Teaching hypothesis-oriented thinking to medical students: the University of Florida's clinical investigation program.

Recent studies show alarming decreases in the proportions of physicians applying for federal resources and of graduating medical students who declare strong interest in pursuing careers as physician-scientists. To expose medical students in their formative years to hypothesis-driven experimental investigations in a clinical setting, the first-year curriculum at the University of Florida has involved students as both investigators and study subjects in patient-oriented research conducted in the General Clinical Research Center (GCRC). Each year a hypothesis-driven experiment is conceived by first-year medical students in the university's MD-PhD program. Later in the year, the protocol is implemented in the GCRC by the entire freshman class, whose members serve as volunteer study subjects or as investigators. The experimental data are analyzed by the MD-PhD students, who report their findings at national biomedical research meetings and submit a manuscript on their project to a peer-reviewed journal. The authors describe students' research projects over the first six years of this GCRC-based program. They also describe the responses of former students to a questionnaire about their perceptions of the value of the research program. Most respondents considered the GCRC research exercise to have been useful and relevant to their overall education, and many more declared a current interest in pursuing research careers compared with the number who had declared such interest as freshmen. The authors conclude that early integration of hands-on, patient-oriented research into the medical school curriculum is a positive educational experience for students, and may contribute to their ultimate pursuit of academic research careers.

Guidelines for cardiac sonographer education: recommendations of the American Society of Echocardiography Sonographer Training and Education Committee.

In 1992, the American Society of Echocardiography published a report of the Sonographer Education and Training Committee's recommendations for education of sonographers who perform echocardiographic procedures. Since the publication of the original document, there has been continual progress in technology with the development of more sophisticated diagnostic applications that allow more information to be obtained from echocardiographic procedures. These recent changes in the clinical application of echocardiography should be included in all cardiac sonographer education programs. The American Society of Echocardiography, a professional society that currently represents approximately 2500 cardiac sonographers, provides these updated guidelines.

Concept, development, administration, and analysis of a certifying examination in echocardiography for physicians.

In 1993, the American Society of Echocardiography appointed a committee to develop an objective examination in echocardiography. In 1995, a pilot of this examination was administered, with operational examinations offered each year from 1996 to 1999. This report describes the development of the examination, including its underlying philosophy, the test itself, and the scoring process, and includes results from the first 4 examinations. To date, 1266 physicians have taken the examination, and roughly 60% of those have passed. The number of echocardiograms performed or interpreted each week had the largest effect on examination scores; the effects of both the amount of training and the practice discipline were small but significant. The evolution of the original committee and new directions for the testing organization are also discussed.

Digital analysis of myocardial contrast echocardiography: a clinical study using an air-filled agent in normal subjects.

The purpose of the present study was to determine whether direct digital image analysis would allow improved detection of myocardial contrast. Eighteen normal subjects were recruited and separated into two groups. In group 1, the time-brightness curves of the left ventricular cavity and three myocardial perfusion beds were formed from digitized video tape, with output power and imaging time as secondary variables. In group 2, curves constructed from direct polar digital data were compared, with fundamental and second harmonic image formation as variables. In group 1 subjects, using fundamental imaging, the area under the curve in the left ventricular cavity increased slightly with intermittent imaging. No consistent myocardial opacification was identified. In group 2 subjects, using intermittent imaging, the area under the myocardial curve and peak intensity increased with high output, second harmonic imaging in the left anterior descending and right coronary artery regions. Intermittent, second harmonic imaging and digital processing can demonstrate myocardial contrast even with an air-filled agent.

Dobutamine stress echocardiography in patients undergoing liver transplantation evaluation.

BACKGROUND: Coronary artery disease has an important impact on perioperative morbidity and mortality in patients undergoing liver transplantation. To assess the role of dobutamine stress echocardiography (DSE) in these patients, DSE was included in the preoperative evaluation. METHODS: Patients under consideration for liver transplantation underwent detailed clinical history, electrocardiography, and echocardiography. Patients with documented coronary disease or symptoms of myocardial ischemia underwent angiography. The remaining patients with cardiac risk factors, atypical chest pain, or age > or = 60 years underwent DSE. RESULTS: These 121 patients (77 men and 44 women) ranged in age from 34 to 73 years (mean 53). Among the 61 patients who underwent liver transplantation, DSE was normal in 25, nondiagnostic in 34 because of inadequate heart rate response, and abnormal in two patients. Major perioperative events occurred in eight patients, all with normal or nondiagnostic DSE studies (negative predictive value 86%). CONCLUSIONS: In patients with low to moderate risk of cardiac disease, DSE performed as part of an evaluation for liver transplantation is a poor predictor of major perioperative events.

Speckle reduction and contrast enhancement of echocardiograms via multiscale nonlinear processing.

This paper presents an algorithm for speckle reduction and contrast enhancement of echocardiographic images. Within a framework of multiscale wavelet analysis, we apply wavelet shrinkage techniques to eliminate noise while preserving the sharpness of salient features. In addition, nonlinear processing of feature energy is carried out to enhance contrast within local structures and along object boundaries. We show that the algorithm is capable of not only reducing speckle, but also enhancing features of diagnostic importance, such as myocardial walls in two-dimensional echocardiograms obtained from the parasternal short-axis view. Shrinkage of wavelet coefficients via soft thresholding within finer levels of scale is carried out on coefficients of logarithmically transformed echocardiograms. Enhancement of echocardiographic features is accomplished via nonlinear stretching followed by hard thresholding of wavelet coefficients within selected (midrange) spatial-frequency levels of analysis. We formulate the denoising and enhancement problem, introduce a class of dyadic wavelets, and describe our implementation of a dyadic wavelet transform. Our approach for speckle reduction and contrast enhancement was shown to be less affected by pseudo-Gibbs phenomena. We show experimentally that this technique produced superior results both qualitatively and quantitatively when compared to results obtained from existing denoising methods alone. A study using a database of clinical echocardiographic images suggests that such denoising and enhancement may improve the overall consistency of expert observers to manually defined borders.

Autonomous epicardial and endocardial boundary detection in echocardiographic short-axis images.

An autonomous endocardial and epicardial boundary detection (ABD) method is reported. One hundred ten cycles from 55 clinical studies were selected retrospectively. Image sequences were digitized at 512 x 480 pixel resolution. The point-by-point boundary positions of the ABD and the areas enclosed were compared with positions and enclosed areas drawn by three independent observers. Correlation coefficients for epicardial end-diastolic (ED) and end-systolic (ES) areas, endocardial ED and ES areas, muscle area, and fractional area change were 0.970, 0.976, 0.951, 0.985, 0.887, and 0.878, respectively. Bland-Altman analysis showed negligible biases with standard deviations comparable to those of the observers. The mean difference between the ABD border and the consensus observer border positions in 64 directions falls within the mean range of interobserver border positions, suggesting that shape is also well defined by the ABD.

Dobutamine echocardiography for prediction of ischemic events in heart transplant recipients.

The purpose of this study was to assess the use of dobutamine stress echocardiography in predicting cardiac events in heart transplant recipients. Dobutamine echocardiography was performed in 63 consecutive heart transplant recipients, 52 males and 11 females ranging in age from 12 to 77 years (mean 54), undergoing routine yearly evaluation. Twenty-one patients had abnormal wall motion at baseline or during dobutamine infusion. Over a mean follow-up of 8 months (range 4 to 14), there were six major cardiac events: five occurred among patients with abnormal echocardiography study results; only one event occurred in a patient with a normal echocardiography result. These data suggest that normal wall motion during dobutamine echocardiography identifies a subset of heart transplant recipients at low risk for development of cardiac events, whereas an abnormal study result serves as an important predictor of subsequent cardiac events.

Inhaled gases affect the ultrasound contrast produced by Albunex in anesthetized dogs.

In anesthetized animals maintained with isoflurane using 100% oxygen as a carrier gas, Albunex (Molecular Biosystems, Inc., San Diego, Calif.) produced no ultrasound contrast in the left ventricle after intravenous administration. The current study tested the hypothesis that the inhalation of gas mixtures with increased concentrations of oxygen decreased the quality and duration of Albunex-induced contrast. Albunex (0.22 mL/kg) was injected intravenously into anesthetized dogs (n = 9) breathing compressed air, oxygen, mixtures of oxygen and nitrogen, or combinations of oxygen and nitrous oxide. Albunex produced ultrasound contrast of shorter duration and decreased quality during the inhalation of gas mixtures containing increased amounts of oxygen. In the presence of inhaled gas mixtures containing nitrous oxide, Albunex produced no contrast in the left ventricle, regardless of the oxygen content. These data indicate that the inhalation of gas mixtures containing smaller amounts of nitrogen, compared with air, decreased the ability of Albunex to cause ultrasound contrast in the heart after intravenous administration.

Automatic identification of papillary muscles in left-ventricular short-axis echocardiographic images.

An automatic method for identifying the location of the papillary muscles in two-dimensional (2-D) short-axis echocardiographic images is described. The technique uses both spatial and temporal information to identify the presence and track the location of the muscles in the left ventricle from end-diastole to end-systole. The three main steps of the method are spatial preprocessing, spatial processing, and temporal processing. The spatial preprocessing step includes a region of search estimation. The spatial processing step includes a papillary muscle existence test and an initial approximation of the papillary muscle points. The temporal processing includes motion-pattern evaluation and final papillary muscle location. The estimates of existence and position for the automatic method were compared with estimates made by an independent expert observer. Two hundred and ten frames, three taken from each of 70 image sequences, were evaluated. Since two regions of search were processed for each frame (one for the posterior-inferior and one for the anterior-lateral papillary muscle), a total of 420 approximations were made. Of this total, 340 automatic estimates were judged to be in close agreement with estimates made by the expert. Of the remaining 80 approximations, 54 estimates were made by the expert when the computer determined that no papillary muscle was present, 17 estimates provided poor results, and nine estimates were made by the computer when the observer concluded that no papillary muscle was present.

Evidence for a relation between inspired gas mixture and the left ventricular contrast achieved with Albunex in a canine model.

BACKGROUND: In a previous experiment, a marked reduction in the right- and left-sided contrast effect of Albunex was noted in an intubated animal spontaneously breathing isoflurane in 100% oxygen. The theory suggests that the time course of echogenicity of microbubbles in liquid is dependent on the pressure and the gradients of dissolved gases. The present set of experiments tested whether the loss of contrast occurs at commonly used therapeutic concentrations of inspired oxygen. HYPOTHESIS: This research tested the hypothesis that the left ventricular (LV) contrast effect achieved with intravenous injection of the ultrasound contrast agent Albunex is related to the inspired oxygen content. METHODS: Intubated dogs were maintained in a spontaneously respiring anesthetic state on isoflurane and mixtures of oxygen (12-50%) in nitrogen. FIO2 was held steady for 15 min prior to injection of 0.08 ml/kg of Albunex. The contrast effects were recorded from a transthoracic short-axis view. Left and right ventricular brightness curves were generated from digitized sequences of end-diastolic frames. The minimum and maximum brightness and area under the time-brightness curves were determined. RESULTS: The LV maximum brightness and area under the curve showed significant negative correlations (p = < 0.004) with the FIO2, while the minimum brightness showed a significant positive correlation (p = < 0.002). No significant correlations were found for the right ventricular brightness parameters. CONCLUSIONS: These findings show an important relationship between the FIO2 and loss of the contrast effect of Albunex. This loss occurs at oxygen concentrations in the therapeutic range, but could be overcome by increasing the dose of Albunex. The mechanism is likely related to an outward nitrogen gradient causing a loss of echogenicity. The clinical implication is that patients on supplemental oxygen may require higher doses of Albunex to achieve optimal opacification.

Transesophageal echocardiographic guidance of transseptal left heart catheterization during radiofrequency ablation of left-sided accessory pathways in humans.

UNLABELLED: Radiofrequency ablation (RFA) of left-sided accessory pathways can be achieved using catheters introduced by a retrograde or transseptal approach. Transesophageal echocardiography (TEE) has previously been demonstrated to be safe and efficacious in guiding transseptal puncture in patients during mitral valvuloplasty (MV). This study was undertaken to assess the feasibility, safety, and clinical utility of TEE during transseptal puncture and RFA of left-sided accessory pathways. METHODS: TEE was performed during transseptal puncture in 30 patients (41 +/- 12 years, 19 females), 15 patients during attempted RFA of a left-sided accessory pathway and 15 patients during attempted balloon MV. RESULTS: There was no difference in age, sex distribution, or procedural complications when MV patients were compared to RFA patients. At baseline, left atrial dimension was increased and congestive heart failure was more common when MV patients were compared to RFA patients (P < 0.05) Adequate baseline two-dimensional and Doppler TEE images were obtained in all patients. One patient sustained mild esophageal bleeding during the TEE. Positioning of the transseptal catheter in the fossa ovalis was facilitated and confirmed by TEE in 29 of 30 cases. One case of cardiac perforation occurred and was associated with inadequate TEE localization of the fossa ovalis. Thrombus was detected on the transseptal catheter by TEE in two cases prior to systemic heparinization. In both cases, thrombus was removed without embolic event. CONCLUSIONS: TEE safely guides transseptal puncture in patients undergoing RFA of left-sided accessory pathways. TEE markers of the fossa ovalis facilitate puncture and may reduce the risk of cardiac perforation particularly in patients with a normal size left atrium. TEE may be especially valuable for identifying thrombus during transseptal puncture.

Catheter entrapment in the mitral valve apparatus during radiofrequency ablation.

Catheter ablation of accessory atrioventricular pathways in patients with Wolff-Parkinson-White syndrome has become an increasingly popular therapeutic option. Catheter technology is rapidly evolving, allowing physicians to tailor the choice of catheter to the location of the pathway. We describe catheter entrapment in the mitral valve apparatus while using a valve mapping catheter with a peanut shaped tip to approach a left free-wall pathway retrogradely across the aortic valve.

Use of transesophageal echocardiography to visualize an anomalous right coronary artery arising from the left main coronary artery (single coronary artery).

This case report demonstrates a role for transesophageal echocardiography in defining the course of anomalous coronary arteries. Origin of the right coronary artery (RCA) from the left main (LM) (single coronary artery) is an exceedingly rare congenital anomaly. It is not always benign and may result in myocardial infarction. This may be due to compression between the aorta and the pulmonary artery. Transesophageal echocardiography offers a low-risk, noninvasive means of imaging the proximal coronary arteries. In the majority of patients, the proximal segments of the three major coronaries can be clearly visualized. With the addition of color flow, it is possible to visualize flow in most patients. Proximal obstructive lesions can be seen in some patients although sensitivity thus far seems low.

A method for evaluation of enhancement operations in two-dimensional echocardiographic images.

A means of estimating the degree of enhancement of structure and suppression of background noise in filtered two-dimensional echocardiographic images is described. The method is termed the peak-to-background ratio. To test the method, two-dimensional short-axis echocardiographic images were enhanced with Laplacian operations of increasing mask size. There was excellent correlation between the calculated peak-to-background ratio and the subjective opinion of trained echocardiographers. Furthermore, radial length measurements made from images that were thought to be optimally enhanced by the peak-to-background ratio calculation showed the lowest interobserver mean differences. We conclude that the peak-to-background ratio does reflect improvement in characteristics of the image that favor more precise measurement (amplification of peaks and suppression of background) and can be used to help guide a dynamic approach to image processing.