Cardiac CT: The Future of Diagnostic Cardiology?
As a medical student eyeing the field of radiology, the science of imaging of was all too seductive. Ultimately, a love for cardiac physiology won me over, but an interest in imaging lingered. As it turns out, cardiologists are part-time radiologists with expertise in a number of cardiac imaging modalities.
CT has become the latest frontier in cardiac imaging with a number of useful applications.
By now, coronary calcium scoring is a well-established tool for risk stratification in subclinical coronary artery disease. Cross-sectional imaging is also useful for evaluating pericardial thickening in constrictive pericarditis. Beyond these traditional applications, newer techniques are poised to change the way we use CT to evaluate heart disease.
Coronary CT Angiography
Using fast, EKG-gated scanners, coronary CT angiography (CCTA) is a noninvasive means to detect coronary anomalies and obstructive plaque. CCTA is a sensitive tool for excluding coronary disease, with a nearly perfect negative predictive value in the ACCURACY trial1. However, specificity is poor and the presence of stents or calcium degrades image quality.
The specificity of CCTA is improved with FFR-CT (HeartFlow), a noninvasive method that mimics invasive fractional flow reserve measurements. Computational fluid dynamics are applied to a 3D model of coronary anatomy in order to simulate the hemodynamic effects of stenotic lesions. The PLATFORM trial2 showed how these technologies can safely reduce unnecessary catheterizations with no detriment to outcomes.
CT Myocardial Perfusion Imaging
CT myocardial perfusion imaging is also possible. Indeed, a key advantage of CT is the ability to combine anatomic and physiologic evaluation in a single study. However, exposure to radiation and iodinated contrast is an important consideration when comparing this to SPECT imaging.
As our diagnostic tools multiply, cardiac testing will become less invasive yet choosing the right study will become more complicated. Cardiology is a fortunate field that controls much of its own imaging, but with the emergence of cardiac CT, we will need to collaborate with our radiology colleagues to push our fields forward in tandem.
References:
1Budoff MJ, Dowe D, Jollis JG, et al. Diagnostic performance of 64-multidetector row coronary computed tomographic angiography for evaluation of coronary artery stenosis in individuals without known coronary artery disease: results from the prospective multicenter ACCURACY (Assessment by Coronary Computed Tomographic Angiography of Individuals Undergoing Invasive Coronary Angiography) trial. J Am Coll Cardiol 2008;52:1724-32.
2Douglas PS, Pontone G, Hlatky MA, et al. Clinical outcomes of fractional flow reserve by computed tomographic angiography-guided diagnostic strategies vs. usual care in patients with suspected coronary artery disease: the prospective longitudinal trial of FFR(CT): outcome and resource impacts study. Eur Heart J. 2015;36:3359–3367. doi: 10.1093/eurheartj/ehv444.