Implantable loop recorder: evaluation of unexplained syncope.

Syncope is a relatively common occurrence in the general population accounting for up to 6% of hospital medical admissions and at least 3% of accident and emergency visits each year. 2 In a proportion of cases, syncope continues to pose a clinical dilemma despite the development of new diagnostic techniques. Mortality and serious morbidity associated with syncope are generally low overall but one year mortality is up to 33% in high risk groups of patients with a cardiac cause of symptoms. 2 Recurrent syncope has additional deleterious eVects on lifestyle, sense of physical wellbeing, and employment opportunities. Major obstacles to diagnosis are the intermittent nature of the symptoms, which are both periodic and often unpredictable, high spontaneous remission rates, and the lack of a diagnostic gold standard. Despite the absence of a diagnostic gold standard for syncope and a paucity of data from randomised trials, several statements have emerged from a recent position paper on clinical guidelines from the American College of Physicians. In summary, these guidelines emphasise that: + history, physical examination, and electrocardiography are the core of the investigations of syncope (with a combined diagnostic yield of 50%) + neurological testing is rarely helpful unless additional neurological signs or symptoms are present (the diagnostic yield for electroencephalography, computed tomography, and Doppler ultrasound is only 6%) + and patients are at higher risk of adverse outcomes if heart disease is known or suspected, or if patients have explained syncope. It is recommended that these patients should have additional cardiac testing including echocardiography, stress testing, head up tilt testing, Holter monitoring or intracardiac electrophysiological studies, either alone or in combination, depending on the clinical index of suspicion. Despite these recommendations, syncope continues to pose diagnostic problems if it remains unexplained, occurs in the absence of structural heart disease, or if the clinical characteristics are atypical. Many centres use prolonged ambulatory monitoring as a first line of investigation, yet this most frequently identifies non-specific arrhythmias in the absence of symptoms. Documentation of significant arrhythmias or syncope during monitoring is rare. At best, symptoms correlating with significant arrhythmias occur in up to 4% of patients, asymptomatic arrhythmias occur in up to 13%, and symptoms without arrhythmias in a further 17%. Patient activated external loop recorders have a higher diagnostic yield than prolonged ambulatory monitoring but do not yield a symptom–rhythm correlation in over two thirds of patients, either because of device malfunction, patient non-compliance, or inability to activate the recorder. 9 Head up tilt testing reproduces presyncopal and syncopal symptoms in patients with vasovagal syncope. The specificity of head up tilt testing, in the absence of pharmacological provocation, is between 50% and 90%, but test application is limited by variation in sensitivity, which ranges from 30% to 85%. 11 The diagnostic yield from cardiac electrophysiology ranges from 14–70%; this variability is primarily dependent on the characteristics of patients studied, in particular the presence or absence of comorbid cardiovascular disease. Thus, the underlying cause of unexplained syncope is not determined in up to a quarter of patients despite investigations including head up tilt testing, ambulatory cardiac monitoring, external loop recording, and electrophysiological testing.