Ahlberg Sarah E, Ripplinger Crystal M, Skadsberg Nicholas D, Iaizzo Paul A, Mulligan Lawrence J
Department of Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota, USA.
J Cardiovasc Electrophysiol. 2007 Feb;18(2):212-7. doi: 10.1111/j.1540-8167.2006.00712.x. Epub 2007 Jan 9.
It is known that as stimulation frequency is increased in a healthy heart, a corresponding increase in LV contractile function (dP/dt(max)) is observed, i.e., force-frequency relationship. The impact of this relationship on systolic and diastolic mechanical restitution in an ejecting, in vivo preparation has yet to be explored. Understanding this relationship may lead to further insight on the cellular processes that govern the contraction and relaxation of the heart, in addition to providing a safer, more feasible clinical diagnostic tool.
Anesthetized canines (n = 8) were paced from the RA at rates of 130, 150, and 180 bpm. At each rate, extrasystoles were delivered at varying intervals. The LV dP/dt(max) and dP/dt(min) associated with the extrasystolic beat were expressed as a percentage of steady-state levels and plotted as a function of the extrasystolic interval to obtain mechanical restitution curves. The systolic restitution time constant length decreased significantly with all increases in heart rate, P < 0.05. In the diastolic case, significant decreases in restitution time constants were seen when heart rate was increased from 130 bpm to 180 bpm, and from 150 bpm to 180 bpm, P < 0.05.
This study was the first to quantify the finding that the time constant of restitution significantly and consistently decreased with a consistent increase in heart rate. The identification of such behavior may be employed to develop stimulation protocols and chronic diagnostic tools to more safely and sensitively identify and optimize the clinical status of patients receiving pacing therapy.
众所周知，在健康心脏中，随着刺激频率增加，左心室收缩功能（最大dp/dt）会相应增加，即力-频率关系。这种关系对正在射血的体内心脏收缩期和舒张期机械恢复的影响尚未得到研究。了解这种关系可能会进一步深入了解控制心脏收缩和舒张的细胞过程，此外还能提供一种更安全、更可行的临床诊断工具。
对8只麻醉犬经右心房以130、150和180次/分钟的频率进行起搏。在每个频率下，以不同的间期发放期外收缩。将与期外收缩搏动相关的左心室最大dp/dt和最小dp/dt表示为稳态水平的百分比，并绘制为期外收缩间期的函数，以获得机械恢复曲线。随着心率的所有增加，收缩期恢复时间常数长度显著缩短，P<0.05。在舒张期，当心率从130次/分钟增加到180次/分钟以及从150次/分钟增加到180次/分钟时，恢复时间常数显著缩短，P<0.05。
本研究首次量化了随着心率持续增加恢复时间常数显著且持续缩短这一发现。识别这种行为可用于制定刺激方案和长期诊断工具，以便更安全、更敏感地识别和优化接受起搏治疗患者的临床状态。
