Fananapazir L, Rademaker M, Bennett D H
Pacing Clin Electrophysiol. 1985 Sep;8(5):701-14. doi: 10.1111/j.1540-8159.1985.tb05883.x.
The TX pacemaker uses a conventional transvenous electrode to sense T-waves of paced ventricular complexes and it adapts the pacing rate to varying physiological demands by responding to changes in the QT or, more correctly, the stimulus artifact-to-T-wave (stimulus-T) interval. This pacing system was assessed in 13 patients. The relation between heart rate and stimulus-T interval and the effect of programming on the performance of this pacemaker were studied on several occasions in each patient. Treadmill exercise performance during TX pacing mode was compared with atrial synchronized ventricular (VAT) and asynchronous ventricular demand (VOO and VVI--70 beats per minute) pacing modes. T-wave sensing problems arose in three patients. In one, this was overcome by reducing the pulse amplitude from 5.0 to 2.5 V. In another patient, spontaneous recovery of T-wave sensing occurred 5 months after pacemaker implantation. T-wave sensing deteriorated with the passage of time in most patients. Satisfactory rate response as assessed by treadmill exercise testing and Holter monitoring was achieved in 12 patients through adjustments of two programmable parameters: the slope that defines the alteration in heart rate in response to a millisecond change in stimulus-T interval and the "sensing window" that is the interval during which T-waves can be sensed and a rate response is possible. Exercise performance was significantly better during rate responsive pacing (TX) mode as compared with VVI pacing but was comparable to that during VAT pacing. The resting heart rate/stimulus-T interval can be described by the following linear regression equation: stimulus-T interval = 466 - 1.68 X paced-rate, r2 = -0.62. This relation, however, was subject to wide inter- and intra-patient variation. Consequently, given identical programmed parameters and exercise protocol, the chronotropic response differed significantly from patient to patient and in the same patient from one occasion to another. Our results show that a physiologically beneficial chronotropic response can be achieved in most patients. However, reprogramming, based on results of exercise tests and Holter monitoring, may be necessary to adjust for changes in T-wave sensing and the heart rate/stimulus-T interval relation and, thus to ensure that the pacemaker continues to function optimally.
TX起搏器使用传统的经静脉电极来感知起搏心室复合波的T波，并通过响应QT间期（或更准确地说是刺激伪迹到T波的间隔，即刺激-T间隔）的变化来使起搏频率适应不同的生理需求。对13例患者的这种起搏系统进行了评估。在每位患者中多次研究心率与刺激-T间隔之间的关系以及编程对该起搏器性能的影响。将TX起搏模式下的跑步机运动表现与心房同步心室（VAT）和非同步心室按需（VOO和VVI——每分钟70次搏动）起搏模式进行比较。3例患者出现T波感知问题。其中1例通过将脉冲幅度从5.0V降至2.5V得以解决。另一例患者在起搏器植入5个月后T波感知自发恢复。大多数患者的T波感知随时间推移而恶化。通过调整两个可编程参数，12例患者经跑步机运动测试和动态心电图监测评估获得了满意的频率反应：一个参数定义了刺激-T间隔每毫秒变化时心率的改变斜率，另一个参数是“感知窗口”，即能够感知T波并可能产生频率反应的间隔。与VVI起搏相比，频率应答起搏（TX）模式下的运动表现明显更好，但与VAT起搏时相当。静息心率/刺激-T间隔可用以下线性回归方程描述：刺激-T间隔 = 466 - 1.68×起搏频率，r2 = -0.62。然而，这种关系在患者之间和患者自身存在很大差异。因此，在给定相同的编程参数和运动方案的情况下，变时反应在患者之间以及同一患者在不同时间之间存在显著差异。我们的结果表明，大多数患者可以实现有益的生理变时反应。然而，可能需要根据运动测试和动态心电图监测结果重新编程，以调整T波感知和心率/刺激-T间隔关系的变化，从而确保起搏器继续最佳运行。
