EP Testing and Evaluation of Syncope

Typically, ICD implantation is accepted as first-line therapy in patients presenting with syncope of unknown origin who have hemodynamically significant sustained ventricular tachycardia (VT) induced at EP study (EPS). This indication is supported by substantial observational data showing an annual cardiovascular mortality of approximately 20% in such patients, much of which appears to result from sudden death.2-5 A related indication includes patients with recurrent syncope of uncertain etiology in the presence of ventricular dysfunction when other causes of syncope are excluded. Such cases, usually associated with nonischemic dilated cardiomyopathy, may suffer a risk of SCD as high as 45%.

Few studies have been conducted in the setting of nonischemic dilated cardiomyopathy and syncope. One evaluated patients with syncope, inducible ventricular arrhythmias, and previously documented VT.6 ICDs proved useful in reducing arrhythmic deaths. Another study compared dilated nonischemic cardiomyopathy patients with unexplained syncope and an ICD with a group of cardiac arrest survivors with ICDs.7 It demonstrated that the number of appropriate ICD discharges in the syncope group were similar to those of the cardiac arrest group. Such data, although rudimentary, do provide insight into recommending strategies for clinical ICD implantation until more definitive evidence is available.

The predictive accuracy of EP testing in nonischemic cardiomyopathy is limited.8-12 On the one hand, when such patients present with spontaneous ventricular arrhythmias, ventricular arrhythmias can be induced in more than two-thirds.9 On the other hand, EP testing is less likely to induce VT in patients with nonischemic dilated cardiomyopathy and a presentation of aborted SCD or nonsustained VT than in patients with underlying coronary artery disease.8,11,12 Furthermore, EP can induce ventricular arrhythmias in 10% to 40% of these patients, even in the absence of previous clinical arrhythmias.8 Thus EP testing is not useful for risk stratification in nonischemic cardiomyopathy. Overall, the magnitude of LV dysfunction remains the best predictor of both SCD and total mortality in this population.12

In the setting of ischemic cardiomyopathy and prior infarction, routine EP risk stratification is not recommended. EP testing followed by ICD implantation for inducible sustained VT can be considered for patients in whom there is concern that they are at risk for SCD, but who do not meet guidelines based on the severity of chronic LV dysfunction. This approach may be considered in patients with nonsustained VT who are more than 5 days after MI, or who have had recent revascularization, or who have LV ejection fraction (LVEF) >0.35.13,14