(Circulation. 2001;103:381.)
© 2001 American Heart Association, Inc.
Clinical Investigation and Reports |
Critical Analysis of Dual-Chamber Implantable Cardioverter-Defibrillator Arrhythmia Detection
Results and Technical Considerations
From the Dept of Cardiology, Cleveland Clinic Foundation, Cleveland, Ohio (B.L.W.); Eberhard Karis Universitat, Tubingen, Germany (V.K.); Dept of Medicine, New Jersey Heart Institute, Haddonfield (K.V.); Dept of Medicine, Medical College of Virginia, Richmond (K.E.); Justus-Liebig-Universitat, Giessen, Germany (B.W.); Hopital Cardiologique, Lille Cedex, France (S.K.); and Medtronic, Inc, Minneapolis, Minn (J.M.G., C.M.D.).
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Abstract |
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Background—One of the perceived benefits of dual-chamber implantable cardioverter-defibrillators (ICDs) is the reduction in inappropriate therapy due to new detection algorithms. It was the purpose of the present investigation to propose methods to minimize bias during such comparisons and to report the arrhythmia detection clinical results of the PR Logic dual-chamber detection algorithm in the GEM DR ICD in the context of these methods.
Methods and Results—Between November 1997 and October 1998, 933 patients received the GEM DR ICD in this prospective multicenter study. A total of 4856 sustained arrhythmia episodes (n=311) with stored electrogram and marker channel were classified by the investigators; 3488 episodes (n=232) were ventricular tachycardia (VT)/ventricular fibrillation (VF), and 1368 episodes (n=149) were supraventricular tachycardia (SVT). The overall detection results were corrected for multiple episodes within a patient with the generalized estimating equations (GEE) method with an exchangeable correlation structure between episodes. The relative sensitivity for detection of sustained VT and/or VF was 100.0% (3488 of 3488, n=232; 95% CI 98.3% to 100%), the VT/VF positive predictivity was 88.4% uncorrected (3488 of 3945, n=278) and 78.1% corrected (95% CI 73.3% to 82.3%) with the GEE method, and the SVT positive predictivity was 100.0% (911 of 911, n=101; 95% CI 96% to 100%).
Conclusions—A structured approach to analysis limits the bias inherent in the evaluation of tachycardia discrimination algorithms through the use of relative VT/VF sensitivity, VT/VF positive predictivity, and SVT positive predictivity along with corrections for multiple tachycardia episodes in a single patient.
Key Words: pacemakers • defibrillation • tachycardia • cardioversion • ventricles • atrium
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Introduction |
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The basic goal of implantable cardioverter-defibrillator (ICD) therapy is to preserve life by terminating life-threatening ventricular tachycardia (VT) and ventricular fibrillation (VF) episodes. However, the secondary goal is to do so in the least obtrusive manner, delivering VT and VF therapy only when required. The addition of the atrial lead, used in dual-chamber ICDs, provides an opportunity to improve detection accuracy.
Detection accuracy measurements are difficult and depend on many factors. Patients present with a diversity of ventricular and supraventricular rhythms, at differing frequencies, heart rates, and therapy responses. ICDs classify rhythms differently, depending on the algorithms available in the device. Finally, the mechanics of arrhythmia detection are programmable and thus represent a variable in dynamic tension with the patient characteristics, which also change over time.
Although they are desirable, randomized studies of a direct comparison of detection algorithms have limited usefulness because new devices and algorithms are quickly implemented and the results of such studies soon become irrelevant. However, some control over the bias introduced by nonrandomized trials is required to permit comparison with as little manipulation as possible. It was the purpose of the present investigation to report the arrhythmia detection clinical results of the Medtronic Inc GEM DR dual-chamber ICD and to propose methods to minimize bias in the evaluation of arrhythmia detection algorithms.
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Methods |
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Dual-chamber rate-responsive ICDs (model 7271 GEM DR ICD; Medtronic Inc) were implanted into 933 patients in a prospective multicenter evaluation of a tachycardia detection algorithm, PR Logic, between November 1997 and October 1998. The mean follow-up time was 3.9 months, with a cumulative follow-up of 3622 months. Follow-up examinations were conducted at 1, 3, and 6 months after device implantation and every 6 months thereafter. Eligible patients were recruited who had (1) cardiac arrest due to a ventricular tachyarrhythmia, (2) spontaneous sustained VT, or (3) inducible VT on electrophysiological studies at 1 of 82 centers in North America, Europe, and Australia. Voluntary participation was documented with a signed institutional review board–approved written informed consent.
Tachycardia episodes for rhythms classified as VT, VF, or supraventricular tachycardia (SVT) were automatically documented with stored atrial and ventricular electrograms. This information was copied to disk for investigator evaluation and confirmation of classification. The investigator’s diagnosis was confirmed through a blinded review of a subset of the episodes and became the standard for the determination of the true nature of the rhythm. This review was performed on a subsample of 1845 of 4876 episodes (151 of 311 patients) by 1 of the ICD manufacturer’s experts (J.M.G.), who was blinded to the physician classification. The reviewers agreed in 98.2% (1812 of 1845) of the episodes.
The stored events were classified as (1) VT or VF or (2) SVT without a coexistent ventricular tachyarrhythmia. Calculations were made from the perspective of the ability of the ICD to accurately detect VT or VF (true positive [TP]), accurately detect SVT (withhold VT/VF therapies) without coexistent VT or VF (true negative [TN]), falsely detect SVT as VT or VF (false-positive [FP]), and falsely detect VT or VF as SVT (false-negative [FN]).
Device Description
The Medtronic model 7271 implantable defibrillator is
a dual-chamber rate-responsive pacemaker and implantable defibrillator.
The dual-chamber tachyarrhythmia detection algorithm in the ICD, PR
Logic, has 3 independently programmable criteria (SVT criteria) to
discriminate between SVT and VT/VF, with the goal of reducing the
incidence of inappropriate VT/VF therapy. The 3 SVT criteria are
programmed on or off for the detection of (1) sinus tachycardia, (2)
atrial fibrillation (AF)/flutter, and (3) other 1:1 SVT episodes. In
addition, the SVT limit parameter sets the fastest ventricular rate
that can be identified as an SVT; tachycardias faster than the SVT
limit are detected as VT or VF based on the ventricular rate criterion
alone. Tachycardia discrimination with PR Logic is performed with the
(1) atrial and ventricular rate, (2) pattern of atrial and ventricular
events, (3) ventricular cycle length regularity, (4) atrioventricular
(AV) dissociation, (5) evidence of AF, and (6) evidence of far-field
R-wave sensing on the atrial lead. If SVT is confirmed and a double
tachycardia, coexistence of a ventricular tachyarrhythmia during an
SVT, has been excluded, then antitachycardia therapy is
withheld.1
Statistical Methods
All spontaneous episodes with stored electrograms,
the investigating physician’s classification of the rhythm, and 
1
SVT criterion programmed ON were included in the analysis.
The sensitivity of a detection algorithm is the probability that VT/VF is detected when present. The absolute sensitivity of VT/VF detection cannot be computed from these data, because the ICD stores data only for those episodes that are rapid and long enough to be considered VT or VF based on the rate criterion. Therefore, we measured relative sensitivity defined as (sensitivity of detection with SVT criteria ON)/(sensitivity of rate-only detection). In this study, the sensitivity of rate-only detection is by definition 100% for episodes that are fast enough and long enough to be detected by the rate-only criterion. The relative sensitivity is [TP/(FN+TP)]x 100.
To determine the likelihood that a delivered ventricular arrhythmia pacing or shock therapy was appropriately required for treatment of a potentially life-threatening arrhythmia, the ventricular tachyarrhythmia (VT/VF) positive predictivity was calculated: [TP/(TP+FP)]x 100.
To determine the likelihood that ventricular arrhythmia pacing or shock therapy was appropriately not required during a rapid supraventricular rhythm, the supraventricular tachyarrhythmia (SVT) positive predictivity was calculated: [TN/(TN+FN)]x 100.
The specificity of a detection algorithm is the probability that VT/VF was NOT detected given that VT/VF was not present. The absolute specificity of VT/VF detection cannot be measured from these data for the same reasons that absolute VT/VF detection sensitivity cannot be computed. Therefore, we measured incremental specificity, which is the degree of improvement provided by the SVT criteria in reducing the number of FP VT/VF detections. VT/VF incremental specificity is defined as (specificity with SVT criteria ON)[minus](specificity with SVT criteria OFF). The specificity with SVT criteria OFF was 0%, because all episodes that meet rate detection criterion when enhancements are OFF will be detected and treated as VT/VF. Incremental specificity is equivalent to the observable specificity of detection with SVT criteria ON: [TN/(FP+TN)]x 100.
Bias is introduced in these performance numbers when an individual patient contributes multiple tachycardia episodes. Therefore, we corrected the algorithm performance calculations using the generalized estimating equations (GEE) statistical method2 3 with an exchangeable correlation structure to remove this bias. This technique controls for multiple responses within a patient by assuming a common correlation between any 2 responses. The resulting corrected observed performance measures are estimates of the average patient performance of the algorithm.
Patients
The clinical characteristics of the 933 patients are
similar to those of previously reported ICD populations and are listed
in
Table 1
. There were 4856 spontaneous sustained
tachycardias with 1 SVT criterion programmed ON that were recorded in
311 patients during the observation period. Physician classification
defined 3488 episodes of spontaneous VT/VF from 232 patients
(ventricular cycle length 329±75 ms) and 1368 episodes of spontaneous
SVT from 149 patients (ventricular cycle length 373±69
ms).
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Programming
The ICDs were programmed to detect VT with a
tachycardia detection interval (TDI) of 395±40 ms, VF with a
fibrillation detection interval (FDI) of 314±21 ms, and SVT with an
SVT limit interval of 260±112 ms.
Table 2 lists the ventricular cycle lengths of the
physician-classified VT/VF and SVT rhythms and the programmed TDI and
FDI for the 311 ICDs that responded to arrhythmias.
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The VT/VF and SVT rate detection parameters were clinically selected for each patient. The ventricular interval stability criterion was programmed off. The SVT criteria for sinus tachycardia and AF/flutter were programmed on at the time of discharge, and after the atrial lead was allowed to stabilize for 1 month, the "Other 1:1 SVT" criterion was usually enabled.
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Results |
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All 4856 sustained arrhythmia episodes in 311 patients, with
1 SVT criterion programmed ON, were included in the detection
performance calculations. There were a total of 3488 episodes of VT/VF
in 232 patients and 1368 episodes of SVT in 149 patients. The
percentage of rhythms with ventricular cycle length at least equal to
the SVT limit (eligible for SVT classification by PR Logic) was 85.5%
(4154 of 4856) of all (VT+VF+SVT) episodes and 81.9% (2855 of 3488) of
all VT/VF episodes.
Table 3 lists the device classification of the sustained
tachycardia episodes by number of episodes and the number of patients.
Also shown is the average ventricular cycle length of the episodes.
Figure 1 presents a waterfall diagram that outlines
the detection result for each of the 4856 sustained tachyarrhythmia
episodes.
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Figure 2 presents the PR Logic detection results compared
with physician classifications for the 4856 episodes. All 3488
sustained ventricular arrhythmias in 232 patients were detected and
treated with the ICD. There were 12 nonsustained episodes that did not
receive VT/VF therapy (<21-second duration). The combined sensitivity
for sustained VT and/or VF was 100.0% (95% CI 98.3% to
100%).
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Detection was appropriate for 3488 VT/VF episodes from a total of 3945 VT/VF episodes, for a VT/VF positive predictivity of 88.4% uncorrected and 78.1% corrected (95% CI 73.3% to 82.3%) with the GEE method. Detection was appropriate for all 911 SVT episodes (101 patients), for an SVT positive predictivity of 100.0% (95% CI 96% to 100%).
Of the 1368 SVT episodes (149 patients) rapid enough to be detected as a ventricular arrhythmia, 911 were recognized as SVT, not VT or VF. None of these 911 device-classified SVT episodes accelerated to VF or caused patient harm. The VT/VF incremental specificity was 66.6% uncorrected (911 of 1368) and 56.1% corrected (95% CI 48.9% to 63.1%) with the GEE method.
There were 457 episodes (86 patients) for which the PR Logic
SVT criteria did not withhold VT or VF detection when the episode was
SVT. The reasons are delineated in
Table 4 and are related to (1) placement of the atrial or
ventricular lead, (2) programming of the ICD, or (3) characteristics of
the detection algorithm.
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Discussion |
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The development of sophistication and complexity in any technology implies improvement. The improvement does not have to be manifest as reduced cost, improved survival, or improved quality of life but does suggest that it can be measured. The addition of an atrial lead and its impact on tachyarrhythmia detection provide an example of technological advance that is in the process of evaluation. This comparison is prone to manipulation, and the results have been misleading. Results from other dual-chamber detection algorithm trials have been reported but not with sufficient detail to accurately compare and draw conclusions.4 5 6 7 The essential issue is to determine the parameters that, when improved, make an important impact on the care of the patient. The second issue is to determine the assumptions made when the parameter is measured, so results can be accurately reported. The answers to these issues will change over time, but the development of standardized reporting methods must be initiated.
Algorithm Performance Measures
When evaluating any ICD tachycardia detection
algorithm, we propose that there are 3 prominent clinical questions
that need to be answered. (1) Does the algorithm detect all dangerous
ventricular tachyarrhythmias? (2) When therapy is delivered, how likely
is it that the rhythm required treatment with antitachycardia therapy?
(3) When therapy is withheld from a rapid rhythm, how likely is it that
it was safe to withhold therapy? The use of relative VT/VF sensitivity
(GEM DR results 100% [95% CI 98.3 to 100]), VT/VF positive
predictivity (GEM DR results 88.4% uncorrected and 78.1% corrected
[95% CI 73.3 to 82.3]), and SVT positive predictivity (GEM DR
results 100% [95% CI 96 to 100]) addresses each of these questions.
To remove bias introduced by patients who contribute multiple episodes
to the results, statistical methods such as the GEE method should be
used to correct the observed performance measures. Although there are
many other questions, when these 3 questions are answered in a
consistent manner, meaningful comparisons can then be made with other
devices and algorithms. Incremental specificity may not be used for
these comparisons because different ventricular rate-only algorithms
may have different specificities. Incremental specificity is useful
only to compare enhanced detection with the assumption of exactly the
same ventricular rate-only algorithm.
Control for clinical and technical variances is very
difficult. Future technological advances may obsolete some of the
currently important parameters, but we propose that there are 4 ICD
and 4 clinical parameters that are essential for any comparison. The
ICD parameters are (1) the slowest tachycardia detection rate, below
which no tachycardia is detected; (2) the fibrillation detection rate,
above which the rules for detection change; (3) the number of intervals
or time for detection to take place; and (4) the SVT limit, or rate
above which SVT tests are no longer applied. The clinical parameters
are (1) the inclusion of all arrhythmias; (2) the number, type, and
ventricular rate of arrhythmias presented to the algorithm (ventricular
versus supraventricular); (3) the mechanism of the supraventricular
rhythms presented to the algorithm (sinus tachycardia, AF, atrial
flutter, atrial tachycardia, AV node reentry tachycardia, etc); and (4)
the frequency and distribution of each tachycardia in the population
tested.
ICD Parameters
The tachycardia detection rate influences the number
and type of tachycardias presented to the detection algorithm. The
tachycardia detection rate not only affects the relative distribution
of the SVT mechanism for episodes being evaluated (eg, slower rates
will result in more sinus tachycardia presented to the algorithm) but
also may influence the relative challenge that the SVT presents to the
algorithm. Kühlkamp et al8
demonstrated that AF becomes more regular (and thus more similar to VT)
as ventricular rate increases.
Some manufacturers have intentionally designed less capability for discrimination of SVT and ventricular tachyarrhythmias for rhythms with ventricular rates faster than the fibrillation detection rate. For some algorithms, this limit is tied specifically to 1 of the programmed ventricular tachyarrhythmia detection zones; others, such as PR Logic, have a separately programmable SVT limit parameter. Regardless of the detection algorithm design, all fast SVT rhythms should be included in detection algorithm performance evaluation because the results will be influenced by the number of rhythms (supraventricular or ventricular in origin) that are faster than the fibrillation detection rate.
The duration or number of intervals to detect tachycardia will depend on the programmed detection parameters and the type of ventricular interval counting algorithms used for detection (eg, consecutive count or probabilistic counting), which in turn influences the number and type of tachycardias presented to the detection algorithm. Shorter detection times may yield more tachycardias per patient and may skew the distribution of SVT or VT/VF episodes depending on which type of episodes are more likely to be the result of short runs of tachycardia.
Clinical Parameters
Bias in the detection performance numbers will be
introduced when any subset of episodes is excluded. This bias can cause
discrepancies in the observed performance measures and the actual
clinical performance. The measures that describe detection algorithm
performance (positive predictivity, relative sensitivity, incremental
specificity) are probabilities that are derived from the number, type,
and detection result for the rhythms presented to the algorithm.
Without full disclosure of the number and type of tachyarrhythmias
presented, these probabilities are less relevant (eg,
1/1=1000/1000=100%).
The frequency and distribution of the arrhythmia mechanisms represented in the clinical trial and their match or mismatch to the strengths of the particular algorithms will determine the performance of the defibrillator. If an algorithm is weak in distinguishing sinus tachycardia from VT and there is little sinus tachycardia represented in the trial, then the weakness will not be identified. The outcome of the evaluation will depend on the weakness and strength of an algorithm and its opportunity in the clinical population.
Clinical Observations
A complete picture of detection algorithm performance
is not provided by statistical measures alone. An analysis of algorithm
weaknesses with corresponding clinical observations and occurrence
rates serves to complement the statistical performance measures. The
clinical observations for PR Logic are presented in
Table 4
with potential weakness being the inability to
consistently withhold VT/VF detection for certain types of SVT with
ventricular rates in the VT/VF detection zones, including (1) sinus or
atrial tachycardia or with intermittent far-field R-wave oversensing on
the atrial lead, (2) AF with ventricular rates in the VF zone, and (3)
sinus tachycardia or atrial tachycardia with long PR intervals (PR
interval 50% RR interval).
The influence of intermittent far-field R-wave oversensing on the atrial lead during SVTs in VT/VF zones may permit VT/VF detection to occur despite the dual-chamber algorithm. Intermittent far-field R-wave oversensing was the reason for 17% (84 of 457) of all inappropriate detections. The clinical solution to this problem is careful placement of atrial lead with close tip-ring spacing9 and/or careful programming of atrial sensitivity.
Discrimination of AF with a conducted ventricular rate in the VF detection zone is another potential point of vulnerability for PR Logic. No other manufacturer’s dual-chamber detection algorithms are in effect in the VF zone, so this is a point of vulnerability for all dual-chamber ICDs. In this study, 9.6% (44 of 457) of inappropriate detections were due to rapidly conducted AF in the VF zone despite the SVT limit being programmed appropriately to allow PR Logic to reject the rhythm. PR Logic can discriminate SVTs with AV association (eg, 2:1 atrial flutter) from true VF; however, PR Logic cannot discriminate rhythms with AV dissociation (eg, rapidly conducted atrial fibrillation) from true VF. One clinical solution is to reprogram the ICD detection zones such that the ventricular rates during AF are in the VT detection zone (or fast VT via VT), where the VT/AF discrimination algorithm is more powerful. However, care must be taken in making this change so the true VF is not underdetected.
PR Logic may interpret sinus or atrial tachycardia with long
PR intervals (PR interval 50% RR interval) for VT with 1:1 VA
conduction and not withhold VT/VF detection. Long PR intervals during
1:1 SVTs were the reason for 38% (174 of 457) of all inappropriate
VT/VF detections. In theory, VT with 1:1 VA conduction with long RP
intervals (such that the resulting PR interval is <50% of the RR
interval) may have therapies withheld inappropriately by the PR Logic
algorithm. Although there were no sustained tachycardia episodes of VT
with 1:1 VA and long RP intervals, there were 8 nonsustained episodes
(all <21 seconds in duration). The clinical incidence of SVT with long
PR intervals is low: 3% of patients in this study and in the
single-center experience reported by Wolpert et
al.10
Alternative Methods
An alternative to comparisons of detection algorithm
performance that result from clinical evaluations is to perform in
vitro studies with recordings of induced tachycardia episodes during
electrophysiology studies or during the implantation of implantable
defibrillators. This methodology has advantages in that it is easier to
control detection algorithm and clinical parameters. However, this
method is questionable in its ability to generate clinically meaningful
detection algorithm performance estimates, because the results will be
highly dependent on how closely the induced tachycardia recordings
match the clinically observed spontaneously occurring tachycardias for
cycle length, type, and distribution.
Study Limitations
Despite attempts to limit bias, there are limitations
to the techniques used in this evaluation. This was an observational
study of consecutive patients. Tachycardias below the detection rate or
persisting for less than the programmed detection duration were
excluded from this analysis regardless of the tachycardia mechanism,
ventricular or supraventricular, because they are by definition not
collected by the ICD. Tachycardia episode classification was based on
investigator classification according to symptoms, clinical
presentation, electrograms, and marker channel analysis. The
programming of the parameters was not prospectively prescribed but
individualized according to the clinical situation. Therefore,
programming to the mean values reported here may not produce similar
results.
Conclusions
A structured framework is required for valid
comparative analyses of tachycardia discrimination algorithms. This
report of the clinical results of the GEM DR PR Logic tachycardia
detection algorithm has been structured to answer 3 clinical questions:
(1) Does the algorithm detect all dangerous ventricular
tachyarrhythmias? (2) When a therapy is delivered, how likely is it
that the rhythm needed to be treated with antitachycardia therapy? (3)
When therapy is withheld from a rapid rhythm, how likely is it that it
was safe to withhold therapy? The use of relative VT/VF sensitivity,
VT/VF positive predictivity, and SVT positive predictivity and the
correction for multiple tachycardia episodes in a single patient
address each of these questions in a responsible fashion and may be
applied generally to all ICD detection algorithms. In addition, it is
essential to thoroughly characterize the clinical arrhythmias and the
defibrillator programming used to evaluate the algorithm so useful
comparisons can be made. Finally, it was valuable to characterize the
rhythms that proved difficult for the algorithm in identifying
areas of vulnerability and the mechanism of the detection failure. This
analytical process produced a firm foundation for future evaluations
and avoided much of the bias inherent in the clinical evaluation of new
therapies.
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Acknowledgments |
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This work was supported in part by Medtronic Inc (Minneapolis, Minn).
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Footnotes |
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Reprint requests to Bruce L. Wilkoff, MD, 9500 Euclid Ave, Desk F-15, Cleveland, OH 44195.
Dr Wilkoff served on physician review boards for Medtronic Inc, Guidant, Inc, and St Jude Inc. Dr Kühlkamp received an honorarium for medical education from Medtronic Inc and CPI/Guidant (1996 to 2000). Mr Gillberg and Dr DeSouza are employees of Medtronic, Inc.
Received June 5, 2000; revision received August 23, 2000; accepted August 31, 2000.
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M. O. Sweeney Overcoming the Defects of a Virtue: Dual-Chamber Versus Single-Chamber Detection Enhancements for Implantable Defibrillator Rhythm Diagnosis: The Detect Supraventricular Tachycardia Study Circulation, June 27, 2006; 113(25): 2862 - 2864. [Full Text] [PDF]
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P. A. Friedman, R. L. McClelland, W. R. Bamlet, H. Acosta, D. Kessler, T. M. Munger, N. G. Kavesh, M. Wood, E. Daoud, A. Massumi, et al. Dual-Chamber Versus Single-Chamber Detection Enhancements for Implantable Defibrillator Rhythm Diagnosis: The Detect Supraventricular Tachycardia Study Circulation, June 27, 2006; 113(25): 2871 - 2879. [Abstract] [Full Text] [PDF]
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A. Capucci, M. Santini, L. Padeletti, M. Gulizia, G. Botto, G. Boriani, R. Ricci, S. Favale, F. Zolezzi, N. Di Belardino, et al. Monitored Atrial Fibrillation Duration Predicts Arterial Embolic Events in Patients Suffering From Bradycardia and Atrial Fibrillation Implanted With Antitachycardia Pacemakers J. Am. Coll. Cardiol., November 15, 2005; 46(10): 1913 - 1920. [Abstract] [Full Text] [PDF]
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Z. Goldberger, B. Elbel, C. A. McPherson, A. D. Paltiel, and R. Lampert Cost Advantage of Dual-Chamber Versus Single-Chamber Cardioverter-Defibrillator Implantation J. Am. Coll. Cardiol., September 6, 2005; 46(5): 850 - 857. [Abstract] [Full Text] [PDF]
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D. A.M.J. Theuns, A. P. J. Klootwijk, D. M. Goedhart, and L. J.L.M. Jordaens Prevention of inappropriate therapy in implantable cardioverter-defibrillators: Results of a prospective, randomized study of tachyarrhythmia detection algorithms J. Am. Coll. Cardiol., December 21, 2004; 44(12): 2362 - 2367. [Abstract] [Full Text] [PDF]
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C. Kouakam, S. Kacet, J.-R. Hazard, A. Ferraci, H. Mansour, P. Defaye, J.-M. Davy, M. Lambiez, and on behalf of the Ventak AV Investigators Performance of a dual-chamber implantable defibrillator algorithm for discrimination of ventricular from supraventricular tachycardia Europace, January 1, 2004; 6(1): 32 - 42. [Abstract] [Full Text] [PDF]
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E. Aliot, Rém. Nitzsché, and A. Ripart Arrhythmia detection by dual-chamber implantable cardioverter defibrillators: A review of current algorithms Europace, January 1, 2004; 6(4): 273 - 286. [Abstract] [Full Text] [PDF]
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J. L. Rojo-Alvarez, A. Arenal, A. Garcia-Alberola, M. Ortiz, M. Valdes, and A. Artes-Rodriguez A new algorithm for rhythm discrimination in cardioverter defibrillators based on the initial voltage changes of the ventricular electrogram Europace, January 1, 2003; 5(1): 77 - 82. [Abstract] [PDF]
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K. M. Stein, D. E. Euler, R. Mehra, K. Seidl, D. J. Slotwiner, S. Mittal, S. M. Markowitz, B. B. Lerman, and Jewel AF Worldwide Investigators Do atrial tachyarrhythmias beget ventricular tachyarrhythmias in defibrillator recipients? J. Am. Coll. Cardiol., July 17, 2002; 40(2): 335 - 340. [Abstract] [Full Text] [PDF]
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V. Kuhlkamp and InSync 7272 ICD World Wide Investigators Initial experience with an implantable cardioverter-defibrillator incorporating cardiac resynchronization therapy J. Am. Coll. Cardiol., March 6, 2002; 39(5): 790 - 797. [Abstract] [Full Text] [PDF]
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S. W. Adler II, C. Wolpert, E. N. Warman, S. K. Musley, J. L. Koehler, and D. E. Euler Efficacy of Pacing Therapies for Treating Atrial Tachyarrhythmias in Patients With Ventricular Arrhythmias Receiving a Dual-Chamber Implantable Cardioverter Defibrillator Circulation, August 21, 2001; 104(8): 887 - 892. [Abstract] [Full Text] [PDF]
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