Alan C. Yeung

Close Relation of Endothelial Function in the Human Coronary and Peripheral Circulations

OBJECTIVES The relation between endothelium-dependent vasodilator function in the brachial and coronary arteries was determined in the same subjects. BACKGROUND Coronary artery endothelial dysfunction precedes the development of overt atherosclerosis and is important in its pathogenesis. A noninvasive assessment of endothelial function in a peripheral conduit vessel, the brachial artery, was recently described, but the relation between brachial artery function and coronary artery vasodilator function has not been explored. METHODS In 50 patients referred to the catheterization laboratory for the evaluation of coronary artery disease (mean age +/- SD 56 +/- 10 years), the coronary vasomotor response to serial intracoronary infusions of the endothelium-dependent agonist acetylcholine (10(-8) to 10(-6) mol/liter), was studied. Endothelium-dependent vasodilation was also assessed in the brachial artery by measuring the change in brachial artery diameter in response to reactive hyperemia. RESULTS Patients with coronary artery endothelial dysfunction manifested as vasoconstriction in response to acetylcholine had significantly impaired flow-mediated vasodilation in the brachial artery compared with that of patients with normal coronary endothelial function (4.8 +/- 5.5% vs. 10.8 +/- 7.6%, p < 0.01). Patients with coronary artery disease also had an attenuated brachial artery vasodilator response compared with that of patients with angiographically smooth coronary arteries (4.5 +/- 4.6% vs. 9.7 +/- 8.1%, p < 0.02). By multivariate analysis, the strongest predictors of reduced brachial dilator responses to flow were baseline brachial artery diameter (p < 0.001), coronary endothelial dysfunction (p = 0.003), the presence of coronary artery disease (p = 0.007) and cigarette smoking (p = 0.016). The brachial artery vasodilator response to sublingual nitroglycerin was independent of coronary endothelial responses or the presence of coronary artery disease. The positive predictive value of abnormal brachial dilation ( < 3%) in predicting coronary endothelial dysfunction is 95%. CONCLUSIONS This study demonstrated a close relation between coronary artery endothelium-dependent vasomotor responses to acetylcholine and flow-mediated vasodilation in the brachial artery. This noninvasive method may become a useful surrogate in assessing the predisposition to atherosclerosis in patients with cardiac risk factors.

Coronary vasomotor response to acetylcholine relates to risk factors for coronary artery disease.

In animals, acetylcholine dilates normal arteries and produces vasoconstriction in the presence of hypercholesterolemia, hypertension, or atherosclerosis, reflecting endothelial cell dysfunction. In patients with angiographically smooth coronary arteries, acetylcholine has been reported to produce both vasodilation and constriction. To test the hypothesis that the acetylcholine response relates to risk factors for coronary artery disease, acetylcholine 10(-8) to 10(-6) M was infused into the left anterior descending or circumflex coronary artery, and diameter changes were assessed with quantitative angiography in 34 patients with angiographically smooth coronary arteries. The acetylcholine response ranged from +37% (dilation) to -53% (constriction) at the peak acetylcholine dose. All coronary arteries dilated in response to nitroglycerin (26 +/- 17%), suggesting an abnormality of endothelial function in the patients with a constrictor response to acetylcholine. By multiple stepwise regression analysis, serum cholesterol (p less than 0.01), male gender (p less than 0.001), family history (p less than 0.05), age (p less than 0.05), cholesterol level (p less than 0.01), and total number of risk factors (p less than 0.0001) were independently associated with the acetylcholine response. Thus, coronary risk factors are associated with loss of endothelium-dependent vasodilation. The development of vasoconstriction is likely to be an abnormality of endothelial function that precedes atherosclerosis or an early marker of atherosclerosis not detectable by angiography.

The Effect of Cholesterol-Lowering and Antioxidant Therapy on Endothelium-Dependent Coronary Vasomotion

BACKGROUND Patients with coronary artery disease and abnormalities of serum lipids often have endothelial vasodilator dysfunction, which may contribute to ischemic cardiac events. Whether cholesterol-lowering or antioxidant therapy can restore endothelium-dependent coronary vasodilation is unknown. METHODS We randomly assigned 49 patients (mean serum cholesterol level, 209 +/- 33 mg per deciliter [5.40 +/- 0.85 mmol per liter]) to receive one of three treatments: an American Heart Association Step 1 diet (the diet group, 11 patients); lovastatin and cholestyramine (the low-density lipoprotein [LDL]-lowering group, 21 patients); or lovastatin and probucol (the LDL-lowering-antioxidant group, 17 patients). Endothelium-dependent coronary-artery vasomotion in response to an intracoronary infusion of acetylcholine (10(-8) to 10(-6) M) was assessed at base line and after one year of therapy. Vasoconstrictor responses to these doses of acetylcholine are considered to be abnormal. RESULTS Treatment resulted in significant reductions in LDL cholesterol levels of 41 +/- 22 percent in the LDL-lowering-antioxidant group and 38 +/- 20 percent in the LDL-lowering group (P < 0.001 vs. the diet group). The maximal changes in coronary-artery diameter with acetylcholine at base line and at follow-up were -19 and -2 percent, respectively, in the LDL-lowering-antioxidant group, -15 and -6 percent in the LDL-lowering group, and -14 and -19 percent in the diet group (P < 0.01 for the LDL-lowering-antioxidant group vs. the diet group; P = 0.08 for the LDL-lowering group vs. the diet group). (The negative numbers indicate vasoconstriction). Thus, the greatest improvement in the vasoconstrictor response was seen in the LDL-lowering-antioxidant group. CONCLUSIONS The improvement in endothelium-dependent vasomotion with cholesterol-lowering and antioxidant therapy may have important implications for the activity of myocardial ischemia and may explain in part the reduced incidence of adverse coronary events that is known to result from cholesterol-lowering therapy.

Estrogen Improves Endothelium-Dependent, Flow-Mediated Vasodilation in Postmenopausal Women

Coronary artery disease is the leading cause of death among women in the United States, accounting for 23% of all deaths [1, 2]. The incidence of coronary artery disease in women aged 35 to 44 years is 1 per 1000, increasing to 4 per 1000 in women aged 45 to 54 years [3, 4]. Among women in their fifth decade, the incidence of coronary artery disease is one half that of men. By the sixth decade, however, women and men have the same incidence of coronary disease [2, 5, 6]. This disparity between premenopausal women and men of similar age suggests that endogenous sex hormones such as estrogen may have a significant cardioprotective influence. In postmenopausal women, estrogen replacement therapy independently decreases the risk for cardiovascular events and mortality [6, 7]. Estrogen therapy limited the uptake of cholesterol ester into the arterial wall and attenuated the development of dietary-induced atherosclerosis in monkeys and baboons that had ovariectomy [8-10]. Angiographic studies have consistently found less coronary artery disease in women who receive estrogen replacement therapy [7, 11, 12]. Beneficial effects of estrogen replacement therapy include its ability to reduce low-density lipoprotein (LDL) cholesterol levels and increase high-density lipoprotein (HDL) cholesterol levels [13]. Nonetheless, multiple regression analyses suggest that only 25% to 50% of the reduction in cardiovascular events is attributable to the lipid-lowering effects of estrogen replacement therapy [14], suggesting that other mechanisms contribute to its cardioprotective potential. One such mechanism may involve the effect of estrogen on vascular function. Specifically, estrogen may directly enhance the activity of the endothelium-derived relaxing factor nitric oxide [10, 15-17] and thereby lessen the potential for coronary vasoconstriction and thrombosis [18-21]. When administered to rabbits that had ovariectomy, long-term estrogen replacement improved endothelium-dependent relaxation in vitro [15, 16]. In addition, both short-term and long-term estrogen administration improves in vivo the endothelium-dependent vasodilation in coronary arteries of atherosclerotic cynomolgus monkeys that had ovariectomy [10, 17]. Several recent studies have suggested that short-term estrogen administration improves endothelium-dependent vasodilation of the coronary arteries of postmenopausal women [22, 23]. We hypothesized that long-term estrogen administration would improve vasomotor function in postmenopausal women. Accordingly, we conducted a double-blind, randomized, crossover, placebo-controlled trial to assess the effect of estrogen replacement therapy on endothelium-dependent vasodilation in postmenopausal women. We used high-resolution ultrasonography to serially assess vasomotor function in a peripheral conduit vessel, the brachial artery. Methods Patients The patients enrolled in this study were recruited from a larger cohort that was participating in a clinical research trial investigating the effect of estrogen replacement therapy on lipoprotein metabolism. Thirteen postmenopausal women aged 44 to 69 years (average age, 55 7 years) participated in this study. Women were eligible if menopause had occurred at least 1 year previously. Menopause was confirmed by measuring serum follicle-stimulating hormone levels. No patient had received hormone replacement therapy for at least 2 months before the study began. A history and physical examination were done to exclude persons with clinical evidence of coronary or peripheral atherosclerosis. Initial evaluation included a Papanicolaou smear (if not done in past year), complete blood count, routine chemistry panel, and lipid profile. Inclusion criteria included mild hypercholesterolemia, defined as a serum cholesterol level of 5.17 mmol/L to 6.20 mmol/L and an LDL cholesterol level of 3.36 mmol/L to 4.13 mmol/L. Exclusion criteria included hypertension, diabetes mellitus, tobacco use, obesity (body weight > 135% of ideal weight), history of breast or uterine cancer, thromboembolism, and liver or renal disease. Eligible patients were placed on a low-cholesterol diet (American Heart Association phase I) for 6 weeks before randomization. Patients were randomly assigned to one of three treatment groups: placebo, oral 17 -estradiol (Estrace, Mead Johnson, Evansville, Indiana.) at a dose of 1 mg/d, or oral 17 -estradiol at a dose of 2 mg/d. At the conclusion of each 9-week treatment period, the patients were given progesterone (Provera, Upjohn, Kalamazoo, Michigan) at 10 mg/d for 10 days. Hormone replacement therapy was discontinued for 3 weeks before patients crossed over to the next treatment regimen. All patients received placebo and the two doses of estrogen in random order. Vascular function studies (described below) were done during the eighth or ninth week of each treatment period. Experimental Protocol Studies were done in a temperature-controlled vascular research laboratory. All patients were placed in the supine position. We studied vascular reactivity in a conduit vessel, the brachial artery, as previously described. An imaging study of the brachial artery was done using a high-resolution ultrasound machine (Toshiba, Model SSA-270, Otawara-shir, Tochigi-Ken, Japan) that was equipped with a 7.5 MHz linear-array transducer. Baseline images of the brachial artery were obtained proximal to the antecubital fossa. Imaging of the artery was done longitudinally, allowing clear visualization of the posterior wall intima-lumen interface and the anterior wall media-adventitial interface. We assessed endothelium-dependent vasodilation by measuring the change in the caliber of the brachial artery during reactive hyperemia, a maneuver that increases flow through the conduit segment being studied (flow-mediated vasodilation). To create this stimulus, a cuff placed on the upper arm was inflated to suprasystolic pressure for 5 minutes, thereby occluding flow to the forearm. This results in dilatation of downstream forearm resistance vessels. After cuff deflation, reactive hyperemia occurs, as brachial artery blood flow increases to accommodate the dilated resistance vessels. Imaging of the brachial artery was continually done for the 5-minute period after cuff deflation until basal conditions were re-established. Thereafter, sublingual nitroglycerin (at a dose of 0.4 mg) was administered to assess endothelium-independent vasodilation. The artery was studied for an additional 5 minutes. Blood pressure and heart rate were monitored continuously throughout the procedure. All images were recorded on Super VHS videotape for subsequent analysis. Image analysis was done on a personal computer that was equipped with a video frame grabber. Images recorded on videotape were analyzed by an investigator blinded to treatment assignment. Previous studies have shown that the peak diameter change during reactive hyperemia occurs approximately 1 minute after cuff deflation and 3 minutes after nitroglycerin administration [41]. We used these time points in our study. Images corresponding to the end of the T wave on a simultaneous electrocardiograph were selected and digitized. Image analysis was then done using a proprietary analysis software that searched for the shortest distance between the points on the arterial wall, creating 10 to 20 paired measurements along a 10-mm length. We measured arterial diameter from the intima-lumen interface on the posterior wall to the media-adventitial interface on the anterior wall. We calculated brachial artery diameter by averaging these paired lumen measurements and reported them in millimeters using calibration factors derived from real-time ultrasonography. We used an average of three separate measurements for each condition. In our laboratory, this technique has a variability of only 0.0 0.1 mm [24]. To assure that the blood flow stimulus during reactive hyperemia was similar during each treatment phase, forearm blood flow was measured by venous occlusion strain gauge plethysmography using calibrated mercury-in-silastic strain gauges as previously described [25]. Statistical Analysis The variables compared during the placebo period and during therapy with each dose of estrogen included blood pressure, heart rate, forearm blood flow, basal brachial artery diameter, and the percentage increase in diameter during reactive hyperemia and after patients received sublingual nitroglycerin. Values are expressed as the mean SE. For statistical analysis, we used repeated-measure analysis of variance and the Scheffe-F post hoc test [26]. Significance was accepted at P 0.05. Results Baseline Hemodynamic Measurements The effect of estrogen treatment on blood pressure, heart rate, forearm blood flow and forearm vascular resistance is presented in Table 1. Estrogen therapy did not affect blood pressure or heart rate. Basal forearm blood flow tended to be higher during both estrogen treatment phases (P = 0.08). Basal forearm vascular resistance was similar during all three treatment phases. The peak forearm blood flow during reactive hyperemia was similar during placebo receipt and each estrogen treatment period. However, peak forearm blood flow was greater when patients received the 1-mg dose of estradiol than when they received the 2-mg dose (P = 0.05). Table 1. Effect of Estrogen Replacement on Hemodynamic Measurements Flow-Mediated Endothelium-Dependent Vasodilation We obtained technically adequate ultrasound images during reactive hyperemia for 12 of the 13 patients. The brachial artery diameter, under basal conditions, measured 3.5 mm, 3.4 mm, and 3.3 mm while patients received placebo, estradiol at 1 mg/d, and estradiol at 2 mg/d, respectively (P > 0.2). The percentage increase in brachial artery diameter during reactive hyperemia for each treatment period is shown in Figure 1. The change in brachial artery diameter was greater when patients received estradiol treatment (13.5% and 11.6

The effect of atherosclerosis on the vasomotor response of coronary arteries to mental stress.

BACKGROUND Mental stress can cause angina in patients with coronary artery disease, but its effects on coronary vasomotion and blood flow are poorly understood. Because atherosclerosis affects the reactivity of coronary arteries to various stimuli, such as exercise, we postulated that atherosclerosis might also influence the vasomotor response of coronary arteries to mental stress. METHODS We studied 26 patients who performed mental arithmetic under stressful conditions during cardiac catheterization. (An additional four patients who did not perform the mental arithmetic served as controls.) Coronary segments were classified on the basis of angiographic findings as smooth, irregular, or stenosed. In 15 of the patients without focal stenoses in the left anterior descending artery, acetylcholine (10(-8) to 10(-6) mol per liter) was infused into the artery to test endothelium-dependent vasodilation. Changes in coronary blood flow were measured with an intracoronary Doppler catheter in these 15 patients. RESULTS The response of the coronary arteries to mental stress varied from 38 percent constriction to 29 percent dilation, whereas the change in coronary blood flow varied from a decrease of 48 percent to an increase of 42 percent. The direction and magnitude of the change in the coronary diameter were not predicted by the changes in the heart rate, blood pressure, or plasma norepinephrine level. Segments with stenoses (n = 7) were constricted by a mean (+/- SE) of 24 +/- 4 percent, and irregular segments (n = 20) by 9 +/- 3 percent, whereas smooth segments (n = 25) did not change significantly (dilation, 3 +/- 3 percent; P less than 0.0002). Coronary blood flow increased by 10 +/- 10 percent in smooth vessels, whereas the flow in irregular vessels decreased by 27 +/- 5 percent. The degree of constriction or dilation during mental stress correlated with the response to the infusions of acetylcholine (P less than 0.0003, r = 0.58). CONCLUSIONS Atherosclerosis disturbs the normal vasomotor response (no change or dilation) of large coronary arteries to mental stress; in patients with atherosclerosis paradoxical constriction occurs during mental stress, particularly at points of stenosis. This vasomotor response correlates with the extent of atherosclerosis in the artery and with the endothelium-dependent response to an infusion of acetylcholine. These data suggest that in atherosclerosis unopposed constriction caused by a local failure of endothelium-dependent dilation causes the coronary arteries to respond abnormally to mental stress.

Radiolabeled Cell Distribution After Intramyocardial, Intracoronary, and Interstitial Retrograde Coronary Venous Delivery Implications for Current Clinical Trials

Background—Several clinical studies are evaluating the therapeutic potential of delivery of various progenitor cells for treatment of injured hearts. However, the actual fate of delivered cells has not been thoroughly assessed for any cell type. We evaluated the short-term fate of peripheral blood mononuclear cells (PBMNCs) after intramyocardial (IM), intracoronary (IC), and interstitial retrograde coronary venous (IRV) delivery in an ischemic swine model. Methods and Results—Myocardial ischemia was created by 45 minutes of balloon occlusion of the left anterior descending coronary artery. Six days later, 107 111indium-oxine–labeled human PBMNCs were delivered by IC (n=5), IM (n=6), or IRV (n=5) injection. The distribution of injected cells was assessed by γ-emission counting of harvested organs. For each delivery method, a significant fraction of delivered cells exited the heart into the pulmonary circulation, with 26±3% (IM), 47±1% (IC), and 43±3% (IRV) of cells found localized in the lungs. Within the myocardium, significantly more cells were retained after IM injection (11±3%) compared with IC (2.6±0.3%) (P<0.05) delivery. IRV delivery efficiency (3.2±1%) trended lower than IM infusion for PBMNCs, but this difference did not reach significance. The IM technique displayed the greatest variability in delivery efficiency by comparison with the other techniques. Conclusions—The majority of delivered cells is not retained in the heart for each delivery modality. The clinical implications of these findings are potentially significant, because cells with proangiogenic or other therapeutic effects could conceivably have effects in other organs to which they are not primarily targeted but to which they are distributed. Also, we found that although IM injection was more efficient, it was less consistent in the delivery of PBMNCs compared with IC and IRV techniques.

Flow-induced vasodilation of the human brachial artery is impaired in patients < 40 years of age with coronary artery disease

The objective of this study was to determine whether abnormal flow-induced endothelium-dependent vasodilation in the brachial artery identifies young patients with coronary artery disease (CAD). High-resolution ultrasonography was used to measure vascular reactivity in a peripheral conduit vessel, the brachial artery, in 14 young men with CAD and in 11 age-matched, healthy, male volunteers. Endothelium-dependent vasodilation was determined by measuring the change in brachial artery diameter during increases in flow induced by reactive hyperemia. Endothelium-independent vasodilation was assessed by administration of sublingual nitroglycerin. To ascertain whether flow-mediated vasodilation in humans is mediated by endothelium-derived nitric oxide, brachial artery diameter was measured during reactive hyperemia, before and during administration of the nitric oxide synthase antagonist NG-monomethyl-L-arginine (L-NMMA). Brachial artery diameter was also measured during intraarterial infusion of acetylcholine and nitroprusside before and after administration of L-NMMA. Flow-induced vasodilation was less in patients with CAD than in healthy volunteers (1.3 +/- 1.1% vs 6.2 +/- 0.7%, p <0.05). Nitroglycerin increased brachial artery diameter similarly in each subject group (11.3 +/- 1.0% vs 15.8 +/- 1.2%, p =0.05). L-NMMA inhibited flow-mediated vasodilation and the vasodilative response to acetylcholine, but did not affect the response to nitroprusside. It is concluded that abnormal flow-induced endothelium-dependent vasodilation occurs in the brachial artery of young patients with CAD.

Novel Index for Invasively Assessing the Coronary Microcirculation

Background—A relatively simple, invasive method for quantitatively assessing the status of the coronary microcirculation independent of the epicardial artery is lacking. Methods and Results—By using a coronary pressure wire and modified software, it is possible to calculate the mean transit time of room-temperature saline injected down a coronary artery. The inverse of the hyperemic mean transit time has been shown to correlate with absolute flow. We hypothesize that distal coronary pressure divided by the inverse of the hyperemic mean transit time provides an index of microcirculatory resistance (IMR) that will correlate with true microcirculatory resistance (TMR), defined as the distal left anterior descending (LAD) pressure divided by hyperemic flow, measured with an external ultrasonic flow probe. A total of 61 measurements were made in 9 Yorkshire swine at baseline and after disruption of the coronary microcirculation, both with and without an epicardial LAD stenosis. The mean IMR (16.9±6.5 U to 25.9±14.4 U, P =0.002) and TMR (0.51±0.14 to 0.79±0.32 mm Hg · mL−1 · min−1, P =0.0001), as well as the % change in IMR (147±66%) and TMR (159±105%, P =NS versus IMR % change), increased significantly and to a similar degree after disruption of the microcirculation. These changes were independent of the status of the epicardial artery. There was a significant correlation between mean IMR and TMR values, as well as between the % change in IMR and % change in TMR. Conclusion—Measuring IMR may provide a simple, quantitative, invasive assessment of the coronary microcirculation.

Arterial Remodeling: Mechanisms and Clinical Implications

The presentation of coronary atherosclerosis can be gradual, because of progressive flow-limiting stenosis and exertional angina, or dramatic, with plaque rupture and thrombosis causing unstable angina, myocardial infarction, or sudden death. The importance of arterial remodeling, or persistent change in vessel size, has recently become apparent in both situations. Arterial remodeling, not plaque size, has been identified as the primary determinant of lumen size in the presence of stable lesions. Similarly, luminal stenosis in transplant vasculopathy and with restenosis after angioplasty occur mainly because of inward remodeling rather than plaque growth. However, recent evidence also suggests that adequate outward remodeling may be associated with an increased risk of plaque rupture, the underlying cause of acute coronary syndromes and sudden cardiac death. The term “arterial remodeling” has previously been used to describe any change in vessel wall structure. More recently, however, it has been used specifically to refer to a change in vessel size (or cross-sectional area within the external elastic lamina), and it is on this entity that this review is focused. Inward remodeling denotes a reduction in vessel size. Outward remodeling denotes an increase in vessel size. Various other terms are used in the literature (the Table⇓). When outward remodeling is present but insufficient to prevent luminal stenosis, it is referred to as inadequate outward remodeling. View this table: Table 1. Terminology of Arterial Remodeling It has been known for more than a century1 that blood vessels enlarge to accommodate increasing flow to the organ downstream (eg, during natural growth or in left ventricular hypertrophy). Widespread interest in this phenomenon was stimulated by observations that radial enlargement of vessels (outward remodeling) can compensate for progressive growth of atherosclerotic plaques, thus postponing the development of flow-limiting stenosis.2 3 These pathological findings were subsequently supported by in vivo intravascular ultrasound (IVUS) studies that …

Inhibition of Restenosis With β-Emitting Radiotherapy Report of the Proliferation Reduction With Vascular Energy Trial (PREVENT)

BackgroundIntracoronary &ggr;- and &bgr;-radiation have reduced restenosis in animal models. In the clinical setting, the effectiveness of &bgr;-emitters has not been studied in a broad spectrum of patients, particularly those receiving stents. Methods and ResultsA prospective, randomized, sham-controlled study of intracoronary radiotherapy with the &bgr;-emitting 32P source wire, using a centering catheter and automated source delivery unit, was conducted. A total of 105 patients with de novo (70%) or restenotic (30%) lesions who were treated by stenting (61%) or balloon angioplasty (39%) received 0 (control), 16, 20, or 24 Gy to a depth of 1 mm in the artery wall. Angiography at 6 months showed a target site late loss index of 11±36% in radiotherapy patients versus 55±30% in controls (P <0.0001). A low late loss index was seen in stented and balloon-treated patients and was similar across the 16, 20, and 24 Gy radiotherapy groups. Restenosis (≥50%) rates were significantly lower in radiotherapy patients at the target site (8% versus 39%;P =0.012) and at target site plus adjacent segments (22% versus 50%;P =0.018). Target lesion revascularization was needed in 5 radiotherapy patients (6%) and 6 controls (24%;P <0.05). Stenosis adjacent to the target site and late thrombotic events reduced the overall clinical benefit of radiotherapy. Conclusions&bgr;-radiotherapy with a centered 32P source is safe and highly effective in inhibiting restenosis at the target site after stent or balloon angioplasty. However, minimizing edge narrowing and late thrombotic events must be accomplished to maximize the clinical benefit of this modality.