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Ann Thorac Surg 1999;67:457-461
© 1999 The Society of Thoracic Surgeons

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Original Articles

Complete thromboendarterectomy of the calcified ascending aorta and aortic arch

^a Clinic for Cardiovascular Surgery, University Hospital, Zurich, Switzerland
^b Institute for Diagnostic Radiology, University Hospital, Zurich, Switzerland
^c Department of Neurology, University Hospital, Zurich, Switzerland
^d Division of Echocardiography, University Hospital, Zurich, Switzerland
^e Clinic for Cardiovascular Anesthesia, University Hospital, Zurich, Switzerland

Accepted for publication July 23, 1998.

Address reprint requests to Dr Vogt, Clinic for Cardiovascular Surgery, University Hospital, Rämistr. 100, CH-8091 Zurich, Switzerland

	Abstract

Top Abstract Introduction Material and methods Results Comment References

 
Background. Arteriosclerotic plaques of the ascending aorta and transverse arch increase the operative risk of cardiac operations and are strong predictors for late cerebrovascular events.

Methods. Twenty-two patients, mean age 68 ± 6 years (range, 55 to 77 years), with grade IV + V plaques of the ascending aorta and transverse arch underwent coronary artery bypass grafting (n = 21) and aortic valve replacement (n = 8). Cerebrovascular emboli from unknown sources were found preoperatively in 8 patients (36%). All were in sinus rhythm. Complete thromboendarterectomy of the ascending aorta and transverse arch was performed during hypothermic circulatory arrest. After 21 ± 12 months (range, 4 to 44 months), magnetic resonance imaging and transthoracic echocardiography of endarterectomized vessels was performed.

Results. There was one perioperative death (4.5%), one early (4.5%), and one late (4.7%) adverse neurologic event. Follow-up examinations revealed normal diameters of the endarterectomized aorta.

Conclusions. For patients with grade IV + V plaques, thromboendarterectomy of the ascending aorta and transverse arch can be performed with an acceptable surgical risk and a low recurrence rate for cerebrovascular events. Dilatation of the endarterectomized aorta was not observed.

	Introduction

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Noncardiac complications in patients undergoing coronary artery bypass grafting or aortic valve replacement are of increasing medical and socioeconomic importance [1]. Cerebral embolization is one of the most dreaded complications after an otherwise uneventful cardiac operation. The single most important risk factor for an adverse cerebral event after cardiac operation is atheroembolization from a severely atheromatous ascending aorta or aortic arch [2]. Moreover, atherosclerotic plaques of the ascending aorta and transverse arch are recognized as strong predictors of late recurrent adverse cerebral events [3]. In addition, patients with a persistent deficit from a perioperative stroke deteriorate cognitively at a faster rate for up to 5 years after operation and may suffer from long-standing mental depression [4], emphasizing the adverse long-term effect of these atherosclerotic plaques. Thus, severe atherosclerosis of the ascending aorta and transverse arch is not only a risk factor for cardiac operation, but is recognized as an independent disease requiring appropriate treatment.

This study presents indication, surgical technique, and results in patients with severe atherosclerotic aortic plaques who had complete thromboendarterectomy of the ascending aorta and transverse arch during a routine cardiac surgical procedure.

	Material and methods

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Patients
Standard preoperative evaluation suspected severe atheromatous disease of the ascending aorta and transverse arch in 46 of 3,146 patients (1.4%) undergoing primary, isolated aortic valve replacement, coronary artery bypass grafting, or combined aortic valve and bypass grafting from February 1994 to November 1997. In 12 of these 46 patients (26%), atheromatous grade IV and V plaques were confirmed by preoperative transesophageal echocardiography according to the Montgomery modification [5] of Ribakove’s grading system [6], allowing precise planning of the operative procedure. In 8 patients the diagnosis of severe great vessel atherosclerosis had been unexpectedly made after direct inspection of the ascending aorta and transverse arch at the beginning of the operation. Immediate intraoperative transesophageal and direct epiaortic echocardiography confirmed the diagnosis of grade IV and V plaques.

Thus, a total of 54 of 3,146 patients (1.7%) were candidates for aortic thromboendarterectomy. Intraoperative transesophageal and epiaortic echocardiography confirmed grade IV and V plaques in 21 of these 54 patients (39%), who subsequently underwent thromboendarterectomy. In these, coronary artery disease was the primary indication for operation in 13 (59%) and combined coronary artery disease and calcified aortic valve stenosis in 8 patients (36%). The mean age of these 21 patients was 68 ± 12 years (median, 64 years; range, 55 to 77 years).

In addition, a 53-year-old man with normal cardiac findings was also included in this study: in this patient, protruding and mobile plaques of the transverse aortic arch, causing recurrent bilateral cerebrovascular embolization, were the only indication for operation.

A history of cerebrovascular embolization from an unknown source was found in 9 of 21 patients (41%), causing transient hemiparesis in 8 (36%) and recurrent transient ischemic attacks in 1 (4.5%). Two patients (9%) had persistent cerebrovascular embolization despite recent carotid endarterectomy and another patient (4.5%) had Parkinson’s disease known for years. Preoperatively, routine computed tomography of the head has been performed in 7 (32%) and magnetic resonance imaging in 2 patients (9%), revealing multiple silent cerebral ischemic lesions in all.

Cardiovascular risk factors were found as follows: arterial hypertension in 18 (82%), smoking in 18 (82%), high cholesterol blood levels in 8 (36%), and insulin-dependent diabetes in 7 (32%). Peripheral arterial occlusive disease was found in 12 patients (54%) and chronic renal failure requiring dialysis in 1 (4.5%). All patients were in stable sinus rhythm. Preoperatively, 14 of 22 patients (64%) had already sustained a myocardial infarction, resulting in a mean left ventricular ejection fraction of 56% ± 15% (median, 59%; range, 20% to 78%).

Operative technique
Cardiopulmonary bypass
Median sternotomy and standard cardiopulmonary bypass techniques with cold blood cardioplegia were used. Transesophageal and direct epiaortic echocardiography using a 7.0-MHZ linear transducer (HP Sonos 1500; Hewlett Packard, Andover, MA) was performed in patients with unexpected severe atherosclerosis of the great vessels. Patients with grade IV + V plaques were included in the protocol. Deep hypothermic circulatory arrest was used, the nasopharyngeal temperature being lowered to 16° to 18°C. In 8 of 22 patients (36%) groin vessels were cannulated due to almost complete aortic calcification. Retrograde cerebral perfusion cannulating the superior caval vein was used routinely in the last 12 patients (54.5%) of this study.

No aortic cross-clamping was performed, an intraaortic Foley catheter, containing a guidewire (Fig 1 ) was inserted in all patients, allowing either antegrade application of cold blood cardioplegia or venting of the proximal aorta and aortic root while the balloon was kept inflated. During core cooling, coronary artery bypass grafting or aortic valve replacement incising the aorta proximal to the inflated intraaortic Foley catheter, was started.

View larger version (28K): [in this window] [in a new window]   Fig 1. Balloon catheter with guidewire for internal blockade of the ascending aorta, allowing application of antegrade cardioplegia and venting of the proximal aorta.

View larger version (17K): [in this window] [in a new window]   Fig 2. Circumferential thrombendaterectomy of the ascending aorta during hypothermic circulatory arrest after a cleavage plane between the arteriosclerotic intima and the media. The thromboendarterectomy started 2 cm above the aortic valve commissures.

View larger version (14K): [in this window] [in a new window]   Fig 3. Autopsy specimen of the distal aortic arch, demonstrating the smooth transition zone between the endarterectomized segment of the aortic arch and the arteriosclerotic descending thoracic aorta (van Giemsa-elastin stain; original magnification x120).

Mean cardiopulmonary bypass time was 143 ± 46 minutes (median, 135 minutes, range, 75 to 255 minutes), the mean aortic cross-clamp time 64 ± 24 minutes (median, 62 minutes; range, 21 to 105 minutes), and deep hypothermic circulatory arrest lasted for a mean of 21 ± 8 minutes (median, 20 minutes; range, 8 to 34 minutes).

Follow-up
Before hospital discharge, patients were examined by a neurologic consultant. Thereafter, patients were regularly followed by their family doctor or referring cardiologist to document postoperative adverse cerebral events. During a mean follow-up time of 21 ± 12 months (median, 23.5 months; range, 4 to 44 months) transthoracic echocardiography (n = 11), computed tomography (n = 12), or magnetic resonance imaging (n = 4), all methods providing accurate measurements of true aortic lumen length [7], was performed to assess the diameter of the ascending aorta and transverse arch. Unfortunately, transesophageal echocardiography was not feasible due to ethical reasons. The change in the endoluminal diameter of the ascending aorta and the transverse arch was determined, comparing preoperative data from cardiac catheterization (n = 22), computed tomography (n = 7), magnetic resonance imaging (n = 2), and preoperative or intraoperative transesophageal echocardiography (n = 22) with those obtained by postoperative examination as listed previously. In addition, the change in endoluminal aortic diameter over time was assessed in 14 of 17 long-term survivors (82%) assuming that a possible increase of the diameter of an endarterectomized vessels would be a biological process similar to the aneurysmal dilatation observed in chronic aortic dissection.

Statistical analysis
Descriptive statistics are expressed as means ± standard deviation and as median where appropriate. Patient survival was analyzed using the Kaplan-Meier technique. Pre- and postoperative endoluminal aortic diameters were compared using the Wilcoxon rank sum test. A linear regression analysis was performed to assess a possible increase of the postoperative aortic diameter over time. All calculations were made using the statistical package SPSS (Chicago, IL) for Windows 7.5. All values of p less than 0.05 were considered to be of statistical significance.

	Results

Top Abstract Introduction Material and methods Results Comment References

 
Mortality and morbidity
Hospital mortality was 4.5%; a 70-year-old patient died from a perioperative myocardial infarction. At autopsy, bypass grafts were patent and microscopy did not reveal any coronary artery cholesterol embolization. Histologic examination revealed smooth transition between the endarterectomized aortic arch and the distal intima (Fig 3). Neurologic complications were found in 1 patient (4.5%): a 74-year-old man had right-sided hemiparesis, fully recovering during hospitalization. Thus, the perioperative course was uneventful in 20 of 22 patients (91%) and no further adverse cerebral events were observed. Perioperative, nonneurologic complications were observed in two patients (9%) with severe chronic obstructive pulmonary disease, requiring prolonged mechanical ventilation for up to 35 days in 1 patient.

During this study period, 24 of 3,125 patients (0.7%) died from a perioperative cerebrovascular event and 161 (5%) presented various focal brain injury due to cerebrovascular embolism with persistence of a significant neurologic deficit in 16 patients (0.3%).

However, there were three perioperative neurologic deaths in the 33 patients (11%), evaluated for radical thromboendarterectomy, but subsequently treated by surgical modifications, applied to prevent perioperative cerebral embolization. Another patient (2.7%) suffered from bilateral cortical blindness 4 days after successful revascularization.

Follow-up
Recurrence of cerebrovascular embolization was reported in 1 patient (5%): 8 months postoperatively a 66-year-old man suffered from bilateral retinal artery embolism from an unknown source. Three patients died from chronic heart failure during follow-up, resulting in an actuarial patient survival of 72% ± 14% after 28 months.

The pre- and postoperative endoluminal aortic diameter at the level of the ascending aorta and the midportion of the aortic arch remained stable during the follow-up (Fig 4 ) and linear regression analysis failed to show a statistically significant correlation between changes in the endoluminal aortic diameters and the time of follow-up, again indicating stable aortic diameters over time (r = 0.003).

View larger version (19K): [in this window] [in a new window]   Fig 4. Changes in endoluminal aortic diameter at the level of the ascending aorta and the aortic arch in patients before and after complete thromboendarterectomy of the thoracic aorta (n = 14). Boxes represent minimal and maximal data range; inside each box black dots show mean values and horizontal lines show median values, bars represent upper and lower 95% confidence limits. (arch = transverse arch; asc = ascending aorta; n.s. = statistically not significant; postop = postoperative; preop = preoperative.)

	Comment

Top Abstract Introduction Material and methods Results Comment References

Surgical modifications such as adjustments of aortic cannulation and clamping, no-clamp techniques using hypothermic fibrillatory arrest, arterial revascularization, aortic graft replacement, or segmental endarterectomy, pioneered by Wareing and colleagues [10], have reduced the incidence of adverse perioperative cerebral events. However, these alternative strategies ignore the long-term association between atherosclerotic disease of the aortic arch and recurrent brain infarction. Plaques 4-mm thick in the aortic arch have been found to be a strong risk factor for recurrent ischemic strokes [3] with incidence rates exceeding those with nonvalvular atrial fibrillation [11] and uncorrected carotid stenosis of at least 70% [12]. Thus, coronary artery bypass grafting or aortic valve replacement without complete removal of protruding atheromas of the ascending aorta and transverse arch, although successful, do not appropriately address the long-term prognosis of these particular patients.

Therefore, we performed complete and radical thromboendarterectomy of the ascending aorta and aortic arch in patients with grade IV + V plaques undergoing a routine cardiac surgical procedure. In these patients, the clinical importance of protruding plaques of the ascending aorta and transverse arch has been clearly demonstrated: 41% of patients had a history of cerebrovascular embolization, 32% had multiple silent cerebral infarctions, and 9% had persistent ischemic episodes despite recent carotid thromboendarterectomies. In addition, a severely atherosclerotic aorta, preventing routine bypass grafting or valve replacement, has been found unexpectedly in 36% of our patients. Nevertheless, in this study, radical thromboendarterectomy has proved to be a safe and effective treatment for protruding plaques of the ascending aorta and transverse arch with an acceptable operative mortality and low incidence of perioperative neurologic complications. In addition, there was only 1 patient with recurrent cerebrovascular embolization during follow-up, confirming a beneficial long-term effect regarding recurrent cerebrovascular embolism.

The appropriate timing of thromboendarterectomy in patients with previous stroke is not yet clarified. In patients with a recent stroke, carotid endarterectomy within 2 to 4 weeks is known to increase the risk of perioperative neurologic dysfunction [13], possibly attributable to a loss of blood flow autoregulation after cerebral infarction. Thus, aortic thromboendarterectomy is not performed within the first 6 weeks after an embolic stroke [14].

An important question is, whether the endoluminal diameter of the ascending aorta and transverse arch would increase over time after thromboendarterectomy similar to the aneurysmal dilatation observed in chronic aortic dissection. In chronic dissection, aneurysmal degeneration involves degradative protease activities in the media and adventitia and abnormal production and deposition of elastic or collagen unrelated to the presence or degree of cystic media necrosis [15]. After thromboendarterectomy, the outer wall of the aorta is characterized by an increased perivascular fibrosis [16], similar to the periarterial fibrosis in the outer media and adventitia after carotid thromboendarterectomy [17]. True aneurysmal degeneration after carotid endarterectomy is rarely reported [18]. However, the relation between collagen and elastin in the carotid artery is 2.55, whereas it is only 0.49 in the thoracic aorta [19]. This may explain the sufficient tensile strength of the residual outer media and adventitia after carotid endarterectomy. Thus, the healing process after carotid endarterectomy might be different compared to what will be found after aortic thromboendarterectomy.

In our patients, the endoluminal diameter of the ascending aorta and the midportion of the transverse arch remained stable up to 44 months after radical thromboendarterectomy, which has been confirmed by a similar study [20]. After the preliminary use of several techniques, we decided to follow our patients by magnetic resonance imaging due to several advantages, such as the multiplanar imaging capabilities of magnetic resonance imaging, providing a better delineation of the aortic arch and the lack of ionizing radiation. Transesophageal echocardiography is certainly too invasive and has not been accepted by the majority of our patients as a follow-up technique, whereas transthoracic echocardiography fails to image recurrence of aortic arch calcifications precisely. Thus, patients not amenable to magnetic resonance imaging should be referred to computed tomography.

In conclusion, an aggressive surgical approach to severe atherosclerosis of the ascending aorta and transverse arch, using complete and radical thromboendarterectomy, appears to reduce the perioperative neurologic complications. In addition, the adverse cerebral long-term outcome associated with protruding and mobile plaques of the ascending aorta and aortic arch may be improved. However, a larger amount of patients and a longer follow-up time are necessary to estimate the long-term effect of radical thromboendarterectomy in patients with severely calcified aortas.

	References

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