Performance of a New Leadless Implantable Cardiac Monitor in Detecting and Quantifying Atrial Fibrillation Results of the XPECT Trial

Surveillance of AF recurrence post-surgical AF ablation using implantable cardiac monitor

BACKGROUND

Although pulmonary vein isolation is an effective treatment for recurrent atrial fibrillation (AF), there is no consensus on the definition of success or follow-up strategies. Existing data are limited to intermittent Holter or transtelephonic monitoring with reliance on patient symptoms.

OBJECTIVE

We sought to determine the outcomes of surgical ablation and post-ablation AF surveillance with a leadless implantable cardiac monitor (ICM).

METHODS

Forty-five patients with drug-refractory paroxysmal or persistent AF underwent video-assisted epicardial ablation using a bipolar radiofrequency clamp. An ICM was implanted subcutaneously post-ablation to assess AF recurrence. AF recurrence was defined as ≥1 AF episode with a duration of ≥30 s. The device-stored data was downloaded weekly over the internet, and all transmitted events were reviewed.

RESULTS

A total of 1,220 AF automatic and patient-activated AF episodes were analyzed over a follow-up of 12 ± 3 months. Of these episodes, 46% were asymptomatic. Furthermore, only 66% of the patient-activated episodes were AF. AF recurrence was highest in first 4 weeks and substantially decreased 6 months post-ablation. The overall freedom from AF recurrence at the end of follow-up was 60%. When 48-h Holter recordings were compared with the device-stored episodes, the sensitivity of the device to detect AF was 98%, and the specificity was 71%.

CONCLUSIONS

The ICM provides an objective measure of AF ablation success and may be useful in making clinical decisions. This device may be used in future ablation studies to develop a more rigorous definition of procedural success.

Ablation of paroxysmal atrial fibrillation during coronary artery bypass grafting: 12 months' follow-up through implantable loop recorder

OBJECTIVES

The study aimed to identify responders to atrial fibrillation (AF) ablation, through continuous subcutaneous monitoring in patients with paroxysmal atrial fibrillation (PAF), who underwent epicardial pulmonary vein isolation (PVI) concomitantly with coronary artery bypass grafting (CABG).

METHODS

Seventy-two patients aged 61.6±4.7 years with PAF underwent epicardial PVI with bipolar radiofrequency during CABG. Conduction block was confirmed by pacing. At the end of the procedure, the implantable loop recorder (ILR) for continuous monitoring was implanted in all patients. Follow-up data were collected through the ILR telemetry. Patients with an AF burden (AF%)<0.5% were considered AF free (responders). Patients with AF%>0.5% were classified as non-responders. The AF episodes stored by the implanted device were visually inspected by the investigators to confirm the arrhythmia. The data were collected each month during 1-year follow-up.

RESULTS

No procedure-related complications occurred either for ablation or for the monitoring device. At the first post-ablation follow-up (1 month) during the blanking period, 37 patients (51%) were AF free, that is, with AF%<0.5%. At the end of the blanking period (3rd follow-up), 44 (61%) patients were AF free. At 12 months' follow-up, 52 (72%) patients were AF free. Among 20 (28%) patients with AF recurrence, six (30%) patients were completely asymptomatic. There were no ischaemic strokes during the 1-year follow-up.

CONCLUSION

Concomitant AF ablation during CABG is effective in the treatment of AF, as assessed through 1 year of continuous monitoring. Use of subcutaneous monitors is safe and accurate for AF detection, clinically relevant in identifying responders and non-responders and managing the medical therapies accordingly.

A simple method to detect atrial fibrillation using RR intervals

Implantable loop recorders have been developed for long-term monitoring of cardiac arrhythmia, but their accuracy for atrial fibrillation (AF) detection is unsatisfactory. We sought to develop and evaluate a simple method for detecting AF using RR intervals. The new AF detection algorithm is based on a map that plots RR intervals versus change of RR intervals (RdR). The map is divided by a grid with 25-ms resolution in 2 axes and nonempty cells are counted to classify AF and non-AF episodes. We evaluated the performance of the method using 4 PhysioNet databases: MIT-BIH AF database, MIT-BIH arrhythmia database, MIT-BIH normal sinus rhythm (NSR) database, and NSR RR interval database (total 145 patients, 1,826 hours NSR, 96 hours AF, and 11 hours other rhythms). Each record is divided into consecutive windows containing 32, 64, or 128 RR intervals. AF detection is performed for each window and classification results are compared to annotations. A window is labeled true AF if >1/2 of cycles in the window are annotated as AF or non-AF otherwise. The RdR map shows signature patterns corresponding to various heart rhythms. Optimal nonempty cell cut-off threshold for AF detection was determined by receiver operating characteristic curve analysis, which yields excellent sensitivity and specificity for window sizes 32 (94.4% and 92.6%, respectively), 64 (95.8% and 94.3%), and 128 (95.9% and 95.4%). In conclusion, a single metric derived from the RdR map can achieve robust AF detection within as few as 32 heart beats.

Performance of an implantable automatic atrial fibrillation detection device: impact of software adjustments and relevance of manual episode analysis

AIMS

Implantable loop recorders (ILRs) with specific atrial fibrillation (AF) detection algorithms (ILR-AF) have been developed for continuous AF monitoring. We sought to analyse the clinical value of a new AF monitoring device and to compare it to serial 7-day Holter.

METHODS AND RESULTS

Sixty-four consecutive patients suffering from paroxysmal AF were included in this prospective analysis and received an ILR-AF. Manual electrogram analysis was performed for each automatically detected episode and each was categorized into one of three possible diagnoses: 'no AF', 'definite AF', and 'possible AF' (non-diagnostic). Analysis was performed separately before and after a software upgrade that was introduced during the course of the study. A subgroup of patients (51 of 64) underwent AF catheter ablation with subsequent serial 7-day Holter in comparison with the ILR-AF. A total of 333 interrogations were performed (203 before and 130 after software upgrade). The number of patients with AF misdetection was significantly reduced from 72 to 44% following the software upgrade (P = 0.001). The number of patients with non-diagnostic interrogations went from 38 to 16% (P = 0.001). Compared with serial 7-day Holter, the ILR-AF had a tendency to detect a higher number of patients with AF recurrences (31 vs. 24%; P = 0.125).

CONCLUSIONS

The rate of AF detection on ILR-AF may be higher compared with standard AF monitoring. However, false-positive AF recordings hamper the clinical value. Developments in device technology and device handling are necessary to minimize non-diagnostic interrogations.

[Detection of atrial fibrillation after stroke]

Approximately every fourth stroke results from cardiac embolism. Atrial fibrillation has been recognized as a common cause for thromboembolic stroke. Detection of unknown atrial fibrillation is an important clinical challenge, as anticoagulation may effectively reduce the risk of recurrent ischemic stroke. In all patients with a cryptogenic stroke 24-h Holter monitoring should be performed in addition to a standard ECG to detect paroxysmal atrial fibrillation. In addition, it is useful to pay attention to atrial fibrillation during continuous bedside ECG monitoring on the stroke unit and in pacemaker interrogation. The indication for longer ECG monitoring by implantable loop recorders may be considered individually based on the expected probability of atrial fibrillation. The potential benefit of these devices is currently being evaluated in clinical trials.

Cryptogenic Stroke and underlying Atrial Fibrillation (CRYSTAL AF): design and rationale

BACKGROUND

Patients with atrial fibrillation (AF) are at increased risk for ischemic stroke. In patients who have suffered a stroke, screening for AF is routinely performed only for a short period after the stroke as part of the evaluation for possible causes. If AF is detected after an ischemic stroke, oral anticoagulation therapy is recommended for secondary stroke prevention. In 25% to 30% of stroke patients, the stroke mechanism cannot be determined (cryptogenic stroke). The incidence of paroxysmal AF undetected by short-term monitoring in patients with cryptogenic stroke is unknown, but has important therapeutic implications on patient care. The optimum monitoring duration and method of AF detection after stroke are unknown. The purpose of this study is to evaluate the incidence of AF and time to AF detection in patients with cryptogenic stroke using an insertable cardiac monitor.

STUDY DESIGN

The CRYSTAL AF trial is a randomized prospective study to evaluate a novel approach to long-term monitoring for AF detection in patients with cryptogenic stroke. Four hundred fifty cryptogenic stroke patients (by definition, without a history of AF) will be enrolled at approximately 50 sites in Europe, Canada, and the United States. Patients will be randomized in a 1:1 fashion to standard arrhythmia monitoring (control arm) or implantation of the subcutaneous cardiac monitor (Reveal XT; Medtronic, Inc, Minneapolis, MN) (continuous monitoring arm).

OUTCOMES

The primary end point is time to detection of AF within 6 months after stroke. The clinical follow-up period will be at least 12 months. Study completion is expected at the end of 2012.

Left axillary implantation of loop recorder

BACKGROUND

We compared the clinical course of 10 patients who received an implantable loop recorder (ILR) at a traditional site with 11 patients whose ILRs were implanted via a subpectoral site via a left axillary approach without complications.

METHODS AND RESULTS

R-wave amplitude was determined at implantation and during follow-up. Each patient was followed after 7 days to optimize device setting and then at 1 and 3 months. The R-wave amplitude obtained with the new technique was significantly higher and more stable than that obtained with the standard procedure. Our preliminary experience suggests that axillary access for ILR implantation is feasible, safe, well tolerated, and reliable in terms of sensing function and device performance. Moreover, it is superior aesthetically to the standard approach and carries the potential of minimizing permanent scarring after ILR extraction.

[Atrial fibrillation. New aspects for diagnosis and follow-up]

Continuous rhythm monitoring is the gold standard of objective rhythm assessment in patients with atrial fibrillation, thus, facilitating accurate detection of symptomatic and asymptomatic atrial fibrillation. This is of scientific and clinical interest for the understanding of this arrhythmia, the establishment of evidence-based therapeutic approaches, the definition of clinically indicated monitoring strategies, and for decision-making about oral anticoagulation. This article illustrates the importance of continuous monitoring of atrial fibrillation and presents developing technologies with their advantages and limitations as well as initial clinical experience.