How to use implantable loop recorders in clinical trials and hybrid therapy

Epidemiological studies show that atrial fibrillation (AF) is associated with a doubling of mortality, even after adjustment for confounders. AF can be asymptomatic, but this does not decrease the thromboembolic risk of the patient. Office ECGs, occasional 24-h Holter recordings and long-term ECG event recording might not be sensitive and accurate enough in patients with AF, especially in those with paroxysmal episodes. In one study, 7 days of continuous monitoring with event recorders detected paroxysmal AF in 20 of 65 patients with a previous negative 24-h Holter recording. Over the last decade, enormous improvements have been made in the technology of implantable devices, which can now store significant information regarding heart rhythm. The first subcutaneous implantable monitor (Reveal XT, Medtronic) was validated for continuous AF monitoring by the XPECT study. The dedicated AF detection algorithm uses irregularity and incoherence of R–R intervals to identify and classify patterns in ventricular conduction. Its sensitivity in identifying patients with AF is >96%. Numerous clinical data from continuous monitoring of AF have recently been published. The first applications of this technology have been in the field of surgical and catheter AF ablation. With regard to cryptogenic stroke, an international randomized trial is ongoing to compare standard care with standard care plus the implantable cardiac monitor for AF detection in patients discharged with the diagnosis of cryptogenic stroke: the Crystal AF trial. Continuous AF monitoring provides an optimal picture of daily AF burden, both symptomatic and asymptomatic. Implantable cardiac monitors have high sensitivity, enable better assessment of therapy success and may guide further AF therapy.