Mary Allen
“My dog has something on his heart” is something you often hear, especially when the animal is a bit older. But what is it all about? veterinarian dr Sebastian Goßmann-Jonigkeit gives an insight into the symptoms of heart disease in dogs and cats and shows possible therapies.
Heart Disease… What Does That Actually Mean?
Here is a flying visit to cardiology – the science of the heart.
The heart has the same function in all animals: it pumps blood through the body. This guarantees that the oxygen bound to the red blood cells is available to every cell in the body in sufficient quantities. The requirement can vary from low to high during physical exertion at rest – compensating for this also falls within the heart’s area of responsibility.
Heart Structure
With a few exceptions in the animal kingdom, the heart is structurally very similar to a functional hollow organ. On either side is a larger ventricle below a smaller atrium, clearly separated from each other by a heart valve that acts as a one-way valve so blood only flows in one direction. The blood is kept in constant circulation during the pumping process by a sophisticated system of muscle tension and valve movements.
Low in oxygen, it flows into the interior of the organ via the afferent posterior vena cava. It enters the right ventricle from the right atrium through the so-called tricuspid valve. From there via the pulmonary artery into the vascular system of the lungs, where the red blood cells are loaded with fresh oxygen. The pulmonary vein leads the blood into the left atrium, through the so-called bicuspid valve into the left ventricle, and is discharged from there through the aorta into the systemic circulation, rich in oxygen.
The Stimulation Line
In order for the blood flow to working exactly like this, the contraction of the heart muscle must be precisely controlled. The so-called sinus node sets the pace for this – it sends out an electrical impulse that reaches the respective heart muscle cells in the correct order so that they contract exactly according to the pumping function. This electrical derivation can be displayed using the electrocardiogram (ECG) and shows the stimulus conduction in the heart muscle. It is used to detect possible arrhythmias (e.g. incorrect timing or incorrect conduction) which, undetected, can lead to insufficient blood flow. This is why heart monitoring during anesthesia is so important.
Symptoms of Heart Disease in Dogs and Cats
All signs of heart failure can be explained by the heart’s malfunctioning. One of the main reasons for an appointment during the consultation is a noticeable drop in performance – this usually first becomes apparent when the outside temperatures are higher in early summer. Since the heart with an age-related heart valve defect can often only just cover the oxygen requirement for the organism, the patient usually moves much less motivated or slower than usual. With increased outside temperatures, the cardiovascular system is stressed even more, since a large part of the body’s energy flows into temperature regulation and a minimum supply of oxygen in all organs (especially important in the brain) is not guaranteed at all times. This circumstance causes the typical collapse of an unrecognized or inadequately treated heart patient on hot summer days.
Another symptom can be bluish (cyanotic) discolored mucous membranes (e.g. conjunctiva in the eye or unpigmented gums), which are caused by a lack of oxygen in the blood.
In advanced stages, the so-called ‘cardiac cough’ usually occurs – this is pulmonary edema, which the patient tries in vain to cough up or choke out. It occurs when blood from the left atrium backs up into the lungs and liquid contained in the blood is pressed out of the vascular system into the spaces between the bronchi – if left untreated, animals can literally ‘drown’ or ‘suffocate’.
Diagnosis
There are several ways to examine a heart. The simplest is listening with a stethoscope – the so-called auscultation. In the process, secondary heart noises (hissing, rattling, etc.) can be determined by defective heart valves. At the same time, one can count the heart rate and possibly hear an arrhythmia.
In the case of a heart X-ray (usually possible without sedation), the horizontal and vertical dimensions of the organ are set in relation to the size of the thoracic vertebrae to see whether it is enlarged. If it measures more than a total of 10.5 vertebral bodies in a dog, this is referred to as an enlargement of the heart that requires treatment – this calculation method is called VHS X-rays (Vertebral Heart Score).
In order to be able to assess the functionality of the valves without any doubt, the Doppler ultrasound has proven itself. In addition to the dimensions of the heart valves, any backflow of blood due to defects can be shown in color.
DCM vs HCM
When heart failure occurs in old age, the organism of dogs and cats usually reacts quite differently. Since the blood flow is disturbed by the defective heart valves and can even be reduced in some areas, the heart as the central pumping station has to be rebuilt and adapted accordingly.
Dogs usually develop what is known as dilated cardiomyopathy (DCM). This is an enlargement of the organ that can be easily visualized on X-rays. The volume of both chambers appears massively increased so that a significantly larger amount of blood could be moved per heartbeat. The problem with this adaptation is that the heart muscle becomes very narrow in the area of the chambers – it lacks the strength to serve the enlarged organ optimally.
Cats, on the other hand, develop hypertrophic cardiomyopathy (HCM) almost exclusively in old age if there are corresponding valve defects. With this form of compensation, the heart muscle is massively thickened with a significant reduction in the size of the heart chambers. Therefore, only a small amount of blood can be pumped per heartbeat and the heart has to beat more frequently in order to transport the minimum amount of blood.
Therapy
At the latest when the symptoms of heart disease described above appear in dogs and cats, the veterinarian should be consulted as soon as possible for a heart examination.
Since the heart valves slowly wear down with age, the vast majority of all dogs and cats will sooner or later develop corresponding symptoms and require therapy. In order to compensate for the resulting heart failure, modern veterinary medicine uses four pillars of cardiac (heart medication):
- Lowering afterload with ACE inhibitors (by widening blood vessels, it becomes easier for the heart to pump against existing blood pressure)
- Slowing or reversing the remodeling process that occurs in dilated or hypertrophic cardiomyopathy
- Strengthening of the muscular heart strength through the active ingredient ‘pimobendan’ in dogs
- Drainage of the lungs by activating the kidney function with the active ingredients ‘Furosemide’ or ‘Torasemide’ in the presence of pulmonary edema
In addition, blood circulation-promoting agents such as propentofylline can be used in the area of the terminal flow paths.
Which active substance is used in which patient must be decided on the basis of the available findings and symptoms. A generalization is not possible.
Conclusion
A few years ago, heart disease in dogs and cats, especially age-related cases, was considered extremely difficult. On the one hand, because the medication options were very limited and, on the other hand, a medication that was difficult to dose (e.g. the poison of the red foxglove) was available.
In particular, the strengthening effect of pimobendan has brought enormous progress in the therapy of dogs with heart disease in recent years.
Today, the life expectancy of a well-adjusted and properly monitored heart patient can be just as high as that of a healthy patient – provided early action is taken.