Intraoperative angioscopy: principles of irrigation and description of a new dedicated irrigation pump

The value of intraoperative angioscopy in the detection and immediate correction of technical errors and deficiencies during vascular surgery has been previously documented. The inability to see through blood remains the most significant limitation to the general application of angioscopy. Local irrigation with a balanced salt solution is the most commonly used method to clear the blood from a restricted field in a particular vessel. We have developed a new catheter irrigation pump system (maximum flow rate 340 ml/min) to establish and maintain visibility of the field during intraoperative angioscopy. Furthermore, we have demonstrated the safety of irrigating with high volume flows in the peripheral arteries and defined the basic principles of irrigation for angioscopy. The prototype pump tested in this study provides a wide range of flow rates and permits precise measurements of the fluid delivered. The instrument's display and its control with a single foot pedal makes its use relatively simple, obviating the need for additional support personnel while increasing the efficacy and safety of the angioscopic examination and increasing the number of situations where angioscopy may be very useful.

Routine intraoperative angioscopy in lower extremity revascularization

The inability to see through blood remains the main obstacle to the widespread and routine use of angioscopy. Local irrigation with a balanced salt solution is presently the most widely used method to clear the blood. By applying basic principles of irrigation and using a unique, dedicated, irrigation pump, we found that routine angioscopy during lower extremity revascularization that yields consistent high-quality studies is feasible, clinically useful, and safe. Between May 1, 1987, and July 31, 1988, 136 intraoperative angioscopies were performed during 112 peripheral bypass procedures, 15 thrombectomies, 2 embolectomies, and 7 miscellaneous revascularization procedures. Mean total irrigation fluid used in the peripheral bypasses was 398 mL (range, 0 to 1400 mL). Good visual quality was obtained in more than 80% of angioscopies and the failure rate was only 1.8%. On the basis of the findings in 71 of the 136 angioscopies, 78 clinical or surgical decisions were made. No complications were directly attributable to the insertion of the angioscope or use of the pump.

Imaging human atherosclerosis with 99mTc-labeled low density lipoproteins

The feasibility of localizing human atherosclerotic plaques by gamma scintillation camera external imaging with technetium-99m-labeled low density lipoproteins (99mTc-LDL) was tested in 17 patients who had atherosclerosis. Imaging demonstrated focal accumulation of radiolabel consistent with 99mTc-LDL sequestration by plaques in the carotid, iliac, or femoral vessels of four patients 8 to 21 hours after intravenous injection of the radiopharmaceutical. Focal accumulation of 99mTc-LDL also appeared in the location of coronary lesions in four patients, but this accumulation could not be distinguished with certainty from residual blood pool radioactivity. When carotid endarterectomy specimens from six patients who received 99mTc-LDL 1 day before endarterectomy were examined, the specimens had focal accumulations of radiolabel, with two to four times greater radioactivity in some regions of each specimen than in others; this occurred whether or not the lesions were detected on the gamma camera images. Lesion composition may have determined whether accumulation was quantitatively sufficient to produce an external image. Histologically, the imaged carotid specimen had abundant foam cells and macrophages and poorly organized intramural blood consistent with a plaque hemorrhage; in contrast, nonimaged endarterectomy specimens were mature, fibrocalcific plaques. We conclude that: 1) 99mTc-LDL did accumulate in human atherosclerotic plaques; 2) in some patients, the accumulation of 99mTc-LDL was sufficient for detection by gamma camera imaging; 3) the amount of LDL that accumulated appeared to depend on lesion composition; and 4) the design of new radiopharmaceuticals with reduced residual blood pool activity relative to plaque accumulation should lead to improved external imaging of atherosclerosis.

Lovastatin (mevinolin) in the treatment of heterozygous familial hypercholesterolemia. A multicenter study

STUDY OBJECTIVE

To evaluate the efficacy and tolerability of lovastatin under controlled conditions in heterozygous familial hypercholesterolemia.

DESIGN

Randomized, double-blind, placebo-controlled, multicenter trial.

SETTING

Five lipid clinics with a central laboratory and coordinating center.

PATIENTS

101 adult patients with heterozygous familial hypercholesterolemia.

INTERVENTIONS

Patients were on a lipid-lowering diet throughout the study. After a 4-week placebo baseline period, patients were randomized to five equal treatment groups. Each group received a different sequence of placebo or lovastatin 5 to 40 mg twice daily or 20 to 40 mg once daily in the evening, during three consecutive 6-week periods.

MEASUREMENTS AND MAIN RESULTS

The mean reductions in total plasma cholesterol and low-density lipoprotein cholesterol across the dosage ranges were 14% to 34% and 17% to 39%, respectively (p compared with zero and placebo less than 0.01). High-density lipoprotein cholesterol and apolipoproteins AI and AII rose slightly. Apolipoprotein B fell substantially at the higher dosage levels (-23% at 40 mg twice daily, p less than 0.01), indicating a reduction in the concentration of circulating low-density lipoprotein particles. Maximum response was achieved in 4 to 6 weeks. Twice-daily dosing was slightly more efficient than once-daily dosing. Of those patients receiving 40 mg twice a day, 89% had a fall in low-density lipoprotein cholesterol of at least 20%, and 61% had a fall of at least 40%. Adverse effects attributable to lovastatin were minimal, and no patient was withdrawn from the study.

CONCLUSION

Lovastatin was well tolerated and effective in the treatment of familial hypercholesterolemia.

Accumulation of native and methylated low density lipoproteins by healing rabbit arterial wall

To determine whether healing arterial wall accumulation of low density lipoproteins (LDL) is mediated by the high affinity LDL receptor, normocholesterolemic rabbits were injected with 125I-LDL, 99mTc-LDL, or the reductively methylated analogs of these compounds (125I-MeLDL, 99mTc-MeLDL), 1 month after balloon catheter deendothelialization of the abdominal aorta. If the mechanism of accumulation requires interaction with the LDL receptor, reductively methylated lipoproteins which do not bind to the receptor should not accumulate in healing arterial wall. Twenty-four hours after injection of labelled lipoproteins, each animal was injected with Evans blue dye, in order to distinguish reendothelialized from deendothelialized aorta. One hour after dye injection, the aorta was fixed, removed, divided into abdominal (ballooned) and thoracic (unballooned) regions and counted. For all lipoprotein preparations, there were three to four times as many counts in the abdominal as in the thoracic aorta. En face autoradiographs were made of the aortas that had been exposed to 125I-labelled lipoproteins. In the autoradiographs, the areas of the lowest activity corresponded to the centers of healing endothelial islands. The most intense radioactivity for both lipoproteins occurred in the region of the leading edge of the endothelial islands where active endothelial regeneration was in progress. The overall distribution of native and MeLDL accumulation was the same. The results suggest that low density lipoproteins are accumulated in areas of active endothelial regeneration by a mechanism that does not involve the high affinity LDL receptor.

Adrenal imaging with technetium-99m-labelled low density lipoproteins

Evaluation of adrenal cortical function by external imaging is currently accomplished by injection of radiolabelled analogs of cholesterol. Although the adrenals do utilized exogenous cholesterol for steroid hormone synthesis, the cholesterol is delivered to the glands not as free cholesterol but through the uptake of low density lipoproteins (LDL), which are subsequently degraded within the adrenal cortical cells to provide cholesterol. Thus, we sought to assess the use of 99mTc-labelled LDL injected into rabbits to obtain external images of the adrenal glands. Adrenal images of all nine rabbits tested were obtained within 18 to 21 hours after injection of 99mTc-LDL. Seven of the rabbits were subjected to adrenal cortical suppression with dexamethasone and then all nine rabbits were imaged a second time. In the untreated animals, visualization of the adrenal glands was accompanied by normal serum cortisol concentrations and accumulation of radiolabel in the adrenals, whereas in the dexamethasone-treated animals, lack of visualization of the adrenal glands was correlated with low serum cortisols, and greatly decreased accumulation of the radionuclide in the adrenals. These findings demonstrate for the first time that LDL, when labelled with 99mTc, can be used to evaluate adrenal cortical function by external imaging.

Local variation in arterial wall permeability to low density lipoprotein in normal rabbit aorta

Normal rabbits were injected intravenously with horseradish peroxidase (HRP) and 125I-labeled human low density lipoprotein (LDL), and the aortas were perfusion-fixed. Subsequent visualization of HRP in the aortas was produced by reaction of the tissue with diaminobenzidine and hydrogen peroxide. The luminal surface of the aortas showed many small punctate foci of brown reaction product to the HRP, which represented penetration of the HRP into the vessel wall. The foci were scattered over the luminal surface, and most of the focal areas were less than 1 mm in diameter. The concentration of LDL was up to 47 times greater in these focal areas than in surrounding noncolored regions not showing increased permeability to HRP. Small circumscribed foci of heightened permeability to LDL may predispose to the local accumulation of lipid and ultimately to the formation of atherosclerotic plaques.

Technetium-99m low density lipoproteins: preparation and biodistribution

The focal uptake by human atherosclerotic lesions of 125I bound to low density lipoproteins (LDL) can be demonstrated by external imaging. However, 125I has poor imaging characteristics. Therefore, we have developed a technique for labeling LDL with technetium. To facilitate analysis, LDL was first labeled with 99mTc, by reduction of TcO4- with dithionite in the presence of the protein. The labeled LDL was stable to electrophoresis, ultracentrifugation, and passage in vivo. This technique was repeated with minor modification with 99mTc to prepare [99mTc] LDL for use as an imaging agent. Its biodistribution in 16 rabbits was similar to that of [125I] LDL and it allowed high resolution external imaging of LDL uptake by tissues, including the injured, healing, arterial wall, and the adrenal cortex.

Evaluation of aortic stenosis by spectral analysis of the murmur

A relation between the peak transaortic pressure gradient and the frequency content of the murmur (r = 0.79) was demonstrated in a prospective "test" set of 50 patients with the clinical diagnosis of aortic stenosis. After heart sounds were recorded and digitized, three segments of the systolic murmur were isolated and analyzed by fast Fourier transform technique. An average frequency spectrum was quantitated by a previously described empiric spectral estimator. Clinical data and spectral ratio were correlated with the transaortic pressure gradient and aortic valve area was calculated from cardiac catheterization data. The best prediction of the transaortic pressure gradient was obtained when a 170 ms murmur segment was analyzed and when the predictive algorithm also included the aortic dimension (r = 0.87). The aortic valve area was poorly predicted (r = -0.48) unless estimates of blood flow and valvular calcification were included in the algorithm (r = 0.84). Further refinement of this technique may provide a non-invasive and clinically useful method for the estimation of aortic valve stenosis.

Simultaneous therapy with antiplatelet and anticoagulant drugs in symptomatic cardiovascular disease

Twenty of approximately 1000 patients attending the arteriosclerosis clinic at MIT during a 13 year period were treated simultaneously with aspirin and warfarin for symptomatic atherosclerotic (19) or rheumatic (1) heart or vascular disease. The average duration of therapy was 5.8 years. Thirteen patients suffered from familial hyperlipoproteinemia; only one patient had none of the major risk factors for arteriosclerosis. Refractory symptoms were related to the central nervous system in 13, peripheral vascular system in 5 and the heart in 2. All twenty patients became asymptomatic or showed marked clinical improvement on aspirin plus warfarin therapy. While on this therapy, complications, both thrombotic and hemorrhagic, occurred in 7 of the 20 patients (graft embolus in 1, and bleeding in 6; with one death as a result of intracranial bleeding) and sudden death, probably from acute myocardial ischemia, in a further 2 patients. We conclude that when alternative therapies are impossible or have proven to be of no avail in patients suffering from the complications of advanced atherosclerosis, the simultaneous administration of aspirin and warfarin may be a therapeutic alternative, although very close and careful followup of the patients' prothrombin times and clinical status is essential.

Vascular calcification in types II and IV hyperlipoproteinemia: radiographic appearance and clinical significance

Nearly 90% of patients with clear-cut hyperlipidemia seen in clinical practice have type II or IV hyperlipoproteinemia. Previous studies have shown that these syndromes have different distributions of coronary artery atherosclerosis and different outcomes after coronary bypass grafting. A characteristic pattern of vascular calcification on chest films might have some prognostic value. Therefore, to determine the location and extent of aortic root and coronary artery calcification seen on chest films, 33 consecutive patients with type II and 17 with type IV hyperlipoproteinemia were studied who were admitted for coronary arteriography between 1970 and 1982. Among the 33 patients with type II disease, 21 women and 12 men, 22 had radiographically visible calcification that was different in distribution from that usually found in atherosclerotic disease. The ascending aorta was involved in 21 and the arch in 12. In eight patients, the calcium outlined a distinctive narrowing of the ascending aorta. Six patients had significant left ventricular obstruction; in five it was from aortic valve stenosis. Of the 17 type IV patients, 16 men and one woman, none had aortic calcification or left ventricular outflow obstruction, and only one had coronary artery calcification. These data demonstrate that patients with type II hyperlipoproteinemia have severe calcific atherosclerosis of the aortic root that often is visible on chest films. Such calcification may alert physicians to the presence of type II hyperlipoproteinemia and the high probability of severe coronary artery disease.

Noninvasive diagnosis of extracranial cerebrovascular disease

Noninvasive methods for diagnosis of carotid and vertebrobasilar disease may be divided into passive techniques and those in which the body is interrogated by the introduction of some sort of signal such as an ultrasound beam. Older techniques have been of limited value, whereas newer noninvasive methods can give specific, accurate, and quantitative information as to the location and extent of arterial stenosis.

Transport of 125I-albumin across normal and deendothelialized rabbit thoracic aorta in vivo

Transmural concentration profiles of 125I-albumin in vivo were measured across the normal and balloon catheter-deendothelialized rabbit descending thoracic aorta as a function of time following intravenous injection. A tracer was injected 5 or 60 minutes after deendothelialization, and the animals were sacrificed after circulation times of 10, 30 or 60 minutes. The aorta was immediately excised and frozen flat between glass slides. Samples were serially sectioned parallel to the intimal surface in a refrigerated microtome, washed with trichloroacetic acid (TCA), and counted. Relative tissue concentration profiles of TCA-precipitable radioactivity from the media of control animals showed entry from both luminal and adventitial sides, as previously found with conscious normal rabbits, but spatial gradients at both luminal and medial-adventitial borders were less steep. Relative concentration levels in ballooned animals were 10- to 40-fold higher than in controls, and the profiles were flatter. Uptake rates at equivalent circulation times were greater in experiments initiated 60 minutes, as compared with 5 minutes, after deendothelialization, suggesting that progressive medial edema may have occurred following balloon injury. These results show that the intact endothelium is the dominant mass transfer resistance for 125I-albumin transport across the aortic wall. The data also suggest that the incomplete monolayer of platelets adherent to the subendothelium after balloon deendothelialization is not a substantial resistance to transport, as compared to that of the media, and that convection plays a more important role than diffusion for 125I-albumin transport across the deendothelialized aortic wall.

Phonoangiography: qualitative and quantitative

Bruit analysis (phonoangiography) has been performed for many years as a method of characterizing arterial disease. Time displays of arterial bruits, particularly at the carotid bifurcation, have been used in an attempt to quantitate arterial narrowing. Despite the generalization that longer bruits and bruits which look and sound higher in frequency are often associated with severe disease, prospective studies have shown no useful predictive value for qualitative phonoangiography. In marked contrast, spectral bruit analysis or quantitative phonoangiography has been quite accurate in predicting the location and extent of carotid stenosis, and in distinguishing intrinsic from transmitted bruits. With this method, the peak systolic portion of the bruit is subjected to fast Fourier transform analysis. The peak frequency, beyond which amplitude drops as frequency increases further, is directly related to the residual lumen diameter of the stenotic common or internal carotid artery. Several blinded trials of this method have given results accurate to within 1 mm of angiographic values in 83-93% of cases studied. When used in conjunction with duplex doppler ultrasound scanning, 95% accuracy in diagnosis of patients with and without bruits may be achieved. This completely noninvasive method deserves more widespread use and may also be applicable to other cardiovascular sounds.

Adrenal cortical function in homozygous familial hypercholesterolemia

The biosynthesis of adrenal corticosteroids requires a supply of cholesterol that can be derived from both local synthesis and uptake of plasma lipoproteins. Recent studies have provided evidence that receptor-mediated uptake of low density lipoproteins provides an important source of cholesterol for corticosteroid synthesis by human adrenocortical cells that are grown in tissue culture. In the present study we have examined parameters of adrenocortical function in three patients with homozygous familial hypercholesterolemia (two receptor negative, one receptor defective) to assess whether a decreased number of LDL receptors, measured in vitro, influences in vivo corticosteroid production under basal conditions and in response to prolonged stimulation with ACTH. Basal adrenocortical function (assessed by the serum concentrations of cortisol and ACTH plus urinary excretion of 17 OHCS, 17 KS, and urine-free cortisol) was normal in all three patients. Stimulation with intravenous ACTH resulted in rapid increases in the serum concentrations of cortisol in all patients. Plateau concentrations of cortisol during prolonged ACTH stimulation were lower in the two receptor-negative patients (36 to 41 micrograms/dl) but all subjects had at least a threefold increase over basal values. Excretion of urine-free cortisol was reduced in both receptor-negative patients (33% to 36% of controls); this was paralleled by decreased excretion of 17 KS in both patients and of 17 OHCS in one patient. Urine-free cortisol excretion was reduced in the receptor-defective patient (57% of controls), but excretion of 17 OHCS and 17 KS was not.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective accumulation of low density lipoproteins in damaged arterial wall

To determine whether damaged arterial wall selectively accumulates lipoproteins, normocholesterolemic rabbits were injected with human radiolabeled low density lipoproteins, high density lipoproteins, and/or albumin 24 hr to 12 weeks after balloon-catheter de-endothelialization of the abdominal aorta. When 125I-labeled low density lipoproteins and 99mTc-labeled albumin were injected simultaneously, the amount of 125I-low density lipoprotein present 24 hr later in abdominal aortas increased steadily, for several weeks, above the amount present at 24 hr in control animals. The increase correlated closely with the degree of re-endothelialization and correlated closely with the degree of re-endothelialization and reached an average maximum for the whole abdominal aorta of three times control when re-endothelialization was between 75 and 85% complete. By contrast, the amounts of 99mTc-albumin or 125I-labeled high density lipoprotein in balloon-damaged abdominal aortas, and the amounts of 125I-low density lipoprotein, 125I-high density lipoprotein, or 99mTc-albumin in undamaged thoracic aortas of injured animals showed no such increase. As early as 2 weeks after de-endothelialization, en face radioautographs made following injection of 125I-labeled low density lipoproteins revealed localized areas of greatest radioactivity around the leading edges of regenerating endothelial islands, broad areas of intermediate radioactivity corresponding to the de-endothelialized areas, and very like radioactivity in the re-endothelialized areas. This pattern occurred rarely with 125I-labeled high density lipoproteins and not at all with 125I-labeled albumin. The results suggest that low density lipoproteins are selectively accumulated by the healing rabbit aorta and that the accumulation is greatest in regions where the endothelium is actively regenerating.

Low density lipoprotein degradation by mononuclear cells from normal and dyslipoproteinemic subjects

Three major characteristics of cell surface low density lipoprotein (LDL) receptor activity in fibroblasts or lymphocytes are high-affinity LDL binding or degradation, specificity for LDL, and "inducibility"--that is, the ability to increase when cells are cultured in the absence of lipoproteins. Cells from patients with receptor-negative homozygous familial hypercholesterolemia (FH) have been reported to express none of these characteristics, and the patients are thought to have a genetic absence of LDL receptors. We found that, although induced receptor-negative lymphocytes degraded less LDL than did normal lymphocytes, the curves for LDL degradation versus LDL concentration were biphasic, with greater concentration-dependence at LDL concentrations less than 60 micrograms/ml, indicating high-affinity LDL degradation. The percentage of specific LDL degradation by induced receptor-negative lymphocytes was two-thirds of normal with LDL at 10 micrograms/ml and increased to normal at 50 micrograms/ml, an LDL concentration still within the range of high-affinity degradation. Receptor-negative lymphocytes could be induced by incubation in the absence of lipoproteins to degrade twice as much LDL as they did when freshly isolated. Freshly isolated cells from abetalipoproteinemic patients and one receptor-negative patient degraded as much LDL as did fresh normal cells. The findings indicate that receptor-negative lymphocytes have a mechanism for facilitated uptake of LDL that resembles that of normal lymphocytes, although it is not as efficient.

Detection of aortic porcine valve dysfunction by maximum entropy spectral analysis

A high-resolution method of spectral analysis, of the class generally called "maximum entropy method," was used in a study of aortic porcine valve closing sounds in 37 patients (ages 19 to 76). Spectra from 27 normal xenografts, implanted from 2 weeks to 61 months previously, were characterized by a dominant frequency peak, F1, at 89 +/- 15 Hz (mean +/- SD), with a lower amplitude peak, F2, at 154 +/- 25 Hz. Eight of nine patients with aortic porcine valve dysfunction were proved surgically to have leaflet degeneration or infection and had either F1 (139 +/- 54 Hz) and/or F2 (195 +/- 74 Hz) significantly higher than normal (p less than .001). In two patients with paravalvar leak but no leaflet abnormality, F1 and F2 were in the normal range. Estimation of F1 and F2 was highly reproducible and was unaffected by duration of implant up to 5 years. Spectral analysis of aortic porcine valve closing sounds by the maximum entropy method may be useful for detection of intrinsic xenograft dysfunction.

Transmural [125I]albumin concentration in the rabbit aorta during acute hypoxia

We have quantified the concentration profile of 125I-labeled rabbit albumin in the avascular intima and media of the rabbit descending thoracic aorta following intravenous injection under control and acute hypoxic conditions in vivo. Our purpose was to determine if alterations occurred in the transmural concentration profiles which could be attributed to hypoxia-induced changes in the permeability of the intimal endothelium to plasma-borne macromolecules. The profiles were obtained with frozen serial sections of the aorta from experiments of 30 min duration. Acute hypoxia was induced by addition of nitrogen to the breathing mixture. The hypoxia resulted in arterial pO2 values of 23--32 mm Hg while the arterial pO2 in the control animals ranged from 80 to 88 mm Hg. All animals were under sodium pentobarbital anesthesia. The results revealed no detectable changes in the concentration profile in the inner media accompanying hypoxia. However, increases in the label concentration in the outer media of the hypoxic animals suggested either dilation or increased permeability of the adventitial blood vessels.

External imaging of human atherosclerosis

Autologous plasma low-density lipoproteins labeled with I-125 were used as a tracer to identify atherosclerotic lesions in the carotid arteries of the neck. Following intravenous injection of I-125-LDL, images were made at intervals from 6 to 36 hr with the gamma camera in three patients with known carotid disease and one control subject. The carotid lesions, confirmed by angiography, were imaged successfully in all three patients, whereas no focal LDL accumulation was visible in the carotid arteries of the control subject. The findings suggest that it may be possible to image atherosclerosis externally and thus to follow the course of the disease.