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Biomedical subjects

B H Strauss

Publications and source records attributed to B H Strauss.

At least 37 records · Page 2Linked to original sources
PubMed1994

Predictors of outcome of percutaneous excimer laser coronary angioplasty of saphenous vein bypass graft lesions. The Percutaneous Excimer Laser Coronary Angioplasty Registry.

A total of 495 patients underwent treatment with excimer laser angioplasty for 545 saphenous vein graft stenoses. Clinical success was achieved in 455 of 495 patients (92%), as indicated by < or = 50% residual stenosis at every target lesion and no complication during hospitalization. At least 1 in-hospital complication occurred in 30 of 495 patients (6.1%): death (1.0%), bypass surgery (0.6%), and Q-wave (2.4%) or non-Q-wave (2.2%) myocardial infarction. Relative risk analysis showed that ostial lesions (n = 65) tended to have higher clinical success (success rate = 95%, adjusted odds ratio [OR] = 2.1 [95% confidence interval (CI) 0.62, 6.88]; p = 0.24) and lower complications (complication rate = 0%, OR = 0.10 [CI 0.01, 0.79]; p = 0.03) than lesions in the body of the vein graft. Lesions > 10 mm (n = 131) had lower success (success rate = 84%, OR = 0.30 [CI 0.16, 0.56]; p = 0.001) and higher complications (complication rate = 12%, OR = 3.3 [CI 1.6, 6.6]; p = 0.004) than discrete lesions. Lesions in small vein grafts < 3.0 mm (n = 76) tended to have increased success (success rate = 94%, OR = 1.55 [CI 0.70, 3.44]; p = 0.39) and lower complications (complication rate = 2.2%, OR = 0.31 [CI 0.10, 0.94]; p = 0.03). Thus, excimer laser-facilitated angioplasty has the most favorable outcome for discrete lesions located at the ostium of all grafts and in the body of smaller saphenous vein grafts.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1994

Lupus anticoagulant: a potential risk factor for complication following percutaneous transluminal coronary angioplasty.

A patient is described with antiphospholipid antibodies who died approximately 24 hr after an uncomplicated balloon angioplasty. Since the literature suggests a relationship between the presence of antiphospholipid antibodies and thromboses, we suggest that these antibodies may be a risk factor for abrupt closure after percutaneous transluminal coronary angioplasty.

Adult↗
PubMed1994

Proliferation and extracellular matrix synthesis of smooth muscle cells cultured from human coronary atherosclerotic and restenotic lesions.

OBJECTIVES: The purpose of this study was to examine the proliferative capacity and extracellular matrix synthesis of human coronary plaque cells in vitro. BACKGROUND: Common to both primary atherosclerosis and restenosis are vascular smooth muscle cell proliferation and production of extracellular matrix proteins. The applicability to humans of experimental animal models of these processes has been questioned. METHODS: Primary atherosclerotic and restenotic lesions were excised by percutaneous directional coronary atherectomy in 93 patients. Smooth muscle cells were cultivated by an explant technique and identified by their morphology in culture, ultrastructural features under electron microscopy and immunostaining using monoclonal antibodies to smooth muscle cell alpha-actin. Proliferation in secondary culture was assessed with growth curves and the synthesis of collagen and sulfated glycosaminoglycans by the incorporation of 3H-proline and 35S-sulfate, respectively. These studies were also performed in cells derived from human umbilical artery media. RESULTS: Success rates for primary (45%) and secondary (12%) culture of coronary cells were not influenced by clinical variables or lesion category. Primary culture success was improved by the presence of organized thrombus in the plaque and in relation to increased maximal cell density of the atherectomy specimen. Restenotic cells displayed more rapid growth than did cells of primary atherosclerotic origin, which grew in a manner similar to that of umbilical artery cells. Mean calculated population-doubling times for the three cell groups were 52 h (95% confidence interval [CI] 48 to 58 h), 71 h (95% CI 62 to 83 h) and 74 h (95% CI 65 to 84 h), respectively. Restenotic and primary atherosclerotic cells did not differ in the synthesis of collagen ([mean +/- SEM] 0.034 +/- 0.004 vs. 0.033 +/- 0.004 nmol isotope.microgram protein-1, p = NS) or sulfated glycosaminoglycans (11.47 +/- 1.07 vs. 15.37 +/- 3.10 nmol isotope.microgram protein-1, p = NS), but the coronary cells synthesized significantly more collagen and sulfated glycosaminoglycans than did umbilical artery cells (0.019 +/- 0.004 and 5.43 +/- 1.00 nmol isotope.microgram protein-1, respectively, both p < 0.05). CONCLUSIONS: These data indicate that increased smooth muscle cell proliferation contributes to coronary restenosis in humans and support the concept that the extracellular matrix synthesis of adult smooth muscle cells is important to lesion formation.

Cell Division↗
PubMed1994

Late effects of locally delivered mitomycin C on formation of neointima and on vasomotor response to acetylcholine.

BACKGROUND: Balloon angioplasty damages endothelial cells and stimulates smooth muscle cell proliferation. The effects of local cytotoxic drug therapy on formation of neointima and late endothelial function are not known. This study was designed to determine whether direct infusion of mitomycin C via a microporous balloon catheter could significantly reduce formation of neointima after angioplasty. Furthermore, we investigated whether endothelial cell function is normal 7 weeks after the initial microporous angioplasty procedure. METHODS: In 34 New Zealand white rabbits, bilateral external iliac arteries underwent balloon angioplasty, followed by either high-dose (0.66 mg/kg) or low-dose (0.025 mg/kg) mitomycin C in one iliac artery and saline infusion in the contralateral artery, and a control group was given saline in both vessels. Formation of neointima was measured in the iliac arteries after 7 weeks by morphometry. Before sacrifice of 17 'angioplasty' rabbits and three undamaged rabbits, graded doses of acetylcholine and isosorbide dinitrate were infused in the distal aorta, and the iliac artery diameter was measured by computerized quantitative angiography. RESULTS: No significant differences in the absolute area of the intima or the intima: media ratio were demonstrated between control arteries and arteries that were directly infused with either high-dose or low-dose mitomycin. However, within the high-dose group, the mitomycin-treated vessel had a significantly lesser extent of formation of intimal hyperplasia (0.17 +/- 0.03 versus 0.27 +/- 0.03 mm2, P < 0.03) and lower intima: media area ratio (0.60 +/- 0.31 versus 1.09 +/- 0.42, P < 0.03) than the contralateral saline-treated vessel. Significant increases in mean luminal iliac artery diameter [0.18 mm (10.5%) at 1 min and 0.23 mm (13%) at 3 min, P < 0.05)] from baseline values following acetylcholine were observed in previously damaged iliac arteries. This vasodilatory response was not different from that in undamaged arteries. CONCLUSIONS: Local delivery of mitomycin C had no favorable effect on the inhibition of intimal hyperplasia compared with control saline-treated arteries. Normal endothelial function, determined on the basis of dilatory response to acetylcholine, can be demonstrated 7 weeks after balloon angioplasty injury.

Acetylcholine↗
PubMed1994

Extracellular matrix remodeling after balloon angioplasty injury in a rabbit model of restenosis.

Remodeling of the vessel wall after balloon angioplasty injury is incompletely understood, and in particular, the role of extracellular matrix synthesis in restenosis has received little attention. The objective of the present study was to determine the sequence of changes in collagen, elastin, and proteoglycan synthesis and content after balloon injury and to relate these changes to growth of the intimal lesions and extent of cell proliferation. In a double-injury non-cholesterol-fed model, right iliac arterial lesions in 43 rabbits were treated with balloon angioplasty, and the rabbits were killed at five time points ranging from immediate to 12 weeks. Vessel wall collagen and elastin content and synthesis were measured after incubation with 14C-proline and separation with a cyanogen bromide extraction procedure. Sulfated glycosaminoglycan synthesis was measured after incubation with [35S]sulfate, papain digestion, and ethanol precipitation. Continuous in vivo infusion of bromodeoxyuridine (96 hours) was used to assess cell proliferation. The intimal area significantly increased from 0.27 +/- 0.08 to 0.73 +/- 0.11 mm2 between 0 and 12 weeks. Intimal and medial cell proliferation were modest and peaked at 1 week (labeling indexes of 4.8% and 3.0%, respectively) and then markedly declined by 2 weeks. Significant increases in collagen, elastin, and proteoglycan synthesis, up to 4 to 10 times above control nondamaged contralateral iliac arteries, were noted at 1, 2, and 4 weeks. These increases in synthesis were accompanied by significant increases in collagen and elastin content (by approximately 35%) that coincided with the temporal increase in cross-sectional area.(ABSTRACT TRUNCATED AT 250 WORDS)

Angioplasty, Balloon↗
PubMed1993

Electrocardiographic prediction of ejection fraction and site of LAD occlusion in anterior myocardial infarction.

Q-wave anterior myocardial infarctions due to occlusion of the left anterior descending artery (LAD) are generally associated with the most extensive left ventricular damage. The presence of abnormal Q waves on the electrocardiogram (ECG) provides important information to localize the site of left ventricular infarction. However, the relationship between abnormalities of the QRS morphology in the precordial leads and angiographic information such as ejection fraction and the site of LAD occlusion (before or after the first septal perforator) has not been studied extensively. Seventy-three patients with single-vessel disease with complete LAD occlusion, abnormal QRS morphology in leads V1-V4 on ECG, and abnormal wall motion with contrast ventriculography were studied retrospectively. LAD occlusions were proximal to the first septal perforator in 33 patients and distal in 40 patients. Q waves were present in 59 patients, and the other 14 patients had either minimal R waves (< 0.25 mm), poor R-wave progression, or R-wave regression. A significantly higher ejection fraction was associated with the presence of R wave in V2 (0.52 +/- 0.18 vs. 0.39 +/- 0.15 in the absence of R wave, p < 0.003). LAD occlusion after and before the first septal perforator was associated with R wave in V2 in 67 and 36% of patients, respectively. Sensitivity and specificity of predicting occlusion after the first septal perforator based on R wave in V2 was 0.68 and 0.64, respectively. In patients with anterior myocardial infarctions, occluded LAD artery, and abnormal QRS morphology in the precordial leads, the presence of R wave in V2 is a useful predictor of higher ejection fraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Matching based on quantitative coronary angiography as a surrogate for randomized studies: comparison between stent implantation and balloon angioplasty of native coronary artery lesions.

Although intracoronary stenting has been advocated as an adjunct to balloon angioplasty to circumvent late restenosis, its effectiveness has not yet been verified. Therefore the aim of this study was to determine the differences in the immediate and long-term changes in stenosis geometry between Wallstent implantation and balloon angioplasty in native coronary artery lesions. To obtain two study populations with identical baseline stenosis characteristics, patients were matched for lesion site, vessel size, and minimal luminal diameter. Only patients undergoing elective and successful coronary intervention of a native coronary artery, in whom a control angiographic study had been performed, were included. A total of 186 patients (93 in each group) were selected. The coronary angiograms were analyzed with the computer-assisted cardiovascular angiographic analysis system. Matching was considered adequate, since there was an equal number of lesion sites in each study population and there were no differences in baseline reference diameter and minimal luminal diameter. Wallstent implantation resulted in a significantly greater increase in minimal luminal diameter (from 1.22 +/- 0.34 mm to 2.49 +/- 0.40 mm, p < 0.00001) compared with balloon angioplasty (from 1.21 +/- 0.29 mm to 1.92 +/- 0.35 mm, p < 0.00001). Despite a greater decrease in minimal luminal diameter after Wallstent implantation (0.48 +/- 0.74 mm) than after balloon angioplasty (0.20 +/- 0.46 mm), the minimal luminal diameter at follow-up was significantly greater after stent implantation (2.01 +/- 0.75 mm vs 1.72 +/- 0.54, p < 0.0001). It was concluded that Wallstent implantation results in a superior immediate and long-term increase in minimal luminal diameter compared with balloon angioplasty. The larger initial gain after stent implantation compensates for the late loss, and thus an improved initial result and not lessened neointimal hyperplasia is responsible for a reduced incidence of restenosis. Studies based on matching of angiographic variables are a surrogate for randomized studies, forecasting their results and offering insight into the effects of different interventional techniques. Moreover, these studies yield statistical information that may be helpful for the proper design of a randomized study (sample size, type II error).

Angioplasty, Balloon, Coronary↗
PubMed1992

Quantitative angiographic follow-up of the coronary Wallstent in native vessels and bypass grafts (European experience--March 1986 to March 1990).

The coronary stent has been investigated as an adjunct to percutaneous transluminal coronary angioplasty to obviate the problems of early occlusion and late restenosis. From March 1986 to March 1990, 265 patients (308 lesions) were implanted with the coronary Wallstent in 6 European centers. For this study, the patients were analyzed according to date of implantation (group 1, March 1986 to January 1988; group 2, February 1988 to March 1990) and vessel type (native arteries versus bypass grafts). Quantitative angiographic follow-up was performed in 82% of the study patients. The early in-hospital occlusion rate in the overall group was 15%. Group 1 patients had a 20% rate in contrast to 12% rate in group 2 (p = not significant [NS]). The early occlusion rate in native vessels and bypass grafts was 19 and 8%, respectively (p = 0.019). Restenosis was determined by 2 criteria (criterion 1, greater than or equal to 0.72 mm loss in minimal luminal diameter from poststent to follow-up; criterion 2, greater than or equal to 50% diameter stenosis at follow-up) within the stent and in the segments immediately proximal and distal to the stent. The restenosis rate with criterion 1 was 43% in the overall group of patients, 35% in group 1 versus 49% in group 2 (p = NS), and 34% in native vessels versus 54% in bypass grafts (p = 0.016). The second criterion was met by 27% of patients in the overall group, 21% in group 1 versus 32% in group 2 (p = NS), and 18% in native vessel versus 39% in bypass grafts (p = 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Actuarial Analysis↗
PubMed1992

Methodological problems related to the quantitative assessment of stretch, elastic recoil, and balloon-artery ratio.

The (inflated) balloon is important to determine the extent of stretch (theoretical maximal gain in diameter or area during PTCA), elastic recoil (the loss in diameter or area immediately after PTCA), and whether under- or over-sizing (balloon-artery ratio) of the dilated lesion occurred. In these assessments, the inflated balloon is used as scaling device with assumed uniformity along its entire length. In order to assess more accurately stretch, elastic recoil, and the balloon-artery ratio, the balloon diameter was measured over its entire length with edge detection and videodensitometry in 505 lesions (453 patients). With an average inflation pressure of 8.3 +/- 2.6 atm a difference between the minimal and the maximal balloon diameter of 0.59 +/- 0.23 mm was measured using edge detection and 1.70 +/- 0.90 mm2 difference in area using videodensitometry. This results in large variations in the calculated stretch, elastic recoil, and balloon-artery ratio depending on the site of the balloon chosen for assessment. The mean difference +/- SD between stretch and elastic recoil assessed by edge detection and videodensitometry (using the minimal luminal diameter or area of the balloon) are respectively 0.00 +/- 0.19 and 0.00 +/- 0.24, suggesting that both methods are appropriate.

Angioplasty, Balloon, Coronary↗
PubMed1992

Stenting of venous bypass grafts: a new treatment modality for patients who are poor candidates for reintervention.

During a 2-year period, 136 self-expanding Wallstents were implanted in saphenous vein bypass grafts in 69 patients with end-stage coronary artery disease. All patients had severe symptoms and the majority were poor candidates for either repeat surgery or conventional bypass coronary angioplasty because of unfavorable native anatomy, impaired left ventricular function, or a high-risk bypass lesion anatomy for coronary angioplasty. All procedures were technically successful without major complications and a need for emergency bypass surgery. However, during the hospital stay acute thrombotic complications occurred in seven patients (10%) resulting in one death and acute myocardial infarction in five patients and necessitating emergency repeat PTCA in two patients and repeat CABG in four. Twenty-three patients had serious hemorrhagic complications directly related to the rigorous anticoagulation schedule. Two patients died of fatal cerebral bleeding. During follow-up, another five patients died accounting for a total mortality rate of 12%. At late angiographic follow-up (4.9 +/- 3.4 months, n = 53), 25 patients (47%) had a restenosis (greater than or equal to 50% DS) within or immediately adjacent to the stent, necessitating reintervention in 19 patients (PTCA, n = 12; repeat CABG, n = 7). In the group without stent-related restenosis (n = 28), 15 patients had progression of disease in either the native or bypass vessels leading to recurrence of major anginal symptoms within 1 to 24 months. Ten of these patients required further intervention (stent, n = 6; PTCA, n = 3; repeat CABG, n = 1). Stenting in saphenous coronary bypass grafts can be performed safely with excellent immediate angiographic and clinical results.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1992

Directional atherectomy for treatment of restenosis within coronary stents: clinical, angiographic and histologic results.

OBJECTIVES: The safety and long-term results of directional coronary atherectomy in stented coronary arteries were determined. In addition, tissue studies were performed to characterize the development of restenosis. METHODS: Directional coronary atherectomy was performed in restenosed stents in nine patients (10 procedures) 82 to 1,179 days after stenting. The tissue was assessed for histologic features of restenosis, smooth muscle cell phenotype, markers of cell proliferation and cell density. A control (no stenting) group consisted of 13 patients treated with directional coronary atherectomy for restenosis 14 to 597 days after coronary angioplasty, directional coronary atherectomy or laser intervention. RESULTS: Directional coronary atherectomy procedures within the stent were technically successful with results similar to those of the initial stenting procedure (2.31 +/- 0.38 vs. 2.44 +/- 0.35 mm). Of five patients with angiographic follow-up, three had restenosis requiring reintervention (surgery in two and repeat atherectomy followed by laser angioplasty in one). Intimal hyperplasia was identified in 80% of specimens after stenting and in 77% after coronary angioplasty or atherectomy. In three patients with stenting, 70% to 76% of the intimal cells showed morphologic features of a contractile phenotype by electron microscopy 47 to 185 days after coronary intervention. Evidence of ongoing proliferation (proliferating cell nuclear antigen antibody studies) was absent in all specimens studied. Although wide individual variability was present in the maximal cell density of the intimal hyperplasia, there was a trend toward a reduction in cell density over time. CONCLUSIONS: Although atherectomy is feasible for the treatment of restenosis in stented coronary arteries and initial results are excellent, recurrence of restenosis is common. Intimal hyperplasia is a nonspecific response to injury regardless of the device used and accounts for about 80% of cases of restenosis. Smooth muscle cell proliferation and phenotypic modulation toward a contractile phenotype are early events and largely completed by the time of clinical presentation of restenosis. Restenotic lesions may be predominantly cellular, matrix or a combination at a particular time after a coronary procedure.

Actins↗
PubMed1992

Immediate changes in stenosis geometry following stent implantation: comparison between a self-expanding and a balloon-expandable stent.

The immediate changes in stenosis geometry following Wallstent and Wiktor stent implantation in native coronary arteries were compared in 92 patients (46 in each group) using automated edge detection. Patients with comparable baseline stenosis characteristics were selected. Lesions were matched for lesion site, reference diameter, and minimal luminal diameter. In both groups, the stented coronary artery was the left anterior descending artery in 27 patients (59%), the left circumflex artery in four patients (9%), and the right coronary artery in 15 patients (33%). The baseline reference diameter was 2.86 +/- 0.39 mm and 2.87 +/- 0.42 mm in the Wallstent and Wiktor stent study group, respectively (NS). The baseline minimal luminal diameter was identical in both groups (1.13 +/- 0.24 mm). The nominal size (mean +/- SD) of the unconstrained Wallstent was 3.5 +/- 0.3 mm and 3.3 +/- 0.3 mm for the Wiktor stent (P less than 0.05). Both types of stents resulted in a similar increase in minimal luminal diameter immediately following implantation (Wallstent: 2.34 +/- 0.38 mm, Wiktor stent: 2.43 +/- 0.27 mm, NS). Furthermore, there was a similar decrease in diameter stenosis and increase in minimal luminal cross-section area following implantation of both stents. These morphological changes were associated with a normalization of the hemodynamic parameters in both groups. It is concluded that, although the Wallstent and Wiktor stent are different in design and mechanical characteristics, there is a similar immediate improvement in stenosis geometry following implantation of both devices.

Angioplasty, Balloon, Coronary↗
PubMed1991

Edge detection versus densitometry for assessing coronary stenting quantitatively.

The optimal method used to analyze quantitatively the immediate angiographic results of coronary stenting in the coronary arteries has not been studied. Accordingly, minimal luminal cross-sectional area was determined by 2 methods, edge detection and densitometry, in 19 patients who underwent percutaneous transluminal coronary angioplasty (PTCA) and then coronary stent implantation for symptomatic coronary stenoses. The correlation coefficient, 0.73 before angioplasty, decreased to 0.59 after coronary angioplasty and then increased to 0.83 after stent implantation. The mean differences between edge detection and densitometric determinations of minimal luminal cross-sectional area were 0.31 +/- 0.51 mm2 before PTCA, -0.38 +/- 1.22 mm2 after angioplasty and 0.35 +/- 0.79 mm2 after coronary stenting. It is concluded that, although the correlation and variability in the measurement of minimal luminal cross-sectional area between edge detection and densitometry deteriorate after PTCA, they are improved after stenting, probably because of smoothing of the vessel contours by the stent and remodeling of the stented segment into a more circular configuration. Therefore, in the stented coronary artery, edge detection and densitometry are equally acceptable methods of analysis.

Absorptiometry, Photon↗
PubMed1991

Angiographic follow-up after placement of a self-expanding coronary-artery stent.

BACKGROUND: The placement of stents in coronary arteries after coronary angioplasty has been investigated as a way of treating abrupt coronary-artery occlusion related to the angioplasty and of reducing the late intimal hyperplasia responsible for gradual restenosis of the dilated lesion. METHODS: From March 1986 to January 1988, we implanted 117 self-expanding, stainless-steel endovascular stents (Wallstent) in the native coronary arteries (94 stents) or saphenous-vein bypass grafts (23 stents) of 105 patients. Angiograms were obtained immediately before and after placement of the stent and at follow-up at least one month later (unless symptoms required angiography sooner). The mortality after one year was 7.6 percent (8 patients). Follow-up angiograms (after a mean [+/- SD] of 5.7 +/- 4.4 months) were obtained in 95 patients with 105 stents and were analyzed quantitatively by a computer-assisted system of cardiovascular angiographic analysis. The 10 patients without follow-up angiograms included 4 who died. RESULTS: Complete occlusion occurred in 27 stents in 25 patients (24 percent); 21 occlusions were documented within the first 14 days after implantation. Overall, immediately after placement of the stent there was a significant increase in the minimal luminal diameter and a significant decrease in the percentage of the diameter with stenosis (changing from a mean [+/- SD] of 1.88 +/- 0.43 to 2.48 +/- 0.51 mm and from 37 +/- 12 to 21 +/- 10 percent, respectively; P less than 0.0001). Later, however, there was a significant decrease in the minimal luminal diameter and a significant increase in the stenosis of the segment with the stent (1.68 +/- 1.78 mm and 48 +/- 34 percent at follow-up). Significant restenosis, as indicated by a reduction of 0.72 mm in the minimal luminal diameter or by an increase in the percentage of stenosis to greater than or equal to 50 percent, occurred in 32 percent and 14 percent of patent stents, respectively. CONCLUSIONS: Early occlusion remains an important limitation of this coronary-artery stent. Even when the early effects are beneficial, there are frequently late occlusions or restenosis. The place of this form of treatment for coronary artery disease remains to be determined.

Angiography↗
PubMed1991

Do stents interfere with the densitometric assessment of a coronary artery lesion?

This in vitro study was designed to assess the contribution of three currently investigated coronary stents to the densitometric measurement of a known stenosis contained within two different sized plexiglass phantoms. These studies were performed at two concentrations of the contrast agent iopamidol (50 and 100%). The calculated minimal luminal cross-sectional area values in the control phantom ranged from 0-18% higher than the theoretical values. Insertion of a stainless steel stent (Wallstent, Schneider, Zürich or Palmaz-Schatz, Johnson and Johnson, Warren, NJ) resulted in further minor increases (less than or equal to 8% in the calculated minimal luminal cross-sectional area, except in the smaller phantom filled with 50% contrast medium. The Wiktor (tantalum) stent (Medtronic, Minneapolis, MN) had the largest impact of the three stents depending on the concentration of iopamidol (100% contrast medium: 9-13% values above control; 50% contrast medium; 23-56% higher). We conclude that although densitometry may overestimate the minimal luminal cross-sectional area in stented vessels, this effect is usually minor with stainless steel stents. However, tantalum-containing stents may result in serious overestimation of lesion area, particularly if contrast is diluted or the vessel is not well filled.

Coronary Angiography↗