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New Improved Risk Model for Predicting CAD


June 14, 2012 (Rotterdam, the Netherlands) — An international group of researchers has developed what they say is an improved model for predicting the presence of coronary artery disease (CAD) in patients with chest pain presenting to cardiology departments [1].
Lead author Dr Tessa SS Genders (Erasmus University Medical Center, Rotterdam) explained to heartwire that the new prediction tool is designed for use in those who have already seen a primary-care physician and are suspected of having coronary artery disease. "Deciding whether you should do further diagnostic testing with imaging or exercise ECG is the next step," she notes. The current study--which she reports with colleagues online June 12, 2012 in BMJ--is likely to lead to better decisions about further diagnostic steps, not least because the current models used were developed so long ago, she says.
At the moment, guidelines on this differ from country to country, she notes. In the US guidance, the Diamond and Forrester model, developed in 1979, is recommended to estimate the pretest probability of CAD in those presenting with stable chest pain, while in Europe, the Duke Clinical Score, designed in 1993, is employed. But both of these have limitations, she says.
This is interesting, well-conducted, and important.
Asked to comment on the new findings for heartwire , Dr Ionna Tzoulaki(Imperial College London, UK), who was not involved in this study, said: "This is interesting, well-conducted, and important. The risk model shows that it improves the predictive performance of previously developed models. However, before any conclusions can be drawn, the risk model needs to be prospectively externally validated in other populations. In addition, as with any prediction model, we need information on its impact in clinical practice--in other words, whether it improves patient outcomes." 
Results Based on More Than 5000 Patients From 18 Hospitals
Genders and colleagues performed a retrospective pooled analysis of individual patient data from 5677 patients with chest pain but no history of heart disease who were referred for CT angiography or catheter-based coronary angiography, from 18 hospitals across Europe and the US.
Their results showed that the Duke Clinical Score overestimates the likelihood of CAD, says Genders. The model they developed included hypertension as a predictor, something that is not included in the Duke Score, and excluded the resting ECG findings.
Of the 5677 patients, 1634 had obstructive CAD (defined as >50% diameter stenosis in at least one vessel found on catheter-based coronary angiography). The new, stepwise model improved the estimate of the pretest probability of CAD, the researchers report.
This refined estimate would, Genders believes, improve risk stratification, enabling doctors to make better decisions as to which diagnostic test is best in a particular patient and to decide on further management based on the results of such tests. The new risk tool has been designed as an online calculator and is available in the web appendix of the BMJ paper. It could easily be implemented in electronic patient records or smartphone or tablet applications, the researchers say.
Coronary Calcium Score Helps Further Refine Predictive Value
Genders and colleagues were also able to add in to their model information on coronary calcium scores for the majority of patients (because the data used were primarily collected in the setting of research related to CT coronary angiography, information on coronary calcium was available).
They found that calcium scores significantly improved the estimate of the probability of CAD, "suggesting that the calcium score should be considered for patients with chest pain."
And while Genders acknowledges that coronary calcium scores are currently not routinely recommended for this type of patient, at least not in the ACC/AHA guidelines or those from European Society of Cardiology, the UKNational Institute for Health and Clinical Excellence (NICE) does recommend use of the calcium score when the pretest probability of CAD is low, at 10% to 29%, she says.
"You can use coronary calcium score to exclude a diagnosis of obstructive CAD, when the pretest probability based on clinical information is low," she explains. "If you get a low or zero calcium score, the pretest probability of CAD drops even further, and this may justify not continuing with any further diagnostic tests." If, however, adding the coronary calcium increases the pretest probability of CAD, "you can go on and do other diagnostic tests."
According to the UK NICE guidelines, if the likelihood of CAD is 30% to 60%, for example, functional imaging, single-photon-emission computed tomography (SPECT) scans, or stress echocardiography could be performed. A score of 60% to 90% indicates that invasive coronary angiography should be performed, Genders says.
Genders says she hopes the BMJ paper will encourage others to take up use of the new model, although she agrees with Tzoulaki that it will be important to externally validate the model.
Genders reports no conflicts of interest; disclosures for other authors are listed at the end of the manuscript.

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