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Syllabus of Clinical Thoracic and Cardiac Embryologic Problems with anatomic correlations
Case studies involving the thorax, mediastinum, embryology of the heart & circulatory systems
Anatomic and clinical reviews that will include basic symptoms and findings, diagnosis & treatment
Tufts University school of Medicine
Joan F. Tryzelaar, M.D., F.A.C.S, F.A.C.C.P.
Before we go on to congenital heart problems, it is good to review how to get into the chest:
You have just been invited to participate in an operation. The surgeon plans a posterolateral thoracotomy to enter the chest. He will tell you that he plans entry via the 6th intercostals interspace(Pearl: found two finger widths below the tip of the scapula).
What are the structures (besides skin & subcutaneous tissue) you will encounter on your way in?
Answer: (From outside – in):
Latissimus dorsi, Serratus Anterior, long thoracic nerve and intercostals muscle, ribs, parietal pleura.
Why the 6th interspace?
Because that incision corresponds with the major fissure of the lung, facilitating exposure & resection
Although some thoracic surgeons perform a muscle splitting technique, many surgeons still transect the latissimus dorsi and split the serratus anterior muscles
Many surgeons elevate these muscles by placing their finger or a large dissecting forceps into the ausculatory triangle formed by an opening in the muscle layer where the latissimus, trapezius, and the medial border of the scapula intersect.
If extended in a posterior and superior direction (upwards behind the scapula), the muscle layers of the rhomboid and trapezius are incised, with care taken to avoid dividing the spinal accessory nerve (which innervates the trapezius) by remaining parallel to the spine.
Intercostal vein, artery & nerve (“Chevy VAN”)
What would an injury to the long thoracic nerve (thoracodorsal nerve (C7, 8) from the posterior cord of the brachial plexus) cause?
Do you enter the chest over or under the rib?
Over the lower rib
What is the Triangle of auscultation (Auscultatory Triangle)?
The triangle located medial to the inferior angle of the scapula; it is bounded by the trapezius m. medially, rhomboideus major m. superiorly and the latissimus dorsi m. inferiorly; its floor is the posterior thoracic wall. The triangle of auscultation is a space on the back where the relatively thin musculature allows for respiratory sounds to be heard more clearly with a stethoscope.
Landmark & Structures to be divided:
1. Supra sternal notch with inter-clavicular ligament
3. Linea Alba
4. Anterior Mediastinum
What do you find after completion of the median sternotomy in the anterior-superior Mediastinum?
Thymic Fat pad (or Thymus in infants and young children
In the Lower portion of the sternotomy incision?
In the Abdominal portion of the incision?
Linea Alba (divided), Peritoneum
For a review of the cardiac embryology and pre natal circulation, please take a look here: Introduction to Cardiac congenital defects
Name the Adult structures of the following:
- Umbilical vein
- Ductus venosus
- Foramen ovale
- Ductus arteriosus
- Umbilical arteries
Name two vein systems that carry oxygenated blood
Umbillical vein, pulmonary veins
What circulatory changes occur at birth?
Answer: See below
- Closure of the foramen secundum:
- Fossa Ovalis
- Closure of the ductus arteriosus:
- Ligamentum arteriosum
- Closure of the umbillical vein and ductus venosus:
- Ligamentum teres & Ligamentum Venosum
- Closure of the umbillical arteries
- L+R Medial umbilical ligaments
Before birth there is only mixed blood in the circulation system.
The numbers provide the approximate O2 saturation in the various sections of the heart
After birth O2 saturations and pressures.
After birth the two circulation systems are separated and now only blood that is saturated with O2 gets into the aorta.
In prenatal circulation, what portion of the fetal circulation carries the highest and lowest O2 saturations and why?
IVC & SVC respectively. Highest, IVC, because it carries the maternal blood via the umbilical vein. Lowest, SVC. O2 sats are lowest because of the high O2 extraction by the brain.
You are on Pediatrics rotation in the ER. A young mother shows up with her infant, complaining she doesn’t want to eat and seems to breathe faster than other babies. The baby looks sickly, is small for her age and is tachycardic & tachypneic (look it up!).
When you examine the baby, you hear a murmur that seems continuous throughout systole & diastole (“machinery”).
Astutely, you order a cardiac ECHO, which shows a Patent Ductus Arteriosus (PDA).
What type of shunt is present in a PDA (w/o other anomalies?
L⇒R from the aorta to left pulmonary artery
What is Eisenmenger's syndrome?
Eisenmenger's syndrome is a complication of uncorrected left-to-right shunting. Because of increased pulmonary resistance that (if untreated) developes over time, a left-to-right shunting changes to a right-to-left shunt.
Congenital heart anomalies that, if untreated, result in Eisenmenger's syndrome include
- Ventricular septal defect
- Atrioventricular canal defect
- Atrial septal defect
- Patent ductus arteriosus
- Persistent truncus arteriosus
- Transposition of the great arteries
Right-to-left shunting due to Eisenmenger's syndrome results in cyanosis and its complications. Systemic desaturation leads to clubbing of fingers and toes, secondary polycythemia, hyperviscosity, hemoptysis, CNS events (eg, brain abscess or cerebrovascular accident), and sequelae of increased RBC turnover (eg, hyperuricemia causing gout, hyperbilirubinemia causing cholelithiasis, iron deficiency with or without anemia).
A 12 y.o. boy with a long continuous heart murmur at the second intercostal space near the left sternal border. A systolic thrill is also noted in the same region. The patient's mother tells you that he had periods of cyanosis and breathlessness as an infant. The boy tires easily during physical activity.
CXR shows slight left ventricular hypertrophy. A diagnosis of a patent PDA is made. After corrective surgery, he is hoarse. What happened?
Recurrent nerve injury with vocal cord paralysis
The recurrent (inferior) laryngeal nerve is a branch of the vagus nerve (tenth cranial nerve) that supplies motor function and sensation to the larynx.
The left laryngeal nerve branches from the vagus nerve to loop under the arch of the aorta, posterior to the ligamentum arteriosum before ascending. On the other hand, the right branch loops around the right subclavian artery.
Mrs. Smith has brought her baby to the Emergency Room, because she says ‘he has started turning blue’.
Baby Smith is only 3 days old. He was born at home, at term, and everything had seemed fi ne until he started turning blue around the mouth a couple of hours ago. Mrs Smith put this down to him crying at the time but it did not seem to improve when he calmed down. He was feeding well initially, but has not seemed interested today. He is breathing a little faster than normal, but does not seem to be struggling.
Testing shows the baby is cyanotic with a Pao2 less than 50 mm Hg, even while breathing oxygen and a cardiac ECHO confirms a Tetralogy of Fallot.
What determines the severity of the disease?
2.RV Outflow tract obstruction
2. The degree of RV outflow obstruction (and thus the blood available for oxygenation in the lung determines how severity and thus urgency of repair.
A VSD (with RàL shunt) allows the blood to “escape” to the Left Ventricle and is relatively well tolerated by comparison.
The Overriding Aorta occurs in consequence of the spiral septation of the truncus arteriosus during the first 8 weeks of development.
The RV has to work extra hard to pump blood into the pulmonary artery and therefore hypertrophies to accommodate the extra work.
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