Endless Validation of Diagnostic Imaging Modalities to Assess Acute Coronary Syndrome: Has the Time Finally Come for Computed Tomography Angiography? La interminable validación de las técnicas de imagen diagnósticas para evaluar el sı́ndrome coronario agudo:

Acute chest pain as a presenting syndrome in the emergency department is by far one of the most prevalent worldwide. Validation of several diagnostic-imaging modalities for this syndrome has been the focus of several research groups over the last 3 decades. Unfortunately, from the simple and inexpensive exercise stress electrocardiography to the most advanced and complex tests such as positron emission tomography, cardiac computed tomography angiography (CTA), and magnetic resonance angiography, no imaging modality has been successfully validated to be the ‘‘reference standard’’ for this purpose. The difficulties start with the study methodology described in the manuscripts published to date. Designing a study to assess the diagnostic accuracy of a test in clinical practice can be cumbersome and problematic. First of all, the vast majority of studies have several recurrent limitations, most notably ‘‘differential verification bias’’ and ‘‘review bias.’’ This basically means that the index test results are verified by a different gold standard test. In this scenario, those patients with a positive noninvasive imaging test result will receive verification by one reference standard (ie, coronary angiography) whereas those with a negative test result will be discharged and followed up for the occurrence of major cardiovascular events. Conducting a study in which all patients undergo coronary angiography would require subjecting a large number of subjects to more than minimal risk simply for research purposes and would be considered unethical. Since only those patients with a positive noninvasive test result undergo cardiac catheterization, a ‘‘review bias’’ is introduced, leading to inflated measures of diagnostic accuracy because the analysis of the reference standard is influenced by knowledge of the results of the index test. Second, comparison of performance characteristics for different noninvasive tests has been attempted