Arrhythmic syncope: what to do when ambulatory monitoring is non-diagnostic.

The two new methods for defining arrhythmic syncope described in this report represent important additions to the traditional syncope workup. Both techniques uncovered a substantial number of arrhythmic causes of syncope which had not been found by standard techniques. A major strength of each method is that symptoms can be directly related to the arrhythmia. The 68% incidence of diagnostic EPS abnormalities which we found was identical to the study of DiMarco but higher than reported by others (which have ranged from 12 to 48%) (18, 20, 21). More critical patient selection and more comprehensive study techniques most likely account for these differences. It is our opinion that a significant number of patients whose diagnosis was "syncope of undetermined etiology" in previous studies did indeed have an arrhythmic basis for their symptoms which was not identified. At this point the issue of "cost effectiveness" inevitably arises. Do all patients with syncope in whom a cause is not initially apparent (i.e., up to 50% of such patients) require either TTEM or EPS? The answer is obviously no, not for this whole population. However, the evident power of TTEM and EPS requires that the question should be raised. Furthermore, the results of the invasive EPS study strongly suggest that mortality and morbidity can be reduced. Table 11 shows the relative costs for all of the diagnostic tests for arrhythmic syncope. From this it can be seen that TTEM is quite inexpensive and therefore very cost-effective. It is an ideal adjunct to 24 hour ambulatory monitoring in selected patients. Although invasive EPS studies are costly, it is not difficult to incur equal costs by use of several days of prolonged monitoring, especially if done in the hospital. Thus, in identified patients with abnormal but "not diagnostic" ambulatory monitoring studies, patients with abrupt syncope, patients with frequent symptoms or patients with known underlying heart disease, further evaluation with TTEM or EPS should be strongly considered.