GAPS - PRACTICAL IMPLICATIONS

The French translations of the word ''gap'' include ''hole, breach, op ening''. In the Anglo-saxon literature, the conduction gap or the gap phenomenon is defined as the period of the cardiac cycle during which a premature beat is blocked whereas more delayed or more premature bea ts are conducted. This rare phenomenon, observed mainly during extrasy stolic stimulation, was previously called supernormal conduction, The underlying mechanism is distal block in the conduction system occurrin g when more premature beats lead to delay in the proximal conduction w hich gives the distal sice time ro become excitable again. The excitab ility gap is one of the main characteristics of reentrant arrhythmias. Its presence in a reentrant circuit ensures the regularity and stabil ity of the arrhythmia. It also allows penetration of the circuit by ex ternal stimuli. This different extrasystolic stimulation technique (re setting) or rapid fixed rate pacing (entrainment) may be used diagnost ically and therapeutically. It enables the identification of the arrhy thmia circuit and a critical zone (protected isthmus, zone of slow con duction) which may constitute a target for ablation. It also offers a possibility for terminating the arrhythmia by external stimulation. Fi nally, the duration of the excitable gap may guide the choice of antia rrhythmic agent during pharmacological cardioversion of a reentrant ta chycardia.