Detecting Left Ventricular Thrombi
September 1, 2023 4 minutes read
By Michael H. Crawford, MD, Editor
SYNOPSIS: A study of early post-ST-elevation myocardial infarction patients who underwent echocardiographic testing and cardiac MRI showed echo misses about two-thirds of cardiac MRI-discovered left ventricular thrombi. However, an echo apical wall motion score can identify most patients in whom echo may miss thrombi for the selective use of cardiac MRI.
SOURCE: Reindl M, Lechner I, Holzknecht M, et al. Improved detection of echocardiographically occult left ventricular thrombi following ST-elevation myocardial infarction. Eur Heart J Acute Cardiovasc Care 2023; Jun 22: zuad069. doi: 10.1093/ehjacc/zuad069. [Online ahead of print].
After a patient experiences a ST-elevation myocardial infarction (STEMI) and is treated by percutaneous coronary intervention (PCI), cardiologists usually order transthoracic echocardiography (TTE). But what about TTE’s sensitivity for detecting left ventricular (LV) thrombus, even when using echo contrast? How does that compare to cardiac MRI.
Reindl et al enrolled 870 first STEMI patients (mean age, 57 years; 17% were women) who were revascularized by primary PCI between 2011 and 2022. These patients could undergo cardiac MRI and had undergone a TTE within the first week after primary PCI. Using echo contrast was at the discretion of the examiner. Clinicians performed TTE within a mean of 15 hours of MRI, at an average of three days post-primary PCI. TTE segmental wall motion analysis used the 16 segment model. Each segment scored as: 1 = normal wall motion, 2 = hypokinesis, 3 = akinesis, and 4 = dyskinesis. There were four apical segments in this model: The apical anterior and apical inferior segments were seen in the apical two-chamber view; the apical septal and apical lateral segments were seen in the four-chamber and apical long axis views.
The severity of wall motion abnormalities at the apex in the 16-segment model of the LV correlated best for predicting TTE occult thrombi detected by cardiac MRI (HR, 1.74; 95% CI, 1.47-2.06; P < 0.001; AUC, 0.91), and was independent of LV ejection fraction, body mass index, and angiographic culprit lesion. With an apical wall motion score of 8 or higher (30% of the total population), the incidence of TTE occult thrombi was 10%, resulting in a sensitivity of 100%, a specificity of 77%, and a number needed to perform a cardiac MRI of 10 to detect one TTE occult thrombus. The authors concluded assessing TTE LV apical wall motion was a simple and robust way to select patients after acute STEMI for additional cardiac MRIs to detect thrombi not seen on TTE.
COMMENTARY
When thrombi form in the LV after a STEMI, they almost always are in the apex, which often is the most difficult part to image adequately by two-dimensional echocardiography. Cardiac MRI remains expensive and limited in its availability. Thus, exploring how to pick the patients who are most likely to show TTE-detected occult thrombi is a worthwhile endeavor.
Reindl et al demonstrated using the wall motion score of 8 or higher in the four apical segments of the 16-segment LV wall motion analysis was the best predictor of TTE occult thrombi, with sensitivity of 100% and an AUC of 0.91. However, the apical wall motion score of 8 or higher carried a specificity of 77%. This means about one-quarter of cardiac MRIs would not show thrombi. This seems like a reasonable number compared to ordering cardiac MRI for all STEMI patients. Body mass index also was a multivariate predictor of occult TTE thrombi, but of weaker significance and it did not improve the AUC of the apical wall motion score. Also, since it was related to TTE occult thrombi but not apparent thrombi, it probably is related to image quality. However, the authors suggested that it could be considered a cofactor for choosing whom to select for cardiac MRI.
There were limitations to the Reindl et al study. Few patients had undergone contrast-enhanced echo, which could be a better way to detect LV thrombi. Perhaps if contrast were ordered for every early post-STEMI patient, there would be less need for cardiac MRI. The median day post-STEMI on which researchers conducted the cardiac MRI was day 3 (interquartile range, 2-5); some LV thrombi could have been missed. However, the optimal timing of imaging to detect post-STEMI LV thrombi has not been defined. All 25 cardiac MRI-detected thrombi patients were treated with anticoagulation, but few of the others were (overall anticoagulation rate = 7%).
Anticoagulation therapy is controversial after STEMI, partly because the incidence of thrombi is low (4% in the Reindl et al study), and the stroke or systemic emboli frequency is even lower. Therefore, it makes sense to concentrate our efforts for preventing systemic emboli on patients at highest risk. If cardiac MRI is not available where you practice, then anticoagulating those identified at highest risk would be a reasonable option.
A study of early post-ST-elevation myocardial infarction patients who underwent echocardiographic testing and cardiac MRI showed echo misses about two-thirds of cardiac MRI-discovered left ventricular thrombi. However, an echo apical wall motion score can identify most patients in whom echo may miss thrombi for the selective use of cardiac MRI.
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