Walter H. Olson

Detection of atrial fibrillation and flutter by a dual-chamber implantable cardioverter-defibrillator

BACKGROUND To distinguish prolonged episodes of atrial fibrillation (AF) that require cardioversion from self-terminating episodes that do not, an atrial implantable cardioverter-defibrillator (ICD) must be able to detect AF continuously for extended periods. The ICD should discriminate between atrial tachycardia/flutter (AT), which may be terminated by antitachycardia pacing, and AF, which requires cardioversion. METHODS AND RESULTS We studied 80 patients with AT/AF and ventricular arrhythmias who were treated with a new atrial/dual-chamber ICD. During a follow-up period lasting 6+/-2 months, we validated spontaneous, device-defined AT/AF episodes by stored electrograms in all patients. In 58 patients, we performed 80 Holter recordings with telemetered atrial electrograms, both to validate the continuous detection of AT/AF and to determine the sensitivity of the detection of AT/AF. Detection was appropriate in 98% of 132 AF episodes and 88% of 190 AT episodes (98% of 128 AT episodes with an atrial cycle length <300 ms). Intermittent sensing of far-field R waves during sinus tachycardia caused 27 inappropriate AT/AF detections; these detections lasted 2.6+/-2.0 minutes. AT/AF was detected continuously in 27 of 28 patients who had spontaneous episodes of AT/AF (96%). The device memory recorded 90 appropriate AT/AF episodes lasting >1 hour, for a total of 2697 hours of continuous detection of AT/AF. During Holter monitoring, the sensitivity of the detection of AT/AF (116 hours) was 100%; the specificity of the detection of non-AT/AF rhythms (1290 hours) was 99.99%. Of 166 appropriate episodes detected as AT, 45% were terminated by antitachycardia pacing. CONCLUSIONS A new ICD detects AT/AF accurately and continuously. Therapy may be programmed for long-duration AT/AF, with a low risk of underdetection. Discrimination of AT from AF permits successful pacing therapy for a significant fraction of AT.

Feasibility of using an implantable system to measure thoracic congestion in an ambulatory chronic heart failure canine model.

Background: Noninvasive measures of impedance reflect alterations in thoracic fluid and pulmonary edema in acute animal and human studies.

Atrial Response to Ventricular Antitachycardia Pacing Discriminates Mechanism of 1:1 Atrioventricular Tachycardia

Background: Inappropriate shocks from implantable cardioverter defibrillators (ICD) remain a significant clinical problem despite device discrimination algorithms. The atrial response to antitachycardia pacing (ATP) may determine the mechanism of 1:1 A:V tachycardia.

Functional Similarity Between Electrograms Recorded from an Implantable Cardioverter Defibrillator Emulator and the Surface Electrocardiogram

MAZUR, A., et al.: Functional Similarity Between Electrograms Recorded from an Implantable Cardioverter Defibrillator Emulator and the Surface Electrocardiogram. Clinical use of stored electrogram (EGM) configurations currently used in ICDs is limited. The hypothesis that EGMs recorded from electrodes on the ICD surface may improve diagnostic capabilities of the device was tested in the present study. The Buttons on Active Can Emulator (BACE), an ICD‐sized device containing four button electrodes, was temporarily placed into a subcutaneous or submuscular left pectoral pocket in 16 patients during ICD implantation. Simultaneous recordings were obtained from the ECG lead II, bipolar EGMs using BACE electrodes, and a bipolar atrial EGM during sinus rhythm (SR), ventricular pacing (VP) at cycle lengths of 500 and 400 ms, and VT. Visible P waves were present in all patients during SR (n = 15), in 5 (33%) of 15 patients during VP, and none of the patients during VT (n = 4) using BACE EGMs and lead II. P and QRS amplitudes and the P:QRS ratio during SR in BACE EGMs were significantly lower than those in lead II. BACE EGMs showed prominent changes in QRS morphology and duration during VP and VT compared to SR, and the magnitude of QRS prolongation during VP was similar to that in lead II. Measurements of PR, QRS, and QT duration during SR showed good agreement between BACE EGMs and lead II. In conclusion, EGMs recorded from electrodes embedded on the ICD housing may potentially improve visual discrimination between supraventricular and ventricular arrhythmias. They also may be useful as a surrogate of the ECG for analysis and monitoring of different components of P‐QRS‐T complex.

Incidence of Nonsustained and Sustained Ventricular Tachyarrhythmias in Patients with an Implantable Cardioverter Defibrillator

Introduction: Nonsustained ventricular tachycardia (NSVT) is a frequent phenomenon in some patients with heart disease, but its association with sustained ventricular tachycardias (ventricular tachycardia [VT]/ventricular fibrillation [VF]) is still not clear. The aim of this study was to determine whether NSVT incidence was associated with sustained VT/VF in patients with an implantable cardioverter defibrillator (ICD).

Discrimination of fast ventricular tachycardia from ventricular fibrillation and slow ventricular tachycardia for an implantable pacer-cardioverter-defibrillator

Implantable Pacer-Cardioverter-Defibrillators (PCD) sense ventricular electrograms from epicardial or endocardial leads with an auto-adjusting threshold and analyze a recent series of cycle lengths with algorithms to detect ventricular tachycardia (VT) and ventricular fibrillation (VF) for tiered therapies. A new algorithm to detect fast ventricular tachycardia (FVT) in a zone between VT and VF either via VT-type counting or via VF-type counting is described. Gaussian strings of cycle lengths with uniformly distributed means and standard deviations and databases of human tachyarrhythmias are analyzed. Detection algorithm sensitivity, specificity with 95% confidence intervals and the predictive value of a positive test for VF (PVP) are studied as a function of programmable defection parameters. While maintaining 100% VF sensitivity, VF specificity is increased by 20% for FVT via VF thereby safely reducing the number of painful shocks.<<ETX>>

Identification of an Implantable Defibrillator Lead Fracture With a New Holter System

In the last few years, implantable cardioverter defibrillators (ICDs] have found increasing use in patients at high risk for sudden cardiac death because of their ability to sense and terminate ventricular tachyarrhythmias. A vexing side effect, often estimated to affect 20%-30% of ICD recipients, is the delivery of inappropriate therapy, due to incorrect sensing by the ICD. This article describes an adaptation of Holter monitoring techniques that facilitated the detection of a fractured ICD lead wire not visible by X ray in a woman who was receiving occasional inappropriate shocks.

Acute human testing of a dual chamber ventricular tachyarrhythmia detection algorithm at Mayo clinic

A new dual chamber ventricular tachyarrhythmia detection algorithm has been incorporated into an external prototype dual chamber implantable cardioverter defibrillator, the Model AMD 7250, for the purpose of acute human testing of the algorithm. Testing has been performed during ICD implants and electrophysiologic studies. The detection algorithm uses a hierarchical rule-based approach to combine pattern and timing information to reach a rhythm decision. Rules for atrial fibrillation (AF) and atrial flutter/tachycardia (AT), sinus tachycardia (ST) and other 1:1 SVT are designed to reject these rhythms that would otherwise be detected by rate-based detection. Thirty-five patients were studied during EP study (N=32) or ICD implant (N=3). Appropriate detection occurred in 23/23 episodes of VT and 8/8 episodes of VF. Inappropriate detection of VT was prevented in 11/15 episodes of ST and 23/32 episodes of AF/AT.

Properties and performance of rate detection algorithms in three implantable cardioverter-defibrillators

Three detection algorithms used in implantable cardioverter defibrillators (ICDs) are described and compared. Synthetic and prerecorded human tachyarrhythmias were applied to algorithm simulations. As rhythm variability increased, the consistency of the result near detection zone boundaries fell and had different trends for each algorithm. For 456 prerecorded rhythms and fixed zones, VT-VF sensitivities were 96-97% and specificities were 83-85%.<<ETX>>

Temporal Stability of Sequential Pulse Defibrillation Threshold

We have shown that sequential pulse defibrillation threshold voltage and total delivered energy do not change with maturation of the electrode tissue interface for up to 12 weeks after implantation of two different electrode configurations. This result is important to predict the future performance of an implantable defibrillator that is tested only at implant.