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.


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

In This Article

ICMs in the Assessment of Asymptomatic Arrhythmias

Due to the lack of sufficient trial-based evidence, for the European Heart Rhythm Association guidelines on the use of implantable and external ECG loop recorders,[13] the followings represent nonestablished indications (Table I).

Silent AF

The success and efficacy of any rhythm-control therapy for AF and other atrial arrhythmias (i.e. drugs and ablation) are not easy to establish, as paroxysmal asymptomatic episodes are very frequent. Moreover, asymptomatic episodes carry the same clinical risks of thromboembolic events and heart failure as symptomatic events.[42] Indeed, assessing a patient's AF status is often a challenge. First, there is extensive evidence that symptoms correlate poorly with AF episodes, as many AF episodes are asymptomatic and many symptoms are not related to AF episodes.[43] Secondly, intermittent and/or short-term AECG monitoring can lead to underestimation of AF recurrences.[44,45] Thus, symptom-based and traditional follow-up tend generally to overestimate the success rate and efficacy of antiarrhythmic therapy. Therefore, the detection of both symptomatic and silent AF episodes is essential in order to ascertain the real success of any kind of antiarrhythmic treatment and to assess the need to continue antithrombotic therapy. In this setting, the new-generation ICMs may play a relevant role in the long-term evaluation of AF burden in patients undergoing rhythm-control therapies; indeed, some data on their use in patients who have undergone AF ablation are already available.[46–56]

ICMs could also find application in the evaluation of ischemic stroke. AF and atrial flutter account for approximately 10% of all strokes and 50% of cardioembolic strokes.[57] Because anticoagulation treatment dramatically reduces the recurrence rate of stroke, detection of this arrhythmia after a cerebral ischemic event is essential to starting the appropriate treatment. However, many cases of stroke remain without a clear diagnosis, so-called "cryptogenic stroke"; this may be due to the fact that AF may be underdiagnosed, as it is often asymptomatic and paroxysmal,[58,59] and it suggests the importance of an extended AECG monitoring duration in patients with unexplained stroke. Moreover, some studies based on continuous monitoring through an implanted dual-chamber pacemaker or ICD with AF features have shown the link between AF burden (i.e. the duration of AF episodes detected by the devices) and the risk of ischemic stroke.[44,60–62]

If additional evidence of the link between AF burden and the risk of stroke emerges, ICMs might play an important role in both risk stratification and management of the most appropriate antithrombotic therapy, in that reliable prolonged AECG monitoring could identify patients with silent paroxysmal AF who should receive anticoagulation therapy instead of taking aspirin.[57] On the other hand, patients with silent AF and contraindication for anticoagulation therapy could be treated more aggressively in order to prevent AF relapses. The detection of AF in this patient population can therefore strongly influence both therapy and the expected outcome. An international, randomized trial (Crystal AF) is currently evaluating the usefulness of an ICM with special features for AF detection in patients with cryptogenic stroke.[63] Finally, reliable prolonged ECG monitoring by means of a ICM could be also proposed, together with antiarrhythmic drugs and the new short-acting antithrombotic therapies, in the "pill in the pocket" approach for targeting high-risk periods in patients with paroxysmal/persistent AF.[57]

Silent Ventricular Arrhythmias

Another application of ICMs to consider could be the long-term monitoring of asymptomatic ventricular arrhythmic events in patients at risk of ventricular arrhythmias, but without clear indication, according to the current guidelines, for ICD implantation.[64] This could be the case of those patients with mild forms of arrhythmogenic heart disease (i.e. hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, Brugada syndrome, Short and Long-QT syndrome), or with ischemic or nonischemic dilated cardiomyopathy with only moderately depressed left ventricular ejection fraction.[66–70]

Moreover, according to current guidelines,[13,14] ICM implantation is suggested in patients with unexplained syncope and hypertrophic cardiomyopathy, long-QT syndrome, Brugada syndrome, or arrhythmogenic right ventricular cardiomyopathy, when the risk of sudden death is not considered high.