Athula Abeyratne

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.

Downloadable software algorithm reduces inappropriate shocks caused by implantable cardioverter-defibrillator lead fractures: a prospective study.

Background— Downloadable software upgrades are common in consumer electronics but not in implantable medical devices. Fractures of implantable cardioverter-defibrillator (ICD) leads present commonly as inappropriate shocks. A lead-integrity alert (LIA) designed to reduce inappropriate shocks is the first software download approved to enhance nominally functioning, previously implanted ICDs. Methods and Results— We performed a prospective study to determine whether an LIA could reduce inappropriate shocks. Patients were included if they had ICD lead fractures confirmed by analysis of explanted leads. The LIA group included the first 213 patients who met the inclusion criteria after the LIA was approved who had the LIA downloaded. The LIA is triggered either by high impedance or rapid oversensing. It responds by delaying detection of ventricular fibrillation and initiating a patient alert every 4 hours. The control group included the first 213 patients who did not have the LIA downloaded. They were monitored by conventional daily impedance measurements that respond with a daily alert. The LIA group had a 46% relative reduction (95% confidence interval 34% to 55%) in the percentage of patients with ≥1 inappropriate shock (LIA 38% versus control 70%, P<0.001) and a 50% relative reduction (95% confidence interval 33% to 61%) in the percentage with ≥5 shocks (25% versus 50%, P<0.001). The LIA group also had a higher percentage of patients who either did not receive a shock or had ≥3 days of warning before the shock (72% versus 50%, P<0.001). Conclusions— A software download that upgrades previously implanted ICDs without surgical revision reduces inappropriate shocks caused by lead fractures.

Clinical outcomes with synchronized left ventricular pacing: analysis of the adaptive CRT trial.

BACKGROUND Acute studies have suggested that left ventricular pacing (LVP) may have benefits over biventricular pacing (BVP). The adaptive cardiac resynchronization therapy (aCRT) algorithm provides LVP synchronized to produce fusion with the intrinsic activation when the intrinsic atrioventricular (AV) interval is normal. The randomized double-blind adaptive cardiac resynchronization therapy trial demonstrated noninferiority of the aCRT algorithm compared to echocardiography-optimized BVP (control). OBJECTIVE To examine whether synchronized LVP (sLVP) resulted in better clinical outcomes. METHODS First, stratification by percent sLVP (%sLVP) and multivariate Cox proportional hazards model was used to assess the relationship between %sLVP and clinical outcomes. Second, outcomes were compared between patients in the aCRT arm (n = 318) and control patients (n = 160) stratified by intrinsic AV interval at randomization. RESULTS In the aCRT arm, %sLVP ≥50% (n = 142) was independently associated with a decreased risk of death or heart failure hospitalization (hazard ratio 0.49; 95% confidence interval 0.28-0.85; P = .012) compared with %sLVP <50% (n = 172). A greater proportion of patients with %sLVP ≥50% improved in Packers clinical composite score at 6-month (82% vs. 68%; P = .002) and 12-month (80% vs. 62%; P = .0006) follow-ups compared to controls. In the subgroup with normal AV (n = 241), there was a lower risk of death or heart failure hospitalization (hazard ratio 0.52; 95% confidence interval 0.27-0.98; P = .044) with the aCRT algorithm. A greater proportion of patients in the aCRT arm improved in the clinical composite score at 6-month (81% vs. 69%; P = .041) and 12-month (77% vs. 66%; P = .076) follow-ups compared to controls. CONCLUSIONS Higher %sLVP was independently associated with superior clinical outcomes. In patients with normal AV conduction, the aCRT algorithm provided mostly sLVP and demonstrated better clinical outcomes compared to echocardiography-optimized BVP.

High Amplitude T-wave Alternans Precedes Spontaneous Ventricular Tachycardia or Fibrillation in ICD Electrograms

BACKGROUND T-wave alternans (TWA) increases acutely prior to ventricular tachycardia (VT) or fibrillation (VF) in animal studies, suggesting that it may provide a warning for VT/VF in implantable cardioverter defibrillator (ICD) patients. Clinically, measurement of surface ECG TWA requires preprocessing the input signal to reduce noise and/or analyzing more sinus beats than are recorded in ICDs as pre-onset, stored intracardiac electrograms (EGMs) before VT/VF. Our objective was to measure TWA from the few sinus EGMs stored in ICDs before spontaneous VT/VF in humans. OBJECTIVE The purpose of this study was to evaluate the technical feasibility of measuring TWA from pre-onset ICD EGMs and to measure EGM TWA before spontaneous VT/VF in humans. METHODS We developed a method to measure EGM TWA as a simple average (AVE) of peak-to-peak alternans. Using simulation, we determined the effect of ICD signal processing on EGM TWA for durations comparable to those in pre-onset EGMs. We then applied this method to pre-onset ICD EGMs that preceded 101 episodes of sustained VT/VF in 10 patients. In 6 of these patients, EGM recordings in atrial pacing and sinus rhythm provided control data. RESULTS In simulation, the AVE method discriminated input TWA differences > or = 15 microV. In patients, EGM TWA was 78 +/- 62 microV prior to VT/VF vs. 13 +/- 10 microV in control recordings (p< .0001). Eighty percent of pre-onset measurements exceeded 30 microV, while 95% of control measurements were less than 30 microV. CONCLUSIONS A simple averaging method can measure TWA preceding VT/VF in stored ICD EGMs. Pilot data indicate that high-amplitude EGM TWA usually precedes spontaneous VT/VF and is infrequent in control recordings. They provide a rationale for developing ICD technology to measure EGM TWA continuously, both to warn patients and to initiate pacing algorithms to prevent VT/VF.

Intracardiac Electrogram T-Wave Alternans/Variability Increases Before Spontaneous Ventricular Tachyarrhythmias in Implantable Cardioverter-Defibrillator Patients A Prospective, Multi-Center Study

Background— T-wave alternans (TWA) increases before ventricular tachycardia (VT) or fibrillation (VF), suggesting that it may warn of VT/VF in implantable cardioverter-defibrillator patients. Recently, we described a method for measuring alternans and nonalternans variability (TWA/V) from electrograms (EGMs) stored in implantable cardioverter-defibrillators before VT/VF. The goal of this prospective, multicenter study was to determine whether EGM TWA/V was greater before VT/VF than at baseline. Methods and Results— We enrolled 63 implantable cardioverter-defibrillator patients. TWA/V was computed from stored EGMs before spontaneous VT/VF and from sequential windows of 8 pairs of beats using 4 different control recordings: baseline rhythm, rapid pacing at 105 bpm, segments of ambulatory Holter EGMs matched to the time of VT/VF episodes, and EGMs before spontaneous supraventricular tachycardia. During follow-up, 28 patients had 166 episodes of VT/VF. TWA/V was greater before VT/VF (62.9±3.1 &mgr;V; n=28) than during baseline rhythm (12.8±1.8 &mgr;V; P<0.0001; n=62), during rapid pacing (14.5±2.0 &mgr;V; P<0.0001; n=52), before supraventricular tachycardia (27.5±6.1 &mgr;V; P<0.0001; n=9), or during time-matched ambulatory controls (12.3±3.5 &mgr;V; P<0.0001; n=16). By logistic regression, the odds of VT/VF increased by a factor of 2.2 for each 10-&mgr;V increment in TWA/V (P<0.0001). Conclusions— In implantable cardioverter-defibrillator patients, EGM TWA/V is greater before spontaneous VT/VF than in control recordings. Future implantable cardioverter-defibrillators that measure EGM TWA/V continuously may warn patients and initiate pacing therapies to prevent VT/VF.

Intracardiac QT integral on far-field ICD electrogram predicts sustained ventricular tachyarrhythmias in ICD patients

BACKGROUND Prediction of sustained ventricular tachycardia (VT)/ventricular fibrillation (VF) could help to guide preventive interventions in at-risk patients. The QRST integral (∫QT) reflects intrinsic repolarization properties. OBJECTIVE The objective of this study was to determine whether intracardiac ∫QT predicts VT/VF in the next few months in patients with implantable cardioverter defibrillators (ICDs). METHODS Far-field (FF) and near-field (NF) right ventricular intracardiac electrograms (EGMs) were recorded via telemetry in 46 patients with structural heart disease and ICDs implanted for secondary prevention of sudden cardiac death. Epochs of 4.9 ± 0.4 minutes during sinus rhythm (mean heart rate 70.9 ± 15.2 beats/min) and ventricular pacing at 105 beats/min were analyzed. Mean ∫QT was calculated on FF and NF EGMs as the algebraic sum of areas under the QRST curve and adjusted by mean heart rate. Patients were followed up for at least 3 months. True VT/VF events treated by the ICD served as the end point. RESULTS During a mean follow-up of 4.6 months, 22 patients (48%) were treated for VT/VF. Unadjusted and adjusted by heart rate, FF EGM ∫QT in sinus rhythm was a significant predictor of VT/VF (unadjusted ∫QT hazard ratio 1.007; 95% confidence interval 1.002 to 1.0013; P = .007; adjusted ∫QT hazard ratio 1.68; 95% confidence interval 1.19 to 2.36; P = .002). The highest quartile of intracardiac ∫QT predicted VT/VF (log-rank test P = .042) and identified patients at risk with a specificity of 86% and positive predictive value of 73%. CONCLUSION Increased intracardiac FF EGM ∫QT predicts VT/VF in patients with structural heart disease and secondary prevention ICDs.

Downloadable Software Algorithm Reduces Inappropriate Shocks Caused by Implantable Cardioverter-Defibrillator Lead Fractures

Background— Downloadable software upgrades are common in consumer electronics but not in implantable medical devices. Fractures of implantable cardioverter-defibrillator (ICD) leads present commonly as inappropriate shocks. A lead-integrity alert (LIA) designed to reduce inappropriate shocks is the first software download approved to enhance nominally functioning, previously implanted ICDs. Methods and Results— We performed a prospective study to determine whether an LIA could reduce inappropriate shocks. Patients were included if they had ICD lead fractures confirmed by analysis of explanted leads. The LIA group included the first 213 patients who met the inclusion criteria after the LIA was approved who had the LIA downloaded. The LIA is triggered either by high impedance or rapid oversensing. It responds by delaying detection of ventricular fibrillation and initiating a patient alert every 4 hours. The control group included the first 213 patients who did not have the LIA downloaded. They were monitored by conventional daily impedance measurements that respond with a daily alert. The LIA group had a 46% relative reduction (95% confidence interval 34% to 55%) in the percentage of patients with ≥1 inappropriate shock (LIA 38% versus control 70%, P<0.001) and a 50% relative reduction (95% confidence interval 33% to 61%) in the percentage with ≥5 shocks (25% versus 50%, P<0.001). The LIA group also had a higher percentage of patients who either did not receive a shock or had ≥3 days of warning before the shock (72% versus 50%, P<0.001). Conclusions— A software download that upgrades previously implanted ICDs without surgical revision reduces inappropriate shocks caused by lead fractures.

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

Downloadable Software Algorithm Reduces Inappropriate Shocks Caused by Implantable Cardioverter-Defibrillator Lead FracturesClinical Perspective

Background— Downloadable software upgrades are common in consumer electronics but not in implantable medical devices. Fractures of implantable cardioverter-defibrillator (ICD) leads present commonly as inappropriate shocks. A lead-integrity alert (LIA) designed to reduce inappropriate shocks is the first software download approved to enhance nominally functioning, previously implanted ICDs. Methods and Results— We performed a prospective study to determine whether an LIA could reduce inappropriate shocks. Patients were included if they had ICD lead fractures confirmed by analysis of explanted leads. The LIA group included the first 213 patients who met the inclusion criteria after the LIA was approved who had the LIA downloaded. The LIA is triggered either by high impedance or rapid oversensing. It responds by delaying detection of ventricular fibrillation and initiating a patient alert every 4 hours. The control group included the first 213 patients who did not have the LIA downloaded. They were monitored by conventional daily impedance measurements that respond with a daily alert. The LIA group had a 46% relative reduction (95% confidence interval 34% to 55%) in the percentage of patients with ≥1 inappropriate shock (LIA 38% versus control 70%, P<0.001) and a 50% relative reduction (95% confidence interval 33% to 61%) in the percentage with ≥5 shocks (25% versus 50%, P<0.001). The LIA group also had a higher percentage of patients who either did not receive a shock or had ≥3 days of warning before the shock (72% versus 50%, P<0.001). Conclusions— A software download that upgrades previously implanted ICDs without surgical revision reduces inappropriate shocks caused by lead fractures.

Downloadable Software Algorithm Reduces Inappropriate Shocks Caused by Implantable Cardioverter-Defibrillator Lead FracturesClinical Perspective: A Prospective Study

Background— Downloadable software upgrades are common in consumer electronics but not in implantable medical devices. Fractures of implantable cardioverter-defibrillator (ICD) leads present commonly as inappropriate shocks. A lead-integrity alert (LIA) designed to reduce inappropriate shocks is the first software download approved to enhance nominally functioning, previously implanted ICDs. Methods and Results— We performed a prospective study to determine whether an LIA could reduce inappropriate shocks. Patients were included if they had ICD lead fractures confirmed by analysis of explanted leads. The LIA group included the first 213 patients who met the inclusion criteria after the LIA was approved who had the LIA downloaded. The LIA is triggered either by high impedance or rapid oversensing. It responds by delaying detection of ventricular fibrillation and initiating a patient alert every 4 hours. The control group included the first 213 patients who did not have the LIA downloaded. They were monitored by conventional daily impedance measurements that respond with a daily alert. The LIA group had a 46% relative reduction (95% confidence interval 34% to 55%) in the percentage of patients with ≥1 inappropriate shock (LIA 38% versus control 70%, P<0.001) and a 50% relative reduction (95% confidence interval 33% to 61%) in the percentage with ≥5 shocks (25% versus 50%, P<0.001). The LIA group also had a higher percentage of patients who either did not receive a shock or had ≥3 days of warning before the shock (72% versus 50%, P<0.001). Conclusions— A software download that upgrades previously implanted ICDs without surgical revision reduces inappropriate shocks caused by lead fractures.