Distal Vessel Segments Research Articles

Local vascular dysfunction after coronary paclitaxel-eluting stent implantation

Background Paclitaxel-eluting stents (PES) have been shown to reduce the rate of restenosis and the need for repeated revascularization procedures compared with bare metal stents. However, long-term effects of paclitaxel on vascular function are unknown. The purpose of the present study was to assess coronary vasomotor response to exercise after paclitaxel-eluting stent implantation. Methods Coronary vasomotion was evaluated by biplane quantitative coronary angiography at rest and during supine bicycle exercise in 27 patients with coronary artery disease. Twelve patients were treated with a bare metal stent (controls), and fifteen patients with a paclitaxel-eluting stent. All patients were restudied 6 ± 2 (range 2–12) months after stent implantation. Minimal luminal diameter, stent diameter, proximal, distal and a reference vessel diameter were determined. Results Reference vessels showed exercise-induced vasodilation in both groups (+ 20 ± 5% controls; + 26 ± 3% PES group). Vasomotion within the stented vessel segments was abolished. In the controls, the adjacent segments proximal and distal to the stent showed exercise-induced vasodilation (+ 17 ± 3% and + 24 ± 4%). In contrast, there was exercise-induced vasoconstriction of the proximal and distal vessel segments adjacent to the paclitaxel-eluting stent (− 13 ± 6% and − 18 ± 4%; p < 0.005). After sublingual nitroglycerin, the proximal and distal vessel segments dilated in both groups. Exercise-induced vasoconstriction adjacent to paclitaxel-eluting stent correlated inversely with the time interval after stent implantation. Conclusions Paclitaxel-eluting stent implantation is associated with exercise-induced vasoconstriction in the peristent region suggesting endothelial dysfunction as the underlying mechanism. Improvement of vascular function occurs over time, indicating delayed vascular healing.

Effect of Lumen Narrowing Within Sirolimus-Eluting Stents on Proximal and Distal Vessel Segments

Flow dynamics and shear stress may influence downstream vessel segments. The aim of this study was to investigate the potential impact of lumen narrowing within sirolimus-eluting stents (SES) on vessel response at adjacent reference sites. In 135 patients after SES implantation, minimal lumen area (MLA) within the stent and average lumen area at distal or proximal adjacent reference segments (5 mm) were obtained at baseline and follow up. In the smaller in-stent MLA group (MLA <3 mm(2)), lumen area decreased significantly at the distal reference compared with the larger in-stent MLA group (MLA >or=3 mm(2)), although no significant difference was seen at the proximal reference. In-stent lumen patency may influence vascular responses at adjacent reference segments after SES implantation.

Effect of Nicardipine Prolonged-Release Implants on Cerebral Vasospasm and Clinical Outcome After Severe Aneurysmal Subarachnoid Hemorrhage

The purpose of this study was to investigate the effect of nicardipine prolonged-release implants (NPRIs) on cerebral vasospasm and clinical outcome after severe subarachnoid hemorrhage. Thirty-two patients with severe subarachnoid hemorrhage and undergoing aneurysm clipping were included into this single center, randomized, double-blind trial. Sixteen patients received NPRIs implanted into the basal cisterns in direct contact to the exposed proximal blood vessels; in 16 control patients, the basal cisterns were opened and washed out only without leaving implants. Angiography was performed preoperatively and at day 8+/-1. Computed tomography imaging was analyzed for the incidence of territorial infarcts unrelated to surgery. Patient outcome was assessed using the modified Rankin and National Institute of Health Stroke scales. The incidence of angiographic vasospasm in proximal vessel segments was significantly reduced after implantation of NPRIs (73% control versus 7% NPRIs). Significant differences occurred also for the majority of distal vessel segments. Computed tomography scans revealed a lower incidence of delayed ischemic lesions (47% control versus 14% NPRIs). The NPRI group demonstrated more favorable modified Rankin and National Institute of Health Stroke scales as well as a significantly lower incidence of deaths (38% control versus 6% NPRIs). Implantation of NPRIs reduces the incidence of cerebral vasospasm and delayed ischemic deficits and improves clinical outcome after severe subarachnoid hemorrhage.

Evaluation of the Spatial Resolution with 1.5–4 Tesla in a Stenosis Model

Since it was first described in the early 1990s, magnetic resonance coronary angiography has evolved into a promising noninvasive modality for imaging the coronary arteries. The aim of this study was to evaluate the detection accuracy and spatial resolution of vascular stenosis in contrast-enhanced 3-dimensional magnetic resonance angiography on a flow phantom. The examinations were performed with 1.5, 3, and 4 T whole-body imaging systems. For imaging at 4 T, we used a gradient-echo-multi-slice sequence. The system was flushed with gadopentetate dimeglumine contrast medium at flow rates of 40 and 60 mL.min(-1). The accurate detection of in vitro stenoses was possible in segments of 0.4 mm in diameter at 4 T. The best results were obtained at a flow velocity of 40 mL.min(-1) and a contrast medium concentration of 0.2 mmol.L(-1). Contrast-enhanced high-field 3-dimensional magnetic resonance imaging provided a highly accurate evaluation of the degree of stenosis in this model. Exact evaluation of vessel diameters < 0.4 mm was not possible, even with 4 T. In vivo studies are necessary to overcome the current limitations in the visualization of small distal vessel segments.

Assessment of Global Hemodynamic Alterations in Patients after Subarachnoid Hemorrhage Using Perfusion MRI

Perfusion MRI (P-MRI) in subarachnoid hemorrhage (SAH) was found sensitive to detect focal disturbances of cerebral hemodynamics. Though vasospasm may be the major reason for disturbances of cerebral perfusion, also other factors, e.g. increase of intracranial pressure, brain edema etc., alter cerebral hemodynamics. The depiction and analysis of possible global changes of cerebral perfusion in patients after SAH was the aim of this study. 16 patients between day 6–11 after acute SAH who were suspected of suffering from vasospasm due to increased flow velocities in transcranial Doppler sonography were examined with P-MRI. After calculation of standardized time to peak (stdTTP) parameter maps the results were compared to age-matched controls using an adapted morphometrical evaluation procedure, which was designed to assess common cerebral perfusion alterations in the tested SAH group. Volumes showing decreased stdTTP values could be related to proximal vessel segments also exhibiting increased flow velocities in transcranial Doppler sonography. Volumes suffering from hemodynamic stress, as defined by an increase of stdTTP values, were detected in the periventricular parenchyma and the borderzones in both hemispheres. The results are suggestive of global perfusion disturbances, which mainly affect the distal cerebral vessel segments, additionally to the main effects of vasospasm, in patients after SAH.

High-Field MR Angiography on an In Vitro Stenosis Model Determination of the Spatial Resolution on 1.5 and 3T in Correlation to Flow Velocity and Contrast Medium Concentration

Since the first description of coronary magnetic angiography (MRA) in the early of 1990, this method seems to be shaped us a promising noninvasive modality to view the coronary arteries. Since several years dedicated high-field MR systems up to 4T are available for human use. The aim of the study was the evaluation of an in vitro vessel model with defined stenoses on 1.5T and 3T. For imaging at 3T, we used a 3d gradient-echo-sequence (fast SPGR). Furthermore, we examined the influence of the flow velocity and the contrast medium concentration on the spatial resolution. The accurate detection of in vitro stenoses was possible in segments up to 0.6 mm at 3T, the best results were obtained at a flow velocity of 40 ml/min and a contrast medium concentration of 0.2 mmol/l. The influence of the contrast medium concentration was statistically not significant. These results show that the spatial resolution can be increased by the use of a high-field MR scanner. Further in vivo studies are necessary to eliminate the method's limitation in visualizing small distal vessel segments.

Effect of Lumen Narrowing Within Coronary Stents on Proximal and Distal Vessel Segments Following Bare Metal Stent Implantation

Adjacent reference vessel response to smaller lumens at stented segments was examined with 3-dimensional intravascular ultrasound analysis. In 128 patients after bare metal stent implantation, minimal lumen area (MLA) within the stent and average lumen area at distal/proximal adjacent reference segments (5 mm) were obtained at baseline and follow-up. In the smaller in-stent MLA group (MLA <3 mm2), lumen area decreased significantly at the distal edge compared with the larger in-stent MLA group (MLA > or =3 mm2), although no significant difference was seen at the proximal edge. In-stent lumen patency may influence vascular responses at adjacent reference segments after bare metal stent implantation.

Coronary vessel visualization using true 16-row multi-slice computed tomography technology

Multi-slice computed tomography (MSCT) scanners with retrospective ECG-gating permit visualization of the coronary arteries. Limited spatial and temporal resolution as well as breathing artefacts due to the scan time can cause poor distal vessel segment and side branch visualization. The latest MSCT generation with true 16-detector slices (Sensation 16), Siemens, Forchheim, Germany) provides furthermore improved temporal and spatial resolution, as well as significantly reduced scan time. To assess, whether this technical improvement has also an impact on image quality we conducted the following study. Sixty-two consecutive patients (33 male, 29 female, mean age 63+/-8 [47-79] years, heart rate after beta-blockade 63+/-7 [45-86] bpm) with suspicion of coronary artery disease (CAD) were examined by cardiac MSCT. Parameter settings were: 0.75 mm collimation, 2.8mm table feed/rotation, caudocranial scan direction, 80 cc contrast media biphasic injection protocol, gantry rotation time 375 ms, temporal resolution 188 ms). Thirteen coronary segments (sgts) were evaluated in each patient (total number: 806 sgts). Image quality of each segment was determined as: excellent--free of motion artefacts, good--mild motion artefacts, relevant artefacts--still diagnostic value, severe calcification and insufficient image quality--not visualized segment. 301/806 (37%) sgts showed excellent and 294/806 (36%) sgts good image quality. Relevant artefacts were seen in 107/806 (13%) sgts, calcifications in 41/806 (5%) sgts. 63/806 (8%) sgts could not be visualized (34 of them (54%) either segment 9 or 10). Diagnostic image quality was achieved in 702/806 (87%) sgts. Due to true 16-slice technology and faster gantry rotation time MSCT image quality could be improved and allows a visualization of the entire coronary tree. Larger, randomized, catheter-controlled studies have to be conducted to determine, whether this improved visualization also translates into better diagnostic accuracy.

A morphological–mechanical explanation of edge restenosis in lesions treated with vascular brachytherapy

Purpose Edge restenosis in stenotic lesions treated by implantation of a conventional stent followed (or preceded) by a catheter-based brachytherapy is often attributed to “geographic miss” (GM). We propose a complementary (or, possibly, alternative) explanation based on the concept that a clear postprocedural mismatch between the in-stent lumen and the normal (undilated) lumens of the proximal and/or distal vessel segments results in an excessive, damageable increase of axial wall stress in these segments. Methods The possible poststenting situations at both margins of a stent are examined, and based on the presence or absence of an increase in axial wall stress, predictions are made about the lesion evolution. The concept is then also examined in the light of published observations. Results None of the analyzed observations appeared to be incompatible with the proposed morphological–mechanical explanation. Conclusion From a mechanical point of view, optimal matching of the proximal and distal stent diameters to the corresponding normal diameters of the adjacent arterial segment is likely to reduce the rate of edge restenosis.

Enhanced coronary vasoconstriction after PTCA in patients with acute ischemia.

Coronary vasoconstriction of the distal vessel segment has been reported after percutaneous transluminal coronary angiography (PTCA), which was explained by increased vasoconstrictor influences. In patients with acute ischemia these changes may be even enhanced. Thus, vasomotion of the epicardial coronary arteries was studied before and after PTCA in patients with acute ischemia due to unstable angina or acute infarction. 52 patients were divided into 2 groups: Group 1 (controls) consisted of 31 patients who underwent elective (PTCA) and group 2 of 21 patients who underwent emergency PTCA for unstable angina or acute infarction. Coronary artery dimensions proximal and distal to the culprit lesion were determined by quantitative coronary angiography before and after PTCA as well as after 0.2 mg nitroglycerin i.c. at the end of the procedure. Stenosis severity was similar before and after PTCA in both groups (before, 91 +/- 8% in group 1 vs 90 +/- 9% in group 2; after, 28 +/- 9% vs 23 +/- 10%, resp.). Heart rate and mean blood pressure remained unchanged. In the group with acute ischemia no vasodilation of the proximal (2 +/- 3%) and distal vessel (-1 +/- 4%) occurred after PTCA, whereas in the control group significant vasodilation of both vessel segments (11 +/- 2% resp. 13 +/- 3%) was found. The response to nitroglycerin was maintained in both groups. In the control group there was a significant correlation between stenosis severity and percent diameter change of the distal vessel segment. However, in the acute ischemic group this relationship was shifted downwards suggesting an enhanced vasoconstrictor response in these patients. Epicardial coronary arteries in patients with acute ischemia show an enhanced vasoconstriction after PTCA. Nevertheless, the response to nitroglycerin is maintained suggesting that functional (endothelial dysfunction) rather than structural factors are responsible for this phenomenon.

Evaluation of coronary artery stenosis with respiratory gated NMR angiography

Respiratory gated MR coronary angiography is a new MR imaging technique which permits reconstruction of the coronary arteries from a three-dimensional data set obtained from contiguous parallel sections. In this study, respiratory gated MR angiography was applied to assess significant coronary artery stenoses (> or = 50%). MR imaging was performed in 68 patients (50 men, 18 women) who had been referred to cardiac catheterization because of suspected or known coronary artery disease. The evaluation of coronary artery stenoses was performed in a blinded manner in the proximal, middle, and distal vessel segments after multiplanar coronary reconstruction of the MR images. Of the 680 coronary segments, 275 (40%) were located outside the imaging volume and were, therefore, excluded from further analysis. The highest sensitivity for stenosis detection was found in the proximal left anterior descending (LAD) and right coronary artery (RCA) with 75% and 71%, respectively. The overall sensitivity, however, was low with 48%. The overall specificity was 92%. The positive and negative predictive values were 67% and 85%, respectively. This study shows that significant coronary artery stenoses, especially in the proximal LAD and RCA, can be correctly identified using respiratory gated MR angiography. However, further technical improvements are necessary before this method may become a reliable diagnostic tool in clinical practice.

Vasoconstriction of rat renal interlobar arteries by noradrenaline and neuropeptide Y.

1. We have studied the contractile effects of noradrenaline and neuropeptide Y given alone and in combination on isolated rat renal interlobar arteries. 2. Noradrenaline contracted proximal and distal intrarenal microvessels in a concentration dependent manner, with similar potency (EC50 approximately equal to 550 nM), but maximal effects were greater in the proximal than in the distal vessel segments (approximately equal to 10 and 6 nM, respectively). 3. The noradrenaline-induced contraction was inhibited by low prazosin concentrations (3-10 nM) but not by 1 microM yohimbine indicating involvement of alpha(1)-but not alpha(2)-adrenoceptors. The alpha(1)A-adrenoceptor-selective antagonist, 5-methylurapidil and tamsulosin, had high potency (apparent affinities of approximately equal to 8 nM and 57 pM, respectively) while the alpha(1)D-adrenoceptor-selective antagonist, BMY 7378, had only low potency (apparent affinity approximately equal to 300 nM). The alpha(1)B-adrenoceptor-alkylating agent, chloroethylclonidine (10 microM for 30 min at 37 degrees C), had no inhibitory effects. The Ca2+ entry blocker, nitrendipine (300 nM), reduced the potency and maximal effects of noradrenaline. 4. Neuropeptide Y (1-100 nM) also contracted interlobar arteries in a concentration dependent manner, with greater effects in the proximal than in the distal segments, but maximal effects were only small in either segment (< 2 mN). In addition, neuropeptide Y also potentiated the response to noradrenaline, i.e. lowered its EC50 but this enhancement was also small. 5. We conclude that noradrenaline contracts rat interlobar arteries by an alpha(1)A-adrenoceptor; its co-transmitter, neuropeptide Y, affects the response only marginally in this vascular bed.

Acute effect of cigarette smoking on the coronary circulation: Constriction of epicardial and resistance vessels

Objectives. This study was performed to determine the acute effect of cigarette smoking on proximal and distal epicardial condult and coronary resistance vessels.Background. Cigarette smoking causes constriction of epicardial arteries and a decrease in coronary blood flow in patients with coronary artery disease, despite an increase in myocardial oxygen demand. The role of changes in resistance vessel tone in the acute coronary hemodynamic effect of smoking has not been examined.Methods. Twenty-four long-term smokers were studied during cardiac catheterization after vasoactive medications had been discontinued. The effect of smoking one cigerette 10 to 15 mm long on proximal and distal conduit vessel segments was assessed before and immediately after smoking and at 5, 15 and 30 min after smoking (n = 8). To determine the effect of smoking on resistance vessels, coronary flow velocity was measured in a nonobstructed artery with a 3F intracoronary Doppler catheter before and for 5 min after smoking (n = 8). Eight patients were studied without smoking to control for spontaneous changes in conduit arterial diameter (n = 5) and vessel tone (n = 3).Results. The average diameter of proximal coronary artery segments decreased from 2.56 ± 0.12 mm (mean ± SEM) before smoking to 2.41 ± 0.09 mm 5 min after amoking (−5 ± 2%, p < 0.05). Distal coronary diameter decreased from 1.51 ± 0.07 to 1.39 ± 0.06 mm (−8 ± 2%, p < 0.01). Marked focal vasoconstriction after smoking was observed in two patients. Coronary diameter returned to baseline by 30 min after smoking. There was no change in vessel diameter in control patients. Despite a significant increase in the heart rate-mean arterial pressure product, coronary flow velocity decreased by 7 ± 4% (p < 0.05) and coronary vascular increased by 21 ± 4% (p < 0.01) 5 min after smoking. There was no change in these variables in the control subjects.Conclusions. Smoking causes immediate constrictioin of proximal and distil epicardial coronary arteries and an increase in coronay resistance vessel tone despite an increase in myocardial oxygen demand. These acute coronary hemodynamic effects may contribute to the adverse cardiovascular consequences of cigarette smoking.

High dose intravenous aspirin, not low dose intravenous or oral aspirin, inhibits thrombus formation and stabilizes blood flow in experimental coronary vascular injury

Objectives. The purpose of this study was to assess the antithrombotic potential of various forms of aspirin administration.Background. Platelet activation in response to endothelial injury has been implicated in acute coronary syndromes.Methods. Delivering 100-/gmA anodal direct current to the intima of the left circumtlex coronary artery in dogs at a site of moderate external stenosis provides a thrombogenic model of vascular injury. Animals were treated with aspirin (Group I, 20 mg/kg intravenously [n - 11]; Group II, 4.6 mg/kg intravenously [n = 6]; Group III, 4.6 mg/kg orally 18 h before the experiment [n = 7]J or vehicle (Group IV, control [n = 11]).Results. The time required for thrombotic occlusion to occur was longer and the incidence of thrombosis was lower in Group 1 (Group I, 238 ± 7 min [n = 2]; Group II, 127 ± 25 min [n = 3]; Group III, 156 ± 35 min [n = 6]; Group IV, 90 ± 11 min [n = 11]) (p < 0.05). Thrombus mass was smaller In Group I (Group 1, 5.0 ± 0.8 mg; Group II, 12.2 ± 2.6 mg; Group HI, 11.6 ± 3.9 mg; Group IV, 9.1 ± 1.6 mg) (p < 0.05). Initial hemodynamic variables did not differ among groups. An increase in mean arterial pressure was noted for several hours after intravenous aspirin administration in Group I(99 ± 5 to 110 ± 4 mm Hg) (p < 0.05). Left circumflex coronary artery blood flow was stable for 5 h in Group I (Group I, 31 ± 2 to 26 ± 4 ml/min) but decreased in all the other groups (Group II, 26 ± 4 to 10 ± 5 ml/min; Group III, 27 ± 5 to 7 ± 7 ml/min; Group IV, 29 ± 4 to 0 ml/min) (p ⩽ 0,05). The in vivo area or left ventricle perfused by the left circumflex coronary artery was not different among groups. Platelet counts were similar and did not change over the course of the protocol. Ex vivo arachidonic acid-induced platelet aggregation decreased in all groups after aspirin (p ⩽ 0.001). Indium-III-labeled platelet adherence to the coronary vasculature was decreased in distal vessel segments after all doses of aspirin (p < 0.05), Platelet deposition in thrombi was similar for all treatment groups.Conclusions. High dose intravenous aspirin has salutary effects. It stabilizes left circumflex coronary- artery blood flow, prolongs the time to thrombosis, reduces the incidence of thrombolic occlusion, reduces thrombus mass and limits platelet adherence to sites of arterial injury. Low dose aspirin given intravenously or orally was ineffective. When persistent intracoronary thrombi precipitate unstable coronary syndromes, high dose intravenous aspirin may be useful in the acute period even though platelets continue to interact with injured vascular segments through aspirin-insensitive mechanisms.

Effect of endothelin on normal and diseased human coronary arteries.

We have examined the action of endothelin on healthy and diseased human epicardial coronary arteries to assess its possible role in coronary vascular disorders such as vasospasm and atherosclerosis. Endothelin (10(-10) mol l-1-10(-7) mol l-1) produced dose-dependent contractions in both normal and diseased vessels. The level of constriction was significantly greatly in healthy vessels at 10(-8) mol l-1 endothelin. A greater response was recorded in smaller, more distal vessel segments, irrespective of the pathology of the tissue. Endothelium denudation of disease-free segments had no significant effect on the response to endothelin. In the presence of a threshold dose of endothelin (10(-9) mol l-1), there was no measurable increase in the tension generated by potassium chloride, the thromboxane-mimetic U46619, noradrenaline and histamine. However, the response to 5-HT showed a large increase in arteries from four patients (440-147%) but slight or no increase in arteries from another three patients. We conclude that the interaction with other vasoconstrictor substances is a possible mechanism whereby endothelin may be involved in coronary artery vasospasm. In addition, endothelin may also be involved in the regulation of vascular tone of the small vessels of the heart.

Potential role of coronary vasoconstriction in ischaemic heart disease: effect of exercise

Coronary vasomotion plays an important role in the regulation of coronary perfusion at rest and during exercise. Normal coronary arteries show coronary vasodilation of the proximal (+20%) and distal (+40%) vessel segments during supine bicycle exercise. However, patients with coronary artery disease show exercise-induced vasoconstriction of the stenotic vessel segments. The exact mechanism of exercise-induced stenosis narrowing is not clear but might be related to a passive collapse of the disease-free vessel wall (Venturi mechanism), elevated plasma levels of circulating catecholamines, an insufficient production of the endothelium-derived vasorelaxing factor or increased platelet aggregation due to turbulent blood flow with release of thromboxane A2 and serotonin. Various vasoactive drugs, such as nitroglycerin and calcium antagonists, prevent exercise-induced stenosis vasoconstriction. An additive effect on coronary vasodilation of the stenotic vessel segment was observed after combination of nitroglycerin with diltiazem. Thus, exercise-induced stenosis narrowing plays an important role in the pathophysiology of myocardial ischaemia during dynamic exercise. The antianginal effect of vasoactive substances can be explained--besides the effect on pre- and afterload--by a direct action on coronary stenosis vasomotion.

Abnormal coronary vasomotion during exercise in patients with normal coronary arteries and reduced coronary flow reserve.

A reduced coronary flow reserve has been reported in patients with ischemialike symptoms and normal coronary arteries. In 13 such patients, both coronary vasomotion and flow reserve were studied. The luminal area of the proximal and distal third of the left anterior descending and left circumflex artery were determined by biplane quantitative coronary arteriography using a computer-assisted system. Patients were studied at rest, during submaximal supine bicycle exercise (4.0 minutes, 116 W), and 5 minutes after sublingual administration of 1.6 mg nitroglycerin. Heart rate, mean pulmonary pressure, and mean aortic pressure as well as the percent change of both proximal and distal luminal area were determined. In 10 of the 13 patients, coronary sinus blood flow was measured by coronary sinus thermodilution technique at rest and after dipyridamole infusion (0.5 mg/kg in 15 minutes) 10 +/- 5 days after quantitative coronary arteriography. Coronary flow ratio (dipyridamole/rest) and coronary resistance ratio (rest/dipyridamole) were determined in these patients. Patients were divided into two groups according to the behavior of the coronary vessels during exercise (vasodilation, group 1; vasoconstriction, group 2). Coronary vasodilation of the proximal (luminal area +26%, p less than 0.001) and distal (+45%, p less than 0.001) artery was observed in seven patients (group 1) during exercise and after sublingual nitroglycerin (+46%, p less than 0.001; and +99%, p less than 0.001, respectively). In group 2 (n = 6), however, there was coronary vasoconstriction of the distal vessel segments (-24%, p less than 0.001) during exercise, whereas the proximal coronary artery showed vasodilation (+26%, p less than 0.001) during exercise. After sublingual nitroglycerin, both vessel segments elicited vasodilation (distal coronary, +44%, p less than 0.001; proximal coronary artery, +47%, p less than 0.001). Coronary flow ratio amounted to 2.5 in group 1 and 1.2 in group 2 (p less than 0.05) and coronary resistance ratio to 2.7 in group 1 and to 1.2 in group 2 (p less than 0.05), respectively. Thus, among patients with ischemialike symptoms and normal coronary arteries, there is a group of patients (group 2) with an abnormal dilator response of the distal coronary arteries to the physiologic dilator stimulus of exercise and a reduced dilator capacity of the resistance vessels after dipyridamole (abnormal coronary vasodilator syndrome). The nature of this exercise-induced distal coronary vasoconstriction is not clear but might be due to an abnormal neurohumoral tone that may cause or contribute to the blunted vascular response during exercise.

Effect of coronary collaterals on left ventricular function at rest and during stress

The influence of coronary collateral vessels on resting left ventricular function was investigated in 87 consecutive patients with complete coronary artery occlusion of at least one of the three major coronary vessels. The morphology of coronary and collateral circulation was evaluated by coronary arteriography. Left ventricular function was assessed by biplane ejection fraction and segmental wall motion was evaluated by hemiaxes shortening. Collaterals to occluded arteries were graded as good or poor, according to the caliber of the distal vessel segment. Patients were divided into those with good collaterals (n =35), and those with poor or absent collaterals (n = 52), furthermore, these two groups were subdivided according to the location of coronary artery occlusion. Collateralized single vessel occlusions were found more frequently than collateralized multiple vessel occlusions. Ejection fraction and segmental wall motion was significantly better in well collateralized occlusions than in poorly collateralized occlusions of LAD or RC and was normal or depressed only slightly if compared to 17 patients without heart disease. In contrast, total and regional myocardial function was severely depressed in poorly collateralized LAD or RC occlusion. Ventriculography after rapid ventricular pacing was performed in 12 of 87 patients with well collateralized or poorly collateralized LAD occlusion to evaluate to what extent coronary collaterals protect anterior wall motion during increased oxygen demand. Pacing induced a drastic fall of anterior wall motion in well collateralized segments whereas no change was found in poorly collateralized segments. Reviewing clinical data of two patient groups with comparable numbers and locations of occlusions revealed in the well collateralized group more severe angina (p < 0.001) and ST-segment changes during exercise (p < 0.01) than in the poorly collateralized group. The latter showed more severe dyspnoe (p < 0.01) and more histories of previous infarctions (p < 0.001). We conclude that well-developed collateral vessels to a complete occluded artery prevent severe asynergy at rest but not during stress.