Rapid correction of hypokalemia in a patient with an implantable cardioverter-defibrillator and recurrent ventricular tachycardia

We present the case of a 74-year-old man with non-ischemic dilatated cardiomyopathy and an implantable cardioverter-defibrillator presenting with a serum potassium of 2.6 mmol/L, recurrent unstable ventricular tachycardia, and multiple defibrillations. Administration of a rapid bolus of 20 mEq KCL solution via central venous access, followed by an additional total of 80 mEq (orally and intravenously [i.v.]) over the next 2 h, resulted in immediate resolution of his recurrent unstable dysrhythmia without toxic side effects. Guidelines for rapid correction of hypokalemia quote a maximum safe administration of 20 mEq i.v./h. In addition to discussing the clinical relevance and physiologic interactions of the variables leading to this patient's presentation, we discuss the successful termination of his sustained recurrent ventricular dysrhythmia by rapid potassium repletion above currently recommended rates. The patient we present is representative of a growing population, given medical and technological advances over the years. Potassium boluses may be reasonable in such circumstances, particularly in patients with ICDs.     

Feasibility of magnetic resonance imaging in patients with an implantable loop recorder

Background: The implantable loop recorder (ILR) is a useful tool in the diagnosis of syncope. Our understanding of their functional and safety profile in interfering environments such as magnetic resonance imaging (MRI) becomes increasingly important as they become more prevalent.
Methods: We report four patients with an ILR who underwent MRI. The ILR memory was cleared before MRI and no changes were made to programmed settings. Device interrogation took place immediately after the scan. Patients were surveyed for device movement and heating, in addition to cardiopulmonary symptoms after their MRI.
Results: Following MRI scanning, all patients were asymptomatic and no device movement or heating was observed. In addition, the functionality of the device remained unaffected. Artifacts mimicking arrhythmias were seen in all ILR patients regardless of the type of MRI scan.
Conclusions: MRI scanning of ILR patients can be performed without harm to patient or device, but artifacts that could be mistaken for a tachyarrhythmia are seen frequently.     

Recurrence of atrial tachyarrhythmias in implantable cardioverter-defibrillator recipients

BACKGROUND: Because the natural history of atrial tachyarrhythmia (AT) is not known in patients with implantable cardioverter-defibrillators (ICDs) but without device-based atrial therapies, we aimed to describe the characteristics and recurrence of AT in such patients. METHODS: In this multicenter trial, 269 patients with standard indications for ICD placement and 2 episodes of AT in the preceding year received a dual-chamber ICD capable of logging AT. Patients were randomly assigned to 3-month periods of atrial therapies "on" or "off." This analysis considered only the 118 patients with atrial therapies programmed off at ICD placement. RESULTS: Fifty-eight patients (49%) had at least 1 AT episode longer than 1 minute, and 21 (18%) had at least 1 prolonged episode (>24 hours). The median episode frequency for each patient (episodes per month) was 1.8 episodes longer than 1 minute, 0.8 longer than 1 hour, and 0 longer than 24 hours. The median AT burden was 12.2 hours per month. CONCLUSIONS: Patients with standard ICD indications and history of AT have infrequent episodes, frequent short episodes, or prolonged episodes of AT-atrial fibrillation. However, the clinical characteristics examined did not distinguish among the groups. Improved diagnostic tools may help identify patients at risk for development of AT, thereby allowing specific therapies to be targeted to each group of patients.     

Strategy for safe performance of magnetic resonance imaging on a patient with implantable cardioverter defibrillator

Clinically indicated magnetic resonance imaging (MRI) of the brain was safely performed at 1.5 T on a patient with an implantable cardioverter defibrillator (ICD). The ICD was reprogrammed to detection only, and imaging hardware and protocols were modified to minimize radiofrequency power deposition to the ICD system. The integrity of the ICD system was verified immediately post-MRI and after 6 weeks, including an ICD test with induction of ventricular fibrillation. This case demonstrates that in exceptional circumstances, in carefully selected patients, and using special precautions, an MRI exam of the brain may be possible in patients with ICDs.     

Innovative techniques for placement of implantable cardioverter-defibrillator leads in patients with limited venous access to the heart

BACKGROUND: Because of venous occlusion, intracardiac shunting, previous surgery, or small size placement of implantable cardioverter-defibrillator (ICD) leads may not be possible using traditional methods. The purpose of this study was to evaluate and describe innovative methods of placing ICD leads. METHODS: The records of all patients undergoing ICD implantation at our institution were reviewed to identify patients with nontraditional lead placement. Indications for ICD, method of lead and coil placement, defibrillation thresholds, complications, and follow-up results were reviewed retrospectively. RESULTS: Eight patients (aged 11 months to 29 years) were identified. Six patients with limited venous access to the heart (four extracardiac Fontan, one bidirectional Glenn, one 8 kg 11-month-old) underwent surgical placement of an ICD coil directly into the pericardial sac. A second bipolar lead was placed on the ventricle for sensing and pacing. Two patients with difficult venous access had a standard transvenous ICD lead inserted directly into the right atrium (transatrial approach) and then positioned into the ventricle. All patients had a defibrillation threshold of <20 J, although one patient required placement of a second coil due to an elevated threshold. There have been no complications and two successful appropriate ICD discharges at follow-up (median 22 months, range 5-42 months). CONCLUSIONS: Many factors may prohibit transvenous ICD lead placement. Nontraditional surgical placement of subcutaneous ICD leads on the pericardium or the use of a transatrial approach can be effective techniques in these patients. These procedures can be performed at low risk to the patient with excellent defibrillation thresholds.     

功能磁共振成像/弥散张量成像图像融合:脑肿瘤治疗术前计划新方法(英文)

Objective To develop and test an image fusion software(fDf,fMRI/DTI fusion) which can overlap the anatomical(T1WI images),functional MRI(fMRI) and diffusion tensor imaging(DTI) simultaneously for preoperational evaluation of patients′ tumor.Methods fMRI with bilateral hands grasp movement and DTI were performed using GE 1.5 T magnetic resonance system on 10 subjects(5 healthy volunteers and 5 patients with brain tumor,of which 3 were metastases,1 was cavernous hemangioma and 1 was glioma).All data were input to the personal computer and off line postprocessing of fMRI and DTI data was performed using SPM5 and Volume One software package to visualize the activated functional cortex areas and corticospinal tracts.fDf was used to import the fMRI and structural images to Volume One to show them simultaneously.Results Brain functional activation maps and diffusion tensor fiber tracking images were obtained in all five healthy volunteers and four patients except one who suffered from left hemiplegia.The functional activation maps and the fiber tracking images were successfully fused by the fDf software,where the activations areas and the white matter fiber were displayed together.The fusion images of healthy volunteers showed the hand motion areas and corresponding corticospinal tracts,while that of the patients display the relationship of the eloquent cortex and peritumoral fiber tracts,which were useful in guiding the treatments for the surgeons and radiotherapists.It only took hours to present the fused images to the neurosurgeons or the radiotherapists.Conclusions All the results confirm that the image fusion software work well for all the data.It is an easy,free and fast way to realize the image fusion.The neurosurgeon and radiotherapist consider the software were very helpful for preoperative planning.     

ICD围术期未停口服抗凝药的临床观察和护理

目的探讨植入型心律转复除颤器（ICD）围术期未停口服抗凝药的临床观察和护理。方法回顾ICD植入术35例患者,其中围术期未停抗凝药15例,总结护理要点和并发症的处理方法。结果 35例行ICD植入术患者均痊愈出院,随访患者无不良反应和并发症。结论术前全面评估患者围术期是否停用或替代抗凝剂,同时做好患者教育及凝血监测工作,术后严密观察术区情况,发现异常及时处理。     

Normal spinal anatomy on magnetic resonance imaging

Over the past few decades, spinal magnetic resonance imaging (MR imaging) has largely replaced computed tomography (CT) and CT myelography in the assessment of intraspinal pathology at institutions where MR imaging is available. Given its high contrast resolution, MR imaging allows the differentiation of the several adjacent structures comprising the spine. This article illustrates normal spinal anatomy as defined by MR imaging, describes commonly used spinal MR imaging protocols, and discusses associated common artifacts.     

Lead fracture and free-wall perforation in a patient with an implantable cardioverter-defibrillator

Intracardiac lead fracture or free-wall perforation is a rare complication of implantable defibrillators. Complete disconnection of the fractured electrode has not been reported yet. Here, we report a case of lead fracture/disconnection and free-wall perforation, which occurred consecutively in a patient.     

Cranial magnetic resonance imaging findings in patients with migraine

OBJECTIVE: To investigate the frequency of cranial magnetic resonance imaging abnormalities in patients with migraine and their relationship to type, duration, and frequency of migraine attacks. METHODS: Forty-five patients (43 women, 2 men) with migraine whose ages ranged between 19 and 53 years (mean, 40.91 [SD, 7.69]) were evaluated. Of the 45 patients, 20 had migraine with aura and 25 had migraine without aura, according to the diagnostic criteria of the International Headache Society. RESULTS: In 13 (28.8%) of 45 patients, white matter foci were present on magnetic resonance imaging. Eight of these patients (61.5%) had migraine with aura, and 5 patients (38.4%) had migraine without aura. The presence of white matter foci was significantly higher in the patients with aura (8 [40%] of 20) than in those without aura (5 [20%] of 25). It was found that as the frequency of attacks per month increased, the number of patients with white matter foci also increased. Although the mean duration of migraine was longer in patients with white matter foci (149.5 months [SD, 87.9]) than in those without white matter foci (134.1 months [SD, 88.3]), there was no significant difference (P >.05). CONCLUSION: Although there are no specific magnetic resonance imaging findings peculiar to migraine, detection of white matter foci should be taken into consideration in patients with migraine (especially migraine with aura). Frequency of attacks is an important indicator of existence of white matter foci.     

Outcome of magnetic resonance imaging (MRI) in selected patients with implantable cardioverter defibrillators (ICDs)

OBJECTIVE: To determine if simple strategies used to safely scan pacemaker patients could be applied to implantable cardioverter defibrillator (ICD), patients undergoing MRI allowing ICD patients to undergo MRI as well. INTERVENTIONS: Screening, reprogramming, and monitoring strategies were used to facilitate MRI. RESULTS: Seven patients underwent eight MRI scans at 1.5 T. Post-MRI, all devices demonstrated no change in pacing, sensing, impedances, charge times, or battery status. The patient undergoing a lumbar spine scan experienced a "power-on-reset" of his ICD without permanent impairment of his device. CONCLUSION: Scanning of ICD patients might be performed if appropriate reprogramming and monitoring is implemented.     

Infarct tissue characterization in implantable cardioverter-defibrillator recipients for primary versus secondary prevention following myocardial infarction: a study with contrast-enhancement cardiovascular magnetic resonance imaging

Knowledge about potential differences in infarct tissue characteristics between patients with prior life-threatening ventricular arrhythmia versus patients receiving prophylactic implantable cardioverter-defibrillator (ICD) might help to improve the current risk stratification in myocardial infarction (MI) patients who are considered for ICD implantation. In a consecutive series of (ICD) recipients for primary and secondary prevention following MI, we used contrast-enhanced (CE) cardiovascular magnetic resonance (CMR) imaging to evaluate differences in infarct tissue characteristics. Cine-CMR measurements included left ventricular end-diastolic and end-systolic volumes (EDV, ESV), left ventricular ejection fraction (LVEF), wall motion score index (WMSI), and mass. CE-CMR images were analyzed for core, peri, and total infarct size, infarct localization (according to coronary artery territory), and transmural extent. In this study, 95 ICD recipients were included. In the primary prevention group (n = 66), LVEF was lower (23 ± 9 % vs. 31 ± 14 %; P < 0.01), ESV and WMSI were higher (223 ± 75 ml vs. 184 ± 97 ml, P = 0.04, and 1.89 ± 0.52 vs. 1.47 ± 0.68; P < 0.01), and anterior infarct localization was more frequent (P = 0.02) than in the secondary prevention group (n = 29). There were no differences in infarct tissue characteristics between patients treated for primary versus secondary prevention (P > 0.6 for all). During 21 ± 9 months of follow-up, 3 (5 %) patients in the primary prevention group and 9 (31 %) in the secondary prevention group experienced appropriate ICD therapy for treatment of ventricular arrhythmia (P < 0.01). There was no difference in infarct tissue characteristics between recipients of ICD for primary versus secondary prevention, while the secondary prevention group showed a higher frequency of applied ICD therapy for ventricular arrhythmia.     

Cardiac magnetic resonance imaging investigation of sustained ventricular fibrillation in a swine model--with a focus on the electrical phase

OBJECTIVES: We sought to develop a method to evaluate the rapidly changing cardiac dimensions during sustained ventricular fibrillation (VF). We also present details of our CPR research imaging program to facilitate this avenue of clinically important research. BACKGROUND: The changes in cardiac dimensions occurring during the initial critical electrical phase of sustained VF are not entirely known. Conventional cardiac magnetic resonance imaging (CMR) functional imaging lacks the temporal resolution necessary to capture the dynamic changes within this early time period of sustained VF. We hypothesized that changes in the middle short axis slice of the ventricles will reflect changes in ventricular volumes accurately. METHODS: Ventricular dimensions were determined from CMR for 30 min of untreated VF in a closed chest, closed pericardium model in seven swine. Ungated steady-state free precession images (SSFP) from the cardiac base to the apex were acquired, taking care to align the anatomical short axis (SAX) imaging planes maximally. The middle slice of the ventricles was determined as the mathematical center of the stack of SAX slices. We then compared the relative changes of right ventricle (RV) and left ventricle (LV) volumes to relative changes in mid-ventricular single slice area. RESULTS: During 30 min of sustained VF, there was an excellent correlation between the changes in exact mid-slice area and the quantitative changes in ventricular volumes (r(2)>0.95). CONCLUSIONS: Mid-slice area data can be used as a surrogate marker of prompt ventricular volume changes during VF. By imaging the heart 10 times faster, the rapid anatomical changes occurring during the initial few minutes of sustained VF can be understood better.     

Cardiac magnetic resonance imaging in valvular heart disease

Cardiac magnetic resonance imaging (CMR) has rapidly gained acceptance as an accurate, reproducible and non‐invasive imaging method for assessment of a wide range of cardiovascular diseases. However, CMR has not been used widely for diagnostic purposes in valvular heart disease (VHD). Unlike echocardiography it has no body habitus‐related limitations and can thus be used to complement echocardiography. It is an especially good alternative for clinical follow‐up in patients with VHD, as it allows accurate measurement of valvular dysfunction and related ventricular burden. Additionally, CMR is an ideal method for evaluating complex congenital heart disease and determining the significance of its components. It can also be used to study the physiological course of valvular dysfunction and response to therapeutic interventions. In this review, we present a basic introduction to CMR methodology, including its advantages and potential problems, and the physiology and quantification in VHD. We also discuss clinical applications of CMR in VHD. Furthermore, we describe how a CMR study statement should be structured in order to increase clinical use of this valuable methodology in cardiology.     

Cardiac pacemakers and implantable cardioverter defibrillators: in vitro magnetic resonance imaging evaluation at 1.5-tesla.

RATIONALE AND OBJECTIVES: To evaluate the effect of Magnetic Resonance Imaging (MRI) performed at 1.5-Tesla on current generation pacemakers and ICDs to identify safe parameters for MRI examinations. METHODS: Pacemakers (Identity ADx XL DR+ 5386 and Identity ADx DR + 5380 generators; 1688T/52-cm atrial and ventricular leads) and ICDs (Atlas + V-243, Epic + V-236, and Epic + HF V-350 generators; Riata 1581/65-cm and QuickSite 1056K/75-cm leads; St. Jude Medical, Sylmar, California, USA) were evaluated for magnetic field interactions. MRI-related heating was assessed using various levels of RF power (SARs) and conditions that included scans on different body regions. Functional aspects of the devices were evaluated immediately before and after MRI procedures utilizing nine different pulse sequences. Induced currents were measured using a custom built system. RESULTS: Magnetic field interactions will not create a hazard for these pacemakers and ICDs. All scans of the "head" and "lumbar" regions resulted in temperature changes < or =0.5 degrees C at SARs ranging from 2.0 to 3.0-W/kg. For the "chest" area, temperature increases ranged from 0.4 degrees C to 3.6 degrees C at an SAR of 2.0-W/kg. No memory corruption, hardware changes, or changes in device parameters were seen. Magnetic field gradients have a low likelihood of inducing currents that would stimulate the heart. CONCLUSIONS: No hazardous magnetic field interactions or physiologically significant heating occurred for certain conditions. There was no permanent effect on device function. By following specific conditions, these pacemakers and ICDs may be safe for patients scanned at 1.5-Tesla.