Pitfalls of the concept of incremental specificity used in comparisons of dual chamber VT/VF detection algorithms

Improving SVT Discrimination in Single-Chamber ICDs: A New Electrogram Morphology-Based Algorithm

INTRODUCTION

Wide-spread adoption of ICD therapy has focused efforts on improving the quality of life for patients by reducing "inappropriate" shock therapies. To this end, distinguishing supraventricular tachycardia from ventricular tachycardia remains a major challenge for ICDs. More sophisticated discrimination algorithms based on ventricular electrogram morphology have been made practicable by the increased computational ability of modern ICDs.

METHODS AND RESULTS

We report results from a large prospective study (1,122 pts) of a new ventricular electrogram morphology tachycardia discrimination algorithm (Wavelet Dynamic Discrimination, Medtronic, Minneapolis, MN, USA) operating at minimal algorithm setting (RV coil-can electrogram, match threshold of 70%). This is a nonrandomized cohort study of ICD patients using the morphology discrimination of the Wavelet algorithm to distinguish SVT and VT/VF. The Wavelet criterion was required ON in all patients and all other supraventricular tachycardia discriminators were required to be OFF. Spontaneous episodes (N = 2,235) eligible for ICD therapy were adjudicated for detection algorithm performance. The generalized estimating equations method was used to remove bias introduced when an individual patient contributes multiple episodes. Inappropriate therapies for supraventricular tachycardia were reduced by 78% (90% CI: 72.8-82.9%) for episodes within the range of rates where Wavelet was programmed to discriminate. Sensitivity for sustained ventricular tachycardia was 98.6% (90% CI: 97-99.3%) without the use of high-rate time out.

CONCLUSIONS

Results from this prospective study of the Wavelet electrogram morphology discrimination algorithm operating as the sole discriminator in the ON mode demonstrate that inappropriate therapy for supraventricular tachycardia in a single-chamber ICD can be dramatically reduced compared to rate detection alone.

Comparison of the Specificity of Implantable Dual Chamber Defibrillator Detection Algorithms

The aim of the study was to compare the specificity of dual chamber ICDs detection algorithms for correct classification of supraventricular tachyarrhythmias derived from clinical studies according to their size to detect an impact of sample size on the specificity. Furthermore, the study sought to compare the specificities of detection algorithms calculated from clinical data with the specificity calculated from simulations of tachyarrhythmias. A survey was conducted of all available sources providing data regarding the specificity of five dual chamber ICDs. The specificity was correlated with the number of patients included, number of episodes, and number of supraventricular tachyarrhythmias recorded. The simulation was performed using tachyarrhythmias recorded in the electrophysiology laboratory. The range of the number of patients included into the studies was 78-1,029, the range of the total number of episodes recorded was 362-5,788, and the range of the number of supraventricular tachyarrhythmias used for calculation of the specificity for correct detection of these arrhythmias was 100 (Biotronik) to 1662 (Medtronic). The specificity for correct detection of supraventricular tachyarrhythmias was 90% (Biotronik), 89% (ELA Medical), 89% (Guidant), 68% (Medtronic), and 76% (St. Jude Medical). There was an inverse correlation (r = -0.9, P = 0.037) between the specificity for correct classification of supraventricular tachyarrhythmias and the number of patients. The specificity for correct detection of supraventricular tachyarrhythmias calculated from the simulation after correction for the clinical prevalence of the simulated tachyarrhythmias was 95% (Biotronik), 99% (ELA Medical), 94% (Guidant), 93% (Medtronic), and 92% (St. Jude Medical). In conclusion, the specificity of ICD detection algorithms calculated from clinical studies or registries may depend on the number of patients studied. Therefore, a direct comparison between different detection algorithms based on clinical data is difficult. In contrast, simulation of supraventricular tachyarrhythmias using a uniform database may be a better tool for direct comparison of the specificity of ICD detection algorithms.

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

INTRODUCTION

Despite continuing advances, inappropriate implantable cardioverter defibrillator (ICD) therapies in response to nonventricular tachyarrhythmias continue to cause patient discomfort and increased follow-up demands.

METHODS AND RESULTS

We investigated the performance of a new dual-chamber ICD (Photon DR, St. Jude Medical), with specific attention to its arrhythmia discrimination and detection capabilities. The system uses a hierarchical approach to tachyarrhythmia classification utilizing a new AV Rate Branch feature and subsequently utilizing morphology analysis, onset, and stability criteria. The arrhythmia discrimination results from this study group were compared to historical control group data from a recent clinical investigation of single-chamber Contour MD (Morphology Discrimination) and Angstrom MD ICDs without the Rate Branch feature. Rhythm discrimination was evaluated by comparing ventricular tachycardia diagnosis sensitivity and specificity between the two groups. To determine whether the new discrimination scheme affected detection speed, median ventricular fibrillation (VF) detection and redetection times also were compared. The study group consisted of 107 patients, and the control group consisted of 161 patients. Use of the AV Rate Branch feature was associated with significant improvements in both sensitivity (100% vs 97.9%, P < 0.0001) and specificity (84% vs 55.7%, P = 0.0002) of ventricular tachycardia diagnosis. Use of the new scheme slightly but significantly accelerated VF detection times (2.8 vs 3.0 sec, P < 0.0001) and redetection times (1.3 vs 1.4 sec, P < 0.0001). Adverse events were typical for this patient population.

CONCLUSION

Compared with earlier St. Jude Medical ICDs, the Photon DR ICD offers improved rhythm discrimination without compromising VF detection time.