Assessing the Risks Associated with MRI in Patients with a Pacemaker or Defibrillator.

BACKGROUND: The presence of a cardiovascular implantable electronic device has long been a contraindication for the performance of magnetic resonance imaging (MRI). We established a prospective registry to determine the risks associated with MRI at a magnetic field strength of 1.5 tesla for patients who had a pacemaker or implantable cardioverter-defibrillator (ICD) that was "non-MRI-conditional" (i.e., not approved by the Food and Drug Administration for MRI scanning). METHODS: Patients in the registry were referred for clinically indicated nonthoracic MRI at a field strength of 1.5 tesla. Devices were interrogated before and after MRI with the use of a standardized protocol and were appropriately reprogrammed before the scanning. The primary end points were death, generator or lead failure, induced arrhythmia, loss of capture, or electrical reset during the scanning. The secondary end points were changes in device settings. RESULTS: MRI was performed in 1000 cases in which patients had a pacemaker and in 500 cases in which patients had an ICD. No deaths, lead failures, losses of capture, or ventricular arrhythmias occurred during MRI. One ICD generator could not be interrogated after MRI and required immediate replacement; the device had not been appropriately programmed per protocol before the MRI. We observed six cases of self-terminating atrial fibrillation or flutter and six cases of partial electrical reset. Changes in lead impedance, pacing threshold, battery voltage, and P-wave and R-wave amplitude exceeded prespecified thresholds in a small number of cases. Repeat MRI was not associated with an increase in adverse events. CONCLUSIONS: In this study, device or lead failure did not occur in any patient with a non-MRI-conditional pacemaker or ICD who underwent clinically indicated nonthoracic MRI at 1.5 tesla, was appropriately screened, and had the device reprogrammed in accordance with the prespecified protocol. (Funded by St. Jude Medical and others; MagnaSafe ClinicalTrials.gov number, NCT00907361 .).

Design and Evolution of the Asporto Heart Preservation Device.

The Asporto Heart Preservation Device is a system providing perfusion of cardioplegia to the donor heart using a computer-controlled peristaltic pump in a thermoelectrically cooled and insulated container. In 1998, a user interface was developed at the University of Minnesota consisting of a touch screen and battery-backed microcontroller. Power was supplied by a 120 VAC to 12 VDC converter. An upgrade to the insulated cooler and microcontroller occurred in 2002, which was followed by proof of concept experimental pre-clinical transplants and tests demonstrating the efficacy of the device with isolated donor hearts. During the period between 2002 and 2006, a variety of donor organ containers were developed, modified, and tested to provide an optimal sterile environment and fluid path. Parallel development paths encompass formalized design specifications for final prototypes of the touch screen/microcontroller, organ container, and thermoelectric cooler.

Evaluation of self-contained PACS viewers on CD-ROM.

Providing patients and clinicians with self-contained PACS viewer on CD format is a common and necessary tool to share vital imaging data. However, to be useful, this tool should be reliable, robust, and convenient. Numerous PACS viewer options are available, often without empirical data to guide in choosing one for routine use. To assist in making a standardized choice for our institution, we chose four common viewers, benchmarked on four different workstations reflecting the variety of environments used by non-radiologist clinicians who would receive a CD. Four CD-based DICOM viewers from eFilm, Philips, Pacsgear Gearview, and iSite were examed on two radiology PACS workstations, a standard desktop computer, and a laptop using a test case consisting of a multi-series CTA with 13 series and 3,035 total images. Multiple objective measures, subjective measures, and presence of key features were evaluated including program time to load, image time to load, cine/movie mode, ability to adequately window and level, pan and zoom functionality, basic measurement tools, and perceived lag when scrolling through a multi-image series. Substantial differences in speed of operation and behavior on multiple systems were documented, which could potentially add several minutes to the time required to open and view a patient's imaging data. The eFilm and iSite viewers operated consistently and reliably across all tested computer environments. The iSite viewer, having among the quickest load times in the group tested and consistently low subjective scroll lag during series viewing, and also beneficially allowing partial viewing while images load in the background, was found to generate the best overall user experience. Because of these significant differences, we have recommended that our institution standardize all patient imaging CD creation using the iSite viewer.

Transmural atrial fibrosis after epicardial and endocardial argon-powered CryoMaze ablation.

BACKGROUND: The CryoMaze procedure is usually limited to endocardial ablation under cardio-pulmonary bypass. Epicardial ablation is considered inferior as endocardial islets of atrial tissue could theoretically remain viable, protected from cryoinjury by epicardial fat and endocardial circulating warm blood. Novel argon-powered cryoprobes with lower ablation temperatures have recently become available. It is unclear if these instruments can reliably induce transmural atrial fibrosis by epicardial cryoablation on the beating heart. METHODS: Ten sheep were divided into two equal groups. CryoMaze ablations were applied using an argon-powered cryoprobe with an ablation temperature of -185°C. In the control group, standardized ablations (n = 50) were applied endocardially under cardiopulmonary bypass. In the experimental group, corresponding ablations (n = 50) were applied epicardially on the beating heart. Postoperatively the animals were monitored for 30 days. At necropsy, the lesions were explanted and analyzed histologically for evidence of transmural fibrosis. RESULTS: Two animals in the control group and one animal in the experimental group died prematurely. Autopsy of the remaining animals showed that all lesions (n = 70) had retained their structural integrity. In the control group, histology demonstrated transmural fibrosis in 94% (28/30) of the endocardially applied lesions. In the experimental group, histology demonstrated transmural fibrosis in 95% (38/40) of the epicardially applied lesions. Statistical analysis revealed no significant difference between the two groups (p = 0.96). CONCLUSION: Argon-powered epicardial cryoablation on the beating heart is as efficient in inducing transmural fibrosis as the traditional technique of endocardial ablation under cardio-pulmonary bypass.

Benefit of 3D volume rendered CT scans in the diagnosis and treatment of cardiac anomalies: a report of 3 cases.

3D volume rendered computed tomography (3D-CT) produces detailed, three-dimensional models that can be rotated and viewed in any orientation to provide a more natural and functional view of the patient's anatomy. This technology is especially beneficial in diagnosing and repairing cardiovascular anomalies. Three cases are presented where 3D-CT was used to diagnose and plan a course of treatment for patients with cardiac anomalies.

From Clinical Clues to Final Diagnosis: The Return of Detective Work to Clinical Medicine in Cardiac Amyloidosis.

Cardiac amyloidosis is frequently misdiagnosed, denying patients the opportunity for timely and appropriate management of the disease. The purpose of this review and case studies is to raise awareness of the diagnostic "red flags" associated with cardiac amyloidosis and the currently available non-invasive strategies for diagnosis. The review focuses on the identification of one of the two main types of cardiac amyloidosis, transthyretin amyloid cardiomyopathy, and non-invasive tools to distinguish this from light-chain amyloidosis. A diagnostic algorithm centered around the use of non-invasive imaging and laboratory analysis is presented. The algorithm generates four differential diagnoses for patients presenting with signs and symptoms consistent with cardiac amyloidosis. Case examples are presented, representing the four potential outcomes of diagnosis using the algorithm. The review provides a guide on how to recognize the often-overlooked presentations of this disease in clinical practice. Non-invasive imaging techniques and diagnostic tools that do not require the involvement of a specialty center have allowed for the improved diagnosis of cardiac amyloidosis. Timely diagnosis of this life-threatening disease is essential for optimal management and it is imperative that clinicians have a high index of suspicion for patients presenting with "red flag" symptoms.

Evaluation of aortic root and valve calcifications by multi-detector computed tomography.

BACKGROUND AND AIM OF THE STUDY: In percutaneous aortic valve replacement (AVR), whilst calcifications are used as landmarks in fluoroscopic placement of the stent, they may also complicate stent placement. In response to this problem, the study aim was to examine severe aortic root calcification by using multi-detector computed tomography (MDCT), to better understand the pathology complicating percutaneous valve placement. METHODS: In 33 patients with severe aortic stenosis and scheduled for surgery, the 'inner orifice' and 'outer fibrous' annulus diameter and area (with and without calcification) were measured, in addition to the distances of the calcifications and coronary ostia from the annulus, using by ECG-gated 64-slice MDCT. Aortic root calcification was evaluated as minimal (< 25% of total circumference), mild (25-50%), moderate (50-75%), and severe (75-100%). RESULTS: The inner orifice annulus area was 5.9 +/- 1.9 cm2 (range: 1.4-10.1 cm2), while the outer fibrous area was 7.5 +/- 1.8 cm2 (range: 4.7-11.5 cm2). The proximal-to-distal extent of valve calcification from the annulus in the mid-center of leaflets was 0.8 +/- 0.26 cm. In 36% of patients, valvular calcification extended +/- 3 mm within the coronary-ostium level. The distance of the coronary ostia from the annulus was variable, with a mean of 1.3 +/- 0.35 cm (range: 0.6-2.4 cm) for the left coronary artery. In 42% of patients, a 'low coronary ostium' (< or = 1.1 cm), and in 6% a 'critical-low-coronary ostium' (< or = 8 mm) was identified. Annulus calcification was present in 100% of cases, but the severity varied widely (severe 50%, moderate 35%, mild 15%). In 36% of cases, the aortic annulus calcification extended caudally into the membranous part of the interventricular septum (and thus into the left ventricular outflow tract), and in 42% of cases (n = 14) into the anterior mitral valve leaflet. CONCLUSION: The present results indicated that cardiac MDCT may qualify as a primary pre-procedural imaging modality to select patients for percutaneous AVR, based on the measurement and characterization of the aortic root and valve calcification. In comparison to echocardiography, CT will reduce--if not eliminate--difficulties in visualizing the aortic orifice area in heavily calcified valves. Furthermore, knowledge of the exact location of calcific deposits provides a distinct advantage to the fluroscopist for precise placement of the percutaneous aortic valve. Likewise, knowledge of the coronary arteries orifice in relation to the valve plane is critical to prevent inadvertent coronary artery occlusion, and would clearly be beneficial when planning future valve designs.

Perfusion preservation of the donor heart: basic science to pre-clinical.

As a consequence of technology improvements and refinement, perfusion of the donor heart has moved from the research laboratory to clinical studies. Multiple investigators are currently leading pre-clinical trials of devices using perfusion preservation, and one device is now in European clinical trials. One major problem with the donor heart is the high metabolism relative to other organs, and depletion of ATP leads rapidly to acidosis and necrosis of the myocardium. Two techniques in development to address the issue are normothermic and hypothermic perfusion. This review examines the current issues regarding donor heart preservation and techniques of preclinical evaluation necessary for regulatory approval.

Intermittent antegrade cardioplegia: isolated heart preservation with the Asporto heart preservation device.

BACKGROUND: A major problem in procurement of donor hearts is the limited time a donor heart remains viable. After cardiectomy, ischemic hypoxia is the main cause of donor heart degradation. The global myocardial ischemia causes a cascade of oxygen radical formation that cumulates in an elevation in hydrogen ions (decrease in pH), irreversible cellular injury, and potential microvascular changes in perfusion. OBJECTIVE: To determine the changes of prolonged storage times on donor heart microvasculature and the effects of intermittent antegrade perfusion. MATERIALS AND METHODS: Using porcine hearts flushed with a Ribosol-based cardioplegic solution, we examined how storage time affects microvascular myocardial perfusion by using contrast-enhanced magnetic resonance imaging at a mean (SD) of 6.1 (0.6) hours (n = 13) or 15.6 (0.6) hours (n = 11) after cardiectomy. Finally, to determine if administration of cardioplegic solution affects pH and microvascular perfusion, isolated hearts (group 1, n = 9) given a single antegrade dose, were compared with hearts (group 2, n = 8) given intermittent antegrade cardioplegia (150 mL, every 30 min, 150 mL/min) by a heart preservation device. Khuri pH probes in left and right ventricular tissue continuously measured hydrogen ion levels, and perfusion intensity on magnetic resonance images was plotted against time. RESULTS: Myocardial perfusion measured via magnetic resonance imaging at 6.1 hours was significantly greater than at 15.6 hours (67% vs 30%, P = .00008). In group 1 hearts, the mean (SD) for pH at the end of 6 hours decreased to 6.2 (0.2). In group 2, hearts that received intermittent antegrade cardioplegia, pH at the end of 6 hours was higher at 6.7 (0.3) (P = .0005). Magnetic resonance imaging showed no significant differences between the 2 groups in contrast enhancement (group 1, 62%; group 2, 40%) or in the wet/dry weight ratio. CONCLUSION: Intermittent perfusion maintains a significantly higher myocardial pH than does a conventional single antegrade dose. This difference may translate into an improved quality of donor hearts procured for transplantation, allowing longer distance procurement, tissue matching, improved outcomes for transplant recipients, and ideally a decrease in transplant-related costs.

Development of a sheep model of atrial fibrillation for preclinical prosthetic valve testing.

Currently, prosthetic heart valve testing is performed on animal models with no underlying cardiovascular pathologies. Unfortunately, unforeseen adverse events may occur when heart valves tested in animals in normal sinus rhythm are implanted in patients suffering from arrhythmias. For example, the Medtronic Parallel valve functioned well in pre-clinical testing, but a high rate of thromboembolic complications appeared when the valve was placed in patients with atrial fibrillation (AF). Given the increasing number of patients afflicted with AF, an animal model of the disorder is needed to more accurately predict a valve's function in the clinical setting. Among methods available for inducing AF, electrophysiological pacing is the most practiced, but the challenges associated with pacing have led to the development of alternative methods of inducing AF These methods include gene transfer and a pharmacologic approach with acetylcholine and catecholamines. Finally, although stem cells have been widely investigated in terms of their therapeutic benefits, the use of their well-reported pro-arrhythmic behavior shows great promise for the development of an AF model in sheep. Such a model would have the potential for detecting adverse outcomes with mechanical heart valves before implantation in the clinical setting.

Administration of tauroursodeoxycholic acid (TUDCA) reduces apoptosis following myocardial infarction in rat.

Black bear bile has been used in traditional Chinese medicine to treat liver and eye related illnesses for centuries. A major constituent of bile is ursodeoxycholic acid (UDCA). Recent analysis of the cellular effects of UDCA and its taurine conjugate tauroursodeoxycholic acid (TUDCA) have demonstrated their antiapoptotic properties through regulation of Bcl-2 family and survival signaling proteins (Bax, Bad, phosphatidylinositol-3-kinase). In this study, we tested the hypothesis that TUDCA administered to rats prior to a myocardial infarction (MI) would exhibit anti-apoptotic effects and improve cardiac function. Prior to ligation of the left anterior descending (LAD) coronary artery, TUDCA (50 mg/ml, 400 mg/kg, IV) or PBS was administered to rats. Animals were sacrificed 24 hours after ligation for terminal transferase-mediated dUTP-digoxigenin nick end-labeling (TUNEL) and caspase-3 activity to assess apoptosis. Additional TUDCA or PBS treated rats underwent pre-operative,1 and 4 week transthoracic ultrasounds to assess heart function by quantification of shortening fraction (SF) and infarct area. TUNEL labeling of the cardiac tissue revealed a significant reduction in apoptotic cells in rats given TUDCA prior to ischemic injury (p = 0.05). In support of reducing apoptosis, caspase-3 activity in the TUDCA treated animals also decreased (p = 0.02). By 4 weeks, a significantly smaller infarct area was present in the TUDCA group compared to the PBS group (0.05 vs. 0.13 cm(2), p = NS) and there was also an improvement in SF. The results provide evidence for TUDCA as a viable treatment for reducing apoptosis in a model of myocardial infarction. Additional studies will distinguish the functional result of improved cell survival following infarction, suggesting the potential for clinical application of this anti-apoptotic drug in treatment of acute MI.

In-vivo experience with the Triflo trileaflet mechanical heart valve.

BACKGROUND AND AIM OF THE STUDY: The in-vivo performance of the Triflo trileaflet mechanical valve was evaluated in an ovine model. The aim of long-term follow up was to gather site-specific performance data demonstrating device safety, as required for regulatory approval of this new valve design, prior to its use in clinical trials. METHODS: The Triflo trileaflet valve was implanted in 26 sheep using 29-mm mitral (n=8; animal body weight 63.3 +/- 10.3 kg, age 112.0 +/- 30.7 weeks) or 21-mm aortic mechanical valves (n=19; body weight 73.0 +/- 4.36 kg, age 112.6 +/- 23.6 weeks) using standard techniques. Animals were allocated to 150- or 365-day survival cohorts. The 150-day cohort was further subdivided into mitral valve (n=6) and aortic valve (n=11) implants. The 365-day cohort was organized into aortic (n=7) and mitral (n=2) implants. Angiography, echocardiography, and pathology were performed to assess valve performance. RESULTS: Angiographically monitored pressure measurements for the trileaflet mitral valve at 150 and 365 days were within established ranges in terms of mean aortic pressure, systolic and diastolic aortic pressure, and left ventricular end-diastolic pressure. In animals receiving a mitral valve the transvalvular gradient was 3.5 +/- 0.71 mmHg at 365 days, and 0.2 +/- 0.4 mmHg at 150 days. The Triflo mitral valve had only mild (physiologic) regurgitation. Cardiac output was within normal limits in animals receiving the Triflo valve in the aortic position. Laboratory values reflected no ongoing infection or destruction of blood cells as a result of device implantation. No significant abnormality was noted at necropsy in any animal, except for evidence of thromboembolic events in the kidneys (4-20%). Pathological evaluation was reflected by mild to moderate fibrous tissue formation at the inflow orifice (n=15), and minimal growth was observed in the outflow tract of one valve. This was consistent with that seen in sheep implanted with a standard St. Jude Medical bileaflet valve. CONCLUSION: The study results showed the Triflo valve to perform to safety levels comparable with those of the standard St. Jude Medical bileaflet design, when implanted in the aortic and mitral positions. Additional analysis of historic control data suggested that the trileaflet valve design may offer a reduction in outflow tract obstruction by allowing for a greater effective orifice area index when compared to an equal-sized-orifice bileaflet valve. Notably, the Triflo valve was associated with a statistically significant reduction in myocardial hypertrophy, further reducing the potential for patient-prosthesis mismatch. Overall, the Triflo valve appeared to more closely emulate the hemodynamic properties of the native tissue valve than the traditional bileaflet design. Hence, the trileaflet design may offer the function of a tissue valve while retaining the durability of the mechanical valve.

Rat intubation and ventilation for surgical research.

Effective outcomes in cardiothoracic surgical research using rodents are dependent upon adequate techniques for intubation and mechanical ventilation. Multiple methods are available for intubation of the rat; however, not all techniques are appropriate for survival studies. This article presents a refinement of intubation techniques and a simplified mechanical ventilation setup necessary for intrathoracic surgical procedures using volatile anesthetics. The procedure is defined and complications of the procedure are elucidated that provide a justification for animal numbers needed for initiating new studies. Lewis rats weighing 178-400 g (287 +/- 44) were anesthetized using Enflurane and intubated with a 16-G angiocatheter using transillumination. Mechanical ventilation (85 bpm, 2.5 mL TV, enflurane 1.5-2%) maintained adequate sedation for completion of an intrathoracic procedure. Complications of the intubation and ventilation included mortality from anesthetic overdose, intubation difficulty, pneumothorax, traumatic extubation, and ventilation disconnection. Anesthetic agents and their related effects on the rat heart and reflexes are compared. This article also underscores the importance of refinement, reduction, and replacement in the context of cardiothoracic surgery using rodent models.

The current state of in-vivo pre-clinical animal models for heart valve evaluation.

For over 30 years, animal models have remained a central critical component in the pre-clinical safety evaluation of prosthetic heart valves developed for use in humans. Though many advances have been made in valve design, no ideal replacement prosthesis has yet been developed. As a result, valve manufacturers continue to address issues relating to thrombogenicity, structural integrity, fluid dynamics and calcification in their designs. Many animal models have been developed to examine these issues, including dog, pig, calf and sheep, yet no standard model has been accepted. Recently, the International Standard Organization has provided guidelines in document 5840 to address cardiovascular implants. The aim of this report is to provide a summary of the current state of pre-clinical valve evaluation in animals. Changes in ISO 5840 will be addressed that have occurred between 1998 and the present date, and the role of current available animal models. The aim also is to provide rational guidance in the selection of appropriate animal models to match the purpose of valve implantation studies.

Preoperative predictors for postoperative problems in heart transplantation: psychiatric and psychosocial considerations.

The psychiatric and psychosocial evaluation of the heart transplant candidate can identify particular predictors for postoperative problems. These factors, as identified during the comprehensive evaluation phase, provide an assessment of the candidate in context of the proposed transplantation protocol. Previous issues with compliance, substance abuse, and psychosis are clear indictors of postoperative problems. The prolonged waiting list time provides an additional period to evaluate and provide support to patients having a terminal disease who need a heart transplant, and are undergoing prolonged hospitalization. Following transplantation, the patient is faced with additional challenges of a new self-image, multiple concerns, anxiety, and depression. Ultimately, the success of the heart transplantation remains dependent upon the recipient's ability to cope psychologically and comply with the medication regimen. The limited resource of donor hearts and the high emotional and financial cost of heart transplantation lead to an exhaustive effort to select those patients who will benefit from the improved physical health the heart transplant confers.

Sodium polystyrene sulfonate used to reduce the potassium content of a high-protein enteral formula: a quantitative analysis.

BACKGROUND: Sodium polystyrene sulfonate (Kayexalate) commonly is used in treating hyperkalemia. As a cation exchange resin, it also can be used to reduce the potassium content of enteral nutrition formulas. This study evaluates the use of Kayexalate to reduce potassium in one high-protein enteral formula and describes the quantitative analysis of the product. METHODS: Sodium polystyrene sulfonate and enteral formula were mixed into a slurry and allowed to settle, and then the supernatant was decanted off and tested as samples. Three sample concentrations were analyzed: a control not subjected to potassium reduction, 0.5 g of Kayexalate per mEq K+ sample, and a 1 g/mEq K+ sample. Of these samples, moisture, lipid, protein, carbohydrate, ash, and mineral content were obtained. RESULTS: Compared with the control, the percentage decrease of potassium ranged from 25% to 36%, depending on the concentration of Kayexalate. A significant increase of 324% in sodium concentration was found in the 1.0 g/mEq K+ sample. Although there was no change in magnesium content, a slight increase in phosphorus, iron, and zinc was evident. CONCLUSIONS: The treatment of an enteral formula with sodium polystyrene sulfonate significantly increases its sodium content, with a modest decrease in potassium content. Clinicians using this method in clinical practice should be aware of the increase in sodium content.

The basic science aspect of donor heart preservation: a review.

In cardiac transplantation, the transport time between harvest and recipient is limited by the viability of the donor heart. The problem of viability is a consistent limitation in cardiac transplantation. Since the 1960s, techniques, including hypothermia, perfusion, oxygenation, and hyperbaria, have been used to prolong the preservation of the transplantable heart. Continuing development of cardioplegic solutions has minimized edema and oxygen radical formation, which have resulted in extension of the donor heart viability. New research into the events leading to necrosis, oncosis, and apoptosis may allow further advancement of protective cardioplegic solutions in combination with technology of transporting the heart. With a prolonged preservation time there is potential to increase the donor pool and ultimately improve post-operative outcomes.