CARDIOVASCULAR JOURNAL OF AFRICA • Volume 34, No 3, July/August 2023 184 AFRICA in the apixaban group and 7.1% in the VKA group.8-10 It is worth noting that in these studies, TEE was not performed routinely. In the meta-analysis of the above studies (excluding the EMANATE study), the incidence of thrombus in the LAA was estimated to be approximately 5% in both the VKA and NOAC groups.29 A similar rate of thrombus occurrence was demonstrated by Frenkel et al., who analysed the results of TEE performed in 388 patients prior to AF/flutter ablation.30 A thrombus was detected in 4.4% of 183 patients treated with NOACs and in 2.9% of 205 patients treated with warfarin. In the NOAC group, a thrombus was found in 5.4% of 93 dabigatran users and 4.8% of 62 rivaroxaban users. Interestingly, no thrombi were recorded in the group of 28 patients treated with apixaban. In another study in which the results of TEE performed before electrical cardioversion of persistent AF (lasting at least seven days) were analysed among 127 patients treated with apixaban, the incidence of LAA thrombus was 5.5%.31 Furthermore, in a retrospective study of 559 patients in the Asian population, thrombi in the LAA were detected in 2.6 and 2.8% of patients treated with NOAC and VKA, respectively, despite prior anticoagulation treatment for a minimum of three weeks.32 Predictive factors of embolic material in the heart cavities It should be remembered that the thrombotic process in the LAA may take place despite adequate and long-term anticoagulation with the use of both vitamin K-derivative and non-vitamin K-derivative drugs. It is challenging to extract patients at high risk of LAA by thrombus appearance. Scales for the clinical risk of thromboembolic events in AF (CHADS2 and CHA2DS2VASc) can be helpful; both scales have the potential to predict LAA thrombus occurrence. Most studies showed a positive correlation with the scores 0.62 and 0.75 for the CHADS2 and CHA2DS2VASc scores, respectively. In studies by Uz et al. and Tang et al., which enrolled a total of 1 100 patients, no thrombus was detected in patients in the studies with a score of 0–2 and 0, respectively, on the CHA2DS2VASc scale.33,34 However, a low CHADS 2 score cannot reliably rule out embolic material in the LAA. In the ACUTE study, a thrombus was detected by TEE among 14 out of 138 patients without anticoagulant treatment, despite a CHADS2 score of 0. 35 Various biomarkers have been shown to increase the diagnostic utility of these scales in detecting thromboembolic material in the LAA. B-type natriuretic peptide concentration, mean red blood cell volume (MCV), mean platelet volume (MPV), uric acid concentration, eosinophil count and D-dimer levels provide additional prognostic information for the occurrence of embolic material.36-40 Among patients treated with anticoagulants, separate clinical factors such as chronic heart failure, age, female gender, structural heart disease, other cardiomyopathy, use of anti-arrhythmic drugs, duration of arrhythmia, and higher CHADS2 or CHA2DS2VASc scores may be helpful in identifying patients with a high probability of thrombus in the LAA.41-46 Echocardiographic predictors of thrombosis in the LAA include features and parameters assessing the structure and function of the heart as a whole, as well as the atrium or its appendage separately. It has been shown that a reduced ejection fraction (EF) (EF < 50%), hypertrophy, increased left ventricular end-diastolic pressure, left atrial enlargement [left atrium (LA) > 50 mm, LA area > 30 cm2, LA volume index > 28 ml/m2], or degree of spontaneous blood contrasting in the LA cavity may indicate patients with a higher risk of LAA thrombus.41-45,47-51 The LAAs differ in shape, size and orientation with regard to the surrounding structures.52 Based on pathomorphological studies, it is known that the LAA most often has two lobes (54%), and less frequently three lobes (23%), one lobe (20%) and four lobes (3%).53 The number of lobes has been shown to be an independent risk factor for thrombus occurrence, as is the higher position of the appendage and its increased volume.54,55 Based on computed tomography images, Di Base et al. divided the morphology of the LAA into four types: chicken wing (48%), cactus (30%), sleeve (19%) and cauliflower (1%).56 They demonstrated that cerebrovascular events were significantly more frequent in the group of patients with LAA morphologies other than the chicken wing. The reason for this dependence may be the lower flow velocity in non-chicken wingshaped appendices.57,58 Low LAA flow velocity is correlated with thrombus formation and ischaemic stroke.59,60 Should patients using NOACs for three weeks or more undergo TEE prior to electrical cardioversion? Based on the published results of the European Heart Rhythm Association (EHRA) survey containing knowledge about everyday clinical practice in 54 European clinical centres, it is known that TEE remains the most frequently performed imaging test before electrical cardioversion and AF ablation (94% of centres).61 But it has been shown that only 12% of centres perform this examination routinely before restoring sinus rhythm, regardless of the type and duration of the arrhythmia. There are currently discussions about the routine performance of TEE prior to electrical cardioversion. The latest 2021 EHRA guidelines for the use of NOACs in patients with AF recommend ruling out LA/LAA thrombus with TEE in case of doubt about treatment adherence or if deemed high risk for LA thrombus.62 However, the authors do not specify in which patients the risk of the incidence of embolic materials in heart cavities is elevated. Experts leave the decision to perform a TEE to the physician. It is difficult to compare results of VKA-based study with treatment with NOAC, but the findings of Siedl et al. are very interesting.63 In that study, the authors included patients with persistent AF and effective anticoagulation (receivingwarfarin for three or more weeks, with INR 2–3) and divided the population into two groups; 719 patients in which cardioversion was performed after TEE (TEE-guided approach) and 357 patients undergoing cardioversion without TEE. In the TEE-guided approach the thrombus in the LAA was observed in 7.7% of the patients. During the first four weeks after ECV, the rate of thromboembolic complications were 0.8 in both groups. These results suggest that TEE-guided ECV does not reduce the risk of embolism, and the thrombus, even if present, may not necessarily be dislocated to cause thromboembolic complications. Furthermore, thromboembolic complications may be caused by embolic material formed after ECV. New development of thrombus may be associated with the transient LA and LAA dysfunction (‘stunning’) caused by electric shock.64,65 Berger
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