Atrial Tachyarrhythmia Detection and Termination Accuracy

The foundation for all device-based treatments of AT/AF and its associated diagnostic information is the ability to accurately and reliably detect the arrhythmia. Algorithms for detecting AT/AF must be designed for high specificity to avoid overtreatment of nonsustained atrial tachyarrhythmias. The desired time course for automatic therapy for atrial tachyarrhythmias may vary from several minutes to several hours, depending on patient symptoms and acceptance of the therapies. This is in contrast to automatic detection and therapy for ventricular tachyarrhythmias, which must be performed with high sensitivity and within several seconds to avoid loss of patient consciousness and arrhythmic death.

High specificity for AT/AF detection has been achieved by use of more sophisticated detection algorithms, which incorporate atrial rate estimations with pattern-based algorithms to recognize atrial tachyarrhythmias with higher atrial rate than ventricular rate (e.g., >1:1 A:V pattern) and reject far-field R-wave oversensing on the atrial sensing channel. These algorithms also include methods for discrimination of AT (organized atrial tachycardia) from AF (atrial fibrillation, or disorganized atrial tachycardia). AT/AF discrimination algorithms are important for guiding therapies, since AT rhythms are more likely to respond to atrial antitachycardia pacing.

Early research efforts were directed at quantifying the detection accuracy so physicians could be confident that devices were treating true arrhythmias and that the diagnostic data provided by the device were valid. The performance of this rate and pattern-based AT/AF detection algorithm was prospectively evaluated in 58 patients using a custom telemetry Holter device to simultaneously record ECG and device markers for 24 hours. The results of this analysis validated the continuous detection of AT/AF with a sensitivity of 100% and a specificity of 99.9% (116 hours of AT/AF, 1,290 hours of non-AT/AF).121 Further evaluation of AT/AF detection performance has been performed in prospective evaluations of implanted devices, providing AT/AF therapy by analyzing the portion of EGM data that is automatically stored for a limited number of episodes at the time of detection. The positive predictive value of AT/AF detection has been reported to range from 95 to 99%, depending on the population studied.122'123 Figure 13a presents an example of continuous AT/AF detection with successful atrial antitachyarrhythmia pacing therapy, and Fig. 13b presents an example of atrial undersensing that resulted in delayed AT/AF detection.

Equally important to detecting the initiation of an atrial arrhythmia is the ability to accurately and reliably detect its termination. This allows implantable devices to accurately calculate the duration of specific episodes and to tabulate the cumulative percentage of time spent in AT/AF (AT/AF burden). These metrics have important clinical implications since a physician may classify a patient's arrhythmia status as being paroxysmal, persistent, or permanent based in part on the episode duration and AT/AF burden reported by the device. Incorrect classification of the patient's arrhythmia status could lead to prescribing inappropriate therapies. Providing EGM information at the termination of an episode allows physicians to verify that the device correctly identified the end of the arrhythmia. Undersensing of the atrial signal is one of the primary causes of inappropriate episode termination (Fig. 13b). The rate of appropriate detection of sinus rhythm at the termination of an AT/AF episode has been shown to be 92% in an ICD

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Figure 13: Examples of appropriate atrial tachycardia and atrial fibrillation (AT/AF) detection. (a) AT/AF onset is detected promptly (no electrogram [EGM] available). Atip-Vring EGM stored prior to successful atrial antitachycardia pacing (after 1 min of continuous detection) allows confirmation of appropriate detection. The smaller amplitude deflections on the Atip-Vring EGM signal are atrial activations, and the alignment of these deflections with atrial event markers indicates accurate atrial rate sensing. Note that atrial antitachycardia pacing successfully terminates the atrial tachyarrhythmia. (b) Atrial undersensing resulting in delayed detection of AT/AF onset t"1

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