The exercise test as gatekeeper. Limiting access or appropriately directing resources?

Body sensor network based ECG segmentation and analysis

In this paper, a body sensor network based ECG signal segmentation approach is presented. Hidden Markov Modeling (HMM) technique is employed. Since people's heart rates vary a lot, the corresponding characteristic waveform intervals and durations change with time as well. For patients with cardiac diseases, such as arrhythmia, the heart beat interval may even change abruptly and irregularly. Because traditional HMM parameter adaptation is conservative and slow to respond to beat interval changes, inadequate and slow parameter adaptation is largely responsible for the low positive predictivity rate (+P). To solve the problem, we introduce an active HMM parameter adaptation and ECG segmentation algorithm, which includes three parts: the pre-segmentation and classification, the HMM model training, and the detailed segmentation. Body sensor networks are used to collect and pre-segment the raw ECG data by performing QRS detection. Then the R-R interval information that directly reflects the beat variation is extracted and used to classify the raw ECG data into several groups. One specific HMM is trained for each of the groups. Instead of one single generic HMM, multiple individualized HMMs are set up and each HMM is only responsible for extracting the characteristic waveforms of the ECG signals with similar temporal features in the detailed segmentation, so that the temporal parameter adaptation can be naturally achieved.

Body sensor network based context aware QRS detection

In this paper, a body sensor network (BSN) based context aware QRS detection scheme is proposed. The algorithm uses the context information provided by the body sensor network to improve the QRS detection performance by dynamically selecting the leads with best SNR and taking advantage of the best features of two complementary detection algorithms. The accelerometer data from the BSN are used to classify the patients' daily activity and provide the context information. The classification results indicate both the type of the activities and their corresponding intensity, which is related to the signal/noise ratio of the ECG recordings. Activity intensity is first fed to lead selector to eliminate the leads with low SNR, and then is fed to a selector for selecting a proper QRS detector according to the noise level. MIT-BIH noise stress test database is used to evaluate the algorithms.

Improving the positive predictive value of exercise testing in women

OBJECTIVE

To identify exercise test variables that can improve the positive predictive value of exercise testing in women.

DESIGN

Cohort study.

SETTING

Regional cardiothoracic centre.

SUBJECTS

1286 women and 1801 men referred by primary care physicians to a rapid access chest pain clinic, of whom 160 women and 406 men had ST depression of at least 1 mm during exercise testing. The results for 136 women and 124 men with positive exercise tests were analysed.

MAIN OUTCOME MEASURES

The proportion of women with a positive exercise test who could be identified as being at low risk for prognostic coronary heart disease and the resulting improvement in the positive predictive value.

RESULTS

Independently of age, an exercise time of more than six minutes, a maximum heart rate of more than 150 beats/min, and an ST recovery time of less than one minute were the variables that best identified women at low risk. One to three of these variables identified between 11.8% and 41.2% of women as being at low risk, with a risk for prognostic disease of between 0-11.5%. The positive predictive value for the remaining women was improved from 47.8% up to 61.5%, and the number of normal angiograms was potentially reducible by between 21.1-54.9%. By the same criteria, men had higher risks for prognostic disease.

CONCLUSIONS

A strategy of discriminating true from false positive exercise tests is worthwhile in women but less successful in men.

Clinical logistics in treadmill exercise stress testing

The predictability as to a positive or negative outcome of treadmill exercise stress testing in 341 consecutively studied patients referred for diagnostic purposes is presented. A clinical decision as to the result was derived by asking 2 simple questions and reviewing the pretest ECG. Additional clinical logistics included the type of physician ordering the study, smoking history, symptoms, and basic patient history. The predictable accuracy was 77.7% for the total patient group and 81.5% when the questionable cases (reflecting a neutral or ambivalent cardiologist's opinion) were eliminated.

Simple treadmill score to diagnose coronary disease

OBJECTIVE

Our aim was to derive and validate a simplified treadmill score for predicting the probability of angiographically confirmed coronary artery disease (CAD).

BACKGROUND

The American College of Cardiology/American Heart Association guidelines for exercise testing recommend the use of multivariable equations to enhance the diagnostic characteristics of the standard treadmill test. Most of these equations use complicated statistical techniques to provide diagnostic estimates of CAD. Simplified scores derived from such equations that require physicians only to add points have been developed for pretest estimates of disease and for prognosis. However, no simplified score has been developed specifically for the diagnosis of CAD using exercise test results.

METHODS

Consecutive patients referred for evaluation of chest pain who underwent standard treadmill testing followed by coronary angiography were studied. A logistic regression model was used to predict clinically significant (> or = 50% stenosis) CAD and then the variables and coefficients were used to derive a simplified score. The simplified score was calculated as follows: (6 x maximal heart rate code) + (5 x ST-segment depression code) + (4 x age code) + angina pectoris code + hypercholesterolemia code + diabetes code + treadmill angina index code. The simplified score had a range from 6 to 95, with < 40 designated as low probability, between 40 and 60 was intermediate probability, and > 60 was high probability for CAD.

RESULTS

A total of 1,282 male patients without a prior myocardial infarction underwent exercise treadmill testing and coronary angiography in the derivation group, and there were 476 male patients in the validation group from another institution. The area under the receiver operating characteristic curve (+/- SE) for the ST-segment response alone was 0.67 as compared to 0.79 +/- 0.01 for the diagnostic score (p > 0.001). The prevalence of significant disease for the men was 27% in the low-probability group, 62% in the intermediate-probability group, and 92% in the high-probability group, which was similar to the prevalence in the validation group, with 22%, 58%, and 92% in low-, intermediate-, and high-probability groups, respectively. The low-probability group had < 4% prevalence of severe disease. In both populations, 7 more patients out of 100 were correctly classified than with the use of ST-segment criteria. When used as a clinical management strategy, the score has a sensitivity of 88% and a specificity of 96%.

CONCLUSION

This simplified exercise score that estimates the probability of CAD can be easily applied without a calculator and is a useful and valid tool that can help physicians manage patients presenting with chest pain.

Exercise testing in clinical medicine

Exercise-induced changes in the electrocardiogram have been used to identify coronary artery disease for almost a century. Over the past decade, however, clinicians have increasingly focused on more expensive diagnostic tools believing them to offer improved diagnostic accuracy. In fact, by incorporating historical data, the simple exercise test can in most cases outperform the newer tests. The use of prediction equations and non-staged exercise protocols can improve the test still further, while advances in the use of the test for prognosis, with the discovery of novel risk factors and the addition of gas analysis, may in the future shift the primary emphasis away from diagnosis. Brief, inexpensive, and done in most cases without the presence of a cardiologist, the exercise test offers the highest value for predictive accuracy of any of the non-invasive tests for coronary artery disease.

A survey of exercise testing: methods, utilization, interpretation, and safety in the VAHCS

BACKGROUND

Healthcare organizations are being graded in terms of their adherence to practice guidelines. The authors sought information on practice patterns of exercise testing within the Veterans Affairs Health Care System (VAHCS) to determine how well current practice patterns adhere to current guidelines. In addition, we sought to update past surveys to determine methods, indications, utilization of alternative diagnostic modalities, criteria for interpretation, safety, and physician supervision of exercise testing within the VAHCS.

METHODS

Questionnaires were sent to 72 of the largest Veterans Affairs Medical Centers with cardiology divisions. The centers were queried regarding volume and type of exercise testing (standard, nuclear, and echocardiographic), indications, safety, protocols used, and criteria for interpretation.

RESULTS

Seventy-one questionnaires were returned, comprising a total of 75,828 exercise tests performed within the last year. Virtually all indications for exercise testing fit the American Heart Association/American College of Cardiology (AHA/ACC) guidelines Class I criteria; 46% of patients were tested for the evaluation of chest pain; 14% were tested to evaluate patients at high risk for coronary artery disease; 10% were preoperative evaluations; and 8% were post-myocardial infarction evaluations. The most commonly used diagnostic test was the standard exercise electrocardiogram; a patient was five times more likely to undergo a standard exercise electrocardiogram or nuclear exercise test than an exercise or pharmacologic echocardiogram. The largest proportion of centers (49%) used 1.0-mm horizontal or downsloping ST depression as a criterion for an abnormal test, although 22% considered 1.5-mm upsloping ST depression to be abnormal, and 25% relied on a treadmill score. Seventy-eight percent of respondents used the treadmill, and of these, 82% used the Bruce or modified Bruce protocol. Four major cardiac events were reported (three myocardial infarctions, one sustained ventricular tachycardia) representing an event rate of 1.2/10,000. A physician was present during 73% of all standard exercise tests; 21% of respondents reported that a physician was required to be present "only for high-risk patients."

CONCLUSION

Indications for exercise testing are in close agreement with the AHA/ACC guidelines; thus, the test continues to have an important role in diagnosis and prognosis among patients with or suspected of having coronary artery disease. The exercise test is an extremely safe procedure, with an event rate similar to other recent surveys. However, a great deal of variation exists in terms of criteria for abnormal results and whether physician presence is required during exercise testing.

Cost analysis of diagnostic testing for coronary artery disease in women with stable chest pain. Economics of Noninvasive Diagnosis (END) Study Group

BACKGROUND

Seven clinical sites compiled data from 4638 women who were referred directly to coronary angiography (catheterization-first strategy; n = 3375) or who underwent stress myocardial perfusion imaging (MPI) first (n = 1263) followed by coronary angiography if at least one reversible myocardial perfusion abnormality was detected. The study examines the cost minimization potential of these available invasive and noninvasive diagnostic strategies in women with chest pain.

METHODS AND RESULTS

Women in both groups were subclassified by the core laboratory as being at low (<0.15), intermediate (0.15 to 0.60), or high (>0.60) pretest likelihood for coronary artery disease (CAD). Among the catheterization-first patients, at least one coronary stenosis >70% was present in 13% of low likelihood patients, 29% of intermediate likelihood patients, and 52% of patients with high CAD likelihood. Perfusion abnormality rates in the MPI-first group were 23% in low likelihood patients, 27% in intermediate likelihood patients, and 34% in high CAD likelihood patients. Of the MPI-first subset, 50%, 55%, and 76%, respectively, underwent catheterization in at least one coronary stenosis >70%. Cardiac death rates ranged from 0.5% to 2.2% in patients with CAD and did not differ from the 2 testing strategies (P = not significant). The composite cost per patient of diagnostic testing plus follow-up medical care over a period of 2.5 +/- 1.5 years (calculated for both strategies from inflation-corrected Medicare charges, adjusted for institutional cost-charge ratios) ranged from $2490 for patients with low likelihood to $3687 for patients with high likelihood with the catheterization-first strategy and from $1587 to $2585 for patients undergoing MPI first (P < .01 between risk subsets and strategies).

CONCLUSIONS

In women referred for diagnostic evaluation of stable chest pain, MPI followed by selective coronary angiography in patients with at least 1 perfusion abnormality minimizes the near-term composite cost per patient compared with a direct catheterization-first strategy, regardless of pretest CAD likelihood.

The economic consequences of available diagnostic and prognostic strategies for the evaluation of stable angina patients: an observational assessment of the value of precatheterization ischemia. Economics of Noninvasive Diagnosis (END) Multicenter Study Group

OBJECTIVES

The study aim was to determine observational differences in costs of care by the coronary disease diagnostic test modality.

BACKGROUND

A number of diagnostic strategies are available with few data to compare the cost implications of the initial test choice.

METHODS

We prospectively enrolled 11,372 consecutive stable angina patients who were referred for stress myocardial perfusion tomography or cardiac catheterization. Stress imaging patients were matched by their pretest clinical risk of coronary disease to a series of patients referred to cardiac catheterization. Composite 3-year costs of care were compared for two patients management strategies: 1) direct cardiac catheterization (aggressive) and 2) initial stress myocardial perfusion tomography and selective catheterization of high risk patients (conservative). Analysis of variance techniques were used to compare costs, adjusting for treatment propensity and pretest risk.

RESULTS

Observational comparisons of aggressive as compared with conservative testing strategies reveal that costs of care were higher for direct cardiac catheterization in all clinical risk subsets (range: $2,878 to $4,579), as compared with stress myocardial perfusion imaging plus selective catheterization (range: $2,387 to $3,010, p < 0.0001). Coronary revascularization rates were higher for low, intermediate and high risk direct catheterization patients as compared with the initial stress perfusion imaging cohort (13% to 50%, p < 0.0001); cardiac death or myocardial infarction rates were similar (p > 0.20).

CONCLUSIONS

Observational assessments reveal that stable chest pain patients who undergo a more aggressive diagnostic strategy have higher diagnostic costs and greater rates of intervention and follow-up costs. Cost differences may reflect a diminished necessity for resource consumption for patients with normal test results.