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Department of Cardiovascular Surgery, Nagoya First Red Cross Hospital, Nagoya, Aichi, Japan
Accepted for publication November 11, 2009.
* Address correspondence to Dr Yamana, 3-35 Michishita, Nakamura, Nagoya, Aichi 453–8511, Japan (Email: koyamanakomaki{at}gmail.com).
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Abstract |
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Methods: Transesophageal echocardiography was used to measure the peak velocities of each perfusion method in the aortic arch. The latest 15 patients with perfusion toward the aortic valve in the arch procedure were compared with 15 patients with perfusion toward the aortic arch in other cardiac operations as controls. Between April 2005 and February 2009, 65 consecutive patients underwent total arch replacement for atherosclerotic aneurysms. Among them, 48 patients underwent operations with perfusion toward the aortic valve and were reviewed.
Results: The peak forward aortic flow velocities with perfusion toward the aortic valve were 48 ± 26 cm/s before cardiopulmonary bypass and 29 ± 13 cm/s on cardiopulmonary bypass. The velocities with perfusion toward the aortic arch were 67 ± 28 cm/s before cardiopulmonary bypass and 226 ± 114 cm/s on cardiopulmonary bypass (p < 0.001). Of the 48 patients with perfusion toward the aortic valve, postoperative temporary and permanent neurologic dysfunctions occurred in 4 (8.2%) and in 1 (2.0%), respectively. One (2.0%) hospital death occurred.
Conclusions: Perfusion toward the aortic valve resulted in a significant decrease in peak forward aortic flow velocity in the aortic arch during cardiopulmonary bypass, which might reduce the risk of erosion or disruption of existing atheroma and ensuing embolic complications in patients with atherosclerotic aneurysm.
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Introduction |
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To avoid this devastating complication, perfusion toward the aortic valve has been proposed by several investigations [8, 9], but its flow dynamics have not been elucidated. The present study was conducted to quantify the differences in blood flow in the aortic arch produced by perfusion toward the aortic valve or toward the aortic arch and to evaluate whether perfusion toward the aortic valve was able to reduce in-hospital death and postoperative neurologic dysfunction in the patients with atherosclerotic arch aneurysm.
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Material and Methods |
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Velocity Measurements in the Aortic Arch
Transesophageal echocardiography (TEE) was performed in 15 patients undergoing total arch replacement with perfusion toward the aortic valve. The control group comprised 15 patients who underwent other routine cardiac operations with perfusion toward the aortic arch, including coronary artery bypass grafting (CABG) in 4, aortic valve replacement in 3, and mitral valve repair in 7 and replacement in 1.
Using the SONOS Echo Unit (Philips Medical Systems, Andover, MA), we performed echocardiography with an Omniplane transesophageal probe (Philips Medical Systems) in the continuous-wave mode at 4.4 MHz. Measurement of the velocity in the aortic arch was taken after color Doppler recorded the perfusion image. Velocity was measured at the point where brachiocephalic artery branches out because of the anatomic limitations, and the deposition of cholesterin on the aortic wall is prevalent on the point due to flow stagnation and the highest wall pressure was observed at this area where jet flow impingement occurred in the computational simulation [10]. Velocity before CPB was measured just after the induction of general anesthesia, and velocity on CPB was measured once CPB was stabilized at 2.5 L/min/m2 output. Velocity was measured five times continuously at each period, and mean peak flow velocity was calculated.
Pre-CPB velocity measurements into the aortic arch, pre-CPB mean arterial pressure, and mean arterial pressure and flow (L/min) during CPB were recorded. Mean blood pressure on CPB was kept steady, and hematocrit, perfusion line pressure, velocity measurements in the aortic arch pre-CPB, mean arterial pressure during CPB, and CPB flow were monitored.
All patients underwent epiaortic ultrasonography of the ascending and transverse aorta using a hand-held ultrasound probe (PVF-738H probe, Toshiba Inc, Tokyo, Japan) just before CPB to determine an atherosclerotic plaque-free site for the cannulation. A dispersion cannula (Edwards Lifescience Research Medical, Midvale, UT) was used for all 30 patients, with the size determined by whether the body surface area was greater than 1.5 m2. A 24F cannula was used in 21 patients (13 in the toward the aortic valve group, and 8 in the toward the arch group) and a 21F cannula was used in 9 patients (2 in the toward the aortic valve group, and 7 in the toward the arch group). Cannulas were placed into the midportion of the ascending aorta.
Patient Profile in Clinical Studies
Between April 2005 and July 2009, 65 consecutive patients (9 women [19%]), underwent total arch replacement for atherosclerotic arch aneurysm at Nagoya First Red Cross Hospital, Japan, of which 48 with perfusion toward the aortic valve were analyzed (Table 1). The mean age was 72 ± 9 years (range, 42 to 91 years). Operations were elective in 36 patients (75%) and were emergency procedures in the remaining 12 (25%) because of aneurysm rupture. Concomitant procedures included CABG in 7 patients (15%) and left ventricular plasty in 1 (2%).
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Operations and Brain Protection
All operations were performed through a median sternotomy. During CPB, arterial blood pH was managed according to the pH-stat strategy. CPB was composed of a roller pump (Senko Medical Instrument Corp, Tokyo, Japan), a hollow-fiber polypropylene oxygenator (HPO-23H; Senko), and a heparin-coated circuit (EXCELINE-S NSH, 0.5-in; Senko). Our first choice for arterial cannulation for CPB was the ascending aorta. If atherosclerotic plaques were present in the ascending aorta, we selected the other sites of arterial cannulation. Cannulation sites selected were the ascending aorta in 48 patients (74%), the femoral artery in 7 (11%), the right axillary artery in 4 (6%), and the combination of two cannulation sites in the remaining 6 (9%).
For brain protection using selective cerebral perfusion (SCP), the 15F and 12F ballon-tipped cannulas (Senko Medical Instrument) were inserted into the brachiocephalic artery and the left common carotid artery, respectively. The left subclavian artery was occluded with the 5F Fogarty balloon catheter (Edwards Lifescience Research Medical). The temperature of the antegrade cerebral perfusate was 15°C during SCP, and flows of SCP were 7 mL/kg/min.
Definition of Neurologic Deficits and Other Variables
Permanent neurologic dysfunction was defined as the presence of permanent deficits persisting at discharge. Transient dysfunction was defined as the occurrence of confusion, agitation, obtundation, or delay of full awakening, together with consultation with neurologists. Cerebrovascular disease included old cerebral infarction and cerebral hemorrhage. Carotid artery disease was defined as the presence of more than 50% stenosis or multiple plaques on ultrasound examination. Chronic renal failure was defined as a serum creatinine level of more than 2.0 mg/dL or the requirement of hemodialysis. Reoperation was defined as resternotomy after cardiac or aortic root to arch operation.
Statistical Analysis
The continuous data in this study are expressed as the mean ± SD, and categoric variables are expressed as percentages. Statistical analysis was performed by the paired t test (SPSS Inc, Chicago, IL).
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Results |
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Mean CPB time was 204.6 ± 40.5 minutes, mean cardiac ischemic time was 139.3 ± 29.7 minutes, mean systemic circulatory arrest time was 72.4 ± 22.6 minutes, and mean operation time was 363.7 ± 137.6 minutes.
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Comment |
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Grooters and colleagues [8] reported perfusion toward the aortic valve eliminates the sandblast effect of the perfusion cannula into the aortic arch and thereby reduces the rate of embolic stroke in CABG patients. Morishige and colleagues [9] reported no postoperative cerebral embolism in 16 patients when this perfusion technique toward the aortic valve in arch operations. Fukuda and colleagues [12] reported that directing the cannula tip of the Dispersion cannula toward the aortic root generated slower and less turbulent flow in the transverse arch of the glass models of both healthy and aneurysmal aortic arches. Tokuda and colleagues [10] showed three-dimensional computational simulation of blood flow with perfusion toward the aortic arch during CPB. They reported the highest wall pressure and the maximum wall shear stress were observed at the superior-posterior wall of the aorta below the orifice of the brachiocephalic artery where jet flow impingement occurred.
With this method in our study, postoperative cerebral infarction occurred in only 1 patient. The patient had an ischemic stroke after preoperative hemorrhagic shock due to the aortic arch aneurysm rupture and was in a semicoma postoperatively with a large defect observed on CT scanning. The neurologist determined this stroke was caused by preoperative hypoperfusion because the brain artery appeared normal on postoperative magnetic resonance angiography. So this perfusion method did not cause intraoperative atheroembolism in patients who had atherosclerosis of the transverse aortic arch.
Cannulation at the ascending aorta has several advantages. First, because it is easy to access and establish CPB, it makes pre-CPB time short, especially in an emergency procedure. Second, we can use the necessary-sized cannula, although the cannula size was limited when cannulating at the femoral artery or axillary artery.
Barbut and associates [13] demonstrated that high-grade, mobile plaque (grade 5) is found more frequently in the aortic arch (18%) and descending aorta (34.5%) than in the ascending aorta (5.3%). In our study, we found mobile plaque in the ascending aorta and therefore changed the cannulation site from ascending aorta to the other site in 6 of 65 patients (9.2%). So cannulation at the ascending aorta can be implemented even if the atheromatous aneurysm exits in the transverse aorta.
We actually measured the difference of the velocity between perfusion toward the aortic valve and perfusion toward the aortic arch by using TEE in patients undergoing CPB. The continuous kinetic energy and turbulence produced by the jet of blood from the standard perfusion into the aortic arch produces a sandblast effect that can dislodge debris, which can then be carried by the blood flow to the brain and cause embolic events. Our echocardiographic and clinical studies showed that perfusion into the aortic arch may be hazardous especially in the surgery of atherosclerotic arch aneurysm, whereas perfusion toward the aortic valve may reduce intraoperative stroke by decreasing the likelihood of plaque disruption in the arch.
The issue of the most suitable cannulation site for patients with atherosclerotic arch aneurysm continues to be investigated. The right subclavian artery or axillary artery have been proposed as possible options [8, 14–16]. Axillary artery perfusion is becoming popular as an alternative route for accessing the severely atherosclerotic aorta. Svensson and colleagues [15] concluded that axillary artery cannulation with a side graft was superior to aortic cannulation and femoral cannulation to avoid stroke and hospital death, as shown by propensity analysis.
Christian and colleagues [16] reported axillary cannulation significantly improves survival and neurologic outcome after atherosclerotic aneurysm repair of the aortic root and ascending aorta compared with cannulation at the ascending aorta and at the femoral artery. They mentioned axillary artery cannulation preserves antegrade flow in the descending aorta while eliminating some of the risks associated with direct cannulation of ascending aorta. It lowers the potential for embolization into right-sided cerebral vessels, and also eliminates the sandblasting effect of turbulent flow from a catheter tip close to atherosclerotic lesions in the ascending aorta or aortic arch, and increases the ease of using selective cerebral perfusion during arch repairs. But the effect of the jet flow from the orifice of the brachiocephalic artery is not clearly known.
Minakawa and colleagues [17] evaluated the flow dynamics of the axillary artery perfusion model. They found that flow from the brachiocephalic artery in the right axillary artery perfusion goes toward the lesser curvature of the proximal aortic arch. And shear stress caused by retrograde rapid flow from the axillary artery perfusion may detach the frail plaque on the inner curvature of the brachiocephalic ostium.
The present study has several limitations:
In conclusion, perfusion toward the aortic valve yields gentle blood flow in the aortic arch and may reduce postoperative neurologic dysfunction in operations for atherosclerotic arch aneurysm.
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References |
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