Healthy hearts in both pets and humans have a natural internal pacemaker called the sinus node. This node sends out electrical signals to set the rate of the heartbeat, keeping it regular and responding to an increased need for blood flow, for example during exercise. Certain diseases can affect how well this pacemaker works. And it can cause the heart to beat too fast or too slowly for the conditions it is under. If the heart rate is too slow or the heart is missing beats, an artificial pacemaker might be needed to improve the heart rate and rhythm.

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The first artificial pacemaker was invented in 1960. Artificial pacemakers are small electrical devices about the size of a matchbox. They are implanted under the skin of the neck or between the shoulder blades and deliver electrical impulses, via a wire, to the heart telling it when to contract. 

In dogs there are two main heart conditions that can result in the need for a pacemaker; sick sinus syndrome and heart block.

Sick sinus syndrome

In sick sinus syndrome, the sinus node (the natural pacemaker) that usually sets the heart rate in a healthy heart malfunctions, and there is a delay in producing an impulse. This means that the heart does not beat frequently enough. This can result in a slow overall heart rate, termed bradycardia, and intermittent long pauses between beats. That said, some animals with this condition can have heart rates that are too fast rather than too slow. The most commonly affected dog breeds are west highland white terriers; but dachshunds, miniature schnauzers, boxers and cocker spaniels can also suffer from this condition. 

Heart block

Heart block is another condition that can also result in low heart rates. This time the problem is with a second node in the heart, called the atrioventricular or AV node. This AV node essentially works to connect the two upper chambers of the heart; the atria, to the stronger lower chambers, the ventricles, transmitting instructions to ventricles to tell them when to contract.

In a healthy heart, the sinus node starts by sending regular electrical electrical signals which are then transmitted around the top of the heart, telling the muscle to contract the atria, then the signal travels through the AV node which coordinates the contraction of the ventricles, completing the two parts of a heart beat. 

In heart block, the sinus node sends a signal as normal. But when it reaches the AV node it is slowed or blocked altogether. This means that the lower part of the heart muscle fails to receive the signal to contract or there is a delay in the signal being transmitted. Heart block can affect any breed of dog. Although there are medications that may help with the condition, often a pacemaker is the best treatment. 

Signs of these heart conditions

Dogs suffering from either of these conditions are likely to show signs such as lethargy; tiring more easily on walks, weakness and episodes of collapse. If the condition is not treated it can lead to heart failure which can cause a worsening of these signs; as well as coughing, difficulty breathing and a buildup of fluid in the lungs, chest cavity or abdomen. If your vet suspects either of these conditions they will likely recommend tests to rule out other causes of these signs, then diagnose the condition and check for possible underlying problems. Tests may include blood tests, an ECG trace, x-rays and a scan of the heart called an echocardiogram. 

Fitting a pacemaker

If your vet thinks that your dog needs a pacemaker they will refer them to a specialist heart vet called a cardiologist. Most veterinary cardiologists are based at large multidisciplinary referral centres. Artificial pacemakers are fitted to dogs under anaesthetic. A small incision is made in the skin of the neck over the jugular vein, and a wire is threaded through the incision and along the vein to the heart. The other end of the wire is connected to the impulse generator which is implanted under the skin. The surgery is not without risks as the anaesthetic puts an extra strain on a heart that is already struggling, but it is usually the best chance for dogs suffering from these conditions.  

Life with a pacemaker

Pets that have had a pacemaker fitted often feel much better quite quickly. For the first month they need to be extra cautious to ensure the leads in the heart do not become dislodged. This usually means strict rest, and jumping up and down or using stairs needs to be avoided until sufficient scar tissue has formed to hold the leads more securely in place. After this time they can generally live a pretty normal life with a few precautions.  It’s still important that any trauma to the neck is avoided and so dogs should only wear collars for identification purposes. Leads must only be used with a suitable harness. Some electrical devices can interfere with pacemakers and care needs to be taken. 

Regular check ups are essential to check that the device is still working and has sufficient battery. If the device no longer works, or the battery runs out, further surgery to fit a new device will be needed. There are certainly downsides to pacemakers. The risks should not be underplayed; the recovery process requires real commitment from the owner and it is an expensive procedure. However, for dogs affected by these conditions it can be life-changing and allow them to get back to doing the things they love the most.

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