(activation, voltage, and entrainment mapping). In addition, multielectrode catheters (with electrodes ranging from 20 to 64 per catheter) that are capable of rapidly recording electrical signals simultaneously from multiple areas of the heart permitting the construction of high-density EAMs are now available, thus improving the precision of arrhythmia mapping. The use of preprocedural computerized tomography (CT) or magnetic resonance imaging (MRI) and intraprocedural intracardiac echocardiography and image integration into 3D EAM systems further helps improve the precision of anatomical mapping particularly in patients undergoing ablation of complex arrhythmias including atrial fibrillation (AF) and ventricular arrhythmias (VAs).
the arrhythmia. Activation mapping during focal arrhythmias helps identify the site of origin of tachycardia whereas in orthodromic AVRT and antidromic AVRT, the site of earliest chamber activation helps localize the site of attachment of APs which are then targeted for ablation. Activation at successful ablation sites usually precedes the P-wave or QRS complexes (during atrial arrhythmias and VAs) by 30 milliseconds or more. In reentrant tachycardias (atrial flutter and scar-based reentrant ventricular tachycardia [VT]) activation mapping helps identify reentrant circuits, with localization of areas critical for the tachycardia (critical isthmus—typically areas of low-voltage fractionated signals with slow conduction) that are then targeted for ablation (Figure 59.3). Although activation mapping helps achieve precise localization of the site of origin of tachycardia, it is not always feasible because several tachycardias (especially VT) are hemodynamically unstable. In such scenarios, other mapping techniques such as pace mapping and voltage mapping are useful.
than or equal to 11/12 ECG leads or greater than or equal to 95% using clinically available pace match software (CARTO® PASOTM, Biosense Webster, Diamond Bar, CA; Score Map, Abbott, Abbott Park, IL) is usually seen at sites of successful ablation. Although pace mapping is useful, it has several limitations including the inability to capture (1) local myocardium within areas of scarring at lower outputs and (2) neighboring tissue at higher outputs, thus reducing its accuracy. Further, pace mapping is not useful for atrial arrhythmias because surface P-waves are often not clearly discernible during atrial tachycardia, which limits any comparisons.
The current then flows through the body and returns via the grounding patch to the RF generator completing the circuit. The larger surface area of the dispersive electrode prevents heating and injury to the skin in contact with the grounding patch. Since its inception, the RF ablation catheter has undergone several iterations including changes in size, electrode type (platinum-iridium vs gold), and use of tip irrigation (closed-loop vs open-loop irrigation) in an attempt to achieve relatively larger and deeper lesions as compared to the initial nonirrigated catheters. Monitoring of the electrode tip-tissue interface temperature via thermocouples at the electrode tip is useful to titrate power in nonirrigated 4-mm tip catheters. However, they are not useful with larger tip (8 mm) and irrigated catheters owing to the greater passive and active cooling of the catheter tip, respectively, thus lowering the tip temperature although the temperature of tissue just beneath the surface is much greater.
associated with higher recurrence rates. The development of pulmonary vein isolation procedures for FAT arising from the pulmonary veins and AF has further helped refine the ablation of these arrhythmias with improvements in outcomes (Table 59.1).
TABLE 59.1 Catheter Ablation of Supraventricular Arrhythmias