The potential role for ultrafast cardiac computed tomography in patients with stroke

CT angiography vs echocardiography for detection of cardiac thrombi in ischemic stroke: a systematic review and meta-analysis

BACKGROUND AND PURPOSE

Cardiac thrombi are an important cause of embolic stroke. We studied the diagnostic yield and diagnostic accuracy of cardiac CT angiography (CTA) compared to echocardiography for detection of cardiac thrombi in ischemic stroke patients.

METHODS

We performed a systematic review and meta-analysis of the literature on cardiac CTA versus echocardiography for detection of cardiac thrombi in ischemic stroke patients. We included studies (N ≥ 20) in which both cardiac CTA (index test) and echocardiography (reference test) were performed and data on cardiac thrombi were reported. Results were stratified for type of echocardiography: transesophageal (TEE) vs transthoracic (TTE).

RESULTS

Out of 1530 studies, 14 were included (all single center cohort studies), with data on 1568 patients. Mean age varied between 52 and 69 years per study and 66% were men. Reported time intervals ranged from 0 to 21 days between stroke and first test, and from 0 to 199 days between tests. In ten studies that compared CTA to TEE, CTA detected cardiac thrombi in 87/1385 (6.3%) patients versus 68/1385 (4.9%) on TEE (p < 0.001). In four studies comparing CTA to TTE, CTA detected thrombi in 23/183 (12.5%) patients versus 12/183 (6.6%) on TTE (p = 0.010). Pooled sensitivity and specificity of CTA versus TEE were 86.0% (95% CI 65.6-95.2) and 97.4% (95% CI 95.0-98.7), respectively.

CONCLUSIONS

CTA may be a promising alternative to echocardiography for detection of cardiac thrombi in patients with ischemic stroke, especially now that CTA is standard care for patient selection for endovascular treatment. However, studies were too heterogeneous and of insufficient methodological quality to draw firm conclusions. Large, prospective studies on this topic are warranted.

Preablation assessment for the left atrium: comparison of ECG-gated cardiac CT with echocardiography

RATIONALE AND OBJECTIVES

Evaluate the role of two-dimensional echocardiography and electrocardiographically (ECG)-gated contrast-enhanced multislice computed tomographic (MSCT) cardiac imaging to assess cardiac anatomy, specifically pulmonary venous anatomy and left atrial thrombus, in a selected group of patients before catheter-based atrial fibrillation ablation.

MATERIALS AND METHODS

Left atrial anatomy and associated findings in 34 consecutive patients scheduled for electrophysiologic testing who underwent both echocardiography and ECG-gated 16-slice MSCT cardiac imaging were retrospectively compared. Results from two-dimensional transthoracic echocardiography (TTE), cardiac MSCT, electrophysiologic study (EPS), and transesophageal echocardiography (TEE) (when performed) were taken from the official medical record without prior knowledge of this study when interpretation was rendered for clinical use. Electronic record review included: presence of left atrial thrombus (defined as constant filling defect on at least two echocardiographic views or filling defect on computed tomography) and location, pulmonary venous anatomy, and other cardiac, mediastinal, or pulmonary abnormalities.

RESULTS

Left atrial thrombus was identified by cardiac MSCT alone in five patients (15%). Pulmonary venous variants were identified with cardiac MSCT in two patients (6%). Both MSCT and echocardiography were normal in 17 subjects (79%). Echocardiography was better at identifying associated valvular abnormalities that were seen in 10 patients (29%). Cardiac MSCT angiography alone identified other cardiac and noncardiac abnormalities, including suspicious pulmonary malignancy, mediastinal adenopathy, and coronary stenosis in 15 patients (44%).

CONCLUSIONS

Echocardiography and cardiac MSCT angiography often provide complimentary findings during the preprocedural evaluation for patients with atrial fibrillation requiring ablation. Cardiac MSCT may provide significant additional information about the left atrium, mediastinum, coronary circulation, and visualized lung fields. Based on this study, we would advise that patients considered for radiofrequency ablation for uncontrolled right atrial fibrillation have both echocardiography and ECG-gated contrast-enhanced cardiac MSCT performed as part of the preprocedure evaluation.

Usefulness of electron beam tomography in the prone position for detecting atrial thrombi in chronic atrial fibrillation

OBJECTIVE

We compared the usefulness of electron beam tomography (EBT) in the prone position relative to that in the supine position for detecting atrial thrombi.

METHODS

We studied 96 patients with chronic atrial fibrillation, of whom 71 were scanned in the supine position and 25 were scanned in the prone position. Electron beam tomography was performed twice after contrast medium injection to obtain early- and late-phase images.

RESULTS

Filling defects were detected in 13 patients in the supine position by EBT. Transesophageal echocardiography (TEE) revealed a thrombus in the region of the filling defect in 9 patients. In 4 patients, filling defects in the left atrial appendage were not confirmed as thrombi by TEE. Filling defects were detected in 4 patients in the prone position, all of which were confirmed as thrombi by TEE.

CONCLUSION

Electron beam tomography in the prone position is an effective technique for reducing false-positive results in the detection of atrial thrombi.

Value of cardiac ultrafast computed tomography for detecting right atrial thrombi in chronic atrial fibrillation

We evaluated the accuracy of cardiac ultrafast computed tomography in diagnosing atrial thrombi in 70 patients with chronic atrial fibrillation, and identified the predictors of atrial thrombi from among clinical, echocardiographic, and ultrafast computed tomographic features. Ultrafast computed tomography identified 11 atrial thrombi in 9 patients: 4 patients had thrombi in the left atrium, 3 in the right, and 2 in both. Transthoracic echocardiography detected only 4 left atrial thrombi, and enlargement of the left or right atrium was associated with atrial thrombi (p <0.05).

Transesophageal echocardiography for detecting intracardiac thrombi in embolic stroke

The authors studied 56 patients with cardioembolic stroke to search for intracardiac thrombi by use of transesophageal and transthoracic echocardiography. Forty consecutive patients were examined within four weeks of stroke onset and the remaining 16 in the chronic stage. They also performed ultrafast computed tomography in 9 of them. Underlying heart disease was present in all subjects. Anticoagulant therapy had already been started in 29 at the time of examinations. Using their own criteria for echocardiography, they diagnosed intracardiac thrombus in 7 cases and valvular vegetation in 1. Six thrombi were located in the left atrial appendage, 4 of which were smaller than 10 mm in diameter. These small thrombi were not found by either transthoracic echocardiography or computed tomography. Transesophageal echocardiography appears to be superior to the other two methods, especially for detecting small intracardiac thrombi in the left atrial appendage.

Ultrafast CT and the cardiovascular system

Ultrafast computed tomography (CT) is a new imaging technique that relies on electron beam technology. Its rapid image acquisition speeds make it ideal for evaluating the cardiovascular system. The high-resolution, flow, and cine-modes are unique and provide complimentary information about cardiovascular anatomy, function, and flow dynamics. Ultrafast CT can provide quantitative measurements of cardiac output, ejection fraction, ventricular volumes, and ventricular mass as well as evaluation of segmental cardiac function. This technique can be used to assess coronary artery bypass graft patency as well as to screen for coronary artery calcium. Intracardiac thrombus or tumor, valvular disease, and disorders of the pericardium can be evaluated and characterized using ultrafast CT. The diagnosis of congenital lesions of the heart and great vessels is facilitated by this imaging modality, which can help determine complex anatomic abnormalities and quantitate shunt lesions. Acquired lesions of the great vessels, such as aortic dissection and aneurysm, can be diagnosed by ultrafast CT, which can also be used for serial examination and conservative management.

Is atrial fibrillation an independent risk factor for stroke?

That non-rheumatic atrial fibrillation is an independent risk factor for cerebral infarction has not been established with certainty. The rationale underlying contemporary clinical trials of warfarin therapy for the prevention of stroke in patients who have non-rheumatic atrial fibrillation is that the majority of strokes in such patients are due to cardiogenic cerebral embolism. However, there is evidence to suggest that the increased probability of stroke attributed to this arrhythmia is due to its association with other risk factors such as hypertension, diabetes mellitus, and atherosclerosis. The question of who should be anticoagulated is a major public health issue since atrial fibrillation is present in approximately ten per cent of the general population aged 65 or more years.