CT Triple rule out is an ECG gated multi detector computerized tomographic scan which can be used in for patients presenting to the emergency department with acute chest pain. Three important potential causes: aortic dissection, pulmonary embolism and coronary artery disease constitute the ‘triple’ rule out . It can be done rapidly in potentially life threatening cases of acute chest pain and has high negative predictive value . A potential chance for misdiagnosis of aortic dissection with CT is the pulsation artefact due to movement of ascending aorta due to cardiac contraction . It has been successfully eliminated by ECG gating and certain reconstruction algorithms. Other potential errors causing misdiagnosis of aortic dissection are the presence mediastinal clips and indwelling catheters. Contrast enhancement of adjacent superior vena cava can also occasionally be misleading. This has been taken care of by adjustment of volume of iodinated radiocontrast injected and the rate of injection. Though CT triple rule out is useful for assessing proximal coronaries, it is not as good as conventional coronary angiogram to visualize the details of the coronary anatomy. In visualizing details of coronary anatomy, standard CT coronary angiogram is also superior to CT triple rule out. Significant pulmonary embolism can very well be picked up by CT triple rule out.
Wnorowski AM et al evaluated the diagnostic yield of CT triple rule out in an emergency setting . It was a retrospective study of all CT triple rule outs performed in one centre between 2006 to 2015. 256 slice multi detector CT (MDCT) scanner with ECG gating and a biphasic contrast injection was used. 1192 cases were included in the study. 970 (81.4%) were negative studies without significant coronary or non coronary diagnosis. 139 had significant coronary artery disease of 50% stenosis or greater. Pulmonary embolism was noted in 28 patients, aortic aneurysm in 24, aortic dissection in 4 cases, and pneumonia in 20 patients. Of these 30 cases of pulmonary embolism and aortic pathology would not have been detected on CT coronary angiography.
Russo V et al studied the feasibility of CT triple rule out in an emergency radiology set up comparing the diagnostic performance of cardiovascular and general radiologists . From a study of 350 patients presenting with acute and atypical chest pain, concordance rate was 100% for acute aortic syndromes. General radiologists could exclude with good diagnostic accuracy the presence of obstructive coronary stenosis. This was without the use of time consuming software and/or reconstructions.