The pathophysiology of sinus bradycardia depends on the underlying cause. People who are athletes or young adults tend to have bradycardia. Pathologic causes of bradycardia include electrolyte disorders, myocardial infarction, sleep apnea, infection, hypothyroidism, hypoglycemia, increased intracranial pressure and drug effects. Bradycardia could also be caused by sick sinus syndrome, which is a dysfunction in the sinus node to transmit action potential to the atria. This condition most often occurs in elderly patients who have cardiovascular problems.
