Transient pacing in pigs with complete heart block via myocardial injection of mRNA coding for the T-box transcription factor 18.

The adenovirus-mediated somatic transfer of the embryonic T-box transcription factor 18 (TBX18) gene can convert chamber cardiomyocytes into induced pacemaker cells. However, the translation of therapeutic TBX18-induced cardiac pacing faces safety challenges. Here we show that the myocardial expression of synthetic TBX18 mRNA in animals generates de novo pacing and limits innate and inflammatory immune responses. In rats, intramyocardially injected mRNA remained localized, whereas direct myocardial injection of an adenovirus carrying a reporter gene resulted in diffuse expression and in substantial spillover to the liver, spleen and lungs. Transient expression of TBX18 mRNA in rats led to de novo automaticity and pacemaker properties and, compared with the injection of adenovirus, to substantial reductions in the expression of inflammatory genes and in activated macrophage populations. In rodent and clinically relevant porcine models of complete heart block, intramyocardially injected TBX18 mRNA provided rate-adaptive cardiac pacing for one month that strongly correlated with the animal's sinus rhythm and physical activity. TBX18 mRNA may aid the development of biological pacemakers.

A Network-based Cardiac Electrophysiology Simulator with Realistic Signal Generation and Response to Pacing Maneuvers.

Diagnosis and localization of cardiac arrhythmias, especially supraventricular tachycardia (SVT), by inspecting intracardiac signals and performing pacing maneuvers is the core of electrophysiology studies. Acquiring and maintaining complex skill sets can be facilitated by using simulators, allowing the operator to practice in a safe and controlled setting. An electrophysiology simulator should not only display arrhythmias but it has to respond to the user's arbitrary inputs. While, in principle, it is possible to model the heart using a detailed anatomical and cellular model, such a system would be unduly complex and computationally intensive. In this paper, we describe a freely available web-based electrophysiology simulator (http://svtsim.com), which is composed of a visualization/interface unit and a heart model based on a dynamical network. In the network, nodes represent the points of interest, such as the sinus and the atrioventricular nodes, and links model the conduction system and pathways. The dynamics are encoded explicitly in the state machines attached to the nodes and links. Simulated intracardiac signals and surface ECGs are generated from the internal state of the heart model. Reentrant tachycardias, especially various forms of SVT, can emerge in this system in response to the user's actions in the form of pacing maneuvers. Additionally, the resulting arrhythmias respond realistically to various inputs, such as overdrive pacing and delivery of extra stimuli, cardioversion, ablation, and infusion of medications. For nearly a decade, svtsim.com has been used successfully to train electrophysiology practitioners in many institutions. We will present our experience regarding best practices in designing and using electrophysiology simulators for training and testing. We will also discuss the current trends in clinical cardiac electrophysiology and the anticipated next generation electrophysiology simulators.

Generation of Monophasic Action Potentials and Intermediate Forms.

The monophasic action potential (MAP) is a near replica of the transmembrane potential recorded when an electrode is pushed firmly against cardiac tissue. Despite its many practical uses, the mechanism of MAP signal generation and the reason it is so different from unipolar recordings are not completely known and are a matter of controversy. In this work, we describe a method to simulate realistic MAP and intermediate forms, which are multiphasic electrograms different from an ideal MAP. The key ideas of our method are the formation of compressed zones and junctional spaces-regions of the extracellular and bath or blood pool directly in contact with electrodes that exhibit a pressure-induced reduction in electrical conductivity-and the presence of a complex network of passive components that acts as a high-pass filter to distort and attenuate the signal that reaches the recording amplifier. The network is formed by the interaction between the passive tissue properties and the double-layer capacitance of electrodes. The MAP and intermediate forms reside on a continuum of signals, which can be generated by the change of the model parameters. Our model helps to decipher the mechanisms of signal generation and can lead to a better design for electrodes, recording amplifiers, and experimental setups.

Theoretical Modeling and Experimental Detection of the Extracellular Phasic Impedance Modulation in Rabbit Hearts.

Theoretical cardiac electrophysiology focuses on the dynamics of the membrane and sarcoplasmic reticulum ion currents; however, passive (e.g., membrane capacitance) and quasi-active (response to small signals) properties of the cardiac sarcolemma, which are quantified by impedance, are also important in determining the behavior of cardiac tissue. Theoretically, impedance varies in the different phases of a cardiac cycle. Our goal in this study was to numerically predict and experimentally validate these phasic changes. We calculated the expected impedance signal using analytic methods (for generic ionic models) and numerical computation (for a rabbit ventricular ionic model). Cardiac impedance is dependent on the phase of the action potential, with multiple deflections caused by a sequential activation and inactivation of various membrane channels. The two main channels shaping the impedance signal are the sodium channel causing a sharp and transient drop at the onset of action potential and the inward rectifying potassium channel causing an increase in impedance during the plateau phase. This dip and dome pattern was confirmed in an ex-vivo rabbit heart model using high-frequency sampling through a monophasic action potential electrode. The hearts were immobilized using a myosin-inhibitor to minimize motion artifacts. We observed phasic impedance changes in three out of four hearts with a dome amplitude of 2 - 4Ω. Measurement of phasic impedance modulation using an extracellular electrode is feasible and provides a non-invasive way to gain insight into the state of cardiac cells and membrane ionic channels. The observed impedance recordings are consistent with the dip and dome pattern predicted analytically.

A review of bioelectrodes for clinical electrophysiologists.

The theory of bioelectrodes describes the rules governing the passage of electrical charge between electrodes and electrolytes. In this review, we explain the basis of bioelectrodes with focus on clinical electrophysiology. The central concept is the double-layer capacitance that forms in the interface between the electrode and tissue. This phenomenon controls charge transfer between electrodes and tissues and contributes to detrimental effects such as electrode polarization and motion artifacts. Many methods critical to the practice of electrophysiology, including fractally coated pacemaker leads, biphasic stimuli, signal filtering, and the use of nonpolarizable electrodes, are devised to mitigate these problems. Our goal is to provide a robust and intuitive background on these topics for practicing electrophysiologists to help them better understand how catheters and leads work and to assist them with optimizing and troubleshooting electrophysiology systems.

Long-term performance of a pacing lead family: A single-center experience.

BACKGROUND: The performance of Abbott/St. Jude Medical (Sylmar CA) Tendril pacing leads has not been well characterized. OBJECTIVE: We sought to assess the performance of Tendril leads as compared with that of different pacing leads. METHODS: We retrospectively identified patients implanted with the following leads: Tendril leads 1888 TC, 2088 TC, and 1688 TC, Medtronic (Fridely, MN) 4076 CapSureFix Novus, and Boston Scientific (Natick, MA) FINELINE II Sterox Pacing EZ leads (models 4469, 4470, and 4471). The primary end point was the incidence of lead malfunction assessed by Kaplan-Meier analysis. RESULTS: During the study period, 9782 leads were implanted, including 8512 Tendril leads, 731 Medtronic 4076 CapSureFix Novus leads, and 539 FINELINE II leads. A total of 540 leads (5.5%) malfunctioned during a mean follow-up of 3.6 ± 2.9 years. Lead malfunction manifested predominantly as noise and/or low impedance (95%). Lead malfunction rates were significantly higher at 5 years for Tendril vs non-Tendril leads (7.0% vs 2.1%; P < .001). The highest rate of failure at 5 years was seen in the Tendril 1888 TC leads (9.9%), followed by Tendril 1688 (5.7%) and Tendril 2088 (5.2%) leads. In contrast, malfunction rates were significantly lower for the Medtronic 4076 (2.6%) and FINELINE II (1.7%) leads. During follow-up to 10 years, the incidence of lead malfunction for Optim-insulated Tendril leads (models 1888 TC and 2088 TC) was significantly higher than that for the non-Optim-insulated Tendril 1688 TC lead (24.5% vs 7.1%) (P = .008). CONCLUSION: Tendril leads appear to have a higher rate of malfunction than do comparator leads. Optim insulation may partly explain the higher failure rate.

Use of microelectrode near-field signals to determine catheter contact.

BACKGROUND: The utility of standard distal bipolar electrograms (sEGMs) for assessing catheter-tissue contact may be obscured by the presence of far-field signals. Microelectrode electrograms (mEGMs) may overcome this limitation. METHODS: We compared 5 mEGM characteristics (amplitude, frequency content, temporal signal variability, presence of injury current, and amplitude differential between bipoles) with the sEGM for determining tissue contact in 20 patients undergoing ablation of typical atrial flutter. Visualization of catheter-tissue contact by intracardiac echocardiography (ICE) served as the gold standard for assessing contact. Correlation between electrograms and ICE-verified contact level was reported as percent concordance. RESULTS: Three of 5 mEGM characteristics demonstrated significantly better concordance with ICE-verified contact level than the sEGM (52% concordance with ICE): mEGM frequency content (59% concordance with ICE, P < .001 for comparison with sEGM); mEGM amplitude (concordance 59%, P < .001); and mEGM presence of injury current (56% concordance, P = .001). Concordance of amplitude differential between mEGM bipoles with ICE (49%) was not significantly different than the sEGM (P = .638) whereas mEGM temporal variability (39%) was significantly worse than the sEGM. Using a median of all 5 mEGM characteristics provided additive information (concordance with ICE 64%) and was significantly better than all of the individual mEGM characteristics except frequency content (P = .976). CONCLUSION: Microelectrode EGMs (in particular frequency content, amplitude, and presence of injury current) can improve real-time assessment of catheter contact compared to the use of standard bipolar EGMs. Broader use of mEGMs may enhance ablation efficacy.

Minimally Invasive Delivery of Hydrogel-Encapsulated Amiodarone to the Epicardium Reduces Atrial Fibrillation.

BACKGROUND: Atrial fibrillation (AF) is the most common cardiac arrhythmia. Although treatment options for AF exist, many patients cannot be maintained in normal sinus rhythm. Amiodarone is an effective medication for AF but has limited clinical utility because of off-target tissue toxicity. METHODS: Here, we use a pig model of AF to test the efficacy of an amiodarone-containing polyethylene glycol-based hydrogel. The gel is placed directly on the atrial epicardium through the pericardial space in a minimally invasive procedure using a specially designed catheter. RESULTS: Implantation of amiodarone-containing gel significantly reduced the duration of sustained AF at 21 and 28 days; inducibility of AF was reduced 14 and 21 days post-delivery. Off-target organ drug levels in the liver, lungs, thyroid, and fat were significantly reduced in animals treated with epicardial amiodarone gel compared with systemic controls in small-animal distribution studies. CONCLUSIONS: The pericardium is an underutilized therapeutic site and may be a new treatment strategy for AF and other cardiovascular diseases.

Magnetic resonance imaging safety in nonconditional pacemaker and defibrillator recipients: A meta-analysis and systematic review.

BACKGROUND: Recommendations regarding performance of magnetic resonance imaging (MRI) in non-MRI conditional pacemaker and defibrillator recipients are evolving. Previous studies have suggested low adverse event rates with MRI in nonconditional cardiac implantable electronic device (CIED) recipients, but low power limits optimal characterization of risk. OBJECTIVE: The purpose of this study was to perform a systematic review and meta-analysis to characterize the clinical risk associated with MRI in CIED recipients in order to improve power. METHODS: PubMed and CINAHL indexed articles from 1990 to 2017 were queried. A random effects model was used for meta-analysis of continuous variables. Safety outcomes were evaluated with descriptive statistics. RESULTS: Seventy studies of non-MRI conditional devices undergoing MRI were identified, allowing for analysis of 5099 patients who underwent a total of 5908 MRI studies. Heterogeneity in lead parameter changes was observed within studies, although smaller variances were noted between studies. All lead characteristics and battery voltages showed very small, clinically insignificant changes when assessed as a pooled cohort, although cases of clinically relevant outcomes were also noted (lead failure 3, implantable cardioverter-defibrillator shock 1, electrical reset 94). Electrical resets were found only in older devices. Defibrillator function was unchanged, and inappropriate shocks were avoided with pre-MRI programming changes. CONCLUSION: This review demonstrated low lead failure and clinical event rates in non-MRI conditional pacemaker and defibrillator recipients undergoing MRI. Observed changes were small and interstudy variance was low, suggesting that the composite event rates offer a reasonable estimate of true effect. The observed adverse events reinforce the need for ongoing vigilance and caution, particularly with older devices.

Critical phase transitions during ablation of atrial fibrillation.

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia with significant morbidity and mortality. Pharmacological agents are not very effective in the management of AF. Therefore, ablation procedures have become the mainstay of AF management. The irregular and seemingly chaotic atrial activity in AF is caused by one or more meandering spiral waves. Previously, we have shown the presence of sudden rhythm organization during ablation of persistent AF. We hypothesize that the observed transitions from a disorganized to an organized rhythm is a critical phase transition. Here, we explore this hypothesis by simulating ablation in an anatomically-correct 3D AF model. In 722 out of 2160 simulated ablation, at least one sudden transition from AF to an organized rhythm (flutter) was noted (33%). They were marked by a sudden decrease in the cycle length entropy and increase in the mean cycle length. At the same time, the number of reentrant wavelets decreased from 2.99 ± 0.06 in AF to 1.76 ± 0.05 during flutter, and the correlation length scale increased from 13.3 ± 1.0 mm to 196.5 ± 86.6 mm (both P < 0.0001). These findings are consistent with the hypothesis that transitions from AF to an anatomical flutter behave as phase transitions in complex non-equilibrium dynamical systems with flutter acting as an absorbing state. Clinically, the facilitation of phase transition should be considered a novel mechanism of ablation and may help to design effective ablation strategies.

Clinical Performance of Magnetic Resonance Imaging Conditional and Nonconditional Cardiac Implantable Electronic Devices.

OBJECTIVES: This study compared risks associated with magnetic resonance imaging (MRI) in patients with non-MRI conditional and MRI conditional pacing and defibrillator systems with particular attention to clinically actionable outcomes. BACKGROUND: While recipients of new MRI conditional pacemaker and defibrillator systems may undergo MRI scanning with very low risk, safety and regulatory concerns persist regarding such scanning in recipients of non-MRI conditional systems. METHODS: Patients with any cardiac device who were referred for MRI were prospectively enrolled at a single center and underwent scanning at 1.5 Tesla. Pre- and postscan lead characteristic changes, system integrity, and symptoms were analyzed. A comparison was made between non-MRI conditional and MRI conditional devices. RESULTS: 105 patients were evaluated allowing for comparison of 97 scans with non-MRI conditional devices and 16 scans with MRI conditional devices. The cohort included those with pacemaker dependency, defibrillator, and cardiac resynchronization devices. Small, nonsignificant changes were observed in lead characteristics following scanning, and there was no significant difference when comparing non-MRI and MRI conditional devices. Lead parameter changes did not require lead revision or programming changes. No device reset, failures, or premature scan termination was observed. CONCLUSIONS: 1.5 T MRI scanning in patients with MRI conditional and non-MRI conditional cardiac devices was performed with similar, low clinical risk.

A Minimally Invasive, Translational Method to Deliver Hydrogels to the Heart Through the Pericardial Space.

Biomaterials are a new treatment strategy for cardiovascular diseases but are difficult to deliver to the heart in a safe, precise, and translatable way. We developed a method to deliver hydrogels to the epicardium through the pericardial space. Our device creates a temporary compartment for hydrogel delivery and gelation using anatomic structures. The method minimizes risk to patients from embolization, thrombotic occlusion, and arrhythmia. In pigs there were no clinically relevant acute or subacute adverse effects from pericardial hydrogel delivery, making this a translatable strategy to deliver biomaterials to the heart.

Time Course of Subsequent Shocks After Initial Implantable Cardioverter-Defibrillator Discharge and Implications for Driving Restrictions.

IMPORTANCE: Although guidelines recommend driving restrictions for 3 to 6 months after appropriate implantable cardioverter-defibrillator (ICD) shocks, contemporary data to support these recommendations are lacking. OBJECTIVE: To define the time course of subsequent shocks after an initial ICD discharge. DESIGN, SETTING, AND PARTICIPANTS: Retrospective analysis of a nationwide cohort of 14 230 ICD recipients enrolled in a remote monitoring program. Participants underwent ICD implantation from October 1, 2008, to December 31, 2013, and experienced at least 1 shock. The risk of driving after an ICD shock was estimated using the risk for harm (RH) formula, and an annual RH of less than 5 events per 100 000 ICD recipients was deemed safe. The likelihood of loss of consciousness associated with an ICD shock was estimated using a cautious value of 32% and an estimate of 14% based on contemporary data. Data were extracted and analyzed from December 17, 2014, to October 31, 2015. MAIN OUTCOMES AND MEASURES: Time course of subsequent shocks after an initial ICD discharge. RESULTS: Of 73 503 ICD recipients who underwent remote monitoring, 14 230 (19.4%) experienced at least 1 ICD shock and were included in this analysis (10 870 men [76.4%]; 3360 women [23.6%]; median age at device implantation, 68 years; interquartile range [IQR], 60-76 years). The cumulative incidence of receiving a second shock was 14.5% (IQR, 13.9%-15.1%) at 1 month and 28.7% (IQR, 27.9%-29.5%) at 6 months. The time from implantation to initial shock had an inverse association with the likelihood of receiving a second shock (lowest quartile of time at 6 months, 31.6% [95% CI, 30.2%-33.2]; highest quartile of time at 6 months, 25.3% [95% CI, 23.8%-26.9%]). The number of ICD therapy zones was also significantly associated with the incidence of a second shock (1 therapy zone, 20.8% [95% CI, 19.4%-22.3%] at 3 months to 51.5% [95% CI, 48.5%-53.7%] at 3 years; 3 therapy zones, 26.9% [95% CI, 24.8%-29.0%] at 3 months to 57.3% [95% CI, 54.1%-60.5%] at 3 years). When a likelihood of loss of consciousness of 32% associated with an ICD shock was used, the RH while driving fell below the accepted threshold at 4 to 6 months after an initial shock. However, when a contemporary estimate for loss of consciousness associated with an ICD shock of 14% was used, the RH fell below the threshold at 1 month after an initial shock. CONCLUSIONS AND RELEVANCE: In this large cohort of ICD recipients, the incidence of a second shock after an initial ICD discharge was lower than previously reported and depended on several programmed ICD variables. These data, with future research to derive contemporary estimates of the likelihood of fatality resulting from an ICD shock while driving, should support the development of evidence-based guidelines for driving restrictions in ICD recipients.

Electrogram Characteristics of Ablated and Non-Ablated Myocardium in Humans: A Comparison of Miniaturized Embedded Electrodes and Conventional Ablation Electrodes.

INTRODUCTION: Intracardiac electrogram voltage remains an important metric for radiofrequency lesion application. Embedded micro-electrodes within ablation catheters are now approved for use in humans. OBJECTIVE: This study examined electrogram characteristics of miniaturized electrode bipoles (iEGMmini ) compared to distal ablation tip bipoles (iEGMstandard ) in the setting of typical atrial flutter in humans. METHODS: This was a single-center prospective trial involving 21 patients. A total of 54 non-ablated and 56 ablated sites were analyzed offline by separate blinded observers for iEGM voltage after a clinically successful radiofrequency (RF) ablation for typical atrial flutter. Ablation sites were defined as sites that were localized anatomically within the RF lesion set and did not have atrial capture at 10 mA and 2 milliseconds. Non-ablated sites were defined as sites adjacent to or remote from the ablation lesion set with capture at 10 mA and 2 milliseconds. RESULTS: iEGMmini had greater voltages at non-ablated sites and lower voltages at ablated sites than iEGMstandard (non-ablated sites iEGMstandard 0.64 mV vs. iEGMmini 1.0 mV; ablated sites iEGMstandard 0.15 mV, iEGMmini 0.08 mV, P < 0.001). The difference for each patient between ablated and non-ablated sites was greater for iEGMmini compared to iEGMstandard (0.94 mV ± 0.57 iEGMmini vs. 0.52 mV ± 0.35 iEGMstandard , P < 0.001). Inter-observer agreement was good among all non-ablated sites and iEGMmini ablated sites, but was less robust for ablated sites using iEGMstandard . CONCLUSIONS: Imbedded mini-electrode iEGM bipoles had higher voltages in non-ablated tissue, lower voltages in ablated tissue, and significantly greater intra-patient differences between ablated and non-ablated sites. These data suggest a potential role for miniaturized electrode bipole use in RF lesion monitoring.

Sudden and Fatal Malfunction of a Durata Defibrillator Lead due to External Insulation Failure.

Defibrillator lead malfunction can be a disastrous complication, leading to loss of protection from sudden cardiac death in a high-risk patient population. Recognition of lead-specific risk for failure can assist in development of focused screening or surveillance, as in the case of the Riata lead (St. Jude Medical, St. Paul, MN, USA) or the Sprint Fidelis lead (Medtronic Inc., Minneapolis, MN, USA). A case of defibrillation failure secondary to a Durata lead insulation failure is presented. A brief review of the literature and current St. Jude Medical implantable cardiac defibrillator lead design is presented. Identification of arcing is identified as a potential sign of catastrophic insulation failure.

Predictors of Long-Term Survival Following Transvenous Extraction of Defibrillator Leads.

BACKGROUND: Little data exist on long-term outcomes following extraction of implantable cardioverter defibrillator (ICD) leads, particularly for noninfectious indications. We sought to identify predictors of long-term survival after ICD lead extraction. METHODS: We retrospectively reviewed ICD lead extractions at our institution (n = 508). Procedural outcomes and long-term survival were ascertained by medical records review. RESULTS: Indication for lead extraction was infection in 32.5% and lead failure in 61.8%. Mean dwell time of the oldest extracted lead was 5.1 ± 5.9 years. Complete procedural success was achieved in 96.5% of cases. Major procedure-related complications occurred in 1.6% with six periprocedural deaths. During a mean follow-up of 866 ± 798 days, survival was significantly worse among patients with infection as the indication for extraction. At 1 year after extraction, survival among those with infection was 88.2%, compared to 95.0% in the lead failure cohort (P < 0.001). Procedural failure was a significant predictor of long-term mortality, even after excluding periprocedural deaths. In multivariate models, the presence of chronic kidney disease, increased number of leads requiring extraction, lower ejection fraction, and procedural failure were predictors of mortality. CONCLUSION: Despite high rates of procedural success, infectious indication for ICD lead extraction is associated with increased long-term mortality. In contrast, among patients undergoing extraction for lead failure, long-term survival was excellent. The presence of procedural failure was a significant predictor of long-term mortality. Further studies will be necessary to better understand the mechanisms by which procedural failure may adversely impact long-term outcomes.

Pulse Generator Exchange Does Not Accelerate the Rate of Electrical Failure in a Recalled Small Caliber ICD Lead.

BACKGROUND: St. Jude Riata/Riata ST defibrillator leads (St. Jude Medical, Sylmar, CA, USA) were recalled by the Food and Drug Administration in 2011 for an increased rate of failure. More than 227,000 leads were implanted and at least 79,000 patients still have active Riata leads. Studies have examined clinical predictors of lead failure in Riata leads, but none have addressed the effect of implantable cardioverter defibrillator (ICD) generator exchange on lead failure. The purpose of this study is to assess the effect of ICD generator exchange on the rate of electrical failure in the Riata lead at 1 year. METHODS: A retrospective chart review was conducted in patients who underwent implantation of a Riata/Riata ST lead at one center. Patients with a functioning Riata lead (with/without externalized conductor) at the time of ICD exchange were compared to controls with Riata leads implanted for a comparable amount of time who did not undergo generator replacement. RESULTS: Riata leads were implanted in 1,042 patients prior to the recall and 153 of these patients underwent generator exchange without lead replacement. Conductor externalization was noted in 21.5% of Riata leads in the ICD exchange cohort, which was not different from the control group (19.2%; P = 0.32). Two leads failed in the first year after generator replacement (1.5%) which did not significantly differ from the control group (2.0%; P = 0.57). At change-out, 54% received a commanded shock (18.6 ± 0.9 J) that did not result in any change in the high-voltage lead impedance (46.1 ± 1.1 ohms). CONCLUSIONS: Conductor externalization was seen frequently in our cohort of patients. ICD generator exchange did not accelerate the rate of Riata lead failure at 1 year. Although both the control and the change-out cohorts failed at a rate much greater than nonrecalled leads, generator exchange did not appear to add to the problem.

User-reported abrasion-related lead failure is more common with durata compared to other implantable cardiac defibrillator leads.

BACKGROUND: Following increased rates of inside-out abrasion with the St Jude Medical Riata lead, the Durata implantable cardiac defibrillator (ICD) lead was introduced with modifications intended to increase abrasion resistance. Recent case reports have described insulation failures of the Durata. OBJECTIVE: To determine if increased rates of abrasion-related failure are present with the Durata lead. METHODS: The Food and Drug Administration Manufacturer and User Facility Device Experience database was queried for reports of insulation failure of the Durata lead from 2014. Comparison was made to other ICD leads. Incidence was estimated and case characteristics were compared. RESULTS: The estimated incidence of abrasion was significantly higher for the Durata lead than for the Boston Scientific Endotak or the Medtronic Quattro leads. The mode of abrasion was most often lead-to-can, as compared to "inside-out" abrasion with the Riata lead. Full-thickness abrasion was associated with failure to defibrillate or inappropriate therapy. Four patients had failure of therapy or death. CONCLUSIONS: The findings indicate higher rates of insulation failures of the Durata lead, despite design modifications. External abrasion from the pulse generator to the adjacent lead within the device pocket was the most common etiology. Shocks unmasked previously undetected abrasion, resulting in failure to defibrillate. Data are presented indicating a possible time dependency to abrasion risk. This limited query suggests need for ongoing scrutiny of Durata lead performance. Careful inspection of Durata leads at the time of ICD replacement is warranted, as are vigorous attempts to gather information about terminal events in patients with Durata leads.