Diagnostic Testing and Monitoring
Core concepts
Match the test to the question. A 12-lead ECG answers "what is the rhythm now." A Holter monitor (24–48 h continuous) captures frequent or daily symptoms; an event monitor or patch is better for symptoms every few days to weeks; an implantable loop recorder suits infrequent, unexplained syncope or palpitations over months to years. Ambulatory monitoring yield depends on symptom frequency - choose the device whose wear time matches the symptom interval.
Exercise stress testing assesses rate-related ischemia and exercise-induced arrhythmias and chronotropic competence. Echocardiography evaluates structure and function (ejection fraction, valve disease, hypertrophy) that shape arrhythmia risk and device decisions. Electrophysiology study uses programmed stimulation and intracardiac recordings to test inducibility, map circuits, and guide ablation. Laboratory tests (electrolytes, magnesium, thyroid function, digoxin level, troponin) screen for reversible causes. Signal-averaged ECG and genetic testing have niche roles.
Question traps
- Ordering a 24-hour Holter for symptoms that occur once a month - the monitor will likely be nondiagnostic.
- Forgetting to check electrolytes and thyroid function before labeling an arrhythmia "primary."
- Assuming a normal resting ECG excludes an arrhythmia.
Rule of thumb
Match monitor duration to symptom frequency: daily symptoms → Holter; weekly → event/patch monitor; rare → implantable loop recorder.