Management of abdominal aortic graft complications

OBJECTIVE

This study reviews the outcome of 61 patients who underwent 66 reoperations for complications of aortic grafts. There were 25 patients with false aneurysm of an aortic anastomosis and 41 patients with graft infection, 17 of whom had involvement of the gastrointestinal tract.

SUMMARY BACKGROUND DATA

Significant late complications of aortic grafting occurred in 2% of patients. The mode of clinical presentation, the clinical characteristics, and outcome in these patients has not been emphasized.

METHODS

This study reviews our experience with patients with complications of aortic grafts requiring graft excision or replacement with a view towards identifying prominent and important clinical characteristics and predictors of successful treatment.

CONCLUSIONS

Patients with involvement of the gastrointestinal tract have higher mortality and morbidity than patients with simple aortic graft infection or those who require aortic graft replacement for pseudoaneurysm formation at the aortic anastomosis. These patients require longer hospitalization, more blood transfusion, and have higher operative and long-term mortality. Revascularization of the lower extremities should be attempted and has a high rate of limb salvage although revision or thrombectomy may be required. The authors recommend complete graft excision and extra-anatomic bypass for patients with aortic graft infections.

Reduction of experimental vein graft intimal hyperplasia by ketanserin

Intimal hyperplasia is considered to be the result of smooth muscle cell proliferation. Experimental vein grafts (VG) in the rabbit develop intimal hyperplasia and a contractile response to serotonin (5-HT), mediated by a 5-HT2 receptor. 5-HT is known to stimulate smooth muscle cell proliferation in vitro and therefore may be linked to the development of intimal hyperplasia. This study examines the effect of a 5-HT2 antagonist, ketanserin (KT) on vein graft morphology and function at 14 and 28 days after grafting. Forty-three New Zealand White rabbits underwent common carotid interposition bypass grafting. Twenty-two were treated with KT (0.86 mg/kg/day po) 5 days prior to surgery and thereafter until harvest. The remaining 21 animals acted as controls. VG were harvested at 14 (VG14) and 28 (VG28) days for histology or vasoreactivity. Twenty-three VG were harvested by pressure fixation and the midportions of the grafts were examined by videomorphometry. Standard isometric tension studies in response to serotonin and norepinephrine (NE) were performed on the rings from the remaining 20 VG. Contralateral external jugular veins (CV) from both groups were studied to assess the functional toxicity of KT. There were no toxic effects to KT noted. KT therapy did not affect the functional activity of the CV at 14 or 28 days when compared to controls. When compared to controls, KT significantly reduced the intimal thickness (49 +/- 11 vs 113 +/- 24 microns; P = 0.04) and there was an increase in luminal area (16.89 +/- 2.13 vs 8.41 +/- 1.59 mm2; P < 0.02) in VG28 only.(ABSTRACT TRUNCATED AT 400 WORDS)

Hypercholesterolemia and experimental vein grafts: accelerated development of intimal hyperplasia and an increase in abnormal vasomotor function

Hypercholesterolemia is an important risk factor for the development of atherosclerosis. Late vein graft failure has been attributed to a combination of both intimal hyperplasia and atherosclerosis. This study examines the effect of hypercholesterolemia on the early morphology and vasomotor function of experimental vein grafts. Forty New Zealand White rabbits received either a 1% cholesterol diet (n = 24; HC) or a standard diet (n = 16; CON) for 4 weeks before operation and thereafter until harvest. All animals underwent a reversed vein common carotid artery bypass. The vein grafts and contralateral veins were harvested at 2 and 4 weeks after operation in both groups for either histological and morphometric analysis (n = 8 for each group) or for in vitro isometric tension studies using serotonin (5-HT), norepinephrine (NE), bradykinin (BK), and endothelin-1 (ET) and following NE precontraction, relaxation in response to acetylcholine (ACh) and sodium nitroprusside (SNP). Serum cholesterol levels were measured after 4, 6, and 8 weeks of the cholesterol diet. Serum cholesterol concentrations were 20 to 30 times higher than controls in the hypercholesterolemic animals at all times. The intimal area of the grafts in the HC group increased by twofold at 2 weeks and threefold at 4 weeks compared to corresponding controls. In contrast to the CON vein grafts, the intima of the vein grafts from HC consisted mainly of lipid-laden smooth muscle cells with scattered interspersed macrophages and occasional lipid plaques between the intima and the media. Medial areas were similar in all grafts. HC grafts became progressively more sensitive to 5-HT at 2 and 4 weeks. A supersensitivity to NE and BK developed at 4 weeks in HC grafts. There was no change in sensitivity to ET. While no graft relaxed to ACh, HC grafts contracted at low doses. All grafts responded to SNP in a dose-dependent manner. In contrast to CON veins, HC veins demonstrated an increase in sensitivity to NE and a contractile response to 5-HT (at 4 weeks only). HC veins did not relax in a dose-dependent manner in response to ACh. No changes in the morphology of HC veins were noted. HC produces changes in the structure and associated vasomotor abnormalities of vein grafts. Closely related functional changes also occur in contralateral veins. HC appears to induce intrinsic changes in smooth muscle cells which are linked to a greater proliferative and abnormal vasomotor capability. Clinically, applications of vigorous anti-HC regimens perioperatively may be beneficial in maintaining patency over the longer term.

Computer-assisted modeling of blood-flow: theoretical evidence for the existence of optimal flow wave patterns

The purpose of this study was to model blood-flow waveforms in order to examine the relationship between various waveform shapes and input impedance spectra. Twenty distinct single cardiac cycle flow waveforms having the same mean flow and heart rate were created based on clinical and published observations. The "best" waveform was one with a steep flow upstroke, a high peak flow value, swift deceleration following peak flow, and flow reversal during diastole. Each flow waveform was paired with 20 computer-generated pressure waveforms to calculate input impedance spectra by discrete Fourier transformation. "Favorable" flow waveforms were associated consistently with a lower characteristic impedance (average of 4th-10th harmonics, Zav) irrespective of the shape or magnitude of the input pressure wave. Zav corresponds to the degree of compliance of the vascular bed and could be expected to be lower under favorable outflow conditions and in non-diseased vessels. In conclusion, this study provides theoretical evidence for the existence of optimal flow wave patterns and supports the notion of flow waveform assessment for diagnostic purposes.

Appearance of oxidized cellulose (Surgicel) on postoperative CT scans: similarity to postoperative abscess

OBJECTIVE

Oxidized regenerated cellulose (Surgicel), a sterile knitted fabric that causes thrombus formation because of its physical properties, is frequently used for intraoperative hemostasis. Unlike traditional surgical sponges, it is bioabsorbable and can be left in the surgical bed. On CT scans, the appearance of the retained oxidized cellulose can mimic that of an abscess. The purpose of this study was to describe the appearance of oxidized regenerated cellulose on postoperative CT scans so that an erroneous diagnosis of an abscess can be avoided.

MATERIALS AND METHODS

We reviewed the CT examinations of five postoperative patients in whom oxidized regenerated cellulose had been used for surgical hemostasis. Operative reports and surgeons confirmed the use of oxidized cellulose. Four CT scans were abdominal examinations, and one was a head examination.

RESULTS

In four cases, CT scans showed focal, linear collections of gas within masses with mixed attenuation in or near the operative site. No air-fluid levels were present. In three patients, cultures of specimens obtained by aspiration were negative for pyogenic organisms.

CONCLUSION

Retained oxidized cellulose can mimic an abscess on CT scans. Focal collections of air centrally located within a mass should alert the radiologist that oxidized cellulose may have been placed in the operative site, and an appropriate history should be sought.

Saphenous vein endothelium-dependent relaxation in patients with peripheral vascular disease

In vitro vasomotor responses of saphenous veins of 15 patients undergoing peripheral vascular bypass procedures were studied. Vessels were harvested by standard techniques, sectioned into 4 mm rings, and suspended in organ baths under isometric tension. Stimulation with cumulative doses of norepinephrine revealed a -logED50 of 6.85 +/- 0.12 M and maximal tension of 8.64 +/- 1.77 g. Patient characteristics suggesting high maximal response (by univariate analysis) included male sex (male 11.69 +/- 2.49 g versus female 5.08 +/- 1.69 g; p = 0.058). Intact and denuded rings were additionally tested for endothelium-dependent relaxation following submaximal norepinephrine precontraction. The vessels relaxed in response to acetylcholine (maximal relaxation 31.1 +/- 10.7% at 1 x 10(-6) M), calcium ionophore A23187 (85.3 +/- 11.8% at 1 x 10(-5) M), and sodium nitroprusside (150.8 +/- 15.2% at 1 x 10(-5) M), but only acetylcholine relaxation was completely endothelium-dependent. Calcium ionophore A23187 relaxation was partially dependent on the endothelium while sodium nitroprusside relaxation was entirely endothelium-independent. Negligible relaxation was observed in response to adenosine diphosphate (ADP) (12.1 +/- 12.8% at 1 x 10(-5) M) while histamine and serotonin caused additional contraction only. We concluded that, in patients undergoing vascular surgical procedures, the saphenous vein (1) demonstrates variable contractile function which appears to be greater in males following spinal anesthesia, and (2) exhibits moderate endothelium-dependent relaxation in response to acetylcholine and calcium ionophore A23187 but not to ADP, histamine, or serotonin.

Parenteral anticoagulation with the heparinoid Lomoparan (Org 10172) in patients with heparin induced thrombocytopenia and thrombosis

Progressive thrombocytopenia may develop in as many as 5% of patients receiving heparin anticoagulation. In these patients, the risk of thromboembolic complications as well as continued thrombocytopenia necessitates discontinuation of heparin and initiation of an alternative anticoagulant when indicated. The heparinoid Lomoparan (Org 10172) is a mixture of several non-heparin low molecular weight glycosaminoglycans with proven anticoagulant efficacy that is generally non-reactive with platelets in the presence of plasma from patients with heparin induced thrombocytopenia, whereas standard heparin will induce platelet aggregation. We evaluated the role of heparinoid as a potential alternative anticoagulant in patients with heparin induced thrombocytopenia. During a 6 month period, we identified six patients with heparin induced thrombocytopenia who required an alternative parenteral anticoagulant, four as primary treatment for specific medical problem, and two as anticoagulation during a necessary surgical procedure. Heparinoid was used successfully in both medical and surgical patients requiring parenteral anticoagulation. In no case was there an exacerbation of the thrombocytopenia nor thromboembolic complications while on heparinoid therapy. Three of our patients sustained hemorrhagic complications, predominantly in the post-surgical setting in association with elevated anti-factor Xa levels and additional anticoagulant agents. We feel that these results confirm the utility of heparinoid anticoagulation in a select subset of patients with heparin induced thrombocytopenia who require continued parenteral anticoagulation.

Myointimal thickening in experimental vein grafts is dependent on wall tension

This study examines the relative contributions of intraluminal pressure, blood flow, wall tension, and shear stress to the development of myointimal thickening in experimental vein grafts. To study these different hemodynamic parameters, several experimental models were created in 30 New Zealand White rabbits separated into six groups: common carotid interposition vein grafts harvested at 4 weeks (VG-4) or 12 weeks (VG-12), common carotid-linguofacial vein arteriovenous fistulas harvested at 4 weeks (AVF-4) or 12 weeks (AVF-12), AVFs with partial outflow obstruction harvested at 4 weeks (AVFobs), and combination VG-AVFs in series harvested at 4 weeks (VGAVF). Blood pressure and flow in the graft or vein were measured by use of a transducer-tipped pressure catheter and electromagnetic flow meter. At harvest, veins were perfusion-fixed and proximal, middle, and distal sections were subjected to computerized morphometric analysis. Vein grafts were characterized by a high mean pressure (VG-4, 51 +/- 4; VG-12, 62 +/- 3 mm Hg), low mean flow (VG-4, 17 +/- 1; VG-12, 16 +/- 4 ml/min), large luminal area (VG-4, 19.7 +/- 2.4; VG-12, 19.3 +/- 3.9 mm2), high wall tension (VG-4, 17.0 +/- 1.5; VG-12, 19.5 +/- 2.4 x 10(3) dyne/cm), low shear stress (VG-4, 0.75 +/- 0.13; VG-12, 0.96 +/- 0.38 dyne/cm2), and a high degree of myointimal thickening (VG-4, 5.89 +/- 0.90; VG-12, 4.72 +/- 0.83 mm2). Arteriovenous fistulas were characterized by a low mean pressure (AVF-4, 5 +/- 1, AVF-12, 6 +/- 2 mm Hg), elevated blood flow (AVF-4, 82 +/- 16; AVF-12, 82 +/- 17 ml/min), small luminal area (AVF-4, 2.43 +/- 0.58; AVF-12, 7.14 +/- 2.68), low wall tension (AVF-4, 0.62 +/- 0.19; AVF-12, 0.89 +/- 0.24 x 10(3) dyne/cm), elevated shear stress (AVF-4, 108 +/- 32; AVF-12, 71 +/- 50 dyne/cm2), and decreased myointimal area (AVF-4, 1.18 +/- 0.26; AVF-12, 1.90 +/- 0.55 mm2). The addition of outflow obstruction to AVFs (AVFobs) resulted in elevated pressure (48 +/- 2 mm Hg), decreased flow (17 +/- 4 ml/min), larger luminal area (8.71 +/- 2.31 mm2), elevated wall tension (10.3 +/- 1.7 x 10(3) dyne/cm), and a degree of myointimal thickening approaching that of vein grafts (3.79 +/- 0.66 mm2).(ABSTRACT TRUNCATED AT 400 WORDS)

Chronic ACE inhibition reduces intimal hyperplasia in experimental vein grafts

Intimal hyperplasia is an important factor in the pathophysiology of vein graft failure. Local renin-angiotensin systems recently have been shown to modulate the development of intimal hyperplasia in arteries after intimal injury. The effect of chronic angiotensin-converting enzyme (ACE) inhibition on the development of intimal hyperplasia in experimental vein grafts was examined in this study. Ten New Zealand White rabbits received 10 mg/kg of captopril daily in their drinking water. One week later the right carotid artery was divided and bypassed with the reversed right external jugular vein in these rabbits and in 10 matched controls. Captopril was continued for 28 days after operation, when all the grafts were harvested. Five grafts from each group were perfusion fixed, and the intimal thickness in the proximal, middle, and distal segments was determined. Rings from the remaining grafts (n = 20 in each group) were studied in vitro under isometric tension, and their responses to norepinephrine (NE), histamine (HIST), serotonin (5-HT), angiotensin I (AI), and angiotensin II (AII) was measured. The intimal thickness of the proximal, middle, and distal segments of the captopril-treated grafts were significantly less than controls, being reduced in all segments by approximately 40% (p less than 0.0001). With regard to vasoreactivity, the captopril-treated grafts were hypersensitive to 5-HT (control ED50 5.5 +/- 0.5 X 10(-7) mol/L vs. captopril-treated 1.1 +/- 0.2 X 10(-6) mol/L; p less than 0.005) although the maximal response was significantly reduced (control 1.6 +/- 0.3 g vs. captopril-treated 0.8 +/- 0.1 g; p less than 0.05). There were no differences in sensitivity between control and captopril-treated rings with respect to NE, HIST, AI, or AII. Four of the ten captopril-treated segments, however, failed to respond to AI, and the maximal active tension of the responders was significantly reduced (control 0.47 +/- 0.06 g vs. 0.20 +/- 0.05 g; p less than 0.02). These results suggest that ACE is involved in the modulation of vein graft intimal hyperplasia, and that ACE inhibitors may have therapeutic applications in patients undergoing vein bypass procedures.

Quantitation of vascular outflow by measurement of impedance

One of the most important determinants of graft patency is the degree and character of vascular outflow. This study was designed to evaluate input impedance as a functional assessment of the outflow bed of vascular grafts. Four distinct outflow environments were created for external jugular vein conduits in 42 New Zealand white rabbits. Vein grafts (n = 14) were fashioned as end-to-side common carotid interposition bypass grafts. Arteriovenous fistulas (n = 15) were created by side-to-side anastomosis of the distal common carotid artery and linguofacial vein. Arteriovenous fistulas with outflow obstruction (n = 7) were fistulas with a metal clip partially obstructing the distal outflow channel (1 mm lumen). Vein graft/arteriovenous fistula combinations (n = 6) consisted of a vein graft and arteriovenous fistula in series. Pressure and flow in the external jugular vein were measured, and input impedance spectra were calculated by Fourier methods. By use of a PC-based acquisition and processing system, impedance results for 20 cardiac cycles could be obtained in approximately 10 minutes. The results revealed that vein grafts typically demonstrated high resistance to steady state flow (Rin = 235 +/- 50 x 10(3) dyne . sec/cm-5) and steadily decreasing impedance to pulsatile flow resulting in a characteristic impedance (Z0; average of fourth to tenth harmonics) of 35.5 +/- 8.0 x 10(3) dyne . sec/cm-5. Phase angle values were usually negative, especially at low harmonics (first harmonic phase angle = -1.11 +/- 0.10 radians) indicating that flow led pressure. In contrast, arteriovenous fistula Rin was minimal (6.3 +/- 1.4 x 10(3) dyne . sec/cm-5; p less than 0.05 compared to vein graft, and the impedance was flat across the frequency spectrum (Z0 = 8.5 +/- 1.5 x 10(3) dyne . sec/cm-5; p less than 0.05) with pressure and flow nearly in phase (first harmonic phase angle = -0.05 +/- 0.10 radians). Creation of outflow obstruction in arteriovenous fistulas resulted in significantly elevated Rin (136 +/- 41 x 10(3) dyne/sec . cm-5; p less than 0.05 compared to arteriovenous fistula and Z0 (23 +/- 9 x 10(3) dyne . sec/cm-5, p less than 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)

Vascular complications of cardiac catheterization

Femoral artery injury after diagnostic and therapeutic cardiac catheterization is a frequently encountered clinical problem. This study reviews 150 femoral artery injuries that occurred in 16,350 patients over a 5-year period. A prospective computerized cardiac catheterization data bank was used to determine significant risk factors associated with the occurrence of vascular injury. Logistic regression analysis revealed that congestive heart failure, female gender, and percutaneous transluminal coronary angioplasty or valvuloplasty procedure were significantly associated with occurrence of vascular injury. Greater age, smaller body surface area, and smaller weight were also associated with injury. Recommendations for management include an aggressive approach to obstruction even if local vascular reconstruction is required. False aneurysms are studied by ultrasonography, and small ones may be observed expectantly. Larger aneurysms and aneurysms that persist beyond a few days are managed by use of general or regional anesthesia and by gaining proximal control of the iliac artery. Arteriovenous fistulas resulting from catheterization are rarely hemodynamically significant and often close spontaneously. Thus repair should be delayed.

Effects of distention and short-term grafting on vasoreactivity in rabbit external jugular veins

The relative effects of distention, intraluminal pressure, and wall tension on venous smooth muscle and endothelial cell function were examined in 40 external jugular veins from New Zealand white rabbits. Vein grafts (n = 5) were interposed in the common carotid artery and explanted after 10 minutes. Distended veins were inflated in vitro with modified Krebs' solution at 37 degrees C for 10 minutes at pressures of either 20 mm Hg (D-20; n = 5) or 80 mm Hg (D-80; n = 5). Externally supported veins (ES-80; n = 5) were inflated at 80 mm Hg pressure, but distention was prevented by covering with a 3 mm internal diameter polytetrafluoroethylene sleeve. Bradykinin-induced in vitro maximal tension was attenuated significantly in vein grafts (0.13 +/- 0.04 g) and D-80 rings (0.27 +/- 0.07 g) compared with D-20 rings (1.20 +/- 0.14 g), ES-80 rings (0.99 +/- 0.13 g), or nondistended control rings (n = 40; 1.19 +/- 0.10 g; p less than 0.001). The attenuation in contraction in the vein graft and D-80 groups was nonspecific (i.e., similar results were obtained with respect to other smooth muscle agonists). Contractile function was inversely associated with wall tension, the product of pressure and radius (r2 = 0.7438; p = 0.06). In contrast, there were no differences in endothelium-dependent or endothelium-independent relaxation among the five groups. It is concluded that, in this experimental system, (1) venous smooth muscle function is significantly attenuated after short-term in vitro distention or grafting although endothelial function is largely preserved, and (2) the decrement in contraction is due to elevated wall tension.

Systemic hypertension alters vasomotor function in experimental vein grafts

Hypertension is an established risk factor for atherosclerosis, a disease that is important in the pathophysiology of vein graft failure. Hypertension can also alter arterial vasoreactivity. The vasomotor function and histologic characteristics of autogenous vein grafts in hypertensive rabbits were assessed in this study. Hypertension was induced in 13 male New Zealand white rabbits by use of the Goldblatt one clip two kidney method. The right carotid artery was divided and bypassed with the reversed right external jugular vein 7 days later in these animals and in 13 normotensive controls. Blood pressure and renal function were assessed serially, and all the grafts were harvested after 28 days. Three grafts in each group were examined by light microscopy. The responses of the remaining grafts to norepinephrine, histamine, serotonin, and angiotensin II were determined in vitro under isometric tension. Endothelium-dependent relaxation to acetylcholine and calcium ionophore (A23187) was assessed in precontracted grafts. The mean arterial pressure was significantly increased after the Goldblatt procedure was performed. Intimal hyperplasia was observed in both groups, but the grafts in the hypertensive groups showed increased adventitial and medial fibrosis and a reduced number of vasa vasora. The grafts in the hypertensive rabbits were hypersensitive to all agonists as indicated by a significant reduction in their median effective dose values, and their maximal responses to all agonists were also significantly reduced. No graft relaxed in response to acetylcholine, and whereas precontracted grafts in normotensive rabbits had a maximal relaxation of 24% +/- 6% of precontraction with A23187, this was absent in the grafts in the hypertensive rabbits. The results suggest that angiotensin-induced hypertension may adversely affect vein graft patency by inducing hypersensitivity to physiologically important agonists and reducing the effect of receptor-independent endothelium-derived relaxation on vasomotor tone.

Alterations in serotonergic receptor expression in experimental vein grafts

Rabbit external jugular veins, normally unresponsive to serotonin (5-HT), develop a constrictive response when grafted into the arterial circulation. The mechanisms responsible for this alteration were examined in this study. The right external jugular vein was grafted into the right carotid artery in 37 New Zealand white rabbits. The vein grafts were harvested at 3, 7, 9, 14, and 28 days after operation; contralateral external jugular veins were harvested at 9 days in six animals. Rings of these vessels were mounted under isometric tension, and dose-response curves to 5-HT were obtained. None of the grafts harvested at day 3 responded to 5-HT. All the grafts harvested from day 7 through day 28 constricted to 5-HT. The maximal response increased from 258 +/- 30 mg at 7 days to 734 +/- 108 mg at 28 days. No change occurred in the sensitivity to 5-HT with time. The increase in maximal response was paralleled by a linear increase in percent intimal area (intimal area/intimal + media areas) from 11.6% +/- 2.1% at 3 days to 48.7% +/- 1.9% at 28 days. Preincubation with ketanserin, a 5-HT2 and alpha 1-adrenergic antagonist, produced a concentration-dependent rightward shift in the 5-HT dose-response curve. The median effective dose for 5-HT increased progressively from 1.9 +/- 0.3 x 10(-6) mol/L (in the absence of ketanserin) to 6.1 +/- 1.7 x 10(-5) mol/L (ketanserin 8 x 10(-7) mol/L; p less than 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Functional and morphologic endothelial damage in rabbit external jugular veins stored in heparinized normal saline

Previous studies have demonstrated that vein storage in normal saline leads to significant mechanical morphological, and biochemical aberrations. However, little information is available regarding the functional damage that occurs. The purpose of this study was to evaluate the effect of saline storage on venous smooth muscle and endothelial function. Segments of ten external jugular veins from male New Zealand White rabbits were placed nondistended in either modified Krebs solution at 37 degrees C (Krebs-stored, KS) or heparinized normal saline at room temperature (saline-stored, SS) for 1 h. Segments 4 mm in length were then simultaneously studied in vitro under isometric tension. There was no difference in maximum tension or sensitivity to either bradykinin or histamine. Acetylcholine-induced relaxation in KS segments was not significantly different from relaxation in a historical cohort of nonstored segments (nonstored 87.4 +/- 1.0% vs. KS 84.5 +/- 2.0%; p = NS). However, there were significant attenuations in SS segment endothelium-dependent relaxation in response to both acetylcholine (KS 84.5 +/- 2.0% vs. SS 76.4 +/- 2.7%, p less than 0.02) and adenosine diphosphate (KS 47.9 +/- 2.9% vs. SS 40.6 +/- 3.7%, p less than 0.002). Relaxant responses to sodium nitroprusside (endothelium-independent) were not significantly different in the two groups (KS 94.6 +/- 1.6% vs. SS 95.7 +/- 2.2%; p = NS). Electron microscopic evaluation of SS segments revealed endothelial cell disruption with cellular edema and loss of intact junctions.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction of intimal hyperplasia and enhanced reactivity of experimental vein bypass grafts with verapamil treatment

Recent studies have shown that calcium antagonists exert an antiatherogenic effect in animals fed cholesterol. Vein graft intimal hyperplasia is believed to be an early event in atherosclerotic lesion formation, which is a significant cause of graft failure. Altered vasoreactivity has also been postulated in the etiology of vein graft failure. Therefore this study examined the effect of verapamil treatment on the development of intimal hyperplasia and the vasoreactivity of experimental vein bypass grafts. The right external jugular vein was grafted into the right carotid artery of 30 male New Zealand white rabbits fed normal rabbit chow. The left external jugular vein was used as the control vein. Fifteen animals received verapamil (1.25 mg/day for 28 days) via the femoral vein by means of an osmotic pump. In 15 control animals the pump contained saline. Plasma verapamil concentration was 50.9 +/- 13.2 ng/mL (x +/- SEM), a dose that showed no effect on either blood pressure, total serum cholesterol, or in vitro platelet aggregation to ADP. Fourteen of fifteen grafts were patent in each group, for a patency rate of 93%. Histologic examination using computer morphometry showed significant reduction of intimal hyperplasia at the proximal, middle, and distal graft segments (p less than 0.05). In addition in vitro isometric tension studies of the vein grafts and control veins showed that verapamil causes enhanced reactivity of both vein grafts and control veins in response to norepinephrine and histamine (p less than 0.05). Reactivity of vein grafts to serotonin was unaltered. While none of the normal veins in the control group responded to serotonin, normal veins treated with verapamil contracted readily in response to serotonin. Endothelial-dependent relaxation to acetylcholine was absent in both control and verapamil-treated vein grafts, while normal veins from both groups responded to the same extent to acetylcholine. Because we could not demonstrate any difference in platelet or endothelium function between untreated and verapamil-treated animals, we examined the direct effect of verapamil on smooth muscle. Verapamil significantly inhibited [3H]-thymidine incorporation into DNA in vascular smooth muscle cells in culture in a dose-dependent manner. Verapamil treatment significantly reduces intimal hyperplasia in experimental vein grafts and inhibits smooth muscle cell proliferation in culture. Furthermore the enhanced reactivity to norepinephrine and histamine in the verapamil-treated vessels has no detrimental effect on the patency rate at 4 weeks. Thus by inhibiting intimal hyperplasia, calcium antagonists may improve the long-term patency of vein bypass grafts.

Estimation of left ventricular volume and ejection fraction by two-dimensional transoesophageal echocardiography: comparison of short axis imaging and simultaneous radionuclide angiography

We have compared short axis images of the left ventricle (LV) obtained with transoesophageal echocardiography (TOE) to assess LV size and function with those obtained by radionuclide angiography (RNA). Simultaneous TOE and RNA images were attempted in 14 patients and results obtained in 12 patients undergoing repair of abdominal aortic aneurysms. The area of the LV cavity seen in the short axis images at a mid-papillary muscle level at end-systole (ESA) and end-diastole (EDA) were compared with volumes measured by RNA at end-systole (ESV) and end-diastole (EDV). An area ejection fraction (AEF) calculated from the TOE images (AEF = EDA-ESA/EDA) was compared with the RNA ejection fraction (EF) where EF = EDV-ESV/EDV. Good correlations were found between TOE log EDA and RNA log EDV (r = 0.86), TOE log ESA and RNA log ESV (r = 0.92) and TOE AEF and RNA EF (r = 0.96). This suggests that TOE short axis imaging at a mid-papillary muscle level is generally adequate for monitoring LV function during operation.