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Syncope is a transient symptom and not a disease. Typically, patients are asymptomatic at the time of evaluation and the opportunity to capture a spontaneous event during diagnostic testing is rare. As a result, diagnostic evaluation has focused on the detection of abnormalities that could plausibly cause loss of consciousness. This type of reasoning necessarily leads to uncertainty in establishing a cause. In other words, the causal relation between an abnormality found during the diagnostic workup and syncope is often presumptive. Indeed, in the tests used to evaluate the aetiology of syncope, it is not possible to measure test sensitivity and specificity, owing to the lack of a reference standard for most of the tests. Because of the episodic behaviour of syncope, the opportunity of correlating the spontaneous syncopal episodes with an abnormal finding can be considered as a reference standard.
Role of the implantable loop recorder
An implantable ECG event monitor has recently become available (Reveal, Medtronic). This device is placed subcutaneously under local anaesthesia, and has a battery life of 15–18 months. The device has a solid state loop memory and, with the current version, the ECG of up to 40 minutes before and two minutes after activation can be stored. With these characteristics, if patients activate the device when consciousness has been restored, there is a high probability of having a correlation of ECG signals and syncope. In the first reported experience, the device was used in a heterogeneous population of 85 patients affected by unexplained syncope,1 which included patients with and without structural heart disease as well as patients with and without abnormalities in baseline ECG. Syncope-ECG correlation was achieved in 27% of patients and presyncope-ECG correlation in 32%; the rhythm recorded during the event was heterogeneous, thus reflecting the various clinical settings of the population enrolled: 29 patients were in …