Sinus bradycardia is an abnormally slow heart rate that has its origins in the sinus node in the heart, according to Mayo Clinic. The sinus node is found in the right atrium of the heart, and it controls the heart's rhythm by way of electrical impulses.
In patients with sinus bradycardia, something interferes with these electrical impulses, according to Mayo Clinic. It may be age-related damage to the heart, heart disease or high blood pressure. The patient may have been born with a heart problem or might be suffering from a cardiac infection. The condition may also occur as a result of heart surgery, hypothyroidism, sleep apnea or an imbalance in the electrolytes that regulate the electrical impulses from the sinus node.
Inflammatory disease can also disrupt the electrical signals, as can too much iron in the organs and certain medications, according to Mayo Clinic. These medications often treat high blood pressure or heart conditions.
Though sinus bradycardia doesn't cause symptoms in all patients, some people with the condition feel lightheaded or dizzy and find it hard to catch their breath, says WebMD. Patients may also feel fatigued, experience chest pains or palpitations, and find it hard to concentrate. If blood pressure drops too low, patients may pass out.