心脏核磁共振成像与心内电生理

透视介导的心脏内电生理术一个主要缺点为术中无法正确识别软组织及其与比邻结构关系,然而,心脏核磁共振成像介导的心内电生理术却弥补了这一缺陷.心脏核磁共振成像-心内电生理术不仅可精确地展示出心脏的三维空间形态结构,而且能直接识别心律失常病灶及观察射频消融的疗效,提高复杂心律失常手术成功率及减少并发症有重要作用.因而,心脏核磁共振成像被认为在心内电生理领域具有广泛运用前景.     

Left Atrial Volume and Function Assessment by Magnetic Resonance Imaging

Left Atrial Volume and Function Assessment Introduction: In patients with atrial fibrillation undergoing catheter ablation, magnetic resonance imaging (MRI) can determine left atrial (LA) volume and function before and after ablation. The most accurate, but time consuming, method to determine LA volume is the multiple slice method (MSM), which involves manual tracing of LA area on each slice. The area length method (ALM) offers a simplified, but unvalidated, alternative for LA volume assessment by MRI. The aim of this study was to compare LA volume and function assessment by ALM with MSM. Methods and Results: MRI was performed before and after catheter ablation in 40 patients with atrial fibrillation (30 male, mean age 57 years). All patients had sinus rhythm during imaging. In total, 72 MRI scans were available. LA end‐diastolic and end‐systolic volumes (EDV, respectively ESV) were measured by both methods. LA function was determined by calculating LA ejection fraction (EF = (EDV‐ESV)/EDV). Measured by ALM, mean LA EDV and ESV were significantly lower than using MSM (102 mL and 49 mL vs 111 mL and 65 mL, respectively, P < 0.001) with a larger difference in mean ESV than EDV (16 mL vs 9 mL). This resulted in an overestimation of LA EF by ALM with a mean of 11% (54% by ALM and 42% by MSM, P < 0.001). ALM correlated well with MSM for LA EDV and ESV (r = 0.77, respectively 0.85), and showed no significant difference in intraobserver and interobserver variability. Conclusion: ALM significantly underestimates LA volumes and overestimates LA function, but correlates well with the more accurate MSM. (J Cardiovasc Electrophysiol, Vol. 21, pp. 1247‐1250, November 2010)     

Unipolar Mapping and Magnetic Resonance Imaging of "Idiopathic" Right Ventricular Outflow Tract Ectopy

Unipolar Mapping and MRI of Ventricular Ectopy. Radiofrequency catheter ablation of symptomatic ventricular ectopy guided by bipolar mapping was successfully accomplished at the right ventricular outflow tract in a patient who did not exhibit apparent structural heart disease. A "QS" morphology with a fast slope of the downstroke deflection at the successful ablation site was observed on the unipolar electrogram. Focal thinning of the lateral wall of the right ventricular outflow tract was shown in the magnetic resonance image, similar to that reported in patients with "idiopathic" right ventricular outflow tract tachycardia.     

Morphologic Analysis of Left Atrial Anatomy by Magnetic Resonance Angiography in Patients With Atrial Fibrillation: A Large Single Center Experience

LA and PV Anatomy in Patients With AF. Introduction: Although transcatheter atrial fibrillation (AF) ablation requires accurate anatomic knowledge, pulmonary vein (PV) anatomy has not been fully investigated. Aim of this study is to describe left atrium (LA) and PV anatomy by magnetic resonance angiography (MRA) in a large cohort of patients with AF. Methods: MRA was performed in 473 patients preceding transcatheter AF ablation (paroxysmal 60.9%; persistent 39.1%). The Venice Chart classification was used to classify PV branching patterns. Results: About 40% of the patients presented typical PV branching pattern (2 left and 2 right PVs). A representative number of patients presented a common left trunk (19.9% and 11.0% short and long, respectively). A right middle PV was described in 12.5% and 2 right middle PVs in 1.5% patients. The remaining patients presented other complex, previously unclassified patterns: 6.3% presented an accessory PV originating from LA areas not describable as right or “upper” and 8.7% a common left trunk plus right middle PV. Diameters and circumference of each PV, LA, and LA appendage volumes resulted larger in patients presenting persistent compared to paroxysmal AF (P < 0.001). Conclusion: This study highlights that “typical” PV branching pattern is not a common finding. That 25.6% of the patients present at least 1 accessory PV needs to be kept in careful consideration when planning and performing transcatheter AF ablation. In addition, not only LA volume, but also each PV ostia and LA appendage are significantly enlarged in patients with persistent compared to paroxysmal AF. (J Cardiovasc Electrophysiol, Vol. 22, pp. 1‐7, January 2011)     

Atrial Volume Reduction Following Catheter Ablation of Atrial Fibrillation and Relation to Reduction in Pulmonary Vein Size: An Evaluation Using Magnetic Resonance Angiography

Introduction: Catheter ablation to achieve pulmonary vein (PV) isolation has become an increasingly used treatment strategy for patients with atrial fibrillation (AF). The purpose of this study was to evaluate the impact of segmental isolation of PVs on volume of left atrium and its relation to the decrease in the size of the pulmonary veins.Methods: Gadolinium enhanced Magnetic Resonance Angiography (MRA) was performed in 51 AF patients before and 6 ~ 8 weeks post PV isolation, using cooled radio-frequency (RF) energy. Three-dimensional reconstruction with maximum intensity projections and multiplanar reformations was performed. Oblique coronal projections were used to measure the ostial size of PVs. Three orthogonal dimensions of LA chamber were measured and computed to assess the volume of the left atrium.Results: The mean LA volume decreased by 15.7% after ablation (p < 0.001). The mean PV ostial diameter decreased by 11%, from 18.3 ± 0.8 mm to 16.7 ± 1.0 mm (p = 0.005). Moderate PV stenosis was noted in two veins out of the 192 veins analyzed. There was a significant correlation between changes in the size of PV ostium to that of the LA.Conclusions: Catheter ablation of AF using a segmental PV isolation approach results in a significant reverse remodeling in the left atrium. Significant stenosis of PVs appears to be rare after the segmental isolation procedure.These two authors contributed equally to this study and are the principle investigators.     

Current Status and Issues Concerning Magnetic Resonance Imaging in Patients with a Magnetic Resonance Conditional Cardiac Implantable Electrical Device: A Single-center Study

Objective Following the introduction of magnetic resonance (MR)-conditional cardiac implantable electrical devices (CIEDs), patients with CIEDs have undergone MRI scanning more frequently. As the required settings of MRI equipment for scanning patients with a CIED vary by device, a number of precautions should be taken to allow safe examinations, including the confirmation of conditions and selection of MRI modes appropriate for pacing status in individual patients. In this study, we examined the current status and issues concerning the performance of MRI examinations in patients with an MRI-conditional CIED. Method and Results We reviewed a total of 262 MRI scans. The most common site of MRI scanning was the head, followed by the spine, abdomen, and heart in order. Regarding the MRI mode, DOO was most often used, followed by OFF, AOO, and finally VOO mode, to maintain atrioventricular synchrony. Although no obvious adverse events were observed related to MRI scanning, there were several cases encountered that might have been predisposed to a significant incident or in which the patient''s intrinsic pulse rates or subjective symptoms changed before and during scanning. Conclusion As MRI is a very useful diagnostic tool for cerebrovascular diseases and orthopedic disorders, the demand for MRI scanning is high when treating these areas. Although MRI scanning in patients with MR-conditional devices was performed without any adverse events, there were incidents that could have potentially led to major harm. This highlights the importance of confirming the appropriate MRI mode is being used before scanning and monitoring patients during scanning.     

Accurate and Reproducible Target Navigation with the Stereotaxis Niobe® Magnetic Navigation System

Introduction: The Stereotaxis Niobe® Magnetic Navigation System (MNS, Stereotaxis, Inc., St. Louis, MO, USA) allows for remote-control navigation of magnetically enabled catheters and guidewires for clinical ablation and electrophysiology (EP) device placement using two permanent magnets located on opposite sides of the patient table. Our objective was to provide a clinical framework for expected navigational accuracy during a case by calibrating the system's reproducibility using a realistic heart phantom under various conditions.
Methods and Results: We performed two sets of experiments to demonstrate the accuracy of magnetic catheters using the MNS. The first experiment calibrated deviations in the deflection of an EP catheter by the magnetic system from the expected angles using proprietary algorithms based on predicted geometry. We found that the magnetic fields produced catheter angulation movements within a mean of 4° of biophysical predictions. The second experiment used the MNS to navigate these catheters to previously labeled target positions within a phantom heart model and estimated the actual displacement from desired target positions. We found that the accuracy for reaching the desired targets was 100%.
Conclusions: Remote navigation of magnetically enabled EP catheters using the MNS accurately and reproducibly navigates to target sites in a heart phantom. This may enable more complex, successful, and time-efficient procedures in the cardiac catheterization laboratory.     

磁共振成像对高血压性心脏病左心室肥厚的诊断价值

对 2 5例原发性高血压、血压≥ 16 0 /90mmHg ,且经过心电图、心脏远达距离摄片、超声心动图检查 ,其中至少一项符合左心室肥厚 (LVH)标准的患者 ,进行磁共振扫描成像 (MRI) ,并与上述检测结果对比 ,以估价MRI对高血压性心脏病LVH的诊断价值。结果表明 ,MRI对LVH的诊断率 (96 % )明显高于超声心动图(5 6 % )、X线 (40 % )和心电图 (2 8% )对LVH的诊断率 (P均 <0 .0 1)。且MRI可测定收缩及舒张期室壁厚度 ,可对LVH准确分型 ,可对比心脏大小、心室容量及心肌重量。MRI对LVH是一种极好的诊断方法     

Magnetic Resonance Imaging‐Confirmed Ablative Debulking of the Left Atrial Posterior Wall and Septum for Treatment of Persistent Atrial Fibrillation: Rationale and Initial Experience

LA Debulking for Atrial Fibrillation. Introduction: Though pulmonary vein (PV) isolation has been widely adopted for treatment of atrial fibrillation (AF), recurrence rates remain unacceptably high with persistent and longstanding AF. As evidence emerges for non‐PV substrate changes in the pathogenesis of AF, more extensive ablation strategies need further study. Methods: We modified our PV antrum isolation procedure to include abatement of posterior and septal wall potentials. We also employed recently described image‐processing techniques using delayed‐enhancement (DE) MRI to characterize tissue injury patterns 3 months after ablation, to assess whether each PV was encircled with scar, and to assess the impact of these parameters on procedural success. Results: 118 consecutive patients underwent debulking procedure and completed follow‐up, of which 86 underwent DE‐MRI. The total left atrial (LA) radiofrequency delivery correlated with percent LA scarring by DE‐MRI (r = 0.6, P < 0.001). Based on DE patterns, complete encirclement was seen in only 131 of 335 PVs (39.1%). As expected, Cox regression analysis showed a significant relationship between the number of veins encircled by delayed enhancement and clinical success (hazard ratio of 0.62, P = 0.015). Also, progressive quartile increases in postablation posterior and septal wall scarring reduced recurrences rates with a HR of 0.65, P = 0.022 and 0.66, P = 0.026, respectively. Conclusion: Pathologic remodeling in the septal and posterior walls of the LA helps form the pathogenic substrate for AF, and these early results suggest that more aggressive treatment of these regions appears to correlate with improved ablation outcomes. Noninvasive imaging to characterize tissue changes after ablation may prove essential to stratifying recurrence risk. (J Cardiovasc Electrophysiol, Vol. 21, pp. 126‐132, February 2010)     

Magnetic Resonance Imaging of the Thoracic Aorta

Magnetic resonance imaging (MRI) is well-suited for imaging the vascular system and is of particular value in assessing the anatomy and pathologies of the thoracic aorta. The intrinsic contrast between the blood pool and the vascular structures allows excellent depiction of intra- and extravascular anatomy and eliminates the need for intravenous contrast agents. A large field of view provides a complete evaluation of the mediastinum and chest. Both qualitative and quantitative techniques are available, which can yield physiological data in addition to anatomical information. The multiplanar capability offers images in any plane, allowing an accurate assessment of the longitudinal extent of disease and providing images perpendicular to vessels, even when tortuous. MRI currently represents an essential component of the imaging strategies available to assess the thoracic aorta and may come to function as a gold standard for certain conditions. As the technology continues its rapid evolution, MRI will most likely be able to serve as an effective noninvasive evaluation to provide all of the anatomical, pathological, and physiological information required of a comprehensive examination of the thoracic aorta.     

颅内出血的磁共振成像

MRI的常规序列T1加权成像、T2加权成像和液体衰减反转恢复(FLAIR)序列均可敏感地检出亚急性期和慢性期颅内出血;梯度回波成像可检出各期颅内出血,但血肿信号强度与血肿存在的时间无相关性。弥散加权成像和表观弥散系数能提供更多有关血肿中心区、周围区和梗死后出血的信息。     

Catheter Ablation of the Left Ventricular Outflow Tract Tachycardia from the Left Atrium

RF ablation of idiopathic left ventricular outflow tract ventricular tachycardia (LOT-VT) may imply in significant risk of damaging the proximal left main if RF pulses are being delivered from the left sinus of Valsalva or from inside an epicardial coronary vein. This report describes a new approach to control LOT-VT by means of RF catheter ablation.