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Subaortic stenosis, =
affectionately know=20
as =93SAS=94, is the most common congenital heart disease of =
large breed=20
dogs. This web page attempts to present a review of this =
condition=20
including its diagnosis and treatment.
BUT =
FIRST
In order to understand what =
subaortic=20
stenosis is, it is necessary to understand some normal heart =
anatomy. The heart sits more of less centrally in the =
chest and=20
is divided into a left side, which receives oxygen-rich =
blood from=20
the lung and pumps it to the rest of the body, and a right =
side,=20
which receives =93used=94 blood from the body and pumps it =
to the lung=20
to pick up fresh oxygen. Because the left side of the =
heart=20
must supply blood to the whole body, its muscle is =
especially thick=20
and strong. Blood is pumped from the left ventricle (pumping =
chamber) to a particularly large blood vessel called the=20
=93aorta.=94 (The aorta is the body=92s largest =
artery.) The=20
valve that separates the left ventricle from the aorta is =
called the=20
=93aortic valve.=94 The left ventricle narrows as it =
leads to the=20
aorta and this area is called the =93aortic outflow =
tract.=94
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![3D"Heart](3D"http://www.marvistavet.com/assets/images/Heart_Diagram.gif"=20 "3D\"Heart")
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Diagram of the (human) heart. Aorta and =
Left=20
Vetricle colored=20
=
blue | |
In subaortic stenosis, the =
left=20
ventricular outflow tract just below the aortic valve has a=20
scar-like narrowing or =93stenosis=94 (which is another word =
for=20
=93narrowing.=94 This means that the left ventricle =
must pump extra=20
hard to get the correct blood volume through the narrowed =
area. The=20
blood squirts through in a turbulent fashion which creates a =
sound=20
known as a =93heart murmur.=94 While any cause of =
turbulent blood=20
flow can be heard as a murmur and a murmur does not always =
indicate=20
disease is present, the murmur is usually the first sign =
that the=20
puppy in question might have SAS.
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![3D"aortic](3D"http://www.marvistavet.com/assets/images/aortic_stenosis.gif"=20 "3D\"aortic")
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This picture =
from the=20
Mayo Clinic shows a normal left ventricle =
compared to=20
one where the patient has aortic stenosis. The =
extra=20
hard work of the ventricle manifests as extra =
thick=20
muscle. While this is a human heart graphic, the =
concept=20
is the=20
=
same. | |
The most commonly affected =
breeds for=20
SAS include the Golden retriever, Rottweiler, Newfoundland, =
Great=20
Dane, Boxer, German Shepherd and German Short-haired =
pointer.
When a puppy with SAS is born, =
the=20
stenosis is very small, barely a ridge near the valve, but =
over the=20
first six months of live the stenosis grows and the murmur=20
(hopefully) becomes more apparent.
The murmur is best heard on =
the left=20
side of the chest at the level of the base of the heart. The =
louder=20
the murmur, the worse the obstruction of the valve. The =
murmur is=20
famous for radiating its sound up the carotid arteries of =
the=20
neck. Over time, the muscle of the left ventricle =
thickens and=20
grows due to the excess work it must =
perform. Eventually this=20
interferes with the pumping chamber=92s flexibility and =
ability to=20
fill (see how small the chamber in the above graphic has =
become=20
compared to normal). Abnormal muscle in the heart makes =
for=20
abnormal electrical conduction in the heart and soon the =
heart=92s=20
normal electrical rhythm is disrupted. Since pumping and =
filling are=20
highly coordinated electrically, when this coordination is =
lost,=20
fainting spells or even sudden death during exercise can=20
result. Most dogs with SAS do not survive beyond age 3 =
years=20
without treatment, though dogs with milder cases can have =
normal=20
life spans. A dog with SAS is always predisposed to =
electrical=20
arrhythmia, heart failure, and infection of the abnormal =
aortic=20
valve.
RECOGNIZING THE=20
DISEASE
Obviously, the pup is not =
going to=20
receive proper treatment unless the condition is=20
recognized. The first step is hearing the murmur.
As mentioned, murmur is the =
sound made=20
by turbulent blood flow. In other words, a murmur is a =
sound=20
which might or might not indicate heart disease. Puppies =
under age=20
six months sometimes demonstrate what are called =93innocent =
murmurs,=94=20
which simply represent temporary turbulent blood =
flow. Innocent=20
murmur should disappear by age six months so that any murmur =
that=20
persists beyond this time should be pursued as potentially =
abnormal.=20
Prior to age six months, diagnostics may be difficult to =
interpret=20
depending on the patient=92s size.
AFTER THE =
MURMUR
Radiographs are helpful in =
assessing any=20
evidence of actual heart failure, and may even show a =
dilation of=20
the aorta near the valve (caused by the high pressure squirt =
of=20
blood through the narrowing). This said, the real key to =
diagnosis=20
is ultrasound (=93echocardiography=94) where chamber sizes =
and heart=20
wall thickness are measured. Generally the =
cross-sectional area=20
of the left ventricle outflow tract is compared to that of =
the aorta=20
in a ratio to assess the severity of the stenosis. This =
information is generally adequate to confirm the diagnosis =
though a=20
mild case might have values that overlap the normal range. =
Such a=20
patient might have to be followed over time.
TREATMENT: =
DRUGS
The goal in treating SAS is to =
create=20
normal exercise tolerance and normal life span. The =
most=20
popular class of drug for SAS are the =93beta =
blockers.=94 Beta=20
receptors are the neurologic areas on the heart that =
respond to=20
adrenaline (we call it =93epinephrine=94 now) and cause the =
heart to=20
rate to speed up during exercise. In SAS, this kind of =
racing pulse=20
is what leads to the abnormal electrical rhythm (and =
ultimately=20
fainting). The beta blockers keep the heart from racing. In =
one=20
study, dogs with SAS treated with a beta blocker called =
=93atenolol=94=20
had a median survival of 56 months vs. 19 months for dogs =
receiving=20
no treatment.
TREATMENT: =
SURGERY
Open heart surgery is =
uncommonly=20
performed in dogs but it is possible to surgically excise =
the collar=20
of scarring that is narrowing the outflow tract. One would =
think=20
this would solve the whole problem but in fact resulting =
survival=20
times are similar to those for dogs simply taking =
atenolol.
TREATMENT: =
BALOON=20
VALVULOPLASTY
With balloon valvuloplasty, =
the patient=20
is anesthetized and a special catheter is threaded into the =
heart so=20
that it spans the stenosis. The catheter has a tough balloon =
at the=20
end which is then inflated, breaking down the scarring and =
dilating=20
the stenosis. Again, one would think that this would solve =
the=20
problem but survival times are similar to those for dogs =
simply=20
taking atenolol.
At this time, invasive =
procedures cannot=20
be recommended over medication. More complete studies in the =
future=20
may change this so watch this=20
=
space.
| ![3D"Subaortic](3D"http://www.marvistavet.com/assets/images/autogen/Subaortic_Stenosi= "3D\"Subaortic")
![3D"Heart](3D"http://www.marvistavet.com/assets/images/autogen/Heart_Failure__Th= "3D\"Heart")
![3D"Kidney
Failure"=20](3D"http://www.marvistavet.com/assets/images/autogen/Kidney__Failure_N= "3D\"Kidney
Failure\"=20")
![3D"Pregnancy
Termination"=20](3D"http://www.marvistavet.com/assets/images/autogen/Pregnancy__Termin= "3D\"Pregnancy
Termination\"=20")
![3D""=20](3D"http://www.marvistavet.com/assets/images/autogen/clearpixel.gif"=20){kind=tracking}