Operational definition of normal sinus heart rate.
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Aged↗
Biomedical subjects
R D Rifkin
Publications and source records attributed to R D Rifkin.
Detection of coronary artery disease by vasodilator thallium imaging of the heart with amyl nitrite inhalation: a pilot study.
Thallium imaging of the heart using dipyridamole-induced coronary arteriolar vasodilation has proven to be an effective means of detecting significant coronary stenosis. However, intravenous dipyridamole has not yet been made available for general use. We therefore examined the feasibility of substituting amyl nitrite inhalation as an arteriolar vasodilator prior to thallium imaging. Seventeen patients, all of whom had catheterization-proven coronary stenosis, inhaled amyl nitrite for 2-5 min. Thallium was injected after 45-60 s of inhalation. Completion of inhalation was followed immediately by planar imaging. Of 6 patients who inhaled amyl nitrite for at least 4 min, 5 had moderate or severe image defects on immediate scans which completely resolved on delayed scans. Only 3 of 11 who inhaled amyl nitrite for 2 min or less prior to scanning had similarly positive tests. Overall sensitivity for significant stenosis was 8 of 17 (47%). Inhalation was well tolerated with only one episode of angina and hypotension. We conclude that amyl nitrite inhalation for at least 4 min may offer an effective and readily available alternative to intravenous dipyridamole for vasodilator imaging of the heart.
Administration, Inhalation↗
Postinfarction septal aneurysm with delayed formation of left-to-right shunt.
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Aged↗
Comparison with radionuclide angiography of two new geometric and four nongeometric models for echocardiographic estimation of left ventricular ejection fraction using segmental wall motion scoring.
Two new echocardiographic methods for estimating left ventricular ejection fraction, both based on segmental wall motion scoring on a continuous scale, were developed and compared to radionuclide angiography in 50 patients. The first method used a geometric model in which the ventricle was represented by a tubular base section joined to a hemielliptical apex section, each containing 4 quadrants. Contraction was scored visually in 12 regions of the ventricle. The 12 scores were converted to dimensional shortenings, which were then used to calculate separate ejection fractions for each of the 8 quadrants. These 8 values were averaged to obtain the global ejection fraction. Assuming an elliptical end-systolic cross-section shape for each quadrant, the correlation between the echocardiographic and radionuclide ejection fractions was 0.917 with a regression slope of 0.93 and an intercept of 1.5. Results were identical assuming circular end-systolic quadrant shapes. The second approach used a linear combination of the mean wall motion score at the base, midleft ventricle and apex to predict ejection fraction. Coefficients for the 3 mean scores were optimized by least squares best fit with radionuclide ejection fraction in all 50 patients. The simplest linear model showed a correlation of 0.90 between the echocardiographic and radionuclide ejection fraction but underestimated low, and overestimated high, ejection fractions. However, these systematic errors could be removed by regression, which added a constant term of 8.1 and a slope factor of 0.87 to the linear model, improving the correlation with radionuclide ejection fraction to 0.91.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Effect of self-correlation on the relation between QT interval and cardiac cycle length.
The electrocardiographic QT interval, with a wide variety of practical and theoretic applications in medicine, pharmacology, and cardiology, is critically dependent on heart rate as expressed by cycle length (RR). To account for this and permit intraindividual and interindividual comparisons of changing QT intervals, a wide variety of formulas have been offered as single rate-correcting expressions over the range of heart rates. Yet as rate rises, the QT interval occupies more and more of the cycle length, until at the highest heart rates almost the entire cycle length is QT interval, and the QT-RR correlations become largely self-correlation. To elucidate this we investigated 150 consecutive patients divided into high, mid, and low rate terciles. For the entire group, and in each tercile, we determined the level of correlation between the QT interval and cycle length (RR interval). To remove the self-correlation, we repeated the calculations, correlating QT interval with RR interval minus QT interval. For the group, correlation (r) of QT with RR was 0.65. For the high, mid, and low rate terciles, correlation fell sharply, respectively: 0.58 to 0.36 to 0.25. When the self-correlation was removed by subtracting QT from cycle length (RR-QT), all correlations were even further sharply reduced for each tercile, respectively: 0.35, 0.16, and 0.03 (the latter being virtually no correlation). We conclude that at low heart rates, when it is not being correlated with itself, the correlation between QT and RR is low; at high heart rates the higher correlation is spurious because it is mainly self-correlation.
Electrocardiography↗
Value of fluoroscopy in the detection of coronary stenosis: influence of age, sex, and number of vessels calcified on diagnostic efficacy.
Although fluoroscopically detected coronary artery calcification is known to correlate with the presence of coronary artery stenosis, age, sex, and extent of calcification influence the strength of this association. To clarify its diagnostic potential, we performed fluoroscopy before coronary angiography in 600 patients and analyzed the results according to all three factors simultaneously. The sensitivity of fluoroscopy for significant stenosis exceeded 65% in all groups except women less than 45 years of age. Specificity exceeded 90% in patients less than 45 years and 85% in patients less than 55 years of age, and declined significantly with age. The number of vessels calcified was an important determinant of predictive value, except in those less than 45 years of age in whom even a single mild calcification markedly increased the chance of stenosis. In patients aged 45 to 64 years, calcification of two or three vessels substantially increased the chances of stenosis, but single-vessel calcification increased the risk only slightly. In patients more than 65 years of age, fluoroscopy was not helpful in detecting stenosis, regardless of the number of vessels calcified. Our findings were similar in men and women. We conclude that if both age and the number of vessels calcified are considered, fluoroscopy can provide useful information regarding the presence of stenosis in young and middle-aged patients.
Age Factors↗
Maximum Shannon information content of diagnostic medical testing. Including application to multiple non-independent tests.
The increase in Shannon information available from a diagnostic test associated with grading of the test results into many outcomes, rather than simply positive or negative, was examined to determine its upper limit as the number of test outcomes is increased indefinitely. Numerical methods were employed to find the optimal locations of outcome boundaries when a single normally distributed test variable is classified into 2, 3, 4, 5, 6, 8, 14, or 20 outcome categories. In each case Shannon information was computed for values of prior probability between 0.01 and 0.99 and for distances between the means in diseased and nondiseased populations ranging from 0.5 to 5.0 standard deviations. There is an important improvement in Shannon information as the number of outcomes defined is increased, but the increment in information diminishes rapidly with each additional category. A 20%-30% increment in information may be achieved with three outcomes instead of two. A further important increase in information occurs with four to seven outcomes, but beyond this the increment in inforation is negligible. The findings were similar over a wide range of prior probabilities and distances between the means. The analysis was extended to the case of multiple nonindependent tests by demonstrating their application to a Fisher discriminant function incorporating such tests. It was concluded that for normally distributed test variables: grading of test results significantly improves the information content of both single and multiple tests; the value of information content for 8-20 outcomes represents very nearly the maximum information content of a test; there is little value in using more than five to seven test outcomes; multiple grading should not be neglected for discriminant functions.
Bayes Theorem↗
Coronary calcification in the diagnosis of coronary artery disease.
Clinical, postmortem and angiographic studies of coronary calcification are reviewed to define the value of fluoroscopy in the diagnosis and management of coronary artery disease. Autopsy studies consistently show a unique association between calcification of the coronary arteries and atherosclerosis. The relation of coronary calcification to the presence of major stenosis is more variable but is strong enough to be of clinical value, particularly in the younger subject. The diagnostic value of fluoroscopy can be improved by attention to the detailed features of calcification observed with the technique. Combined use of fluoroscopy and exercise testing appears to be a valid and as yet unexploited approach to the noninvasive diagnosis of coronary stenosis. Fluoroscopy has been a neglected method of noninvasive diagnosis and is sufficiently promising to warrant greater clinical use.
Calcinosis↗
ECG multiple lead systems.
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Electrocardiography↗
Bayesian analysis of electrocardiographic exercise stress testing.
We evaluated the diagnostic accuracy of exercise-induced ST-segment depression in detecting coronary-artery disease by applying the likelihood-ratio formulation of Bayes's theorem to stress-test data, which were partitioned into half-millimeter ranges of depression. The graphic relation between the predictive value of a given test result and the pretest risk of disease in the test subjects was obtained for each of these half-millimeter intervals. This method reveals that the predictive value of testing depends on the degree of ST-segment depression, and that the pretest risk of coronary-artery disease is an important determinant of the predictive value of any test result in the individual patient. These findings suggest that the use of the terms "positive" and "negative" are inappropriate to describe most stress-test results. Instead, the results should be interpreted in terms of a continuum of risk based on the extent of ST-segment depression.
Adult↗