Bruce D. Gunderson

Detection of atrial fibrillation and flutter by a dual-chamber implantable cardioverter-defibrillator

BACKGROUND To distinguish prolonged episodes of atrial fibrillation (AF) that require cardioversion from self-terminating episodes that do not, an atrial implantable cardioverter-defibrillator (ICD) must be able to detect AF continuously for extended periods. The ICD should discriminate between atrial tachycardia/flutter (AT), which may be terminated by antitachycardia pacing, and AF, which requires cardioversion. METHODS AND RESULTS We studied 80 patients with AT/AF and ventricular arrhythmias who were treated with a new atrial/dual-chamber ICD. During a follow-up period lasting 6+/-2 months, we validated spontaneous, device-defined AT/AF episodes by stored electrograms in all patients. In 58 patients, we performed 80 Holter recordings with telemetered atrial electrograms, both to validate the continuous detection of AT/AF and to determine the sensitivity of the detection of AT/AF. Detection was appropriate in 98% of 132 AF episodes and 88% of 190 AT episodes (98% of 128 AT episodes with an atrial cycle length <300 ms). Intermittent sensing of far-field R waves during sinus tachycardia caused 27 inappropriate AT/AF detections; these detections lasted 2.6+/-2.0 minutes. AT/AF was detected continuously in 27 of 28 patients who had spontaneous episodes of AT/AF (96%). The device memory recorded 90 appropriate AT/AF episodes lasting >1 hour, for a total of 2697 hours of continuous detection of AT/AF. During Holter monitoring, the sensitivity of the detection of AT/AF (116 hours) was 100%; the specificity of the detection of non-AT/AF rhythms (1290 hours) was 99.99%. Of 166 appropriate episodes detected as AT, 45% were terminated by antitachycardia pacing. CONCLUSIONS A new ICD detects AT/AF accurately and continuously. Therapy may be programmed for long-duration AT/AF, with a low risk of underdetection. Discrimination of AT from AF permits successful pacing therapy for a significant fraction of AT.

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.

Performance of ICD Lead Integrity Alert to Assist in the Clinical Diagnosis of ICD Lead Failures: Analysis of Different ICD Leads

Background —The Lead Integrity Alert (LIA) was developed for Medtronic ICDs to reduce inappropriate shocks for rapid, oversensing caused by conductor fractures and reported for Medtronic FidelisTM conductor fractures. The goal of this study was to compare the performance of LIA with conventional impedance monitoring for identifying lead system events (LSE) and lead failures (LF) in lead families that differ from FidelisTM. Methods and Results —We analyzed data from 12,793 LIA enabled ICD and lead combinations including 6,123 St. Jude RiataTM or DurataTM, 5,114 Boston Scientific EndotakTM, and 1,556 FidelisTM combinations followed in the CareLinkTM remote monitoring network for LSEs and LFs. Each alert was adjudicated based on ICD stored EGMs/diagnostics and clinical data as a LSE or non-lead system event (NLE) by two physicians after reviewing the EGMs and clinical data. During 13,562 patient-years of LIA follow-up, there were 179 adjudicated alerts, of which 84 were LSE (including 65 LFs) and 95 were NLE. LIA identified greater than 66% more LSE and 67% more LF compared to conventional impedance monitoring and did not differ by lead family for LSE (P=0.573) or LF (P=0.332). Isolated spikes on EGM were associated more often with LF in St. Jude leads (71%) compared to EndotakTM (9%; P<0.001) and FidelisTM leads (11%; P<0.001). The NLE detection rate was different among lead families (P<0.001) ranging from one in every 78.5 years (EndotakTM), 228.9 years (St. JudeTM leads), and 627.6 years (FidelisTM). Conclusions —LIA markedly increased the detection rate of LSE over conventional impedance monitoring.Background—The Lead Integrity Alert (LIA) was developed for Medtronic implantable cardioverter defibrillators to reduce inappropriate shocks for rapid oversensing caused by conductor fractures and reported for Medtronic Fidelis conductor fractures. The goal of this study was to compare the performance of LIA with conventional impedance monitoring for identifying lead system events (LSEs) and lead failures (LFs) in lead families that differ from Fidelis. Methods and Results—We analyzed data from 12 793 LIA enabled implantable cardioverter-defibrillator and lead combinations including 6123 St. Jude Riata or Durata, 5114 Boston Scientific Endotak, and 1556 Fidelis combinations followed in the CareLink remote monitoring network for LSEs and LFs. Each alert was adjudicated based on implantable cardioverter-defibrillator stored electrograms/diagnostics and clinical data as an LSE or non–lead system event by 2 physicians after reviewing the electrograms and clinical data. During 13 562 patient-years of LIA follow-up, there were 179 adjudicated alerts, of which 84 were LSEs (including 65 LFs) and 95 were non–lead system events. LIA identified >66% more LSE and >67% more LF compared with conventional impedance monitoring and did not differ by lead family for LSE (P=0.573) or LF (P=0.332). Isolated spikes on electrogram were associated more often with LF in St. Jude leads (71%) compared with Endotak (9%; P<0.001) and Fidelis leads (11%; P<0.001). The non–lead system event detection rate was different among lead families (P<0.001) ranging from 1 in every 78.5 years (Endotak), 228.9 years (St. Jude leads), and 627.6 years (Fidelis). Conclusions—LIA markedly increased the detection rate of LSE compared with conventional impedance monitoring.

Performance of Lead Integrity Alert to Assist in the Clinical Diagnosis of Implantable Cardioverter Defibrillator Lead Failures Analysis of Different Implantable Cardioverter Defibrillator Leads

Background —The Lead Integrity Alert (LIA) was developed for Medtronic ICDs to reduce inappropriate shocks for rapid, oversensing caused by conductor fractures and reported for Medtronic FidelisTM conductor fractures. The goal of this study was to compare the performance of LIA with conventional impedance monitoring for identifying lead system events (LSE) and lead failures (LF) in lead families that differ from FidelisTM. Methods and Results —We analyzed data from 12,793 LIA enabled ICD and lead combinations including 6,123 St. Jude RiataTM or DurataTM, 5,114 Boston Scientific EndotakTM, and 1,556 FidelisTM combinations followed in the CareLinkTM remote monitoring network for LSEs and LFs. Each alert was adjudicated based on ICD stored EGMs/diagnostics and clinical data as a LSE or non-lead system event (NLE) by two physicians after reviewing the EGMs and clinical data. During 13,562 patient-years of LIA follow-up, there were 179 adjudicated alerts, of which 84 were LSE (including 65 LFs) and 95 were NLE. LIA identified greater than 66% more LSE and 67% more LF compared to conventional impedance monitoring and did not differ by lead family for LSE (P=0.573) or LF (P=0.332). Isolated spikes on EGM were associated more often with LF in St. Jude leads (71%) compared to EndotakTM (9%; P<0.001) and FidelisTM leads (11%; P<0.001). The NLE detection rate was different among lead families (P<0.001) ranging from one in every 78.5 years (EndotakTM), 228.9 years (St. JudeTM leads), and 627.6 years (FidelisTM). Conclusions —LIA markedly increased the detection rate of LSE over conventional impedance monitoring.Background—The Lead Integrity Alert (LIA) was developed for Medtronic implantable cardioverter defibrillators to reduce inappropriate shocks for rapid oversensing caused by conductor fractures and reported for Medtronic Fidelis conductor fractures. The goal of this study was to compare the performance of LIA with conventional impedance monitoring for identifying lead system events (LSEs) and lead failures (LFs) in lead families that differ from Fidelis. Methods and Results—We analyzed data from 12 793 LIA enabled implantable cardioverter-defibrillator and lead combinations including 6123 St. Jude Riata or Durata, 5114 Boston Scientific Endotak, and 1556 Fidelis combinations followed in the CareLink remote monitoring network for LSEs and LFs. Each alert was adjudicated based on implantable cardioverter-defibrillator stored electrograms/diagnostics and clinical data as an LSE or non–lead system event by 2 physicians after reviewing the electrograms and clinical data. During 13 562 patient-years of LIA follow-up, there were 179 adjudicated alerts, of which 84 were LSEs (including 65 LFs) and 95 were non–lead system events. LIA identified >66% more LSE and >67% more LF compared with conventional impedance monitoring and did not differ by lead family for LSE (P=0.573) or LF (P=0.332). Isolated spikes on electrogram were associated more often with LF in St. Jude leads (71%) compared with Endotak (9%; P<0.001) and Fidelis leads (11%; P<0.001). The non–lead system event detection rate was different among lead families (P<0.001) ranging from 1 in every 78.5 years (Endotak), 228.9 years (St. Jude leads), and 627.6 years (Fidelis). Conclusions—LIA markedly increased the detection rate of LSE compared with conventional impedance monitoring.

Causes of ventricular oversensing in implantable cardioverter-defibrillators: implications for diagnosis of lead fracture.

BACKGROUND Implantable cardioverter-defibrillator (ICD) ventricular oversensing may result in inappropriate therapy, which may be triggered by lead/connection issues that require surgical revision or physiologic oversensing that may be resolved with reprogramming. The sensing integrity counter (SIC) is an oversensing diagnostic that increments for very rapid ventricular intervals < or =130 ms. OBJECTIVE The purpose of this study was to determine the causes of a high SIC and the ability of additional diagnostics to differentiate lead/connection issues from other causes of oversensing for patients with normal impedance. METHODS Frequent SICs were identified in patients during routine follow-up visits. To diagnose the cause of oversensing, patients wore a modified 24-hour digital Holter monitor that recorded ECG, ventricular electrogram, and the ICD Marker Channel (Medtronic). Recordings were reviewed to determine the causes of oversensing. Patients with confirmed oversensing and adequate data were analyzed. The number of SICs per day and the presence of a nonsustained tachycardia (NST) episode with ventricular mean cycle length <220 ms were retrieved from stored ICD data. RESULTS Forty-eight patients had a median of 13 SICs/day. Presumed lead/connection issues occurred in 23% of patients, whereas physiologic oversensing occurred in 77% of patients. A rapid NST was recorded more commonly in patients with lead/connection issues than in those without (9/11 vs 1/37; P < .0001). CONCLUSION Oversensing resulting in frequent, very short intervals typically are caused by either lead/connection issues or physiologic signals. The additional finding of rapid NSTs usually indicates a lead/connection issue, even in the absence of impedance abnormalities.

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)

Automatic Identification of Clinical Lead Dysfunctions

Implantable cardioverter defibrillators (ICD) lead dysfunctions can cause inappropriate shocks. Current ICDs store lead diagnostics and detected episodes. This stored information with intracardiac electrograms (EGM) and sensed RR interval patterns may characterize the ICD lead performance. The aim of this analysis was to determine the sensitivity and positive predictive value (PPV) of an automatic lead dysfunction identification algorithm. This algorithm uses RR and EGM data to distinguish noncardiac oversensing (OS), for example, due to conductor fracture, and cardiac OS, for example, T‐wave OS, from detected episodes. The algorithm also uses lead diagnostics: sensing integrity counter trends (e.g., RR intervals <140 ms), nonsustained tachyarrhythmias episodes with a mean RR <200 ms and impedance trends to identify lead fractures. The PPV was determined using the stored memory from 1,756 ICD patients enrolled in a 13‐center long‐term lead study with an average follow‐up of 18.3 patient‐months. Sensitivity was determined in 35 patients who presented with OS or lead fracture‐related adverse events confirmed by stored ICD diagnostics. The algorithm sensitivity was 97.1% (34/35). There were 43 additional patients identified by the algorithm without an adverse event. Stored ICD diagnostics confirmed lead dysfunctions in 32 of 43 patients corresponding with an 85.7% PPV (66/77). ICD memory diagnostics and episodes with intracardiac EGM may be used to identify ICD lead dysfunctions with high sensitivity and PPV. This algorithm may be implemented in postprocessing ICD environments (e.g., remote server, programmer) to rapidly identify lead dysfunction prior its clinical manifestation.

Diagnosis of high-voltage conductor fractures in Sprint Fidelis leads.

BACKGROUND Fractures of pace/sense conductors in implantable cardioverter-defibrillator (ICD) leads have been studied extensively, but little is known about fractures of high-voltage (HV) conductors. OBJECTIVE To characterize the presentation of isolated HV conductor fractures, define the optimal impedance threshold for identifying them, and compare it to the existing nominal impedance threshold (200 Ω) for patient and remote-monitoring alerts. METHODS This retrospective study analyzed HV fractures in explanted, dual-coil, model 6949 Sprint Fidelis leads (Medtronic, Minneapolis, MN). The study group consisted of 25 leads with structurally and electrically confirmed HV conductor fractures; 41 leads that were structurally and electrically intact served as controls. We analyzed long-term HV impedance trends from stored ICD data files of both groups to determine the optimal impedance threshold that would discriminate fractures from normal leads. RESULTS In the study group, 14 leads (56%) had fractures of the cable to the right ventricular coil, 9 (36 %) leads had fractures of the cable to the superior vena cava (SVC) coil, and 2 (8%) had both. We found that an impedance threshold of >100 Ω and/or an abrupt 75% increase in chronic HV impedance were diagnostic of HV conductor fractures with 100% sensitivity and specificity. HV fractures proximal to the SVC coil were more likely to be associated with concomitant pace/sense fractures. Large (200 Ω to infinity), abrupt increases in impedance were more common when fractures occurred proximal to the right ventricular coil but distal to the SVC coil. CONCLUSIONS HV conductor fractures can be diagnosed when HV impedance exceeds 100 Ω or abruptly increases by 75% from baseline.

Incidence of Nonsustained and Sustained Ventricular Tachyarrhythmias in Patients with an Implantable Cardioverter Defibrillator

Introduction: Nonsustained ventricular tachycardia (NSVT) is a frequent phenomenon in some patients with heart disease, but its association with sustained ventricular tachycardias (ventricular tachycardia [VT]/ventricular fibrillation [VF]) is still not clear. The aim of this study was to determine whether NSVT incidence was associated with sustained VT/VF in patients with an implantable cardioverter defibrillator (ICD).