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Changes of left ventricular contractility in alternating left bundle branch block.

A case of intermittent and at times alternating, nonrate-dependent left bundle branch block, with alternation of normal and reduced indexes of contractility (dP/dt, dP/dt/P) in a borderline normal heart is reported. The reduction of left ventricular contractility in the presence of left bundle branch block, as compared to what is found by other authors, is supposedly related to a different location of the block in the left branch (peripheral vs high).