which the valve leaflets,
chordae tendinae, and papillary muscles are formed from the ventricular
wall. One example of such a defect is the formation of valve atresia,
in which the valve orifice is completely closed. However, this defect is
not understood. Another example is of tricuspid valve anomaly, Ebstein's
disease. In this defect the valve is displaced downward into the right
ventricle and the leaflets have an abnormal ballooned shape. Because this
valve is dysfunctional, blood flows back into the right atrium and also
blocks the pulmonary trunk. This causes the uneven distribution of blood
in the ventricles, which in turn causes the left ventricle to enlarge while
the right ventricle becomes hypoplastic.
Valari, M.D. Junctional epidermolysis bullosa and pyloric
atresia, a distinct entity: clinical and pathological studies in five patients.
The Journal of the American Medical Association. Feb. 14, 1996: 275:420.
Summary: This article details how epidermolysis bullosa is
associated with pyloric atresia through the analysis of case studies.
Good, Gary R., and Mark J. DiNubile. Cyclic fever in Hodgkin's
disease. The New England Journal of Medicine. Feb. 16, 1995: 332:436.
Tetralogy of Fallot
This defect represents a group of cardiac malformations that arise through
a pathogenetic cascade. In other words, a primary malformation sets off
a cascade of effects that lead to other malformations. There are four classic
malformations in this syndrome: pulmonary stenosis, ventricular septal
defect, overriding aorta, and right ventricular hypertrophy.
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Murphey, Joseph G., Bernard J. Gersh, et. al. Long-term
outcome in patients undergoing surgical repair of tetralogy of Fallot. The
New England Journal of Medicine. August 26, 1993: 329:593 -600.
Summary: This article deals with the long term effects of
this disease.
Rosenthal, Amnon. Adults with tetralogy of Fallot--repaired,
yes; cured, no. The New England Journal of Medicine. August 26, 1993: 329:655-657..
Summary: This article deals with the surgical repair of the
tetralogy of Fallot.
Chen, Chuan-Rong, Tsung O. Cheng, et. al. Percutaneous balloon
valvuloplasty for pulmonic stenosis in adolescents and adults. The New England
Journal of Medicine. July 4, 1996: 335:21-26.
Summary: This article deals with the surgical repair of pulmonary
stenosis.
Sources:
1. Developmental Anatomy. Leslie Brainerd
Arey. W. B. Saunders Co., 1966.