Antonioli E G, Baggioni F G, Grassi G
G Ital Cardiol. 1980;10(5):536-53.
Small surface area electrodes are accused of sensing defects which were related to alterations that they induce in the endocardiac electrograms. Since several factors affect the cardiac signal coming from electrode to sensing circuit, i.e. electrode surface area, electrode-tissue interface, pacemaker input impedance and sensing amplifier pass-band, Authors present their studies performed on 252 implanted electrodes of various type. Study was carried out by connecting in parallel to the recorder a variable resistor in order to simulate different pacer input impedances. The results showed a significant reduction in RS amplitude when recorder was paralleled with resistor values lower than 40 K. Slew rates showed a similar behaviours since RS steep tract did not change his duration with load, while total QRS duration is reduced. High speed analysis has shown that the RS segment is not linear in about 40% of cases: the main tract is used for calculations. The most significant attenuations and distortions of endocardial electrogram were observed with smallest electrodes and lowest resistances parallel connected: in these cases the sensing impedance at the electrode-tissue interface appears to be between 3 to 5 K ohms. The results suggest that the most of the alledged sensing faults experienced in the past were probably due to small tip electrodes connected to low input impedance generators or to impending failure situations. The AA. conclude that the main question does not concerne a true electrode inefficiency but a wrongly chosen pacemaker-electrode combination, i.e. small tip electrode connected with old generator models. To avoid the evaluation error, it would be instrumental that the pacemaker manufacturers would specify input characteristics of their generators. So, the implanting clinician becomes able to exactly evaluate the true signal arriving to the sensing circuit by connecting in parallel with the recorder input a resistor whose value approximates the input resistance of the generator to be implanted.
小表面积电极被指责会检测到与它们在心内膜电图中引起的改变相关的缺陷。由于有几个因素会影响从电极到传感电路的心脏信号，即电极表面积、电极 - 组织界面、起搏器输入阻抗和传感放大器通带，作者展示了他们对252个不同类型植入电极进行的研究。研究是通过将一个可变电阻与记录器并联来进行的，以模拟不同的起搏器输入阻抗。结果表明，当记录器与阻值低于40K的电阻并联时，RS波幅会显著降低。转换速率表现出类似的行为，因为RS陡峭段的持续时间不会随负载而改变，而总QRS持续时间会缩短。高速分析表明，在约40%的情况下，RS段不是线性的：主要部分用于计算。在心内膜电图中，观察到的最显著的衰减和失真出现在最小的电极和并联连接的最低电阻情况下：在这些情况下，电极 - 组织界面处的传感阻抗似乎在3至5千欧姆之间。结果表明，过去经历的大多数所谓的传感故障可能是由于连接到低输入阻抗发生器的小尖端电极或即将出现故障的情况。作者得出结论，主要问题不在于电极本身效率低下，而在于起搏器 - 电极组合选择错误，即小尖端电极与旧型号发生器相连。为避免评估误差，起搏器制造商明确其发生器的输入特性将很有帮助。这样，植入临床医生通过将一个阻值近似于待植入发生器输入电阻的电阻与记录器输入并联，就能准确评估到达传感电路的真实信号。
