A perspective on standardizing the predictive power of noninvasive cardiovascular tests by likelihood ratio computation: 2. Clinical applications

Optimized electrocardiographic criteria for prior inferior and anterior myocardial infarction

BACKGROUND AND PURPOSE

The first purpose of the study was to optimize empirically the detection of prior inferior myocardial infarction (IMI) and prior anterior myocardial infarction (AMI) by electrocardiogram (ECG). The second purpose was to compare the diagnostic performances of the new criteria with those of 3 widely used commercial diagnostic ECG algorithms.

MATERIALS AND METHODS

We analyzed the digital ECG data from 1138 subjects with suspected coronary artery disease in whom the presence or absence of prior IMI or AMI was documented by coronary angiography and left ventriculography. We used receiver operating characteristic curves to develop the new criteria for prior IMI and AMI using a training set of 562 subjects and then tested their diagnostic performances using a separate test set of 576 subjects. In both the training and test sets, we used χ(2) test to compare the performances of the new criteria with those of 3 commercial computerized diagnostic algorithms.

RESULTS

The best criterion for prior IMI was the algebraic sum of the Q and T amplitudes in leads III and aVF. Its sensitivities/specificities were 71%/98% and 74%/98% in the training and test sets, respectively. The best criterion for prior AMI was the algebraic sum of the Q, R, and T amplitudes minus the Q duration in leads V(2), V(3), and V(4). Its sensitivities/specificities were 68%/98% and 65%/98% in the training and test sets, respectively. In both the training and test sets, these diagnostic performances were generally superior to those of the 3 commercial algorithms.

CONCLUSIONS

Using digital ECG data, we developed and tested new criteria for prior IMI and AMI whose diagnostic performances are generally superior to each of 3 widely used commercial ECG diagnostic algorithms.

Noninvasive detection of left-ventricular systolic dysfunction by acoustic cardiography in atrial fibrillation

Objectives. Assessment of left ventricular (LV) systolic function in patients with atrial fibrillation can be difficult. Acoustic cardiography provides several parameters for quantifying LV systolic function. We evaluated the ability of acoustic cardiography to detect LV systolic dysfunction in patients with and without atrial fibrillation. Design. We studied 194 patients who underwent acoustic cardiography and cardiac catheterization including measurement of angiographic ejection fraction (EF) and maximum LV dP/dt. LV systolic dysfunction was defined as LV maximum dP/dt <1600 mmHg/s. Acoustic cardiographic parameters included electromechanical activation time (EMAT) and the systolic dysfunction index (SDI). Results. Acoustic cardiography detected systolic dysfunction with high specificity and moderate sensitivity with similar performance to EF (sensitivity/specificity without afib: EMAT 30/96, SDI 40/90, EF at 35% 30/96; sensitivity/specificity with afib: EMAT 64/82, SDI 59/100, EF at 35% 45/82). Conclusions. Acoustic cardiography can be used for diagnosis of LV systolic dysfunction in atrial fibrillation.

Incorporating Uncertainty Into Medical Decision Making: An Approach to Unexpected Test Results

The utility of diagnostic tests derives from the ability to translate the population concepts of sensitivity and specificity into information that will be useful for the individual patient: the predictive value of the result. As the array of available diagnostic testing broadens, there is a temptation to de-emphasize history and physical findings and defer to the objective rigor of technology. However, diagnostic test interpretation is not always straightforward. One significant barrier to routine use of probability-based test interpretation is the uncertainty inherent in pretest probability estimation, the critical first step of Bayesian reasoning. The context in which this uncertainty presents the greatest challenge is when test results oppose clinical judgment. It is this situation when decision support would be most helpful. The authors propose a simple graphical approach that incorporates uncertainty in pretest probability and has specific application to the interpretation of unexpected results. This method quantitatively demonstrates how uncertainty in disease probability may be amplified when test results are unexpected (opposing clinical judgment), even for tests with high sensitivity and specificity. The authors provide a simple nomogram for determining whether an unexpected test result suggests that one should ``switch diagnostic sides.'' This graphical framework overcomes the limitation of pretest probability uncertainty in Bayesian analysis and guides decision making when it is most challenging: interpretation of unexpected test results.

Acoustic cardiography augments prolonged QRS duration for detecting left ventricular dysfunction

BACKGROUND

Prolonged QRS duration has been used as a marker for left ventricular (LV) systolic dysfunction (SD) and is used in the evaluation of patients presenting with known or suspected heart failure. The goal of this study was to compare the abilities of QRS duration and simultaneous digital ECG and heart sounds, that is acoustic cardiographic, parameters to identify patients with LV dysfunction.

METHODS

Our learning population consisted of 171 patients with possible chronic compensated or mildly decompensated heart failure who presented to an ambulatory cardiology clinic for echocardiographic examination. We defined LVSD as a LV ejection fraction < 50%, and estimated LV filling pressures from diastolic measurements. These patients also had acoustic cardiographic recordings from which we obtained a variety of individual ECG and acoustic cardiographic parameters. We used the product of four of these parameters to obtain a diagnostic score for LV dysfunction. We then compared the diagnostic performances of QRS duration and the score on a test population of patients who presented to an emergency department with possible heart failure.

RESULTS

In the learning population, the sensitivities/specificities of QRS duration > or =120 ms and the score for prediction of LVSD were 51%/92% and 77%/90%, respectively. In the test population, the score remained superior to QRS duration for detecting LVSD as well as acute decompensated heart failure.

CONCLUSIONS

Improved identification of LVSD and clinical heart failure can be achieved with a cost-effective bedside screening tool with the simple combination of simultaneously acquired digital ECG and heart sound data.

Usefulness of acoustic cardiography to resolve ambiguous values of B-type natriuretic Peptide levels in patients with suspected heart failure

B-type natriuretic peptide (BNP) levels are helpful to diagnose left ventricular (LV) systolic and/or diastolic dysfunction. BNP levels that are only moderately increased have limited diagnostic ability, and an additional test to resolve this problem would be desirable. The hypothesis that acquiring combined electrocardiographic and electronic cardiac acoustical data can improve the detection of LV dysfunction in patients with nondiagnostic values of BNP was tested. Both BNP and combined 12-lead electrocardiograms with electronic heart sound (acoustic cardiographic) recordings were obtained from 164 outpatients referred for echocardiographic evaluation for suspected heart failure. Acoustic cardiographic parameters included the third heart sound (S(3)) and percentage of electromechanical activation time, measured as the interval from onset of the Q wave of the electrocardiogram to the first heart sound (S(1)) and expressed as a proportion of the cardiac cycle. Sixty-nine of 164 patients (42%) had BNP values in the "gray zone" of 100 to 500 pg/ml. Sensitivity and specificity for LV dysfunction of BNP in the gray zone were 55% and 75%, with a positive likelihood ratio of 2.3. The use of acoustic cardiographic parameters in these 69 patients increased sensitivity and specificity to 69% and 100%, with a corresponding positive likelihood ratio of 69. In conclusion, easily obtainable acoustic cardiographic data substantially improved the diagnostic evaluation of patients with nondiagnostic BNP values and therefore can increase the confidence with which physicians diagnose and treat LV dysfunction.

Assessment of patients with low-risk chest pain in the emergency department: Head-to-head comparison of exercise stress echocardiography and exercise myocardial SPECT

OBJECTIVES

The aim of the study was to compare head-to-head the performance of exercise tolerance test-stress echocardiography (ex-Echo) and exercise stress-perfusion nuclear imaging (exercise-single-photon emission computed tomography [ex-SPECT]) for the diagnosis of coronary artery disease (CAD) in patients evaluated at the chest pain unit with delay from chest pain (CP) onset.

BACKGROUND

As an early triage strategy for CAD in emergency medicine, ex-Echo could have the advantage of widespread availability and low costs.

METHODS

In the years 2000-2002, 503 consecutive patients (mean age 60 years) with recent (<24 hours) CP and nonischemic electrocardiogram (ECG), in whom CAD remained undiagnosed after first line 6-hour work-up including serum markers of myocardial injury and resting echocardiogram, underwent ex-Echo and ex-SPECT within 24 hours. Patients with (+)ex-Echo or (+)ex-SPECT or (+)ex-ECG or abnormal troponin I were referred to coronary angiography; otherwise, they were discharged and followed up. End points were coronary stenosis > or =50% and cardiovascular events at 6-month follow-up.

RESULTS

Ninety-nine patients (20%) had (+)ex-Echo and 121 (24%) (+)ex-SPECT; CAD was diagnosed in 81% and 67%, respectively; positive tests were concordant in 69%. In negative ex-Echo and ex-SPECT, final evidence of CAD emerged in 14 and 13, respectively. Ex-Echo demonstrated higher accuracy than ex-SPECT (93% +/- 1% vs 89% +/- 1%), optimal specificity (95% +/- 5% vs 90% +/- 5%), and positive predictive value (81% +/- 4% vs 67% +/- 4%); moreover, in the case of (-)ex-ECG, observed effective likelihood ratio indicates a (+)synergy between ex-ECG and ex-Echo.

CONCLUSIONS

Ex-Echo can be an effective diagnostic strategy in the early triage of CP patients, improving diagnosis in case of (-)ex-ECG and reducing unnecessary angiography number. Its drawback is represented by the 5% of missed diagnosis.

The predictive power of serum κ/λ ratios for discrimination between monoclonal gammopathy of undetermined significance and multiple myeloma

The predictive power of serum κ/λ ratios on initial presentation of immunoglobulin G (IgG) or IgA monoclonal component was studied to differentiate between monoclonal gammopathy of undetermined significance (MGUS) and multiple myeloma (MM) patients. The retrospective study involved 145 patients clinically diagnosed with monoclonal gammopathy of undetermined significance or multiple myeloma, who had serum M-protein IgG <35g/L or IgA <20g/L at M-protein detection. Serum light chains κ and λ were measured by fixed-time nephelometry. Test performance indices, predictive values and likelihood ratios were calculated according to the Weissler recommendation. MM patients were considered as diseased and MGUS patients as non-diseased in order to estimate the performance characteristics of serum κ/λ ratios. There was a statistically significant difference in κ/λ ratios distribution between both groups of patients, in both M-protein κ-type (Mann-Whitney U=168, p<0.001) and in M-protein λ-type (Mann-Whitney U=143, p<0.001). Negative likelihood ratios at threshold levels of 0.6 and 4.2 were 2.17- and 3.32-fold greater, respectively, than positive likelihood ratios, so that the predictive power of a serum κ/λ ratio within these limits is better in ruling out (negative predictive power) than ruling in disease (positive predictive power). The post-test characteristics of a serum κ/λ ratio interval between 0.6 and 4.2 in discriminating MGUS from MM in our geographic population were: sensitivity 0.96 (0.93–0.99 95%CI); specificity 0.70 (0.63–0.77); positive predictive value 0.68 (0.64–0.73); negative predictive value 0.96 (0.94–0.99); likelihood ratios (+)LR 3.23 (2.68–4.04); and (−)LR 17.16 (11.00–63.00). Thus, serum M-protein with a κ/λ ratio between 0.6 and 4.2 increases the posterior probability of MGUS from 0.60 to 0.96 in asymptomatic patients, for whom only monitoring may be suggested when the serum κ/λ ratio is within these limits.

Is readmission to hospital an indicator of poor process of care for patients with heart failure?

BACKGROUND

Controversy exists about the appropriateness of using readmission as an indicator of the quality of care. A study was undertaken to measure the validity and predictive ability of readmission in this context.

METHODS

An evaluation study was performed in patients discharged alive with heart failure from three Swiss academic medical centres. Process quality indicators were derived from evidence based guidelines for the management and treatment of heart failure. Readmissions were calculated from hospital administrative data. The predictive ability of readmissions was evaluated using bivariate and multivariate analyses, and validity by calculating sensitivity, specificity, positive and negative predictive value, using process indicators as the "gold standard".

RESULTS

Of 1055 eligible patients discharged alive, 139 (13.2%) were readmitted within 30 days. The adjusted odds ratio (OR) for absence of measurement of left ventricular function was 0.70 (95% CI 0.45 to 1.08) for readmissions. In patients with left ventricular systolic dysfunction, three dose categories of angiotensin converting enzyme inhibitor were examined using ordinal logistic regression. The adjusted OR for these categories was 1.07 (95% CI 0.56 to 2.06) for readmissions. When using process indicators as the gold standard to assess the validity of readmissions, sensitivity ranged from 0.08 to 0.17 and specificity from 0.86 to 0.93.

CONCLUSIONS

Readmission did not predict and was not a valid indicator of the quality of care for patients with heart failure admitted to three Swiss university hospitals.

Utility of white cell count and ultrasound in the diagnosis of acute appendicitis

BACKGROUND

Despite considerable advances in imaging, the diagnosis of acute appendicitis remains a clinical one. Nonetheless, knowledge of the characteristics of commonly used investigations for appendicitis may aid surgical decision-making.

METHODS

The pathology, full blood counts and ultrasounds of 1013 patients who underwent appendicectomy were reviewed and subjected to statistical analysis in order to determine diagnostic characteristics of various white cell count and ultrasound results.

RESULTS

Total white cell count was found to be higher among patients with complicated appendicitis than those with simple appendicitis or normal appendices. Ultrasound was found to be less accurate than white cell count and neutrophil count in the diagnosis of acute appendicitis by estimation of area under the receiver operator characteristic curve.

CONCLUSION

Knowledge of the meaning of various white cell count values may be invaluable in clinical decision-making with regard to the diagnosis of acute appendicitis. Ultrasound is of limited utility in the diagnosis of appendicitis and should only be used in selected clinical situations.

Detection of coronary artery stenoses with multislice helical CT angiography

OBJECTIVES

The authors compared multislice CT angiography and selective angiography for the assessment of coronary artery disease.

METHODS

In 28 patients, the presence and degree of coronary artery stenoses were determined in coronary segments prepared with beta-blocker for good image quality with multislice CT.

RESULTS

In 187 coronary artery segments, sensitivity, specificity, and negative predictive value for the detection of stenoses >50% with multislice CT angiography were 81%, 90%, and 97%, respectively. The agreement for determining the degree of stenoses with multislice CT angiography and selective coronary angiography was only moderate (kappa = 0.58).

CONCLUSIONS

Because of the limited spatial resolution, it is not possible with multislice CT angiography to determine the degree the coronary artery stenoses precisely. However, the high negative predictive value indicates that multislice CT may be a suitable tool to reliably rule out coronary artery disease.

A perspective on standardizing the predictive power of noninvasive cardiovascular tests by likelihood ratio computation: 1. Mathematical principles

The current practice of reporting positive and negative predictive value (PV), sensitivity (Se), and specificity (Sp) as measures of the power of noninvasive cardiovascular tests has significant limitations. A test result's PV and its comparison with other test results are highly dependent on the pretest disease prevalence at which it is determined; the citation of sensitivity and specificity provides no succinct or explicit quantitation of the rule-in and rule-out power of a test. This article presents a rationale for the use of an alternative standard for expressing predictive power in the form of positive and negative likelihood ratios, (+)LR and (-)LR. The likelihood ratios are composite expressions of test power, which incorporate the Se and Sp and their respective complements [(1 - Se) and (1 - Sp)], thus yielding single unambiguous measures of positive and negative predictive power. The likelihood ratios are calculated as follows: (+)LR = Se/(1 - Sp) and (-)LR = Sp/(1 - Se). On analysis of the predictive value equations, the likelihood ratios equal the quotients of the posttest predictive value odds to the pretest prevalence odds for disease and no disease, respectively, as follows: (+)LR = (+)PVOd/POD and (-)LR = (-)PVOn/PON, where (+)PVOd is positive predictive value odds for disease, POD is prevalence odds for disease, (-)PVOn is negative predictive value odds for no disease, and PON is prevalence odds for no disease. Thus, the likelihood ratios are measures of the odds advantage in posttest probability of disease or no disease relative to pretest probability, independent of disease prevalence in the tested population. The quotients of the (+)LR or the (-)LR among test results studied in a common population are direct expressions of their relative predictive power in that population. The likelihood ratio principle is applicable to the evaluation of the predictive power of multiple tests performed in a common population and to estimating predictive power at multiple test thresholds.