Differential Diagnosis: Bradycardia

Bradycardia: Differential Diagnosis

The younger the patient the higher the resting pulse generally is. Therefore, the pulse should be put into the proper context of the age of the patient and their clinical status.
A pulse of < 60 bpm is considered bradycardia in adults, whereas in newborns a pulse < 60 bpm with evidence of low perfusion considered a reflection of a life threatening situation where chest compressions are recommended to be started.

Differential Diagnosis: Bradycardia

Athletes

Beta-Blockers

Associations: History of hypertension +/- atrial fibrillation with rapid ventricular response +/- migraine headaches (for propranolol) +/- stage fright. Medications include: atenolol, bisoprolol, carvedilol, labetalol, metoprolol, propranolol, nadolol, nebivolol.
Pathophysiology: Reduces chronotropy via inhibition of SA Node and AV nodal.

Calcium Channel Blockers (Non-Dihydropyridine; e.g., diltiazem, verapamil)

Associations: History of hypertension +/- atrial fibrillation with rapid ventricular response +/- migraine headaches. This only applies to diltiazem and verapamil and not other dihydropyridine calcium channel blockers such as amlodipine and nifedipine.
Pathophysiology: Slowing of AV nodal conduction in the heart.

Digoxin

Associations: Past medical history of heart failure +/- atrial fibrillation with rapid ventricular response
Pathophysiology: Increase vagal or parasympathetic mediated tone on the AV node, thereby reducing the pulse.

Hypothermia

Associations: Report of cold exposure + change in mental status + impaired coagulation
Pathophysiology: Not completely known but in part due to reduced metabolic demands and increased cholinergic effects on the heart.

Hypothermia

Associations: Fatigue +/- weight gain +/- depression +/- hypotension (if severe) +/- hypoglycemia (if severe) +/- hypoglycemia (if severe)
Pathophysiology: Thyroid hormone binds to nuclear receptors in various organ tissues that help to regulate their metabolism and function. Severe hypothyroidism such as seen with myxedema coma can be associated with hypotension, hypothermia, hyponatremia and hypoglycemia.

Increased Intracranial Pressure (ICP)

Associations: Head injury or bleed + hypertension + widening pulse pressure (larger difference between the systolic and diastolic blood pressure).
Pathophysiology: Cushing's triad or reflex (hypertension + bradycardia + widening pulse pressure [increased systolic BP compared to the diastolic pressure) that occurs with rising intracranial pressure (ICP) with resulting impending risk of brain stem herniation.

Lyme's Disease

Associations: Tick bite (recent) +/- presence of a target lesion on skin + heart block on ECG + dizziness or syncope
Pathophysiology: Known to cause significant heart block.

Medications

Associations: Antiarrhythmics (amiodarone, sotalol), Beta-blockers (atenolol, bisoprolol, carvedilol, labetalol, metoprolol, nadolol, propranolol), Non-dihydropyridine calcium channel blockers (diltiazem and verapamil), clonidine, digoxin, sotalol.

Myocardial Infarction

Associations: Chest pain/pressure +/- SOB +/- nausea +/- sweating +/- CV risk factors
Pathophysiology: Decrease blood flow (especially involving the right coronary artery) to heart muscle containing nodal cells that function as a pacemaker.

Sick Sinus Syndrome

Associations: Dizziness +/- syncope + usually in older adult +/- irregular pulse on exam
Pathophysiology: Abnormalities in sinoatrial node impulse formation and propagation within the atrium.

Sotalol (Betapace)

Associations: History of cardiac dysrhythmia requiring antiarrhythmic medications
Pathophysiology: Sotalol is a class III antiarrhythmic medication known to inhibit potassium conduction during phase 3 of the action potential in a ventricular myocyte.

Vasovagal Response

Associations: Usually stressful response/experience + period of hypotension + pale appearance
Pathophysiology: Reduction in sympathetic tone resulting a decreased pulse and blood pressure that temporarily results in a reduction in cardiac output and blood flow to the brain which results in a short period of syncope (usually < 30-60 sec).