Ambulatory Monitoring (Holter and Event Monitoring)
Matching device to symptom
Holter monitors record continuously for 24–48 hours on 2–3 channels; patch monitors extend wear over several days; external loop/event recorders and implantable loop recorders serve symptoms that occur weekly to monthly and may be patient- or auto-triggered. Match the device to symptom frequency and document the reasoning.
Technically, know the modified bipolar leads - CM5 or CC5 approximating V5, plus a V1-like channel - so that both P waves and ST segments remain visible. Preparation mirrors a resting ECG: clip hair, abrade, alcohol, dry, then secure cable and electrodes with tape and a belt so they are not pulled. Teach the patient to keep a contemporaneous diary, press the event button at symptom onset, avoid bathing or showering during wear, and avoid strong magnetic fields.
Traps: electrode displacement creates baseline wander that can look like a pause or asystole, and loose leads create artifact mimicking VT. Diary times are often written from memory - reconcile them with the device clock. A normal Holter does not exclude paroxysmal arrhythmia, and a symptomatic patient with no arrhythmia on the recording is an important positive finding, not a failed test.
Rule of thumb: analyze in three passes - global rate/rhythm trend with minimum and maximum heart rate, then pauses and arrhythmia burden, then symptom-to-strip correlation for every diary entry.