Clinical investigation of a new dual-chamber implantable cardioverter defibrillator with improved rhythm discrimination capabilities

Detection and discrimination of tachycardia in ICDs manufactured by St. Jude Medical

Modern implantable cardioverter/defibrillator (ICD) systems offer a multitude of algorithms to optimize performance in sensing and tachycardia detection even in difficult circumstances (e. g., ventricular tachycardia during supraventricular tachycardia, fine ventricular fibrillation with intermittent undersensing), to reliably discriminate sustained ventricular tachyarrhythmia from noise, nonsustained and supraventricular tachyarrhythmia, and to limit shock therapy only to those arrhythmias that definitely need to be treated by a shock. A disadvantage of these multiple algorithms is the complexity of annotated tracings that makes it sometimes difficult to understand why the ICD did what it did. If a tachycardia classification was wrong, it may be thus difficult to find the best way to reprogram the device to avoid another misclassification. This review explains in detail the algorithms used for tachycardia detection, discrimination, and prevention of inappropriate therapy in single- and dual-chamber ICDs manufactured by St. Jude Medical. Knowledge of these features may help to optimize ICD treatment in patients fitted with these devices.

Prospective comparison of discrimination algorithms to prevent inappropriate ICD therapy: primary results of the Rhythm ID Going Head to Head Trial

BACKGROUND

Inappropriate therapy for supraventricular arrhythmias remains a significant source of morbidity in implantable cardioverter-defibrillator (ICD) recipients.

OBJECTIVE

The Rhythm ID Goes Head to Head Trial (RIGHT) was designed to compare rhythm discrimination and inappropriate therapies among patients with ICDs from 2 manufacturers.

METHODS

Patients with standard ICD indications were randomized to receive a Guidant VITALITY 2 with Rhythm ID or selective Medtronic pulse generators using the Enhanced PR Logic or Wavelet discrimination algorithms. A single- or dual-chamber device was implanted based on clinical indications and programmed in 2 detection zones with detection enhancements enabled for rates between 150 and 200 bpm. Algorithm performance was compared between randomization groups, stratified by single or dual chamber, for the primary end point of first inappropriate therapy (shock or antitachycardia pacing) for supraventricular arrhythmias.

RESULTS

There were 1962 patients enrolled and followed for 18.3 ± 9.2 months, with no difference in all-cause mortality between groups. There were 3973 treated episodes where electrograms were available and adjudicated. The primary end point of inappropriate therapy occurred in 246 of 985 VITALITY 2 patients vs 187 of 977 specific Medtronic ICD patients (hazard ratio = 1.34; confidence interval = 1.11-1.62; P = .003). Differences in inappropriate therapy were confined to single-chamber ICDs. Inappropriate shocks were more frequent in VITALITY 2 ICDs (hazard ratio = 1.63; confidence interval = 1.29-2.06; P < .001), with most therapies and performance differences occurring at slower rhythms (rates < 175 bpm).

CONCLUSION

Rhythm discrimination performed better in the specific Medtronic than in VITALITY 2 ICDs evaluated, particularly for single-chamber devices. Inappropriate therapies, and differences in performance, may be reduced with the use of rate cutoff above 175 bpm.

Tools and strategies for the reduction of inappropriate implantable cardioverter defibrillator shocks

Implantable cardioverter defibrillators (ICDs) have been shown to provide a survival benefit in patients at high risk of sudden cardiac death. A major problem associated with ICD therapy is the occurrence of inappropriate shocks which impair patients' quality of life and may also be arrhythmogenic. Despite recent technological advances, the incidence of inappropriate shocks remains high, thus posing a challenge that we have to meet. In the present review we summarise the available tools and the strategies that can be followed in order to reduce inappropriate ICD shocks.

A new method to investigate the response to the morphology discrimination algorithm in patients with ICD

BACKGROUND

Inappropriate therapy for supraventricular tachyarrhythmia is still a major problem in implantable cardioverter defibrillators (ICD). The morphology discrimination algorithm compares the morphology of a tachycardia electrogram with a stored template on a beat-to-beat basis. However, algorithm responders could not yet be identified prior to the occurrence of first tachycardia episodes. We analyzed whether rapid atrial pacing and/or exercise testing can be used for identification of responders and compared the results with ICD detected tachycardia.

METHODS

22 patients (16 male, 61+/-14 years) with dual-chamber ICDs have been enrolled. Patients underwent a standardized bicycle exercise testing and an atrial pacing protocol. For both tests, morphology match scores of 8 consecutive beats were analyzed for each 10-bpm-step increment above sinus rhythm. Patients were categorized as responders, if morphology match was > or = 90% of tested heart rates. During follow-up, ICD stored episodes with morphology discrimination activated were evaluated.

RESULTS

There were no significant differences between morphology match (85+/-29% vs. 84+/-27%) and linear regression slope B (-0.19+/-0.87 vs. -0.20+/-0.48) during exercise testing and atrial pacing. 16 patients (73%) were classified as responders. During follow-up (739+/-338 days) 121 sustained supraventricular (n=88) and ventricular tachycardia (n=33) were detected in 10 patients (45%). Specificity for tachycardia discrimination was 78% overall, 100% in responders and 22% in non-responders.

CONCLUSION

Exercise testing and atrial pacing were equally suitable for identification of patients who seem to respond to the morphology discrimination algorithm with a high specificity for ventricular tachycardia discrimination. Thus, morphology match tests are suggested to optimize tachycardia discrimination and to reduce inadequate therapies.

Evaluation of morphology discrimination for ventricular tachycardia diagnosis in implantable cardioverter-defibrillators

BACKGROUND

To reduce inappropriate therapy from implantable cardioverter-defibrillators (ICDs), electrogram morphology discrimination has been developed to improve arrhythmia discrimination without compromising device safety.

OBJECTIVES

The purpose of this study was to determine the accuracy of the morphology discrimination algorithm for detecting ventricular tachycardia (VT).

METHODS

Stored electrograms of 795 tachyarrhythmias from 106 patients with a St. Jude Medical ICD (51 single-chamber and 55 dual-chamber) were analyzed by the investigators. The data were analyzed for morphology discrimination alone, sudden onset and stability, and morphology discrimination in combination with sudden onset and stability. Data were corrected for multiple episodes within a patient with the generalized estimating equation method.

RESULTS

Using the nominal template match of 60%, morphology discrimination alone provided sensitivity and specificity of 78% and 95% for single-chamber ICDs and 63% and 92% for dual-chamber ICDs, respectively. Based on the receiver operator characteristic curve, the optimal-match percent threshold was 80% to 85% but at the expense of specificity. Morphology discrimination combined with sudden onset and stability increased sensitivity to 98% with specificity of 86% in single-chamber devices. In dual-chamber devices, the loss in sensitivity is compensated by rate branch analysis, yielding a sensitivity of 98%.

CONCLUSION

Arrhythmia discrimination based on electrogram morphology has the potential to reject atrial tachyarrhythmias. However, there is a risk for underdetection of ventricular tachyarrhythmias if arrhythmia discrimination is primarily based on morphology. To guarantee patient safety in single-chamber devices, the morphology discrimination algorithm must be programmed in combination with established detection algorithms. In dual-chamber devices, loss of sensitivity is compensated by the V > A rate branch.

Continuous template collection and updating for electrogram morphology discrimination in implantable cardioverter defibrillators

INTRODUCTION

Electrogram morphology analysis improves discrimination of supraventricular tachycardias (SVTs) from ventricular tachycardias (VTs) in implantable cardioverter defibrillators (ICDs), but electrogram morphology may change with lead maturation, drugs, or disease progression. We report the clinical performance of an automatic algorithm that creates and updates templates from non-paced, slow rhythm and continuously checks the quality of the template used for arrhythmia discrimination.

METHODS AND RESULTS

We studied this algorithm in 193 patients with single-chamber ICDs (Marquis VR, Medtronic Inc., Minneapolis, MN, USA). Of the 112 patients who completed 6-month follow-up, 99.1% of the patients had > or =1 automatic template created. Match scores between template and ongoing rhythm are computed using Haar Wavelets. Of the 435 automatic templates evaluated at follow-up, 423 (97.2%) had a median match score > or =70%. Intrinsic rhythm at 1 month had significantly higher match scores (P < 0.001) with automatic templates (90.3 +/- 7.0%) than with manual templates (85.7 +/- 10.9%) generated at pre-hospital discharge (PHD). The percentage of appropriately rejected SVTs was slightly higher with the automatic template (280/339 episodes) than with the manual template at PHD (272/339 episodes) while the Wavelet detection of VT was the same (218/220 episodes).

CONCLUSIONS

In patients receiving ICDs, the automatic templates were successfully created during a 6-month follow-up period, and consistently matched the patients' intrinsic rhythm at the nominal match threshold. Both early (<1 month postimplant) and late (1- to 3-month follow-up period) changes in electrogram morphology were identified, confirming the need for automatic template updating.

Incidence and Clinical Relevance of Slow Ventricular Tachycardia in Implantable Cardioverter-Defibrillator Recipients

Background— This study aims to assess the incidence and clinical relevance of slow ventricular tachycardia (VT) and the effectiveness and/or deleterious effects of antitachycardia pacing in slow VT in implantable cardioverter-defibrillator recipients.

Methods and Results— This multicenter prospective randomized study included 374 patients (326 men) without prior history of slow VT (<148 bpm) implanted with a dual-chamber implantable cardioverter-defibrillator. Patients had a 3-zone detection configuration: a slow VT zone (101 to 148 bpm), a conventional VT zone (>148 bpm), and a ventricular fibrillation zone. Patients were randomized to a treatment group (n=183) with therapy activated in the slow VT zone or a monitoring group (n=191) with no therapy in the slow VT zone. During follow-up (11 months), 449 slow VTs occurred in 114 patients (30.5% slow VT incidence); 181 VTs (54 patients) occurred in the monitoring group; 3 were readmitted to the hospital; and lightheadedness and palpitations occurred in 4 and 250 (60 patients) in the treatment group treated by antitachycardia pacing (89.8% success rate) and shock delivery (n=2). There were 10 crossovers from the monitoring to treatment group and 3 crossovers from the treatment to monitoring group ( P =0.09). Quality of life scores were not different between groups.

Conclusions— Slow VT incidence (<150 bpm) is high (30%) in implantable cardioverter-defibrillator recipients without prior history of slow VT, has limited clinical relevance, and is efficiently and safely terminated by antitachycardia pacing.

Optimal Combination of Discriminators for Differentiating Ventricular from Supraventricular Tachycardia by Dual-Chamber Defibrillators

Discriminators for ventricular/supraventricular tachycardia.

INTRODUCTION

Dual-chamber implantable cardioverter defibrillators (ICDs) use discriminators to differentiate between supraventricular tachycardias (SVTs) and ventricular tachycardias (VT), the accuracy of which may depend on the type and method used. ICDs can combine rate branching of tachyarrhythmias according to their A:V relationship with two SVT-VT discriminators in each rate branch, using ANY (either) or ALL (both) logic. Our goal was to determine the optimal discriminator combination.

METHODS

Stored electrogram data from 596 spontaneous tachyarrhythmias from 203 patients with Photon DR ICDs were analyzed. Arrhythmias are first classified by the relationship of atrial and ventricular rates (rate branches V<A, V=A, and V>A) followed by additional discriminators: morphology and/or sudden onset if V=A; morphology and/or interval stability if V<A. Data were analyzed for all combinations of ANY and ALL logic.

RESULTS

Sensitivity and specificity were calculated for all spontaneous episodes in each analysis. V=A branch: ALL logic produced unacceptably low sensitivity, whereas morphology provided only similar sensitivity but better specificity than ANY logic. A>V branch: ANY logic provided adequate sensitivity. The combination of morphology only in V=A with interval stability or morphology (ANY logic) in V<A, provided the optimal result with sensitivity, specificity, positive, and negative predictive values of 99%, 79%, 87%, and 98%, respectively.

CONCLUSION

SVT-VT combined discriminators strongly influence dual-chamber SVT-VT discrimination performance. In our study, optimal programming is morphology only in the V=A branch and morphology or interval stability (ANY) in the V<A branch. ALL logic should be used with caution due to loss of sensitivity.

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.

METHODS

For this study we refer to sinus tachycardia, atrial tachycardia (AT), atrial fibrillation, and flutter as atrial tachycardia (AT), and all other tachycardia as "non-AT." Three atrial response patterns during the burst of ATP were determined. The atrial cycle length (ACL) may be unchanged (type 1) indicating AT. The ACL may show variation during ATP (type 2) indicating variable VA block and does not discriminate between an AT and a non-AT mechanism, in which case a default diagnosis of non-AT is made. The ACL may accelerate to the ATP cycle length (type 3) indicating entrainment. A VAAV response at the end of ATP was considered diagnostic of AT (type 3A) whereas a VAV or VVA response was considered a non-AT mechanism (type 3B). This algorithm was applied to ICD tracings from 68 episodes of spontaneous 1:1 A:V tachycardia that had 136 sequences of ATP administered. The rhythm "truth" was determined by consensus of two experienced clinicians.

RESULTS

The algorithm correctly identified AT with a sensitivity of 71.9% (95% CI: 67.1-73.6), and specificity of 95% (83.5-99.1). The PPV was 97.2% (90.9-99.5), and NPV 58.5% (51.4-61.0). Kappa was 0.57 (0.43-0.62). If used clinically the algorithm would have aborted 53.3% (8/15) of inappropriate shocks delivered into an AT-mechanism tachycardia and would not have withheld a shock for any episode of VT.

CONCLUSION

Analysis of atrial response patterns during and after ventricular ATP can successfully discriminate tachycardia mechanism and may reduce inappropriate ICD shocks.

Enhanced Specificity of a Dual Chamber ICD Arrhythmia Detection Algorithm by Rate Stability Criteria

Inappropriate therapy remains an important limitation of implantable cardioverter defibrillators (ICD). PARAD+ was developed to increase the specificity conferred by the original PARAD detection algorithm in the detection of atrial fibrillation (AF). To compare the performances of the two different algorithms, we retrospectively analyzed all spontaneous and sustained episodes of AF and ventricular tachycardia (VT) documented by state-of-the-art ICDs programmed with PARAD or PARAD+ at the physicians' discretion. The results were stratified according to tachycardia rates <150 versus > or =150 beats/min. The study included 329 men and 48 women (64 +/- 10 years of age). PARAD was programmed in 263, and PARAD+ in 84 devices. During a mean follow-up of 11 +/- 3 months, 1,019 VT and 315 AF episodes were documented among 338 devices. For tachycardias with ventricular rates <150 beats/min, the sensitivity of PARAD versus PARAD+ was 96% versus 99% (NS), specificity 80% versus 93% (P < 0.002), positive predictive value (PPV) 94% versus 91% (NS), and negative predictive value (NPV) 86% versus 99% (P < 0.0001). In contrast, in the fast VT zone, the specificity and PPV of PARAD (95% versus 84% and 100% versus 96%) were higher than those of PARAD+ (NS, P < 0.001). Among 23 AF episodes treated in 16 patients, 3 episodes triggered an inappropriate shock in 3 patients, all in the PARAD population. PARAD+ significantly increased the ICD algorithm diagnostic specificity and NPV for AF in the slow VT zone without compromising patient safety.