The ECG is the basis for all arrhythmia diagnosis. The ECG tracing is a series of waves that represent the electrical events of the various chambers and conduction pathways within the heart. The small initial wave, called the P wave, represents the electrical activation of the atria. Next comes the QRS complex, the tallest wave on the ECG, representing the stimulation of the ventricles. Finally, the T wave represents the period when the ventricles recover their electrical forces so they may be stimulated again.
Long-Term ECG Recording
Patients with heart rhythm irregularities or heart rhythms which are not documented on the routine electrocardiogram will usually require some type of home or ambulatory monitoring. Quite often the person’s symptoms occur only once a day, once a week, once a month, or even less often. There are recording methods that allow such infrequent event to be captured and analyzed. The electrophysiologist might use any or all of these methods and techniques. The methods are 24-hour Holter recording, loop continuous recording and transtelephonic event recording.
You can find further information here: The American Heart Association Website