Bradycardia refers to a slow pulse rate less than 60 beats per minute.  When there are no other abnormalities on the EKG other than the rate, the abnormality is termed sinus bradycardia.  Sinus bradycardia may occur after procedures such as eye surgery or coronary arteriography or with certain disease states such as hypothyroidism, meningitis, intracranial tumors, hypokalemia, hyperkalemia, increased intracranial pressure, hypoxia, hypothermia, acute myocardial infarction, obstructive sleep apnea, and gram-negative sepsis.  Other causes of bradycardia may occur secondary to sick sinus syndrome or heart block.  Bradycardia is common during sleep.  This is important to remember when patients are monitored in telemetry units.  Bradycardia may occur as a drug side effect, and it may also be a normal variant in well conditioned athletes.  Medications associated with bradycardia include beta-blockers, clonidine, amiodarone, verapamil, diltiazem, lithium, encainide, propafenone and digoxin.  Bradycardia may also result when there is an atrioventricular conduction block.  Symptoms are generally due to decreased perfusion and generally manifest as presyncope or syncope, dizziness, fatigue, or weakness.  Patients with bradycardia who are asymptomatic require no therapy.  Acutely, atropine is effective for patients with symptomatic bradycardia, and pacemakers may be required for patients with chronic or recurrent bradycardia.  Atropine is not effective for use in cardiac transplant recipients with denervated hearts.

     Relative bradycardia refers to an inappropriate increase in the pulse rate for a given level of temperature elevation.  The expected increased pulse rate for a given fever can be calculated by subtracting one from the singles column of a temperature greater than 100 degrees Farenheight, multiplying by 10 and then adding 100 (example: if the temperature were 104, then the expected pulse rate would be 130).  Relative bradycardia does not apply to patients with an underlying arrythmia, who have a pacemaker, or who are on beta blockers.  Relative bradycardia may imply certain etiologies in the evaluation of fever of unknown origin (FUO) such as occult neoplasm, enteric fever, drug fever, or lymphoma.  There are many infectious etiologies associated with a relative bradycardia to include legionnaires disease, psittacosis, tularemia, Q fever, typhoid fever, typhus, babesiosis, malaria, yellow fever, dengue fever, Mycoplasma pneumonia, Chlamydia pneumonia, and Rocky Mountain spotted fever.