Comprehensive assessment of patients with aortic valve disease by non-invasive cardiac imaging
Today, invasive coronary angiography is still the gold standard to perform the diagnosis of coronary artery disease. But it is an invasive procedure that carries non negligible morbidity (1.5%) and mortality (0.15%), and results in high costs. Less invasive and more cost-effective techniques are highly desirable. Over the past 15 years, substantial advances have been made in non-invasive cardiac imaging.
In the first part of this work, we prospectively evaluated the diagnostic accuracy of 40-slice multidetector CT (MDCT) to detect coronary artery disease prior to cardiac valve surgery in 82 patients. On a per-patient basis, MDCT correctly identified 14/15 patients with (sensitivity 93%) and 60/67 patients without coronary disease (specificity 90%). Performing invasive angiography only in case of abnormal CT might have avoided invasive angiography in 60/82 (73%) patients without coronary disease. Thus, MDCT could be potentially useful in the preoperative evaluation of such patients, allowing to avoid systematic cardiac catheterization in a large number of patients. Magnetic resonance coronary angiography (MRCA) has also emerged as a promising alternative due to the lack of ionizing radiation and absence of iodinated contrast injection. Therefore, we compared diagnostic accuracy of whole-heart MRCA and MDCT, against QCA, to identify >50% stenosis basis in 77 patients. WH-MRCA acquisition failed in a high number of patients. This was caused by an unstable breathing pattern or drift of the diaphragm position. Because of higher success rate, MDCT had higher diagnostic accuracy than WH-MRCA to detect coronary stenosis. Thus MDCT is superior to WH-MRCA, however WH-MRCA can perform as well as CT in interpretable segments with adequate image quality.
In the second part of this work, to evaluate whether MDCT and cardiac magnetic resonance (cMR) might allow simultaneous assessment of aortic valve area (AVA), we compared measurements of AVA by MDCT to cMR, transesophageal and transthoracic echocardiography. AVA by MDCT and cMR correlated highly with AVA by other techniques. In our study, we compared 3 planimetric approaches to AVA calculated by the continuity equation using TTE. We did observe excellent correlations between planimetric and continuity equation-derived AVA, but all 3 planimetric measures were found to overestimate continuity equation AVA. A potential explanation for this observation could be that we measure different aortic valve orifices. Indeed planimetric techniques measure the true dimensions of the anatomical orifice, whereas the continuity equation measures the "effective" orifice area. The ability of MDCT and cMR to accurately assess aortic valve area at the time of non-invasive coronary imaging, places these techniques in a strong position for the comprehensive assessment of such patients.
However, despite these good results, it must nonetheless be emphasized that to be acceptable in daily clinical practice, a strategy in which invasive coronary angiography would not be performed systematically but rather selectively in only a subset of patients, requires a perfect sensitivity for disease detection in individual patients. Unfortunately, the present work shows that MDCT and WH-MRCA have not yet reached such a level of accuracy. Finally, these tests are not a substitute for other imaging techniques in all cardiovascular conditions. Unlike an echocardiogram machine, the MRI and MDCT scanners cannot be brought to the bedside of an acutely ill patient.
School:Université catholique de Louvain
Source Type:Master's Thesis
Keywords:cardiac magnetic resonance multidector row computed tomography aortic stenosis coronary artery disease
Date of Publication:09/15/2008