What is
Aortic Rupture?
Aortic rupture occurs as a result of a spontaneous tear in the wall of the aorta. There is no treatment for aortic rupture, and no matter the manner in which it presents, humane euthanasia is recommended.
Aortic rupture is not a condition that is unique to Friesian horses. Horses of all breeds may suffer from this alarming and fatal condition. In all other breeds of horses, aortic rupture is most often seen in older horses engaged in strenuous physical activity at the time of rupture. In other breeds, the classic location for the aorta to rupture is at the connection between the aorta and the heart, also known as the aortic root. However, in Friesian horses, the aorta almost always ruptures in the aortic arch, near the scar of the ductus arteriosus.
The ductus arteriosus is a blood vessel that is only functional during fetal life when the unborn foal is still in the womb. After birth, the ductus arteriosus, which serves the function of connecting the fetal aorta with the fetal pulmonary artery, actually closes itself. The only proof of the ductus arteriosus after birth is actually a small scar that can be used as a point of orientation while looking at the heart known as the ligamentum arteriosum. The fact that Friesian horses rupture at this location suggests this is a breed-specific condition. In no other horse or animal species is aortic rupture known to occur at this location.
Postmortem examination of the aortic wall of Friesians diagnosed with aortic rupture revealed significant disorganization of collagen fibers. The findings suggest that a connective tissue disorder affecting elastin or collagen in the aortic media is the potential underlying cause of aortic rupture in Friesian horses. It is conceivable that an underlying genetic defect of the connective tissue in the aortic media predisposes Friesian horses to aortic rupture, dissection, and aorto-pulmonary fistulation at this specific location. The Friesian horse is also the only known animal species in which aorto-pulmonary fistulation is regularly encountered.
The aorta is the main artery that carries blood from the heart’s left ventricle to all other arteries except the pulmonary artery.
The Ductus Arteriosus connects the fetal aorta with the fetal pulmonary artery and closes at birth.
During the closure of the ductus arteriosus, smooth muscle cells migrated over surfaces in connective tissue coated with collagen to fill the internal space, leaving only a small scar called the ligament arteriosum.
A tear in the wall of the aorta is the equivalent of a hole in a high-pressure firehose.
Sub-acute aortic rupture occurs when a tear in the aorta causes blood to leak from the heart into the pericardial sac.
Chronic aortic rupture occurs when a tear in the aorta is stabilized by the surrounding tissue.
Three Scenarios of
Aortic Rupture
Acute Aortic Rupture
(Immediate)
An aortic rupture is a complete tear through all three layers of the aorta — like a rip or a hole — in the wall of the aorta. Blood bursts through the hole into the thoracic cavity within seconds. There are no clinical signs prior to acute aortic rupture in Friesian horses. These horses die suddenly and are often found dead in their stall or the pasture, or they may collapse during exercise or physical exertion with no warning.
Sub-Acute Aortic Rupture
(Days – Weeks)
Sub-acute aortic rupture occurs when a complete tear through all three layers of the aorta causes blood to leak into the pericardial sac, which due to enormous pressure, squeezes the heart. Due to the pressure, the heart must pump harder to supply enough blood-rich oxygen to the rest of the body. Sometimes, the tear leaks blood into the pulmonary artery, which causes the formation of a fistula, an abnormal connection between two body parts. The pulmonary fistula causes a significant amount of pressure in the lungs and leads to pulmonary edema. Depending on how large the initial tear is, the horse may live for days or weeks, but eventually, the tear will enlarge and lead to an abrupt and rapid decline of the horse and cardiac failure.
Chronic Aortic Rupture
(Weeks – Months)
Chronic aortic rupture occurs when a partial tear in the aortic wall is stabilized by the surrounding tissue, applying compression to the leaking area, almost like a pressure bandage. This scenario does not progress as rapidly as acute or sub-acute aortic rupture, but it will eventually become fatal. Over a period of weeks or months, the tissue surrounding the leaking aorta cannot withstand the enormous amount of blood pressure, and over time blood expands into separate chamber-like spaces in the tissue in an attempt to hold more of the blood. Inevitably at some point, the pressure is too great, and the chamber wall will fail, spilling blood into the pulmonary artery and rapidly accelerating into an acute and fatal cardiac failure. Such as with sub-acute aortic rupture, the initial size of the leak determines how long the situation remains viable.
Symptoms of
Aortic Rupture
Acute Aortic Rupture
(Immediate)
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No clinical signs
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Sudden death within seconds
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Often found deceased with no signs of trauma
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Collapse during or after physical exertion such as exercise or breeding
Sub-Acute Aortic Rupture
(Days – Weeks)
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Colic-like symptoms
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Low-grade fever
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Heavy cough
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Nose bleeds
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Swollen joints
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Alternating leg resting
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Intermittent edema
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Intermittent lameness
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Resting more than normal
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Sudden poor performance
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Increased or “bounding” pulse at rest
Chronic Aortic Rupture
(Weeks – Months)
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Colic-like symptoms
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Low-grade fever
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Poor appetite
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Poor performance
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Coughing
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Pale mucous membranes
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Nose bleeds
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“Bounding” pulse at rest
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Intermittent lameness
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Swollen joints
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Alternating leg resting
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Continuous high pulse at rest (56 – 120 beats per minute)
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Intermittent edema in legs and between the front legs and chest
Acute aortic rupture may occur after physical exertion such as exercise or breeding.
Edema
Bounding pulse at rest
Community Support
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