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Atrial fibrillation (AF) is the most common arrhythmia that is associated with heart failure, hemodynamic impairment, and symptoms affecting quality of life. Patients have an increased risk of thromboembolic events resulting in significant morbidity, mortality, and costs. The adverse effects of paroxysmal AF have been correlated to the duration of the episodes and to the AF burden.
Diagnosis of AF is made by routine ECG recordings and ambulatory Holter monitoring. New methods of monitoring include transtelephonic ECG transmissions, 7-day Holter recording, and 30-day event recording. The diagnostic yield of these methods is limited, but there is a clear relationship between the duration of monitoring and the diagnostic yield. The sensitivity and specificity of any of these methods is modest. Also there is poor correlation between patient symptoms and AF episodes. Thus, technologies for the reliable detection of AF irrespective of symptoms are warranted. Subcutaneous implantable monitors can improve detection of symptomatic and asymptomatic AF and subsequent patient treatment. The study purpose was to quantify the performance of the first implantable leadless cardiac monitor (ICM) with dedicated AF detection capabilities.
Between September 2007 and July 2008, 247 patients (mean age 57 years, 66.8% male) from 24 medical centers (Europe and Canada) with an implanted ICM (Reveal XT, Medtronic Inc, Minneapolis, Minn) who were likely to present with paroxysmal AF were selected. After a stabilization phase of 4 to 6 weeks after ICM implantation, patients underwent 46 hours of continuous recording with a special Holter device, capable of storing the subcutaneous ECG and markers from the ICM, as well as recordings from 2 surface ECG leads. The ICM automatic arrhythmia classification was compared with the core laboratory classification of the surface ECG.
Of the 206 analyzable Holter recordings collected, 76 (37%) contained at least 1 episode of core laboratory classified AF. The sensitivity, specificity, positive predictive value, and negative predictive value for identifying patients with any AF were 96.1%, 85.4%, 79.3%, and 97.4%, respectively. The overall accuracy of the ICM for detecting AF was 98.5%.
The sensitivity, specificity, PPV, and NPV for identifying AF burden were, respectively, 98.1% (CI, 96.6% to 99.7%), 98.5% (CI, 97.5% to 99.5%), 91.9% (CI, 86.6% to 97.3%), and 99.7% (CI, 99.4% to 99.9%). The AF burden measured with the ICM was very well correlated with the reference value derived from the Holter (Pearson coefficient=0.97).
The major finding of this short-term verification study is that a subcutaneous, leadless ICM equipped with a dedicated AF detection algorithm is sensitive in detecting the presence of AF with a high specificity and PPV. It is also reliable in confirming freedom from AF, as shown by the high NPV. These performance metrics have much higher values compared with conventional monitoring methods such as repeated 24-hour Holter recordings, 7-day monitoring, or 30-day monitoring. In addition, the ICM precisely measured AF burden.
The study has some limitations. ICM classifies the heart rhythm for each subsequent time interval of 2 minutes, and only AF episodes with at least 2 minutes duration were included in the analysis. Therefore, the study results are not valid for episodes shorter than 2 minutes. The comparison between ICM detected episodes and the core laboratory annotated surface ECG was limited to a 46-hour period. Consequently, it is difficult to extrapolate the study results to a longer follow-up period. The study was performed in a specific patient population selected for a high risk of AF, and the results may not be generalized to other patient populations. Finally, the study results cannot be generalized to ICM devices other than the studied device.
In this ICM validation study, the dedicated AF detection algorithm reliably detected the presence or absence of AF and the AF burden was accurately quantified. Continuous and precise rhythm follow-up may help uncover the true incidence and duration of both symptomatic and asymptomatic AF episodes and establish a new standard to compare the efficacy of different AF treatment strategies. The ICM will potentially help guide individual patient treatment. Long-term studies are needed to evaluate the clinical benefits of the technology.
Hindricks G, Pokushalov E, Urban L, Taborsky M, Kuck KH, Lebedev D, Rieger G, Pürerfellner H; XPECT Trial Investigators. Performance of a new leadless implantable cardiac monitor in detecting and quantifying atrial fibrillation: Results of the XPECT trial. Circ Arrhythm Electrophysiol. 2010 Apr 1;3(2):141-7
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