Pairs Of Intercostal Arteries Research Articles

Abstract 474: Early Events in Dissecting Aneurysms Induced by Angiotensin-II Infusion: The Geometry-Driven Aspect of a Multifaceted Problem

While research on dissecting aneurysms in Angiotensin-II infused mice spans more than a decade, the temporal sequence of initial events still remains unclear. Recent findings in our group suggested that focal medial tears at the vicinity of suprarenal side branches are the primary event in disease formation. In this study we used a combined experimental-computational approach to investigate the hypothesis that initial events of dissecting AAAs originate at branching sites along the aorta. Male apolipoprotein-deficient mice were infused with Angiotensin-II (n=11) and saline 0.9% (n=6) for 3 days and scanned with contrast-enhanced microCT prior to sacrifice. One animal presented an in-vivo rupture during the microCT scan, and was rescanned after 2.5 hours to observe real-time morphological changes. In all other animals, the excised aortic tissue was imaged with Phase Contrast X-Ray Tomographic Microscopy (PCXTM) at 6.5um isotropic resolution. An automatic morphing code was developed to map the ex-vivo geometry onto the in vivo geometry, and a finite element simulation yielded a stress distribution that represents an estimation of the wall tension, not only due to the pressurization, but also due to the local stretch field. We found that the nanoparticulate microCT contrast agent had infiltrated the aortic wall in 11/11 Ang-II infused animals, while no infiltration was observed in 6/6 control mice. The infiltration affected at least one pair of intercostal arteries in 11/11 mice, and in 9/11 mice the coeliac region was also affected. Image-guided histology allowed us to determine the circumferential distribution of microlesions at branching sites, including disruption of elastin fibers, apoptotic cell appearance, subintimal leukocyte infiltration and intramural hematomas. In the animal whose aorta had ruptured during the in vivo scan, the initial hematoma had originated around 3 pairs of intercostal arteries and quickly propagated afterwards. Mouse-specific finite element simulations revealed a co-location of computed peak stresses at the vessel wall and histologically identified vascular damage. We conclude that the aortic geometry, and side branches in particular, play a pivotal role in the onset of dissecting AAA.

A New Technique for Interrupted Aortic Arch Repair: The Neville Tube

We have developed a new technique for interrupted aortic arch repair in which the pulmonary artery anterior wall is cut off and tailored so as to re-establish aortic continuity with an autologous tube. We are describing this method herein, with an 8-year follow-up of the first patient.

Transapical aortic cannulation via left lateral thoracotomy for descending thoracic and thoracoabdominal aortic surgery

Two patients underwent surgery for a chronic type B dissection using a total cardiopulmonary bypass (CPB) with transapical arterial cannulation. At surgery, a total CPB was established by cannulating the left femoral artery and the ascending aorta via the ventricular apex. The patients were cooled to 30 degrees C. The proximal anastomosis was done after cross-clamping the aortic arch between the left carotid artery and the left subclavian artery in both cases. In the first case, the entire descending thoracic aorta was replaced, and two pairs of intercostal arteries were reconstructed. The other patient underwent replacement of the proximal descending thoracic aorta. Neither patient experienced any complications. Transapical aortic cannulation is a useful option during descending thoracic and thoracoabdominal aortic surgery. It can provide more stable circulation during the cross-clamping, more gentle manipulation of the aorta by nonpulsatile flow, and more liberty in temperature control.

Novel technique for reimplantation of intercostal arteries using tailored patch graft

We developed a simple and secure technique for reimplantation of the intercostal arteries (ICAs) using a patch graft during thoracoabdominal aneurysm repair. With our procedure, a sidearm branch with its base is tailored from a 24 mm one-branch Dacron graft, and then sutured as a patch graft to the trimmed wall of the descending aorta to cover the ICA orifices between Th9 and Th12. The proximal end of the patch graft is then anastomosed to the main tube graft, while the graft is perfused. With this technique, the entire suture lines are clearly visible and hemostasis is secured without difficulty. We used this technique in 6 patients, in whom 2.3+/-0.8 pairs of ICAs were reimplanted. The time required for reimplantation of the ICAs was 14+/-6 min and none of 6 patients developed paraplegia. Our results indicate that this novel technique is a simple method to obtain secure hemostasis under direct vision, which may contribute to reduce the risk of paraplegia during thoracoabdominal aneurysm repair.

An Animal Model for Type II Endoleaks with Use of a Tsuzumi Drum–shaped Stent-Graft

To create an animal model of type II endoleaks after endoluminal deployment of a specially designed stent-graft (SG). Five swine were used. A tsuzumi drum-shaped SG consisting of a covered Z stent with its diameter narrowed at the center was deployed in the midthoracic aorta. In this way, a residual space (RS) was created between the aortic wall and the graft to simulate an aneurysm sac. A 5-F catheter was placed into the RS, and then aortography, RS angiography, and pressure measurements were performed. Follow-up was performed at 3 and 10 days after the procedure. Mean pressure indexes (MPIs) were calculated as the ratio of the mean RS pressure to the aortic pressure. Histologic examination was also performed. RSs with two or three pairs of intercostal arteries were successfully created in all cases. Aortography showed two type II endoleaks in five swine just after SG deployment and four type II endoleaks at 10 days. RS angiography showed circulation between the RS and the intercostal arteries in all cases. The mean MPI was 69.4% +/- 10.4% just after SG deployment and increased to 87.8% +/- 5.2% at 10 days. By gross examination, RS patency was retained. A swine model of type II endoleaks was successfully created endoluminally. This model does not require direct surgery to the aorta and its side branches and promises to be useful to study the mechanism of and therapy for type II endoleaks.

Reversal of delayed-onset paraplegia with thrombectomy of an interposed graft for the intercostal artery after thoracic descending aortic aneurysm repair

A 78-year-old woman who had previously undergone prosthetic graft replacement of the total aortic arch was admitted to repair a chronic expanding type IIIb dissecting aneurysm. Firstly the patient's abdominal aorta was replaced with a prosthetic graft without any complications, then the thoracicdescending aorta was repaired five months later. Surgery for the thoracic descending aorta was performed with distal perfusion, cerebrospinal fluid drainage, somatosensory evoked potential (SEP) monitoring and reimplantation of three pairs of intercostal arteries. During surgery, SEP showed no significant changes, and the patient awoke without paraplegia three hours after the surgery. However, she developed bilateral complete paraplegia eight hours after the surgery. Reexploration demonstrated thrombo-occlusion of the sidearm graft for reimplantation of the Th10 intercostal artery. After thrombectomy of the sidearm graft, there was gradual neurological recovery and the patient was ambulatory when discharged. Quick treatment to restore the spinal cord blood supply promoted recovery from paraplegia.

Aortic dissection: new frontiers in diagnosis and management: Part I: from etiology to diagnostic strategies.

Cardiovascular disease is the leading cause of death in most Western societies and is increasing steadily in many developing countries. Aortic diseases constitute an emerging share of the burden. New diagnostic imaging modalities, longer life expectancy in general, longer exposure to elevated blood pressure, and the proliferation of modern noninvasive imaging modalities have all contributed to the growing awareness of acute and chronic aortic syndromes. Despite recent progress in recognition of both the epidemiological problem and diagnostic and therapeutic advances, the cardiology community and the medical community in general are far from comfortable in understanding the spectrum of aortic syndromes and defining an optimal pathway to manage aortic diseases.1–13 This comprehensive review is organized in two parts, with a focus on the etiology, natural history, and classification (with vascular staging) of aortic wall disease in Part I and emphasis on therapeutic management and follow-up in Part II. Both parts may help to better integrate the complexities of acute aortic syndromes.

The Thoracic Aorta: Imaging in Health and Disease

The Normal Thoracic Aorta The thoracic aorta is the result of a succession of events relating to fusion of the paired primitive dorsal and ventral aortae and the persistence or regression of their connections to the paired arterial stlUctures of the six primitive branchial arches that develop in the embryonic stage. The thoracic aorta can be divided into five segments. The aortic root or bulb begins at the aortic valve, having three uniform cusps of equal size and shape. Each cusp subtends one of the three sinuses of Valsalva, named posterior or (noncoronary), left. The left coronary artery arises from the left sinus, whereas the right coronary artery arises from the right sinus. The sinus portion above the valve plane has a diameter of 3.6-3.9 cm. On a frontal chest radiography, this portion of the aorta is buried within the cardio-pericardial silhouette and is not visible. It is, however, readily distinguishable on aortography. The tubular portion begins above the sinuses at the sino-tubular junction with the ascending aorta, which is 4-5 cm long and of uniform diameter between 2.8-3.5 cm. Much of the ascending aorta is intrapericardial. On a frontal chest radiograph, the normal ascending aorta is not border forming. The transverse arch of the aorta is the remnant of the aortic sac proximally and the left fourth branchial arterial arch distally and courses posterolaterally from right to left in a parasagittal plane. It is approximately 5 cm long, 2.5-3 cm in diameter, and gives rise to the brachiocephalic or innominate artery, the left common carotid artery, and the left subclavian artery, in that order. The brachiocephalic artery branches further into the right subclavian artery and the right common carotid artery. Many variations of the branching pattern of the brachiocephalic vessels exist. On frontal chest radiography, the lateral margin of the left subclavian artery forms the superior left border of the mediastinum, and the lateral margin of the distal transverse arch is recognizable as the aortic knob. Occasionally, the superior intercostal vein appears as a nipple on the aortic knob on a frontal chest radiograph. The aortic isthmus is a distinct zone of narrowing beginning distal to the origin of the left subclavian artery and extending over a short variable distance. It is most apparent on aortography in the pediatric patient and disappears with age. It is probably the result of reduced flow in this region during fetal development, where the left ventricular outflow primarily serves the vessels of the head, neck, and upper extremities prOXimal to the isthmus, and the right ventricular outflow serves the descending thoracic aorta distal to the isthmus through shunting through the ductus arteriosus. A remnant of the infundibulum of the ductus arteriosus frequently can be seen even in adult aortae as the ductus bump along the anteromedial wall of the lesser curve of the aorta just distal to the left subclavian artery origin at the ligamentum arteriosum. Larger ones are called a ductus diverticulum. It is of prime importance to recognize this normal variant, especially in the patient who has suffered blunt chest trauma, because it can be mistaken for an aortic laceration. The descending thoracic aorta begins at the isthmus and courses distally slightly left of the vertebral column and approaches the midline at the aortic hiatus of the diaphragm. It has a diameter of 2.5-3 cm proXimally, or approximately two thirds the diameter of the ascending aorta and tapers distally to 2.4-2.7 cm diameter at the aortic hiatus. The descending thoracic aorta gives off from three to eight pairs of intercostal arteries, those on the left typically arising from the dorsal aspect of the aorta at the level of the vertebral pedicles. Although those on the right usually originate from the dorsal aspect of the aorta, the upper right intercostal arteries may arise from the right lateral or even the ventral surface of the descending thoracic aorta. The descending thoracic aorta also gives rise to the bronchial alteries. The most common pattern encountered is two left bronchial arteries and a single right intercostobronchial trunk. Although a large number of anatomic variation exists, each side usually has one or two bronchial arteries. The bronchial arteries typically arise from the ventral aspect of the descending thoracic aorta between T4 and T8, but can also arise from the undersurface or convexity of the aortic arch, the thyrocervical or costocervical tmnks and can derive collateral supply from many axillary and subclavian artery chest wall branches. It is important to be aware that radicular branches to the anterior spinal artery can arise in conjunction with intercostal or bronchial arteries, partiCUlarly if one is about to undertake embolization of these vessels. High quality, motion-free angiography with analog or digital subtraction is required if one is to recognize and avoid embolization of radiculomedullary feeders.

The origin and pattern of distribution of the posterior intercostal arteries in the baboon (Papio ursinus).

The posterior intercostal arteries of six female and four adult male baboons (Papio ursinus) were investigated by latex injection and subsequent dissection to determine their origin and pattern of distribution. Basic morphological and functional similarities with that of man could provide some base-line data pertinent to future experimental studies in the areas of thoracic aortic aneurysm and aortic atherosclerotic lesion in man. Basic similarities were observed between the baboon and man in the number of intersegmental arteries, the origin of the first two pairs of posterior intercostal arteries, and the anastomosis between the superior intercostal and the third posterior intercostal arteries. However, the baboon showed a craniocaudal sequence of paired orifices giving rise to paired arteries; orifices with incompletely divided septum giving rise to paired arteries; single orifices leading to a common trunk, which finally gives rise to paired arteries; and single orifices opening into single arteries. In addition, there was a craniocaudal decrease in the distance between any given pair of intercostal arteries and an increase in the spacing between adjacent pairs of intercostal arteries. Where a single artery supplied one side of the intercostal space, the contralateral side received a collateral branch, either from the preceding or succeeding intercostal artery. Though the basic organisation of the origin and distribution of the posterior intercostal arteries in the baboon is similar to that of man, the differences observed in the baboon might be attributed to factors such as body size, mode of activity, and even the phylogenetic level of development of the baboon.

Canine Model of Acute Aortic Rupture: Treatment with Percutaneous Delivery of a Covered Z Stent—Work in Progress

To develop a percutaneous treatment for aortic rupture with use of a covered intraluminal stent. A transmural tear was created percutaneously in the thoracic aorta in six dogs with use of a 4-mm angioplasty balloon. Gianturco Z stents were covered with polytetrafluoroethylene, loaded into a 14-F sheath, and advanced through the femoral artery to the site of injury. Within 2 minutes after initiation of the injury, the stent was deployed. Homologous canine blood was given during the procedure. Dogs that survived 24 hours were then killed. The first stent did not expand completely, and the dog died in 1 hour. At necropsy, the first two dogs (1-hour and 8-hour survival) had a large left hemothorax and extensive periaortic hematoma, indicating intrathoracic exsanguination. The next four dogs were treated with a modified stent and survived 2 hours (n = 1), 8 hours (n = 1), and 24 hours (n = 2). At necropsy hemothorax did not exceed 15 mL, and periaortic hematomas were small. The cause of death in the two early casualties with the modified stent is uncertain. There were no signs of spinal cord injury despite occlusion of three pairs of intercostal arteries. The covered Z stent (in its modified form) tamponaded the aortic tear, preventing exsanguination. Long-term studies of biocompatibility of this device appear justified.

Repair in arterial tissue 2 years after a severe single dilatation injury: The regenerative capacity of the rabbit aortic wall

The thoracic aortae from 11 rabbits that survived a single severe dilatation injury for 2 years were studied by vital staining with Evans blue, immunohistochemistry and transmission electron microscopy. Our results have shown almost total restitution of the thoracic aorta. Six of the 11 rabbits submitted to an injury had no blue-stained areas, indicating total reendothelialization. Five rabbits had a few blue areas often on the ventral side of the aorta. The reendothelialization from the first to the seventh pair of intercostal arteries ranged from 82% to 100%. There was intimal thickening inside the original internal elastic lamina in both white and blue areas. All blue areas had a surface composed of smooth muscle cells. Reendothelialized areas consisted of mature endothelium, reticular basal membrane, layered smooth muscle cells and an extracellular matrix consisting of pre-elastin, elastin, collagen and proteoglycans. An effective barrier had apparently been formed against penetration of macromolecules, judged from the absence of fibrinogen/fibrin and unmasked fibronectin. Intimal thickenings without endothelial cover were covered with smooth muscle cells without intercellular junctions. Our results indicate that an extracellular matrix of fibrin and fibronectin plays a role in forming an intimal thickening, and it is suggested that proteoglycans may modulate the biological role of the extracellular matrix in the healing process.

Distal aortic pressure during coarctation operation

Mean distal aortic pressure (DAP) was monitored continuously during operative repair of coarctation of the aorta in 67 children more than 1 year of age between 1982 and 1987. At initial test clamping a DAP of 45 mm Hg or more was considered adequate. In 42 patients (group A), DAP exceeded 45 mm Hg and the operation proceeded. In 25 patients (group B) the DAP was less than 45 mm Hg, and adjustments were made to the position of the proximal and distal clamps and in the use of hypotensive agents. After these adjustments in group B, DAP rose from 34.7 to 50.6 mm Hg ( p < 0.001), achieving the desired level in all but 5 patients, who required temporary shunts to support the distal circulation. The adjustments were as follows: the left subclavian artery was open in 28% of patients before and 60% after ( p < 0.02); no more than one pair of intercostal arteries was clamped in 64% before and 88% after ( p < 0.05); and no hypotensive agents were used in 56% before and 80% after ( p = 0.07). During the first ten minutes of cross-clamping the DAP rose by 5.5 mm Hg ( p < 0.01, n = 52). It is concluded that continuous monitoring of DAP contributed to the operative management of these patients by indicating when adjustments in the position of the clamps or in the use of hypotensive agents were needed. The use of hypotensive agents should be reduced to achieve a higher DAP.

The effect of verapamil on cerebral cortical and spinal cord blood flow during proximal descending thoracic aortic occlusion.

The mechanism of central nervous system (CNS) protection during proximal descending thoracic aortic cross-clamping (PDTAC) for aortic surgery using calcium channel blocking agents is not known. In order to determine the effect of verapamil on CNS blood flow during PDTAC, we calculated cerebral cortical (CC), proximal spinal cord (PSC), and distal spinal cord (DSC) blood flow using the microsphere method in Grade I beagles. Flow calculations were obtained at baseline (pre-PDTAC), following mobilization of the proximal descending aorta for 5-8 cm by ligating 3-5 pairs of intercostal arteries (ICA), during PDTAC (45 min), and during maximal reperfusion. Two groups were studied: 1) control (Cont) untreated (n = 5); 2) verapamil (Ver) treated (0.4 mg/kg IV just before PDTAC and just before reperfusion) (n = 5). I) Proximal ICA ligation produces no compromise to SC blood flow. II) Verapamil may protect the CNS by: 1) maintaining cerebral autoregulation during reperfusion; and 2) dampening hyperperfusion of the distal SC during reperfusion.

Age-related changes in composition and mechanical properties of the tunica media of the upper thoracic human aorta.

A cylindrical segment, free of complex atherosclerotic lesions, was resected at autopsy from each of 59 descending human thoracic aortas by cutting just below the level of the first pair of intercostal arteries and 35 mm distal to this incision. Each isolated tunica media was defatted and subjected to successive treatment with EDTA-Tris, 5 M guanidine hydrochloride-Tris, 5 M guanidine hydrochloride-Tris-DTE, collagenase and either trypsin or hot alkali. After each extraction or digestion, the dimensions and weight of the segments were measured and the extracted materials were analyzed and quantitated. This allowed the total content of the various components of the tunica media to be assessed by both gravimetric and analytical means. An age-related rise was observed in the total content of the following components: proteins and glycoproteins soluble in chaotropic solvents (ranging from 24 mg/cm in the youngest samples to 46 mg/cm in the oldest) and collagen (38 mg/cm to 69 mg/cm). In contrast, the total content of elastin remained constant at 70 mg/cm at all ages, but its concentration decreased due to the rise in the concentration of the other tissue components as the tunica media thickened with age. It was also noted that with increasing age there was an accumulation of protein(s) which could not be solubilized by extraction with chaotropic agents or with collagenase, but which could be removed by treatment with either trypsin or hot alkali. Mechanical measurements conducted before and after trypsin digestion on samples previously subjected to purification with the first four agents used suggest that this accumulated protein(s) influenced the elastic response of the tissue to the applied stress by increasing the incremental modulus, the breaking stress, and the hysteresis. After the removal of this additional protein(s), the mechanical behavior of the elastin component was found to be identical in all samples, irrespective of age. It is therefore proposed that the morphological changes and the stiffening observed in the aging aortic wall are not due to degradation of its elastin network but to variations in the supramolecular organization of connective tissue components.

The effect of angiotensin II on in vivo albumin transport in normal rabbit aortic tissue

Angiotensin II and other vasoactive amines may have a direct effect on the permeability of the arterial wall. We have investigated the effect of angiotensin II in vivo albumin transport across the aortic wall in rabbits following intravenous injection of [ 125I]albumin. Transmural concentration profiles of 125I-labeled albumin across the intima and media of the aorta, generated during 25 min of either angiotensin or saline infusion, were measured by a serial-sectioning technique. The uptake of labeled albumin through the aortic wall was found to be dependent on position and to increase from the descending thoracic up to the arch. Angiotensin infusion increased albumin uptake in the region of the aorta proximal to the first pair of intercostal arteries and magnified the position dependence. Angiotensin infusion did not change the uptake of albumin in the descending thoracic aorta between intercostal arteries. The arterial blood pressure elevation associated with angiotensin infusion was not of prime importance in producing the uptake patterns described above.

Anomalous origins of the posterior intercostal arteries from 915 thoracic aortas: Their role in fractures of the ribs

Nine hundred fifteen aortas were collected from various hospitals during the years 1934 to 1937. All had been fixed in a 10 per cent solution of formalin, and all but three were believed to have been opened anteriorly. The subclavian artery was considered the upper limit of the thoracic aorta, and the diaphragm, the lower. Nine pairs of intercostal arteries should arise in the posterior midline of the aorta above the diaphragm. With allowances for variations, this was found to be true in 25.2 per cent of the cases. In 74.8 per cent they deviated to the right, to the left, or to the anterior wall, or were scattered in their placement of origin, constituting a devious delivery of blood. In the 915 aortas, 673, or 73.6 per cent, had thickening or destruction of the aortic intima, further interfering with the nutritional function of the branches. In 84 patients there had been syphilis, and a tertiary lesion was recognized in fourteen, or 16.7 per cent, of the 84 aortas. Alcoholism was known to have been included in the history of 92 of the patients, and in these the aortas were smooth in twenty, or 21.7 per cent.