Intraoperative Detection of Persistent Endoleak by Detecting Residual Spontaneous Echocardiographic Contrast in the Aneurysmal Sac During Thoracic Endovascular Aortic Repair : Anesthesia & Analgesia

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Perioperative Echocardiography and Cardiovascular Education

Intraoperative Detection of Persistent Endoleak by Detecting Residual Spontaneous Echocardiographic Contrast in the Aneurysmal Sac During Thoracic Endovascular Aortic Repair

Imai, Hidekazu MD, PhD*; Ohashi, Nobuko MD, PhD*; Yoshida, Takayuki MD, PhD*; Okamoto, Takeshi MD, PhD; Kitamura, Nobutaka DDS, PhD; Tanaka, Takahiro PhD; Baba, Hiroshi MD, PhD*

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Anesthesia & Analgesia 125(2):p 417-420, August 2017. | DOI: 10.1213/ANE.0000000000002207
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Abstract

Endoleaks are one of the most common, yet unique, endograft-related complications. They are defined as the persistence of blood flow outside the graft but within the aneurysmal sac after endovascular repair. Persistent endoleaks may lead to aneurysmal sac expansion and rupture.1–3 A recent case report revealed that the change in character of spontaneous echocardiographic contrast (SEC) observed by intraoperative transesophageal echocardiography (TEE) could indicate successful closure of an endoleak during thoracic endovascular aortic repair (TEVAR).4 SEC is defined as a dynamic, smoke-like echo with a characteristic swirling motion, which implies entry of blood into the aneurysmal sac.5–7 As the SEC decreases, the echogeneity within the sac increases, indicating thrombus formation. However, whether residual SEC observed by intraoperative TEE can predict the incidence of a postoperative persistent endoleak remains unknown. Whether the observation of SEC disappearance and thrombus formation is a useful sign for confirming the absence of a postoperative persistent endoleak is also unclear. We hypothesized that patients with residual SEC observed by intraoperative TEE had a higher incidence of endoleaks on postoperative follow-up computed tomography (CT) after TEVAR than did patients without residual SEC. To test this hypothesis, we designed this observational study to examine the relationship between the presence of intraoperative residual SEC and the incidence of endoleak on postoperative follow-up CT examination in patients undergoing TEVAR.

METHODS

Study Population

The institutional ethics committee of Niigata University Medical and Dental Hospital, Niigata, Japan, approved this prospective observational study. All patients gave written informed consent for this study. The study was registered at University Hospital Medical Information Network (UMIN)-Clinical trial and registryas UMIN 000008939.

From July 2010 to June 2013, consecutive adult patients undergoing TEVAR for treatment of a descending thoracic aortic disease caused by an aneurysm, type B aortic dissection, or trauma were included in this study. Patients with contraindications to TEE were excluded.

Intraoperative Management

After induction of general anesthesia, a 5-MHz multiplane TEE probe was inserted and connected to an ultrasound system (ProSound ALPHA 10; Aloka, Tokyo, Japan). The baseline assessments of aortic diseases (morphological characteristics, diameter, and location of aneurysm; number and sites of intimal tears of aortic dissection) and cardiac function were comprehensively evaluated with TEE before performing the skin incision. After administration of IV heparin (60 U/kg) until the targeted activated clotting time of ≥200 seconds was achieved, the guidewire was inserted through the femoral artery and advanced under fluoroscopic and TEE guidance. The activated clotting time was maintained between 200 and 300 seconds during the procedure. The endovascular stent system was also delivered over the guidewire under fluoroscopic and TEE guidance. Subsequently, the TEE probe was withdrawn into the proximal esophagus to allow angiographic examination during endograft deployment. The endografts were deployed under fluoroscopic and angiographic control. Successive balloon expansions were performed to achieve tight contact between the endograft and the aortic wall. Next, angiography was performed to check for endoleaks; when present, additional balloon expansions were performed. If the endoleaks remained after the second additional balloon expansion, more endografts were placed. Finally, the placement system was removed. The mean arterial pressure was maintained at ≥70 mm Hg after endograft deployment to reduce the risk of spinal cord ischemia.

TEE Examination

F1
Figure.:
Change in the character of spontaneous echocardiographic contrast (SEC) within the aneurysmal sac. A, Short-axis view of a proximal descending thoracic aneurysm shows SEC outside the endograft but within the aneurysmal sac (arrow). B, Short-axis view of a proximal descending thoracic aneurysm at the same level as in (A) shows increased echo density within the aneurysmal sac, indicating thrombus formation (arrow).

Intraoperative assessment for residual SEC or thrombi within the aneurysmal sac was started immediately after removing the placement system and completed within 5 minutes before protamine injection. Identification of SEC did not alter the surgical procedure. SEC assessment was performed using standard views of the aortic arch and descending aorta (upper esophageal aortic arch long-axis view at 0° and short-axis view at 90°, mid-esophageal descending aorta short-axis view at 0° and long-axis view at 90°−110°).8 The criteria for assessment of residual SEC and thrombi were standardized among the anesthesiologists who performed the TEE examinations. Residual SEC was defined as observation of SEC in at least a fraction of the sac (Figure). A thrombus was defined as the absence of SEC within the sac regardless of its degree of high echo density. When we could not see even a fraction of the sac because of acoustic shadowing from the endograft, the patient was regarded as “unobservable” and was excluded from the final analysis. In patients with type B aortic dissection, we assessed the false lumen around the intimal tear. SEC around a distal entry tear was not considered an endoleak.9 TEE assessment was performed with the same settings for echocardiographic gain, compression, and transducer frequency before and after the endovascular procedure. To examine the association between the presence of residual SEC and the incidence of endoleak as simply as possible, we used only 2-dimensional imaging, not Doppler, for endoleak detection. The entire length of the endograft was scanned for detection of various endoleaks.10

Study Outcomes

The primary outcome was the presence of an endoleak at the first postoperative follow-up (within a few days after the surgery) using contrast-enhanced spiral CT. The secondary outcome was the presence of a persistent endoleak on CT at the 6-month postoperative follow-up. Additional postoperative intervention (secondary TEVAR, embolization, and open surgery) within 6 months was considered to indicate the presence of a persistent endoleak.

Statistical Analysis

Continuous variables are expressed as the mean ± SD and were compared using the Mann-Whitney U test. Categorical variables are expressed as the number of patients (%) and were compared using the χ2 test or the Fisher exact test. All reported P values are 2-sided, and the level of statistical significance was set at P < .05. Statistical analysis was performed using Stat-Flex software (version 6; Artech, Osaka, Japan).

Multivariable logistic regression analysis was used to adjust for confounding variables of the association between residual SEC and a postoperative endoleak. All variables associated with residual SEC at P < .05 and identified by the forward selection method were selected for inclusion in a logistic regression model.

According to our results, with 60 total patients (20 with SEC and 40 with thrombi), and assuming an observed incidence of 12 of 20 (60.0%) endoleaks in the SEC group and 5 of 40 (12.5%) endoleaks in the thrombus group detected at the first postoperative CT examination, we had about 90% power at a .05 significance level to detect an odds ratio (OR) of ≥10.5 and a difference in proportion with endoleaks of ≥0.475.

RESULTS

Seventy-seven patients underwent TEVAR for descending thoracic aortic disease during the study period. Patients with perioperative death, inadequate TEE records, or incomplete follow-up were excluded (Appendix). Nine patients assessed as “unobservable” were also excluded from the final analysis.

The 60 analyzed patients were divided into 2 groups: the SEC group, in which SEC was observed (n = 20), and the thrombus group, in which no SEC was observed (n = 40). The baseline demographic, preoperative, and intraoperative characteristics of the study patients are shown in Table 1.

T1
Table 1.:
Baseline Demographic and Perioperative Characteristics of Patients
T2
Table 2.:
Association Between Residual SEC and Postoperative Endoleak

As shown in Table 2, an endoleak was observed in 28.3% of patients on the first postoperative CT (60.0% of patients in the SEC group and 12.5% of patients in the thrombus group; P < .001). At the 6-month follow-up CT, a persistent endoleak was observed in 15.0% of patients (40.0% of patients in the SEC group and 2.5% of patients in the thrombus group; P < .001). The diagnostic accuracy of residual SEC is shown in Table 2. For example, residual SEC was found in 12 of 17 patients who had an endoleak at the first postoperative CT, for an estimated sensitivity of 0.71 (95% confidence interval [CI], 0.44−0.90).

T3
Table 3.:
Relationship Between Intraoperative Residual SEC and Postoperative Endoleak in Adjusted Models

In the multivariable logistic regression analysis adjusted for additional intraoperative balloon expansions, additional intraoperative endograft placements, and residual endoleaks detected by intraoperative angiography, the risk of postoperative endoleaks was increased by >3.2-fold (OR, 15.7; 95% CI, 3.2−77.7) and the risk of 6-month postoperative endoleaks was increased by >3.6-fold (OR, 43.8; 95% CI, 3.6−534.0) in patients with SEC versus thrombi (Table 3).

DISCUSSION

Patients with residual SEC had a significantly higher incidence of endoleaks within a few days postoperatively and at 6 months postoperatively than patients with thrombi. The postoperative endoleaks at the first postoperative CT examination closed spontaneously in 5 of 12 (41.6%) patients in the SEC group and in 4 of 5 (80.0%) patients in the thrombus group during the first 6 months after surgery. Persistent endoleaks are more clinically important than spontaneously closing endoleaks. The most important finding of this study is that the absence of SEC may identify patients with a very low risk of persistent endoleaks at 6 months postoperatively. Residual SEC had 0.89 sensitivity and 0.77 specificity for detecting a persistent endoleak at 6 months postoperatively. The positive predictive value of residual SEC was low in the setting of a 15% prevalence of persistent endoleaks. In contrast, the negative predictive value of residual SEC was extremely high. The prevalence of endoleaks in this study (28.3% at the first postoperative CT and 15.0% at the 6-month follow-up CT) was comparable with that in a recent review.11 According to Bayes’ theorem, the positive predictive value and negative predictive value in this study are presumed to indicate the posterior probability of an endoleak in the presence of residual SEC and that of no endoleak in the absence of residual SEC, respectively. The very high negative predictive value of residual SEC provides a clinical benefit for intraoperative management of patients undergoing TEVAR. Persistent endoleaks at 6 months postoperatively rarely occurred if no SEC was present within the aneurysmal sac, as shown by intraoperative TEE.

This study has several limitations. First, we designed the study to assess the possibility of residual SEC or thrombi after completing the endovascular procedure. The assessment did not alter the surgical procedure. However, this study was a nonrandomized, observational study. Therefore, we could not determine whether this intraoperative TEE assessment decreases the incidence of persistent endoleaks. Second, the small sample size of this study made it difficult to adequately adjust for confounding variables. Larger sample sizes would allow for more complete adjustment. Third, color flow Doppler was not used to detect endoleaks. Fourth, we did not assess the degree of SEC. The endoleaks detected at the first postoperative CT examination closed spontaneously in 40% of patients in the SEC group. The extent of some SECs was small; therefore, they may have been more likely to close spontaneously. Graded assessment of SEC might be more useful for detecting persistent endoleaks. Further studies are needed to determine its potential.

FU1

In conclusion, the incidence of persistent endoleaks at 6 months postoperatively is very low if no SEC is observed on intraoperative TEE. This study suggests that confirmation of the absence of SEC within the aneurysmal sac by intraoperative TEE may identify patients with a very low risk of persistent endoleaks after TEVAR.

DISCLOSURES

Name: Hidekazu Imai, MD, PhD.

Contribution: This author helped conceive and design the work; acquire, analyze, and interpret the data; and prepare the manuscript.

Name: Nobuko Ohashi, MD, PhD.

Contribution: This author helped analyze and interpret the data and prepare the manuscript.

Name: Takayuki Yoshida, MD, PhD.

Contribution: This author helped analyze and interpret the data and prepare the manuscript.

Name: Takeshi Okamoto, MD, PhD.

Contribution: This author helped acquire the data and prepare the manuscript.

Name: Nobutaka Kitamura, DDS, PhD.

Contribution: This author helped analyze and interpret the data.

Name: Takahiro Tanaka, PhD.

Contribution: This author helped analyze and interpret the data.

Name: Hiroshi Baba, MD, PhD.

Contribution: This author helped conceive the work.

This manuscript was handled by: Nikoloas J. Skubas, MD, DSc, FACC, FASE.

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