Fibrillation Patients
F. ANTONINI-CANTERIN, G. ALLOCCA, D. RIVABEN, R. KORCOVA-MIERTUSOVA, R. PIAZZA, M. BRIEDA, E. HROVATIN, E. DAMETTO, F. ZARDO, G.L. NICOLOSI
Atrial fibrillation (AF) is the most common arrhythmia in adults, with a prevalence that increases from less than 1% in subjects aged below 60 years to more than 9% in those over 80 years old [1]. In recent years new and potentially curative therapeutic approaches have been developed [1]. Today, the role of echocardiography is very important in the assessment of the mor- phology and functionality of cardiac structures, risk stratification, and in guiding the management of AF. The guidelines consider two-dimensional transthoracic echocardiography (TTE) to be essential for the routine evalua- tion of patients with AF [2]. TTE should be performed in all AF patients to determine left atrial (LA) and left ventricular (LV) dimensions and LV wall thickness and function, and to recognise important underlying pathological conditions. TTE allows the identification of a possible aetiology of the FA, and the exclusion of occult valvular (particularly rheumatic mitral stenosis), myocardial, or pericardial disease. Lone AF, especially in young subjects, sug- gests a triggered mechanism that may be amenable to radiofrequency abla- tion. Abnormal myocardial LV relaxation is detectable from tissue Doppler imaging on the basis of reduced early diastolic mitral annular velocity or a reduced velocity of early mitral flow propagation [3].
The LA dimensions correlate with the probability of successful cardiover- sion and sinus rhythm maintenance. The anteroposterior LA dimension is usually calculated in the two-dimensional short axis view from M-mode imaging, while LA area or volume can be easily measured in four-chamber and two-chamber views from the apical approach. When the anteroposterior diameter of the left atrium is more than 45 mm, the likelihood of success in the maintenance of sinus rhythm after cardioversion is generally poor. It has
Unità Operativa di Cardiologia-ARC, A.O. S. Maria degli Angeli, Pordenone, Italy
been suggested that LA volume measurement could be a stronger predictor of AF than LA dimension alone [4]. In the Stroke Prevention in Atrial Fibrillation (SPAF) III study, LA function and size on TTE were independent predictors of thromboembolism [5]. Furthermore, transoesophageal echocardiography (TEE) maintains an important role in identifying appro- priate candidates for antithrombotic therapy and in guiding decisions regarding antiarrhythmic therapy. To evaluate the recovery of LA mechanical function after successful cardioversion, it is very important to detect the presence of LA stunning. Peak pulsed Doppler velocity of mitral inflow in late diastole produced by the atrial contraction wave (a-wave) was the initial parameter used to evaluate the LA function. An a-wave velocity above 50 cm/s is considered suggestive of atrial mechanical dysfunction. The mitral annular late diastolic velocity from tissue Doppler imaging can also be used as surrogate of LA function [6].
One of the most relevant sequelae of AF is its associations with throm- boembolic disease and stroke. About 90% of LA thrombi are located in the left atrial appendage (LAA), and the TEE is the modality of choice for detect- ing LAA thrombi. Modern multiplanar TEE can detect thrombi with a sensi- tivity and specificity of around 95–100% [7, 8]. The search for cardiac sources of embolism is currently the leading indication for a TEE study in many centres (about 40% of the indications) [9]. The SPAF III study identi- fied ‘high risk’ AF patients by TEE predictors of embolic events. These fac- tors included: the presence of LAA thrombi, LAA flow velocities below 20 cm/s, spontaneous echo contrast (smoke), ‘LAA sludge’, and complex aortic atheroma [5]. LAA emptying velocities can be assessed by TEE using pulsed wave Doppler imaging with the sample volume placed about 1 cm into the appendage itself. LAA smoke, identified as swirling echo density in the LAA and LA, is a marker of blood stasis that is associated with later development of LAA thrombus and with systemic embolisation. LAA sludge is a particu- lar, ‘viscid’ but not solid echodensity, and it represents a further stage along the continuum towards thrombus formation with a greater prognostic value than smoke. With the combination of a LA abnormalities and complex aortic atheromas among patients in AF (not on therapeutic warfarin doses), the annual incidence of embolic events was 20.8% as compared to 1.4% in absence of abnormal findings, while LAA emptying velocities above 40 cm/s predict a greater likelihood of sustained sinus rhythm 1 year after cardiover- sion [10].
In patients undergoing the pulmonary vein isolated procedure for AF ablation it is particularly important to perform TEE because it allows a more accurate assessment of systolic, diastolic, and atrial reversal flow velocities in pulmonary veins and can guide the catheter position [11].
Three-dimensional echocardiographic reconstruction enables excellent visualisation of LAA anatomy, dimensions, and function, with a high degree of accuracy in identifying a multilobed LAA (54% 3D vs 40% 2D ), but there are no differences between two- and three-dimensional reconstruction in the detection of thrombi [12].
Atrial flutter has traditionally been considered an organised arrhythmia carrying a low or no risk of thromboembolic events [13, 14]. More recently, however, several studies have shown that atrial thrombi (prevalence of 4–27%) and atrial spontaneous echo contrast (prevalence of 8–34%) may be detected during TEE in patients with atrial flutter. The FLutter Atriale Società Italiana di Ecocardiografia Cardiovascolare (FLASIEC) multicentre study found that the prevalence of thrombi in LAA is 1–6% and that of LA spontaneous echo contrast is 13% [15]. The results of this study confirm the finding that atrial flutter may be associated with atrial thrombi, although in a smaller percentage of patients than in those with AF. Furthermore, in patients with atrial flutter, reversion to sinus rhythm may lead to throm- boembolic complications, despite preliminary TEE results that are negative for thrombi, and this might be due to post-cardioversion atrial stunning.
Electrical cardioversion (EC) of patients with AF to sinus rhythm is fre- quently performed in symptomatic patients with elevated bleeding risk. In these patients EC offers the opportunity to relieve symptoms, improve car- diac performance rapidly, and possibly reduce cardioembolic risks and bleeding complications caused by prolonged anticoagulation. However, the EC procedure itself has an inherent risk of stroke due to possible embolisa- tion of pre-existing thrombi in the LAA. In the ‘conventional’ approach, to avoid thromboembolic events, stable patients with AF of more than 48 h or of unknown origin must achieve a therapeutic anticoagulation range for at least 3 weeks prior to the procedure [2]. There are many disadvantages in this conventional approach. The 3-week period of anticoagulation prior to EC is based essentially on the theoretical assumption of thrombus stabilisa- tion, but this interval is substantially empirical. In addition, with the conven- tional approach, extension of the interval until EC is attempted may reduce the initial success rate (about 86% of subjects) and the possibility of mainte- nance of sinus rhythm (about 50% at 1 year). Thus, conventional manage- ment necessitates a delay in the return of atrial function and increases the risk of post-cardioversion thrombus formation. The prolonged period of anticoagulation required by the conventional approach, which in routine clinical practice is often more than 6 weeks to reach a stable therapeutic INR level, can increase the risk of bleeding. The TTE-guided approach to EC with short-term anticoagulation offers some potential advantages over the con- ventional approach. TEE facilitates early EC without the need for prolonged
anticoagulation in low risk patients and in those in whom the risk of bleed- ing is high. TEE identifies also high risk patients with LA thrombosis in whom EC should not be performed. TEE should be used to confirm throm- bus resolution before EC is carried out in patients with previously docu- mented thrombus. After 7 weeks of anticoagulation, up to 80% of LA throm- bi are usually resolved. Finally, it has been postulated that earlier EC may increase the likelihood of successful return to and the maintenance of sinus rhythm [16].
The Assessment of Cardioversion Using Transo esophageal Echocardiography (ACUTE) multicentre study compared a TEE-guided strategy with short-term anticoagulation with the conventional anticoagula- tion approach [17]. There was no difference in the composite end-point of stroke, transient ischaemic attack, and peripheral embolism between the TEE-guided arm and the conventional arm (0.81% vs 0.50%; p = 0.50).
However, there was a significant difference in the composite end-point of major and minor bleeding between the TEE-guided arm and the convention- al arm (2.9% vs 5.5%; p = 0.02). There was no significant difference between the two arms in the 8-week maintenance of normal sinus rhythm, cardiac deaths, or cardioversion-related deaths. The results of this randomised study suggested that the TEE-guided approach with short-term anticoagulation may be considered as a clinical alternative to the conventional approach [17]. In combination with low-molecular-weight heparin, TEE-guided car- dioversion may be considered a safe and clinically effective alternative to the conventional treatment strategy for the patients with AF, as recently demon- strated in the Anticoagulant in Cardioversion using Enoxaparin (ACE) trial [18]. Currently, the ACUTE II trial, a randomised study, is in progress evalu- ating the use of low-molecular-weight heparin in comparison with intra- venous heparin as a bridge therapy to warfarin [19].
However, the decision to use one approach or the other is based on the individual characteristics of the patient, the experience of the physician and the centre, and the accessibility of the technique. These factors should be taken into consideration in choosing the best approach: (1) a severity of symptoms and haemodynamic effect of AF that require immediate EC; (2) level and chronicity of anticoagulation; (3) risk of bleeding; and (4) risk and likelihood of left atrial thrombi and risk of recurrence of AF, which require prolonged anticoagulation [16].
Intracardiac echocardiography (ICE) has been recently introduced in this setting. It is performed with a 6- to 12-MHz transducer placed into the right atrium via a 6–8F sheath in the right femoral vein. A high resolution multiple frequency transducer allows tissue penetration enhancement, thus allowing depth control. The ultrasound probes offer the same modalities as TEE,
including colour, pulsed wave, and continuous wave Doppler, to allow assess- ment of the intracardiac flow. ICE has been used successfully to guide catheters during radiofrequency catheter ablation (RFCA) of the pulmonary veins or to visualise their ostia and to monitor the occurrence of acute pul- monary vein stenosis after RFCA at the site of the pulmonary veins, as well as, more recently, for percutaneous closure of the LAA [20, 21]. Continuous imaging with ICE can be performed during RFCA by the operator, and it facilitates trans-septal puncture and guides placement and optimal tissue contact of mapping and ablation catheters. In addition, it allows identifica- tion of LA thrombi before the procedure. ICE also facilitates instant detec- tion of important potential complications such as pericardial effusion or tamponade, and may reduce the frequency of these complications. In up to 40% of patients an asymptomatic increase of peak systolic flow velocities in the pulmonary veins has been observed after RFCA. Progression to pul- monary vein stenosis after ablation is rare; more commonly, the degree of narrowing remains stable or even improves. Many patients with severe nar- rowing or complete occlusion of a single pulmonary vein are asymptomatic.
Using TEE, the pulmonary vein ostia can be easily visualised for the evidence and assessment of stenosis [20, 21].
Percutaneous closure of the LAA is a new approach. It was initially per- formed in an early clinical experience with insertion of the device into the LAA, which was facilitated by ICE, allowing optimal positioning of the device itself [22]. The surgical Maze III procedure (excision or ligation of LAA, iso- lation of the pulmonary veins) abolishes AF in a significant number of patients. Intraoperative TEE can play a major role, with assessment of the efficacy of ligation by Doppler imaging [23].
In conclusion, echocardiography is a unique and very important tech- nique in the management of AF patients, allowing a non-invasive and easily repeatable evaluation of cardiac anatomy and function. In addition, the TEE approach allows reliable exclusion of the presence of LA thrombosis, guiding the best clinical management of AF patients in different stages of the disease.
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