Clinical outcomes and predictors of success with Impella weaning in cardiogenic shock: a single-center experience

Introduction

Cardiogenic shock (CS) is a severe syndrome with poor prognosis. Short-term mechanical circulatory support with Impella devices has emerged as an increasingly therapeutic option, unloading the failing left ventricle (LV) and improving hemodynamic status of affected patients. Impella devices should be used for the shortest time necessary to allow LV recovery because of time-dependent device-related adverse events. The weaning from Impella, however, is mostly performed in the absence of established guidelines, mainly based on the experience of the individual centres.

Methods

The aim of this single center study was to retrospectively evaluate whether a multiparametrical assessment before and during Impella weaning could predict successful weaning. The primary study outcome was death occurring during Impella weaning and secondary endpoints included assessment of in-hospital outcomes.

Results

Of a total of 45 patients (median age, 60 [51-66] years, 73% male) treated with an Impella device, 37 patients underwent impella weaning/removal and 9 patients (20%) died after the weaning. Non-survivors patients after impella weaning more commonly had a previous history of known heart failure (p = 0.054) and an implanted ICD-CRT (p = 0.01), and were more frequently treated with continuous renal replacement therapy (p = 0.02). In univariable logistic regression analysis, lactates variation (%) during the first 12-24 h of weaning, lactate value after 24 h of weaning, left ventricular ejection fraction (LVEF) at the beginning of weaning, and inotropic score after 24 h from weaning beginning were associated with death. Stepwise multivariable logistic regression identified LVEF at the beginning of weaning and lactates variation (%) in the first 12-24 h from weaning beginning as the most accurate predictors of death after weaning. The ROC analysis indicated 80% accuracy (95% confidence interval = 64%-96%) using the two variables in combination to predict death after weaning from Impella.

Conclusions

This single-center experience on Impella weaning in CS showed that two easily accessible parameters as LVEF at the beginning of weaning and lactates variation (%) in the first 12-24 h from weaning begin were the most accurate predictors of death after weaning.

Temporal trend mortality and in-hospital mortality predictors in an ischemic cardiogenic shock population: a 10 years single-centre retrospective study

Background

Cardiogenic shock (CS) after acute myocardial infarction (AMI) is a life-threatening condition with an high rate of in-hospital mortality.

Purpose

This study aims to 1) describe predictors of in-hospital mortality; 2) evaluate ten years mortality temporal trend in our Cardiac Intensive Care Unit (CICU); 3) assess the feasibility of CARDSHOCK risk score in our population; 4) elaborate a simpler version of CARDSHOCK risk score.

Methods

All consecutive patients with CS after AMI admitted at our CICU from March 2012 to July 2021 were included in this single-centre retrospective study.

Results

We included 167 patients [males 67%; age 71 (61–80) years] with ischemic CS. Patients had severe LV dysfunction in 66%. Baseline serum lactate was 5.2 (3.1–8.8) mmol/L. All patients required inotropes: 71% required dopamine [mean dose 5.6 (2.4–11,3) mcg/kg/min], 65% required noradrenaline [mean dose 0.10 (0.05–0.18) mcg/kg/min], 32% required dobutamine [mean dose 4.5 (2.2–15.9) mcg/kg/min]; 17.4% received levosimendan alone [mean dose 0.1 mcg/kg/min]. Mechanical cardiac support (MCS) was pursued in 91.1% [65% IABP, 23% Impella CP, 4% VA-ECMO]. From March 2012 to July 2021 we observed a significative temporal trend mortality reduction (OR=0.90, 95% CI: 0.84–0.96, p=0.0015), in particular in-hospital mortality has reduced from 57% of first time-quartile to 29% of the fourth quartile (Figure 1). In addition we also noted a significant increase in Impella catheter use (p=0.0005) with a consequent reduction of IABP (p=0.01), a reduction in dopamine administration (p=0.0007) and a greater use of dobutamine and levosimendan (p=0.015 and p=0.0001). In our population of AMI-CS patients CARDSHOCK risk score was a reliable in-hospital mortality predictor tool (OR 1.11; 95% CI, 1.06–1.17; p=0.00011). After the multivariate analysis only ejection fraction (EF) at baseline (OR=0.99, 95% CI: 0.98–0.99, p=0.009), lactate level at presentation (OR=1.03, 95% CI: 1.01–1.06, p=0.015) and presence of three-vessels coronary artery disease (OR=0.73, 95% CI: 0.59–0.90, p=0.0038) resulted to be in-hospital mortality predictors. For this reason, a prediction model composed by those three variables was created which exhibited better predictive performance for in-hospital mortality than Cardshock risk score (AUC of 0.94 vs AUC of 0.72 respectively, p=0.015) (Figure 2).

Conclusions

In our retrospective single-centre study a significant reduction of mortality through the years is observed, probably due to more extensive use of micro axial pumps and better manipulation of inotropic drug therapies. The use of Cardshock risk score has been proven to be a feasible tool in prediction on in-hospital mortality also in our sample composed only of AMI-CS patients. In addition, a more simplified risk score made up of only three clinical variables demonstrates at least the same predictive performance. Future validation in a larger population could be advisable to validate the simplified score.

Funding Acknowledgement

Type of funding sources: None.

P50 IMPLEMENTATION OF PROTOCOLS FOR “ENHANCED RECOVERY AFTER CARDIAC SURGERY” IN AORTIC VALVE SURGERY

Objective

Although, the use of protocols for “enhanced recovery after surgery” (ERAS) have been associated with improved results in different surgical disciplines, no data are available for EARS in cardiac surgery, thus far. In the late 2016 a mutlidisciplinary ERAS program to treat patients who require AVR was implemented in our institution. The aim of this study was to assess safety and 30 day outcomes in patients receiving ERAS management.

Methods

To improve multidisciplinary ERAS program, our mini–invasive approach (Fig. 1), that goes beyond a small incision, includes: (i) mini–surgical access (ministernotomy–minithoracotomy), to reduce the traumatic impact, postoperative pain and to increase patient’s satisfaction; (ii) minimal invasive extracorporeal circulation system, to improve end–organ protection and decrease systemic inflammatory response; (iii) ultra fast–track anaesthesia, to decrease the rate of postoperative complications and assure better and earlier recovery (Fig. 2).

Results

Between September 2016 and December 2021, 600 consecutive patients (mean age 72 years, Euroscore II 1,62%) underwent isolated mini–AVR in our institution. UFT anaesthesia was used in 195 patients (32.5%) and MiECC in 173 (28.8%). All patients received a timely rehabilitation therapy (3–6 hours after surgery) and an early family contact in ICU. At 30 days, the overall mortality and stroke rates were 0,3% (n = 2) and 0,5% (n = 3), respectively. Respiratory insufficiency occurred in 16 pts (2,5%). Median blood loss at 12 hours was 174,5 cc; blood transfusions were reduced to minimum intraoperatively and avoided in 66% of patients. Twenty three patients (3,8%) received definitive pacemaker implantation. The median ICU and in–hospital lengths of stay were 1 and 6 days, respectively.

Conclusions

Findings from our study confirms that mini–AVR yields excellent clinical outcomes with very low mortality and morbidity rates. The implementation of ERAS protocol in patients undergoing mini–AVR demonstrated to be safe and was associated with promising results. Thus, by reducing surgical injury and promoting faster recovery, ERAS management may further enhance minimally invasive interventions.

C13 COMPARISON OF MINIMALLY INVASIVE VERSUS CONVENTIONAL THORACIC AORTIC OPERATIONS: EARLY AND MID–TERM RESULTS IN A SERIES OF 624 PATIENTS

Objective

Despite minimally invasive techniques have gained wider clinical application in cardiac surgery, current evidence on mini thoracic aortic surgery is still limited. The aim of this study was to compare early and mid–term outcomes of patients undergoing proximal thoracic aortic interventions through mini–sternotomy (MS) versus full sternotomy (FS).

Methods

Data from 624 consecutive patients undergoing proximal aortic operations through MS (n = 214, 34.3%) and FS (n = 410, 65.7%) at 2 aortic centers, were analysed. Patients with prior cardiac operations and active endocarditis, and those who underwent emergency operation and combined procedures were excluded. Treatment selection bias was addressed by the use of propensity score matching (MS vs FS). After matching, 2 well–balanced groups of 202 patients each were created. Surgical procedures involved aortic valve replacement/repair and ascending aorta replacement in 190 patients (47%), aortic root replacement in 110 patients (27.2%) and isolated ascending aorta replacement in 104 patients (25.7%).

Results

The median cardiopulmonary bypass and cross clamp times were 88 and 68 minutes, respectively, with no difference between groups. Overall 30–day mortality was 0.7%, being 1% (n = 2) in patients underwent MS and 0.5% (n = 1) in those underwent FS (p = 0.6). No difference was found in the rates of stroke (MS n = 5, 2.5%; FS n = 5, 2.5%), dialysis (MS n = 1, 0.5%; FS n = 4,2%), bleeding (MS n = 7, 3.5%; FS n = 7, 3.5%), and blood transfusions (MS n = 67, 33.3%; FS n = 57, 28.4%) (Table 1). Patients receiving MS were associated with a lower incidence of respiratory insufficiency compared with those receiving FS (0% vs. 2.5%, p = 0.03). The median intensive care unit length of stay was 24 and 25 hours in MS and FS group, respectively (p = 0.3), and in–hospital stay was 7 days both in MS and FS group (p = 0.9). Three–year survival rate was 96.6% in patients receiving MS and 95.7% in those receiving FS (p = 0.9).

Conclusions

Our findings showed that mini proximal aortic operations can be performed successfully without compromising the proven efficacy and safety of conventional access. In selected patients, MS was associated with very low mortality and morbidity rates. Additionally, MS demonstrated superior clinical outcomes as regards respiratory adverse events, when compared with FS.

C17 SIMPLIFIED MINIMALLY INVASIVE MITRAL VALVE SURGERY THROUGH A DIRECT VISION TRANSAXILLARY APPROACH: PROCEDURAL AND 30–DAYS OUTCOMES

Background

Minimally invasive cardiac surgery through right mini–thoracotomy access is nowadays an established approach for the treatment of mitral valve pathologies. Several thoracic incisions have been described and different techniques used for cardiopulmonary bypass, myocardial protection and valve exposure. Aim of this study is to review our early results with a minimally invasive approach characterized by a lateral right trans–axillary (TAx) approach and direct vision.

Methods

Prospectively collected data of patients who underwent mitral valve surgery between 2018 and 2021 were reviewed. Among them, 245 patients underwent minimally invasive mitral valve surgery through TAx access. A single incision at the fourth right intercostal space on the anterior axillary line, 3–to–5 cm in length (Fig 1), allowed a 90° direct view exposure of the mitral valve (Fig 2) and the subvalvular apparatus (Fig 3). A transthoracic clamp was invariably used to achieve the cardioplegic arrest.

Results

Mean age of the patients was 63 years and the mean EuroSCORE II was 1.6. Regurgitation was the prevalent mitral valve dysfunction (91%). Mitral valve repair was performed in 87% of the cases using several techniques including a combination of annuloplasty, leaflet resection and sliding, placement of neochordae and repair of the commissures. In patients with degenerative disease, the rate of valve repair was 92%. Tricuspid annuloplasty was associated in 10% of the cases. There was no in–hospital death; the rates of postoperative stroke and TIA were 0.4% and 1.2%, respectively. Median mechanical ventilation time was 3 [0–6] hours with 40% of the patients extubated in theatre at the end of the procedure. Median ICU stay was 24 [21–46] hours. Three patients had superficial complications of the thoracic wound and in 7 cases of the groin incision. After a median time of 7 [6–8] days, all the patients were successfully discharged from the hospital. The pre–discharge echocardiogram revealed none or trace residual mitral regurgitation in up to 96% of the patients who underwent mitral valve repair with a mean gradient across the valve of 3 [2–4] mmHg.

Conclusions

The TAx approach for minimally invasive mitral valve surgery is safe and allows a quick functional recovery. A superb direct view of the mitral apparatus and the ascending aorta, facilitates the exposure and the surgical repair of the valve with no need of any endoscopic nor an endoaortic balloon occlusion system support.

P47 MITRAL VALVE REPAIR FOR INFECTIVE ENDOCARDITIS: A PROPENSITY MATCHED STUDY

Background

The clinical benefits of mitral valve repair over replacement in the setting of mitral infective endocarditis remain not clearly established. We aim to review the clinical experience in mitral valve surgery for infective endocarditis looking at mid–term survival.

Methods

Prospectively collected data of patients who underwent cardiac surgery for infective endocarditis between 2001 and 2021 at two cardiac centres were reviewed. Among them, 282 patients underwent native mitral valve surgery and were included in the study. Nearest–neighbour propensity score matching, including twelve preoperative variables, was performed to account for differences in patients’ profile between the repair and replacement subgroups.

Results

In the unmatched populations, mean age of the patients was 60±15 years and 72% were male. Active infective endocarditis was described in 226 cases (80%). Thirty–four patients (12%) suffered cerebral embolism and in 10% of the cases preoperative inotropic support and/or mechanical ventilation were required. Associated procedure were CABG, aortic valve replacement and tricuspid valve repair, 13%, 36% and 9% of the cases, respectively. Mitral valve repair was performed in 96 cases (32%). Overall in–hospital mortality was 6.7% and was not significantly different between patients who underwent repair or replacement of the mitral valve (7.2% vs 6.4%, p = 0.79). Propensity matching provided 72 well–matched pairs. Mean age was 59±15 years, 75% of the patients were male. Sixteen patients (11%) had a recent cerebral event. An emergency operation was carried out in 15% of the cases, 10% of the patients presented a NYHA class>III and 14 patients (10%) underwent a redo procedure. CABG and aortic valve replacement were associated in 14% and in 35% of the cases, respectively. Overall in–hospital mortality was 6.9% with no difference between the repair and the replacement cohorts 9.7% vs 4.2%, respectively (p = 0.19). Survival probabilities at 1–, 5– and 10–years were 89%, 71% and 67%, respectively after mitral repair, and 90%, 77% and 57%, respectively after mitral replacement; log–rank p = 0.90.

Conclusions

Mitral valve repair was associated with acceptable in–hospital mortality and survival in a high–risk and comorbid cohort of patients with mitral valve infection. We found no difference in early and mid–term survival between patients who underwent repair or replacement of the mitral valve in the setting of infective endocarditis.

P13 COMPLETE ATRIOVENTRICULAR BLOCK IN A 52–YEAR–OLD MAN ASSOCIATED WITH LYMPHATIC CANCER WITH CARDIAC INVOLVEMENT

A 52–year–old man arrived at the local emergency room for worsening dyspnea and asthenia, present for about a month, but significantly worsening during the night of the access. The ECG (Figure 1) revealed complete AtrioVentricular Block (ABV) with a narrow–QRS junctional escape rhythm, with a heart rate of about 30 beats per minute (bpm). The other vital parameters were within the normal limits and no anomalies were detected on the physical examination. Medium–dose intravenous isoprenaline infusion was immediately started, with an increase in the junctional escape rate up to 50 bpm. The patient also underwent chest x–ray, which showed interstitial thickening in the pulmonary hilus, which was judged to be nonspecific. The blood chemistry was normal and the echocardiogram (Figure 2) did not show any abnormalities. Since there were no apparent reversible causes of the complete AV block, on the next day, a bicameral pacemaker was implanted via the left cephalic vein. The procedure was uneventful and the patient was discharged home two days later, in good general condition. Eight days after the discharge, surgical wound control and pacemaker control were performed, with completely normal parameters. About 15 days after the discharge the patient went back to the local emergency room for dyspnea and fever. Chest Computed Tomography (CT) without contrast medium was performed, which revealed the presence of widespread pathological mediastinal lymphadenopathy. Therefore, the patient was admitted to the internal medicine ward. An in–depth diagnostic was performed first with thoraco–abdominal angio–CT, then with Positron Emission Tomography (PET)–CT (see Figure 3), which revealed the presence of diffuse areas of fixation of the radio–drug (18F–Fluorodeoxyglucose –FDG–), at the ilo–mediastinal, hepatic, pulmonary, retrocrural, retrocaval, iliac, supra and subclavicular, and also cardiac area (activation of interatrial brown fat and between aortic root and the superior vena cava). The patient was therefore transferred to another hospital for diagnostic investigations and lymphoma therapy. In the light of the picture that emerged, the arrhythmological disease was considered to be referred to the cardiac involvement of the oncological disease; to date there are few similar cases described in the literature. Legend of the figures: Figure 1: ECG at the admission Figura 2: Echocardiogram at the admission Figura 3: PET / CT with myocardial areas of 18F–FDG fixation.

Octogenarian with an untreated femoral neck fracture: upright position during the postoperative course after aortic valve replacement

We describe a patient with a femoral neck fracture undergoing an aortic valve replacement. The study design was a case report. An 82-year-old female with an untreated right femoral neck fracture, and a severe aortic valve stenosis was admitted to a cardiac surgery department for surgical treatment of the valve disease. She underwent aortic valve replacement with a sutureless biological valve prosthesis through a partial sternotomy. At an early stage, the patient was instructed to make postural changes in the standing position. As a result, she was able to perform body movements associated with either a sitting or standing position. This case shows that appropriate early mobilization of a patient with a femoral neck fracture is feasible after aortic valve replacement, even though this does not necessarily mean that the patient needs to walk.

Axillary and innominate artery cannulation during surgery of the thoracic aorta: a comparative study

AIM

The aim of this paper was to compare hospital outcomes in patients undergoing elective surgery of the thoracic aorta using the right axillary artery (RAA) and the innominate artery (IA) as a cannulation site for cardiopulmonary bypass (CPB) arterial inflow.

METHODS

Between September 2009 and October 2011, 71 patients underwent elective aortic procedures with RAA (N.=27) and IA (N.=44) cannulation. Selection of RAA vs. IA was not randomized, but rather based on surgical judgment of best indication in each patient. Pre-, intra-, and postoperative variables were compared according to cannulation site.

RESULTS

Preoperative comorbidities, underlying aortic pathology, and surgical procedures were similar in RAA and IA patients. Hospital mortality was 11.1% and 6.8% in RAA and IA patients, respectively (P=0.243). Overall, 4 brain infarctions occurred, all left sided (RAA: 3.7% vs. IA: 6.8%; P=0.508). One brachial plexus injury, and 1 arterial dissection occurred in RAA group. No cannulation-related morbidity was observed in IA patients. Theoretical CPB flow could be reached in all patients, but resistances through the cannulation sites were more favourable in IA patients.

CONCLUSION

RAA and IA were associated with similarly valid results. The choice between the two, based on the specific patient's characteristics, can improve outcomes after aortic surgery.

Endovascular approach for acute aortic syndrome

Acute aortic syndrome (AAS) refers to the spectrum of aortic emergencies that include aortic dissection, intramural hematoma and penetrating atherosclerotic ulcer. These aortic pathologies may lead to aortic rupture and a timely treatment is crucial to obtain clinical success and benefit on survival. Endovascular strategies have gained wide acceptance in the management of AAS and currently represent the new minimally invasive alternative to traditional surgery. In particular in acute complicated aortic dissection endovascular therapy demonstrated a better survival and limited complications with respect to open surgery. Aim of the present study was to provide an overview of AAS and to assess the current role of endovascular aortic repair in its treatment.

Urgent/emergent surgical revascularization in unstable angina: influence of different type of conduits

AIM

In patients with unstable angina (UA) undergoing nonelective myocardial revascularization we compare the outcomes of skeletonized bilateral internal mammary arteries (BIMA) vs left internal mammary artery (LIMA) and saphenous vein grafts (SVGs) vs SVGs only.

METHODS

Between January 1997 and December 2003, 758 patients: 612 (80.7%) males, mean age 62+/-12 years, underwent nonelective coronary artery bypass grafting (CABG) for unstable angina; 205 (27%) were operated emergently and 553 (73%) urgently. BIMA were employed in 320 (42%) patients (Group B) , isolated LIMA and/or SVGs in 332 (44%) patients (Group M) and only SVGs in 106 (14%) (Group S).

RESULTS

In-hospital mortality (B=5.9%, M=4.5% and S=7.5%), and perioperative myocardial infarction (B=2.2%; M=1.9%, S=3.7%) were similar between the 3 groups (P=NS). Actuarial survival at 1, 3 and 7 years was 98.7%, 97.5% and 96.2% in group B, 99.3%, 94.8% and 89.4% in group M (P< 0.057 at 7 years follow-up) and 98%, 93.2% and 84.3% in group S (P=0.001). At 7 years follow-up, the event-free cardiac survival (92% vs 89.1%, P=0.045), angina-free survival (98.6% vs 95.8%, P=0.056), reoperation-free cardiac survival (98% vs 96%, P= 0.05) and infarct-free cardiac survival (98.7% vs 96.9%, P=0.062) showed a consistent trend to be superior in group B. Multivariate analysis identified age >65 years (P= 0.02), left ventricular ejection fraction (LVEF) <35% (P= 0.01), >1 ischemic irreversible area (P= 0.03) as independent predictors for late deaths, while the use of the LIMA (P= 0.006) and both mammary arteries (P= 0.001) decreased the risk of late deaths.

CONCLUSIONS

The use of BIMA in nonelective CABG for UA is safe and effective. There is a trend, however, toward a survival benefit with improved freedom from late cardiac events (recurrence of angina, freedom from reoperation and infarction).

Antegrade selective cerebral perfusion during surgery of the thoracic aorta: risk analysis

OBJECTIVE

To determine independent predictors of neurologic outcome and hospital mortality after surgery of the thoracic aorta using moderate hypothermic circulatory arrest and antegrade selective cerebral perfusion.

METHODS

Between November 1996 and June 2000, 96 consecutive patients (69 men, 27 women; mean age 63+/-10 years) underwent operations on the thoracic aorta with the aid of moderate hypothermic circulatory arrest and antegrade selective cerebral perfusion. Sixty-four patients were operated on electively (66.7%), 32 emergently (33.3%). Indications for surgery were: type A acute dissection in 30 patients (31.3%), chronic aneurysm in 66 (68.8%). Seventeen patients (17.7%) had undergone previous aortic/cardiac surgical procedures. The mean selective cerebral perfusion time was 52.2+/-31.9 min (range, 18-220 min). Preoperative, intraoperative, and postoperative factors were analyzed by univariate and multivariate analysis to identify predictors of hospital mortality and neurologic outcome.

RESULTS

There were no operative deaths; the hospital mortality rate was 11.5% (11/96). Stepwise logistic regression revealed preoperative renal dysfunction (P=0.021), type A acute dissection (P=0.053), coronary artery bypass grafting (P=0.058), post-operative pulmonary complications (P=0.000) and repeat thoracotomy for bleeding (P=0.027) as independent predictors of hospital mortality. One patient sustained a permanent neurologic deficit (1%). Transient neurologic deficit occurred in eight patients (8.3%). Coronary artery bypass grafting (P=0.013), and postoperative cardiac complications (P=0.049) were statistically associated with an increased risk of any (transient and permanent) neurologic dysfunction on univariate analysis. Stepwise logistic regression indicated coronary artery bypass grafting as independent factor for any neurologic dysfunction.

CONCLUSION

This study confirmed that selective cerebral perfusion is an effective method of cerebral protection allowing complex thoracic aorta operations to be performed with low risk of hospital mortality and adverse neurologic outcome. We didn't find that the duration of selective cerebral perfusion time influence hospital mortality and any neurologic deficit.

Antegrade selective cerebral perfusion during operations on the thoracic aorta: our experience

BACKGROUND

Various methods of cerebral protection have been used during aortic arch operations. Deep hypothermia with circulatory arrest is the most common technique but has a limited safe period for circulatory arrest. Selective cerebral perfusion has been introduced to prolong this safe period. We reviewed our experience with antegrade selective cerebral perfusion during surgical repair of the thoracic aorta.

METHODS

Between November 1996 and December 1998, 57 consecutive patients were operated on for aortic arch aneurysms using selective cerebral perfusion. Forty-one were men (71.9%), and 16 were women. The mean age was 63.2 years. Thirty-seven patients had chronic aneurysms, and 20 had type A acute dissection. Preoperative, intraoperative, and postoperative factors were analyzed by univariate and multivariate analysis to identify predictors of early mortality and transient neurologic dysfunction.

RESULTS

There were no permanent neurologic deficits. The early mortality rate was 8.8% (5 patients). Multivariate analysis revealed preoperative renal failure (p = 0.0338) and repeat thoracotomy for bleeding (p = 0.0201) to be independent risk factors for early mortality. The factor postoperative cardiac complications (p = 0.0368) was the only independent predictor of transient neurologic dysfunction, and it occurred in 3 patients (5.3%).

CONCLUSIONS

The present study confirmed that preoperative renal failure and repeat thoracotomy for bleeding are significant predictors of mortality in aortic arch operations using selective cerebral perfusion and that cerebral perfusion time has no influence on the postoperative outcome. We believe that selective cerebral perfusion is an optimal technique of cerebral protection during operations on the aortic arch.