What is congenital heart disease?
A heart condition due to structural defect within the heart present at birth. Cardiac defects in Bull terriers include leaky valves or narrowed valves. Both
of these general defects will result in a heart murmur - an abnormal heart sound which is detected with a stethoscope by a veterinary cardiologist or a
Overall view of the normal anatomy of the heart:
The heart has four chambers. The right atrium (RA) collects venous blood from the body, and it passes through the tricuspid valve to the right ventricle
(RV) The right ventricle pumps the venous blood, though the pulmonic valve, into the pulmonary artery and so into the lungs, where the blood is
oxygenated. The blood returns to the heart, into the left atrium(LA) Blood passes though the open mitral valve into the main pumping chamber of the
heart, the left ventricle (LV) When this pumps, the mitral valve closes and blood is ejected out via the open aortic valve into the aorta which divides to
every artery to all the organs of the body.
Mitral dysplasia is a malformation of the mitral valve apparatus. The normal mitral valve apparatus consists of two valve cusps. These are anchored by
chordae tendinae to two papillary muscles in the left ventricle. The papillary muscles and the cow the valve to close when the ventricle contracts, but
restrain the valve so it does not flap back into the left atrium. The closed valve should be a tight seal, allowing no blood into the left atrium.
With mitral Dysplasia in Bull Terriers, the mitral valve apparatus is deformed. The valve cusps become thickened and nodular. The papillary muscles are
very large and thick and only very short, thickened and chordae tendinae attach the papillary muscles to the valve leaflets.
The most common consequence of mitral dysplasia is a leaky mitral valve. During ventricular contraction (systole) instead of the mitral valve sealing
shut it allows a jet of blood to pass backwards into the left atrium, as well as pumping blood forward in the normal direction, into the aorta. This leak is
known as mitral regurgitation The turbulent jet of blood flow due to mitral regurgitation can be heard with a stethoscope it is a systolic heart murmur,
which is most intense over the mitral valve area of the dogs chest. Loud murmurs can radiate to other parts of the dogs chest as well.
Occasionally, the mitral valve in mitral dysplasia can be narrowed as well, called mitral stenosis. It is difficult for the left atrium to empty into the left
ventricle. Pressures can build up in the left atrium. The left atrium may become greatly enlarged.
Consequences of mitral dysplasia:
Dogs with mitral dysplasia will have a heart murmur. If the valve is only slightly leaky, the murmur is only soft and the dog may not be affected at all.
Where there is severe mitral regurgitation, a large volume of blood moves back and forwards across the mitral valve, overloading the left side of the
heart. The left atrium and left ventricle can became very large indeed. Changes occur gradually, but eventually, pressures build up in the left atrium,
and blood dams back into the lungs, and comes out of the circulation into the normally air filled spaces of the lungs - this is called pulmonary oedema.
Once this happens, the dog is in congestive heart failure. Dogs with pulmonary oedema will be breathless and will cough. With mitral stenosis also
present, left atrial enlargement in massive and pulmonary oedema rapidly develops. Where the left atrium becomes very stretched, irregular or chaotic
heart rhythms can develop, such as atrial fibrillation. The rhythm will worsen the symptoms of dogs with congestive heart failure, especially if they have
Dogs with severe mitral dysplasia have poor heart output into their circulation they may faint on exertion or excitement or stress (syncope) as their
brains can become short of oxygen.
The aortic valve is positioned between the left ventricle and the aorta. It opens as the left ventricle contracts, allowing the left ventricle to eject blood into
the aorta. It normally offers no restriction to blood flow.
With aortic stenosis, the aortic valve itself or a fibrous band beneath the valve (Subaortic stenosis) restricts the outflow to blood from the left ventricle.
The left ventricle has to work hard just to eject blood, and the heart muscle becomes thickened to compensate. Blood ejecting past the obstruction to
outflow is very fast and turbulent. This turbulent flow causes a heart murmur which can be detected with a stethoscope over the aortic valve area of the
chest wall. The louder the murmur, the more severe the aortic stenosis and the faster and more turbulent the blood flow passing the obstruction. This
turbulent blood flow can affect the walls of the aorta, and it can stretch, called post-stenotic dilation. As the left ventricle muscle thickens, it exceeds the
coronary artery blood supply to it. This means that areas of the heart can be deprived of oxygen. The muscle becomes irritable and may cause
abnormal beats (called ventricular premature complexes or VPCs)
Diagnosis of congenital heart disease
As explained above, congenital heart disease is manifested by a heart murmur, which is detected by a veterinary surgeon or a veterinary cardiologist by
careful clinical examination, including auscultation, with a stethoscope. Because Bull Terriers are not easy dogs to auscultate, sometimes the dogs own
veterinary surgeon may not have detected the murmur.
Heart murmurs show that there is turbulent blood flow in the heart, which is abnormal. Murmurs are graded out of 6 - where Grade 6 is the loudest
murmur which can be detected. Grade 1 murmurs are the most quiet and difficult to detect. A very quiet room, a good quality stethoscope and a quiet,
calm dog who is not panting are required before the murmur is detected.
Mode of inheritance
This is not yet been proven, However the fact it is common in Bull Terriers and in certain family lines, there is significant clustering of heart disease, it
probably is inherited. Careful family history, cardiac examinations is necessary before breeding and any animals found with heart murmurs of any grade
should be removed from a breeding programme.
It is a devastating thing to watch a young Bull Terrier, who should be in the prime of life, slowly die with heart failure or even drop dead suddenly.
Testing all breeding stock before breeding is the only way we can protect Bull Terriers in the future from being born with heart disease.
|A heart showing the valves and Ventricles