© Kirrawee Veterinary Hospital CANINE DISEASES
Congestive Heart Failure
Congestive heart failure (CHF) is a result of the valves in the
heart failing to completely close. This allows some blood to be
pushed backwards with each contraction, increasing the pressure
in the vessels bringing blood to the heart. On the left side of
the heart the pressure increase is directed toward the lungs,
while on the right it its directed towards the abdomen. This results
in fluid being pushed out of the blood vessels into the surrounding
tissues. Clinical signs relate to the effects of this fluid build
up. The pressure increase also occurs in the heart chambers gradually
stretching the heart muscle. This decreases the strength of the
heart contractions and further reduces the efficiency of the heart.
Where the lungs are effected (pulmonary edema) the clinical signs
begin with a moist cough which predominantly occurs at night or
after resting. As the condition deteriorates these animals experience
shortness of breath especially after exercise, more frequent coughing,
and eventually difficulty breathing when lying down. Fainting
may also be seen. Right sided heart failure is less common and is often associated
with concurrent left sided failure. The clinical signs are swelling
of the abdomen and internal organs such as liver. The deterioration of the valves that leads to their failure to
close correctly occurs mainly in older animals. The underlying
cause is unclear however small to medium sized dogs are more commonly
effected. DIagnosis is based on identifying the changes in the sound of
the heart. Instead of the normal two beat "bom bom" sound, which
is the noise made by the valves snapping shut, a rushing noise
"shhhh" (heart murmur) is heard. This is produced by blood being
pushed backwards at high speed through a small opening in the
faulty valve. Congestive heart failure is a progressive disease
so many dogs will have a heart murmur well before any clinical
signs appear. In these cases the body is still able to compensate
for the failing heart. Other procedures which help to determine
the severity of heart failure include Xray and Ultrasound. Treatment is based on removing the fluid, improving the performance
of the heart muscle, and reducing the pressure in the vessels.
Diuretics are drugs which increase the rate of water excretion
through the kidneys. They have the effect of dragging excess fluid
out of the tissues. Diuretics (e.g. Frusemide) would form part
of most treatment regimes for CHF. Salt levels in the diet are also restricted as animals with CHF
have a reduced ability to get rid of salt from the body. The retention
of salt also leads to the retention of fluid. Digitalis glycosides (digoxin and digitoxin) increases the strength
of contraction (positive inotrophic) and improves the rhythm of
the heart. These drugs have been the traditional treatment of
heart failure for over 200 years and still have a prominent role
in modern medicine. They are derived from the leaves of the foxglove
plant. One major drawback of their use is the low safety margin
resulting in toxic signs being seen at therapeutic doses in some
animals. One of the most recent advances in the treatment of CHF has been
the use of angiotensin-converting enzyme inhibitors (ACE inhibitors).
These drugs increase the output of the heart and reduce the pressure
in the blood vessels against which the heart is pushing. They
are used in combination with diuretics and are proving very effective
with few side effects.Enalapril is the most commonly available
ACE inhibitor. Bronchodilators (e.g. aminophyline) have also been used routinely
for CHF however they do not directly effect the performance of
the heart. By reducing secretions and opening up the airways they
indirectly improve the clinical appearance of animals with CHF.
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