Glenn Meininger

Pulmonary vein anatomy in patients undergoing catheter ablation of atrial fibrillation: lessons learned by use of magnetic resonance imaging.

Background—This study sought to define the technique and results of magnetic resonance imaging (MRI) of pulmonary vein (PV) anatomy before and after catheter ablation of atrial fibrillation (AF). Methods and Results—Twenty-eight patients with AF underwent ablation. Patients underwent gadolinium-enhanced MRI before and 6 weeks after their procedures. A control group of 27 patients also underwent MRI. Variant PV anatomy was observed in 38% of patients. AF patients had larger PV diameters than control subjects, but no difference was observed in the size of the PV ostia among AF patients. The PV ostia were oblong in shape with an anteroposterior dimension less than the superoinferior dimension. The left PVs had a longer “neck” than the right PVs. A detectable PV narrowing was observed in 24% of veins. The severity of stenosis was severe in 1 vein (1.4%), moderate in 1 vein (1.4%), and mild in 15 veins (21.1%). All patients were asymptomatic, and none required treatment. Conclusions—This study demonstrates that AF patient have larger PVs than control subjects and demonstrates the value of MRI in facilitating AF ablation. The benefits of preprocedural MRI of PVs include the ability to evaluate the number, size, and shape of the PVs. MRI also provides an assessment of the severity of PV stenosis.

Magnetic Resonance Assessment of the Substrate for Inducible Ventricular Tachycardia in Nonischemic Cardiomyopathy

Background— Patients with left ventricular dysfunction have an elevated risk of sudden cardiac death. However, the substrate for ventricular arrhythmia in patients with nonischemic cardiomyopathy remains poorly understood. We hypothesized that the distribution of scar identified by MRI is predictive of inducible ventricular tachycardia. Methods and Results— Short-axis cine steady-state free-precession and postcontrast inversion-recovery gradient-echo MRI sequences were obtained before electrophysiological study in 26 patients with nonischemic cardiomyopathy. Left ventricular ejection fraction was measured from end-diastolic and end-systolic cine images. The transmural extent of scar as a percentage of wall thickness (percent scar transmurality) in each of 12 radial sectors per slice was calculated in all myocardial slices. The percentages of sectors with 1% to 25%, 26% to 50%, 51% to 75%, and 76% to 100% scar transmurality were determined for each patient. Predominance of scar distribution involving 26% to 75% of wall thickness was significantly predictive of inducible ventricular tachycardia and remained independently predictive in the multivariable model after adjustment for left ventricular ejection fraction (odds ratio, 9.125; P=0.020). Conclusions— MR assessment of scar distribution can identify the substrate for inducible ventricular tachycardia and may identify high-risk patients with nonischemic cardiomyopathy currently missed by ejection fraction criteria.

Modern Pacemaker and Implantable Cardioverter/Defibrillator Systems Can Be Magnetic Resonance Imaging Safe In Vitro and In Vivo Assessment of Safety and Function at 1.5 T

Background—MRI has unparalleled soft-tissue imaging capabilities. The presence of devices such as pacemakers and implantable cardioverter/defibrillators (ICDs), however, is historically considered a contraindication to MRI. These devices are now smaller, with less magnetic material and improved electromagnetic interference protection. Our aim was to determine whether these modern systems can be used in an MR environment. Methods and Results—We tested in vitro and in vivo lead heating, device function, force acting on the device, and image distortion at 1.5 T. Clinical MR protocols and in vivo measurements yielded temperature changes <0.5°C. Older (manufactured before 2000) ICDs were damaged by the MR scans. Newer ICD systems and most pacemakers, however, were not. The maximal force acting on newer devices was <100 g. Modern (manufactured after 2000) ICD systems were implanted in dogs (n=18), and after 4 weeks, 3- to 4-hour MR scans were performed (n=15). No device dysfunction occurred. The images were of high quality with distortion dependent on the scan sequence and plane. Pacing threshold and intracardiac electrogram amplitude were unchanged over the 8 weeks, except in 1 animal that, after MRI, had a transient (<12 hours) capture failure. Pathological data of the scanned animals revealed very limited necrosis or fibrosis at the tip of the lead area, which was not different from controls (n=3) not subjected to MRI. Conclusions—These data suggest that certain modern pacemaker and ICD systems may indeed be MRI safe. This may have major clinical implications for current imaging practices.

Feasibility of Real-Time Magnetic Resonance Imaging for Catheter Guidance in Electrophysiology Studies

Background— Compared with fluoroscopy, the current imaging standard of care for guidance of electrophysiology procedures, magnetic resonance imaging (MRI) provides improved soft-tissue resolution and eliminates radiation exposure. However, because of inherent magnetic forces and electromagnetic interference, the MRI environment poses challenges for electrophysiology procedures. In this study, we sought to test the feasibility of performing electrophysiology studies with real-time MRI guidance. Methods and Results— An MRI-compatible electrophysiology system was developed. Catheters were targeted to the right atrium, His bundle, and right ventricle of 10 mongrel dogs (23 to 32 kg) via a 1.5-T MRI system using rapidly acquired fast gradient-echo images (≈5 frames per second). Catheters were successfully positioned at the right atrial, His bundle, and right ventricular target sites of all animals. Comprehensive electrophysiology studies with recording of intracardiac electrograms and atrial and ventricular pacing were performed. Postprocedural pathological evaluation revealed no evidence of thermal injury to the myocardium. After proof of safety in animal studies, limited real-time MRI-guided catheter mapping studies were performed in 2 patients. Adequate target catheter localization was confirmed via recording of intracardiac electrograms in both patients. Conclusions— To the best of our knowledge, this is the first study to report the feasibility of real-time MRI-guided electrophysiology procedures. This technique may eliminate patient and staff radiation exposure and improve real-time soft tissue resolution for procedural guidance.

Anatomic Stereotactic Catheter Ablation on Three-Dimensional Magnetic Resonance Images in Real Time

Background—Targets for radiofrequency (RF) ablation of atrial fibrillation, atrial flutter, and nonidiopathic ventricular tachycardia are increasingly being selected on the basis of anatomic considerations. Because fluoroscopy provides only limited information about the relationship between catheter positions and cardiac structures and is associated with radiation risk, other approaches to mapping may be beneficial. Methods and Results—An electromagnetic catheter positioning system was superimposed on 3D MR images using fiducial markers. This allowed the dynamic display of the catheter position on the true anatomy of previously acquired MR images in real time. In vitro accuracy and precision during catheter navigation were assessed in a phantom model and were 1.11±0.06 and 0.30±0.07 mm (mean±SEM), respectively. Left and right heart catheterization was performed in 7 swine without the use of fluoroscopy, yielding an in vivo accuracy and precision of 2.74±0.52 and 1.97±0.44 mm, respectively. To assess the reproducibility of RF ablation, RF lesions were created repeatedly at the identical anatomic site in the right atrium (n=8 swine). Average distance of the repeated right atrial ablations was 3.92±0.5 mm. Straight 3-point lines were created in the right and left ventricles to determine the ability to facilitate complex ablation procedures (n=6 swine). The ventricular lesions deviated 1.70±0.24 mm from a straight line, and the point distance differed by 2.25±0.63 mm from the pathological specimen. Conclusions—Real-time display of the catheter position on 3D MRI allows accurate and precise RF ablation guided by the true anatomy. This may facilitate anatomically based ablation procedures in, for instance, atrial fibrillation or nonidiopathic ventricular tachycardia and decrease radiation times.

Chest Pain Relief by Nitroglycerin Does Not Predict Active Coronary Artery Disease

Context Many people think that relief of chest pain by nitroglyc-erin helps diagnose coronary artery disease. Contribution In this prospective study, 459 patients who received nitro-glycerin for chest pain in the emergency department were admitted for further evaluation and then followed for 4 months. Nitroglycerin relieved pain in 39% of all patients, in 35% of the 141 patients with subsequent evidence of active coronary disease, and in 41% of the 275 patients with no subsequent evidence of active coronary disease. Implications In emergency department settings, relief of chest pain with nitroglycerin does not help diagnose active coronary artery disease. The Editors In the United States, chest pain accounts for up to 20% of emergency department visits and hospitalizations and uses valuable hospital resources (1). The major concern in most patients presenting with chest pain is that it represents active coronary artery disease (CAD). However, the causes of chest pain in patients presenting to the emergency department vary, and only a small percentage of such patients are actually having angina or an acute coronary syndrome as the manifestation of their CAD (2). Nitrates are an accepted mainstay in treating both acute and chronic coronary disease; however, the diagnostic and prognostic value of chest pain relief with nitroglycerin has been poorly studied. The Coronary Artery Surgery Study (CASS) (3) used prompt relief of chest pain by rest or nitroglycerin as 1 of the criteria for definite angina, and Diamond and colleagues (4, 5) listed prompt relief of chest pain by rest or nitroglycerin as 1 of 3 diagnostic criteria for angina. In addition, Sox and colleagues (6) gave chest pain relief by nitroglycerin the greatest weight in their chest pain decision rule. In contrast, in developing their chest pain protocol, Goldman and colleagues (7) gathered information on chest pain response to nitroglycerin but did not use it in their decision-making algorithm. Its absence implies that it may not have substantial prognostic information. Recent research reports (8), handbooks (9), and current publications by the American Heart Association and American College of Cardiology (10-12) list chest pain relief by nitroglycerin as a poor prognostic sign in materials meant for physicians and describe it as a defining characteristic of angina in materials meant for physicians and patients. In addition, current emergency department literature refers to chest pain relief with rest or nitroglycerin as conferring an intermediate risk (13), although other emergency department literature implies that chest pain relief by nitroglycerin does not predict acute myocardial infarction (14). Nitroglycerin is also useful in treating noncardiac conditions, such as esophageal spasm (15), thus questioning its diagnostic ability in ischemic heart disease. Recently, Shry and colleagues (16) conducted a retrospective evaluation of 223 patients presenting to the emergency department with chest pain and found equal rates of pain relief in patients with cardiac ischemia and those with noncardiac causes of their pain. We designed this prospective study to better assess the diagnostic and prognostic value of response to nitroglycerin as a predictor of an ischemic cause of chest pain. Methods Patients All patients evaluated in the emergency department between February and June 2001 and subsequently admitted to the cardiac intensive care unit, progressive care unit, medicine housestaff service, nurse practitioner service, or emergency department extended-stay unit with the admission diagnosis of rule out myocardial infarction or chest pain were study candidates. To be enrolled in the study, patients had to have documented chest pain while under medical supervision and be given sublingual nitroglycerin or spray nitroglycerin by a medical professional. To ensure that all eligible patients admitted with chest pain were enrolled, patient study lists were checked against hospital admission logs. Clinical care in the emergency department was not protocolized but was at the discretion of the emergency department physicians. In the study emergency department, similar to many others, patients presenting with chest pain and CAD risk factors are generally admitted to rule out myocardial infarction. For patients with chest pain but a less serious risk profile, short-stay hospitalization is common. Trained study investigators completed study forms for each patient. To verify the accuracy of data collection, a designated study investigator randomly audited 20% of charts. Only patients presenting to the Johns Hopkins Bayview Emergency Department, Baltimore, Maryland, were enrolled in this study. The Johns Hopkins Bayview Medical Center Institutional Review Board approved the study before its initiation. This study received a waiver of informed consent, because it was observational, did not affect routine clinical care, and posed minimal risk to participants. The clinical nurse or physician caring for the patient gave a standard explanation of why nitroglycerin was being used (to treat chest pain), instructions on its use, and a brief statement that it may cause a transient headache or lightheadedness. Data Collection A standardized form was used to record demographic characteristics, CAD risk factors, history of CAD, electrocardiography findings, and basic laboratory values. History of CAD was defined as a history of myocardial infarction, coronary revascularization, cardiac catheterization with flow-limiting stenoses ( 70% lesions), or a positive stress test result with or without imaging. The standardized data collection form was also used to record the patients initial rating of severity of chest pain on a scale of 1 to 10 (1 = mild; 10 = severe), nitroglycerin preparation used (sublingual or spray), repeated assessment of chest pain intensity within 5 minutes, and other medications given at the time of nitroglycerin administration (17). Nitroglycerin was given by emergency medical services personnel (if given before arrival in the emergency department) or the emergency department nurse. The person administering the medication assessed level of pain immediately before and approximately 5 minutes after administration and recorded the values in the chart. The standard protocol used by emergency medical services and in the emergency department consists of administering 1 dose of nitroglycerin every 5 minutes for chest pain. Thus, the 5-minute assessment of pain level was done before administering any additional nitroglycerin. The first 12-lead electrocardiogram, which was generally obtained while the patient was having pain, was used for assessing electrocardiographic findings. Definitions Nitroglycerin-responsive chest pain was defined as a 50% or greater reduction in the intensity of chest pain within approximately 5 minutes of administering 0.4 mg of sublingual or 0.4 mg of spray nitroglycerin. There has been little previous quantitative work on chest pain. We used a 50% or greater reduction in chest pain as a marker of pain relief for several reasons. Because pain is highly subjective, we felt that a relative reduction in reported pain, rather than an absolute reduction, would be more valuable in assessing the effectiveness of nitroglycerin therapy. From preliminary observations, we found that few patients have complete relief of chest pain with a single nitroglycerin dose. Many patients received additional doses at 5-minute intervals. They also generally received other interventions with the additional doses, especially if pain relief was not substantial. Such therapies would potentially obscure the effect of the nitroglycerin alone. We therefore chose to evaluate the effect of nitroglycerin alone by assessing the response to the first dose. However, to better assess the diagnostic significance of other degrees of chest pain relief, we completed receiver-operating characteristic (ROC) curves for percentage and absolute reductions in chest pain intensity, as described in the Statistical Analysis section. Active CAD was defined as appropriate symptoms with at least 1 of the following during the index hospitalization or during the follow-up period: any measurement of elevated serum troponin T level ( 0.1 g/L [normal level < 0.1 g/L in the study laboratory]) (18), coronary angiography demonstrating a 70% or greater stenosis, a positive exercise test result with or without imaging, or the diagnosis of active CAD without testing (defined as the primary diagnosis for admission being active CAD as noted by the clinical attending physician, with concurrence by a study cardiologist who was blinded to nitroglycerin response, on the basis of standard clinical criteria). For patients who had both stress testing and cardiac catheterization during hospitalization or follow-up, the results of coronary angiography were considered to be the gold standard in determining the presence (or absence) of active CAD. If no other cardiac testing was performed, results of testing performed up to 6 months before the index hospitalization were used to determine active CAD. No active CAD was defined as no troponin T level elevation during the index hospitalization or the follow-up period and at least 1 of the following: coronary angiography without flow-limiting stenoses or a negative exercise test result with or without imaging. In addition, if patients had no history of CAD, did not have cardiovascular testing during the index hospitalization or the follow-up period, and had no other cardiac events, active CAD was not considered the cause of their index hospitalization. Patients with a known history of CAD but with atypical symptoms, no events during follow-up, and other clinical explanations for their chest pain (neoplasm or obstructive lung disease) were also considered not to have active CAD. Follow-up Trained study investigators conducted telephone interviews with patients approximately 4

Initial experience with a novel focused ultrasound ablation system for ring ablation outside the pulmonary vein

AbstractIntroduction: Atrial fibrillation has been shown to initiate from triggers within pulmonary veins. Several studies have documented that electrical isolation of those triggers can lead to maintenance of sinus rhythm. The complication of pulmonary vein stenosis has limited the utility of delivering ablation energy within the pulmonary vein. We utilize a focused ultrasound catheter ablation system for delivery of transmural ablation lines proximal to the pulmonary vein ostium. Methods: Nine dogs (weight 30–39 kg) were anesthetized and ventilated. Through a transseptal approach, pulmonary veins were engaged with the focused balloon ultrasound catheter. Ultrasound power was delivered at 40 acoustic watts outside the pulmonary vein ostium, focused 2 mm off the balloon surface, with a depth of approximately 6 mm, for 30–120 seconds. Following ablation, lesions were histopathologically analyzed. Results: Of nine animals studied, fourteen pulmonary veins were ablated. We found successful delivery of near circumferential and transmural ablation lines in 6/14 pulmonary veins. In each of the six circumferential ablations, successful alignment of the ultrasound transducer along the longitudinal axis of the parabolic balloon occurred. The final four ablations were conducted with an enhanced catheter design that assured axial alignment. Of these ablations, all four were circumferential. The remaining 8 pulmonary veins had incomplete delivery of lesions. In each of these veins the ultrasound transducer was misaligned with the balloon axis when therapy was delivered. Conclusion: Focused ultrasound ablation is a new means of performing pulmonary vein isolation. This method provides delivery of lesions outside the vein, limiting the risk of pulmonary vein stenosis for the treatment of atrial fibrillation.

Stereotactic magnetic resonance guidance for anatomically targeted ablations of the fossa ovalis and the left atrium

AbstractIntroduction: Targets for radiofrequency ablation (RFA) of atrial fibrillation are increasingly being selected based on anatomic considerations. Because fluoroscopy provides only limited information about the relationship between catheter positions and cardiac structures, we evaluated whether stereotactic catheter guidance might facilitate anatomical catheter navigation and RFA to the great vessels, the fossa ovalis and the left atrium (LA). Methods and Results: An electromagnetic catheters position system was superimposed on three-dimensional (3D) MR images using fiducial markers. This allowed the dynamic display of the catheter position on the true anatomy of previously acquired MRI in real-time. To assess the reproducibility of RFA, repeat ablations were created at the identical anatomic site in the inferior vena cava (IVC) in 5 swine. Average distance of the repeated ablations was 4.4 ± 2.4 mm.In five swine the catheter was anatomically guided with the MRI to the fossa ovalis and a single RFA was performed. On the pathological specimen all ablation sites were located within the fossa ovalis with an average distance of 3.9 ± 2.1 mm from its center. In two of the experiments the ablation catheter was passed into the left atrium and anatomically targeted ablation performed in the lateral wall of the left atrial appendage. Catheter location and ablation site were confirmed by autopsy and histology. Conclusion: Real-time display of the catheter position on 3D-MRI allows anatomically targeted catheter navigation and RFA in the IVC, the fossa ovalis, and the left atrium. This may facilitate anatomically based interventions like septal puncture or pulmonary vein ablation and decrease fluoroscopy times.

Chronic active myocarditis following acute Bartonella henselae infection (Cat Scratch Disease)

An association between Bartonella infection and myocardial inflammation has not been previously reported. We document a case of a healthy young man who developed chronic active myocarditis after infection with Bartonella henselae (cat scratch disease). He progressed to severe heart failure and underwent orthotopic heart transplantation. Bartonella henselae, therefore, should be included among the list of infectious agents associated with chronic active myocarditis.

One Method to Reduce Heart Block Risk During Catheter Ablation of Atrioventricular Nodal Reentrant Tachycardia

The most important complication of catheter ablation of AV nodal reentrant tachycardia (AVNRT) ablation is the inadvertent creation of heart block. This complication has been reported in 0.5% to 2% of patients.1 Since the initial description of the “slow pathway” or “posterior approach” to ablation of AVNRT, a variety of techniques to improve procedural success and reduce the risk of heart block have been described.2 These approaches have generally involved delivery of radiofrequency (RF) energy initially to the most posterior aspect of the triangle of Koch, with subsequent delivery of RF energy to more anterior sites only when posterior sites fail. It also has become well established that the development of junctional beats can be expected during ablation of AVNRT, and that RF energy should be discontinued immediately when “VA” block is seen in order to prevent the creation of AV block. The aim of this brief report is to describe in detail our technique for performing catheter ablation of AVNRT. Particular attention is focused on describing the