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2.5 Basic Principles of Electrophysiological Study, Mapping, and Ablation

2.5.1 Mapping With Multiple and Roving Electrodes

An invasive EP study permits the precise diagnosis of the underlying arrhythmia mechanism and localization of the site of origin and provides definitive treatment if coupled with catheter ablation. There are standards that define the equipment and training of personnel for optimal performance of EP study.141 EP studies involve placement of multielectrode catheters in the heart at ≥1 sites in the atria, ventricles, or coronary sinus. Pacing and programmed electrical stimulation may be performed with or without pharmacological provocation. Making a precise and correct diagnosis of the mechanism of SVT is the key to successful outcome, particularly when multiple arrhythmia mechanisms are possible; as such, appropriate diagnostic maneuvers should be performed before proceeding with ablation. By using diagnostic maneuvers during the EP study, the mechanism of SVT can be defined in most cases.80,142 Complications of diagnostic EP studies are rare but can be life threatening.143

Cardiac mapping is performed during EP studies to identify the site of origin of an arrhythmia or areas of critical conduction to allow targeting of ablation. Multiple techniques have been developed to characterize the temporal and spatial distribution of electrical activation.144 The simplest technique uses several multipole catheters plus a roving catheter that is sequentially positioned in different regions of interest and measures local activation time. Electroanatomic mapping systems and specialized multielectrode catheters, such as circular or multispline catheters, can map simultaneously from multiple sites and improve the speed and resolution of mapping.

2.5.2 Tools to Facilitate Ablation, Including 3-Dimensional

Electroanatomic Mapping Several tools have been developed to facilitate arrhythmia mapping and ablation, including electroanatomic 3-dimensional mapping and magnetic navigation. Potential benefits of these technologies include more precise definition or localization of arrhythmia mechanism, spatial display of catheters and arrhythmia activation, reduction in fluoroscopy exposure for the patient and staff, and shortened procedure times, particularly for complex arrhythmias or anatomy.145 Disadvantages include higher cost, as well as additional training, support, and procedure preparation time. Several studies have demonstrated the advantages of electroanatomic mapping, with

IIb B-R 1.  Sotalol may be reasonable for ongoing management in patients with symptomatic SVT who are not candidates for, or prefer not to undergo, catheter ablation.114

See Online Data Supplement 2. Sotalol is a class III antiarrhythmic agent with beta-blocker properties. Unlike flecainide and propafenone, it can be used in patients with structural heart disease or ischemic heart disease. One study randomized patients with reentrant SVT (AVNRT or AVRT) or other atrial tachyarrhythmias (eg, AF, atrial flutter, AT) to sotalol at a dose of 80 mg or 160 mg twice daily or placebo and found significant reductions in recurrence risk, including for patients with reentrant SVT, with no proarrhythmic adverse effects.114 Because of the potential for proarrhythmia, sotalol should be reserved for patients who are not candidates for catheter ablation and for whom beta blockers, diltiazem, or verapamil are ineffective or cannot be prescribed.

IIb B-R 2.  Dofetilide may be reasonable for ongoing management in patients with symptomatic SVT who are not candidates for, or prefer not to undergo, catheter ablation and in whom beta blockers, diltiazem, flecainide, propafenone, or verapamil are ineffective or contraindicated.107

See Online Data Supplement 2. Dofetilide is a class III antiarrhythmic agent that, unlike sotalol, does not have beta-blocker properties. It may be reasonable in patients with structural heart disease or ischemic heart disease. In a trial of 122 patients randomized to dofetilide, propafenone, or placebo, the probability of remaining free of SVT after 6 months of treatment was 50% for dofetilide, 54% for propafenone, and 6% for placebo, with P<0.001 for either dofetilide or propafenone compared with placebo.107 Because of the potential for proarrhythmia, dofetilide should be reserved for patients who are not candidates for catheter ablation and for whom beta blockers, diltiazem, flecainide, verapamil, or propafenone are ineffective or cannot be prescribed.

IIb C-LD 3.  Oral amiodarone may be considered for ongoing management in patients with symptomatic SVT who are not candidates for, or prefer not to undergo, catheter ablation and in whom beta blockers, diltiazem, dofetilide, flecainide, propafenone, sotalol, or verapamil are ineffective or contraindicated.115

See Online Data Supplement 2. Evidence for amiodarone for the ongoing management of SVT is limited. The drug was evaluated in a small retrospective study and was found to be effective in suppressing AVNRT during outpatient follow-up.115 Amiodarone is a second-line agent for patients who are not able to take beta blockers, diltiazem, dofetilide, flecainide, propafenone, sotalol, or verapamil given the toxicity and side effects that may develop with long-term amiodarone therapy. IIb C-LD 4.  Oral digoxin may be reasonable for ongoing management in patients with symptomatic SVT without pre-excitation who are not candidates for, or prefer not to undergo, catheter ablation.99

See Online Data Supplement 2. Evidence for the use of digoxin is limited. One small study randomized patients with SVT to digoxin (0.375 mg/day), propranolol (240 mg/day), and verapamil (480 mg/day), with 1 week of placebo washout between drug regimens.99 Overall, episodes and duration of SVT (ascertained by diary and weekly 24-h Holter) were similar, and all 3 medications were well tolerated.99 However, the dose of digoxin used was higher than that commonly used in clinical practice today, and in view of the risk of toxicity, digoxin should be reserved for patients who cannot take beta blockers, diltiazem, or verapamil or a class Ic agent (flecainide or propafenone) and must be used with caution in the presence of renal dysfunction. In some clinical studies, digoxin levels >1.2 ng/mL were associated with worse clinical outcomes, while levels <0.8 ng/mL were considered optimal; therefore, caution is advised.116

Recommendations for Ongoing Management of SVT of Unknown Mechanism (Continued) COR LOE Recommendations

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