Wern Yew Ding, MBChB
Atrial fibrillation (AF) is an established risk factor for thromboembolic events, including ischemic stroke. Therefore, identification of patients with this arrhythmia is important to facilitate the implementation of stroke prevention therapy using oral anticoagulation. Nonetheless, as a significant proportion of patients with AF remain asymptomatic, it remains largely under-diagnosed in the general population. Given that the source of emboli in the majority of AF-related strokes originates from the left atrial appendage (LAA), inclusion of this structure in imaging protocols may have a role in aiding the diagnosis of AF.
In a recent retrospective study of consecutive patients with ischemic stroke or transient ischemic attack, Senadeera and colleagues investigated the prevalence of computed tomography angiography (CTA)-detected LAA thrombus during hyperacute stroke imaging and evaluated the association between LAA thrombus and AF. The imaging protocol consisted of non-contrast CT, followed by CT perfusion and CTA from aortic arch to vertex. Two experienced physicians and pre-defined measures were used to assess for LAA thrombus on these scans.
Of 468 patients, 165 were excluded due to mimic stroke diagnoses (n=143) or inadequate CTA coverage (n=22). Among the remaining 303 patients, the median age was 74 years (IQR 66 – 84). The diagnosis of AF was present in 33% of patients at baseline. The overall prevalence of LAA thrombus was 6.6% in the whole cohort, rising to 14.9% in the subgroup with AF. Using multivariable regression analysis, AF was found to be independently associated with the presence of CTA LAA thrombus (OR 3.71 [95% CI, 1.25 – 11.01]), after adjusting for age and congestive heart failure. In conclusion, the authors suggest that LAA thrombus may be used as a potential radiological marker of AF.
Overall, the findings from this study are thought-provoking and support a potential role of routine LAA imaging as part of an acute stroke imaging protocol. In patients with a detected thrombus, early anticoagulation may prevent recurrent strokes.
However, there are several limitations that warrant our attention. As acknowledged by the authors, the use of a non-gated single-phase CTA may have under-estimated the true prevalence of LAA thrombus. Furthermore, one-third (34%) of patients in the ‘no LAA thrombus’ group had an indeterminate scan. This amalgamation of indeterminate and negative subgroups into a single ‘negative’ group creates potential for significant bias. In terms of LAA thrombus as a potential marker for AF, the sensitivity of this approach was only 15%, suggesting that it is not a reliable marker. Moreover, 25% (n=5) of patients with an LAA thrombus were not known to have AF.
