The Electrophysiological Laboratory: Technologic Advances and Future Development

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Chapter 21 The Electrophysiological Laboratory

Technologic Advances and Future Development

Sabine Ernst

Introduction

Crossover or hybrid laboratories were common in the early days of invasive electrophysiology (EP), when the electrophysiological study (EPS) was performed late in the afternoon at the end of the coronary catheterization laboratory (cath lab) list. As the field of EP grew, more and more departments decided to equip dedicated EP labs that would be exclusively designed to support the special needs of an arrhythmia service. Because device implantation does not need any specific equipment besides a C-arm fluoroscopy, many large EP services have decided to transfer these procedures to a lesser specialized area, such as a hybrid operating room (which also meets the requirements for sterile implantation of devices).

Newly Designed or “Retrofit”?

Many considerations need to be taken into account when deciding to either design a state-of-the-art cath lab in a newly constructed area or renovating an older lab with up-to-date technologies (Figure 21-1). One of the biggest problems is having enough space to fit not only all the equipment necessary for the procedure (Figure 21-2) but also equipment needed only in an emergency. In addition, ample space for moving the patient into and out of the room via stretcher or patient bed and sufficient in-room storage are essential. Normal items such as telephone lines, a data point for the hospital information system (HIS), sufficient lighting, and easy access from the sink to the sterile field are involved as well. The placement of gases and suction outlets in the procedure room should also be given attention.

FIGURE 21-1 Retrofit of a conventional catheter laboratory. A, The old equipment is removed. B, The examination room’s walls are fitted with special shielding.

FIGURE 21-2 A, Ceiling-suspended racks allow plenty of storage for generators, patient interface units, and more equipment. Power outlets on top and electrical cabling through cabling tunnels inside the ceiling are seen. B, Rails along the ceiling allow for flexible solutions for monitors and racks as well as radiation protection shield and operation lamp.

Minimal Standards for Invasive Electrophysiology (“The Must Have”)

To visualize catheter positioning, a fluoroscopic imaging system with at least a single C-arm is necessary. The system should be programmable to a certain extent to control radiation exposure (Figure 21-3).¹ Because comparably less radiation exposure is needed to image the metal electrodes of a catheter compared with the resolution required for lesion assessment in coronary artery interventions, a special setting should be reserved for EP procedures. The C-arm should be rotatable by at least 90 degrees in both the right anterior oblique and the left anterior oblique positions, and cranial or caudal angulations are not often necessary. To reduce radiation exposure to the operator, proper Plexiglas lead protection, both “under the table” (closest position to the x-ray beam) and “over the table” against scattered radiation from the patient is a legal requirement. In addition, the image should, whenever possible, be centered on the chamber of interest and the table should be locked in the optimal position for all angulations to avoid unnecessary radiation exposure. Finally, collimation and “fencing in” of the lung fields should be routine, and any unnecessary metallic devices should be removed from the area to be imaged because they result in an automatic intensification of radiation exposure (e.g., transesophageal echocardiography probes should be removed from view). European laws require the documentation of both total exposure time and dosage of the overall deployed radiation. In regard to applied fluoroscopy, the ALARA (as low as reasonably achievable) principle should be followed, and unnecessary imaging should be avoided.¹ If available, the “last image hold” option should be used.²

FIGURE 21-3 A, Monitor gantry with six monitors arranged to allow the best orientation for the operator, with live monitors for fluoroscopy and intracardiac signals side by side. B, Controls of the fluoroscopy system (AXIOMS Artis; Siemens, Munich, Germany) positioned at the table side to allow rapid navigation through recorded scenes, again supporting single-operator functionality.

Electrophysiology Recording System (Including Intracardiac Pressure Recordings)

The minimal requirements for EP recording systems are fairly subjective. Although some operators work with only 32 channels, at least 64 channels seems to be the current standard. In addition to the standard display of the 12-lead electrocardiogram (ECG), bipolar and unipolar signals should be programmable.³ The gain applied to any given recording should be individually adjustable, and electrodes belonging to one catheter are usually grouped (e.g., by color). Although the order of the displayed signals is a question of personal preference and training, the signal accuracy is of utmost importance. Too large a noise level is unacceptable because it could mislead the operator during the mapping process. Signal quality during energy application also is important, and every effort should be made to achieve clean signals to allow drag lesions rather than sequential point-by-point applications. In addition to the electrical signals, the recording of at least one invasive pressure should be possible (e.g., for emergency percutaneous transluminal coronary angioplasty or hemodynamic monitoring).

Cardiac Stimulator

To allow diagnostic pacing maneuvers from various electrodes, a programmable cardiac stimulator is necessary. The properties and pacing output of these stimulators vary; however, the adjustable or programmable timing of the pacing impulses, the pacing output, and the pulse duration are crucial. Automatic sensing of the intrinsic rhythm on the selected pacing electrode allows assessment of the contact of the pacing electrode to the cardiac tissue.

Radiofrequency Generator

In most laboratories, unipolar radiofrequency (RF) current is the routine ablation energy for catheter ablation. Several devices are available, differing mostly in the ability to connect to accessories such as cool flow pumps or to integrate three-dimensional mapping systems. The operator should have the option to start and stop the energy delivery, such as by pressing a foot pedal, because catheter dislodgment is felt first through manual feedback. Any delay in stopping the energy delivery, such as that caused by a second person who has to hear and react appropriately to the operator’s verbal command to stop, may have detrimental effects (e.g., atrioventricular [AV] node block, “pop” formation).

Monitoring Unit for Vital Signs

Monitoring of the basic vital signs such as noninvasive blood pressure, heart rate, and oxygen saturation should be performed during every EP procedure, allowing instant reaction to changes in hemodynamics and safe monitoring of anesthesia.

Cardiac Defibrillator

Because fast arrhythmias may result in instant hemodynamic deterioration, rapid electrical defibrillation must be accessible at any time during EPS. A cardiac defibrillator should be at hand and turned on at the beginning of the procedure. The batteries should be routinely checked and the device tested for appropriate function on at least a weekly basis. The energy level should be adjustable and R-wave triggering possible in a stable arrhythmia; however, during ventricular fibrillation (VF), the R-wave trigger must be deactivated to avoid any delay in shock delivery. Nowadays, biphasic waveform shocks are the gold standard, with defibrillation energies of up to 360 J. The choice of patch versus direct paddle shock delivery is again a matter of debate; the first has the advantage of being fast with no impairment of the sterile field, whereas the paddles are less expensive.

Emergency Equipment

Ventilator

In case of the somewhat rare event of an emergency such as respiratory compromise of the patient, a portable ventilator system should be part of the crash cart in the EP lab. Logically, all necessary tools for intubation must be readily available, and training the staff for such scenarios should be performed regularly.

Anesthesia Equipment

In addition to the minimum crash cart equipment, some departments elect to have a complete anesthesia setup available in the EP lab to give optimal support. Children are investigated only under general anesthesia in some countries, whereas other countries allow a more liberal handling of patient sedation.

Equipment for Advanced Electrophysiology Labs

Although most simple EP substrates can be readily treated by using conventional two-dimensional fluoroscopy in conjunction with intracardiac signals, catheter ablation of complex arrhythmias such as ventricular tachycardia, incisional atrial tachycardia, or atrial fibrillation are facilitated by three-dimensional mapping systems. Following the cardiac activation across a complex three-dimensional geometry of a given cardiac chamber can be extremely helpful in performing confirmative diagnostic pacing maneuvers (e.g., entrainment in the critical isthmus of a re-entry). Because the ablation catheter usually is depicted in a real-time fashion, roaming inside the chamber of interest, three-dimensional movements are possible without controlling the movement with fluoroscopy. Although three-dimensional mapping systems should reduce overall fluoroscopy exposure, some investigators did not observe any change in their practice, whereas others relying completely on the real-time depiction of the mapping catheter demonstrated significant reductions after a learning curve.⁴^–⁶ For reduction of radiation exposure, however, the accuracy with which the catheter position is displayed is key. Two different systems have established themselves as routinely used three-dimensional tools in most cath labs performing advanced EP procedures.

NAVx and EnSite

The concept of the original LocaLisa system (now implemented in the NAVx system; St Jude Medical, St Paul, MN) is based on real-time display of all intracardiac electrodes using surface patches in all three spatial directions, which act like condensators.⁷ By emitting a small current between opposite patches, any interposed catheter changes the received current and thereby becomes locatable. After reconstruction of the geometry, sequentially acquired activation information can be superimposed on the three-dimensional shell to delineate the arrhythmia substrate.

The EnSite balloon (St Jude Medical) works on the same platform by using essentially the same patches and concepts.⁸ In addition to the sequentially acquired three-dimensional geometry, simultaneously acquired unipolar electrical information can be projected from the multi-electrode array using an inverse solution to the Laplace equation. This system has been reported to be of additional benefit, especially in transient and nontolerant arrhythmias.

Electroanatomic Magnetic System: CARTO

The CARTO system (Biosense Webster, Inc., Diamond Bar, CA) acts on a concept similar to that of a global positioning system, in which a small sensor on the tip of the ablation catheter is located in three different ultra-low-energy magnetic fields encoding the chest of the patient via electromagnets positioned below the patient table (so-called location pad).⁹ Through visual display of sequentially acquired sites (and their corresponding electrical information, e.g., voltage amplitude or activation time), a color-coded map is created. Because the mapping electrode is displayed in real time, nonfluoroscopic mapping ideally is enabled, but in clinical practice some fluoroscopy is still required.

Image Integration

Currently, all three-dimensional mapping systems are able to integrate previously acquired three-dimensional DICOM-standard (Digital Imaging and Communications in Medicine) information derived from either computed tomography or cardiac magnetic resonance imaging scans.¹⁰^–¹¹ However, accurate merging requires careful registration (e.g., to contrast injection or distinct anatomic landmarks) to obtain optimal results without the operator being misled. Knowing the targeted chamber ahead of time may lower overall radiation exposure and allows specific planning of the procedure (e.g., larger catheter curves in cases of enlarged cardiac chambers). The display of the acquired three-dimensional map on top of the fluoroscopy reference pictures allows even better orientation during the case.

Alternative Ablation Energy Sources

As an alternative to the commonly used RF current, other ablation sources such as cryothermia techniques have been introduced in recent years.¹² Besides balloon devices for pulmonary vein isolation, some operators choose cryothermia for anteroseptal accessory pathways to use the transient freezing option (approximately –10° C), so-called cryo-mapping, in selected cases.¹³

Further alternative energy sources are laser energy, microwave, and ultrasound energy, modalities mostly reserved for study protocols at this time.¹⁴

Advanced Technologies in the Electrophysiology Lab

Remote Navigation

Remote navigation is the umbrella term for two recently introduced technologies. By using computerized workstations from within the control room, investigators are no longer exposed to scattered radiation (Figure 21-4).

FIGURE 21-4 View of the control area of a catheter laboratory using remote control by magnetic navigation (at St. Georg Hospital, Hamburg, Germany). The monitors are arranged as in a cockpit, allowing a single operator to lead the investigation. Fluoro, Fluoroscopy system; STIM, cardiac stimulator; EP, electrophysiology recording system; 3D, three-dimensional; CT, computed tomography; MRI, magnetic resonance imaging.

Two remote catheter navigation systems have been introduced into clinical practice, both enabling remote control of the ablation catheter.¹^–³ One is based on an electromechanical concept in which two steerable sheaths guide a conventional catheter; the other is based on a steerable, permanent magnetic field in which a magnetically equipped catheter must be aligned in a parallel position (Figure 21-5).