Electrophysiologic Testing
Electrophysiologic (EP) Testing
EP Testing is an invasive procedure that allows direct testing of the electrical behavior of the heart. It can be a very useful study in select patients with syncope. It is described in detail below.
Management Options for Atrial Fibrillation
Direct Current Cardioversion
Direct current (DC) cardioversion is offered to patients with persistent atrial fibrillation in whom it is deemed appropriate to re-establish normal sinus rhythm. Atrial fibrillation is the most common clinical arrhythmia. It is characterized by a chaotic electrica rhythm in the atria that overtakes and suppresses the heart’s normal pacemaker, the sinus node. In many patients this can result in an abnormally fast heartbeat. Additionally it puts patients at risk for developing an embolic cerebrovascular accident (stroke) resulting from the formation of blood clots in the heart. Epidemiologic data indicate that atrial fibrillation is an independent risk factor for increased morbidity and mortality, probably relating to its effect on heart rate and the high incidence of stroke. It is likely that there other factor contribute as well.
At first glance it would seem preferable to attempt to convert all episodes, of atrial fibrillation back to normal sinus rhythm, a process referred to as cardioversion. This can be achieved with certain medications (“pharmacologic cardioversion”) or direct current energy (“DC cardioversion”). However, a recent trial (the AFFIRM Trial) demonstrated no significant difference in outcomes between patients with atrial fibrillation randomized to treatment designed to control heart rate compared with attempted restoration of normal sinus rhythm. There are characteristics of the patients studied and the procedures used in the AFFIRM trial that limit application of the findings to all patients with atrial fibrillation. Accordingly, cardioversion continues to be offered to select patients.
DC Cardioversion
Two large electrode pads connected to a defibrillator are placed on the chest wall. Synchronous direct current energy shock is delivered after the patient has been adequately sedated with an anesthesiologist in attendance. Blood pressure, heart rate and rhythm are closely monitored. Typically up to three shocks are attempted before considering the procedure to be unsuccessful. The success of this approach is improved by use of a biphasic waveform defibrillator that is employed in our laboratory. DC cardioversion will be considered when one of the three following criteria are met: 1) onset of the atrial fibrillation within 48 hours of the procedure; 2) at least 3 weeks of documented therapeutic anticoagulation (INR 2-3); and 3) demonstration that the left atrium and left atrial appendage are free of thrombus at the time of the procedure. If atrial fibrillation has been present for greater than 48 hours the patient must be actively anticoagulated at the time of the cardioversion. These criteria are designed to minimize the risk of stroke associated with DC cardioversion. Typically, anticoagulation is recommended for at least 6 weeks after the cardioversion.
Failed DC Cardioversion Treatment Options
If attempts to restore normal sinus rhythm fail, consideration will be given to repeat cardioversion after administration of an antiarrhythmic agent. Parenteral or oral agents may be used. Class I antiarrhythmic drugs are generally avoided in patients with significant structural heart disease and/or because of an increased risk of induction of rhythm disturbances (pro-arrhythmia). Class III anti-arrhythmic drugs such as sotalol and dofetilide are initiated with in-patient telemetry for up to three days to monitor for excessive QT prolongation and Torsade-de-Pointes. Exercise stress testing is typically performed in patients started on Class IC agents such as flecainide, in order to identify possible use-dependent pro-arrhythmia.
Patients resistant to defibrillation may be pretreated with ibutilide 1 mg intravenous over 10 minutes before repeat cardioversion. This strategy improves the likelihood of successful cardioversion in those with previous failures. This approach should be avoided in patients with severely depressed left ventricular function. Furthermore, this strategy does not maintain normal sinus rhythm. Rather it enhances the probability of successful cardioversion.
A treatment approach of rate control and anticoagulation may be indicated if the above strategies fail. Although many patients with a first episode of atrial fibrillation have a high likelihood of reverting to normal sinus rhythm spontaneously or as a result of the above therapies, there are clinical circumstances that may warrant a more conservative approach at the outset. Patients who remain in atrial fibrillation in whom rate control is difficult to achieve may benefit from AV nodal ablation with permanent implantation of an electronic pacemaker.
Radiofrequency Ablation Procedure for Atrial Fibrillation
Some patients with the paroxysmal form of atrial fibrillation are candidates for a catheter-mediated radiofrequency ablation procedure that can be curative. This procedure is described in greater detail in the section describing radiofrequency procedures.
