Bipolar leads

The conventional limb leads record potentials between two apices of the triangle. Lead 1 records potentials between the right arm and left arm, lead 2 records potentials between the right arm and left leg and lead 3 records potentials between the left arm and left leg. These are known as bipolar leads. In addition there are three unipolar leads attached to the limbs, which record potentials between the limb and a reference zero. 

The reactor is an undivided reactor with flat parallel bipolar lead electrodes [100] (Fig. 15). 

Bipolar Lead Acid Battery, Jet Propulsion Laboratory Review (July 1980). 

Magneli phase TiO (x = 1.67 to 1.9) is conductive. A proprietary material of this composition in the form of solid sheets or a honeycomb has been patented for use as current-collectors in either monopolar or bipolar lead-acid batteries [15]. The honeycombed structure holds the paste and thereby improves paste adhesion and the mechanical stability of the plate, as well as the electrical conductivity. The material is stable at the potentials of the positive plate [16,17]. 

Transvenous lead polarity simply indicates the number of electrodes in contact with the heart. A unipolar lead has only one electrode, the cathode, on his tip. In this configuration, the PM case serves as the anode of the circuit (Fig. 1.1). A bipolar lead has two electrodes at the distal end separated by a short distance. The tip electrode is the cathode, and the proximal ring electrode serves as the anode (Fig. 1.2). In this configuration, the PM case is not involved in the electrical circuit. The distance between tip and ring electrode varies with manufacturer and design. 

Unipolar leads obviously have only one conductor coil, whereas bipolar leads require two -one for the proximal and the other for the tip electrode. Bipolar leads may have a coaxial, a co-radi-al or parallel wound, and a parallel or multiluminal design. Coaxial bipolar leads, standard in treating... 

Insulation is a nonconducting material that prevents electrical current from leaving the lead and entering the surrounding tissue. Usually, lead insulation extends from the lead connector to the cathode tip and, in bipolar leads, is interrupted by the anode ring. Insulation also prevents tissue stimulation, except at the electrode-myocardial interface, and protects the conductor from corrosion due to body fluids and exposure to tissue. 

The connector electrically binds the lead to the PM. Many types of connectors have been developed in the past, and this created considerable confusion among physicians and, in some cases, a potential hazard to the patient. Historically, unipolar leads were 5 or 6 mm in diameter, and bipolar leads required a bifurcated design with similar 5- or 6-mm sizes. Only after some years a bipolar, in-line design with a 3.2-mm diameter was developed. 

Fig. 5.1 Pacemaker patient, anteroposterior chest X-ray. Two functional bipolar leads (atrial and ventricular) are connected to a device housed in a lower left subclavicular region there are also two abandoned, nonfunctional bipolar leads (both in the right ventricle). Note the three anatomically crucial lead extraction points A, the subclavicular region where the leads lie between the clavicle and the first rib B, the innominate-superior vena cava junction, noting lead angle at that level C, lead-tip position in the right ventricle...

The behavior of an electrode pair depends on the application, is it to be CC or is it to be potential reading (PU) with negligible current flow If it is a PU pair the skin contact area is less important, but the skin site may be very important. If bofli electrodes are on skin sites that are under the same nervous control (same dermatome), the potential difference will be small or negligible and with no signal the bipolar lead is useless. But if one of the electrodes are on an indifferent (passive) skin site the signal may be large, the lead is monopolar and useful. 

A bipolar PU electrode pair lead measures the local potential difference and is therefore actually also an electric field strength [V/m] probe. If the conductivity is known, it is also a current density probe since J = aE. Because the electric field is a vector field and the bipolar lead has an orientation being the length Lpu between the PU electrodes, the measured voltage is the dot product v = E-Lp = J-Lpu/ct- The larger the electrode area,... 

An electrode pair and their two wires are called a bipolar lead. A unipolar/monopolar lead is with one PU and an indifferent electrode or a wire from Wilson s terminal. A lead may be defined physically as two signal wires with an associated recording electrode system. 

The position of the electrodes on each limb is uncritical because the distal part of each limb is isoelectric (with respect to ECG, not with respect to, for example, electromyography (EMG) sources of the arm muscles). Such is the reproducibility that the bipolar leads form the basis for determining tbe axis of the electric heart vector. 

Einthoven (1913) proposed an equilateral triangle model with the center in the heart center. Figure 10.5. Each side of the triangle corresponded to each of the three bipolar leads I, II, and III. He proposed the heart modeled as a bound dipole vector (he did not use that expression), and that a lead voltage was the projection of the heart vector on a corresponding triangle side (actually a dot product). He proposed that his model could... 

The typical EGG signal from stomach activity is recorded with a bipolar lead using a pair of standard ECG electrodes on the skin (e.g., 4 cm apart). The signal is typically of about 100 pV amplitude, and periodic with a period of about 20 s (0.05 Hz fundamental). Best position for the EGG electrodes is along the projection of the stomach axis on the abdomen. 

The depolarization shock can be delivered flirough either a unipolar or bipolar lead. Most older leads utilize the unipolar design (Morley-Davies and Cobbe, et al., 1997), in which a single insulated electrode is placed near the myocardium of the heart and acts as a cathode (Tyers et al., 1997 ... 

Tyers, G. F. O., Mills, P., Clark, J., Cheesman, M., Yeung-Lai-Wah, J. A., and Brownlee, R. R., Bipolar leads for use with permanently implantable cardiac pacing systems A review of limitations of traditional and coaxial configurations and the development and testing of new conductor, insulation and electrode designs, /. Invest. Surg., 1997 10(1-2) 1-15. 

High battery voltages and power capacities in a small footprint will also be needed to power equipment in off-grid applications. Bipolar lead-acid batteries are... 

Bullock KR (1995) Progress and challenges in bipolar lead-acid battery development. J Electrochem Soc 142 1726-1731... 

Fig. U Schematic of a bipolar lead illustrating the factors involved in determining system impedance. The arrows denote current flow. Resistance to current flow occurs at the lead conductor (conductor resistance), at the cathode-tissue interface (cathode impedance and polarization), in the myocardium (tissue impedance) and at the anode (anode impedance). The largest contributors to system impedance are the cathode impedance and polarization effects.

Fig. 1.6 Diagram demonstrating differences between unipolar and bipolar lead systems. Note the bipolar lead has both poles anode and cathode on the lead, whereas the unipolar lead has only the cathode. The anode lies on the can of the pulse generator.

Size. The original bipolar lead designs had two parallel conductors individually encased in a stiff, dual-lumen insulated tube and a very bulky bifurcated connector. They were difficult to implant compared to unipolar models. In comparison modem bipolar pacing leads are as thin as their unipolar counterparts and thus size is no longer an issue. 

Right ventricular perforation. Because of their stiffness, certain models of bipolar leads, particularly those insulated with polyurethane, were more prone to right ventricular perforation. The stiff distal end of the lead may damage the endomyocardium and in some cases result in ventricular penetration and perforation (6). Such stiff bipolar leads are no longer available and today there is very little difference in the stiffness between unipolar and bipolar leads. 

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