Pacing anodal

The latter authors used anode and cathode symmetrical cells in EIS analysis in order to simplify the complication that often arises from asymmetrical half-cells so that the contributions from anode/ electrolyte and cathode/electrolyte interfaces could be isolated, and consequently, the temperature-dependences of these components could be established. This is an extension of their earlier work, in which the overall impedances of full lithium ion cells were studied and Ret was identified as the controlling factor. As Figure 68 shows, for each of the two interfaces, Ra dominates the overall impedance in the symmetrical cells as in a full lithium ion cell, indicating that, even at room temperature, the electrodic reaction kinetics at both the cathode and anode surfaces dictate the overall lithium ion chemistry. At lower temperature, this determining role of Ra becomes more pronounced, as Figure 69c shows, in which relative resistance , defined as the ratio of a certain resistance at a specific temperature to that at 20 °C, is used to compare the temperature-dependences of bulk resistance (i b), surface layer resistance Rsi), and i ct- For the convenience of comparison, the temperature-dependence of the ion conductivity measured for the bulk electrolyte is also included in Figure 69 as a benchmark. Apparently, both and Rsi vary with temperature at a similar pace to what ion conductivity adopts, as expected, but a significant deviation was observed in the temperature dependence of R below —10 °C. Thus, one... 

Variations in cathodic peak current with the square of the sweep rate [/p,.. = /(v -)] for. selected PACE/electrolyte systems are shown in Figs. 13a and 13b [194]. In all ca.ses the relation is linear and the correlation coefficient tends to unity, especially in the lower ranges of the potential sweep rates. In agreement with numerous researchers [7,9,14,16,24,26,132], we also suggest that the cathodic peak is due to the reduction of quinonelike groups, whereas the anodic wave is due to the oxidation of hydroquinonelike groups in different environments on the active carbon surface of the electrode. These reactions are faradic... 

Activation polarization is because of a rate-controlling step within the corrosion reaction(s) at either the cathode or anode sites. An example of this can be seen with the H /H2 conversion reaction. The first step of this process, 2H+ + 2e 2H, takes place at a rapid pace. The second part of this reaction, 2H H2, occurs more slowly and can become a rate-controlling factor. 

As with pacing leads, the ICD lead cathode is a platinum, iridium, and titanium combination the electrode structure depends on whether fixation mechanism is passive with tines or active with a screw. In an active-fixation lead, the platinum-iridium screw is usually electrically active, but there are also models with both electrically active collar and helix or others with electrically silent helix and active carbon cathode collar. A platinum-iridium anode lies immediately behind the cathode in a true bipolar system. All models now elute steroids to reduce chronic threshold and prevent pacing threshold rise or exit block. 

Early pacing leads were either nnipolar or bipolar. A bipolar epicardial or epimyocardial system required two leads whereas, a bipolar transvenous system could be achieved using a single lead composed of two parallel insnlation tnbes containing the anode and cathode conductors. By the late... 

Whenever electricity flows across a circuit, there is a resistance to flow encountered by the electrons. For pacing systems, the resistance is determined by the complex interaction of multiple components. Because some of these components are also characterized by the ability to retain charge or capacitance, the term impedance is preferred. At the time of lead implantation, it is this complicated series of resistance and capacitance factors that are measured and are referred to as system impedance. For a pacing circuit, the system impedance has five basic components a low, purely resistive conductor impedance, a high cathode electrode impedance, complex polarization effects at the electrode-tissue interface, a low tissue impedance, and the anode electrode impedance (Fig. 1.3). 

Fig. 1.24 Two designs of pacing leads using cabled conductors. Above A traditional multifilar coiled conductor for stylet delivery lies parallel to a cabled conductor. The lead is slightly oval (Medtronic 5044. Never marketed). Below. Coaxial design (Medtronic 3830 SelectSecure ). The cathode cable lies at the center of the lead and is then covered with a protective cover (ETFE) and over that a conventional silicone insulator. It is then surrounded with a polyurethane insulated multifilar coiled anode conductor. There is no lumen for a stylet. (Permission for use Medtronic.)...

Proper electrode placement is the single most important fector for determining whether transcutaneous pacing will be effective. The proper position of the cathode (negative) electrode is directly over the cardiac apex or over the position of ECG chest leads V3 (Fig. 7.1). The anode (positive) electrode is placed either posteriorly (recommended) on the back between the spine and the lower half of the left or right scapulae, or, alternatively, if the back is inaccessible, over the right upper chest centered approximately 6-10 cm above the... 

Fig. 7.1 Correct position of transcutaneous pacing electrodes. Top Anteroposterior positioning with the cathode (circle) over the cardiac apex and the anode (rectangle) in the back between the spine and the right scapula (the space between the spine and left scapula can also be used). Bottom Anterior-anterior position with the cathode over the cardiac apex and the anode on the right chest.

---