of Atrial Fibrillation
B. DEPICCOLI, A. ROSSILLO
Introduction
The ablation of atrial fibrillation by pulmonary vein antrum isolation (PVAI) through radiofrequency is an effective treatment of symptomatic, drug refractory arrhythmia. In this regard, transoesophageal echocardiography (TEE) is a useful tool to identify those patients eligible for the procedure [1]
and to monitor its possible consequences.
Transoesophageal Echocardiography Before Ablation
Before the procedure, TEE examination of the patients mainly focuses on the interatrial septum (IAS), left atrial (LA) cavity, LA appendage and pul- monary veins (PVs). In people affected by atrial fibrillation, the IAS often exhibits minor abnormalities, such as a floating movement, an aneurism, a patent fossa ovalis or increased thickening [2]. These abnormalities, espe- cially aneurism, can enhance thrombus deposition on the IAS surface; which constitutes a risk factor for embolic complications when the IAS is punc- tured by catheters aimed at the ostium of the PV. Conversely, a patent fossa ovalis can facilitate crossing of the IAS by the catheter; in this case, TEE can be used to determine the optimal approach to the PV.
The LA appendage is the structure most frequently involved [3] in car- diac thrombus formation; thus, it must be excluded before carrying out PVAI in order to avoid embolic complications. Spontaneous echo contrast (SEC) is also considered an embolic risk factor [4] and its presence and intensity are
Division of Cardiology, Cardiovascular Department, Umberto I Hospital, Mestre- Venice, Italy
strictly correlated with dilation of the LA appendage and reduction of its outward and inward flow velocities. Furthermore, Goldman et al. [5] used multivariate analysis to determine that an outward flow velocity < 20 cm/s correlated with the presence of thrombus, intense SEC and embolic events. If such information can be obtained for each patient, an optimal anticoagulant therapy before and during PVAI can be prescribed.
While LA morphology and contractility is adequately investigated by transthoracic echocardiography, TEE exhibits a higher sensitivity and speci- ficity in thrombus detection [6] and can thus be used before PVAI to prevent subsequent embolic events.
The PV–LA junction and the antrum around the vein are the critical zones involved in the application of radiofrequency (RF) for PVAI. It is therefore important to determine the number of PVs, their dimensions, anatomical vari- ants and the velocities of their flow in order to tailor the procedure to the indi- vidual patient. The most frequent variants are additional veins; these involve the right PV in near 30% of cases [7], and the common ostium, which involves the left PV in 10.5–32% of cases [1, 7, 8]. RF must be titrated only on the com- mon ostium, not on the mouth of the single vein, in order to avoid future steno- sis. Additional veins must also be treated since they can be the sites of foci trig- gering atrial fibrillation. Furthermore, the dimensions of the PV must also be determined before carrying out PVAI as it will facilitate choice of the best size Lasso catheter for use during the procedure.
Finally, by measuring the velocities (v) of pulmonary vein flow (pvf), we can calculate possible pressure gradients (gradient = 4v2) along the vein; that is, we can demonstrate PV stenosis, which is not a not rare occurrence in patients previously submitted to other ablation procedures, especially those done under the guidance of angiography or CARTO [9]. In this event, RF must be cautiously titrated so as not to worsen the anatomical features of the vein.
Transoesophageal Echocardiography During Ablation
The use of TEE in the cardiac electrophysiology lab during ablation has been reported in previous studies on RF treatment of supraventricular arrhyth- mias [10]. The method was shown to cause the prolonged discomfort of patients and was thus neglected after the introduction of intracardiac echocardiography.
Transoesophageal Echocardiography After Ablation
Early reports on the use of RF for PVAI in patients with atrial fibrillation [11] reported PV stenosis in subjects submitted to the procedure. Since then,
follow-up studies of the treated patients have been carried out using multidi- mensional computed tomography (CT) [12], nuclear magnetic resonance [13] and TEE [13]. Each of these approaches can document the variations in the dimensions of the PV over time. Nevertheless, the documented calibre of the PV depends on the section of vein explored by the imaging technique and therefore may not reflect the real narrowing of the vein, owing to its elliptical shape [8]. However, TEE can also be used to calculate pvf velocities, whose variation better reflects the functional impact of the stenosis.
Personal Experience
We have recently conducted a follow-up study of 79 patients (65 males, 14 females, mean age 57 ± 9.9 years) who underwent ablation for the treatment of atrial fibrillation. In this series, 34% were affected by paroxysmal, 40% by persistent, and 17% by permanent atrial fibrillation. Many of the patients (35%) were free from cardiac diseases, while hypertensive cardiopathy was the prevailing (27%) pathology.
At the beginning of the study, PVAI was guided by angiography or CARTO, and later by intracardiac echocardiography. Each patient was exam- ined by TEE both before and 48 h (first control), 3 months (second control) and 12 months (third control) after ablation.
A spiral CT was performed in each patient at the third month after the procedure, and was repeated at 6 and 12 months later in patients with sus- pected or certain PV stenosis.
In each study patient, the presence of IAS abnormalities such as floating movement, aneurism or shunt was searched for. In addition, the left atrium and LA appendage (LAa) were examined for the presence of thrombus, SEC, and we focused on the presence of a pericardial effusion. The dimension of each PV at the junction with the left atrium and the velocities of pvf by pulse wave were measured by Doppler. The peak (peak vel) and middle (mid vel) velocities and their ratio (mid vel/peak vel) were calculated.
Results
Qualitative Aspects
A floating IAS was documented in 33% and an aneurism in 4% of the study population. A patent fossa ovalis was observed in 10% of the patients at basal TEE. The incidence increased to 86% at the first control, but returned to the basal level of 10% at follow up. In 9% of the subjects, SEC with an intensity
≥ 2+/4+ was observed in the left atrium and LAa. The incidence increased to
19% at the first control but decreased subsequently. Thrombi were not detected at basal TEE or during the follow up. A pericardial effusion < 150 cc was observed in 26% of patients before ablation, and in 64%, with a maxi- mal amount of 500 cc, at the first control; however, at the time of follow-up, the incidence had decreased to the basal level.
Quantitative Features of the Pulmonary Vein
Three months after ablation (second control), the average size of the PV in the study population had decreased (Table 1) by 7.8% (P = 0.03 compared to the basal values). The peak vel increased by 34.4% (P = 0.0001), the mid vel by 47.27% (P = 0.0001), and the mid vel/peak vel by 8% (P = 0.002). At the last control, there was a further but not significant narrowing of the PV and an increase in the parameters measuring velocity.
Spiral CT, 3 months after ablation, showed a < 50% narrowing of the PV in 75 patients, whereas in three patients there was 50–70% narrowing of the PV. In one patient narrowing was > 70%.
In the first group of 75 patients, the peak vel was 73.6 ± 21.1 cm/s, mid vel 36.9 ± 13 cm/s, and mid vel/peak vel 0.49 ± 0.06. In the four patients with a PV narrowing > 50%, peak vel was 107.7 ± 57.5 cm/s (P = 0.009), mid vel was 58.3 ± 33.6 cm/s (P = 0.05), and mid vel/peak vel 0.54 ± 0.05 (P = 0.05). In each PV with a stenosis > 50%, peak vel was > 139 cm/s, mid vel was > 92 cm/s and mid vel/peak vel was > 0.66, with a more than 100%
increase compared to pre-ablation values.
Discussion
In present study, we observed a rather high prevalence of minor IAS abnor- malities that could facilitate supraventricular arrhythmias, above all atrial fibrillation. This hypothesis is in agreement with the results of other authors [2], who observed a higher prevalence of atrial fibrillation in the presence of pathological IAS.
Table 1.Variation of the parameters 3 months after ablation
Parameters (average values Basal 3 months Variation (%) P of the 4 pulmonary veins)
Dimension (mm) 13.7 ± 1.9 12.9 ± 1.8 ≠ 7.8 0.03
Peak velocity (cm/s) 56 ± 6.5 75 ± 24.4 ≠ 34.4 0.0001 Mid velocity (cm/s) 25.5 ± 8.4 37.8 ± 14.9 ≠ 47.27 0.0001 Mid velocity/peak velocity 0.45 ± 0.05 0.49 ± 0.06 ≠ 8 0.002
We did not detect a thrombus in the left atrium or LAa of any subject of the study population; in contrast with previous reports [14]. Nevertheless, we must emphasise that a high percentage of our patients was affected by parox- ysmal or persistent atrial fibrillation, while previous reports mainly relate to permanent atrial fibrillation. Furthermore, our patients had been previously anticoagulated and thus were in an optimal therapeutic range for at least 4 weeks before ablation.
One day after ablation, there was a high prevalence of pericardial effu- sion. Affected patients were completely asymptomatic and pericardiocenthe- sis was not necessary. Moreover the effusion had been reabsorbed by the end of the study. It is likely that the effusion originated from an inflammation of the pericardium following the delivery of RF to the thin posterior wall of the left atrium during PVAI.
PV stenosis after RF of PVAI has been reported in previous studies, in which imaging studies were carried out [1, 8, 13]. The features of PV narrow- ing may not always provide information about the physiological significance of the stenosis; in fact, symptoms can be absent despite a visible reduction of PV calibre (Fig. 1). By calculating pvf velocities, we were able to document variations with respect to the basal value obtained before ablation and thus better able to quantify the haemodynamic consequences of RF to the ostium of the PV.
Fig. 1.Transoesophageal echocardiography (TEE) image of a pulmonary vein stenosis.
The arrows point out the site of the stenosis. LA Left atrium, LSPV left superior pul- monary vein
Fig. 2.Doppler flow of a critically stenosed pulmonary vein. The spectrum shows a
‘plateau’ configuration
Fig. 3a, b.Normal pulmonary vein flow. a systolic wave, b diastolic wave
a b
Our study also showed that, on average, pvf velocities increased, implying a slight narrowing of the PV. Three months after ablation there was a further but not significant increase in pvf. Only an increase over the basal value of more than 100% identified a > 50% stenosis of the PV at spiral CT.
Moreover, the spectrum of the pulse-wave Doppler of the pvf of these patients was significantly altered owing to the large increase in the middle velocity. Figure 2 shows the Doppler flow spectrum of a patient with a PV stenosis > 70%. The peak vel was 210 cm/s, mid vel 120 cm/s and mid vel/peak vel 0.75. The normal systolic and diastolic waves (Fig. 3) are not dis- tinguishable and the entire flow exhibits a ‘plateau’ configuration. The sub- ject was symptomatic for dispnoea and haemoptysis and his stenosed left inferior PV was successfully treated by angioplasty and stent insertion.
Conclusions
TEE is a useful tool to investigate patients undergoing ablation therapy of atrial fibrillation. The technique provides important information about the presence of thrombus and SEC in the left atrium and LAa, and about minor IAS abnormalities, which seem to occur more frequently than in the normal population. Such information is necessary for planning the approach to the PV by catheters that must cross the septum and the atrial cavity.
After ablation, TEE can be used to monitor possible minor complications, such as a residual IAS shunt or pericardial effusion. It also allows the detec- tion of PV stenosis, a rare but dreaded complication of PVAI. A control TEE examination 3 months after the ablation procedure is probably adequate for this purpose.
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