Paradigms in cardiac resynchronization therapy. Schematic representation of two paradigms of mechanical dyssynchrony in cardiac resynchronization therapy. The left panel shows a "binary approach", according to which mechanical dyssynchrony above a certain cut-off is associated with a benefit from CRT (open circles), whereas dyssynchrony below that cut-off is associated with no benefit (solid circle). The right panel depicts the "lower/upper cut-off approach", according to which patients within a finite range of mechanical dyssynchrony benefit from CRT (open circles), whereas patients with too much dyssynchrony (above the upper cut-off) or too little dyssynchrony (below the lower cut-off) do not benefit (closed circles). It is hypothesized that, outside the critical range, alternative pacing modes (endocardial pacing, LV pacing with multiple leads) may be more effective than conventional CRT. Reproduced with permission from Auricchio and Leyva .