2019 APHRS expert consensus statement on three-dimensional mapping systems for tachycardia developed in collaboration with HRS, EHRA, and LAHRS.

Abstract

This document describes the use of three-dimensional mapping systems and includes recommendations regarding their application in clinical practice based on scientific evidence. Nevertheless, it should be kept in mind that these systems are associated with increased costs. Consequently, their availability as well as reimbursement practice varies widely across different countries largely depending on the economic situation. The societies involved in the development of this document recognize the existence of these factors and the significant barriers that these may pose in everyday practice and on the decision to use or not use a three-dimensional mapping system in a given patient. Thus, in cases where these useful systems are not available or cannot be used in a wide scale due to financial constraints, electrophysiology procedures should certainly be offered to the patients based on established indications. Profound knowledge and experience may compensate lack of advanced technical equipment and prove in the majority of cases sufficient for successful conduction even of complex ablation procedures. Catheter mapping and ablation are widely performed for various complex tachyarrhythmias that need a better understanding of fundamental technologies of mapping to identify triggers or substrate of arrhythmias. The mapping of arrhythmias used to be performed using multipolar electrode catheters, fluoroscopy to localize the anatomic catheter position within the cardiac chamber, and interpretation of recorded intracardiac electrograms to localize the origin of a focal arrhythmia or critical parts of a tachycardia circuit. The general principles, rationale, and working of the various mapping systems have been well described before.1-3 The introduction of the three-dimensional (3D) electroanatomical mapping systems greatly facilitated ablation procedures. Three-dimensional mapping systems are categorized as magnetic-based vs. impedance-based according to the catheter location technology, and are also classified as contact based vs. noncontact based according to the data collection technology. During mapping, the electrogram obtained at a certain site is stored and the activation time is defined as compared with a selected electric signal reference. By projecting the activation time compared with a signal reference on the 3D geometry point-by-point, the system allows intuitive review of the activation mode of the whole chamber through the various isochrones in a 3D fashion. In addition to the activation map, 3D mapping displays the voltage of the recorded electrograms, low voltage or scar region defined by voltage map is known to be correlated with the arrhythmogenic substrate. The 3D map can be integrated with imaging modalities such as magnetic resonance imaging (MRI), computed tomography (CT), and intracardiac echocardiography (ICE) for more accurate and vivid anatomic descriptions. The 3D mapping system does not always accurately represent the mechanism of the tachycardia. The interpretation of the map could lead to a false diagnosis, which may in turn result in an unsuccessful outcome. Good catheter contact, correct interpretation of the colors in the map, appropriate choice of reference electrogram, complete mapping of the correct chamber of interest, and strategies to address catheter tip migration with respiration or change in cardiac rhythm and annotation of complex intracardiac signals are all necessary prerequisites for the success of ablation.4-7 The purpose of this expert consensus statement is to provide a state-of-the-art review of currently available 3D mapping systems in the field of cardiac tachyarrhythmias. Representatives nominated by the Heart Rhythm Society (HRS), European Heart Rhythm Association (EHRA), Asian Pacific Heart Rhythm Society (APHRS), and the Latin American Heart Rhythm Society (LAHRS) participated in the project definition, literature review, recommendation development, writing of the document, and its approval. The classification of the recommendations and the level of evidence follow the recently updated ACC/AHA standard. Class I is a strong recommendation, denoting a benefit greatly exceeding risk. Class IIa is a somewhat weaker recommendation, with a benefit probably exceeding risk, and Class IIb denotes a benefit equivalent to or possibly exceeding risk. Class III is a recommendation against a specific treatment because either there is no net benefit or there is net harm. Level of evidence A denotes the highest level of evidence from more than one high-quality randomized clinical trial (RCT), a meta-analysis of high-quality RCTs, or RCTs corroborated by high-quality registry studies. Level of evidence B indicates moderate-quality evidence from either RCTs with a meta-analysis (B-R) or well-executed nonrandomized trials with a meta-analysis (B-NR). Level of evidence C indicates randomized or nonrandomized observational or registry studies with limited data (C-LD) or from expert opinions (C-EO) based on clinical experience in the absence of credible published evidence. Each society officially reviewed, commented, edited, and endorsed the final document and recommendations. Cardiac mapping is the registration of the spatial distribution of cardiac functional characteristics, typically of localized electrical potentials. The development and availability of accurate 3D localization technology has made this an important part of routine clinical cardiac electrophysiologic care, most frequently by permitting the visualization and ready comprehension of intracardiac activation sequences and contact electrogram characteristics. Electrodes in contact with functioning cardiac tissue can accurately identify local activation and its timing relative to a reference.8 This concept was exploited initially for surgical therapy for Wolff-Parkinson-White syndrome9 and subsequently for endocardial mapping using catheters and fluoroscopy.10 The development of nonfluoroscopic catheter localization technology with computerized graphic representation of electrophysiologic phenomena in a spatially accurate geometry11 led to the advent of catheter mapping and ablation of complex arrhythmias. Activation of cardiac tissue in contact with a unipolar electrode generates the steepest negative slope of the associated electrogram (intrinsic deflection), while for bipolar electrodes local activation is mostly estimated to be at the time of the first sharp peak.12 Activation mapping can be achieved by combining the known location of a roving mapping catheter with the activation time of tissue with which it is in contact. In a stable cardiac rhythm, this permits the point-by-point construction of a 3D map of propagation of activation across a cardiac surface. This is typically graphically represented as a static color-coded map of local activation time, or as a video portrayal of a moving wavefront of activation (Figure 2-1). A detailed activation map gives useful information that can clarify the mechanism of arrhythmia. Focal arrhythmias will demonstrate centrifugal spread from a site of earliest activation from which the arrhythmia arises.13, 14 Macroreentrant arrhythmias are characterized by propagation around anatomic barriers or scar, with demonstration of the full cycle length within the circuit.15, 16 The addition of functional mapping maneuvers such as entrainment may help distinguish focal arrhythmias from microreentrant circuits or from circuits with unmappable portions (eg, deep/epicardial), each of which might result in centrifugal spread along the endocardial surface. Careful attention is required to construct an accurate contact map of cardiac activation. Two assumptions are made during point-by-point activation mapping, namely: (a) Local activation time can be accurately assessed; (b) Location of the mapping electrode is known. Further assumptions are typically made in order to interpret the map: (a) Activation on the cardiac surface also reflects the electrophysiological property of underlying tissue; (b) The entire cardiac surface/chamber is comprehensively mapped; (c) Activation propagates predictably and homogeneously; (d) The mapped rhythm is stable and repetitive; (e) Cycle length matches activation time of a given chamber. Each of these assumptions may be incorrect and may impact map interpretation (Table 2-1). Bipolar recordings reflect differential electrical potential between two closely spaced electrodes, and will thus be minimally impacted by far-field signals, which would typically result in similar influences on both electrodes, and thus would fail to contribute to the potential difference between them. Local activation has been variously defined for bipolar electrograms, since electrode orientation and wavefront direction influence signal morphology, but perhaps most commonly as the first maximum or minimum signal.17 Smaller and more closely spaced electrodes will have lesser far-field contributions, and can be combined in multielectrode arrays to rapidly and accurately map activation. The contribution of known interelectrode spacing may also reduce the potential for mapping errors due to insufficient spatial localization accuracy, and can permit very high-density rapid activation mapping with the addition of automated determination of activation time.18-20 Nonetheless, even ultrahigh-density mapping may encounter challenges with accurately annotating activation time (eg, when a very long-fragmented electrogram is observed in a very small area) and distinguishing reentry from passive activation around conduction barriers or even noise.21 Modern 3D mapping systems achieve high localization accuracy, in most cases using a combination of magnetic field sensors and impedance ranging.22 These measures may be augmented by additional sensors which attempt to confirm tissue contact.23, 24 Furthermore, utilization of catheters with known fixed interelectrode distances may improve the assessment of local activation sequence. Tissue heterogeneity may pose additional challenges to interpretation of 3D contact maps. Detailed correlative studies between cardiac MRI and electrogram characteristics have demonstrated that the myocardium may have 11%-63% scar transmurality beneath an endocardial rim of 2 mm of viable tissue and yet have a bipolar signal amplitude which exceeds 1.5 mV.25 Assessment of deeper tissue characteristics may be enhanced with the addition of unipolar signal amplitude.26 Epicardial,27 intramyocardial,28 and ECG imaging29 recordings have demonstrated the potential 3D complexity of reentry circuits, which may pass deep to endocardial contact catheters. In most cases, cardiac arrhythmias are mapped with the goal of designing an ablation strategy. For focal arrhythmias, this typically requires only focal activation mapping surrounding the site of earliest activation, while for reentrant arrhythmias the strategy must be individualized to the culprit anatomic/functional substrate. Complex atrial arrhythmias may require a comprehensive map in order to fully understand the reentrant circuit and to design an effective strategy to interrupt it with ablation, or identify a common vulnerable isthmus.30 Interpretation of the map requires careful identification of activation sequence, and when complex electrograms are observed, careful annotation of fragmented signals (usually indicative of slow conduction) and of double potentials (usually indicative of activation of closely apposed tissues on either side of a line of block) are required.6, 31, 32 When double potentials are observed, one useful strategy to accurately create an activation map is to annotate their presence on the map, interpreting it as a site of block, and to assign activation times on either side of the site of double potentials to the potential which has timing contiguous with surrounding tissue timing farther away from the line. Activation mapping can be usefully augmented with the use of functional testing, such as entrainment mapping to distinguish portions of activation which are passive and those which are critical to a reentrant circuit,33 or the use of pacing to identify the presence of unexcitable scar.34 3D mapping systems have the potential to portray any value on an anatomic map. There are several useful variations of the most frequently used activation and signal amplitude (voltage) maps. Usual activation maps utilize a continuous scale color gradient; it may be helpful to display the colors as a series of isochrones. Although this is a simplified display of the same information, crowding of isochrones can make zones of slowed conduction more obvious.35 The same information can alternatively be displayed in video format as a propagation map to aid comprehension of the activation sequence in the patient-specific anatomy and arrhythmic substrate.19 Entrainment mapping can be used to provide additional information to an activation map of a cardiac arrhythmia, including ventricular36 and atrial arrhythmias.37 The response to entrainment can establish the proximity of the pacing site to the critical elements of a reentrant circuit. This maneuver is typically used to supplement activation mapping and other mapping strategies rather than to supply values to color code on a 3D map.38 The utility of ablation of sites with complex fractionated atrial electrograms for the treatment of atrial fibrillation has remained a topic of active research.39, 40 Electroanatomic maps may be used to portray tachycardia cycle length, dominant frequency or phase mapping or other indices of fractionation to serve as targets for ablation, although the optimal clinical place of these approaches remains uncertain.41-43 Ablation of sites with abnormal electrograms within the ventricle has been advanced as a useful strategy for the ablation of scar-related ventricular tachycardia.44 Automated identification of arrhythmogenic substrate has included mapping of signal amplitude45 and manual inspection of maps to identify sites of latest ventricular activation,35 or of myocardial bundles surrounded by denser scar based on signal amplitude46 or response to pacing.34, 47-50 A newer technique, known as ripple mapping, retains the complexity of recorded signals and graphically portrays local signal amplitude over time in animated images.51 Rather than simplifying signals into a single activation time, or peak amplitude, this method permits visual analysis of the entire signal and can display conducting channels displayed within scars.52 Pace- mapping has been used for decades as a method to map sources of ventricular activation. The similarity of surface electrocardiography between paced beat and spontaneous ventricular ectopy suggest that catheter tip is near the origin of ventricular ectopy. Quantitative comparison of paced beat and spontaneous ventricular ectopy can assist catheter ablation.53, 54 The investigation and localization of complex arrhythmias with fluoroscopy is inaccurate, burdensome, and associated with a high-radiation exposure for the patient and operator. The 3D mapping systems have been introduced into clinical electrophysiology over the decades. On top of the anatomical information, they can nonfluoroscopically provide the precise geometry of any chamber of the heart, movement and position of the catheters, and electrical activation sequences and voltage of tissues. The 3D mapping system helps to interpret the mechanism of complex arrhythmias and targets the ablation site in an effective and safe manner. The commonly used 3D mapping systems are the CARTO 3 (Biosense Webster) and EnSite Precision (Abbott). The Rhythmia system (Boston Scientific) has recently been launched and has played an important role in initiating high-density mapping of complex arrhythmias. The fundamental principle of the three systems will be compared in detail. The system consists of a location pad with three separate low-level magnetic field emitting coils (5 × 10−6 to 5 × 10−5 tesla) arranged as a triangle under the patient and six electrode patches positioned on the patient's back and chest (Figure 3-1). The latest version is based on a hybrid of magnetic and current-based localization technologies with an accuracy of less than 1mm. Three magnetic field emitters generate three different low-intensity magnetic fields. The magnetic field strength from each coil is detected by a location sensor embedded at the tip of a specialized mapping catheter. The strength of each coil's magnetic field measured by the location sensor is inversely proportional to the distance between the sensor and coil. Hence, by integrating each coil's field strength and converting this measurement into a distance, the location of the catheter tip can be displayed in a 3D geometry of the heart chamber.55, 56 Additionally, the CARTO system sends a small current across the catheter electrode and collects the current-based information, which is used for an adjustment with the magnetic-based data. Each electrode emits current at its own frequency. A current ratio is created by the measurement of the current strength at each patch and stored by the system. The current data from the six electrode patches make the various catheter electrodes visible in the system.22, 57 Visualization of the catheters is confined to a 3D virtual area called the "matrix," which can be built only by a mapping catheter with a magnetic sensor.58 The catheter position can be affected by the artifact caused by respirations, patient movement, cardiac contractions, and system movement. Three back patches are used along with the location pad for an anatomical reference, which allows the system to measure the catheter location relative to this anatomical reference for the compensation of patient and system movements. The six patches have magnetic sensors for the localization of the catheters, and the impedance changes detected by the back and chest patches are mainly used for compensation of the respiratory motion. The AccuRESP module supports the compensation of the respiratory artifact by monitoring the respiratory movement of the sensor-based catheter and interpatch currents. For the artifact from cardiac contractions, the system uses an electrical reference to match the catheter location with the time in a cardiac cycle. There are two different modes to show the mapping catheter: stable mode and gated mode. The gated mode locates the mapping catheter at the end of diastole of the electrical reference chamber. The stable mode locates the mapping catheter at the average location of 60 samples per one second; hence, the motion of the mapping catheter is smooth and stable. The stable mode is used in the most recent module and software including the Fast Anatomical Mapping (FAM), Visitag, Time force integral, ablation index, etc The EnSite system consists of a set of three pairs of skin patches and a system reference patch. This system is based on impedance-based localization and tracking technologies. The six patches are placed on the skin of the patient to create electrical fields along three orthogonal axes. The patches are placed on both sides of the patient (x-axis), the chest and back of the patient (y-axis), and the back of the neck and inner left thigh (z-axis). The three-paired patches are used to send low-power currents of 350 mA at a frequency of 8 kHz to form a 3D electrical field with the heart at the center. The electrical current transmitted between the patches through the thorax will cause a drop in the voltage across the heart. Intracardiac catheters are equipped with sensing electrodes. The electrodes on the catheters read the relative voltages with respect to a reference electrode. The position of the electrode is identified upon an analysis of the voltages.59 The 3D localization of the catheters is calculated based on an impedance gradient in relation to a reference electrode. However, the catheter locations are often distorted by a nonlinear impedance of the human body. A process called "field-scaling" may correct that to some extent and adjusts for the nonlinearity of the geometry by considering the measured interelectrode spacing for all the locations within the geometry. The EnSite system uses either the system reference patch on the patient's body or an intracardiac electrode for the anatomical reference and it can improve the compensation for cardiac and respiratory motion artifact. The EnSite system collects the impedance data over a period of 12 seconds from the patches and intracardiac catheters. It can identify respirations by the breading-dependent changes of the transthoracic impedance. The system provides an algorithm for the compensation of the catheter shift due to the respiratory motion, which makes all catheters look static. It is recommended to use an intracardiac catheter for the anatomical reference that is not used for pacing because the EnSite system does not use an electrical reference for the compensation of the cardiac motion artifact. Hence, the dislocation of the reference catheter may lead to uncorrectable map shifts. The main advantage of the EnSite system is the visualization of multiple catheters from different manufacturers. All displayed catheters in the 3D electrical field can be used for generating the geometry of the cardiac chambers. The electrophysiologic data from the catheter can be integrated into the geometry to form the 3D map.60 The EnSite Precision cardiac mapping system is the latest version, which uses the advantages of the hybrid impedance and magnetic field technologies. It allows for a much higher precision and accuracy compared to the prior version of the EnSite system. The Precision system requires an additional source of a magnetic field (EnSite Precision field frame) and two additional sensors on the patient (one on the back and the other on the chest; Figure 3-2). The EnSite Precision field frame is attached under the patient's table and it generates a weak magnetic field like the location pad of the CARTO system. The magnetic field technology works with the new sensor-enabled technology. Sensor-enabled catheters, which interact in the magnetic field, can be used to refine the impedance-based location, especially in the peripheral areas. The magnetic field data help preserve the localization accuracy in case of gradual changes in the impedance field such as lengthy procedures for atrial fibrillation or ventricular arrhythmia ablation. This hybrid technology leads to a navigation accuracy of < 1 mm. For the creation of the left atrial geometry, the Advisor FL circular mapping catheter and Advisor HD grid catheter can be used. For ablation, both the FlexAbility catheter (without contact force) and TactiCath Quartz (with contact force) are available. This system has been available in the field of electrophysiology since several years ago. The Rhythmia mapping system uses a hybrid tracking technology utilizing both magnetic and impedance-based localization features for the map creation. For magnetic tracking, the system needs one sensor coil embedded back patch and magnetic field generator underneath the patient's table. For an impedance-based localization, the impedance field is generated by applying current to the back patch, patches for the electrocardiographic limb leads, and the V1, V3, and V6 chest leads. The Rhythmia system is the first 3D mapping system to allow for automated high-density mapping with a dedicated steerable 64-electrode mini-basket catheter.18, 61, 62 Both point-by-point and continuous mapping can be performed with this system. Continuous mapping can be performed by a rapid and automated annotation based on a set of user predefined beat acceptance criteria. The system is optimally designed to work with the IntellaMap Orion high-resolution mapping catheter (Figure 3-3). The IntellaMap Orion Catheter is a sensor embedded, 8.5 Fr bidirectional deflectable 64-pole basket array. The catheter has a variable diameter of 3-22 mm that can be adjusted based upon the anatomic needs. It is made up of eight splines, each having eight equispaced flat, printed electrodes at 2.5 mm apart. The iridium oxide-coated flat electrode (0.4 mm2) without sensing from the back side of the splines helps avoid far-field signals and records very low local potentials, resulting in a 0.01 mV noise floor. Magnetically tracked catheters are coupled with impedance mapping, such that the system tracks the impedance measurements at each location during the creation and validation of the magnetic-based map. The surface geometry is continuously obtained by the outer most electrode locations associated with acceptable beats. The electrogram of the accepted beat is included in the 3D mapping only when the electrode is within 2 mm of the geometry for a new map. The Rhythmia system has been shown to collect 25 times more data points per map on average compared to manual mapping.63 The high density of the points reduces the amount of interpolation between annotated points, which allows for a more accurate and visible propagation pattern and identifies small gaps more precisely. During acquisition of the activations and voltages, the software can display the specified surface and intracardiac electrograms of each beat. A magnetic sensor-embedded open-irrigated ablation catheter is available, but a contact-force catheter has not yet been launched. High-density mapping is the process of simultaneous acquisition and annotation of multiple electrograms by the automated algorithm, including activation and voltage information. For the fast acquisition of data and better signal quality with a lesser noise to far-field ratio, multiple electrodes with a smaller electrode size have been developed. Each 3D mapping system has developed its own multiple electrode catheters. The Rhythmia system uses the IntellaMap Orion catheter, which has 64 small-printed electrodes. The PentaRay, which is used with the CARTO 3 system, is a magnetic-sensor based catheter with 20 poles arranged in five soft-radiating splines (1 mm electrodes separated by 4-4–4 or 2-6–2 spacing) laid out flat to cover an area with a diameter of 3.5 cm. The EnSite Precision system can use the Advisor HD Grid Mapping Catheter, Sensor Enabled, which has four splines with four electrodes on each spline (1 mm electrodes with 3-3–3 equidistant spacing) in a spade of a grid. The size of the grid is 1.3 × 1.3 cm2. The continuous acquisition of data points is based on a set of user predefined beat acceptance criteria. All three 3D mapping systems have similar categories of the beat acceptance. The criteria include the cycle length stability and/or range, position/distance stability, QRS morphology/electrocardiogram stability, respiratory phase, speed of the catheter motion, etc. These criteria help the system to discern a particular tachycardia or morphology in the presence of multiple arrhythmias or complex ectopy, which allows the system to quickly create an individual 3D map. The Turbo map of the EnSite system provides the ability to map the coexisting arrhythmia using the same recording segments. The Rhythmia system has a unique propagation reference for the atrial arrhythmias, which is used as a secondary reference to confirm the current beat is from the same tachycardia. The time interval between the reference and propagation reference is monitored, and the beat will be accepted if the difference is within a 5 milliseconds range. The automated annotation methods differ among the systems. In order to find the appropriate target for an effective ablation, the operator should understand the mechanism of the automated algorithm. The activation map is greatly influenced by how precisely each beat is annotated. For the timing of the activation at each point, it is generally accepted to annotate the first peak of the near-field bipolar electrogram or rapid downstroke of the unipolar signal.64 The CARTO system uses the CONFIDENSE™ module for the auto-annotation. It uses the maximum negative slope of the distal unipolar signal to set the timing of the annotation, and the annotation is displayed on the corresponding bipolar signal. The AutoMap module of the EnSite system allows the user to select which parameter will be used for the annotation including the peak positive/negative voltage, negative/positive slope, absolute slope (steepest slope, either +/−), and absolute voltage (largest voltage, either +/−). The grid mapping catheter with the EnSite system uses a duplicate algorithm. It uses the bipolar electrogram in both directions, along the splines and across the splines. The voltage of the bipolar electrogram can be affected by the direction of the wavefront. The duplicate algorithm displays the largest bipolar voltage at the positive electrode. The Rhythmia system annotates the greatest peak-to-peak voltage of the bipolar signals with the help of the unipolar signals to reduce the far-field signals. The detailed mechanism of the automated annotation algorithm is not open yet, but the efficacy of the algorithm has been proven by clinical experience.62 The systems provide their own algorithms for special mapping of CFAEs, late potentials, fragmented potentials, etc, based on their fundamental principles. Color-coded activation maps with thousands of electrograms can be created within minutes. Postprocessing is not necessary and is impossible in most cases with thousands of electrograms. Noninvasive panoramic mapping combines a noncontrast CT scan to acquire the anatomical information with a 256-electrode vest to obtain the cardiac surface potentials to project them on the epicardial surface of a 3D shell. It offers a comprehensive assessment of the mechanisms and localization of cardiac arrhythmias and it has the proportionated important information to characterize drivers of AF.41, 65 Noninvasive panoramic mapping has been recently used