Is vasospasm related to platelet deposition? Relationship in a porcine preparation of arterial injury in vivo

Importance of antithrombin therapy during coronary angioplasty

Angioplasty procedures with balloons, cutters or lasers all may greatly enlarge the arterial lumen, but luminal diameter may decrease because of mural thrombus in 70% to 80%, smooth muscle proliferation, vasoconstriction or recoil. Thrombin binds to arterial wall matrix and fibrin within a thrombus. Heparin dose-dependently decreases platelet and thrombus deposition but does not eliminate these even at high doses. Specific thrombin inhibition started before angioplasty experimentally prevents mural thrombus and limits platelet deposition to a single layer or less. Experimentally, anticoagulant and antifibrin effects occur at lower antithrombin blood levels and lower activated partial thromboplastin times (1.7 times control). Because platelets are so sensitive to thrombin, the higher level of thrombin inhibition required may occur at a specific level (activated partial thromboplastin time greater than or equal to 2 times control); this is not defined in humans. The duration of therapy is not defined in animals or humans. Thrombus and thrombin may be related to cellular proliferation.

Effects of serotonin-receptor blockade on angioplasty-induced vasospasm in an atherosclerotic rabbit model

Vasospasm occurs both in patients and animal models after angioplasty and may be associated with early closure of the dilated vessel. To investigate the mechanism of angioplasty-induced vasospasm, the effect of serotonin-receptor blockade with two serotonin2 (S2) antagonists, LY53857 and sergolexole, was examined in rabbits with focal femoral artery atherosclerosis. In preliminary studies, local infusion of 1-100 micrograms serotonin caused significant femoral artery vasoconstriction (p less than 0.05) in both normal and atherosclerotic rabbits. There was no significant difference in the degree of vasoconstriction induced by equal doses of serotonin in normal and atherosclerotic animals. Infusion of 10 micrograms serotonin produced a 23 +/- 5% decrease in luminal diameter in atherosclerotic femoral arteries. This was blocked by pretreatment with both S2 inhibitors given separately in different animals before serotonin infusion (p less than 0.002). In contrast, LY53857 (sergolexole was not tested) had no significant effect on phenylephrine-induced vasoconstriction, confirming its specificity as an S2-receptor antagonist. Balloon angioplasty of atherosclerotic vessels caused a significant increase in vessel diameter at the angioplasty site (45% increase from baseline diameter, p less than 0.05). This was associated with significant luminal narrowing both proximal (21% reduction from baseline, p less than 0.05) and distal (17% reduction from baseline, p less than 0.03) to the angioplasty site. These proximal and distal changes are most likely due to vasospasm, as there was no histological evidence of thrombus or dissection at these sites to explain the luminal narrowing. Pretreatment of animals with 10 mg LY53857 or 20 mg sergolexole blocked the proximal vasospasm (2.6 +/- 0.4 before versus 2.2 +/- 0.1mm after angioplasty for LY53857, 2.1 +/- 0.4 before versus 2.1 +/- 0.4 mm after angioplasty for sergolexole; p = NS). Treatment with 20 mg LY53857 inhibited both proximal (2.3 +/- 0.1 before versus 2.2 +/- 0.2 mm after angioplasty, p = NS) and distal (1.7 +/- 0.1 before versus 1.6 +/- 0.2 mm after angioplasty, p = NS) vasospasm after angioplasty. Proximal (2.3 +/- 0.5 before versus 2.5 +/- 0.3 mm after) and distal (1.7 +/- 0.2 before versus 1.7 +/- 0.4 mm after) vasospasm was also prevented by pretreatment with 40 mg sergolexole.(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence for superoxide radical-dependent coronary vasospasm after angioplasty in intact dogs

BACKGROUND

Active oxygen species can influence vascular tone and platelet activation through a variety of mechanisms. This study assessed the role of the superoxide anion, the hydroxyl radical, and hydrogen peroxide in vasoconstriction and mural thrombosis after coronary artery angioplasty in intact dogs.

METHODS AND RESULTS

Injury was induced by inflation of a balloon catheter 50 +/- 6% above baseline arterial diameter; dogs were followed for 2 hours before death. Epicardial coronary diameters at arteriography and extent of thrombus deposition at serial histological sections were analyzed in controls (n = 20) and in dogs pretreated with superoxide dismutase (SOD, a superoxide radical scavenger, n = 10); other dogs were pretreated with the hydrogen peroxide scavenger catalase (n = 8), the iron chelator deferoxamine (n = 6), or the hydroxyl radical scavenger 1,3-dimethyl-2-thiourea (n = 9). Angioplasty-induced injury was similar among groups. After angioplasty, control dogs exhibited localized and persistent vessel constriction, which was maximal at the initial 5 minutes (28.9 +/- 6.3% diameter decrease versus baseline). Corresponding arterial diameters of SOD-treated dogs were 24-69% larger (95% confidence interval, p less than 0.001) than controls at 5 minutes and, on average, 32% larger than controls thereafter (p less than 0.01). Vasoconstriction was not prevented by the other treatments. The SOD dose used accounted for inhibition of zymosan-stimulated blood cytochrome c reduction versus baseline (7 +/- 3 versus 30 +/- 6 nmol/min/10(6) cells, respectively, p = 0.003); such inhibition occurred in no other group. Prevalence of mural thrombosis was similar among all groups, but large thrombi (greater than 15% of lumen area) were absent in SOD-treated dogs, contrary to control group (p = 0.028); other groups were similar to control. In the absence of injury, SOD alone induced no change in coronary diameter, coronary blood flow, or platelet aggregation.

CONCLUSIONS

These data provide evidence implicating the superoxide radical in the genesis of vasoconstriction after coronary angioplasty in vivo. Such effects seem to be independent of its conversion to hydroxyl radicals and availability of hydrogen peroxide or catalytic iron complexes.

Intracoronary thrombus formation causes focal vasoconstriction of epicardial arteries in patients with coronary artery disease

BACKGROUND

Experimental studies have demonstrated that intracoronary platelet aggregation and thrombus formation may induce marked vasoconstriction of epicardial arteries with endothelial injury.

METHODS AND RESULTS

To examine the effects of intracoronary thrombus formation on coronary vasomotor tone of human epicardial arteries in vivo, we studied 15 patients who developed intracoronary thrombi adherent to the guide wire during balloon dilatation. Epicardial artery luminal area was evaluated by quantitative coronary angiography proximal and distal to the site of intracoronary thrombus formation and in a reference vessel before and after thrombus formation as well as after intracoronary injection of 0.2-0.3 mg nitroglycerin. All artery segments distal to the site of thrombus formation showed vasoconstriction with a luminal area reduction of -27.4 +/- 17.1% (p less than 0.001), whereas proximal vessel segments and reference vessels not manipulated during percutaneous transluminal coronary angioplasty did not demonstrate any significant luminal area changes during thrombus formation. Angiographic measurements after advancing the guide wire with the adherent thrombus (performed in six of the 15 patients) revealed in all patients that vasoconstriction did develop at a new site distal to the thrombus persistence of the initial vasoconstriction now residing proximal to the thrombus. Thus, there was a sequential association between thrombus formation and subsequent distal vasoconstriction. Intracoronary injection of nitroglycerin abolished the thrombus-induced vasoconstriction. No significant luminal area changes were observed in 20 patients without angiographic evidence of intracoronary thrombus formation.

CONCLUSIONS

Intracoronary thrombus formation during percutaneous transluminal coronary angioplasty causes focal vasoconstriction of epicardial arteries in patients with coronary artery disease. Although caution must be advised in the extrapolation of this phenomenon, which was observed in a manipulated artery during coronary angioplasty, the vasoconstrictor response to intracoronary thrombus formation in vivo may play an important role in the dynamic mechanisms of acute coronary heart disease syndromes.

Angiographic demonstration of hyperconstriction induced by serotonin and aggregating platelets in porcine coronary arteries with regenerated endothelium

In isolated porcine coronary arteries, the endothelium inhibits the contractions induced by serotonin and aggregating platelets. This effect is reduced by regeneration after balloon denudation. The present study was designed to examine whether those in vitro observations could be reproduced in vivo. Sixteen male Yorkshire pigs underwent balloon removal of the endothelium from either the left anterior descending (n = 9) or left circumflex (n = 7) coronary artery. An angiographic study was performed before and 4 weeks after endothelial denudation; in the latter condition the presence of a full endothelial lining was confirmed histologically. Before endothelial denudation, intracoronary injection of serotonin (10 micrograms/kg) caused only mild constriction in both arteries. However, 4 weeks after the denudation, intracoronary serotonin repeatedly caused marked hyperconstriction in the previously denuded artery compared with the control coronary artery. Intracoronary injection of aggregating platelets stimulated by collagen caused constriction in the previously denuded artery but not in the control artery. The hyperconstriction induced by serotonin and aggregating platelets was inhibited by intravenous injection of ketanserin (a 5-HT2-serotonergic blocker). These data indicate that 1) the normal endothelium blunts the coronary vasoconstriction induced by serotonin and aggregating platelets in vivo, and 2) the inhibitory effect of the endothelium is reduced after regeneration, allowing coronary hyperconstriction or vasospasm, or both.

Relative efficacy of antithrombin compared with antiplatelet agents in accelerating coronary thrombolysis and preventing early reocclusion

BACKGROUND

Optimal coronary thrombolysis should be prompt and persistent. Although activation of platelets and increased thrombin activity have been associated with clinical thrombolysis, the role of each in delaying thrombolysis or inducing early coronary reocclusion has been difficult to define.

METHODS AND RESULTS

In conscious dogs with coronary thrombosis induced by electrical current, we assessed the impact on the rapidity of thrombolysis and the incidence of reocclusion of two types of adjunctive treatment given concomitantly with intravenous tissue-type plasminogen activator (t-PA): 1) inhibition of platelet function with a peptide mimetic antagonist of platelet glycoprotein IIb/IIIa receptors or with lysine acetylsalicylic acid (ASA) and 2) inhibition of thrombin activity with recombinant hirudin or with heparin. ASA but not the receptor antagonist shortened the time to thrombolysis with t-PA (20 +/- 13 [mean +/- SD] minutes with ASA, 36 +/- 15 minutes with receptor antagonist, and 43 +/- 16 minutes with the saline control). Reocclusion occurred promptly after completion of the infusion of t-PA in all seven dogs given saline. Reocclusion was delayed and prevented in some dogs within 90 minutes after the end of the infusion of t-PA by both antiplatelet agents but still occurred in 42% despite continued inhibition of platelet function (i.e., three of six dogs given ASA and two of six given receptor antagonist). In contrast, inhibition of thrombin activity with recombinant hirudin in a dose that prolonged the partial thromboplastin time modestly (1.5-2-fold) resulted in accelerated lysis (19 +/- 10 minutes) and prevention of reocclusion in each of six dogs. Heparin given in doses that elicited similar prolongation of the partial thromboplastin time did not accelerate lysis nor prevent reocclusion, which occurred in five of six dogs.

CONCLUSIONS

Inhibition of thrombin by recombinant hirudin facilitates thrombolysis and maintains patency of coronary arteries recanalized with t-PA particularly effectively. The benefit conferred may reflect direct anticoagulant effects plus diminished activation of platelets secondary to decreased thrombin activity.

Acute complications of percutaneous transluminal coronary angioplasty for total occlusion

The incidence of major complications after percutaneous coronary angioplasty (PTCA) of a totally occluded artery was assessed retrospectively. A total of 1649 PTCA procedures were analyzed. After exclusion of procedures for acute myocardial infarction or total occlusion that resulted from restenosis, 90 patients were selected. Forty-four patients (49%) had stable angina and 46 (51%) had unstable angina. The estimated duration of occlusion was 87 +/- 78 days in patients with stable angina, as compared with 10 +/- 8 days in patients with unstable angina (p less than 0.001). Abrupt vessel closure during PTCA occurred only in patients with unstable angina (0% versus 17%, p less than 0.05). The major complication rate was 2.5% in the stable angina group, and 20% in unstable angina group (p less than 0.01). This rate was also significantly higher than the complication rate of 8% observed in 442 procedures that were performed during the same period in patients with the unstable angina and nonocclusive stenosis (p less than 0.01). Patients with unstable angina who undergo PTCA of a totally occluded artery represent a subset of high risk for major complications.

Effects of sodium pentothal and sufentanil on serotonin induced constriction of canine coronary artery rings without endothelium

1. The individual and combined effects of sufentanil and sodium pentothal on canine coronary artery vasomotor responses to 5-HT were studied in an isolated vascular ring preparation. 2. Clinical concentrations of sufentanil have little effect on basal coronary tension or constriction induced by either 5-HT or sodium pentothal individually, until very high doses greater than 0.26 microM are reached. 3. Sodium pentothal causes coronary constriction at clinical concentrations and this effect is additive and possibly potentiated when combined with 5-HT. 4. Sufentanil inhibits coronary constriction induced by the combination of sodium pentothal and 5-HT.

Spontaneous alterations in coronary blood flow velocity before and after coronary angioplasty in patients with severe angina

Cyclic coronary artery flow variations with a spontaneous decline in coronary blood flow to very low levels have been documented in stenosed canine coronary arteries with endothelial injury. These flow variations are associated with transient platelet aggregation and dislodgment and the release of selected mediators, including thromboxane A2 and serotonin. However, cyclic or spontaneous flow variations have not been demonstrated in stenosed coronary arteries in humans. In this study, the hypothesis was tested that spontaneous coronary blood flow velocity variations occur in some patients with stenosed coronary arteries before or after coronary artery angioplasty. Thus, 13 patients with severe and limiting angina underwent intracoronary pulsed Doppler velocimetry of their dilated artery immediately before and after percutaneous transluminal coronary angioplasty, whereas 9 control patients underwent velocimetry of an angiographically normal coronary artery. A 3F catheter with a 20 MHz Doppler crystal was positioned to achieve a maximal stable signal, and the flow velocity signal was recorded continuously for 20 min. Spontaneous flow velocity variations (greater than or equal to 38% change in Doppler frequency shift with wide morphologic changes) were present in 3 of the 13 patients tested. Spontaneous flow velocity variations occurred before angioplasty in one patient, after angioplasty in another and both before and after angioplasty in a third. In addition, 2 of the 13 patients, 1 with spontaneous coronary artery flow velocity variations before angioplasty, had frank vasospasm in an adjacent area just distal to the area of coronary dilation immediately after balloon inflation. These data establish that spontaneous coronary artery flow velocity variations occur in some patients with severe and limiting angina before and after coronary angioplasty. These variations may be related to platelet aggregation or coronary vasoconstriction, or both, at sites of endothelial injury resulting from plaque fissuring or ulceration and endothelial and medial injury occurring during coronary angioplasty.

Determinants of smooth muscle injury during balloon angioplasty

To study the determinants of smooth muscle injury during balloon angioplasty, we conducted a series of experiments to examine the effects of degree of arterial stretching, duration of balloon inflation, and arterial precontraction on smooth muscle injury after balloon angioplasty in isolated, perfused whole-vessel segments of rabbit aortas and dog carotid arteries. Freshly dissected rabbit thoracic aortas and dog carotid arteries were mounted in a muscle bath-perfusion chamber and perfused at 80 mm Hg. The proximal half of each aorta was dilated with a 5-mm (41 +/- 6% stretch), 6-mm (64 +/- 6% stretch), or 8-mm (97 +/- 9% stretch) balloon angioplasty catheter, and the uninjured half of each vessel served as the control. The vasoconstrictor behavior of the dilated segment was then assessed by dose-response testing; long-axis, ultrasonic imaging combined with computerized edge-detection image processing was used to measure changes in segmental internal vessel diameters that were induced by phenylephrine. A similar series of experiments was performed in dog carotid arteries with 5-mm balloon catheters (42 +/- 2% stretch) to compare the susceptibility to smooth muscle injury between elastic (aortic) and muscular (carotid) arteries. Additional experiments were performed to determine the roles of prolonged (30 minutes) balloon inflation and arterial precontraction on smooth muscle injury after balloon angioplasty. In rabbit aortas, the dilated arterial segments demonstrated normal reactivity to phenylephrine after dilatation with 5- and 6-mm balloons (p = NS versus control). Severe smooth muscle injury (histopathologically) with "arterial paralysis" was observed after severe stretch (8-mm balloon) and after 5-mm balloon dilatation (46 +/- 5% stretch) in precontracted vessels. Prolonged balloon inflations did not impair aortic vasoconstrictor behavior. Dog carotid (muscular) arteries demonstrated angioplasty-induced smooth muscle injury with less severe degrees of stretch (47-52% stretch). Geometric modeling suggests that medial stretching during balloon angioplasty of diseased vessels in vivo is in the range of 15-41%.(ABSTRACT TRUNCATED AT 400 WORDS)

Vascular reactivity after balloon angioplasty in an atherosclerotic rabbit

Alterations in vessel wall reactivity (VR) at or adjacent to the dilation site after balloon angioplasty (BA) may vary according to the inflation protocol and the time after angioplasty and may influence outcome. In 64 atherosclerotic rabbit femoral arteries, we evaluated VR after BA with intravenous ergonovine (ERGO) (40 micrograms/min for 5 minutes) and intra-arterial nitroglycerin (NTG) (2,500 micrograms single bolus) 24-72 hours and 28 days after BA. Comparisons were made with atherosclerotic, nonangioplastied, age-matched controls. BA was standardized to three 1-minute inflations, each 1 minute apart. For each balloon size, 2.5- (appropriate size) or 3.0-mm (oversized) vessels were allocated to either 5 or 10 atm inflation pressure. For the analysis, four groups were compared: Group 1, 3.0/5; group 2, 3.0/10; group 3, 2.5/5, and group 4, 2.5 mm/10 atm. Angiographic diameters were measured at, proximal, and distal to the lesion at baseline, 10 minutes after ERGO, and 5 minutes after NTG. Angiograms were measured with electronic calipers by two blinded observers. All segments of control vessels vasoconstricted to ERGO and vasodilated to NTG (p less than 0.05 versus baseline), indicating a normal response. At 24-72 hours after dilatation, the angioplasty sites for all inflation pressure/balloon size combinations were not responsive to either ERGO or NTG. All segments distal to the dilatation sites vasoconstricted to ERGO and dilated to NTG (p less than 0.05 versus baseline), indicating a normal response. Proximal segments of vessels dilated with a 2.5-mm balloon (appropriate size) responded positively to both stimuli (p less than 0.05). Those vessels dilated with a large balloon (3.0 mm) were nonreactive in the segment proximal to the angioplasty site. Twenty-eight days later angioplasty sites dilated with a 2.5-mm balloon (appropriately sized) regained reactivity; however, segments dilated with a large balloon (3.0 mm) remained unresponsive. All proximal segments, including those from vessels dilated with a large balloon, reacted positively. All distal segments reacted appropriately. Restenosis rates were not different between the over- and appropriately sized balloon groups. These data demonstrate that immediately after angioplasty, vessels lose reactivity at the dilatation site. Those vessels dilated with the smaller-size balloon (2.5 mm) regained reactivity. For large balloons, reactivity is not regained at 28 days. For segments proximal to the site of dilatation, transient loss of reactivity is seen only when a large balloon is used. Thus, acute closure originating at the site of dilatation is not a result of spasm.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of cooling on smooth muscle response to 5-hydroxytryptamine in human hand veins

5-Hydroxytryptamine has been suggested to be a mediator in peripheral cold-induced vasospasm. In order to investigate the contribution of different 5-hydroxytryptamine receptor subtypes in the contractile response during cooling, segments of subcutaneous hand veins obtained from 50 patients undergoing hand surgery were examined in vitro in organ baths. The temperature in the bath was initially 37 degrees C and was either continuously lowered to 10 degrees C or kept constant at 37 degrees C, 29 degrees C. Cooling to 25 degrees C augmented the contractile response to 5-hydroxytryptamine in intact as well as in endothelium-denuded segments. The 5-hydroxytryptamine2 receptor antagonist ketanserin antagonized the contractile response to 5-hydroxytryptamine at 37 degrees C, and in addition abolished the cold-induced enhancement of the response during cooling. This points to a major role of the 5-hydroxytryptamine2 receptor in the cold-induced augmentation of the response to 5-hydroxytryptamine, which was further supported by increased contractions to the 5-hydroxytryptamine2 receptor agonist alpha-methyl-5-hydroxytryptamine during cooling. Contractile responses were also obtained by the selective 5-hydroxytryptamine1-like receptor agonist GR43175 interpreted to indicate the presence of a smaller 5-hydroxytryptamine1-like receptor population. However, the response to GR43175 was unaffected by cooling. These results warrant further investigations of the role of 5-hydroxytryptamine in cold-induced peripheral vasospasm.

Hirudin, heparin, and placebo during deep arterial injury in the pig. The in vivo role of thrombin in platelet-mediated thrombosis

Three dosages (0.3, 0.7, and 1.0 mg/kg) of recombinant hirudin, a specific inhibitor of thrombin, were compared with heparin (50 units/kg) and placebo for reducing thrombus formation in the carotid arteries of 50 pigs after deep injury by balloon dilatation. Each drug was administered as a bolus followed immediately by a continuous infusion of the same dose per hour. Major end points were quantitative indium-111-labeled platelet and iodine-125-labeled fibrinogen deposition and the incidence of mural thrombosis. This study showed that heparin, at a dose that prolonged the activated partial thromboplastin time (APTT) to twice the control time, did not prevent mural thrombosis or significantly reduce platelet deposition compared with placebo but did reduce fibrinogen deposition. Recombinant hirudin markedly reduced platelet and fibrinogen deposition in a dose-related manner and totally eliminated mural thrombosis at an APTT of two to three times that of control. Platelet deposition (x 10(6)/cm2, mean +/- SEM) in areas of deep arterial injury for the placebo, heparin, and 0.3, 0.7, and 1.0 mg/kg hirudin groups was 54 +/- 21, 33 +/- 9, 22 +/- 6, 8 +/- 1, and 7 +/- 1, respectively; electron microscopy showed a single layer (or less) of platelets at the two highest hirudin dosages. The incidence of macroscopic mural thrombosis was 76% with placebo, 57% with heparin, 46% with 0.3 mg/kg hirudin; there were no thrombi with 0.7 or 1.0 mg/kg hirudin (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of thrombosis on vascular tone in rat mesenteric arteries with endothelium in vivo

We examined the effects of thrombosis on vascular tone in vivo, using small mesenteric arteries of rats (about 300 microns i.d.) and a video recording system attached to a microscope. To induce thrombosis we damaged the vessel wall over a short segment by compression and exposed the media to the bloodstream. A thrombus mainly consisting of platelets gradually enlarged at the damaged site and caused 50-100% narrowing of the lumen. The diameter at the site downstream from the thrombus did not change as long as the blood flow was not interrupted. Instead, vasoconstrictor response to serotonin (3.0 and 30 micrograms/ml) or norepinephrine (0.1, 0.3, and 1.0 microgram/ml) given topically was significantly inhibited at the site downstream from the thrombus compared with that at the upstream site (p less than 0.01). Nonthrombotic mechanical narrowing of the vascular lumen did not affect vascular constriction by these agents. After damage to the endothelium by intra-arterial infusion of a detergent (0.3% CHAPS), the inhibition of the constrictor response by the thrombus was no longer observed. Once the thrombus occluded the vascular lumen and the blood flow was interrupted, the diameter at the downstream site declined markedly, from 291 +/- 22 to 77 +/- 21 microns (mean +/- SEM, n = 7, p less than 0.01) even without endothelial damage. Mechanical nonthrombotic occlusion of the vascular lumen induced only a small diameter reduction to 241 +/- 16 microns. We conclude that a partially occlusive thrombus may release a material that inhibits vascular constriction by serotonin or norepinephrine through an endothelium-dependent mechanism and that an occlusive thrombus induces constriction of the downstream vascular bed even with endothelium.

Evidence for altered epicardial coronary artery autoregulation as a cause of distal coronary vasoconstriction after successful percutaneous transluminal coronary angioplasty

To determine whether vasoconstriction distal to the site of successful percutaneous transluminal coronary angioplasty (PTCA) is a result of altered autoregulation in a hypoperfused coronary artery, we examined the association of this distal vasoconstriction with lesion severity in 20 patients. Lesion severity was classified as moderate, severe or critical (greater than 1.0, 0.5-1.0, and less than 0.5 mm, respectively). Quantitative coronary measurements were made at 3, 15, and 30 min after PTCA, and then after intracoronary (IC) nitroglycerin, in coronary segments distal to the dilated lesion (distal) and in a nonmanipulated vessel (control). Coronary vasoconstriction in the Distal segment after PTCA correlated with lesion severity, with 14 +/- 4%, 28 +/- 2%, and 41 +/- 5% vasoconstriction (vs. IC nitroglycerin, 30 min after PTCA) in the moderate, severe and critical lesion severity subgroups, respectively (P less than 0.01 for critical or severe vs. moderate). This vasoconstriction was significantly greater than that observed in the corresponding control segment for patients with severe (P less than 0.01), and critical (P less than 0.001) lesions. These findings suggest that hypoperfused human epicardial coronary arteries "reset" their autoregulatory responsiveness and that distal vasoconstriction after PTCA is the result of this altered autoregulation. These findings have clinical implications concerning the etiology, prophylaxis and treatment of coronary spams after PTCA and coronary bypass surgery.

Adjuvant therapy for intracoronary stents. Investigations in atherosclerotic swine

Early thrombosis has complicated human stent implantation in several trials. To determine the best anticoagulation/antiplatelet therapy to maintain stent patency after percutaneous transluminal coronary angioplasty, we implanted the flexible balloon-expandable coil stent into the left anterior descending coronary artery of 28 atherosclerotic 8-month-old Hanford miniature swine. Animals were randomly assigned to one of three treatment groups: group A, aspirin (1 mg/kg/day) and dipyridamole (1 mg/kg three times a day); group B, aspirin and dipyridamole (same doses) plus Coumadin (dose required to prolong prothrombin time 1.3-1.5-fold that of normal); and group C, control. Adjuvant therapy was begun 3 days before stenting. Two pigs (one from group A and one from group B) died during implantation, both without thrombosis. Twenty-six animals survived until follow-up angiography and sacrifice at 1 month. No occlusive thrombosis of the stent occurred in survivors. Reduction of the stent lumen diameter was observed in every case at follow-up. Percent lumen reduction was 19% in group A, 26% in group B, and 24% in group C. Marked smooth muscle cell hyperplasia was seen by light and transmission electron microscopy at stent struts. Scanning electron microscopy of the luminal surface showed a variable morphology consisting of normal endothelium, adherent leukocytes, stellate periluminal cells, and occasional fibrin strands and red blood cells. Luminal narrowing was not affected by anticoagulation therapy, antiplatelet drugs, cholesterol level, or stent sizing. We conclude that occlusive thrombosis does not complicate stent implantation in this model but that substantial luminal narrowing due in part to smooth muscle hyperplasia does occur. The significance of luminal narrowing at the stent site requires further study.

Threshold concentrations of endothelin-1 potentiate contractions to norepinephrine and serotonin in human arteries. A new mechanism of vasospasm?

Endothelin-1 is an endothelium-derived vasoconstrictor peptide. Its circulating levels are below those known to evoke direct vascular effects. To study whether low concentrations of endothelin-1 potentiate the effects of other vasoconstrictor hormones, we suspended isolated human internal mammary and left anterior descending coronary artery rings in organ chambers for isometric tension recording. In mammary artery rings, the contractions to norepinephrine (3 x 10(-8) M) were potentiated by threshold (3 x 10(-10) M) and low concentrations (10(-9) M) of endothelin-1 (96 +/- 35% and 149 +/- 58% increase from control; p less than 0.01 and 0.001; n = 6). The inhibitor of endothelial nitric oxide formation L-NG-monomethyl arginine did not affect the potentiating effects of the peptide. The calcium antagonist darodipine (10(-7) M) prevented the potentiation of the response to norepinephrine evoked by endothelin-1. Similarly, contractions to serotonin (10(-7) or 3 x 10(-8) M) were amplified by endothelin-1 (3 x 10(-10) M) in the mammary (30 +/- 9%) and in the coronary arteries (59 +/- 25%). Endothelin-1 (10(-9) M) further potentiated the response (57 +/- 23% in mammary and 87 +/- 26% in coronary arteries; p less than 0.05; n = 7 and 3). The sensitivity of mammary arteries to calcium chloride was markedly enhanced in the presence of endothelin-1 (3 x 10(-10) M; concentration shift, eightfold; p less than 0.01; n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term impairment of endothelium-dependent relaxations to aggregating platelets after reperfusion injury in canine coronary arteries

Experiments were designed and performed to determine whether endothelial function remained chronically impaired after coronary artery reperfusion. Canine left anterior descending coronary arteries were exposed to ischemia (60 minutes) followed by reperfusion (12 weeks). Rings (3-4 mm wide) of the reperfused artery and of normal left circumflex (control) coronary artery segments were suspended in organ chambers containing physiological saline solution (37 degrees C, gassed with 95% O2-5% CO2) for isometric force measurement. Endothelium-independent contractions to KCl or prostaglandin F2 alpha and endothelium-independent relaxations to nitric oxide or isoproterenol were comparable in control and chronically reperfused arteries. However, chronically reperfused coronary arteries exhibited impaired endothelium-dependent relaxations to aggregating platelets. In addition, the reperfused coronary arteries exhibited impaired endothelium-dependent relaxations to the platelet-derived compounds adenosine diphosphate, serotonin, and thrombin. However, the endothelium-dependent relaxations to acetylcholine were comparable between control and reperfused arteries. Thus, after 12 weeks of reperfusion, previously occluded coronary arteries exhibited a selective impairment of endothelium-dependent relaxation evoked by aggregating platelets. In vivo, this phenomenon could favor platelet adhesion, aggregation, and platelet-induced contraction of coronary smooth muscle and thus facilitate ischemic events such as vasospasm and coronary thrombosis.

Angiographic morphology of recurrent stenoses after percutaneous transluminal coronary angioplasty: are lesions longer at restenosis?

Angiographic morphology was analysed in 32 patients who developed restenosis after initially successful coronary angioplasty. The mean minimal luminal diameter of the dilated coronary segments increased from 0.9 mm to 2.3 mm after dilatation, but decreased to 0.9 mm at restenosis. The reference diameter was unchanged after dilatation and at restenosis. Mean stenosis length before the initial angioplasty was 7.0 mm but at the repeat procedure had increased to 8.7 mm (mean increase 1.7 mm, 95% confidence interval 0.6 to 2.8 mm, p less than 0.01). There were no significant differences in mean trans-stenotic pressure gradient and mean eccentricity ratio between the initial and repeat angioplasty procedures. In individual patients the changes in stenosis morphology were unpredictable, but overall stenoses tended to be longer at restenosis. In some patients stenosis length increased by several millimetres but the success rate of repeat angioplasty was high and the clinical importance of the changes in stenosis morphology are uncertain.

Experimental argon laser thermal angioplasty as an adjunct to balloon angioplasty in peripheral arteriosclerotic disease

Laser thermal recanalization has been used clinically as an adjunct to balloon angioplasty in the treatment of peripheral arteriosclerotic disease, with improved initial success rates in total peripheral occlusions and greater 1 yr vessel patency suggested, as compared to balloon angioplasty alone. However, the morphological effects of laser-assisted balloon angioplasty are unknown. Therefore, the goals of the present study were to evaluate 1) the angiographic and histologic effects of laser thermal recanalization followed by balloon angioplasty and 2) the hypothesis that balloon-catheter-induced neointimal fracture could be sealed by subsequent laser thermal angioplasty in an experimental rabbit iliac artery atherosclerotic model. In Group 1 (7 vessels), a 1.5 mm metal capped argon laser fiberoptic was introduced via femoral arteriotomy and 10 W of thermal power was applied to the iliac artery stenosis for 5 sec while maintaining constant back-and-forth motion. Thereafter, balloon angioplasty was performed in the same vessel segment with a 2.5 mm balloon catheter inflated 3 times at 5 atm for 30 sec each. Mean angiographic luminal diameter increased from 1.1 mm to 2.0 mm after both procedures, and mean final post balloon dissection grade was 0.6 on a scale of 0, 1+, and 2+. Perforation occurred once with the laser probe and once with the balloon catheter. Histologic examination of these vessels was characterized by irregular thermal erosions with minimal reactive thrombosis. In Group 2 (10 vessels), the sequence was reversed, with laser thermal angioplasty following balloon dilation. Mean angiographic luminal diameter improved from 1.2 mm to 1.8 mm after both procedures.(ABSTRACT TRUNCATED AT 250 WORDS)

Short- and long-term outcome of percutaneous transluminal coronary angioplasty in chronic dialysis patients

Accelerated atherosclerosis occurs in chronic renal failure. The role of percutaneous transluminal coronary angioplasty (PTCA) in chronic renal failure patients requiring dialysis has not been characterized. We studied 17 chronic dialysis patients requiring PTCA over a 6-year period. Their mean age was 60 years, four were diabetic, eight had severe hypertension, and seven had unstable angina. Angiographic success was achieved in 47 of 49 (96%) stenoses attempted, including multivessel PTCA in 12 patients. There was one procedural death, two non-Q wave myocardial infarctions following PTCA, and one additional in-hospital noncardiac death. The 15 survivors were asymptomatic on discharge (mean stay 11 days), but recurrent angina developed within 6 months in 12 patients. Angiography in 11 of these 12 patients demonstrated restenosis of 26 of 32 (81%) dilated sites. Repeat PTCA in six patients was followed by return of angina in four patients with restenosis in 11 of 12 sites. Bypass surgery was ultimately performed in four patients with long-term angina relief. During follow-up (mean 20 months), seven patients died (five from chronic renal failure, two cardiac deaths). Thus although PTCA in chronic dialysis patients is technically feasible and provides relief of angina, aggressive restenosis limits the long-term benefit. Coronary bypass surgery may be the preferred therapy for this unique patient group.

New approaches to treatment of myocardial infarction

Survival of patients with acute transmural infarction is largely related to the size of the myocardial infarction. The goal of thrombolytic therapy in acute myocardial infarction is maximal salvage of myocardium by reestablishment of flow in the occluded infarct-related artery and the establishment and maintenance of a patent infarct-related artery. Results of randomized trials show a significant reduction in mortality in patients who have undergone thrombolysis. A patent infarct-related artery, even in the absence of a change in left ventricular function, is associated with reduced mortality. The Thrombolysis in Myocardial Infarction Trial and the European Cooperative Trial showed that recombinant tissue-type plasminogen activator is superior to streptokinase in reestablishing flow in a totally occluded artery. Experimental and clinical evidence suggests that thrombolysis and thrombosis occur simultaneously, and that lysis appears to increase both thrombin and platelet activity. Effective reduction of thrombosis accelerates thrombolysis. Rethrombosis after thrombolysis is due to anchored residual thrombus, which alters the hemorrheology of blood flow and produces a highly thrombogenic substrate that is largely due to residual fibrin-bound thrombin. Platelet deposition is directly related to severity of residual stenosis and shear rate. Thrombin appears to be the most potent of the 5 potential stimulators of platelet activation during arterial thrombosis. Proper anticoagulation can play an important role in reducing thrombosis. Experimental evidence strongly supports the use of heparin during and after thrombolysis. A recently reported study shows continued reduction of residual stenosis after 1 month of vigorous anticoagulation with intravenous heparin and subsequent oral anticoagulation.(ABSTRACT TRUNCATED AT 250 WORDS)

An in vivo method for studies of traumatic vasospasm

A study was undertaken to develop a model for investigations of traumatically induced vasospasm. The left ear of the rabbit was denervated under short anesthesia. With the animal under light sedation, spasm of the central ear artery was repeatedly induced with a clip applying forceps. To evaluate the vasospasm, the vessel was transilluminated with cold light, and the internal diameter was continuously measured. The spasm was assessed in terms of its duration, intensity (reduction of initial diameter) and severity (integrated change in diameter over time). Repetitive application of the forceps on the same vessel segment shortened the spasm duration. With prolonged pinch duration, the spasm duration was lengthened. The preparation was stable for at least 3 hours. This model was effective for manipulating small vessels and producing spasm and is of potential value for studying the treatment of vasospasm by topical local intra-arterial and systemic methods.

Effect of bleeding and hypervolaemic haemodilution on traumatic vasospasm in rabbits

The effect of bleeding (20% of total blood volume) and of hypervolaemic haemodilution with dextran infusion (20% of total blood volume) on traumatic vasospasm was studied in the central ear arteries of 10 rabbits. The blood pressure dropped significantly after bleeding and the packed cell volume was significantly lower after dextran infusion. Neither treatment had any effect on the duration, intensity or severity of the vasospasm. The results suggest that moderate changes in blood volume do not influence traumatic vasospasm.

[Relation between post-thrombotic syndrome, ADP-induced thrombocyte aggregation and intrathrombocyte calcium content]

Correlation between postthrombotic syndrome, ADP-induced aggregation and intracellular calcium concentration. This study presents a comparison of the ADP-induced platelet aggregation and free cytosolic platelet calcium concentration between patients with postthrombotic syndrome and healthy volunteers. The half maximal effective dose of the platelet aggregation induced by ADP was significantly decreased in postthrombotic syndrome (p less than 0.005). The mean values were 0.42 mumol/l in postthrombotic syndrome (n = 22) and 1.00 mumol/l in normal controls (n = 25). The free intracellular calcium concentration was slightly but significantly diminished in patients compared with healthy volunteers. In both groups there was seen a remarkable interindividual spread of platelet calcium concentrations. There was seen no significant correlation between cytosolic calcium concentration of platelets and the half maximal effective dose of ADP-induction. Therefore the considerable enhanced aggregability in postthrombotic syndrome cannot explained with altered cytosolic calcium content of platelets.

Platelet inhibitor agents in cardiovascular disease: an update

Platelets interact with the coagulation and fibrinolytic systems in the maintenance of hemostasis. However, these physiologic mechanisms may become pathologic, requiring prevention and treatment. In this review, the following clinical developments are analyzed: 1) the role of platelets in thrombogenesis; 2) the pharmacology of platelet inhibitory agents; and, most important, 3) the results of recent randomized trials of platelet inhibitor agents in different cardiovascular disorders. Aspirin reduces mortality and infarction rates in unstable angina and significantly decreases vascular mortality in acute myocardial infarction. Platelet inhibitors decrease mortality and recurrent cardiovascular events in the chronic phase after myocardial infarction. They also decrease vein graft occlusion rates after coronary bypass surgery. Although platelet inhibitors are beneficial in preventing acute vessel occlusion during coronary angioplasty, they are ineffective in preventing chronic restenosis. Antiplatelet agents, combined with warfarin, reduce thromboembolic events in patients with a mechanical prosthesis. Platelet inhibitors are also effective in secondary prevention of vascular events in patients with cerebrovascular disease. Finally, the use of aspirin for primary prevention of cardiovascular disease is still evolving, particularly in individuals at high risk. In conclusion, platelet inhibitors are effective in patients with a variety of cardiovascular disorders. The best studied, most inexpensive and least toxic agent is aspirin at a daily dose of 160 to 325 mg. Studies using new platelet inhibitor agents with different mechanisms of action are currently underway.

Mechanisms of arterial thrombosis in nonparallel streamlines: platelet thrombi grow on the apex of stenotic severely injured vessel wall. Experimental study in the pig model

The role of thrombosis in various acute coronary syndromes has been established. However, the basic mechanism by which plaque rupture leads to a growing thrombus in the vicinity of stenotic lesions is not well understood. Using a characterized flow chamber in a rheologically controlled system, we have mimicked stenotic vessels and studied for the first time cell-vessel wall interaction in nonparallel streamlines. Stenoses ranging from 0 to 80% were produced with stripped tunica media to mimic severe vessel wall damage, and perfused with heparinized flowing blood. This perfusion device was placed within an extracorporeal system in swine, and blood was perfused for selected times from 1 to 30 min. Platelet deposition on the surface was evaluated by 111Indium-labeled platelets. As percent stenosis increased, platelet deposition significantly increased (P less than 0.001), indicating a shear-induced cell activation. Analysis of the axial distribution of platelet deposition indicated that the apex, and not the flow recirculation zone distal to the apex, was the segment of greater platelet accumulation within 30 min of blood perfusion (P less than 0.001). These results also indicate that the severity of the acute platelet response to plaque rupture probably depends on the location of the rupture with relation to the apex of the plaque.

Endothelium-derived relaxing factor and coronary vasospasm

The endothelium releases the powerful vasodilator and antiaggregatory substance, EDRF, both under basal conditions and upon stimulation by a wide variety of agents. Endothelial injury or dysfunction may play an important role in the spasmogenicity of the coronary artery, although other possible alterations related to atherosclerosis should also be considered. Among the possible stimuli, aggregating platelets are important as a source of vasoconstrictor substances. The endothelium may also produce the vasoactive substances EDHF and EDCF(s). Their pathophysiologic significance remains to be determined.

Increased thromboxane biosynthesis during coronary thrombolysis. Evidence that platelet activation and thromboxane A2 modulate the response to tissue-type plasminogen activator in vivo

Platelet activation is markedly increased during coronary thrombolysis and limits the response to thrombolytic therapy. A possible mediator of platelet activation in this setting is thromboxane (TX) A2, a potent platelet agonist formed in greatly increased amounts during coronary thrombolysis in man. To address this hypothesis, we examined the role of TXA2 in modulating the response to intravenous tissue-type plasminogen activator (t-PA) in a chronic canine model of coronary thrombosis. Reperfusion occurred in 60 +/- 5 minutes and was complicated by spontaneous reocclusion. The times to reperfusion and reocclusion were platelet-dependent. Consistent with a role for TXA2 in this process, TXA2 biosynthesis, determined a excretion of its enzymatic metabolite, 2,3-dinor-TXB2, was markedly increased during coronary thrombolysis. Furthermore, inhibition of TXA2 by aspirin, given alone or in combination with a TXA2/prostaglandin endoperoxide receptor antagonist, accelerated reperfusion and partly inhibited cyclic flow variations during reperfusion. The delay in reperfusion and reocclusion induced by TXA2 appeared to be mediated by platelet aggregation since the F(ab')2 fragment of 7E3, a monoclonal antibody to the platelet GPIIb/IIIa, also accelerated reperfusion and prevented reocclusion without altering TXA2 biosynthesis. These finding suggest that platelet aggregation limits the response to coronary thrombolysis and that platelet activation in this setting is partly TXA2-dependent.

The pathological basis of angina pectoris

Coronary stenoses may be either concentric without any potential for variation in the degree of obstruction to flow or eccentric, where the cross-sectional area of the lumen can alter with vasomotor tone. Variable obstruction at eccentric stenoses is due to the retention of an arc of normal vessel wall opposite the plaque. Abnormal vasomotor responses are a feature of both human and experimental atheromatous coronary arteries; such an abnormality is likely to reflect endothelial dysfunction with loss or neutralization of endothelial-derived relaxant factor (EDRF). Structural studies show that superficial intimal injury, with migration of monocytes and focal endothelial denudation leading to deposition of small numbers of platelets on the exposed intimal collagen, is found in both experimental and human atheroma. Such endothelial changes may be responsible for arterial constriction leading to transient myocardial is-chemia in both patients with stable exertional angina and in those without overt ischemic heart disease. Larger coronary thrombi are associated with deep intimal tears or fissures that extend into the lipid pool of an atheromatous plaque. The resultant thrombi, large enough to be seen angiographically, project into the arterial lumen and are associated with un-stable angina of the abrupt-onset crescendo type. Nonoccluding mural thrombi in a coronary artery are a source of distal microemboli into the myocardium.

Balloon catheter injury to rabbit carotid artery. II. Selective increase in reactivity to some vasoconstrictor drugs

The present study examined the changes in reactivity to a variety of vasoconstrictor drugs of the rabbit carotid artery during development of an intimal thickening induced by injury with an inflated balloon catheter. The injured and the unoperated contralateral carotid arteries were studied at 2 and 6 weeks after the operation. To differentiate areas of the injured artery lined by modified smooth muscle cells from areas lined by regenerated endothelial cells, each rabbit was injected with Evans blue dye before sacrifice. Ring segments (3 mm length) from the control and injured arteries were mounted in organ baths to record the circumferential isometric force with a technique that ensured that all rings were set to equivalent initial resting conditions of passive transmural stretch. Compared with the controls, the experimental arteries had a significantly decreased maximum contraction (Emax) in response to KCl at both 2 and 6 weeks. The experimental arteries were also significantly less sensitive to the alpha 1-adrenoceptor agonist, methoxamine, at both 2 weeks (approximately sevenfold) and 6 weeks (fourfold), with a marked decrease in Emax at 2 weeks, which returned to control values at 6 weeks. There was no change in Emax to either serotonin or the thromboxane A2-mimetic, U46619, in the experimental arteries at either time. There was, however, a small but significant increase in the sensitivity to both drugs. There was no difference in response to any of the constrictor agents between the white and blue regions of the experimental vessels.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelium-dependent arterial vasoconstriction after balloon angioplasty

To determine whether balloon angioplasty can provoke arterial vasoconstriction independent of platelet aggregation and neurogenic input, we studied the spontaneous vasomotor effects of balloon dilatation in isolated, perfused whole-vessel segments of rabbit aorta and pig carotid artery. Freshly dissected rabbit thoracic aortas were mounted in a muscle bath-perfusion chamber, perfused with physiologic saline solution at 70 mm Hg, and allowed to equilibrate. The proximal or distal half of the aortas were dilated with either a "large" (5 mm, 31-51% stretch beyond relaxed diameter) or a "small" (4 mm, 5-16% stretch) balloon angioplasty catheter with the other half of the vessel serving as the control. A similar series of experiments were performed in pig carotid arteries using "large" (6 or 8 mm, 48-90% stretch) balloon catheters. The spontaneous vasomotor effects of balloon angioplasty were examined with long-axis, high-frequency ultrasonic imaging combined with computerized edge detection image processing to measure changes in segmental internal vessel diameters. Additional experiments were carried out in rabbit aortas to determine the roles of the endothelium, extracellular calcium, indomethacin, ibuprofen, and calcium-channel blockade in modulating angioplasty-induced vasoconstriction. Significant arterial vasoconstriction was observed in the balloon angioplasty segments after dilatation with 5-mm balloons but not with 4-mm balloons. After dilatation with 5-mm balloons, the angioplasty segments' cross-sectional areas decreased by an average of 31% versus 4% for the nondilated (control) segments (p less than 0.0001). Similar postangioplasty vasoconstriction was observed in the pig carotid arteries (decrease in minimal vessel cross-sectional area of 41% [angioplasty segment] versus 2% [control segment]) (p less than 0.005). This angioplasty-induced vasoconstriction was prevented by endothelial denudation before angioplasty, removal of extracellular calcium, and pretreatment with indomethacin or ibuprofen. The vasoconstriction was only partially inhibited by calcium channel blockade with verapamil. These findings demonstrate that stretch-pressure-induced arterial vasoconstriction may occur after balloon angioplasty, independent of platelet aggregation and neurogenic input. This angioplasty-induced vasoconstriction appears to be mediated by an endothelially derived cyclooxygenase product(s).

Morphologic features of unstable atherothrombotic plaques underlying acute coronary syndromes

Unstable angina appears to be a good clinical marker for rapidly progressing coronary artery disease. Pathologically, an unstable atherothrombotic coronary lesion, represented by a raised atherosclerotic plaque with ruptured surface causing variable degree of hemorrhage into the plaque and luminal thrombosis (rapid plaque progression), usually is present in patients at autopsy after a period of unstable angina. The thrombus at the rupture site may be mural and limited (just sealing the rupture) or occlusive, depending on the degree of preexisting atherosclerotic stenosis. An occlusive thrombus is seldom seen over ruptured plaques causing less than 75% stenosis (histologic cross-sectional area reduction), but it is found with increasing frequency when severity of stenosis increases beyond 75%. Most occlusive thrombi have a layered structure with thrombus material of differing age indicating an episodic growth by repeated mural deposits, and microemboli/microinfarcts are frequently found in the myocardium downstream to coronary thrombi, indicating intermittent thrombus fragmentation with peripheral embolization. Such a "dynamic thrombosis" (with or without a concomitant focal vasospastic phenomenon) at the site of an unstable (ruptured) atherosclerotic lesion obviously may lead to the other thrombus-related acute coronary events: myocardial infarction or sudden death. Accordingly, progression of unstable angina to myocardial infarction or sudden death should, in principle, be preventable by the correct timing of current available therapies aimed to prevent or eliminate (1) the chronic atherosclerotic obstruction, (2) the acute plaque disruption, (3) luminal thrombosis, and (4) vasospasm.

Effects of thrombin inhibition on the development of acute platelet-thrombus deposition during angioplasty in pigs. Heparin versus recombinant hirudin, a specific thrombin inhibitor

The effect of recombinant hirudin and the dosage of heparin on acute platelet-thrombus deposition during carotid angioplasty in anesthetized pigs was prospectively assessed. Fifty-five animals (mean weight, 33.9 kg) were randomized to one of six heparin dosages: heparin boluses of 35, 50, 100, 150, 200, or 250 units/kg followed by a continuous infusion of 35, 50, 100, 150, 200, or 250 units/kg/hr, respectively. Another five pigs received a bolus of 1 mg/kg hirudin (recombinant desulphatohirudin), a specific thrombin inhibitor, followed by an infusion of 1 mg/kg/hr. Bilateral carotid angioplasty was performed in all pigs 20 minutes after starting the infusion; they were sacrificed 57 +/- 12 minutes after the procedure. Deep medial arterial injury was present in approximately 75% of the dilated segments, and subendothelial injury in the remaining 25%. Mean log of number of platelets and molecules of fibrinogen per centimeter squared of deep injury in segments from all the animals treated with heparin were 4.74 +/- 1.03 and 5.02 +/- 0.64, respectively. A regression analysis showed an inverse correlation of the log of platelet deposition with the heparin group (r = -0.56, p = 0.0001) with administered total units of heparin (r = -0.55, p = 0.0003) and with mean plasma heparin concentration (r = -0.55, p = 0.0004) in deeply injured arteries. Similar inverse relations were obtained for fibrinogen. In contrast, the deposition of platelets and fibrinogen in subendothelial injury was very low and independent of the heparin administered.(ABSTRACT TRUNCATED AT 250 WORDS)

Relation to restenosis after percutaneous transluminal coronary angioplasty to vasomotion of the dilated coronary arterial segment

Among 868 patients with successful percutaneous transluminal coronary angioplasty (PTCA), 437 were restudied angiographically and had a provocative test with ergonovine during coronary angiography performed before and 6 months after the procedure. The relation between provoked coronary artery spasm and restenosis was studied and 4 groups of patients were analyzed. Those in group 1 (n = 63) had spasm before and after PTCA and their rate of restenosis was high (55%), especially when spasm after PTCA was observed on the dilated coronary segment (restenosis rate 58%). Patients in group 2 (n = 78) had spasm before PTCA but without abnormal vasoconstriction at 6 months and their incidence of restenosis was 19%. Sixty-one patients in group 3 had no spasm before PTCA but developed spasm at restudy. The rate of restenosis was high (38%) in this group, especially when the spasm after PTCA was located on the dilated segment (43%). In group 4 (n = 235), patients had no spasm before or after PTCA and the restenosis rate was 20%. Thus, the presence of coronary artery spasm on the dilated coronary segment, 6 months after a successful PTCA, is frequently accompanied (43% in group 3 and 58% in group 1) by restenosis.

Incidence and predictors of early recurrent ischemia after successful percutaneous transluminal coronary angioplasty for acute myocardial infarction

Two hundred forty consecutive patients with acute myocardial infarction treated within 48 hours by successful percutaneous transluminal coronary angioplasty (PTCA) were analyzed to determine the incidence and predictors of recurrent ischemic events during hospitalization. Thirty-nine patients had recurrent ischemia: 20 patients had chest pain or electrocardiographic changes requiring repeat PTCA or bypass surgery, or resulting in a second creatine kinase elevation suggestive of myocardial infarction; 12 had total occlusion of the dilated artery on follow-up angiography; and 7 had exercise-induced ischemia and greater than or equal to 70% diameter stenosis that required PTCA or bypass surgery before hospital discharge. In-hospital mortality was 15% in the recurrent ischemia group, compared to 1% in the group without recurrent myocardial ischemia (p less than 0.001). Angiographic follow-up before hospital discharge was obtained in 198 patients, including 38 of the 39 patients with ischemic events. Thus, the true incidence of recurrent ischemic events was between 39 of 199 and 39 of 240, or 16 and 20%. In multivariate analyses, recurrent ischemia was predicted by translesional gradient greater than 25 mm Hg (p = 0.001), dissection (p = 0.01) and post-PTCA Thrombolysis in Myocardial Infarction 2 flow pattern (p = 0.016). However, even in the absence of these risk factors recurrent ischemic events occurred in 13% of patients. Post-PTCA percent diameter stenosis (whether assessed by objective or visual assessment), degree of the early systemic fibrinolytic state, post-PTCA residual minimal diameter and concomitant use of thrombolytic agents were not predictive.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelin: a potent vasoconstrictor associated with coronary vasospasm

Endothelin, administered into the coronary arteries of anesthetized dogs, produced a profound and long-lasting reduction in coronary blood flow with electrocardiographical evidence of myocardial ischemia. Coronary angiography revealed delayed filling of the distal branches and, in some cases, cessation of the blood flow distal to the epicardial portions of coronary arteries. The coronary vasoconstriction induced by endothelin subsided after intracoronary administration of nitroglycerin. Pretreatment with the Ca2+-channel antagonist, nitrendipine, suppressed endothelin-induced vasoconstriction. These findings suggest that endothelin, produced by vascular endothelial cells, may contribute to the pathogenesis of coronary vasospasm.