‘Lucy’, a nine year-old golden retriever was brought in as her owner was concerned that she seemed lethargic, not so keen to go for her walks, and was tiring very quickly.
The vet on examination noted that her heartbeat was very irregular and she had a loud heart murmur. Her respiratory rate was also increased.

We ran an ECG (Electrocardiograph) on Lucy, and discovered that her sino-atrial node was not working properly. Because the node was not passing correct messages to the heart to beat, the atria were fibrillating (beating very quickly) and all effective heartbeats were originating from below the sino-atrial node, but in a more random fashion. This is why her heart sounded so irregular, her cardiac output was reduced, and she was suffering from symptoms of heart failure.

Below is the first ECG we ran on Lucy.

There are no discernible P waves, and the presence of "f" or fibrillation waves. The heart rate is very fast and irregular.

We referred Lucy to an expert in cardiology. They confirmed our diagnosis of ‘atrial fibrillation’. They also performed an ‘ultra-sound scan’ on her heart to get a precise idea about it’s size and shape.
Lucy’s heart was very enlarged, as she was suffering from a disease called

‘dilated cardio myopathy’. This was causing problems with the conduction system within her heart muscle.
Lucy was started on treatment straight away that would slow her heart down (Digoxin), hopefully prevent atrial fibrillation, and allow the sino-atrial node to function correctly.

Slowing the heart down allows the chambers to fill up properly before they contract and can significantly increase cardiac output. Other drugs were also used to increase contraction of heart muscle, and lower the pressure in the vessels leaving the heart, thus making it easier for the heart to pump blood out. 

...Two weeks later, we ran another ECG on Lucy....

The difference in her was amazing! She looked younger and brighter, and was remarkably lively compared to her last visit. When we listened to her heart, it was slower and more regular, and her breathing had improved.

The ECG this time shows that she is in ‘sinus rhythm’, i.e. the heartbeats are ALL originating from the sino-atrial node. There is now no atrial fibrillation, as the baseline is flat. There are normal P waves present, but as you can see, although the heart rate has slowed down compared to the first ECG, it is still quite irregular.

We ran a test on her blood to check that the levels of ‘digoxin’ were correct. Too high a level can be counter-productive.

The third ECG was run after about 4 weeks of treatment. The heart rate was much slower, and has a steady sinus rhythm.
Six months on Lucy is doing well, is monitored regularly and is stable on medication.

                                Jill Macdonald DipAVN(surg), V.N.

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Heart Murmur:  The normal beating heart makes two distinct sounds during one beat or cycle. The first sound is the valves shutting between the atria and the ventricles. The second sound is the valves shutting as the blood leaves the ventricles and enters the vessels that leave the heart. If there is any kind of problem with the valves, or the heart is enlarged and the shape of the heart has become distorted, then a murmur (a whooshing sound) can be heard. This is usually due to blood leaking back through the valves. It may not cause the patient any problems (be asymptomatic) but makes the heart work harder, and may lead to reduced cardiac output and compromise the patient. Some heart murmurs are due to extreme problems such as ‘patent ductus arteriosis’ or ‘hole in the heart’, or because of inflammation of the inner part of the heart (endocarditis).
 

·             Dilated cardio-myopathy (DCM): involves disease of the heart muscle, which causes it to become thin walled and flaccid. This causes the heart to be dilated and much larger than it should be. Because the heart muscle is thin and the chambers are larger, and therefore contain greater volumes of blood, the heart struggles to empty the heart on each cycle. This reduces cardiac output, whose complex compensatory mechanism unfortunately results in making the heart work even harder.  

·       The distorted shape of the heart muscle may affect the conduction system in the heart and cause arrhythmias that exacerbate the situation further. 

·       Heart failure of any kind will be degenerative, ie get worse, as it follows the ‘vicious cycle’ of heart disease. The drugs we can use will usually improve symptoms, and may slow the vicious cycle and reduce further deterioration. 

·       There are different forms of heart failure that animals can suffer from, but DCM affects dogs, usually larger breeds. All of the disease conditions are very complex, with lots of different symptoms, and involving many different processes.

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Electrocardiography at the Veterinary Health Centre
An electrocardiogram, or ECG, allows us to look at the electrical activity of the heart. Each heartbeat is controlled by an impulse, which in a normal heart, originates from the sino-atrial node in the right atrium (top chamber of the heart). However, abnormalities can occur which can be detected by the ECG.   The ECG can also help us to diagnose heart enlargement, and even pinpoint which area, or chamber of the heart is enlarged.

A normal heartbeat involves the sino-atrial node telling the atria (top chambers) to contract first. This electrical impulse then travels through the centre of the heart and subsequently causes ventricular contraction.

The atria pump blood into the ventricles (bottom chambers), which then contract and pump blood into the vessels and around the body. Then the sequence starts again. If the sino-atrial node does not start the sequence, then conductive fibres further down the heart take over. In some cases, only the ventricles are contracting properly, and this is enough to keep the heart beating, but can be very dangerous for the patient.

Arrhythmias, (irregular heart rhythms) and heart enlargement, can both reduce cardiac output (the effectiveness of the heart pumping blood), and cause the patient problems, including breathlessness, weakness and lethargy, and even fainting and collapse.

If they are diagnosed and treated promptly, we can significantly slow the disease process, and improve the quality of life of our patients.

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