What are the chances of a 24 hour tape detecting the causes for collapse in a patient? What other alternative monitoring devices are now available?

Syncope is a common medical problem accounting for up to 6% of emergency medical admissions. In older patients presenting to casualty this may be as high as 20% when evaluated with a full cardiovascular work up. The annual recurrence rate is as high as 30%.1 Syncope due to cardiac causes is associated with a high mortality (>50% at 5 years) compared with 30% at 5 years in patients with syncope due to non-cardiac syncope and 24% in those with unexplained syncope.2 However, in the elderly, even “benign” syncope can result in significant morbidity and mortality due to trauma, anxiety or depression, which may lead to major changes in lifestyle or financial difficulties.

Syncope is often unpredictable in onset, intermittent and has a high rate of spontaneous remission making it a difficult diagnostic challenge. Thus even after a thorough work up, the cause of syncope may remain unexplained in up to 40% of cases.4 Prolonged ambulatory monitoring is often used as a first line investigation. Documentation of significant arrhythmias or syncope during monitoring is rare. At best, symptoms correlating with arrhythmias occur in 4% of patients, asymptomatic arrhythmias occur in up to 13%, and symptoms without arrhythmias occur in up to a further 17%.5–7 Prolonged monitoring may result in a slight increase in diagnostic yield from 15% with 24 hours of monitoring to 29% at 72 hours.

Patient activated external loop recorders have a higher diagnostic yield but do not yield a symptom-rhythm correlation in over 66% of patients, either because of device malfunction, patient noncompliance or an inability to activate the recorder.9,10 In addition such devices are only useful in patients with relatively frequent symptoms. In a follow up by Kapoor et al,11 only 5% of patients reported recurrent symptoms at 1 month, 11% at 3 months and 16% at 6 months. Thus this type of monitoring is likely to be useful only in a small subgroup of patients with frequent recurrence in whom initial evaluation is negative and arrhythmias are not diagnosed by other means, such as 24 hour ECG or electrophysiology studies.

The diagnostic yield from cardiac electrophysiology ranges from 14–70%. This variability is primarily dependent on the characteristics of patients studied, in particular the absence or presence of co-morbid cardiovascular disease.12 Thus despite the use of investigations such as head up tilt testing, ambulatory cardiac monitoring, external loop recorders and electrophysiological testing, the underlying cause of syncope remains unexplained and continues to pose a diagnostic problem.

The implantable loop recorder (ILR) is a new diagnostic tool to add to the strategies for investigation of unexplained syncope.12 It permits long term cardiac monitoring to capture the ECG during a spontaneous episode in patients without recurrence in a reasonable time frame. It should be considered in those who have already completed the above outlined investigations that have proved negative, and in those in whom the external loop recorder has not yielded a diagnosis in one month. The ILR is implanted under local anaesthetic via a small incision usually in the left pectoral region. It has the ability to “freeze” the current and preceding rhythm for up to 40 minutes after a spontaneous event and thus allows the determination of the cause of syncope in most patients in whom symptoms are due to an arrhythmia. The activation device, used by the patient, family member or friend freezes and stores the loop during and after a spontaneous syncopal episode. This is retrievable at a later stage using a standard pacemaker programmer. The ILR specifically monitors heart rate changes. Hypotensive syndromes including vasovagal syncope, orthostatic hypotension, post-prandial hypotension and vasodepressor carotid sinus hypersensivity may also cause syncope. An ability to record blood pressure variation in addition to heart rate changes during symptoms would be a very helpful and exciting addition to the investigation of people with syncope.