[From provocation tests to clinical practice: invasive and non-invasive electrophysiology]

There are always three main ingredients required for the production of a clinical arrhythmia: the arrhythmogenic substrate, the trigger factor and the modulation factors of which the most common is the autonomic nervous system. These different components may be appreciated by invasive and non-invasive electrophysiological methods, the values of which are extremely variable according to the way they are used and to the particular arrhythmia being investigated. For example, programmed electrical stimulation is extremely valuable whenever a reentry mechanism is suspected and may even provide access to treatment of the underlying arrhythmogenic substrate. On the other hand, it is of little use when the arrhythmia is not caused by an inducible mechanism and anatomically very localised. In this situation, pharmacological adrenergic stimulation or exercise stress testing may be more appropriate given their effects on the autonomic nervous system and their influence on the substrate or the occasional trigger factor, thereby making analysis of the results more difficult. The role of the autonomic nervous system is best assessed by the data provided from Holter recordings, a true electrophysiological investigation, rather than a simple tool for picking up spontaneous arrhythmias. Finally, present day computer techniques have completely revised conventional electrocardiography. For example, the search for the arrhythmogenic substrate by the demonstration of late ventricular potentials on signal-averaged ECG. Even more valuable is the analysis of ventricular repolarisation and its variations as it reflects arrhythmogenic electrophysiological conditions at cellular level.