Kevin S. Attenhofer, MD
As has been reviewed in this blog many times before, embolic stroke of undetermined source (ESUS) is a novel clinical construct that is a hot topic for emerging diagnostic and therapeutic strategies. While many studies are evaluating methods to increase the detection rate of covert atrial fibrillation in this population, the authors of this paper demonstrate improved detection of left ventricular (LV) thrombi in ESUS patients using cardiac MRI versus TTE.
Currently, echocardiography is the test of choice when evaluating for intra-cardiac thrombus. Transesophageal echocardiography (TEE) is the gold standard technique for detecting left atrial or left atrial appendage thrombi. Transthoracic echocardiography (TTE) is used to evaluate the presence of LV thrombus, patent foramen ovale, depressed ejection fraction, etc. Recently, contrast enhanced cardiac magnetic resonance imaging (CE-CMR) has shown significantly better sensitivity than TTE for the diagnosis of LV thrombus (cardiac studies suggesting sensitivity of TTE was 40%, compared with 88% for CE-CMR) in patients with a history of myocardial infarction (MI) or LV dysfunction (LVEF < 30%).
In this study, the authors prospectively investigated 105 acute ischemic stroke patients with a history of MI or LVEF < 50%. Importantly, 45 patients were excluded up front. Most of these patients were excluded because of an inability to tolerate the CE-CMR itself: presence of metal implants, low GFR prohibiting contrast administration, or severe medical disease precluding safe transfer to MRI suite. Non-contrast cardiac MRI (cine-CMR) was not used. Previous cardiac studies have found cine-CMR to be less suitable for LV thrombus detection.
All 60 patients underwent CE-CMR and TTE. 12 (20%) patients were determined to have LV thrombus on CE-CMR while only 1 patient had an LV thrombus identifiable on TTE (p = 0.04). TTE could not identify 8 small (< 1 cm) apical thrombi and 3 lateral or posterior mural thrombi (see Figure). 14 of the 60 patients were determined to be ESUS by the investigators. 4 out of 14 ESUS patients (29%) were found to have LV thrombus on CE-CMR. 3 of these thrombi were not seen on TTE and likely would have gone undiagnosed without CE-CMR.
The investigators have demonstrated increased efficacy of CE-CMR over TTE for the diagnosis of LV thrombus in acute stroke patients with a history of MI and LV dysfunction; however, this benefit may not be easily applicable to the larger stroke population. Cardiac MRIs are not readily available in all centers and, as demonstrated in the authors’ exclusions, almost half of their patients were unable to tolerate CE-CMR. Their population was also limited to those patients seen at a single Japanese center, with a risk factor profile that is not well matched to the stroke population seen in western countries.
As cardiac MRI becomes more readily available, it may certainly find a role in the evaluation of the ESUS patient.