Jeffrey M. Gillberg

Critical Analysis of Dual-Chamber Implantable Cardioverter-Defibrillator Arrhythmia Detection

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 excha...

Downloadable algorithm to reduce inappropriate shocks caused by fractures of implantable cardioverter-defibrillator leads.

Background— The primary method for monitoring implantable cardioverter-defibrillator lead integrity is periodic measurement of impedance. Sprint Fidelis leads are prone to pace-sense lead fractures, which commonly present as inappropriate shocks caused by oversensing. Methods and Results— We developed and tested an algorithm to enhance early identification of lead fractures and to reduce inappropriate shocks. This lead-integrity algorithm, which can be downloaded into presently implanted implantable cardioverter-defibrillators, alerts the patient and/or physician when triggered by either oversensing or excessive increases in impedance. To reduce inappropriate shocks, the lead-integrity algorithm increases the number of intervals to detect (NID) ventricular fibrillation when triggered. The lead-integrity algorithm was tested on data from 15 970 patients with Fidelis leads (including 121 with clinically diagnosed fractures) and 95 other fractured leads confirmed by analysis of returned product. The effect of the NID on inappropriate shocks was tested in 92 patients with 927 shocks caused by lead fracture. Increasing the NID reduced inappropriate shocks (P<0.0001). The lead-integrity algorithm provided at least a 3-day warning of inappropriate shocks in 76% (95% CI, 66 to 84) of patients versus 55% (95% CI, 43 to 64) for optimal impedance monitoring (P=0.007). Its positive predictive value was 72% for lead fractures and 81% for lead fractures or header-connector problems requiring surgical intervention. The false-positive rate was 1 per 372 patient-years of monitoring. Conclusions— A lead-integrity algorithm developed for download into existing implantable cardioverter-defibrillators increases short-term warning of inappropriate shocks in patients with lead fractures and reduces the likelihood of inappropriate shocks. It is the first downloadable RAMware to enhance the performance of nominally functioning implantable cardioverter-defibrillators and the first implantable cardioverter-defibrillator monitoring feature that triggers real-time changes in ventricular fibrillation detection parameters to reduce inappropriate shocks.

The impact of atrial fibrillation with rapid ventricular rates and device programming on shocks in 106,513 ICD and CRT-D patients.

BACKGROUND The relationship between shocks, device programming, and atrial fibrillation (AF) with a rapid ventricular rate (AF + RVR) using continuous daily monitoring has not been studied in large number of patients with implantable cardioverter-defibrillators (ICDs). OBJECTIVE The aim of this analysis was to determine the impact of ICD programming and ventricular rate control during AF on ICD shocks. METHODS An observational cohort analysis was performed with dual-chamber ICD and cardiac resynchronization therapy-defibrillator devices. The primary endpoint was spontaneous all-cause shocked episodes per 100 patient-years. Shock reduction programming strategies were entered into a multivariable model including slowest ventricular tachycardia/ventricular fibrillation (VT/VF) detection threshold, number of intervals to detect VF (NID), supraventricular tachycardia (SVT) discriminators ON, antitachycardia pacing (ATP) ON for fast VTs (FVTs) and AF + RVR (AF ≥1 hour for ≥1 day with average ≥110 beats per minute). We also characterized the predictive ability of AF + RVR to identify patients at risk of subsequent shocks. RESULTS There were 106,513 patients at 2858 institutions, with 2.5 ± 1.4 years of follow-up, 75% being male, age 67 ± 12 years, 59% with dual-chamber ICDs, and 11% with AF + RVR. A total of 22,062 patients (21%) received 82,396 shocks. After adjusting for all variables, AF + RVR, slower VT/VF detection threshold, and shorter VF NID were found to be associated with more shocks (P < .05 for all). Continuous monitoring of AF + RVR identified patients at up to 5-fold increased risk of shocks. CONCLUSIONS Faster VT/VF detection thresholds, longer detection durations, use of SVT discriminators, and delivery of ATP reduces all-cause ICD shocks. Continuous monitoring of AF + RVR identifies patients at the highest risk of future ICD shocks.

Combining Shock Reduction Strategies to Enhance ICD Therapy: A Role for Computer Modeling

Combining Shock Reduction Strategies to Enhance ICD Therapy. Objectives: To develop a computer model to test shock reduction strategies such as antitachycardia pacing and shock withholding for supraventricular rhythms, oversensing, and nonsustained ventricular tachycardia.

An Adaptive Interval‐Based Algorithm for Withholding ICD Therapy During Sinus Tachycardia

Avoiding inappropriate ICD therapy during supraventricular tachycardia (SVT) while assuring 100% sensitivity for VT/VF remains a challenge. Inappropriate VT/VF therapy during sinus tachycardia (ST) is particularly distressing to the patient because the full sequence of ICD therapies is often delivered. ST or 1:1 atrial tachycardia (AT) with long PR intervals and ST or AT with atrial oversensing of far‐field R waves cause the majority of inappropriate therapy in the Medtronic GEM DR (Model 7271) ICD. The goals of the present effort were to define an adaptive interval‐based algorithm for withholding VT/VF therapy in dual chamber ICDs during ST and to compare performance of the adaptive algorithm with that of the original ST withholding algorithm in the GEM DR. The adaptive algorithm uses a combination of 1:1 atrial to ventricular conduction pattern, changes in RR intervals and changes in intrinsic PR intervals to establish evidence for or against the presence of ST. Performances of the adaptive and original ST withholding algorithms were compared on 3 databases collected by implanted GEM DR devices. The first database included 684 spontaneous VT/VF episodes. The second database included 216 spontaneous SVT episodes that received inappropriate VT/VF therapy. These databases included up to 2,000 atrial or ventricular sensed or paced events preceding the spontaneous tachycardias. The third database included 320 spontaneous ST/AT episodes for which therapy was appropriately withheld by the GEM DR. Performance of the adaptive algorithm on the third database was predicted rather than directly computed because of record length limitations. VT/VF therapy was classified as “withheld” if evidence of ST remained high for one algorithm (i.e., at least 7 more beats to VT/VF detection) at the point of VT/VF detection by the other algorithm. For the 684 true VT/VF episodes, the original algorithm withheld VT/VF therapy in 5 episodes and the adaptive algorithm withheld VT/VF therapy in 3 episodes. The 95% confidence interval for the difference in VT/VF sensitivity between the adaptive and original algorithms was [−0.5 to +1.1%]. Twelve of the 320 ST/AT episodes (3.8%) that were appropriately classified by the original algorithm were predicted to receive inappropriate therapy by the adaptive algorithm. However, relative to the original algorithm, the adaptive algorithm appropriately withheld VT/VF therapy for 76 of 216 true SVT episodes (i.e., incremental specificity of 35.2%). For the specific SVT episodes that were the targets for improvement by the adaptive ST algorithm (ST/AT with long PR intervals and ST/AT with intermittent atrial oversensing of far‐field R waves), the adaptive algorithm reduced inappropriate therapy by 63.2%. (PACE 2003; 26:1189–1201)

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.

A fully automatic, implantable cardioverter-defibrillator algorithm to prevent inappropriate detection of ventricular tachycardia or fibrillation due to T-wave oversensing in spontaneous rhythm

BACKGROUND T-wave oversensing (TWOS) may cause inappropriate shocks in patients with implantable cardioverter-defibrillator (ICD). Programming options to prevent TWOS are usually implemented only after TWOS has occurred, and they may compromise sensing of ventricular fibrillation (VF). OBJECTIVE To evaluate an ICD algorithm that differentiates TWOS from ventricular tachycardia (VT) or VF to prevent inappropriate detection of VT/VF when TWOS occurs. METHODS We developed a TWOS algorithm based on both the differential frequency content of R vs T waves and their alternating pattern. Algorithm parameters were developed from a database of stored electrograms. The algorithm was validated on a hardware system consisting of actual ICD circuitry by using an independent database of stored electrograms including inappropriate detections of both VT/VF caused by spontaneous TWOS and induced true VF to assess delays in detection. RESULTS We tested 83 inappropriate detections of VF due to TWOS from 22 patients. All 22 patients had at least 1 successful rejection of TWOS, and rejection was effective in 80 of the 83 episodes. After adjustment for multiple episodes per patient, specificity was 96.6% (95% confidence interval 90.3%-98.8%). In 166 episodes of true VF in 92 patients, the sensitivity for VF detection was 100% (95% confidence interval 98.2%-100%) at a nominal sensitivity of 0.3 mV; the new TWOS algorithm did not delay the detection of VF. CONCLUSION A novel TWOS rejection algorithm is designed to operate in real time. The algorithm reduced inappropriate detections of VF in spontaneous TWOS episodes by 96.6% while maintaining 100% sensitivity for detecting true VF.

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.

Changes in electrical dyssynchrony by body surface mapping predict left ventricular remodeling in patients with cardiac resynchronization therapy

BACKGROUND Electrical activation is important in cardiac resynchronization therapy (CRT) response. Standard electrocardiographic analysis may not accurately reflect the heterogeneity of electrical activation. OBJECTIVE We compared changes in left ventricular size and function after CRT to native electrical dyssynchrony and its change during pacing. METHODS Body surface isochronal maps using 53 anterior and posterior electrodes as well as 12-lead electrocardiograms were acquired after CRT in 66 consecutive patients. Electrical dyssynchrony was quantified using standard deviation of activation times (SDAT). Ejection fraction (EF) and left ventricular end-systolic volume (LVESV) were measured before CRT and at 6 months. Multiple regression evaluated predictors of response. RESULTS ∆LVESV correlated with ∆SDAT (P = .007), but not with ∆QRS duration (P = .092). Patients with SDAT ≥35 ms had greater increase in EF (13 ± 8 units vs 4 ± 9 units; P < .001) and LVESV (-34% ± 28% vs -13% ± 29%; P = .005). Patients with ≥10% improvement in SDAT had greater ∆EF (11 ± 9 units vs 4 ± 9 units; P = .010) and ∆LVESV (-33% ± 26% vs -6% ± 34%; P = .001). SDAT ≥35 ms predicted ∆EF, while ∆SDAT, sex, and left bundle branch block predicted ∆LVESV. In 34 patients without class I indication for CRT, SDAT ≥35 ms (P = .015) and ∆SDAT ≥10% (P = .032) were the only predictors of ∆EF. CONCLUSION Body surface mapping of SDAT and its changes predicted CRT response better than did QRS duration. Body surface mapping may potentially improve selection or optimization of CRT patients.

Comparison of Laplacian and Bipolar ECGs for R-wave Detection during Noise

Body surface Laplacian mapping localizes cardiac activity and provides more detailed distributions compared to body surface potential mapping. Systematic comparison of the performance of bipolar and Laplacian ECGs during noise has not been performed. To determine whether Laplacian ECGs (2.5cm diameter concentric rings) can reduce noise (myopotential and motion artifacts) and improve signal to noise ratio (SNR) compared to bipolar (4cm spacing) ECGs, Laplacian and bipolar ECGs were recorded from the anterior (precordial V3) and lateral (precordial V6) chest regions in 25 patients undergoing posture changes and in-office exercises. Mean peak-to-peak (Vpp ), root mean square noise (Noiserms) and SNR were computed across all activities and patients. Sensing performance using an R-wave detector with an auto-adjusting exponentially decaying threshold was assessed. Across all maneuvers, mean Vpp was larger for the bipolar ECG compared to the Laplacian ECG on the anterior (0.65plusmn0.07 vs. 0.14plusmn0.07 mV, p<0.05) and lateral (0.65plusmn0.07 vs. 0.05plusmn0.07 mV, p<0.05) regions. Laplacian ECGs resulted in least Noiserms compared to bipolar ECGs (anterior: 0.02plusmn0.01 vs. 0.05plusmn0.01, p<0.05; lateral: 0.01plusmn0.01 vs. 0.07plusmn0.01, p<0.05). Bipolar and Laplacian SNRs were comparable on the anterior chest (14.05plusmn0.95 vs. 13.49plusmn0.95, p=NS). On the lateral chest, bipolar SNR was larger than Laplacian SNR (13.78plusmn0.95 vs. 8.67plusmn0.96, p<0.05). Laplacian SNR on the anterior chest was larger compared to the lateral chest, confirming that Laplacian ECGs are sensitive to mapping location. Sensing performance showed that bipolar ECGs resulted in marginally superior sensing accuracy compared to Laplacian ECGs. In conclusion, Laplacian ECGs offer no advantage in SNR compared with standard bipolar ECGs