Fig. 1.

A. The cause versus the mechanism of an arrhythmia. A molecular factor, such as a genetic mutation that alters a protein’s function, can unequivocally be the cause of an arrhythmia, but does not directly define the mechanism. The mechanism of the arrhythmia is defined by the effects of the molecular factor on the dynamic factors and fixed factors at each increasingly integrated scale. B. Fixed factors which increase electrical dispersion decrease the threshold of dynamic instability at which arrhythmias occur. Dynamic factors creating dynamic instability (dark shading) jointly increase the probability of triggers (left oval) and tissue vulnerability (right oval), whose overlap defines the arrhythmia zone (red). Fixed factors that increase structural and electrophysiological heterogeneity act synergistically with dynamic factors to promote triggers and increase vulnerability, widening the arrhythmia zone.