Conditional Pacemakers Research Articles

296 Cardiac MRI of Patients with Implanted Devices - Diagnostic Improvement Using Wide Band Late Gadolinium Enhancement Imaging

Cardiac magnetic resonance (CMR) with Late Gadolinium Enhancement (LGE) is used to evaluate myocardial scar and differentiate cardiomyopathies. However, implanted devices cause susceptibility artefacts often rendering the images uninterpretable. We scanned 31 consecutive cases with implanted devices and substantial susceptibility artefact using a novel Wide Band LGE sequence and evaluated the clinical utility for evaluation of myocardial scar. 31 consecutive stress scans CMR clinically referred for evaluation of myocardial scar were performed on a 1.5T system (MAGNETOM Aera, Siemens Healthcare). Standard breath-held magnitude inversion recovery (Mag-LGE) images were performed 10 minutes after 1.5mg/kg gadobutrol (Gadovist). This was compared to a free-breathing motion corrected Wide Band LGE (WB-LGE) prototype sequence with 4Khz-6KHz increased bandwidth (WIP 1325, Siemens Healthineers). Level-3 expert reader blindly evaluated both sets of images in a randomized order. Image quality and diagnostic confidence were measured on a Likert rating scale from 1 (poor) to 3 (very good). 28 cases had implanted MRI conditional pacemakers or defibrillators, 2 cases with mechanical heart valves, and 1 with a shoulder implant. WideBand imaging was successful in all (100%) cases, demonstrating clinical feasibility. Image quality score for Mag-LGE was 1.033 (poor), compared to 2.866 for WB-LGE (p<0.001). In 30/31 cases (97%) the WB-LGE imaging was superior and provided diagnostic clinical information not available on standard Mag-LGE imaging, with only 1 case having persistent artefact. Wide-Band LGE imaging provide diagnostic CMR imaging of myocardial scar in cases where standard LGE imaging is poor or uninterpretable.

Safety and efficiency of low-field magnetic resonance imaging in patients with cardiac rhythm management devices

PurposeLow-field magnetic resonance imaging (MRI), i.e. MRI with a static magnetic field strength <0.5 T, has been reported to be safe in patients with pacemakers, however there are no data about the safety of low-field MRI in patients with implantable cardioverter defibrillators (ICD) and/or cardiac resynchronization therapy (CRT). We aimed to investigate the safety and diagnostic efficiency of routine low-field MRI in patients with different devices for cardiac rhythm management (i.e. pacemakers and ICD, including devices with CRT). MethodMRI scans of 446 regions of interest were evaluated with field strength of 0.2 T in 338 patients (62% male; age at MRI scan 76.1 ± 9.2 years; time since device implantation 4.1 ± 3.2 years) with cardiac rhythm management devices (298 pacemakers, 25 ICD, 8 CRT-ICD, and 7 CRT pacemakers). This analysis included 62 pacemaker-dependent patients (18.3%), 52 patients with 1.5-Tesla-MR conditional pacemakers (15.4%) and 13 patients with abandoned leads (3.9%). ResultsExcept for one examination, which was interrupted because of recurrent severe nausea, all MRI scans could be analyzed efficiently. No induction of arrhythmia or inhibition of pacemaker function occurred. Compared to the device interrogation before MRI, there were no significant changes in battery voltage, pacing capture threshold, sensing of intrinsic ECG, lead impedance, as well as shock impedance in ICD devices after completed examination. ConclusionsLow-field MRI examinations (0.2 T) were efficient and safe regarding clinical and technical complications in patients with devices for cardiac rhythm management, even in case of pacemaker-dependency or the presence of abandoned leads.

Incidence and predictors of MRI scan utilization in MRI-conditional pacemaker recipients: A multicenter experience.

Patient characteristics, higher device cost, and vendor contracts likely prevent use of magnetic resonance imaging (MRI)-conditional pacemakers (MRC) in all pacemaker (PM)-eligible patients. We sought to identify the incidence and predictors of MRI scan utilization in MRC recipients. Patients receiving an MRC or non-MRI-conditional PM (NMRC) at four centers were included. Incidence of MRI scans following PM insertion was obtained from hospital records and patient phone calls. Of 1,244 patients (74 ± 12 years, 54.6% male), 927 had MRC and 317 had NMRC. At baseline, MRC recipients had a higher incidence of atrial tachycardia and MRI risk factors (syncope, recurrent falls, neurological disease, severe musculoskeletal disease, malignancy). In the MRC group, more patients had commercial health insurance (26%vs 15%, P<0.001). Sixty MRC patients (6.5%) had an MRI during 21 ± 17 months' follow-up. Using the Weilbull parametric survival model, the projected percentage of MRC patients receiving an MRI scan at 7- and 11-year follow-up were 45% and 73%, respectively. By multivariate regression, a prior history of MRI (odds ratio [OR] 4.5, 95% confidence interval [CI] 2.2-9.1, P<0.001) and active smoking (OR 2.65, 95% CI 1.1-6.7, P=0.039) independently predicted the performance of an MRI following MRC implant. In this MRC cohort, MRI scan utilization during follow-up was low but projection analyses showed a higher incidence over the lifetime of the MRC. A history of prior MRI and active smoking independently predicted the performance of an MRI scan during follow-up.

Cost-effectiveness analysis of magnetic resonance imaging–conditional pacemaker implantation: Insights from a multicenter study and implications in the current era

Magnetic resonance imaging (MRI)-conditional pacemakers (M-PPMs) grant patients greater accessibility to MRI scans. The cost-effectiveness of implanting M-PPM is unknown. The purpose of this study was to determine the cost-effectiveness of M-PPM implantation. Cost-effectiveness analysis was performed on patients receiving a M-PPM across 4 institutions. The incremental cost-effectiveness ratio (ICER) was calculated by dividing the sum of the total incremental cost of implanting a M-PPM vs a conventional pacemaker and the cost of MRI scans by the utility of MRI scans in terms of quality-adjusted life-years (QALY) gained. QALY and lifespan of M-PPM (7-11 years) data were obtained from the literature. The benchmark of <$100,000 per QALY was used as the threshold for cost-effectiveness. Computer modeling/simulations were used to calculate the percentage of patients required to achieve this benchmark, to extrapolate the cumulative projected percentage of patients utilizing MRI scans over the lifespan of a M-PPM via the Weibull parametric survival model, and to conduct univariate and multivariate, probabilistic sensitivity analyses. The ICER during the follow-up period (21 ± 17 months) was $451,569. The cost-effectiveness ICER benchmark is reached 7.0 years postimplantation, when a projected 38% of recipients would receive MRI scans. The projected percentage of patients receiving MRI scans at 11 years was 58%, yielding an ICER of $74,221 per QALY. Henceforth, assuming increased MRI usage in regular PPM based on Centers for Medicare & Medicaid Services memo CAG00399R4 and decreased cost of M-PPM, M-PPM implantation is still cost-effective, with a lifetime ICER of $49,817 per QALY. M-PPM implantation is cost-effective over the lifespan of a M-PPM based on projected usage of MRI.

Waikato Hospital Experience of Magnetic Resonance Imaging for Patients with Non-MRI Conditional Pacemakers and Implantable Cardioverter Defibrillators

Waikato Hospital Experience of Magnetic Resonance Imaging for Patients with Non-MRI Conditional Pacemakers and Implantable Cardioverter Defibrillators

Deactivation vs. asynchronous pacing - prospective evaluation of a protocol for rhythm management in patients with magnetic resonance conditional pacemakers undergoing adenosine stress cardiovascular magnetic resonance imaging

BackgroundCardiovascular Magnetic Resonance (CMR) imaging with adenosine stress is an important diagnostic tool in patients with known or suspected coronary artery disease (CAD). However, the method is not yet established for CAD patients with pacemakers (PM) in clinical practice. A possible reason is that no recommendations exist for PM setting (paused pacing or asynchronous mode) during adenosine stress. We elaborated a protocol for rhythm management in clinical routine for PM patients that considers heart rate changes under adenosine using a test infusion of adenosine in selected patients.Methods47 consecutive patients (mean age 72.3 ± 10,0 years) with MR conditional PM and known or suspected CAD who underwent CMR in clinical routine were studied in this prospective observational study. PM indications were sinus node dysfunction (SND, n = 19; 40,4%), atrioventricular (AV) block (n = 26; 55.3%) and bradyarrhythmia in permanent atrial fibrillation (AF, n = 2; 4.3%). In patients with SND, normal AV-conduction and resting HR >45 bpm at the time of CMR and in AF the PM was deactivated for the scan. In intermittent AV-block a test infusion of adenosine was given prior to the scan. All patients with permanent higher degree sinuatrial or AV-block or deterioration of AV-conduction in the adenosine test were paced asynchronously during CMR, in patients with preserved AV-conduction under adenosine the pacemaker was deactivated. CMR protocol included cine imaging, adenosine stress perfusion and late gadolinium enhancement.ResultsThe adenosine test was able to differentiate between mandatory PM stimulation during CMR and safe deactivation of the device. In patients with permanent sinuatrial or AV-block (n = 11; 23.4%) or deterioration of AV conduction in the adenosine test (n = 5, 10.6%) asynchronous pacing above resting heart rate did not interfere with intrinsic rhythm, no competitive stimulation was seen during the scan. 10 of 15 (66,7%) patients with intermittent AV-block showed preserved AV-conduction under adenosine. As in SND and AF deactivation of the PM showed to be safe during CMR, no bradycardia was observed.ConclusionOur protocol for rhythm management during adenosine stress CMR showed to be feasible and safe and may be recommended for pacemaker patients undergoing routine CMR.

Low-Field Cardiac Magnetic Resonance Imaging: A Compelling Case for Cardiac Magnetic Resonance's Future.

Cardiac magnetic resonance (CMR) is arguably unmatched in its ability to evaluate cardiovascular structure and function, to characterize myocardial tissue by a wide variety of mechanisms, and to quantitatively assess blood flow and perfusion without the use of radiation or the need for invasive catheterization. CMR research and development continues at a rapid pace both in academia and by commercial vendors, and every year, new techniques are put forth that improve on existing applications and provide new capabilities that further expand the clinical utility of this powerful modality. Real-time and single-shot techniques have made CMR feasible in patients with rhythm irregularities and inability to breath-hold. Ongoing development and regulatory approval of magnetic resonance imaging (MRI) conditional pacemakers and implanted cardioverter defibrillators continues to grow the patient population amenable to CMR. Larger clinical trials are coming out that support the clinical value of CMR.1–3 Despite the advances in CMR technology over the past decades, the growing data supporting its effectiveness, and the increasing availability of both CMR-capable scanners and practitioners, the penetration of CMR into routine diagnostic cardiovascular imaging remains limited. It is clear that those involved in CMR research must not only engage in developing new and exciting applications made feasible by technological advances, but must also ask whether their technology will promote the routine clinical utilization of CMR beyond academic and isolated private centers. There are many factors at play in answering this question, but important considerations must be affordability and ease of use. A CMR system is one of the most expensive devices in the hospital, and the cost of the system scales with field strength. Prior to 2001, the highest field strength available for clinical MRI was 1.5T; however, recent years have witnessed an expanded utilization of 3T MRI that has been driven mainly …

Cardiovascular magnetic resonance in patients with magnetic resonance conditional pacemaker systems at 1.5T: influence of pacemaker related artifacts on image quality including first pass perfusion, aortic and mitral valve assessment, flow measurement, short tau inversion recovery and T1-weighted imaging.

There are only limited data on the impact of device-related artifacts on image quality in cardiovascular magnetic resonance imaging (CMR) in patients with pacemakers (PM). Adenosine stress perfusion, T1-weighted imaging and flow measurement as well as valve characterization have not been evaluated previously concerning artifact burden. We aimed to assess image quality in all routinely used CMR sequences. We analyzed 2623 myocardial segments in CMR scans of 61 patients with MR conditional PM (mean age 72.1 ± 11.5years), 23 (37.7%) with right sided, 38 (62.3%) with left-sided devices. There were no relevant artifacts in patients with right-sided devices irrespective of the imaging sequence. In left-sided implants no PM-induced artifacts were found in first pass perfusion sequence, flow analysis and T1 weighted imaging. Only few patients with left-sided devices showed significant PM-artifacts in aortic (3/38, 7.9%)/mitral (n = 2/38, 5.3%) valve imaging and STIR (n = 3/35, 8.6%). In STIR only 14/805 (1.7%) segments were involved. In left-sided PM SSFP cine sequences had more artifact burden than LGE with 377/1505 (25.0%) vs. 162/1505 (10.8%) myocardial segments involved by relevant artifacts respectively (p < 0.001). Apart from cine and LGE imaging in anterior myocardial segments with left-sided implants presence of MRI conditional pacemakers does not affect CMR image quality in multimodal CMR examinations to a significant extent. Our data supports evidence that reduced image quality does not need to be a major concern in PM patients undergoing CMR.

Safety evaluation of a leadless transcatheter pacemaker for magnetic resonance imaging use

Increased magnetic resonance imaging (MRI) adoption and demand are driving the need for device patients to have safe access to MRI. The aim of this study was to address the interactions of MRI with the Micra transcatheter pacemaker system. A strategy was developed to evaluate potential MRI risks including device heating, unintended cardiac stimulation, force, torque, vibration, and device malfunction. Assessment of MRI-induced device heating was conducted using a phantom containing gelled saline, and Monte Carlo simulations incorporating these results were conducted to simulate numerous combinations of human body models, position locations in the MRI scanner bore, and a variety of coil designs. Lastly, a patient with a Micra pacemaker who underwent a clinically indicated MRI scan is presented. Compared to traditional MRI conditional pacemakers, the overall risk with Micra was greatly reduced because of the small size of the device and the absence of a lead. The modeling results predicted that the nonperfused temperature rise of the device would be less than 0.4°C at 1.5 T and 0.5°C at 3 T and that the risk of device heating with multiple device implants was not increased as compared with a single device. The clinical case study revealed no MRI-related complications. The MRI safety assessment tests conducted for the Micra pacemaker demonstrate that patients with a single device or multiple devices can safely undergo MRI scans in both 1.5- and 3-T MRI scanners. No MRI-related complications were observed in a patient implanted with a Micra pacemaker undergoing a clinically indicated scan.

Impact of magnetic resonance imaging on ventricular tachyarrhythmia sensing: Results of the Evera MRI Study

Studies have shown that magnetic resonance imaging (MRI) conditional pacemakers experience no significant effect from MRI on device function, sensing, or pacing. More recently, similar safety outcomes were demonstrated with MRI conditional defibrillators (implantable cardioverter-defibrillator [ICD]), but the impact on ventricular arrhythmias has not been assessed. The purpose of this study was to assess the effect of MRI on ICD sensing and treatment of ventricular tachyarrhythmias. The Evera MRI Study was a worldwide trial of 156 patients implanted with an ICD designed to be MRI conditional. Device-detected spontaneous and induced ventricular tachycardia/ventricular fibrillation (VT/VF) episodes occurring before and after whole body MRI were evaluated by a blinded episode review committee. Detection delay was computed as the sum of RR intervals of undersensed beats. A ≥5-second delay in detection due to undersensing was prospectively defined as clinically significant. Post-MRI, there were 22 polymorphic VT/VF episodes in 21 patients, with 16 of these patients having 17 VT/VF episodes pre-MRI. Therapy was successful for all episodes, with no failures to treat or terminate arrhythmias. The mean detection delay due to undersensing pre- and post-MRI was 0.60 ± 0.59 and 0.33 ± 0.63 seconds, respectively (P = .17). The maximum detection delay was 2.19 seconds pre-MRI and 2.87 seconds post-MRI. Of the 17 pre-MRI episodes, 14 (82%) had some detection delay as compared with 11 of 22 (50%) post-MRI episodes (P = .03); no detection delay was clinically significant. Detection and treatment of VT/VF was excellent, with no detection delays or significant impact of MRI observed.

Abstract 14195: Diagnostic Value of MRI in Patients With Implanted Cardiac Devices: Does the Benefit Justify the Risk?

Background: MRI is infrequently performed on patients with conventional pacemakers/ICD’s. Multiple recent studies and registries (MagnaSafe) have documented the safety of MRI in these patients, yet the diagnostic value of this approach has not been established remaining a critical issue to advance this field in an era of progressive MRI useage. Objective: 1) to examine a protocol to assess the diagnostic utility of thoracic and non-thoracic MRI in patients with implantable devices and 2) to determine if there is substantial benefit to the pt with regard to diagnosis and/or management. Methods: Over 8 years, 134 pts with PM/AICD’s underwent MRI (GE, 1.5T Milwaukee, WI) at a single institution. Specific criteria were followed for all pts to objectively define whether final diagnosis by MRI imaging enhanced patient care. A checklist of three questions was answered following scan interpretation by both the technologist and performing MRI physician(s):1) Did the primary diagnosis change? 2) Did the MRI provide additional information to the existing diagnosis? 3) Did patient management change? If ’Yes’ was answered to any of the above questions, it was considered that the MRI scan was of value to patient diagnosis and/or therapy. Results: All 134 pts underwent MRI/CMR without complications: avg scan time 24±9min including 42 pts with ICD’s, 5 pts with a retained lead and 87 non-MR conditional pacemakers. In 83% (n=112) MR added value to patient diagnosis and management. In 64% (n=86) MRI added additional valuable information to the primary diagnosis and in 19% (n=26) MRI was life-saving, changing the principal diagnosis and subsequent management of the pt. There were no deaths, arrhythmias or power-on-resets encountered and no adverse effects were noted in any pt. No post-procedure revisions or reimplantations of generator/lead were required. Conclusions: MR imaging in patients with implanted cardiac devices adds substantial value to patient diagnosis and management justifying the risk of the procedure. In this real-world patient population, we have shown that MR imaging retains its very high diagnostic yield. Risk-benefit ratios clearly justify the performance of MRI even in this higher risk population, that is, until such time as MR-conditional devices are universal.

CMR scanning of MR-conditional pacemakers: a 5-year single centre experience

Background The first MRI conditional pacemaker was introduced in 2008. Though, they represent the minority of all devices implanted, their use has increased. Similarly, CMR imaging in the UK has increased from just over 20,000 studies in 2008 to nearly 40,000 scans in 2010. However, there is limited data describing the frequency, safety and diagnostic quality of CMR scans in patients with MR conditional devices. Our aim was to describe device scanning in our clinical practice and identify reasons why MR conditional pacemakers were selected.

Feasibility and safety of adenosine cardiovascular magnetic resonance in patients with MR conditional pacemaker systems at 1.5 Tesla.

BackgroundCardiovascular Magnetic Resonance (CMR) with adenosine stress is a valuable diagnostic tool in coronary artery disease (CAD). However, despite the development of MR conditional pacemakers CMR is not yet established in clinical routine for pacemaker patients with known or suspected CAD. A possible reason is that adenosine stress perfusion for ischemia detection in CMR has not been studied in patients with cardiac conduction disease requiring pacemaker therapy. Other than under resting conditions it is unclear whether MR safe pacing modes (paused pacing or asynchronous mode) can be applied safely because the effect of adenosine on heart rate is not precisely known in this entity of patients. We investigate for the first time feasibility and safety of adenosine stress CMR in pacemaker patients in clinical routine and evaluate a pacing protocol that considers heart rate changes under adenosine.MethodsWe retrospectively analyzed CMR scans of 24 consecutive patients with MR conditional pacemakers (mean age 72.1 ± 11.0 years) who underwent CMR in clinical routine for the evaluation of known or suspected CAD. MR protocol included cine imaging, adenosine stress perfusion and late gadolinium enhancement.ResultsPacemaker indications were sinus node dysfunction (n = 18) and second or third degree AV block (n = 6). Under a pacing protocol intended to avoid competitive pacing on the one hand and bradycardia due to AV block on the other no arrhythmia occurred. Pacemaker stimulation was paused to prevent competitive pacing in sinus node dysfunction with resting heart rate >45 bpm. Sympatho-excitatory effect of adenosine led to a significant acceleration of heart rate by 12.3 ± 8.3 bpm (p < 0.001), no bradycardia occurred. On the contrary in AV block heart rate remained constant; asynchronous pacing above resting heart rate did not interfere with intrinsic rhythm.ConclusionAdenosine stress CMR appears to be feasible and safe in patients with MR conditional pacemakers. Heart rate response to adenosine has to be considered for the choice of pacing modes during CMR.

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.

A case of complete atrioventricular block: The use of magnetic resonance imaging conditional pacemakers for diagnosing cardiac sarcoidosis

A 50-year-old man presented to the emergency department with repeated episodes of faintness and exertional dyspnea, and was found to have an atrioventricular (AV) block. Chest radiography and transthoracic echocardiography results were normal, without any evidence of heart failure, wall motion abnormalities, interventricular septum thinning, or bilateral hilar lymphadenopathy. A temporary pacemaker was implanted, followed by a permanent pacemaker. Chest computed tomography with contrast enhancement did not show abnormalities, including patent coronary arteries, lymph node adenopathy, and pulmonary abnormalities. Thus, an MRI conditional dual chamber pacemaker and leads were implanted. Six weeks following the implant, a cardiac MRI was performed to test for cardiac sarcoidosis. Although cine imaging showed normal left and right ventricular function, late gadolinium enhancement demonstrated multiple enhanced uptakes. Based on the results of the cardiac MRI, PET, and gallium scintigraphy, the most likely diagnosis was cardiac sarcoidosis. Although no abnormal findings were found on physical examination, blood work, chest radiography, and transthoracic echocardiogram, multiple regions of delayed enhancement were observed in the cardiac MRI. Thus, MRI conditional pacemakers are a useful tool for diagnosing cardiac sarcoidosis and early therapeutic intervention.

Not All Pacemakers Are Created Equal: MRI Conditional Pacemaker and Lead Technology

Due to expanding clinical indications and an aging society there has been an increase in the use of implantable pacemakers. At the same time, due to increased diagnostic yield over other imaging modalities and the absence of ionizing radiation, there has been a surge in demand for magnetic resonance imaging (MRI) assessment, of both cardiac and noncardiac conditions. Patients with an implantable device have a 50-75% chance of having a clinical indication for MRI during the lifetime of their device. The presence of an implantable cardiac device has been seen as a relative contraindication to MRI assessment, limiting the prognostic and diagnostic utility of MRI in many patients with these devices. The introduction of MRI conditional pacemakers will enable more patients to undergo routine MRI assessment without risk of morbidity or device malfunction. This review gives a general overview of the principles and current evidence for the use of MRI conditional implantable cardiac devices. Furthermore, we appraise the differences between those pacemakers currently released to market.

The technical challenges of cardiac MR in patients with pacemakers – a review of our experience

Purpose: The development of MR conditional pacemakers means that these patients are now able to undergo cardiac MRI. There are strict safety requirements for these to be performed. Pacing devices cause MR artefacts due to signal drop out from the pacing generator and leads, and inhomogeneity within the magnetic field. This inhomogeneity can significantly degrade image quality. We review our initial experience of imaging these patients.

Effects of medullary lesions on conditional pacemaker activity of neonatal rat hypoglossal motoneurons in vitro

N-methyl-d-aspartate (NMDA) has been demonstrated to induce rhythmic activity in various neurons, including hypoglossal motoneurons (XIIms) and converts them to conditional pacemakers. Using whole-cell patch clamp recording in a slice preparation from neonatal rats, we confirmed that some XIIms act as conditional pacemakers, with TTX-insensitivity and a burst period that is voltage-dependent during NMDA application. Other XIIms in this study only fired tonically with NMDA application. Effects of medullary structures on conditional pacemaker XIIms were assessed using lesioned preparations. As a result, NMDA-induced rhythm (NIR) in the XIIm was observed with ventral lesions (excluding inspiratory neurons) and with dorsal lesions (excluding the swallowing center located in the nucleus of the solitary tract). The NIR was also observed with lateral lesions, but with a significantly decreased burst period. These data suggest that NMDA receptor activation selects a subset of XIIms and changes them to pacemakers whose properties can be altered by their excitability. The data also demonstrate that structures fundamental to the NIR are located within the area near the XII nucleus, indicating that the NIR is distinct from inspiratory and swallowing activities. The lateral medulla is considered to be a source of modulation of the excitability of XIIms.

Recent innovations in the development of magnetic resonance imaging conditional pacemakers and implantable cardioverter-defibrillators

The first generation of magnetic resonance conditional pacemakers and implantable cardioverter-defibrillators has finally arrived in clinical practice after many years of development. These devices have been optimized to properly function within magnetic fields of 1.5 T and ensure safe operation in controlled environments. Further progress is needed to develop a new generation of magnetic resonance imaging (MRI) conditional devices that can operate in higher powered MRI machines (3 T) which produce clearer images.

Cardiac pacemakers designed for magnetic resonance environment

Electromagnetic fields associated with magnetic resonance imaging (MRI) can cause serious functional disturbances in patients with cardiac pacemakers. Thus, an implanted pacemaker is generally considered a contraindication for an MRI scan. Studies have shown that MRI indication may emerge in about 17% of patients within one year of pacemaker implantation, and up to 75% of these patients may require MRI during the lifetime of their device. Introduction of pacemaker systems designed specifically for the MRI environment is an important development, providing pacemaker patients with access to this important diagnostic modality. In this article, the current status of MR conditional pacemakers is discussed, together with clinical applications.