Bradycardia (Low Heart Rate): Causes, Symptoms, and Evaluation

Definition

Bradycardia: Resting heart rate <60 bpm in adults. Physiologic in athletes; pathologic when symptomatic or due to disease.

Etiologies

Cardiac Conduction / Structural

• AV block (1st, 2nd, 3rd degree)
• Sick sinus syndrome (sinus node dysfunction)
• Post-cardiac surgery / ablation
• Cardiomyopathy, ischemic heart disease, myocarditis
• Pericarditis (constrictive)

Medications (Very Common)

• Beta-blockers, non-DHP calcium channel blockers (verapamil, diltiazem)
• Digoxin, ivabradine
• Clonidine, methyldopa, alpha-2 agonists
• Antiarhythmics (amiodarone, flecainide)
• Lithium, donepezil

Systemic / Metabolic

• Hypothyroidism (↓ SA node automaticity)
• Electrolytes: hyperkalemia, hypercalcemia
• Hypothermia
• Sleep apnea (vagal surges)
• Increased intracranial pressure (Cushing reflex)
• Sepsis (late), anorexia nervosa

Symptoms (When Hemodynamically Significant)

• Fatigue, exercise intolerance
• Lightheadedness, presyncope, syncope
• Confusion, memory lapses (cerebral hypoperfusion)
• Dyspnea, angina (coronary hypoperfusion)
• Cold sweats

Workup

1. ECG + rhythm strip (Holter if intermittent).
2. Medication review → adjust/hold offending agents.
3. Labs: TSH, electrolytes, troponin, CBC, BMP.
4. Echo if structural disease suspected.
5. EP study if high-grade block or symptomatic arrhythmia.

Asymptomatic bradycardia in a fit individual usually requires no treatment.