Many cardiac arrhythmias are intermittent and show no fixed ECG abnormalities; exceptions include Wolff-Parkinson-White syndrome Long QT syndrome Arrhythmogenic right ventricular dysplasia cardiomyopathy Brugada syndrome and its variants If no diagnosis is apparent and symptoms are frequent, Holter monitoring for 24 to 48 hours is useful; for intermittent symptoms, an event recorder worn for longer periods and activated by the patient when symptoms are felt is better.