Figure 1.

Electrophysiological mechanisms of arrhythmias and their study in human atrial cells. A: Representation of premature APs (*) from AA, EADs, or DADs. B: Premature impulse divides at functional or anatomical obstacle, blocks at tissue with normal (left side), but conducts with short (right) ERP and reenters previously inexcitable zone. λ = wavelength; θ = conduction velocity. C: Original APs stimulated in an atrial cell from a patient in SR or in AF by conditioning pulses (S₁) and premature test pulses (S₂). ERP (↔) = longest S₁-S₂ failing to produce S₂ response of amplitude >80% of S₁. D: Original APs stimulated by a pulse train in the presence of 0.05 μM isoproterenol (ISO), producing CADs (•). The * may represent AA. Panels C and D are based on data in references 2 and 3 with permission from Elsevier.