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National Clinical Guidelines Centre (UK). Stable Angina: Methods, Evidence & Guidance [Internet]. London: Royal College of Physicians (UK); 2011 Jul. (NICE Clinical Guidelines, No. 126.)

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Stable Angina: Methods, Evidence & Guidance [Internet].

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14Risk scores

14.1. Introduction

The GDG were interested in whether there were scoring systems available that would predict adverse outcomes. Ideally clinicians would like to be able to predict which patients were likely to have an adverse outcome and to intervene in those patients. In the absence of clear evidence for benefit of pharmacological or revascularistion strategies this might mean providing more intensive education and rehabilitation and support programmes to help patients to engage in secondary prevention strategies.

In this chapter we address the following key clinical question:

In adults with stable angina which tables, equations, engines, models or scoring systems are most reliable/effective for prognostic-risk stratification in prediction of adverse cardiac outcomes?

Two risk scoring systems were found that have been developed to predict adverse outcomes in patients with stable angina. The two risk scoring systems are: ACTION score-derived from a clinical trial population (ACTION trial)171 and Euro heart Angina score - derived from a large cohort population (Euro Heart survey172).

14.2. Clinical Evidence

The “Review Protocol” for this topic can be found in Appendix C, the “Search Strategies” in Appendix D, the “List of Included and Excluded Studies” in Appendix E1, and the “Clinical Evidence Tables” in Appendix E2.

Derivation of risk scores

For each risk score, multivariate analysis of baseline characteristics was performed to ascertain those characteristics which were most strongly associated with adverse outcomes- death or MI in Euro heart Angina score; and death all causes, MI or disabling stroke in the ACTION score. Risk scores were generated from the coefficients with an appropriate number of points given for the presence of each risk factor.

The components of each of the risk scores are shown below:

  1. ACTION risk score for death, MI or disabling stroke at 4.9 years follow-up:
    Age, left ventricular ejection fraction, smoking, white blood cell count, diabetes, casual blood glucose concentration, creatinine concentration, previous stroke, at least one attack a week, coronary angiographic findings (if available), lipid lowering treatment, QT interval, systolic blood pressure ≥155 mm Hg, number of drugs used for angina, previous MI, sex.
  2. Euro heart Angina score for death or MI at one year follow-up:
    co-morbidity, diabetes, duration of symptoms, severity of symptoms, resting electrocardiogram abnormalities, abnormal ventricular function

14.2.1. ACTION risk score

Clayton 2005171

This study used data from the ACTION trial (a coronary disease trial investigating outcome with nifedipine GITS), which followed 7665 patients with stable symptomatic angina for a mean of 4.9 years, to develop a score for predicting the combined risk of death from any cause, MI or stroke.

Participants: The Model was based on 7311 patients with values for all variables in model, of who 1063 had the combined event of death, MI, or disabling stroke.

Inclusion criteria In the ACTION trial: Eligible patients had stable symptomatic angina requiring treatment and either previous MI or proved angiographic coronary artery disease. Patients without a previous MI or coronary angiography could participate only if there was a positive result on an exercise or perfusion test. Key exclusions were ejection fraction below 40%, clinically significant heart failure, major cardiovascular event or intervention within the past 3 months, planned coronary angiography or intervention, and known intolerance to dihydropyridines. The patients were recruited from outpatient cardiology clinics in Western Europe, Israel, Canada, Australia, and New Zealand.

Outcomes and follow-up: The outcome measures were death from any cause or MI or disabling stroke with a follow-up of 4.9 years.

Statistical analysis: Multivariate Cox proportional hazard models used for the outcome time to death, MI, or disabling stroke as adjudicated by the critical events committee, using patients who had no missing values for the predictor variables. Each variables strength of predictive contribution was expressed by its z score (the model co-efficient divided by its standard error) and quantified each variables predictive power as hazard ratio with 95% CI.

For each patient, the risk score was calculated by multiplying each coefficient in the final model by 10, then by the patient‘s variable value, and then summed up the results.

Results: Table 14.1 shows the 16 variables, with the risk scores and Cox regression coefficients that were in the final model as derived for 7311 patients (95%) with complete information

Table 14.1. Predictors of death, MI, or disabling stroke for 7311 participants in the ACTION trial.

Table 14.1

Predictors of death, MI, or disabling stroke for 7311 participants in the ACTION trial. (Cox proportional hazard analysis) – figures are numbers (%)

The table below presents hazard ratios for the individual events of death, MI, and disabling stroke with the same variables as for the combined endpoint.

Table 14.2. Predictors of death, MI, and disabling stroke.

Table 14.2

Predictors of death, MI, and disabling stroke. (Cox proportional hazard analysis) - figures are hazard ratios (95% CI)

Limitations of the score: The risk score did not seem to predict the nature of the event (death in 39%, myocardial infarction in 46%, and disabling stroke in 15%) or the incidence of angiography or revascularisation, which occurred in 29% of patients.

Summary: The risk score combined 16 routinely available variables: age, left ventricular ejection fraction, smoking, white blood cell count, diabetes, casual blood glucose concentration, creatinine concentration, previous stroke, at least one attack a week, coronary angiographic findings (if available), lipid lowering treatment, QT interval, systolic blood pressure ≥ 155 mm Hg, number of drugs used for angina, previous MI, and sex. The patients risk is calculated by using ACTION score which is a number in the range of 0 to 60.

14.2.2. Euro heart angina score

Daly 2006172

The Euro heart survey of stable angina was designed as a prospective observational cohort study of patients presenting to cardiology services with stable angina. Participating centres were a mix of academic and non academic institutions, and hospitals with and without interventional and cardiac surgical facilities.

Participants: N=3031 patients enrolled from 156 centres in 34 countries.

Inclusion criteria: Patients attending cardiology services with a new presentation of stable angina were considered for enrolment, and consecutive patients in whom the cardiologist made a clinical diagnosis of stable angina caused by myocardial ischemia due coronary disease were included in the survey. Exclusion criteria included unstable angina, admission to hospital within 24 hours of assessment, myocardial infarction within one year, previous revascularisation, or a cause of angina other than coronary disease.

Baseline characteristics: The population was relatively young 61 years and 58% male. Most patients had mild to moderate symptoms of angina for 6 months or less before presentation to a cardiologist, although only 48 (1.7%) patients had symptoms for less than one month before cardiology assessment. 10496 (40%) of patients were in class 1. At baseline 1602 (47%) of patients were on aspirin, 1429 (21%) patients on statins and 1142 (38%) on BBs.

Confirmation of coronary disease: Coronary angiography was done at least once during follow-up in 1253 (41%) patients. At the end of the follow-up period, approximately one third (n=994) of patients had had coronary disease confirmed angiographically and a further third (n=1023) had negative investigations. One sixth of patients had no definitive diagnostic test to confirm the presence or absence of coronary disease.

Outcome: The primary outcome of interest was death or non fatal MI.

Follow-up: The median duration of follow-up was −13 months (interquartile range 12–15 months).

Statistical analysis: Cox‘s proportional hazards models were used to determine the effects of clinical and investigative variables on the occurrence of death or non fatal MI in both univariate and multivariate analysis. Starting with clinical variables, stepwise regression was done (using entry/removal P value = 0.15) to determine the factors predictive of death or infarction during follow-up. Models were developed separately for clinical and investigative parameters and then for a combination of clinical and investigative parameters. Final model was refitted for all patients without missing values for the variables selected.

Results: The Euro heart Angina score involves six characteristics: co-morbidity, diabetes, severity of symptoms, duration of symptoms, resting electrocardiogram abnormalities, and abnormal ventricular function.

The major clinical events occurring during follow-up in the overall population with stable angina (N=3031) are shown in the table below.

Table 14.3. Major clinical events occurring during follow-up in the overall population with stable angina.

Table 14.3

Major clinical events occurring during follow-up in the overall population with stable angina.

The table below shows the risk of death or myocardial infarction associated with baseline clinical characteristics and results of investigations. Previous myocardial infarction, signs of heart failure, or a past history of diabetes, hypertension, or any co-morbidity were significant predictors of adverse outcome, as were increasing severity of symptoms and shorter duration of symptoms. Resting electrocardiographic abnormalities (Q wave or ST/T wave changes) were associated with approximately double the risk of death or myocardial infarction, but positive non-invasive stress test results were not significantly associated with adverse outcome.

Table 14.4. Unadjusted hazard ratio of death or MI associated with clinical and investigative parameters in general population with stable angina (n=3031).

Table 14.4

Unadjusted hazard ratio of death or MI associated with clinical and investigative parameters in general population with stable angina (n=3031).

The table below shows stepwise regression selected co-morbidity, diabetes, recent onset of symptoms, more severe symptoms, ST or T wave abnormalities on the resting electrocardiogram, not having any stress test done, and abnormal ventricular function as the variables most predictive of outcome

Table 14.5. Clinical and investigative parameters independently predictive of death or MI, determined by using stepwise selection procedures in general population with stable angina.

Table 14.5

Clinical and investigative parameters independently predictive of death or MI, determined by using stepwise selection procedures in general population with stable angina.

In the model developed to derive the clinical risk score the final predictors of death or MI were co-morbidity, diabetes, severity of symptoms, duration of symptoms, resting electrocardiogram abnormalities, and abnormal ventricular function.

Validity: Applying the model developed on 75% of the population to the remaining 25% of the population gave a C-statistic for the angina score to predict outcome of 0.74.

Cox‘s proportional hazards models were used to determine the effects of clinical and investigative variables on the occurrence of death or non fatal MI in both univariate and multivariate analysis.

To develop a scoring system for predicting probability of death or infarction during the first year after presentation that was based only on objective information generally available to clinicians and not on whether a test was done a further multivariate model was developed without the stress test done/not done variable. The performance of the model was assessed by calculating the Harrels C-statistics (comparable to the area under the receiver operating characteristics curve).

Table 14.6. Score for each factor to calculate risk score for patients presenting with stable angina.

Table 14.6

Score for each factor to calculate risk score for patients presenting with stable angina.

Limitations: Small sample. The Euro heart survey of stable angina population differs from a general selection of people with angina in the community, many of whom may not have a diagnosis, and differs from the overall primary care angina population in that they have been selected for specialist assessment. However, the population is comparatively less highly selected than those in randomised controlled trials. The score has not been validated so far in a stable angina population.

Summary: In the model developed to derive the clinical risk score the final predictors of death or MI were co-morbidity, diabetes, shorter duration of symptoms, increasing severity of symptoms, abnormal ventricular function, resting electrocardiographic changes, or not having any stress test done. Results of the non invasive stress tests did not significantly predict outcome in the population who had tests done. A score was constructed using the parameters predictive of outcome to estimate the probability of the death or myocardial infarction within one year of presentation of stable angina. Applying the model developed on 75% of the population to the remaining 25% of the population gave a C-statistic for the angina score to predict outcome of 0.74.

14.3. Economic evidence

No economic studies were found on this question.

14.4. Evidence statements

ClinicalThere was evidence from 2 studies171,172 that reported the derivation of ACTION risk score and Euro heart Angina score. However, there was no evidence available that validated the ACTION risk score and Euro heart Angina score in a stable angina population.
EconomicNo economic evidence was found on this question.

14.5. Recommendations and link to evidence

RecommendationNo recommendation was made
Relative values of different outcomesNot applicable
Trade off between clinical benefits and harmsNot applicable
Economic considerationsNo economic evidence was identified. If routine clinical indicators are used, costs are negligible.
Quality of evidenceBoth risk scores were derived from selected patient populations that may not be representative of the wider population of patients with stable angina. The Euroheart score was developed from 75% of the total Euroheart survey population (derivation cohort) and tested in the remaining 25% of the population.

The population used to develop the ACTION score was derived from the randomised ACTION trial, which enrolled patients with previous MI, or angiographic or other evidence of coronary heart disease.

The available risk scores have not been validated in populations other than the cohorts in which they were developed.
Other considerationsThe GDG recognised that given the low event rate in stable angina a large cohort is required when developing a predictive model in a general angina population. The GDG did not consider that the evidence was sufficient to recommend using clinical risk scores but acknowledged that the clinical factors identified in the Euroheart study can result in a poorer outcome.
Copyright © 2011, National Clinical Guidelines Centre.

Apart from any fair dealing for the purposes of research or private study, criticism or review, as permitted under the Copyright, Designs and Patents Act, 1988, no part of this publication may be reproduced, stored or transmitted in any form or by any means, without the prior written permission of the publisher or, in the case of reprographic reproduction, in accordance with the terms of licences issued by the Copyright Licensing Agency in the UK. Enquiries concerning reproduction outside the terms stated here should be sent to the publisher at the UK address printed on this page.

The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant laws and regulations and therefore for general use.

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Bookshelf ID: NBK83609

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