Transesophageal echocardiographic monitoring of myocardial ischemia during vascular surgery

Transesophageal echocardiography (TEE) was used to detect segmental ventricular wall motion abnormalities (SWMAs) associated with ischemia in 49 high-risk patients who had 50 major vascular procedures, including 23 infrarenal aortic, five suprarenal aortic, 14 carotid, seven distal, and one axillofemoral reconstructions. A modified gastroscope tipped with an echocardiographic transducer was inserted into the esophagus and positioned behind the heart to obtain a reproducible cross-sectional view of the left ventricle at the level of the papillary muscles. Twelve patients (24%) had SWMA at baseline, probably representing areas of old infarction. Fourteen patients (28%) had new intraoperative SWMAs. Ten of 14 patients were successfully treated and wall motion was normalized. One of the four patients with persistent SWMA suffered a nonfatal subendocardial infarct; another patient suffered intraoperative cardiac arrest and died. No infarcts were documented in the 10 patients successfully treated. The mortality rate in the entire high-risk group was 6%. Alterations in ventricular wall motion were noted in almost 50% of high-risk patients undergoing major vascular surgery. Seventy-one percent of acute SWMAs were reversed without any evidence of myocardial infarction. TEE allowed early recognition of evolving myocardial ischemia and facilitated immediate and specific fluid and pharamcologic interventions. Continued application of this technique may reduce the incidence and morbidity of perioperative cardiac complications.

Shear stress regulation of artery lumen diameter in experimental atherogenesis

We studied the adaptive response of the arterial wall and intimal thickening under conditions of increased flow in an atherogenic model. Blood flow was increased by construction of an arteriovenous fistula between the right iliac artery and vein in six cynomolgus monkeys fed a diet containing 2% cholesterol and 25% peanut oil. The left iliac artery served as the control. Serum cholesterol increased from 135 +/- 22 mg/dl to 880 +/- 129 mg/dl during the experiment. After 6 months, blood flow in the right iliac artery (420 +/- 95 ml/min) was 10 times greater than in the left iliac artery (44 +/- 9 ml/min, p less than 0.005). Flow velocity in the right iliac artery (31 +/- 6 cm/sec) was more than twofold greater than in the left (12 +/- 1 cm/sec, p less than 0.05). Despite the marked difference in blood flow and flow velocity, calculated wall shear stress was the same in both the right (16 +/- 4 dynes/cm2) and left iliac vessels (15 +/- 2 dynes/cm2) because of a twofold increase in lumen diameter (p less than 0.001) of the right iliac artery. Shear stress in the aorta was also normal (12 +/- 2 dynes/cm2). There was no difference in plaque deposition or mean intimal thickness between the right and left iliac arteries. In the right iliac artery there was a twofold increase in media cross-sectional area (p less than 0.001) but no change in media thickness or total wall thickness. Tangential wall tension and tangential wall stress were two times greater on the right than on the left (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Protection from atherosclerotic lesion formation by reduction of artery wall motion

We have studied mechanical factors that could determine how stenosis protects against distal atherosclerosis in cynomolgus monkeys fed an atherogenic diet. Critical aortic stenosis was produced by coarctation of the thoracic aorta. After 3 months, coarcted monkeys had a mean aortic pressure gradient of 25 +/- 1 mm Hg and a 76% +/- 2% lumen stenosis. Aortic wall motion was measured by means of in vivo ultrasonic sonomicrometry. Dynamic tracings of aortic pressure and diameter were recorded simultaneously at standard locations proximal and distal to the stenosis and at comparable sites in noncoarcted control animals. In the proximal aorta, mean blood pressure and pulse pressure were increased (p less than 0.05), but wall motion and intimal lesion area were not different from those determined in control monkeys. In the aorta distal to the coarct, mean blood pressure was no different from that in control animals but pulse pressure was diminished; in addition, there was marked reduction of arterial wall motion (p less than 0.001). This was accompanied by a significant reduction of intimal plaque area (p less than 0.05) and acid lipase activity (p less than 0.001). Thus, inhibition of plaque formation in the distal aorta coincided with reduction of pulse pressure and aortic wall motion rather than with blood pressure or hypercholesterolemia. Inhibition of arterial wall motion may account for the sparing effect often encountered in human arteries distal to stenosing atherosclerotic plaques.

New criteria for placement of a prophylactic vena cava filter

In order to identify patients who, having had an initial pulmonary embolism, are likely to develop recurrent emboli despite adequate anticoagulation therapy, ten patients (group 1) with documented recurrent pulmonary embolism during anticoagulation therapy were compared with 31 patients (group 2) who showed no evidence of recurrent emboli during the treatment period. Risk factors for thromboembolic disease were similar between the two groups. Noninvasive venous studies of the lower extremities, including Doppler venous ultrasound and phleborheography (PRG), were performed upon all patients after the initial embolic event. Of the ten patients in group 1, seven (70 per cent) had clinical signs of deep vein thrombosis (DVT). Doppler studies were positive for eight of the nine patients studied, and PRG studies were positive for eight of eight patients tested. In contrast, of the 31 patients who responded well to medical therapy, one patient (3 per cent) had clinical signs of DVT, three patients (10 per cent) had positive Doppler studies and one patient (3 per cent) had a positive PRG. Combined Doppler and PRG studies were positive in 100 per cent of the patients in group 1 but in only 6 per cent of the patients in group 2 (p less than 0.001). The results of this study suggest that patients having an initial pulmonary embolism and DVT of sufficient extent detected by noninvasive studies may be at an increased risk for recurrent PE despite anticoagulation therapy. Insertion of a vena cava filter should be considered in these patients prior to the second embolic event.

Efficacy of isolated profundaplasty

Profundaplasty has been advocated as an outflow procedure for threatened failure of aortobifemoral grafts as well as a primary procedure for severe claudication and limb ischemia. The authors reviewed their experience with 27 patients who underwent profundaplasty between 1978 and 1983; five patients (group 1) were treated for threatened or complete aortofemoral graft thrombosis while 22 patients (group 2) underwent profundaplasty as an isolated procedure to treat limb ischemia. Preoperative angiograms were assessed for the presence of five criteria associated with a favourable result from profundaplasty: stenosis of the orifice of the deep femoral artery greater than 50%; minimal disease of the distal artery; disease-free collaterals; reconstitution of a patent superficial femoral or popliteal artery; good popliteal outflow with at least one vessel patent to the foot. Profundaplasty was successful in 100% of group 1 patients but relieved symptoms or healed lesions in only 14% of those in group 2. In the latter group 64% required major amputation. The number of favourable angiographic criteria was similar in both groups. Isolated profundaplasty for limb salvage is not recommended. Angiographic criteria do not reliably identify the few patients who will benefit from profundaplasty alone. The principal role of the procedure is increasing outflow for an aortic graft.

Predicting cerebral ischemia during carotid endarterectomy

We reviewed 86 consecutive patients undergoing elective carotid endarterectomy to determine whether preoperative clinical and angiographic data could be used to predict the risk of intraoperative cerebral ischemia during carotid occlusion. Electroencephalographic (EEG) monitoring with on-line Berg-Fourier transformation was carried out in all patients. A total of 32 patients (37.2%) underwent intraoperative shunting. Of these, 13 had no EEG changes but underwent shunting because of the surgeon's preference, while 19 patients underwent shunting because of EEG changes consistent with cerebral ischemia. There was one permanent (1.2%) and one transient (1.2%) neurologic deficit. Angiographic findings, clinical histories, and intraoperative EEGs were retrospectively reviewed to determine which risk factors best predicted the occurrence of intraoperative cerebral ischemia. Stroke within six weeks increased the risk of intraoperative cerebral ischemia 20-fold. Intracranial disease and contralateral carotid stenosis increased the risk of ischemia 17-fold and 16-fold, respectively. Statistical summation of all risk factors yielded a probability equation for EEG change that accurately quantitated pre-operative risk. Prospective application of this probability equation may simplify operative decision making if EEG monitoring is not available.

Repair of a vertebral artery dissection. Case report

The case is presented of a 38-year-old woman who suffered multiple cerebellar infarctions as a result of emboli from a vertebral artery dissection. Surgical therapy led to a satisfactory recovery. This case emphasizes the importance of an aggressive approach to such lesions.

Increased collagenase activity in early aneurysmal dilatation

Increased collagenase activity has been implicated as a basic abnormality in aortic aneurysm formation. We studied a localized aneurysmal change, poststenotic dilatation, and its relation to collagenase and elastase activity of the aortic wall. Cynomolgus monkeys underwent midthoracic aortic coarctation to produce poststenotic dilatation. Serial angiography showed that poststenotic dilatation was minimal or absent at 10 days, just discernible at 3 months, and prominent at 6 months. At the 3-month time interval, collagenase activity in the region of the poststenotic dilatation increased twofold compared with the same region in aortas from animals without poststenotic dilatation (p less than 0.05). There was no change in aortic elastase activity. These data indicate that collagenolysis and aneurysmal dilatation may be induced by local modifications of pressure and/or flow. Increased collagenase activity associated with abdominal aortic aneurysms may not represent an intrinsic metabolic defect but rather a response to altered hemodynamic conditions.

Spontaneous dissection of the extracranial vertebral arteries

Though the syndrome of carotid artery dissection is well known, "spontaneous" vertebral artery dissection is rarely recognized. We now report clinical and radiologic findings in five patients with presumed vertebral dissection, one pathologically confirmed. Mean age was 35.2 years (range 27-41). Two were men; three women. None had hypertension, vascular disease, or trauma. Headache and neck or occipital pain was prominent in all, often preceding other symptoms. Four of five patients had unilateral partial alteral medullary syndromes, in one accompanied by medial medullary signs. One patient had a cerebellar infarct. Angiography in four patients showed severe irregular stenosis of the distal extracranial vertebral artery (three bilaterally). A fifth patient with irregular stenosis above the vertebral origin had verified extensive dissection in the resected segment. No patient developed late ischemia. Repeat angiography in three showed healing. We conclude that spontaneous vertebral artery dissection, though rare, has recognizable clinical and radiologic features.

Role of acid lipase in cholesteryl ester accumulation during atherogenesis. Correlation of enzyme activity with acid lipase-containing macrophages in rabbit and human lesions

Purified acid lipase was previously shown to hydrolyze the artificial substrate, alpha-naphthyl palmitate, as well as triglycerides and cholesteryl esters and to form cholesteryl esters. To determine to what extent these activities are associated with acid lipase-containing cells in atherosclerotic plaques, we examined rabbit aortas at different stages of experimental lesion induction and human atherosclerotic arteries. Assays of cholesteryl ester formation, and alpha-naphthyl palmitate and cholesteryl ester hydrolysis were performed on homogenates of lesions and the hydrolysis of the artificial fatty acid ester was used as a histochemical marker to identify acid lipase positive foam cells in sections of the same lesions. The volume of lesions occupied by cells stained for acid lipase correlated strongly with the enzyme activities of the arterial homogenates. These results suggest that acid lipase-containing cells may mediate the accumulation of cholesteryl ester during atherogenesis. Since acid lipase activity marks macrophages, these methods may be useful for relating macrophage distribution and function to lesion progression, regression, and complication.

Pulsatile flow and atherosclerosis in the human carotid bifurcation. Positive correlation between plaque location and low oscillating shear stress

Fluid velocities were measured by laser Doppler velocimetry under conditions of pulsatile flow in a scale model of the human carotid bifurcation. Flow velocity and wall shear stress at five axial and four circumferential positions were compared with intimal plaque thickness at corresponding locations in carotid bifurcations obtained from cadavers. Velocities and wall shear stresses during diastole were similar to those found previously under steady flow conditions, but these quantities oscillated in both magnitude and direction during the systolic phase. At the inner wall of the internal carotid sinus, in the region of the flow divider, wall shear stress was highest (systole = 41 dynes/cm2, diastole = 10 dynes/cm2, mean = 17 dynes/cm2) and remained unidirectional during systole. Intimal thickening in this location was minimal. At the outer wall of the carotid sinus where intimal plaques were thickest, mean shear stress was low (-0.5 dynes/cm2) but the instantaneous shear stress oscillated between -7 and +4 dynes/cm2. Along the side walls of the sinus, intimal plaque thickness was greater than in the region of the flow divider and circumferential oscillations of shear stress were prominent. With all 20 axial and circumferential measurement locations considered, strong correlations were found between intimal thickness and the reciprocal of maximum shear stress (r = 0.90, p less than 0.0005) or the reciprocal of mean shear stress (r = 0.82, p less than 0.001). An index which takes into account oscillations of wall shear also correlated strongly with intimal thickness (r = 0.82, p less than 0.001). When only the inner wall and outer wall positions were taken into account, correlations of lesion thickness with the inverse of maximum wall shear and mean wall shear were 0.94 (p less than 0.001) and 0.95 (p less than 0.001), respectively, and with the oscillatory shear index, 0.93 (p less than 0.001). These studies confirm earlier findings under steady flow conditions that plaques tend to form in areas of low, rather than high, shear stress, but indicate in addition that marked oscillations in the direction of wall shear may enhance atherogenesis.

Retarding effect of lowered heart rate on coronary atherosclerosis

The role of heart rate in the development of coronary atherosclerosis was assessed in adult male cynomolgus monkeys (Macaca fascicularis). Heart rate was lowered in six animals by surgical ablation of the sinoatrial node. A sham procedure, which included all of the surgical steps except for sinoatrial node ablation, was carried out in eight animals. All of the monkeys were fed an atherogenic high cholesterol diet for 6 months, and heart rates were monitored repeatedly by telemetry during 24-hour test periods. Coronary atherosclerosis in animals with postoperative heart rates less than the preoperative mean for all of the animals that underwent surgery was less than half that of animals with heart rates above the mean or of diet-fed control animals not subjected to surgery. Groups did not differ in blood pressure, serum lipids, or body weight. These results suggest that heart rate in itself may contribute to the mechanisms by which behavioral patterns and physical training influence coronary artery disease.

Combined use of Doppler ultrasound and phleborheography in suspected deep venous thrombosis

Doppler ultrasound and PRG were compared with the results of venography in 216 limbs with suspected DVT. Equivocal or conflicting noninvasive test results were obtained in 40 limbs and thrombi were demonstrated venographically in 18 of these (45 per cent). In the remaining 176 limbs, the sensitivity of the noninvasive test was 88 per cent and the specificity was 99 per cent. Treatment may be confidently chosen without venographic confirmation when the results of Doppler ultrasound and PRG agree. Venography is indicated in the minority of instances when the two noninvasive test results do not agree or are equivocal.

Role of medial lamellar architecture in the pathogenesis of aortic aneurysms

The human abdominal aorta is particularly susceptible to the formation of aneurysms with atrophic walls. This aortic segment normally has fewer medial lamellar units than would be expected for a mammalian aorta of comparable diameter as well as far fewer medial vasa vasorum than would be expected for an aortic wall of comparable thickness. To test the hypothesis that ischemia and/or loss of normal lamellar architecture are predisposing factors for aneurysm formation, we used the pig thoracic aorta, which is furnished with 75 medial layers and vasa supplying the outer two thirds. Vasal blood flow was surgically ablated, and crushing injury was used to reduce the number of intact lamellar units. Mural ischemia alone resulted in necrosis of cells in the medial zone furnished by vasa but did not lead to aneurysmal dilatation, and all the fibrous tissue layers persisted during the 2-month observation period. Mechanical injury resulted in aneurysms in both ischemic and nonischemic aortic segments, but only if fewer than 40 intact lamellae remained and the average tension per lamellar unit exceeded three times the normal value of 1316 +/- 202 dynes/cm (4543 +/- 1624 for ischemic and 4087 +/- 871 for nonischemic segments; p less than 0.01 for each). We conclude that a critical reduction in the number of intact lamellar units results in aneurysmal dilatation. Protracted medial ischemia due to intimal plaque formation in the avascular abdominal aorta may eventually reduce the number of intact lamellae and favor the development of aneurysms.

Morphologic alteration of cultured arterial smooth muscle cells by cyclic stretching

Cyclic stretching of smooth muscle cells in culture resulted in a two- to fivefold increase in protein and collagen synthesis. The same in vitro system was utilized to relate changes in smooth muscle cell morphology to mechanical stress. Smooth muscle cells, grown in culture from rabbit aorta explants, were transferred to purified elastic membranes derived from bovine aorta. The membranes were either subjected to stretching and relaxation 52 times per minute or stretched and held stationary for 8, 48, or 56 hr. Profiles of rough endoplasmic reticulum (RER) were counted and myofilament content estimated from electron micrographs of 100 cells for each experiment. Cells from cyclically stretched preparations were compared with stationary cells derived from the same subculture. Myofilaments were largely replaced by RER in cyclically stretched cells and there was a reciprocal relationship between RER and myofilament content in individual cells. In cells from stationary preparations, myofilament content also diminished with time but RER profiles were few. At 56 hr, RER profiles numbered 16.7 +/- 1.7 in stretched cells compared with 3.6 +/- 1.3 in stationary cells (P less than 0.05). Cyclically stretched cells formed numerous intercellular contacts and showed little evidence of cytoplasmic degradation while stationary cells showed few contacts and contained numerous cytosomes and lamellar bodies. The results suggest that cyclic stretching resulted in the formation of RER or the preservation of myofilaments and that immobility resulted in the disappearance of myofilaments and cytoplasmic degradation.(ABSTRACT TRUNCATED AT 250 WORDS)

Limb salvage in poor-risk patients using transluminal angioplasty

We performed percutaneous transluminal angioplasty (PTA) in 97 limbs of 86 patients with end-stage occlusive disease in whom vascular reconstruction was not possible. Most patients required dilation of long-segment occlusions and/or multiple lesions. Angiographic appearance was improved in 87 limbs of 78 patients (90%). Ankle-brachial pressure index increased from 0.40 +/- 0.03 to 0.64 +/- 0.03, and increased more than 0.15 in 63% of the limbs. Major amputation was required in 19 of the 87 limbs (22%) following PTA. The incidence of restenosis was 19% at three months, 42% at six months, and 57% at one year. Repeated PTA successfully maintained vascular patency in ten limbs, and four patients have since had successful distal bypass. Two limbs that initially improved needed amputation four to 19 months after dilatation. Follow-up ranged from one to 45 months; overall limb salvage rate was 76%. Thus PTA can enhance limb salvage in poor-risk patients with end-stage disease.

Carotid bifurcation atherosclerosis. Quantitative correlation of plaque localization with flow velocity profiles and wall shear stress

The distribution of nonstenosing, asymptomatic intimal plaques in 12 adult human carotid bifurcations obtained at autopsy was compared with the distribution of flow streamline patterns, flow velocity profiles, and shear stresses in corresponding scale models. The postmortem specimens were fixed while distended to restore normal in vivo length, diameter, and configuration. Angiograms were used to measure branch angles and diameters, and transverse histological sections were studied at five standard sampling levels. Intimal thickness was determined at 15 degrees intervals around the circumference of the vessel sections from contour tracings of images projected onto a digitizing plate. In the models, laser-Doppler anemometry was used to determine flow velocity profiles and shear stresses at levels corresponding to the standard specimen sampling sites under conditions of steady flow at Reynolds numbers of 400, 800, and 1200, and flow patterns were visualized by hydrogen bubble and dye-washout techniques. Intimal thickening was greatest and consistently eccentric in the carotid sinus. With the center of the flow divider as the 0 degree index point, mid-sinus sections showed minimum intimal thickness (0.05 +/- 0.02 mm) within 15 degrees of the index point, while maximum thickness (0.9 +/- 0.1 mm) occurred at 161 +/- 16 degrees, i.e., on the outer wall opposite the flow divider. Where the intima was thinnest, along the inner wall, flow streamlines in the model remain axially aligned and unidirectional, with velocity maxima shifted toward the flow divider apex. Wall shear stress along the inner wall ranged from 31 to 600 dynes/cm2 depending on the Reynolds number. Where the intima was thickest, along the outer wall opposite the flow divider apex, the pattern of flow was complex and included a region of separation and reversal of axial flow as well as the development of counter-rotating helical trajectories. Wall shear stress along the outer wall ranged from 0 to -6 dynes/cm2. Intimal thickening at the common carotid and distal internal carotid levels of section was minimal and was distributed uniformly about the circumference. We conclude that in the human carotid bifurcation, regions of moderate to high shear stress, where flow remains unidirectional and axially aligned, are relatively spared of intimal thickening. Intimal thickening and atherosclerosis develop largely in regions of relatively low wall shear stress, flow separation, and departure from axially aligned, unidirectional flow. Similar quantitative evaluations of other atherosclerosis-prone locations and corresponding flow profile studies in geometrically accurate models may reveal which of these hemodynamic conditions are most consistently associated with the development of intimal disease.