Stratification of single-vessel coronary stenosis by ischemic threshold at the onset of wall motion abnormality during continuous monitoring of left ventricular function by semisupine exercise echocardiography.

We studied the relation between the ischemic threshold at the onset of wall motion abnormality on exercise echocardiography (EE) and the severity of coronary stenosis in patients with 1-vessel coronary artery disease (CAD). We screened 216 consecutive patients who underwent coronary angiography and EE for suspected CAD. Ninety-five (74 men; age, 56 +/- 12 years) satisfied the study criteria, that is, the presence of 1-vessel disease or no evidence of CAD on angiography and a normal baseline echocardiogram. Eighty-seven patients had 1-vessel CAD on angiography, and exercise-induced wall motion abnormality occurred in 73 (77%). Optimal cutoff values of percent diameter stenosis and minimal lumen diameter for predicting a positive EE were 61% (sensitivity and specificity of 76%) and 1.12 mm (sensitivity and specificity of 74%). Among patients with positive EE, heart rate-blood pressure product at ischemic threshold was correlated with quantitative coronary stenosis (r = -0.72, P <.001). The ischemic threshold from continuous monitoring of left ventricular function during semisupine EE is correlated with the severity of coronary stenosis among patients with 1-vessel disease and a normal resting echocardiogram.

Low-level exercise echocardiography detects contractile reserve and predicts reversible dysfunction after acute myocardial infarction: comparison with low-dose dobutamine echocardiography.

OBJECTIVES: The aim of this study was to evaluate low-level exercise echocardiography (LLEE) in detecting contractile reserve and predicting functional improvement of akinetic myocardium early after acute myocardial infarction (AMI). BACKGROUND: Experimental and clinical studies have shown that low-dose dobutamine enhances contractile function of dyssynergic but viable myocardium in patients with recent AMI. We hypothesized that endogenous catecholamines produced during a LLEE test could serve as a myocardial stressor to elicit contractile reserve. METHODS: Fifty-two consecutive patients with first AMI and > or =2 akinetic segments in the infarct-related territory underwent 5 +/- 2 days after AMI low-dose dobutamine echocardiography (LDDE) (5, 10 and 15 microg/kg/min) and LLEE (25 W during 3 min on a supine bicycle, with continuous echocardiographic recording). Both tests were performed on the same day, in random order. Follow-up echocardiography was obtained one month later. Regional wall thickening was semi-quantitatively assessed using a 16-segment, 5-grade scale model. Contractile reserve was defined as improvement in wall thickening of > or =1 grade. RESULTS: Mean increase in heart rate during stress tests was 15 +/- 7 beats/min with LLEE and 13 +/- 6 beats/min with LDDE (p = NS). Contractile reserve was detected in 119 (55%) of 217 akinetic segments at LLEE and in 137 (63%) segments at LDDE. At follow-up study, functional improvement was identified in 139 (64%) segments. Sensitivity, specificity and positive and negative predictive values for predicting functional recovery were 81%, 92%, 95% and 73%, respectively, for LLEE, and 91%, 86%, 92% and 84%, respectively, for LDDE. Moreover, there was a good correlation between systolic wall thickening measured in the center of the dyssynergic area during stress tests and at follow-up study: r = 0.77, p < 0.001 with exercise testing and r = 0.73, p < 0.001 with dobutamine testing. CONCLUSIONS: Low-level exercise echocardiography provides a promising alternative to LDDE for identifying myocardial viability and predicting reversible dysfunction early after AMI.

Role of stress echocardiography in heart failure.

Most patients presenting with heart failure have severe coronary artery disease. The identification of viable hibernating myocardium is of paramount clinical importance for a correct indication of revascularization. Contractile reserve may be identified when regional asynergy improves during low or moderate doses of dobutamine. Dipyridamole, given at infra-low dose, alone or preferably in association with a low dose of dobutamine, is another possible pharmacologic stress protocol. Dobutamine echocardiography has been found to be more specific than thallium scintigraphy for predicting functional recovery after revascularization. However, the absence of contractile reserve does not exclude the presence of myocardial viability: perfusion reserve may be too low because of a critical coronary artery stenosis, or profound ultrastructural changes of myocardial cells may be present, including significant loss of contractile material. Inotropic reserve can also be assessed by dobutamine stress echocardiography in patients with idiopathic cardiomyopathy. The evolution of hemodynamic variables can be measured during the stress test. Stress echocardiography, especially during exercise, could probably provide important information about heart failure associated with valvular heart disease.

DXplain on the Internet.

DXplain, a computer-based medical education, reference and decision support system has been used by thousands of physicians and medical students on stand-alone systems and over communications networks. For the past two years, we have made DXplain available over the Internet in order to provide DXplain's knowledge and analytical capabilities as a resource to other applications within Massachusetts General Hospital (MGH) and at outside institutions. We describe and provide the user experience with two different protocols through which users can access DXplain through the World Wide Web (WWW). The first allows the user to have direct interaction with all the functionality of DXplain where the MGH server controls the interaction and the mode of presentation. In the second mode, the MGH server provides the DXplain functionality as a series of services, which can be called independently by the user application program.

Computers for the continuing education of practicing physicians.

Computer-based medical education became practical with the wide-spread availability of personal computers and the ease of dialing in to a central computer via standard telephone lines with a modem. Continuing education credits can now be earned from the privacy and convenience of the physician's home or office via the computer. A variety of courses are available from national medical organizations, medical schools, and medical publishers. While examples can give a flavor of the type of courseware available, only hands-on use can help you decide if this style of education fits yours.

DXplain. An evolving diagnostic decision-support system.

DXplain is an evolving computer-based diagnostic decision-support system designed for use by the physician who has no computer expertise. DXplain accepts a list of clinical manifestations and then proposes diagnostic hypotheses. The program explains and justifies its interpretations and provides access to a knowledge base concerning the differential diagnosis of the signs and symptoms. DXplain was developed with the support and cooperation of the American Medical Association. The system is distributed to the medical community through AMA/NET--a nationwide computer communications network sponsored by the American Medical Association--and through the Massachusetts General Hospital Continuing Education Network. A key element in the distribution of DXplain is the planned collaboration with its physician-users whose comments, criticisms, and suggestions will play an important role in modifying and enhancing the knowledge base.

Computer-aided-instruction in the emergency department.

The Massachusetts General Hospital Laboratory of Computer Science created a library of computer-aided-instruction (CAI) programs in 1972. An experimental network of Cai programs, made possible by National Library of Medicine (NLM) support, was set up in July 1972, operating over commercial communication lines. Programs developed by Massachusetts General, Ohio State University and the University of Illinois Medical College were made available to users with terminals in about 36 cities through a local telephone number. During the first two years of the program over 80 institutions participated. A trial of the Massachusetts General programs, in conjunction with the Continuing Education Committee of the American College of Emergency Physicians, was conducted in five representative community hospitals. The hospitals put up the cost of the terminals and the telephone charges. Results of the study showed that 12 of the 40 (30%) emergency physicians in the target population took 10 or more programs. They gave the programs a favorable overall rating--1.6 on a scale of 1 (strongly positive) to 5 (strongly negative).