Applied Anatomy

Neck and thorax

Luxation of the Atlanto-Axial joint

Position of the heart valves

Esophageal obstructions

Thoracocentesis

Pericardiocentesis Pericardial effusion

Point of maximum intensity

Intracardiac injection

Patent Ductus Arteriosus

Persistent right aortic arch

Neck and Thorax – Luxation of the Atlanto-Axial joint Luxation of the Atlanto-Axial joint ∣ Esophageal obstructions ∣ Thoracocentesis ∣ Pericardial effusion ∣ Pericardiocentesis ∣ Position of the heart valves ∣ Point of maximum intensity Intracardiac injection ∣ Patent Ductus Arteriosus ∣ Persistent right aortic arch ∣ Menu

In the normal animal, the Lig. transversum atlantis helps to maintain the correct dorso-ventral position of the atlas and axis by retaining the Dens on the Fovea dentis. Without a Dens, this support is lost and the body of the axis can tilt such that its cranial part encroaches on the vertebral canal; this can obviously result in serious injury to the spinal cord.

In the normal animal, the Lig. transversum atlantis helps to maintain the correct dorso-ventral position of the atlas and axis by retaining the Dens on the Fovea dentis. It forms a bridge over the floor of the atlas and holds the dens against the Fovea dentis.

Fovea dentis

Atlas Dorso-caudal view

Normal dog and alignment

Axis

Dens

Atlas

Base of skull

Dorsal spinous process

Dens

C1

Axis Atlas

Base of skull

Absence of Dens

Note change in alignment

Axis Lateral view

Partial luxation of the atlanto-axial joint occurs in the smaller dog breeds as a result of fracture, malformation or absence of the Dens.

Neck and Thorax – Esophageal obstructions Luxation of the Atlanto-Axial joint ∣ Esophageal obstructions ∣ Thoracocentesis ∣ Pericardial effusion ∣ Pericardiocentesis ∣ Position of the heart valves ∣ Point of maximum intensity Intracardiac injection ∣ Patent Ductus Arteriosus ∣ Persistent right aortic arch ∣ Menu

Thorax (left lateral aspect, lungs and pleura removed)

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Esophagus Aorta

Neck and Thorax – Thoracocentesis Luxation of the Atlanto-Axial joint ∣ Esophageal obstructions ∣ Thoracocentesis ∣ Pericardial effusion ∣ Pericardiocentesis ∣ Position of the heart valves ∣ Point of maximum intensity Intracardiac injection ∣ Patent Ductus Arteriosus ∣ Persistent right aortic arch ∣ Menu

Thoracocentesis

Fluid

Gas (lateral recumbency)

Neck and Thorax – Pericardial effusion – Page 1 Luxation of the Atlanto-Axial joint ∣ Esophageal obstructions ∣ Thoracocentesis ∣ Pericardial effusion ∣ Pericardiocentesis ∣ Position of the heart valves ∣ Point of maximum intensity Intracardiac injection ∣ Patent Ductus Arteriosus ∣ Persistent right aortic arch ∣ Menu

The pericardium (transverse section, schematic)

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Neck and Thorax – Pericardial effusion – Radiograph - Page 2 Luxation of the Atlanto-Axial joint ∣ Esophageal obstructions ∣ Thoracocentesis ∣ Pericardial effusion ∣ Pericardiocentesis ∣ Position of the heart valves ∣ Point of maximum intensity Intracardiac injection ∣ Patent Ductus Arteriosus ∣ Persistent right aortic arch ∣ Menu

Thoracic radiograph (dorsoventral view) Yellow arrows indicate the pericardial outline

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Cranial

The fact that the heart is enclosed by a fibrous capsule has important clinical implications. If the heart increases in size over a period of time (due to exercise or disease), the pericardium will enlarge to accommodate it. Similarly, in cases of chronic (slow) pericardial effusion (the accumulation of fluid in the Cavum pericardii), the pericardium will again enlarge. However, acute increases in pericardial volume cannot be accommodated: for example, in cases of cardiac tamponade (the rapid accumulation of blood in the pericardial cavity) the chambers of the heart cannot fill properly (especially the atria) and effective pumping by the ventricles ceases; the increased pressure in the pericardial cavity also impedes venous return to the heart and acute death is the usual outcome.

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Neck and Thorax – Pericardial effusion – Pathology - Page 3 Luxation of the Atlanto-Axial joint ∣ Esophageal obstructions ∣ Thoracocentesis ∣ Pericardial effusion ∣ Pericardiocentesis ∣ Position of the heart valves ∣ Point of maximum intensity Intracardiac injection ∣ Patent Ductus Arteriosus ∣ Persistent right aortic arch ∣ Menu

Pericardial effusion in an 8 month old husky that died of severe babesiosis (biliary fever / bosluiskoors)

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Myocardium

Myocardium

Abnormal Pericardial fluid accumulation

Fibrous pericardium – cut open

Fibrous pericardium – cut open

Lung

Lung

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4th 5th

* Hypodermic needle

Neck and Thorax – Position of the heart valves Luxation of the Atlanto-Axial joint ∣ Esophageal obstructions ∣ Thoracocentesis ∣ Pericardial effusion ∣ Pericardiocentesis ∣ Position of the heart valves ∣ Point of maximum intensity Intracardiac injection ∣ Patent Ductus Arteriosus ∣ Persistent right aortic arch ∣ Menu

Various sounds are associated with the closure of the valves and the flow of blood in the beating heart. These sounds are routinely evaluated by auscultation (the use of a stethoscope to amplify and transmit the sounds) during clinical examination. Although the distance between a valve and the thoracic wall is an important factor, the sound associated with the valve is not strictly related to its anatomical position. The reason for this is that the sound is transmitted through a complex matrix of tissues that vary in texture and density. The distance between valves influences the clarity of the sound as does the direction of blood flow through the valve (blood flowing away from the heart carries the sound to the surface). The cardiac incisures do not play an important role in the clinical examination of the heart.

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Left Right

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The various valves are auscultated at the following positions:

The various valves are auscultated at the following positions:

Neck and Thorax – Point of maximum intensity Luxation of the Atlanto-Axial joint ∣ Esophageal obstructions ∣ Thoracocentesis ∣ Pericardial effusion ∣ Pericardiocentesis ∣ Position of the heart valves ∣ Point of maximum intensity Intracardiac injection ∣ Patent Ductus Arteriosus ∣ Persistent right aortic arch ∣ Menu

At the end of the ventricular contraction (systole), the heart rotates slightly and the apex comes into contact with the left thoracic wall between ribs 4 and 6, on the level of the costochondral junction. This is known as point of maximum intensity or apex beat and can be palpated; in lean, short-haired dogs, one can even see the apex beat.

Neck and Thorax – Intracardiac injection Luxation of the Atlanto-Axial joint ∣ Esophageal obstructions ∣ Thoracocentesis ∣ Pericardial effusion ∣ Pericardiocentesis ∣ Position of the heart valves ∣ Point of maximum intensity Intracardiac injection ∣ Patent Ductus Arteriosus ∣ Persistent right aortic arch ∣ Menu

• Intracardiac injections are generally used for administering euthanasia in animals that are difficult to handle, animals with very low blood pressure (cannot raise a vein), animals with damaged peripheral veins and very young animals.

• The right ventricle is preferred for this purpose because it has a thinner wall than the left ventricle; it is also close

to the body wall at the Incisura cardiaca of the right lung.

• The needle is inserted in the right 4-5th intercostal space at the level of the costochondral junction. A direct ventral approach is difficult, because the pectoral muscles are too thick to allow palpation of the interchondral spaces.

• Intracardiac injection is not used for therapeutic purposes because of the risks involved (myocardial damage and

cardiac tamponade).

Right ventricle

4th or 5th right intercostal space

Costochondral junction

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Lungs

Patent Ductus Arteriosus (PDA) is the most common congenital (inborn) cardiovascular defect in the dog. In the fetus, the Duct. arteriosus shunts the blood destined for the lungs, from the pulmonary trunk to the aorta; it normally closes immediately after birth when the lungs become functional. If the Duct. arteriosus remains patent (open) after birth, a vicious cycle is set in motion as some of the blood in the aorta is now shunted to the low pressure pulmonary circulation.

1. The increased pulmonary circulation results in increased venous return to the left side of the heart which causes enlargement of the left ventricle.

2. The over-supply of blood to the lungs also causes the pulmonary artery to enlarge and become less elastic. 3. These changes cause further heart chamber enlargements and eventually 4. the heart becomes incompetent to support the circulatory system and the animal dies.

If diagnosed before irreparable damage is done, the condition is treated by surgical ligation (tying-off) of the Duct. arteriosus.

Right ventricle

Patent Ductus Arteriosus

Left ventricle

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Left aorta

Pulmonary Trunk

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In the normal fetus, the aorta develops from the left aortic arch. Occasionally the aorta develops from the right aortic arch giving rise to a condition known as Persistent Right Aortic Arch (PRAA). In such cases, the oesophagus passes inbetween the pulmonary trunk (in its normal position on the left), and the ascending aorta which now lies to the right. However, the Lig. arteriosum (the remnant of the embryonal Duct. arteriosus) still connects the pulmonary trunk to the aorta and now lies dorsal to the oesophagus. The oesophagus thus lies surrounded by a vascular ring which traps it against the heart base. The vascular ring prevents the esophagus from dilating enough to allow the passage of swallowed food which is eventually regurgitated after damming up in the thoracic esophagus. The condition is usually diagnosed when the puppy starts eating solid food as the passage of fluids is not obstructed. If diagnosed before the esophagus is irreparably damaged, the condition is treated by ligating and transecting the Lig. arteriosum.

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2 3 5 Schematic representation of the vascular ring formed in PRAA (Caudal view)

4 1. Heart 2. Pulmonary trunk

3. Right ascending aorta 4. Lig. arteriosum

5. Oesophagus