Comparing maximum rate and sustainability of pacing by mechanical vs. XXXX in the Langendorff-perfused @entity95 heart.

@entity1 @entity3883 @entity95 @entity8425 @entity1167
AIMS: @entity3883 ( @entity3883 ) represents a readily available, non-invasive means of pacing the @entity1167 or bradycardic heart in @entity1 , but benefits of @entity3883 at higher heart rates are unclear. Our aim was to assess the maximum rate and sustainability of excitation by @entity3883 vs. @entity8425 ( @entity8425 ) in the isolated heart under normal physiological conditions. METHODS AND RESULTS: Trains of local @entity3883 or @entity8425 at rates exceeding intrinsic sinus rhythm (overdrive pacing; lowest pacing rates 2.5  0.5   Hz) were applied to the same mid-left ventricular free-wall site on the epicardium of Langendorff-perfused @entity95 hearts. Stimulation rates were progressively increased, with a recovery period of normal sinus rhythm between each stimulation period. Trains of @entity3883 caused repeated focal ventricular excitation from the site of stimulation. The maximum rate at which @entity3883 achieved 1:1 capture was lower than during @entity8425 (4.2  0.2 vs. 5.9  0.2   Hz, respectively). At all overdrive pacing rates for which repetitive @entity3883 was possible, 1:1 capture was reversibly lost after a finite number of cycles, even though same-site capture by @entity8425 remained possible. The number of @entity3883 cycles until loss of capture decreased with rising stimulation rate. If interspersed with @entity8425 , the number of @entity3883 to failure of capture was lower than for @entity3883 only. CONCLUSION: In this study, we demonstrate that the maximum pacing rate at which @entity3883 can be sustained is lower than that for same-site @entity8425 in isolated heart, and that, in contrast to @entity8425 , the sustainability of successful 1:1 capture by @entity3883 is limited. The mechanism(s) of differences in @entity3883 vs. @entity8425 pacing ability, potentially important for emergency heart rhythm management, are currently unknown, thus warranting further investigation.
