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Original Research |
1 Department of Radiology, Mayo Clinic and Foundation, 200 First St. SW,
Rochester, MN 55905.
2 Department of Medicine, Division of Cardiovascular Diseases, Mayo Clinic and
Foundation, Rochester, MN.
Received October 19, 2006;
accepted after revision October 12, 2007.
Address correspondence to E. E. Williamson.
Abstract
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MATERIALS AND METHODS. Chart review was performed on 214 consecutive patients referred for clinically indicated 64-MDCT angiography. The study cohort consisted of 20 patients who had previously undergone transesophageal echocardiography (TEE). Blinded consensus review of each CT angiography was performed by two experienced cardiac radiologists and results were compared with TEE, which served as a reference standard. CT criteria for the diagnosis of PFO were distinct left atrial "flap" in the expected location of the septum primum, continuous column of contrast material connecting this flap to the right atrium, and a "jet" of contrast material from the column into the right atrium.
RESULTS. Of the 20 patients who underwent both TEE and cardiac CT angiography, six (30%) were found to have a PFO by TEE. Using the presence of a left atrial flap as the only diagnostic criterion, all six cases of PFO were detected using CT (sensitivity = 100%). Of the 14 patients with no PFO seen on TEE, 12 of these were correctly identified using CT (specificity = 86%). Using all three criteria together, the sensitivity decreased to 66% and the specificity increased to 100%.
CONCLUSION. ECG-gated cardiac CT angiography performed with a 64-MDCT scanner can be used to reliably detect PFO.
Keywords: angiography • cardiac CT • patent foramen ovale • transesophageal echocardiography
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Recent technological advances in CT technology, including ECG-gating and faster gantry rotation, have improved temporal resolution to the point that CT of the heart is possible throughout the cardiac cycle. Increases in the number of high-resolution detector elements have further improved the quality and robustness of cardiac CT. Thus far, studies evaluating cardiac MDCT angiography have focused on imaging of the coronary arteries; however, the same technology that allows submillimeter isotropic voxel imaging of coronary anatomy also allows for direct imaging of intracardiac anatomy. Structures that have never been visible previously on CT, such as cardiac valve apparatus, can now be imaged as a part of the routine cardiac evaluation. Currently to our knowledge, no published studies exist describing the use of cardiac CT angiography for the diagnosis of a PFO. In addition, we know of no CT criteria for the detection or description of a PFO.
Our hypothesis is that ECG-gated cardiac CT angiography performed using a 64-MDCT scanner can be used to reliably detect a PFO. Our aim is to describe the CT features of PFO and to determine the sensitivity and specificity of each feature, alone and in combination, using TEE as a reference standard for making this diagnosis.
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The CT examinations were performed on a 64-MDCT scanner (Sensation 64, Siemens Medical Solutions). Patients were supine, with ECG leads paced. The scanning parameters were as follows: kVP, 120; tube rotation, 0.33; detector configuration, 32 x 0.6 mm; reconstructed width, 0.75 mm; reconstructed interval, 0.4 mm; pitch, 0.23; mAs, 650; and field of view, 25 cm. Contrast timing was determined using a test bolus consisting of 16–20 mL of iodixanol (Visipaque, GE Healthcare) with an iodine concentration of 320 mg I/mL injected at 5 mL/s. Cardiac CT angiography was performed using between 80 and 105 mL of iodixanol 320. The total volume of contrast material used for angiography was determined on the basis of the scanning duration, according to the following formula: 5 mL/s x (scanning duration + 5 seconds). The saline flush was performed using 40 mL of 0.9 normal saline to minimize perivenous artifacts in the superior vena cava and to reduce opacification of the right-sided cardiac chambers.
Patients with a heart rate > 67 beats per minute (bpm) received oral metoprolol 100 mg at least 1 hour before scanning. Patients with heart rate < 67 bpm did not receive β-blocker premedication. At the time of CT, patients without contraindications to sublingual nitroglycerin received a one-time sublingual dose of nitroglycerin 0.4 mg.
For evaluation of the CT scans, a set of imaging criteria was developed for the presence of PFO. These criteria were developed on the basis of prior observations of scans obtained using 16-MDCT angiography in patients with known PFO. Correlation was also performed with pathologic cardiac explant specimens from patients with and without PFO to determine which morphologic features of the interatrial septum would most consistently be present in patients with PFO (Fig. 1).
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All CT scans were evaluated by consensus review of two experienced cardiac radiologists (17 and 6 years of experience) for the presence of each of the predefined criteria. Individual correlation was performed for each of the findings alone and in combination with the other findings compared with the results of TEE. The echocardiograms were in dependently reviewed by two experienced cardiologists for the presence or absence of a PFO.
Sensitivity, specificity, and positive and nega tive predictive values were manually calculated for each CT finding compared with the results of echocardiography using standard statistical formulas.
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Six patients in the cohort were diagnosed as having a PFO at TEE (Figs. 3A and 3B). The CT findings on the 20 patients were as follows: eight patients were found to have an atrial septal flap (criterion 1); five patients had both a flap and a continuous contrast column connecting the right and left atria (criterion 2); and four patients had a flap, a continuous contrast column, and a jet of contrast material extending from the contrast column into the relatively unopacified right atrium (criterion 3). CT criteria 2 and 3 were never found in the absence of criterion 1. When using CT criterion 1 alone, no patient found to have a PFO at TEE went undetected. In two cases in which no PFO was detected at TEE, a left atrial flap (criterion 1) was identified at cardiac CT angiography and, in one of these cases, a continuous contrast column was also identified. These findings are summarized in Table 2.
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Traditionally, echocardiography has been the mainstay for the diagnosis of a PFO [5]. However, TEE is not suited for all patients, particularly those who have difficulty with sedation or cannot tolerate cannulation of the esophagus [9]. Recently MRI has proven its usefulness in detecting and evaluating all kinds of intracardiac shunts [10, 11]. MRI enables the noninvasive determination of atrial septal defect size, morphology, and spatial relationships and precisely depicts pulmonary and systemic venous connections, thereby assisting in the planning of treatment [12, 13]. Although not currently as well established, cardiac CT also has the potential to evaluate cardiac structure [14–16].
Previously, limitations of spatial and temporal resolution have prevented CT from being a reliable tool for the diagnosis of PFO. In 2003, Henk et al. [17], reported that insufficient attenuation in the pulmonary arteries at helical CT pulmonary angiography could be secondary to an underlying PFO with right-to-left shunting of contrast material, but the direct diagnosis of a PFO was not made in their study. As CT scanner technology has improved, particularly with the advent of submillimeter isotropic voxel resolution and faster gantry rotation, evaluation of intracardiac structures has become a reality. Unfortunately, because of the rapid application of these new techniques, in many cases CT diagnostic criteria for abnormalities of these structures have not been established. The purpose of this study, the first of its kind to our knowledge, is to establish CT diagnostic criteria for PFO and to determine the diagnostic accuracy of these criteria compared with TEE as a reference standard.
Our study shows the feasibility of ECG-gated cardiac CT angiography performed using a 64-MDCT scanner for the diagnosis of PFO. The use of our predetermined criteria rendered good sensitivity and specificity for making the diagnosis prospectively. Using the first criterion alone, the presence of a left atrial flap in the expected location of the septum primum, we obtained maximum sensitivity (100%). The use of this criterion by itself could be appropriate as a screening test to determine which patients could benefit from further testing with an invasive examination such as TEE. Using all three CT criteria together allows maximum specificity (100%) for the diagnosis. The current study shows that when all the criteria for PFO are present on a cardiac CT scan, we can confidently establish the diagnosis of PFO.
Although cardiac CT is unlikely to supplant echocardiography as a first-line test for the evaluation of PFO, the fact that this potential intracardiac shunt can be reliably detected using ECG-gated CT angiography could change the way that cardiac CT is used in clinical practice. In addition to the routine use of our criteria to evaluate cardiac CT scans obtained for other indications, the importance of detecting a PFO in patients with pulmonary embolism and pulmonary hypertension suggests a role for ECG-gating during pulmonary artery CT angiography. The results of the current study suggest that ECG-gating will allow radiologists to be able to detect and potentially characterize intracardiac shunts that may have important prognostic implications. This initial feasibility study could serve as a pilot study for future investigations.
Limitations to our study include the small number of patients evaluated. Our small sample size did not allow us to evaluate the accuracy of CT for determining PFO size compared with echocardiography. In addition, we did not use provocative maneuvers during CT (i.e., Valsalva maneuver). Use of such maneuvers could show occult PFO that might not otherwise be seen. These issues need to be addressed with larger prospective studies if cardiac CT is to have a role in the detection and characterization of PFO in the future.
In summary, our preliminary experience indicates that the detection of PFO using ECG-gated cardiac CT angiography performed using 64-MDCT is possible and yields high sensitivity and specificity for this diagnosis.
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  Y. J. Kim, J. Hur, C.-Y. Shim, H.-J. Lee, J.-W. Ha, K. O. Choe, J. H. Heo, E.-Y. Choi, and B. W. Choi Patent Foramen Ovale: Diagnosis with Multidetector CT--Comparison with Transesophageal Echocardiography Radiology, January 1, 2009; 250(1): 61 - 67. [Abstract] [Full Text] [PDF]
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