The influence of bias on the subjective interpretation of cardiac angiograms

The gender specific frequency of risk factor and CHD diagnoses prior to incident MI: a community study

BACKGROUND

CHD is a chronic disease often present years prior to incident AMI. Earlier recognition of CHD may be associated with higher levels of recognition and treatment of CHD risk factors that may delay incident AMI. To assess timing of CHD and CHD risk factor diagnoses prior to incident AMI.

METHODS

This is a 10-year population based medical record review study that included all medical care providers in Olmsted County, Minnesota for all women and a sample of men residing in Olmsted County, MN with confirmed incident AMI between 1995 and 2000.

RESULTS

All medical care for the 10 years prior to incident AMI was reviewed for 150 women and 148 men (38% sample) in Olmsted County, MN. On average, women were older than men at the time of incident AMI (74.7 versus 65.9 years, p < 0.0001). 30.4% of the men and 52.0% of the women received diagnoses of CHD prior to incident AMI (p = 0.0002). Unrecognized and untreated CHD risk factors were present in both men (45% of men 5 years prior to AMI) and women (22% of women 5 years prior to first AMI), more common in men and those without a diagnosis of CHD prior to incident AMI (p < 0.0001).

CONCLUSION

A CHD diagnosis prior to incident AMI is associated with higher rates of recognition and treatment of CHD risk factors suggesting that diagnosing CHD prior to AMI enhances opportunities to lower the risk of future CHD events.

Identification of Women's Coronary Heart Disease and Risk Factors Prior to First Myocardial Infarction

PURPOSE

To understand when women's coronary heart disease (CHD) and CHD risk factors are recognized prior to first myocardial infarction (MI).

METHODS

Medical record review of the 10 years prior to incident MI among women with a confirmed incident MI between January 1, 1996, and December 31, 2001, to determine the timing of CHD diagnosis as well as assessment and treatment for risk factors.

RESULTS

One hundred fifty women had incident MIs during the study period. They made 8732 ambulatory visits and had 457 hospitalizations during the period of review (mean 9.1 years, range 6.2-10 years). Average age at incident MI was 74.7 years (SD 12.6, range 38.9-99.8 years). A CHD diagnosis prior to first MI was present in 52% (n = 78) of the women but was less common in those <70 years (p = 0.001). All but 3 women had one or more modifiable risk factors identified prior to their first MI. Treatment of recognized risk factors varied from 81% (antihypertension medications) to only 28% (drug therapy for abnormal lipid levels). Having a diagnosis of CHD was associated with an increased likelihood of having identified risk factors and receiving drug treatment for identified risk factors.

CONCLUSIONS

Women with undiagnosed CHD (48%) and those with unrecognized or untreated risk factors for CHD, especially younger women, represent missed opportunities for prevention of cardiac events.

Validation of the local shortening function as assessed by nonfluoroscopic electromechanical mapping: a comparison with computerized left ventricular angiography

BACKGROUND

Nonfluoroscopic electromechanical mapping (NEM) has been proposed as a new technique for the evaluation of electrical and mechanical functioning of the myocardium. In this system, linear local shortening (LLS) is the parameter used for assessment of local mechanical properties. To validate this parameter, we compared LLS with regional wall motion (RWM) data derived from contrast left ventriculograms acquired in the same patients.

METHODS AND RESULTS

Angiographic left ventricular RWM was analyzed using the area-length method. The right anterior oblique view was divided in five segments, the left anterior oblique view in two. Through a comparison of enddiastolic and endsystolic areas drawn from a computer-defined central point to the respective wall delineation, RWM was calculated as change in area. In the first approach, we compared area changes to comparable NEM segments. In the second part of the study, LLS values for normokinetic, hypokinetic, akinetic and dyskinetic segments were correlated to the change in angiographic RWM. In the first approach, the overall comparison of segments yielded a correlation coefficient of 0.67 (P<0.0005). In the second part of the study, differences in LLS values between dyskinetic (LLS=-3.68+/-8.86%), akinetic (2.84+/-3.96%), hypokinetic (9.35+/-4.27%) and normokinetic (13.66+/-7.98%) segments were highly significant (overall ANOVA: P<0.0005).

CONCLUSION

NEM is a powerful tool for invasive electromechanical assessment of myocardial function.

Automatic quantitation of regional myocardial wall motion and thickening from gated technetium-99m sestamibi myocardial perfusion single-photon emission computed tomography

OBJECTIVES

We developed an automatic quantitative algorithm for the measurement of regional myocardial wall motion and wall thickening from three-dimensional gated technetium-99m sestamibi myocardial perfusion single-photon emission computed tomographic images.

BACKGROUND

The algorithm measures the motion of the three-dimensional endocardial surface using a modification of the centerline method, as well as wall thickening using both geometry (gaussian fit) and partial volume (counts).

METHODS

The algorithm was tested using a "variable thickness" heart phantom, and the quantitative results were compared with visual segmental assessment of myocardial motion and thickening in 79 clinical patients with a wide range of ejection fractions (6% to 87%).

RESULTS

Phantom measurements of simulated motion and thickening were accurate regardless of the camera used (dual or triple detector), the angular span of reconstructed data (180 degrees or 360 degrees), the amount of motion (3 or 6 mm) or the amount of thickening (33%, 50% or 100%). Quantitative measurements of segmental motion and thickening in the patients were correlated with visual scores (r = 0.668, exact agreement 72.6%, kappa 0.433 and r = 0.550, exact agreement 74.7%, kappa 0.408, respectively). Significant inverse linear relations exist between the global (summed) visual motion score and the average quantitative motion, and between the global (summed) visual thickening score and the average quantitative thickening. Automatic quantitative ejection fraction measurements correlated extremely well with average quantitative motion (r = 0.929) and thickening (r = 0.959).

CONCLUSIONS

Our algorithm is accurate and may be the first automatic technique for the quantitative three-dimensional assessment of regional ventricular function in cardiology.

Computer probability estimates of angiographic coronary artery disease: transportability and comparison with cardiologists' estimates

A computer algorithm for estimating probabilities of any significant coronary obstruction and triple vessel/left main obstructions was derived, validated, and compared with the assessments of cardiac clinician angiographers. The algorithm performed at least as well as the clinicians when the latter knew the identity of the patients whose angiograms they had decided to perform. The clinicians were more accurate when they did not know the identity of the subjects but worked from tabulated objective data. Referral and value induced bias may affect physician judgment in assessing disease probability. Application of computer aids or consultation with cardiologists not directly involved with patient management may assist in more rational assessments and decision making.

Accuracy of subjective and computer-assisted assessments of angiographic left ventricular regional wall motion

To evaluate the accuracy of angiographic methods for analysis of left ventricular regional wall motion, we measured the ability of a carefully performed subjective analysis (three independent observers) and that of three computer-assisted methods (centerline, radial, and area) to detect the presence of significant coronary artery disease. Normal ranges were established in 90 studies showing normal wall motion, and accuracy was tested in a second, consecutive series of 43 ventriculograms. The results show that the subjective method best separated those regions with from those without significant coronary disease. The subjective method also demonstrated sensitivity comparable to the centerline and radial methods. Among the computer-assisted methods, the area method was least sensitive but most specific for both anterior and inferior region coronary disease. The centerline and radial methods were highly sensitive, but less specific. When coronary disease was defined by electrocardiographic Q-waves, the area method had superior accuracy. Further analysis showed the following: 1) For the centerline and radial methods, long-axis reregistration of the end-systolic frame resulted in loss of sensitivity but increased specificity for anterior wall coronary disease, and little change in analysis of the inferior wall; 2) inclusion or exclusion of the apex had little effect on predictive accuracy for anterior wall coronary disease; 3) as expected, sensitivity and specificity results of all methods were dependent on the selection of a normal range cutoff value; but when performance was optimized, the subjective and area methods had a higher overall predictive accuracy than the centerline method; 4) It is likely that all three computer-assisted methods could be calibrated to give indications of degrees of hypokinesis, as their results correlated well with subjective observers' evaluations over the entire range of scores. These results should assist in selection of the optimal method for regional wall motion analysis in clinical and research applications. As currently applied, the area method is the most specific of the computer-assisted methods tested; the centerline and radial methods have highest sensitivity and therefore are most suited to detection of mild degrees of hypokinesis.

Exercise testing: uses and limitations considering recent studies

Accurate use and interpretation of exercise test results depend on an understanding of physiologic principles, meticulous attention to proper methodology, and realization of the appropriate applications and limitations of testing. Understanding the relationship between myocardial and ventilatory oxygen consumption and exercise test variables will aid in the diagnosis and prognostic evaluation. Use of proper methodology in preparing the patient, performing the examination, and interpreting the results is critical to obtaining the maximum information with maximum safety for each individual patient. Improvements in methodology including the use of the Borg scale to estimate individual effort, abandonment of the predicted maximum heart rate, and the increased use of ventilatory oxygen uptake measurements should be applied. Exercise capacity should not be reported in total time but rather as the VO2 or MET equivalent of the workload achieved. This permits the comparison of the results of many different exercise testing protocols. The most useful exercise ECG variable for the diagnosis of coronary artery disease remains the ST segment shift. Unfortunately, it is not as helpful in localizing myocardial ischemia. Diagnostic accuracy can be improved by adjusting ST depressions for exercise-induced heart rate increase. Accuracy can be further increased by combining ECG, clinical, and radionuclide variables in probabilistic formulas that retain the independent diagnostic information from each variable and accurately predict disease probability. To avoid errors in clinical decision making, care must be used to insure that the mathematical formula used was derived from a population of patients that is similar to those being tested. The clinical applications for exercise testing include diagnosis of patients with chest pain syndromes, determination of disease severity, and prognosis in patients with known coronary artery disease, evaluation of arrhythmias, screening of asymptomatic patients, and evaluation of medical, surgical, and angioplastic therapy for coronary disease. In spite of studies involving thousands of patients, controversy exists regarding the diagnostic power of exercise testing. The large differences in reported accuracies are largely due to methodologic problems that have been encountered by various investigators. Clinicians should be made aware of these problems when reading the literature on ECG and radionuclide exercise testing. Such awareness will help them understand the limitations of these noninvasive procedures.(ABSTRACT TRUNCATED AT 400 WORDS)

Clinician decisions and computers

The clinician's decisions are subject to numerous distorting influences. Computer decision aids can help avoid these distortions by placing the clinician's limited personal experience into broader perspective through comparison with a larger repository of clinically relevant information; by making explicit the assumptions implied by his or her decisions; and by alerting the clinician whenever the decisions made do not appear consistent with these assumptions, with the available information or with the conventional rules of logic. Practical standards of performance with respect to the development, validation and clinical application of these decision aids are still in evolution, however, and a variety of ethical and legal issues have yet to be addressed. Despite the promise of computer decision aids, it remains to be seen whether their diffusion into medical practice will improve the quality and cost of health care.

Reversal of rest myocardial asynergy during exercise: a radionuclide scintigraphic study

While exercise-induced segmental left ventricular wall motion abnormalities are well described, the phenomenon of improvement in certain asynergic segments during exercise in some patients remains a curiosity. To assess this unexpected finding, results were analyzed in 85 patients with wall motion abnormalities at rest who underwent two view (45 degrees left anterior oblique and anterior) exercise radionuclide ventriculography and exercise thallium-201 myocardial perfusion imaging. Wall motion was scored with a 5 point system (from 3 [normal] to - 1 [dyskinesia]); normalization or increase of 2 or more points with exercise signified improvement. Forty-eight patients (56%) had no change or further deterioration of wall motion at peak exercise, 15 (18%) showed both improvement of wall motion and deterioration and 22 (26%) showed only improvement of wall motion. Wall motion improvement during exercise was found in 57 (20%) of 279 segments with asynergy at rest. Of these 57 segments improving with exercise, 45 (79%) showed mild and 12 (21%) showed severe asynergy at rest. Only seven segments (12%) were associated with pathologic Q waves. Thallium-201 perfusion was normal in 44 segments (77%) while only 6 segments (11%) had reversible and only 7 (12%) had nonreversible thallium-201 defects.

IN CONCLUSION

1) wall motion that is abnormal at rest can sometimes improve with exercise; 2) this phenomenon generally occurs in zones without a Q wave or nonreversible thallium-201 defect. Hence, segments with abnormal wall motion at rest that show improvement with exercise appear to represent viable nonischemic segments.

Digital processing in cardiac imaging

In recent years, imaging modalities have realized the potential for digitizing images of the heart. These modalities include nuclear cardiology, echocardiography, digital subtraction angiography, computed tomography, positron emission tomography, and magnetic resonance imaging. Once the cardiac images have been digitized by the computer and formatted in a pixel array of data, the computer can perform mathematical operations on the input (original) images for the purpose of providing improved output (processed) images. The computer can also analyze the original (or processed) images for the purpose of extracting global, regional, or temporal measurements of cardiac perfusion and function. These processes include the restoration, enhancement, analysis, manipulation, and coding of images. These basic processes are implemented by a combination of image processing operations. These operations include pixel point processing, pixel group processing, frame processing, geometric processing, and information extraction. This article describes how these operations are used to perform processes, and how these processes are applied to cardiac imaging, currently and in the future.