Implantable loop recorders play an increasingly important role in assessing patients for syncope, say several experts as well as the most recent syncope guidelines, released by the European Society of Cardiology last August.
Implantable loop recorders [ILRs], introduced for syncope assessment about a decade ago, “are steadily becoming more and more widely acknowledged as an important diagnostic device by arrhythmologists and other experts active in the investigation of unexplained syncope in daily practice,” said Dr. Panos E. Vardas, an electrophysiologist and professor of cardiology at the University of Crete, Greece, and president of the European Heart Rhythm Association.
“Patients with infrequent, short-duration, transient symptoms, recurring over weeks or months, are unlikely to be diagnosed by conventional Holter monitoring, since the likelihood of symptom-ECG correlation is very low. In such patients, following careful evaluation of the patient's history, physical examination and ECG, when syncopal episodes remain unexplained, ILRs are no longer implemented as a last option but earlier in the evaluation algorithm,” Dr. Vardas said in an interview.
“The main indications include repeated episodes of unexplained syncope, syncope with injury, and syncope with special kinds of loss of consciousness such as differentiating between cardiac syncope and epilepsy. Especially in the case of atrial fibrillation, in which some paroxysms also lead to syncope, I am expecting the use of ILRs will change the whole understanding we have of the natural history of the disease,” he said.
“Today, ILRs are the most valuable tool for the diagnosis of the arrhythmic mechanism of syncope,” and “are expected to become the gold standard for diagnosis of arrhythmic syncope,” said Dr. Richard Sutton, professor of clinical cardiology at Imperial College, London, and cochair of the European Society of Cardiology (ESC) task force that wrote the 2009 guidelines for diagnosing and managing syncope (Eur. Heart J. 2009;30:2631-71). “The new ESC guidelines for syncope attempt to bring the ILR into the forefront of investigation of syncope based on the experience reported in the literature,” Dr. Sutton said in a talk at the ESC annual meeting in Barcelona last August.
“ILRs are clearly underused,” said Dr. Christophe Leclercq, professor of cardiology and vascular diseases at Pontchaillou Hospital in Rennes, France. “I think that in patients with severe syncope, the role of ILRs will dramatically increase, improving the diagnosis of syncope and also avoiding misdiagnoses, such as epilepsy.”
Evidence for the utility of ILRs in distinguishing arrhythmogenic syncope and epilepsy came in a report at the last ESC annual meeting. Researchers from Manchester (England) Royal Infirmary studied 41 adult patients who had been tentatively diagnosed with epilepsy, but for whom further review by a neurologist raised doubt about their status.
All patients receive an ILR, and the researchers eventually identified seven patients (17%) who experienced a heartbeat stop of 4-89 seconds that caused their loss of consciousness.
Despite these views, other electrophysiologists remain skeptical that ILRs play a major part in syncope assessment. “We use ILRs in patients with infrequent episodes, maybe one or two over 18 months, and we probably use ILRs more than we did 5 years ago, but we put in perhaps six a year,” said Dr. S. Adam Strickberger, professor of medicine at Georgetown University in Washington, and head of electrophysiology at Washington Hospital Center.
ILRs are “a useful tool in only a small subset of patients, probably less than 5%,” he said in an interview. “Half of patients with syncope have a vasovagal cause,” and hence are not candidates for ILR assessment. Among the remaining syncope patients, a large fraction have a low ejection fraction that makes them immediate candidates for a defibrillator with no need for ILR assessment.
Dr. Strickberger agreed, however, that tilt table testing is rarely used today, and that electrophysiology testing of syncope patients has also dropped. A patient's history serves as the major starting point for syncope assessment, he said. Dr. Strickberger chaired the most recent American College of Cardiology and American Heart Association committee to issue a scientific statement on syncope assessment, in 2006 (J. Am. Coll. Cardiol. 2006;47:473-84).
An ILR, roughly the size of a memory stick, continuously records a patient's ECG onto a memory loop of about 20 minutes. Patients activate their recorders following an episode so that the prior 20 minutes of ECG recordings are preserved for later assessment to search for correlates between the syncope event and arrhythmia. Implantation of ILRs is subcutaneous on the chest, using local anesthesia, and does not require lead placement, making the process relatively noninvasive. ILRs have a battery life of up to 3 years.