Pacing Capture Threshold Research Articles

136-67: Incidence and Predictors of Phrenic Nerve Stimulation following Cardiac Resynchronization Therapy System Implantation of a Quadripolar Lead

Introduction: Quadripolar (quad) left ventricular (LV) pacing leads are routinely used during cardiac resynchronization therapy (CRT). When phrenic nerve stimulation (PNS) occurs in patients with a quad LV lead, reprogramming is often sufficient to eliminate the problem. However, the incidence and predictors of PNS remain less understood. Methods: Patients implanted with CRT-D during a prospective Investigational Device Exemption study of the Boston Scientific ACUITY X4 quad LV lead were evaluated. Electrical performance including pacing capture thresholds (PCT) and PNS were evaluated intra-operatively, at pre-discharge, and 3 months. The IO PNS safety margin was calculated between PNS (tested up to 7.5V) and PCT. Complications were tracked for 6 months. Results: Clinically documented PNS occurred in 58 (8%) of 744 CRT patients. In 14 (24%) of these patients, PNS occurred within the first day of implant; overall, the median time to PNS was 5.5 days [IQR 0.75, 53]. PNS most commonly occurred when the distal electrode was used (30 of 205 [15%] cases vs 28 of 539 [5%] for non-distal pacing, p < 0.001). In 51 (88%) of the 58 patients, PNS was not present intra-operatively at even maximal pacing output. In the remaining 7 patients, a safety margin between PNS and PCT failed to prevent PNS. When the safety margin was < 2 V, there was 35% risk of PNS. Device reprogramming (lowering pacing output or changing pacing electrode) was sufficient to eliminate the issue in 55 (95%) cases. Conclusion: With an ACUITY X4 quad LV lead, PNS was observed in 8% of patients, often within days of device implantation. When possible, avoidance of the distal electrode for pacing and avoidance of accepting a small “safety margin” for pacing output may mitigate against PNS. However, most patients had no measureable PNS at implant, suggesting an inability of current intra-operative techniques to ensure subsequent absence of PNS.

A Leadless Intracardiac Transcatheter Pacing System

BackgroundA leadless intracardiac transcatheter pacing system has been designed to avoid the need for a pacemaker pocket and transvenous lead.MethodsIn a prospective multicenter study without controls, a transcatheter pacemaker was implanted in patients who had guideline-based indications for ventricular pacing. The analysis of the primary end points began when 300 patients reached 6 months of follow-up. The primary safety end point was freedom from system-related or procedure-related major complications. The primary efficacy end point was the percentage of patients with low and stable pacing capture thresholds at 6 months (≤2.0 V at a pulse width of 0.24 msec and an increase of ≤1.5 V from the time of implantation). The safety and efficacy end points were evaluated against performance goals (based on historical data) of 83% and 80%, respectively. We also performed a post hoc analysis in which the rates of major complications were compared with those in a control cohort of 2667 patients with transvenous pacemakers from six previously published studies.ResultsThe device was successfully implanted in 719 of 725 patients (99.2%). The Kaplan–Meier estimate of the rate of the primary safety end point was 96.0% (95% confidence interval [CI], 93.9 to 97.3; P<0.001 for the comparison with the safety performance goal of 83%); there were 28 major complications in 25 of 725 patients, and no dislodgements. The rate of the primary efficacy end point was 98.3% (95% CI, 96.1 to 99.5; P<0.001 for the comparison with the efficacy performance goal of 80%) among 292 of 297 patients with paired 6-month data. Although there were 28 major complications in 25 patients, patients with transcatheter pacemakers had significantly fewer major complications than did the control patients (hazard ratio, 0.49; 95% CI, 0.33 to 0.75; P=0.001).ConclusionsIn this historical comparison study, the transcatheter pacemaker met the prespecified safety and efficacy goals; it had a safety profile similar to that of a transvenous system while providing low and stable pacing thresholds. (Funded by Medtronic; Micra Transcatheter Pacing Study ClinicalTrials.gov number, NCT02004873.)

Erratum: Newly designed leadless pacemaker

Nat. Rev. Cardiol. 13, 5 (2016); 10.1038/nrcardio.2015.187 In the version of the Research Highlight initially published online and in print, the text “29.3% had an adequate 6-month pacing capture threshold” should have read “98.3% had an adequate 6-month pacing capture threshold”. The error has beencorrected for the HTML and PDF versions of the article.

LEADLESS II: Leadless Pacing Safe, Effective

In the LEADLESS II trial, a leadless cardiac pacemaker was demonstrated to be safe and effective. At 6 months, the serious device-related adverse events occurred in 5.7% of patients, and the primary efficacy end point of acceptable pacing capture threshold and therapeutically acceptable sensing amplitude was achieved in 90% of patients.

Active fixation of a thin transvenous left-ventricular lead by a side helix facilitates targeted and stable placement in cardiac resynchronization therapy.

Suboptimal placement, phrenic nerve stimulation, and dislodgements of left-ventricular (LV) leads are main challenges in cardiac resynchronization therapy. We investigated the handling, performance, safety, and stability for a novel 4Fr LV lead with a small side helix located proximal to the ring electrode for active fixation of the LV lead. The novel LV lead was successfully implanted in 103 of 106 patients. Patients with dislodged LV leads and with demanding coronary vein anatomies were included. The lead body was rotated clockwise to engage the active fixation side helix in the vein wall. The stimulating electrode was located in basal LV segment and middle LV segment in 54 and 46% of the patients, respectively. The lead was targeted to a vein concordant to the LV segment with latest mechanical activation. Concordant LV lead placement was achieved in 73% of the patients and in adjacent segment in 24%. The average pacing capture threshold (PCT) at implantation was 1.04 ± 0.6 V (n = 103) and at an average follow-up at 7 months, the PCT remained low and no dislodgements have been observed. During follow-up, four leads have been explanted without complications. Active fixation of this 4Fr LV lead by using a side helix, offers flexibility to place the lead precisely in targeted vein segments over a wide range of vein anatomies. The average LV pacing threshold was low at implantation and follow-ups. The lead seems to be extractable and no late dislodgements have been observed.

Full-Body MRI in Patients With an Implantable Cardioverter-Defibrillator: Primary Results of a Randomized Study

BackgroundMagnetic resonance imaging (MRI) of patients with conventional implantable cardioverter-defibrillators (ICD) is contraindicated. ObjectivesThis multicenter, randomized trial evaluated safety and efficacy of a novel ICD system specially designed for full-body MRI without restrictions on heart rate or pacing dependency. The primary safety objective was >90% freedom from MRI-related events composite endpoint within 30 days post-MRI. The primary efficacy endpoints were ventricular pacing capture threshold and ventricular sensing amplitude. MethodsSubjects received either a single- or dual-chamber ICD. In a 2:1 randomization, subjects either underwent MRI at 1.5-T of the chest, cervical, and head regions to maximize radiofrequency exposure up to 2 W/kg specific absorption rate and gradient field exposure to 200 T/m/s per axis (MRI group, n = 175), or they underwent a 1-h waiting period without MRI (control group, n = 88). A subset of MRI patients underwent ventricular fibrillation induction testing post-MRI to characterize defibrillation function. ResultsIn 42 centers, 275 patients were enrolled (76% male, age 60.4 ± 13.8 years). The safety endpoint was met with 100% freedom from the composite endpoint (p < 0.0001). Both efficacy endpoints were met with minimal differences in the proportion of MRI and control patients who demonstrated a ≤0.5 V increase in ventricular pacing capture threshold (100% MRI vs. 98.8% control, noninferiority p < 0.0001) or a ≤50% decrease in R-wave amplitude (99.3% MRI vs. 98.8% control, noninferiority p = 0.0001). A total of 34 ventricular tachyarrhythmia/ventricular fibrillation episodes (20 induced; 14 spontaneous) occurred in 24 subjects post-MRI, with no observed effect on sensing, detection, or treatment. ConclusionsThis is the first randomized clinical study of an ICD system designed for full-body MRI at 1.5-T. These data support that the system is safe and the MRI scan does not adversely affect electrical performance or efficacy. (Confirmatory Clinical Trial of the Evera MRI System for Conditionally-Safe MRI Access; NCT02117414)

HRS Expert Consensus Statement on remote interrogation and monitoring for cardiovascular implantable electronic devices.

DavidSlotwiner,MD, FHRS, FACC(Chair),Niraj Varma,MD,PhD, FRCP(Co-chair), JosephG.Akar,MD,PhD, George Annas, JD, MPH, Marianne Beardsall, MN/NP, CCDS, FHRS, Richard I. Fogel, MD, FHRS, Nestor O. Galizio, MD, Taya V. Glotzer, MD, FHRS, FACC, Robin A. Leahy, RN, BSN, CCDS, FHRS, Charles J. Love, MD, CCDS, FHRS, FACC, FAHA, Rhondalyn C. McLean, MD, Suneet Mittal, MD, FHRS, Loredana Morichelli, RN, MSN, Kristen K. Patton, MD, Merritt H. Raitt, MD, FHRS, Renato Pietro Ricci, MD, John Rickard, MD, MPH, Mark H. Schoenfeld, MD, CCDS, FHRS, FACC, FAHA, Gerald A. Serwer, MD, FHRS, FACC, Julie Shea, MS, RNCS, FHRS, CCDS, Paul Varosy, MD, FHRS, FACC, FAHA, Atul Verma, MD, FHRS, FRCPC, Cheuk-Man Yu, MD, FACC, FRCP, FRACP From the Hofstra School of Medicine, North Shore Long Island Jewish Health System, New Hyde Park, New York, Cleveland Clinic, Cleveland, Ohio, Yale University School of Medicine, New Haven, Connecticut, Boston University School of Public Health, Boston, Massachusetts, Southlake Regional Health Centre, Newmarket, Ontario, Canada, St. Vincent Medical Group, Indianapolis, Indiana, Favaloro Foundation University Hospital, Buenos Aires, Argentina, Hackensack University Medical Center, Hackensack, New Jersey, Sanger Heart & Vascular Institute, Carolinas HealthCare System, Charlotte, North Carolina, New York University Langone Medical Center, New York City, New York, University of Pennsylvania Health System, Philadelphia, Pennsylvania, The Arrhythmia Institute at Valley Hospital, New York, New York, Department of Cardiovascular Diseases, San Filippo Neri Hospital, Rome, Italy, University of Washington, Seattle, Washington, VA Portland Health Care System, Oregon Health & Science University, Knight Cardiovascular Institute, Portland, Oregon, Johns Hopkins University, Baltimore, Maryland, Yale University School of Medicine, Yale-New Haven Hospital Saint Raphael Campus, New Haven, Connecticut, University of Michigan Congenital Heart Center, University of Michigan Health Center, Ann Arbor, Michigan, Brigham and Women’s Hospital, Boston, Massachusetts, Veterans Affairs Eastern Colorado Health Care System, University of Colorado, Denver, Colorado, and Department of Medicine and Therapeutics, Prince of Wales Hospital, The Chinese University of Hong Kong, Hong Kong, China.

Termination of Atrial Flutter and Fibrillation by K201's Metabolite M-II: Studies in the Canine Sterile Pericarditis Model.

K201, a 1,4-benzodiazepine derivative, acts on multiple cardiac ion channels and the ryanodine receptor. We tested whether administration of M-II, the main metabolite of K201, would terminate induced atrial flutter (AFL) or atrial fibrillation (AF) in the canine sterile pericarditis model. In 6 dogs, electrophysiologic studies were performed at baseline and after drug administration, measuring atrial effective refractory period (AERP), and conduction time from 3 sites during pacing at cycle lengths (400, 300, and 200 milliseconds) on postoperative days 1-4. In 12 induced episodes of sustained AF/AFL (2/10, respectively), M-II was administered intravenously to test efficacy. Five of the AFL episodes were studied in the open chest state during simultaneous multisite atrial mapping. M-II terminated 2/2 AF and 8/10 AFL episodes, prolonged AERP (P < 0.05), significantly increased atrial pacing capture thresholds but did not significantly change atrial conduction time. AFL CL prolongation was largely explained by prolonged conduction in an area of slow conduction in the reentrant circuit. AFL terminated with block in the area of slow conduction. M-II was very effective in terminating AFL/AF in the canine sterile pericarditis model. AFL terminated due to block in the area of slow conduction of the reentrant circuit.

A detailed view on pacemaker lead parameters remotely transmitted after magnetic resonance.

The purpose of this study was to analyze potential influences of magnetic resonance (MR) on the course of automatically device-based assessed lead parameters remotely transmitted in patients who were implanted with MR-conditional permanent pacemakers (PMs) and who had nondiagnostic brain and lumbar spine MR (1.5T) within the ProMRI single center pilot study. The ProMRI study evaluated the feasibility of the Evia PMs with Safio S leads (Biotronik SE&Co KG, Berlin, Germany) in the MR environment. All patients were equipped with remote monitoring on the day of MR. Atrial (RA) und ventricular (RV) lead parameters (sensing, pacing capture threshold [PCT], pacing impedance) were automatically assessed and remotely transmitted on a daily or event-triggered basis for 3 months post MR. Remotely transmitted data were normalized for potential differences between at-daytime (in-office) and at-night-time (remotely) assessed parameters using the 1-month follow-up data for each patient. Confidence intervals of continuous data were calculated day-wise with one sample t-tests of post-MR/pre-MR differences, respectively. A total of 2,428 data sets (mean 80 ± 20 per patient) were transmitted. Mean values for the different lead parameters were (RA/RV) 3.3 ± 2.0/14.4 ± 6.9 mV for sensing, 0.65 ± 0.17/0.78 ± 0.23 V/0.4 ms for PCT, and 516 ± 60/607 ± 47 Ω for pacing impedance. No significant differences were found compared with pre-MR measurements. No atrial PCT increases ≥0.5 V compared with pre-MR were observed, and in only one patient the ventricular PCT increased by ≥0.5 V from day 76 post-MR, presumably based on new antiarrhythmic therapy with amiodarone. Our analyses of automatically assessed and remotely transmitted PM lead parameters after MR show that sensing amplitudes, PCTs, and pacing impedances are not affected in a clinically relevant way by MR.

Effect of Smaller Left Ventricular Capture Threshold Safety Margins to Improve Device Longevity in Recipients of Cardiac Resynchronization-Defibrillation Therapy

Device longevity in cardiac resynchronization therapy (CRT) is affected by the pacing capture threshold (PCT) and programmed pacing amplitude of the left ventricular (LV) pacing lead. The aims of this study were to evaluate the stability of LV pacing thresholds in a nationwide sample of CRT defibrillator recipients and to determine potential longevity improvements associated with a decrease in the LV safety margin while maintaining effective delivery of CRT. CRT defibrillator patients in the Medtronic CareLink database were eligible for inclusion. LV PCT stability was evaluated using ≥2 measurements over a 14-day period. Separately, a random sample of 7,250 patients with programmed right atrial and right ventricular amplitudes ≤2.5 V, LV thresholds ≤ 2.5 V, and LV pacing ≥90% were evaluated to estimate theoretical battery longevity improvement using LV safety margins of 0.5 and 1.5 V. Threshold stability analysis in 43,256 patients demonstrated LV PCT stability of <0.5 V in 77% of patients and <1 V in 95%. Device longevity analysis showed that the use of a 0.5-V safety margin increased average battery longevity by 0.62 years (95% confidence interval 0.61 to 0.63) compared with a safety margin of 1.5 V. Patients with LV PCTs >1 V had the greatest increases in battery life (mean increase 0.86 years, 95% confidence interval 0.85 to 0.87). In conclusion, nearly all CRT defibrillator patients had LV PCT stability <1.0 V. Decreasing the LV safety margin from 1.5 to 0.5 V provided consistent delivery of CRT for most patients and significantly improved battery longevity.

The Kora Pacemaker is Safe and Effective for Magnetic Resonance Imaging.

BACKGROUNDThe impact of magnetic resonance imaging (MRI) on pacemakers is potentially hazardous. We present clinical results from a novel MRI conditional pacing system with the capability to switch automatically to asynchronous mode in the presence of a strong magnetic field.AIMSThe IKONE (Assessment of the MRI solution: KORA 100™ and Beflex™ pacing leads system) study is an open-label, prospective, multicenter study aimed at confirming the safety and effectiveness of the system, when used in patients undergoing MRI of anatomical regions excluding the chest.METHODSPrimary eligibility criteria included patients implanted with the system, with or without a clinically indicated MRI. The primary endpoint was to confirm no significant change in pacing capture thresholds at 1 month after an MRI, with an absolute difference of ≤0.75 V between the pre- and 1-month post-MRI for both atrial and ventricular capture thresholds.RESULTSOut of 33 patients enrolled (mean age: 72.8 ± 11.4 years, 70% male, implant indication or device), 29 patients implanted with the MRI conditional system underwent an MRI 6–8 week postimplant. The study reached its primary endpoint: the mean absolute difference in pacing capture threshold at 1-month post-MRI versus pre-MRI was less than 0.75 V in the atrium (Δ = 0.18 ± 0.16 V, P-value < 0.001) and in the ventricle (Δ = 0.18 ± 0.22 V, P-value < 0.001). There were no adverse events related to the MRI procedure nor were there reports of patient symptoms or discomfort associated. MR image quality was of diagnostic quality in all patients.CONCLUSIONLead electrical performance as measured by difference in capture thresholds were not impacted by MRI. This first clinical evaluation of a novel MRI conditional system demonstrates it is safe and effective for use in out-of-chest, 1.5-T MR imaging.

MRI scanning in patients with new and existing CapSureFix Novus 5076 pacemaker leads: randomized trial results.

Magnetic resonance imaging (MRI) can be safely performed in patients with magnetic resonance (MR)-conditional pacemaker systems but remains relatively contraindicated with non-MR-conditional pacemaker systems. The purpose of this study was to evaluate the safety of MRI without positioning restrictions in patients with an MR-conditional pacemaker and currently a non-MR-conditional Medtronic CapSureFix Novus 5076 lead(s). The study randomized 266 patients in a 2:1 ratio to the MRI group (177 patients) or to the control group (89 patients). At 9-12 weeks postimplant, the MRI group underwent MRI at 1.5 T. Primary end points were MRI-related complication-free rate and noninferiority of the MRI group compared to the control group with regard to the proportion of patients with an increase of ≤0.5 V in right atrial (RA) and right ventricular (RV) pacing capture thresholds from immediately before MRI to 1-month after MRI. No MRI-related complications occurred in 156 MRI-scanned patients who were followed through 1-month post-MRI. Differences in the proportion of patients with ≤0.5 V pacing capture threshold changes from pre-MRI to 1-month post-MRI were minimal between the groups for RA (proportions of 100% in both groups; a P value cannot be calculated) and RV leads (proportions of 99.3% in the MRI group and 100% in the control group; noninferiority test, P < .0001). Proportions of patients with acceptable sensing amplitude changes from pre-MRI to 1-month post-MRI were also similar between the 2 groups for RA and RV leads (noninferiority test, P < .0001 and P = .0004, respectively). No arrhythmias occurred during MRI. MRI scans can be performed safely without positioning restrictions in patients with Medtronic CapSureFix Novus 5076 leads connected to an MR-conditional pacemaker.

Abstract 14753: A Novel Quadripolar Lead with a Narrow-Spaced Bipole Allows for Effective LV Pacing While Avoiding Phrenic Nerve Stimulation - Attain Performa LV Lead Study Primary Results

Introduction: The Medtronic Attain Performa™ Model 4298 Quadripolar left ventricular (LV) Lead has 4 electrodes, provides 16 different polarities &amp; includes a short bipole (1.3 mm between 2nd &amp; 3rd electrodes). A prospective clinical study was conducted to investigate the safety and effectiveness of this new lead in 20 countries worldwide. Methods: Cardiac resynchronization therapy defibrillator (CRT-D) patients were enrolled &amp; implanted with the Model 4298 LV lead &amp; a Quad CRT-D device. All implanted subjects(SUB) were followed at 1, 3, 6 and every 6 months (M) post-implant. Pacing capture thresholds (PCTs) were measured manually or with automated testing methods. Adverse events (AEs) were reported upon occurrence &amp; reviewed by an independent committee. Events requiring invasive intervention or resulting loss of CRT were considered to be complications. Results: Of 499 SUB (68 + 11 yr, 71% male) who underwent an LV lead implant attempt, 487 (97.6%) had an LV lead implanted, Most (73%) had NYHA Class III or IV symptoms, average LV ejection fraction was 25 ± 7%, QRS duration was 155 ± 24ms &amp; most (71%) had LBBB. There were 20 LV lead related complications in 19 SUB over 6M (LV lead related complication free survival rate = 96%). Phrenic nerve stimulation (PNS) occurred in 31 SUB (6.3%) &amp; resolved with no treatment (N=1) or noninvasive reprogramming (N=29). The average PCT at 6M was 1.1 + 0.7 V at the programmed vector and 93.9% of SUB had a PCT≤ 2.5V. The vast majority (97.7%) of SUB had &gt; 1 additional selectable pacing vector with a PCT ≤ 4V and no PNS. Non-standard pacing polarities (i.e., vectors other than LV1 [LV tip] to right ventricular coil [RVC], LV2 to RVC &amp; LV1 to LV2) were utilized in 56% of SUB. LV1 was not used in the final vector in 46% of SUB. The LV1 to RVC was utilized in 19%, LV1 to LV2 in 18% &amp; the short bipole (LV2 to LV3) in 12%. Conclusions: This large multicenter study demonstrated that implantation of the Model 4298 LV quadripolar lead is associated with a low complication rate and no unanticipated complications. PNS can be readily resolved with reprogramming &amp; that PCT values are low &amp; stable over time. Moreover, At least 1 back-up LV pacing vector was available in the vast majority of SUB. Non-standard vectors, including the short bipole (LV2-LV3) were used in 56% of subjects.

Immediate and 12months follow up of function and lead integrity after cranial MRI in 356 patients with conventional cardiac pacemakers.

BackgroundConventional cardiac pacemakers are still often regarded as a contraindication to magnetic resonance imaging (MRI). We conducted this study to support the hypothesis that it is safe to scan patients with cardiac pacemakers in a 1.5 Tesla MRI, if close supervision and monitoring as well as adequate pre- and postscan programming is provided.MethodsWe followed up 356 patients (age 61.3 ± 9.1 yrs., 229 men) with single (n = 132) or dual chamber (n = 224) cardiac pacemakers and urgent indication for a cranial MRI for 12 months. The scans were performed at 1.5T. During the scan patients were monitored with a 3-lead ECG and pulse oximetry. Prior to the scan pacemakers were programmed according to our own protocol.ResultsAll 356 scans were completed without complications. No arrhythmias were induced, programmed parameters remained unchanged. No pacemaker dysfunction was identified. Follow-up examinations were performed immediately, 2 weeks, 2, 6, and 12 months after the scan. There was no significant change of pacing capture threshold (ventricular 0.9 ± 0.4 V@0.4 ms, atrial 0.9 ± 0.3 V@0.4 ms) immediately (ventricular 1.0 ± 0.3 V@0.4 ms, atrial 0.9 ± 0.4 V@0.4 ms) or at 12 months follow-up examinations (ventricular 0.9 ± 0.2 V@0.4 ms, atrial 0.9 ± 0.3 V@0.4 ms). There was no significant change in sensing threshold (8.0 ± 4.0 mV vs. 8.1 ± 4.2 mV ventricular lead, 2.0 ± 0.9 mV vs. 2.1 ± 1.0 mV atrial lead) or lead impedance (ventricular 584 ± 179 Ω vs. 578 ± 188 Ω, atrial 534 ± 176 Ω vs. 532 ± 169 Ω) after 12 months.ConclusionsThis supports the evidence that patients with conventional pacemakers can safely undergo cranial MRI in a 1.5T system with suitable preparation, supervision and precautions. Long term follow-up did not reveal significant changes in pacing capture nor sensing threshold.

Safe performance of magnetic resonance of the heart in patients with magnetic resonance conditional pacemaker systems: the safety issue of the ESTIMATE study.

BackgroundNo published data exist about the safety of diagnostic magnetic resonance (MR) of the heart performed in a larger series of patients implanted with MR conditional pacemakers (PM). The purpose of our study is to analyse safety and potential alterations of electrical lead parameters in patients implanted with the EnRhythm/Advisa MRI SureScan PM with 5086MRI leads (Medtronic Inc.) during and after MR of the heart at 1.5 Tesla.MethodsPatients enrolled in this single center pilot study who underwent non-clinically indicated diagnostic MR of the heart were included in this analysis. Heart MR was performed for analyses of potential changes in right and left ventricular functional parameters under right ventricular pacing at 80 and 110 bpm. Atrial/ventricular sensing, atrial/ventricular pacing capture threshold [PCT], and pacing impedances were assessed immediately before, during, and immediately after MR, as well at 3 and 15 months post MR.ResultsThirty-six patients (mean age 69 ± 13 years; high degree AV block 18 [50%]) underwent MR of the heart. No MR related adverse events occurred during MR or thereafter. Ventricular sensing differed significantly between the FU immediately after MR (10.3 ± 5.3 mV) and the baseline FU (9.8 ± 5.3 mV; p < 0.05). Despite PCT [V/0.4ms] was not significantly different between the FUs (baseline: 0.84 ± 0.27; in-between MR scans: 0.82 ± 0.27; immediately after MR: 0.84 ± 0.24; 3-month: 0.85 ± 0.23; 15-month: 0.90 ± 0.67; p = ns), 7 patients (19%) showed PCT increases by 100% (max. PCT measured: 1.0 V) at the 3-month FU compared to baseline. RV pacing impedance [Ω/5V] differed significantly at the FU in-between MR scans (516 ± 47), and at the 15-month FU (482 ± 58) compared to baseline (508 ± 75).ConclusionThe results of our study suggest MR of the heart to be safe in patients with the MR conditional EnRhythm/Advisa system, albeit although noticeable but clinically irrelevant ventricular PCT changes were observed.

Computer modeling and MRI-device safety: Modeling, myths, and magical thinking

In this issue of HeartRhythm, Wilkoff et al introduce computer modeling in the evaluation of lead heating, one of the many concerns when scanning patients with devices. The Food and Drug Administration (FDA) has declared its strong support for computer modeling. The FDA could hardly be expected to ignore reports of harm involving lead heating, reported threshold rises after magnetic resonance imaging (MRI), and transient failure to capture, nor the immense complexity encountered when evaluating the problem. Correctly noted by Wilkoff et al, “lead electrode heating is due to a combination of multiple clinical variables including patient size, anatomy, and body composition, patient position in the bore, scan sequence (radiofrequency [RF] power level), lead routing, and lead design.” Regarding this complexity, “FDA recognizes that clinical or animal testing in an MRI scanner cannot characterize worst-case clinical conditions for lead heating.” The failure by some to fully appreciate the complexity of the MRI-device interaction is the basis for many of the myths and magical thinking regarding the interpretation of the current significance of large registries that are used to support the overall safety of off-label device scanning. The Wilkoff model’s 2-fold premise is practical and scientific: mitigating pacing capture threshold (PCT) changes during MRI is a valid metric of patient safety, and the PCT changes directly result from “the amount of radiofrequency (RF) power that reaches the electrode tissue interface.” Importantly, because of “differences in lead body and electrode constructions a different electromagnetic model must be derived for every lead type.” Since RF-induced heating is extremely position sensitive, “one thousand clinically relevant and anatomically correct lead routings were developed, created from pacemaker chest X-ray images,” and these model leads were placed in human body models representing a broad expanse of patients. These patients with “model” pacemakers were placed in simulated commercially available RF coils. In vitro experiments were

Safe magnetic resonance imaging scanning of patients with cardiac rhythm devices: A role for computer modeling

Although there are several hazards for patients with implanted pacemakers and defibrillators in the magnetic resonance imaging (MRI) environment, evaluation of lead electrode heating is the most complex because of the many influencing variables: patient size, anatomy, body composition, patient position in the bore, scan sequence (radiofrequency power level), lead routing, and lead design. Although clinical studies are an important step in demonstrating efficacy, demonstrating safety through clinical trials alone is not practical because of this complexity. The purpose of this study was to develop a comprehensive modeling framework to predict the probability of pacing capture threshold (PCT) change due to lead electrode heating in the MRI environment and thus provide a robust safety evaluation. The lead heating risk was assessed via PCT change because this parameter is the most clinically relevant measure of lead heating. The probability for PCT change was obtained by combining the prediction for power at the electrode-tissue interface obtained via simulations with a prediction for PCT change as a function of radiofrequency power obtained via an in vivo canine study. The human modeling framework predicted that the probability of a 0.5-V PCT change due to an MRI scan for the Medtronic CapSureFix MRI SureScan model 5086 MRI leads is <1/70,000 for chest scans and <1/10,000,000 for either head scans or lower torso scans. The framework efficiently models millions of combinations, delivering a robust evaluation of the lead electrode heating hazard. This modeling approach provides a comprehensive safety evaluation that is impossible to achieve using phantom testing, animal studies, or clinical trials alone.

The Canadian experience with Durata and Riata ST Optim defibrillator leads: A report from the Canadian Heart Rhythm Society Device Committee

The St. Jude Medical Riata family of implantable cardioverter-defibrillator (ICD) leads has demonstrated a high rate of externalized conductors and electrical failure. Given similar design elements of Durata to Riata, the purpose of this study was to assess the rates of failure of the Riata ST Optim and Durata lead families in Canada. All Canadian ICD-implanting centers were invited to submit follow-up information on all Optim-coated ICD leads implanted. Electrical failure was defined as a rapid change in impedance or pacing capture threshold leading to lead revision, or oversensing due to noise. Externalized conductors were defined as appearance of conductor wires outside the lead body. Systematic fluoroscopic screening for externalized conductors was not performed. As of December 1, 2012, 15 of 25 centers provided data on 3981 leads (44% of those sold in Canada during the same timeframe): 3477 Durata and 504 Riata ST Optim leads. The most common model numbers were 7122 (1516 leads [38%]), 7121 (707 leads [18%]), and 7120 (622 leads [16%]). Mean follow-up duration from implant to December 1, 2012, was 4.47 ± 0.48 years for Riata ST Optim leads and 2.00 ± 1.10 years for Durata leads. The annual rate of lead failure was 0.27% per year for Riata ST Optim leads and 0.24% per year for Durata leads. No instances of externalized conductors were identified in the failed leads. No deaths were attributed to lead failure; however, 2 patients experienced inappropriate shocks due to lead failure. The overall electrical failure rates of the Riata ST Optim and Durata leads appear to be low, and no instances of externalized conductors were observed.

Randomized trial of pacemaker and lead system for safe scanning at 1.5 Tesla

Magnetic resonance imaging (MRI) of pacemakers is a relative contraindication because of the risks to the patient from potentially hazardous interactions between the MRI and the pacemaker system. Chest scans (ie, cardiac magnetic resonance scans) are of particular importance and higher risk. The previously Food and Drug Administration-approved magnetic resonance conditional system includes positioning restrictions, limiting the powerful utility of MRI. To confirm the safety and effectiveness of a pacemaker system designed for safe whole body MRI without MRI scan positioning restrictions. Primary eligibility criteria included standard dual-chamber pacing indications. Patients (n = 263) were randomized in a 2:1 ratio to undergo 16 chest and head scans at 1.5 T between 9 and 12 weeks postimplant (n = 177) or to not undergo MRI (n = 86) post-implant. Evaluation of the pacemaker system occurred immediately before, during (monitoring), and after MRI, 1-week post-MRI, and 1-month post-MRI, and similarly for controls. Primary end points measured the MRI-related complication-free rate for safety and compared pacing capture threshold between MRI and control subjects for effectiveness. There were no MRI-related complications during or after MRI in subjects undergoing MRI (n = 148). Differences in pacing capture threshold values from pre-MRI to 1-month post-MRI were minimal and similar between the MRI and control groups. This randomized trial demonstrates that the Advisa MRI pulse generator and CapSureFix MRI 5086MRI lead system is safe and effective in the 1.5 T MRI environment without positioning restrictions for MRI scans or limitations of body parts scanned.

Failure rate of the Riata lead under advisory: A report from the CHRS Device Committee

A unique form of lead failure has been described in the Riata (8-F) and Riata ST (7-F) silicone defibrillation lead degradation of the outer insulation, resulting in the externalization of conductor cables. To assess rates of lead revision due to lead failure in Riata leads affected by the Riata advisory. Nineteen implantable cardioverter-defibrillator implant and follow-up centers were surveyed. As of March 1, 2012, there were 5043 known affected leads implanted in Canada. Data on 4358 (86.4%) leads were obtained; 65.3% of these were Riata (8-F) and 32.4% were Riata ST (7-F) leads. The median time from implant to last follow-up was 5 years. Electrical abnormalities were reported in 4.6% of the affected leads; 8.0% of these were found to have concomitant radiographic evidence of externalization. The rate of electrical failure was higher in the 8-F (5.2%) vs 7-F (3.3%) leads (P = .007). Oversensing with or without inappropriate shocks was reported in 39.8% of the leads with confirmed failure. Abnormally high or low impedance values (29.9%) and elevated pacing capture thresholds (43.8%) were frequently reported. One death (0.5%) attributed to lead failure was reported. Among the leads that were replaced, 21% were extracted. Two major complications (1.0%) were attributed to extraction of these leads. The overall rate of lead failure in the Riata (8-F) and Riata ST (7-F) leads is higher than previously reported by using passive surveillance data. The impact of recent advisories related to these leads is not yet apparent.