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Figure 4 Relationship between duration of mechanical asynchrony and heart failure development, as derived from various randomized clinical trials. This relationship indicates that attempts to avoid asynchronous activation may decrease the risk for developing heart failure most in patients requiring pacing for a longer time (children) and in patients with already-reduced pump function. A.U. = arbitrary units; RVA = right ventricular apex; Cum%VP = cumulative percent ventricular pacing.