Sick Sinus Syndrome in Cats

The sinoatrial node (SA Node, or SAN), also called the sinus node, is the initiator of electrical impulses within the heart, triggering the heart's contractions by firing off electrical surges. One of the disorders that can affect the heart’s electrical impulse formation within the sinus node is called sick sinus syndrome (SSS).

This disorder complicates conduction of the electrical impulse out of the sinus node and the specialized conduction system of the heart. Secondary pacemakers, such as the muscle fibers of the sinus node, will also be affected by sick sinus syndrome. (Note: the body's natural pacemakers are responsible for setting the pace for the heart's rhythm and generating the electrical impulses within the muscle tissue.)

Any irregular contraction of the heart (arrhythmia) will be visible on an electrocardiogram (ECG). Tachycardia-bradycardia syndrome, in which the heart beats too slowly, and then too quickly, is a variant of sick sinus syndrome. Clinical signs of sick sinus syndrome in cats will become apparent when organs begin to dysfunction because they are not receiving a normal amount of blood supply.

Symptoms and Types

If your cat tends to be fairly inactive under normal circumstances, it will take longer for symptoms of sick sinus syndrome to become apparent. When symptoms do show, those that will generally present are:

• Weakness
• Fainting
• Fatigue
• Collapse
• Seizure
• Abnormally fast or abnormally slow heart rate
• Pauses in the heart rhythm
• Rarely, sudden death

Causes

Some of the suspected relationships to SSS are genetic, however, the causes for this condition are mostly unknown. One possible cause is when there is a heart disease that is cutting off the blood supply to or from the heart, disrupting normal heart function and electrical functionality. Cancer in the thoracic or pulmonary (both refer to the chest) region may also lead to SSS.