Current and Emerging Indications for Implantable Cardiac Monitors

Franco Giada, M.D.; Emanuele Bertaglia, M.D; Bernhard Reimers, M.D.; Donatella Noventa, M.D.; Antonio Raviele, M.D.

Disclosures

Pacing Clin Electrophysiol. 2012;35(9):1169-1178. 

In This Article

ICMs in the Diagnostic Evaluation of Transitory Symptoms of Possible Arrhythmic Origin

In patients with transitory symptoms of possible arrhythmic origin, such as syncope and palpitations, that remain unexplained after the initial clinical evaluation (clinical history, physical examination, and standard 12-lead ECG), electrocardiographic recording is considered the diagnostic gold standard.[13–15] Thus, when symptoms are clinically relevant (i.e. recurrent, poorly tolerated, accompanied by reduced quality of life and/or trauma), and/or when there is an high probability of an arrhythmic cause (i.e. the patient is suffering from heart disease), long-term AECG monitoring is often necessary.

AECG monitoring devices (if we exclude the diagnostic functions of pacemakers and ICDs) include the following: Holter devices, event recorders, external loop recorders, mobile cardiac outpatient telemetry, and ICMs (Table II). Generally, ICMs are indicated in poorly compliant patients with infrequent symptoms (i.e. with less than monthly frequency), or when all other investigations have proved negative (Table II).[13–15]

Unexplained Syncope

The first clinical application of ICMs was in the diagnosis of recurrent unexplained syncope. Several studies have shown that in patients with or without structural heart disease, both in older as well as in pediatric subjects, using an ICM yields more diagnosis than conventional testing does[14,16–26] (Table III). Moreover, Krahn et al.[27] showed that a strategy of primary monitoring is more cost-effective than conventional testing in establishing a diagnosis in recurrent unexplained syncope. The European Society of Cardiology guidelines on the management of syncope[14] and the European Heart Rhythm Association guidelines on the use of implantable and external ECG loop recorders[13] provide a class I indication for the use of ICMs in patients with infrequent unexplained syncope of possible arrhythmic origin, or in high-risk patients when all other investigations prove inconclusive. However, an early use of ICMs in the diagnostic work-up can be safely adopted, provided that patients at high risk of life-threatening arrhythmic events are excluded.

Unexplained Palpitations

In patients with unexplained palpitations, the conventional diagnostic strategy sometimes fails to establish a diagnosis, especially in patients with infrequent symptoms.[28] The RUP study[29] showed that, in patients with infrequent unexplained palpitations, the diagnostic yield of the conventional strategy is low, while ICM strategy is more likely to provide a diagnosis and can be more cost-effective. The European Heart Rhythm Association guidelines on the use of implantable and external ECG loop recorders provide a class IIa indication for the use of ICMs in patients with infrequent unexplained palpitations when all other investigations fail to provide a diagnosis.[13]

Difficult Cases of Epilepsy

In clinical practice, it is sometimes difficult to distinguish epilepsy from syncope occurring with myoclonic movements,[30] and ICMs may contribute to the diagnosis in this setting, too.[31–35] Indeed, Zaidi et al.[31] showed that, in patients with drug-refractory epilepsy, cardiovascular evaluation by means of ICMs may yield an alternative diagnosis in many patients. More recently, a prospective study by means of ICMs showed a high incidence of asystole in patients misdiagnosed as epileptic, or when the diagnosis of epilepsy was in doubt.[32] Studies by Petkar et al.[32] and by Ho et al.[36] have also demonstrated the usefulness of ICMs in diagnosing typical epilepsy through the pattern of muscle artifacts associated with tonic-clonic seizures, as stored in the memory of the devices.

Moreover, on evaluating a series of patients who had been referred to neurologists with presumed epilepsy and normal electroencephalograms (EEGs), Rodrigues et al.[33] found the following results: vasovagal syncope in 22 of 55 patients (40%), life-threatening arrhythmias in seven (13%), carotid sinus hypersensitivity in six (11%), orthostatic hypotension in three (5%), and aortic stenosis in one (2%).

Finally, there is growing interest in the evaluation of cardiac arrhythmias in patients with epilepsy, since epilepsy per se, and the drugs used for its treatment, may trigger arrhythmic disorders. Although it is not yet clear whether epilepsy-related arrhythmias are always clinically relevant, some cases of sudden death in epileptic patients—so-called sudden unexpected death in epilepsy (SUDEP)—have already been reported.[34,37] The dysregulation of respiratory physiology, cardiac factors, dysfunction of systemic and cerebral circulation, seizure-induced hormonal and metabolic changes, and multiple antiepileptic drugs might all contribute to SUDEP. Cardiac factors include first of all ictal bradyarrhythmias and asystole, but also tachyarrhythmias and alterations of ventricular repolarization. Although no clear correlation has been identified between any obvious brain abnormality and ictal heart rate changes, several studies reported a high prevalence of ictal bradyarrhythmias in seizures with temporal lobe origin.[34] Thus, the study of epileptic patients at high risk of SUDEP might be an interesting field of application of ICMs in the near future.[37]

In conclusion, ICMs may have a diagnostic role in difficult or dubious cases of epilepsy, in drug-resistant epilepsy, and whenever it is essential to exclude the presence of potentially harmful arrhythmias. The European Heart Rhythm Association guidelines on the use of implantable and external ECG loop recorders[13] provide a class IIb indication for the use of ICMs in "patients in whom epilepsy is suspected but the treatment has proved ineffective and in patients with established epilepsy in order to detect peri-ictal cardiac arrhythmias that require treatment."

Unexplained Falls

Falls remain a major health and socioeconomic problem. Each year, 30% of those over the age of 65 years suffer falls. Up to 5% of falls result in a fracture and 1% in hip fractures.[38]

There is growing evidence of an overlap between syncope and unexplained falls in the elderly.[39,40] Moreover, patients with unexplained falls who attend the emergency room display a high prevalence of carotid sinus hypersensitivity. Thus, ICMs may also play a role in this population, especially in those patients with recurrent unexplained falls and clinical and/or ECG features at high risk of arrhythmic events.[13,14] In this regard, however, the results of the Safepace 2 trial, a study in which patients with unexplained falls and/or syncope and cardioinhibitory carotid sinus hypersensitivity were randomized to dual-chamber pacing or ICM implantation, were quite disappointing.[41] Indeed, syncopal recurrence rate was not statistically different between the active and placebo arms of the study. The European Heart Rhythm Association guidelines on the use of implantable and external ECG loop recorders provide a class IIb indication for the use of ICMs in "older patients with nonaccidental falls to establish the syncopal nature of the event."[13]

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