Electrode catheters
Basic mapping catheters
Catheters used for electrophysiology studies (EPSs) and ablation are composed of multiple insulated wires encased in woven Dacron or polyurethane. Electrodes used in electrophysiology (EP) catheters are usually made of polished platinum-iridium alloy. Platinum is an inert and biologically safe metal with excellent electrical properties but is mechanically soft. The addition of iridium improves mechanical strength without affecting electrical performance. Electrode catheters are typically available in 3 to 8 French (F) diameters and 110 to 120 cm long. Usually 6F quadripolar, hexapolar, or decapolar deflectable catheters composed of 2 mm long electrodes (with a distal tip of 1 or 2 mm) separated by 5-mm distances are used for conventional EPS in adults ( Fig. 5.1 ). Deflectable catheters can be deflected in one or two directions (bidirectional) in the same plane. Smaller electrodes and narrow interelectrode distances (≤1 mm) may be needed for studying complex arrhythmias or multicomponent electrograms.
Advanced mapping catheters
The Halo XP is a 7F catheter that has been designed for electrophysiologic mapping of the tricuspid annulus during atrial flutter ablation procedures. The catheter has a high torque shaft with a halo-shaped tip section containing 10 pairs of platinum electrodes with a 2-18-2-8-2 mm arrangement (see Fig. 5.1 ). The Lasso 7F catheter is designed to record pulmonary vein potentials during AF ablation procedures. A similar design is the Inquiry AFocus II catheter. It uses 20 small 1-mm electrodes for high-resolution mapping. The PentaRay is a 7F catheter with 5 soft, flexible 3F branches and 22 electrodes (1 mm long) in a 4-4-4 mm arrangement that allow higher mapping resolution.
Multipolar recording catheters have become the norm for electroanatomic mapping, and there have been multiple alternative mapping systems that have seen variable success. The EnSite Array catheter has 64 non-contact electrodes formed by breaks in the insulation of braided wires forming a woven basket around a saline-filled balloon. The Advisor HD Grid is a steerable mapping catheter with a grid-patterned configuration of 16 electrodes for faster data collection. It is used with the EnSite Precision mapping system. The IntellaMap Orion mapping catheter is a basketlike catheter designed for use with the Rhythmia mapping system. It offers higher resolution because of its 64-electrode structure. Other basket-like catheters, such as the Constellation, and the TOPERA, are also available. The AcQMap, a non-contact catheter using ultrasound-based technology to localise the catheter and produce the cardiac anatomy whilst recording charge instead of bipolar electrograms, is in an investigational stage at present. All these catheters are connected to the recording/ablation unit via cables specific to the configuration of the catheter.
Sheaths
Usually, ordinary sheaths are used for catheter insertion through the femoral veins. Long sheaths (63 cm) may be needed to gain access and attain stability in specific sites within the heart, such as for transseptal access to the left atrium or for positioning of the ablation catheters in the right free wall aspect of the tricuspid annulus. Some operators use two long sheaths in the left atrium for radiofrequency (RF) ablation of atrial fibrillation. A deflectable long sheath (Agilis Systems, Chesterfield, MO, USA) may be helpful for positioning and maintaining stability of ablation catheters.
Electrogram recording and processing
The hardware of the EP laboratory, apart from the catheters and connecting cables, consists of the recording and processing EP unit, a stimulator for programmed stimulation, the RF or other energy source generators, and low-resistance grounding patches connecting the RF generator to the patient.
Intracardiac electrograms need to be amplified and displayed in an environment of appropriate grounding and isolation to minimize interference offering a signal-to-noise factor of 20 decibels or more. Acquired signals are subjected to filtering that enhances parts of the frequency spectrum and rejects noise. With multiple devices connected, there is a leakage current flowing through the patient at a fundamental frequency of approximately 50 Hz that can produce artifacts on intracardiac signals. Wireless monitors near the laboratory and mobile phones exacerbate these artifacts. Thus the amplifiers used for recording intracardiac potentials apart from gain modification must have high- and low-band pass filters to permit appropriate attenuation of the incoming signals. Modern electronic systems allow a wide range of filtering, but most intracardiac recordings are clearly defined with filtering between 30 and 50 Hz for high pass and 400 and 500 Hz for low pass.
Recorded signals in the EP laboratory are usually bipolar because they are measured as a voltage difference between two electrodes. With the use of a 10-mm interelectrode distance, the normal left ventricular bipolar electrograms have an amplitude of 3 to 10 mV, with a duration of less than 70 ms. However, these amplitudes depend on electrode size and spacing ( Fig. 5.2 ). Standard linear ablation catheters have a 3.5-mm distal electrode separated by 1 mm from a proximal 1-mm electrode, resulting in a center-to-center interelectrode spacing of 3.25 mm. As such, each bipolar electrogram represents an underlying tissue diameter ranging from 3.5 to 5.5 mm, depending on the angle of incidence (from perpendicular to parallel to the tissue, respectively). This sampling resolution is often insufficient for identifying and selectively pacing channels of surviving myocardial bundles embedded in surrounding scar tissue. Thus, bipolar voltage amplitude depends on several factors such as the electrode size and the interelectrode distance, conduction velocity between the bipolar electrodes, and the wavefront of activation ( Fig. 5.3 ). The use of multielectrode mapping catheters with smaller electrode and interelectrode spacing can increase the resolution of mapping, enhancing identification of surviving channels and macro–re-entrant circuits.
