Atrial Fibrillation, Confirm the Diagnosis

Case Description

The patient is a 50-year-old male with mild obstructive sleep apnea (OSA) who was asymptomatic until one month prior to our evaluation, when he started having frequent recurrent episodes of self-limiting, short-lived, somehow regular palpitations associated with dizziness. He underwent a work-up, which included normal blood pressure, electrocardiogram, tilt table test, and stress test. The echocardiogram showed normal left ventricular function, with mild left atrial (LA) dilatation. A 24-hour Holter monitor showed sporadic isolated premature atrial complexes (PACs), as well as a few runs of a fast regular supraventricular tachycardia consistent with focal atrial tachycardia vs atrial flutter (the longest of which lasted 20 beats, with maximal heart rate of 180 bpm). Despite beta-blocker and antiarrhythmic therapy (flecainide), the patient remained symptomatic, and given the history, there was a high suspicion of pulmonary vein tachycardias/paroxysmal atrial fibrillation (AF). Therefore, a decision was made with the patient to proceed with the insertion of an insertable cardiac monitor (ICM) to better estimate the arrhythmia type and burden, its response to antiarrhythmic therapy, and whether it might be amenable to catheter ablation.

The Confirm Rx ICM (Abbott), approved for use by the U.S. Food and Drug Administration in 2017, was implanted. The Confirm Rx ICM is a very small device (around 1.5 cc in size, 3 grams of weight) that is MR conditional (at 1.5 Tesla) and provides up to 2 years of battery life.^1,2 The procedure is simple and can be performed under local anesthesia in under one minute. The ICM is inserted subcutaneously at the level of the fourth rib on the left side of the chest via hand injection using a proprietary insertion tool (Figure 1). After the implant, the ICM is connected via a secure Bluetooth connection to a dedicated mobile phone app (myMerlin, Abbott) for Apple and Android devices, which obviates the use of a radiofrequency-based bedside transmitter and a separate handheld activator. The app allows the patient to trigger recording of the electrograms (EGMs) during symptomatic events, as well as read the device’s stored data and see the transmission history (Figure 1). Along with patient-triggered events (which are stored as EGMs lasting 8 minutes pre- and 1 minute post-trigger), the device can be programmed to automatically store EGMs. More specifically, for this patient, detection of atrial tachycardia was set for supraventricular rhythms of at least 12 beats with a rate ≥180 bpm, and AF episodes longer than 6 minutes. During follow-up (off beta-blockers and flecainide), while no sustained tachycardia had been detected so far and all AF episodes had been shown to be false positive secondary to significant sinus arrhythmia, patient-triggered episodes (palpitations occurring during meals) demonstrated sinus arrhythmia with frequent PACs (Figure 2). This led to the introduction of a proton pump inhibitor, which significantly improved his symptoms.

Discussion

ICMs are increasingly used to detect and monitor AF episodes before and after any intervention (either medical or catheter ablation); therefore, it is important to know the yield of a specific monitoring device/algorithm in this context.³ Of note, the Confirm Rx ICM classifies “AF” using proprietary discrimination criteria, which continuously compares the patient’s RR interval behavior over a 64-beat window to that recorded during known AF/sinus rhythm episodes, as well as evaluates its variance for randomness vs predictable changes (such as those happening during bigeminy). Using Holter monitoring data simultaneously recorded as the gold standard in a cohort of patients with known or suspected paroxysmal AF, the accuracy of the Confirm Rx ICM was found to be adequate to detect AF episodes, with a sensitivity and specificity of 95% and 87%, respectively, and corresponding positive and negative predictive values of 64% and 76%.⁴ While no AF episode was recorded in this patient (as expected, given the absence of fast palpitations during follow-up), sinus arrhythmia was misclassified as AF, which is consistent with the reported positive predictive values. However, the device proved beneficial because the patient was able to easily transmit symptomatic episodes, which were found to be secondary to meal-related vagal-induced prominent sinus arrhythmia/PACs and were successfully treated with antacid therapy. Also, given the patient’s non-negligible pretest probability of AF (OSA, fast irregular palpitations, mild LA dilatation), he can be continuously monitored, allowing for early detection and management of this common arrhythmia. ν

Disclosures: The authors have no conflicts of interest to report regarding the content herein. Outside the submitted work, Dr. Natale reports consulting fee/honoraria from Boston Scientific, Biosense Webster, Medtronic, and Abbott.  

References

1. Confirm Rx Model DM3500 Insertable Cardiac Monitor; User’s Manual.
2. MRI Ready Monitor Systems Manual; MRI Procedure Information for the St. Jude Medical^™ Confirm Rx^™ Insertable Cardiac Monitor Model DM3500.
3. Lee R, Mittal S. Utility and limitations of long-term monitoring of atrial fibrillation using an implantable loop recorder. Heart Rhythm. 2018;15:287-295. 
4. Nölker G, Mayer J, Boldt LH, et al. Performance of an implantable cardiac monitor to detect atrial fibrillation: results of the DETECT AF Study. J Cardiovasc Electrophysiol. 2016;27:1403-1410.