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Bonnie is a 14 year old West Highland White Terrier referred to the RVC's Cardiology department with collapsing and fainting episodes. Her referring vet had observed her heart rate as slow and irregular and thought this might be causing Bonnie's problems.
At the Queen Mother Hospital for Animals Bonnie was connected to an ECG monitor which showed her heart beat was very irregular. Sometimes her heart rate was slow and other times it actually stopped for up to 6 seconds. These periods of slow or no heart beat were causing Bonnie's fainting episodes.
Further investigations ruled out any other cause for the heart irregularities, and Bonnie was diagnosed as suffering from sick sinus syndrome. 
This is a condition most frequently seen in West Highland Terriers, and is so named because the natural pace-setting part of the heart (the atrial sinus) is not working properly. The treatment for this condition is placement of an artificial pacemaker.
Bonnie was monitored closely at the Hospital until the time of her surgery. The pacemaker was identical to those used in humans, which monitors the heart rate and only stimulates it when it slows or stops. The pacemaker unit which contains the battery and controls is fitted under the skin of the neck and connected to the heart with a long lead. This lead passes from the neck down the jugular vein and into the right ventricle (pumping chamber) where tiny anchors attach it to the inside of the heart wall. The anchor holds the lead in place until it becomes firmly stuck down by the body to the heart wall.
Bonnie's surgery went smoothly and the pacemaker worked well. Bonnie was kept in hospital for several days to ensure the pacemaker was working correctly and also to prevent Bonnie from being too active and dislodging the lead the inside the heart before it has the chance to firmly attach.
The pacemaker battery only has a finite life but it would be unusual for an elderly dog to out-live the battery. Regular checks are made on patients like Bonnie at their own vet and at the QMHA for the rest of the patient's life to ensure the pacemaker continues to operate optimally and that the battery does not run out!
