Robert Arzbaecher

Evaluation of techniques for recognition of ventricular arrhythmias by implanted devices

Three methods of electrogram analysis have been investigated: rate, irregularity, and amplitude distribution. In 35 episodes in 19 patients, these three algorithms were applied to 15 s recorded passages of ventricular electrograms during supraventricular tachycardia (N=11), ventricular tachycardia (N=11), and ventricular fibrillation (N=13). Each was individually paired with a recording of sinus rhythm from the same patient. Each algorithm was successful at distinguishing the tachyarrhythmias from sinus rhythm at one or more levels of algorithm parameterization. Rate alone discriminated supraventricular tachycardia from ventricular fibrillation but did not distinguish between supraventricular and ventricular tachycardia. Rate combined with irregularity distinguished between ventricular tachycardia and ventricular fibrillation, but did not discriminate between ventricular and supraventricular tachycardia. It is concluded that algorithms based on rate, irregularity, and amplitude distribution analysis of ventricular electrograms may distinguish sinus rhythm from tachyarrhythmias, but may not distinguish among tachyarrhythmias.<<ETX>>

Tachycardia Detection in Implantable Antitachycardia Devices

Nous avons développé un algorithme permettant lidentification des tachycardies par un microcomputer utilisable dans un pacemaker antitachycardie. Celui ci distingue les tachycardies auriculaires, ventriculaires et de réentrée du noeud AV et ne reconnait pas les tachycordies sinusales. De même a été developpé une nouvelle méthode permettant au pacemaker à laide dun extrastimulus auriculaire de distinguer les tachycardies paroxystiques 1/1 des tachycardies sinusales. Celle ci est actuellement testée au laboratoire déIectro‐physiologie. Les résullats préliminaires indiquent que ces deux tachycardies peuvent être distinguées de façon fiable par un extrastimulus délivré avec un couplage correct dans loreiilette droite.

Evaluation of Esophageal Electrodes for Recording His-Purkinje Activity Based Upon Signal Variance

Signal averaging the ECG to observe low level signals generated by His¿Purkinje system (HPS) has many disadvantages and has not been widely used. This is partly due to the inability to distinguish between atrial and HPS potentials within the PR segment. To more clearly observe the onset of the HPS activity, several leads with an esophageal electrode were studied and compared to a bipolar surface lead. Signal variance was calculated to estimate the noise levels present in all lead systems. The bipolar surface lead consistently provided reproducible HPS waveforms with accurate estimates of noise levels. The leads with an esophageal electrode (bipolar or esophago¿thoracic) failed to show reproducible HPS waveforms and had higher noise levels than the bipolar surface lead as measured by signal variance. The cause of these problems is the motion of the electrode within the esophagus, as visualized fluoroscopically. While the novel lead systems were not adequate for recording HPS waveforms, the analytic methods for evaluating signal averaged recordings from various lead systems provided a basis for optimizing this approach for quantifying low level cardiac signals.

Differentiation of Sinus Tachycardia from Paroxysmal 1:1 Tachycardias Using Single Late Diastolic Atrial Extrastimuli

. Existing antitachycardia devices do not discriminate perfectly between sinus tachycardia and paroxysmal tachycardias with 1:1 atrioventricular relationship (paroxysmal 1:1 tachycardias). The present study tested the hypothesis that the nature of the ventricular response to atrial extrastimulation might distinguish between sinus tachycardia and selected paroxysmal 1:1 tachycardias. In 15 patients, atrial extrastimuli were delivered during sinus tachycardia and in 13 patients during various types of paroxysmal 1:1 tachycardia, and the timing of the next ventricular beat was measured. During sinus tachycardia, in 14 of 15 patients, atrial extrastimuli which were, in turn, early by 80 and 100 ms made the next ventricular beat premature by at least 30 and 50 ms, respectively. In all 13 patients, during paroxysmal 1:1 tachycardia, atrial extrastimuli that were early by 80 and 100 ms failed to make the next ventricular beat premature by more than 10 ms. Single atrial extrastimuli that were premature by less than or equal to 100 ms did not provoke faster tachycardias in any of the patients. In this study, a technique that used single late extrastimuli during tachycardia safely distinguished sinus tachycardia from paroxysmal tachycardias. This technique might be suitable for incorporation into an antitachycardia device. Further investigation of this technique is warranted in a larger number of patients with a wider variety of tachycardias.

Orthogonal Surface Lead Recordings of His-Purkinje Activity: Comparison of Actual and Simulated Waveforms

Noninvasive His-Purkinje system (HPS) recordings can be obtained using high amplification and signal averaging. However, this technique lacks the firm underpinnings necessary for its establishment as a useful clinical tool for the study of the electrical activity of the heart. Previous work has been incomplete resulting in fragmented knowledge of the body surface HPS activity and the nature of the HPS as an electrical source.

A single atrial extrastimulus can distinguish sinus tachycardia from 1:1 paroxysmal tachycardia.

We have developed a tachycardia detection scheme for use in an antitachycardia pacemaker in which the use of a properly timed atrial extrastimulus provides a means of discriminating sinus tachycardia from pace‐terminable 1:1 tachycardias. An atrial extrastimulus is delivered in late diastole (80 ms premature), and the ventricular response is monitored. In sinus tachycardia, the ventricular response is expected to appear early as well, but in pace‐terminable tachycardias, such as AV reentrant and ventricular with VA conduction, the ventricular rhythm will be unperturbed. Testing of the algorithm was performed in 34 patients. In 29 patients, atrial extrastimuli were delivered during sinus tachycardia, and in 22 patients during various types of 1:1 paroxysmal tachycardia. In one patient the procedure was completely automated, i.e., delivery of the atrial extrastimuli and diagnosis were microcomputer controlled. In 28/29 cases, the delivery of an atrial extrastimulus 80 to 120 ms early during sinus tachycardia elicited a ventricular response at least 28 ms early. In 22/22 patients with 1:1 paroxysmal tachycardia, atrial extrastimuli 80 to 120 ms early failed to produce a significant change in ventricular cycle length. This technique appears to be promising for prevention of inadvertent pacing of sinus tachycardia in an antitachycardia pacemaker.

Development of an automatic implanted drug infusion system for the management of cardiac arrhythmias

Conventional management of cardiac arrythmias relies on oral drug therapy which minimizes recurrence of the arrhythmia, but risks unpleasant side effects and even long-term toxicity. The authors propose acute management instead, from an implanted drug pump which automatically senses the onset of arrhythmia, delivers a pharmacokinetically-based infusion to terminate the episode, and discontinues drug delivery until the next occurrence. A bedside system consisting of a personal computer and conventional intravenous pump has been developed and tested in five dogs and 24 patients during a catheter electrophysiologic study. After detection of the arrhythmia plasma levels of the antiarrhythmia drug rose immediately to the therapeutic range and were subsequently well-controlled for 30 to 60 minutes. In all five dogs and in seven of the eight patients in whom atrial fibrillation was induced during the study, conversion to normal rhythm occurred within fifteen minutes. >

Detection of atrial fibrillation via pacemaker threshold scanning

Atrial fibrillation (AF) is the most commonly occurring arrhythmia, often present in addition to more serious arrhythmias. When a patient with an ICD has an episode of atrial fibrillation, the resulting irregular and rapid ventricular rate leads to false identification of a tachycardia. Automatic detection of atrial fibrillation could therefore improve ICD and pacemaker specificity, as well as lead to devices specifically for AF. The major obstacle preventing automatic AF detection is the failure of the sensing threshold to produce consistent rate estimates without over/under-sensing. The authors propose a new algorithm based on the hypothesis that: in sinus rhythm (SR), rate measurements are constant over a wide range of sensing thresholds; whereas in AF, rate measurements are a highly dependent function of threshold.<<ETX>>

Sensitivity and specificity of a dual-chamber arrhythmia recognition algorithm for implantable devices*

Present ventricular rate-based arrhythmia detection algorithms lack specificity. Using a training set of 109 endocardial electrogram recordings, a sensitive and specific dual-chamber arrhythmia recognition algorithm has been developed. The algorithm uses atrial and ventricular rates, irregularity, degree of beat-to-beat similarity, and measure of electrogram complex distinctiveness to arrive at a diagnostic conclusion. A test set of 121 endocardial electrogram recordings obtained during provocative electrophysiology studies was then used for blinded validation of the algorithm. In normal rhythm, 1:1 tachycardia, atrial tachycardia, atrial flutter, atrial fibrillation, ventricular tachycardia, and ventricular fibrillation, the percentages of sensitivity/specificity were, respectively, 100/99, 100/99, 80/99, 89/98, 91/97, 92/100, and 100/98. Although ventricular rate alone can usually distinguish normal rhythm, ventricular tachycardia, and ventricular fibrillation, it is confounded by atrial arrhythmias and 1:1 tachycardias. When tested on a database, a ventricular rate-only algorithm resulted in sensitivity/specificity of 100/65, 90/78, and 100/99%, respectively, for these three rhythms. Therefore, the dual-chamber algorithm based on both temporal and morphologic measures provides better distinction of normal rhythm and ventricular tachycardia than existing methods, without sacrificing sensitivity.

Computer Simulation of Adaptive Drug Infusion

Clinical drug infusion protocols, such as a single bolus followed by a constant drip, do not establish and maintain therapeutic drug levels in an optimal manner. We have investigated a system in which the patient, drug pump, drug assay, and a pump controller are incorporated into an adaptive configuration. The system, which we have simulated on a computer, uses an adaptive approach in which the pump controller operates with a model of the subject response. The model is fit to the specific subject by a regression analysis of the subjects response, obtained by assay of the subjects blood.