Pacemakers

Pacemaker implantation is indicated to treat fainting due to arrhythmias (disorders of the heart rhythm) characterized by slow heart rate (less than 40 beats/ minute).

Fainting has to be differentiated from seizure. Typically, fainting is a transient loss of consciousness lasting less than 1 minute. The animal may stretch his legs and collapse on the ground, remaining motionless. Convulsions, muscles tremors and salivation are not seen. Recovery is usually very quick (seconds). Seizures typically last longer, are associated with convulsions, tremors, hypersalivation and a followed by a prolonged recovery phase (hours).

Arrhythmias that can induce fainting are numerous. They could be associated with fast heart rate (tachycardias) or slow heart rate (bradycardias). Tachycardias are usually treated with medications, where as bradycardias are treated with a pacemaker implantation. Characterization of the arrhythmia may require a regular electrocardiogram (ECG) if sustained or a 24 Hr ECG recording (Holter) if intermittent. Echocardiography to assess the presence of any underlying heart disease is extremely important, to determine the prognosis and the best global approach.

The main 2 types of bradycardias requiring pacemaker implantation are Sick sinus syndrome and complete atrio-ventricular block.

• Sick sinus syndrome is characterized by erratic firing of the area of the heart that generates the electric impulse, with periods of normal rhythm alternating with periods of very slow heart rate. Miniature Schnauzers seem to be predisposed.
• Complete Atrio-ventricular block refers to the non transmission of the electric impulse from the atria to the ventricles. The ventricles end up beating on their own due to the presence of a natural escape mechanism, but at a very low rate (< 40 bpm), leading to fainting, especially at exercise.

There are 2 parts in the pacemaker: the lead and the battery. The lead that will stimulate the heart is introduced via the main vein of the neck (the jugular vein). The tip of the lead is pushed into the right ventricle using fluoroscopy. Once in place, the lead is connected to an external pacer (stimulating unit) to verify its good functioning. Then a pocket is created in the muscles of the neck to place the battery. The extremity of the lead is then connected to the battery, and the skin is closed over the small incisions sites.

Typically the pacemakers used are rate-responsive. They are set to stimulate the heart at a minimum rate of 70 bpm. If the pacemaker senses a spontaneous electrical activity that is above that rate, it does not fire, and waits for the heart to slow down enough to enter in action.

The pacemakers we use are new. The battery can last up to 5 years.

Complications associated with pacemakers include infection at the implantation site, malfunction of the battery or displacement of the lead and blood clot formation. The reported rate of complications is about 20%, and may require the replacement of the pacemaker unit.