Angiographic findings in the coronary arteries after thrombolysis in acute myocardial infarction

Imaging coronary artery disease and the myocardial ischemic cascade: clinical principles and scope

On a subcellular level, atherogenesis is characterized by the translocation of proatherogenic lipoproteins into the arterial wall. An inflammatory response involving complex repair mechanisms subsequently causes maladaptive vascular changes resulting in coronary stenosis or occlusion. The chronology of the underlying processes occurring from atherosclerosis to myocardial ischemia affect the selection and interpretation of diagnostic testing. An understanding of the ischemic cascade, atherosclerosis, coronary remodeling, plaque morphology, and their relationship to clinical syndromes is essential in determining which diagnostic modalities are useful in clinical practice.

Identification of vulnerable atherosclerotic plaques

There has been great interest in the possibility of identifying plaques that might be the site of future acute coronary events. These plaques are termed vulnerable and the majority are lipid-rich with an abundance of inflammatory cells and a thin fibrous cap. Several techniques developed to identify these plaques are in various stages of development and in the near future, one might employ a strategy to potentially identify and therapeutically modify such lesions during percutaneous intervention to avoid future acute events. Although this approach of identifying the vulnerable plaque seems promising, there are significant potential limitations. The natural history of a vulnerable plaque is unknown and clinical trials utilizing this strategy of identification and therapeutic intervention are lacking. Moreover, in any given patient, multiple vulnerable plaques are likely to be present. This article reviews some of the techniques for identifying a vulnerable plaque and discusses the potential advantages and limitations of this strategy.

Localization of culprit lesions in coronary arteries of patients with ST-segment elevation myocardial infarctions: relation to bifurcations and curvatures

BACKGROUND

Although culprit lesions in ST-segment elevation myocardial infarction (STEMI) cluster in the proximal coronary arteries, their relationship to bifurcations and curvatures, where blood flow is disturbed, is unknown. We hypothesized that (a) culprit lesions localize to disturbed flow distal to bifurcations and curvatures and (b) the distribution of culprit lesions in the left (LCA) and right coronary arteries (RCA) and resulting infarct size are related to the location of bifurcations and curvatures.

METHODS

Emory University's contribution to the National Cardiovascular Data Registry was queried for STEMIs. Using quantitative coronary angiography, the distances from the vessel ostium, major bifurcations, and major curvatures to the culprit lesion were measured in 385 patients.

RESULTS

Culprit lesions were located within 20 mm of a bifurcation in 79% of patients and closer to the bifurcation in the LCA compared with the RCA (7.4 ± 7.3 vs 17.7 ± 14.8 mm, P < .0001). Of RCA culprit lesions, 45% were located within 20 mm of a major curvature. Compared with those in the RCA, culprit lesions in the LCA were located more proximally (24.4 ± 16.5 vs 44.7 ± 28.8 mm, P = .0003) and were associated with larger myocardial infarctions as assessed by peak creatine kinase-MB (208 ± 222 vs 140 ± 153 ng/dL, P = .001) and troponin I (59 ± 62 vs 40 ± 35 ng/dL, P = .0006) and with higher in-hospital mortality (5.2% vs 1.1%, P = .04).

CONCLUSIONS

In patients with STEMI, culprit lesions are frequently located immediately distal to bifurcations and in proximity to major curvatures where disturbed flow is known to occur. This supports the role of wall shear stress in the pathogenesis of STEMI.

Comparison of location of "culprit lesions" in left anterior descending coronary artery among patients with anterior wall ST-segment elevation myocardial infarction having ramus intermedius coronary arteries versus patients not having such arteries

Disturbed, nonlaminar flow distal to arterial bifurcations contributes to atherosclerosis development and progression. We hypothesized that the presence of a ramus intermedius (RI) amplifies the flow disturbances in the proximal left anterior descending (LAD) artery causing more proximal LAD lesions and larger ST-segment elevation myocardial infarction (STEMI). Emory University's contribution to the National Cardiovascular Data Registry was queried for STEMIs from January 2006 to July 2008. The distance from the LAD ostium to the lesion was measured in patients with angiographically visible culprit lesions. The peak troponin-I, creatinine kinase-MB, and left ventricular ejection fraction were used as markers for infarct size. Of the 386 patients with STEMI, 150 had LAD culprit lesions. The mean lesion distance from the LAD ostium was 15.2 +/- 11.0 mm in the patients with RI (n = 44) and 29 +/- 19 mm in those without RI (n = 106; p <0.01). LAD lesions were more proximal in the patients with RI, with 43% and 63% of lesions occurring in the first 10 and 20 mm of the LAD, respectively, versus 10% and 32% in those without RI (p <0.01). Patients with RI had greater peak troponin-I (69 +/- 40 ng/ml vs 50 +/- 39 ng/ml, p = 0.01) and peak creatinine kinase-MB (277 +/- 271 ng/ml vs 174 +/- 190 ng/ml, p = 0.01). A trend was seen toward a lower left ventricular ejection fraction in patients with RI (36 +/- 10% versus 40 +/- 11%, p = 0.06). In conclusion, the presence of RI was associated with more proximal LAD lesions and larger anterior infarctions, suggesting anatomy-induced flow disturbances have important clinical implications.

A new imaging technique to study 3-D plaque and shear stress distribution in human coronary artery bifurcations in vivo

OBJECTIVE

Bifurcations of coronary arteries are predilection sites for atherosclerosis and expansive remodeling, the latter being associated with plaque vulnerability. Both are related to blood flow-induced shear stress (SS). We present a new approach to generate 3-D reconstructions of coronary artery bifurcations in vivo and investigate the relationship between SS, wall thickness (WT) and remodeling.

METHODS

The patient specific 3-D reconstruction of the main branch of the bifurcation was obtained by combining intravascular ultrasound and biplane angiography, and the 3-D lumen of the side branch was based on biplane angiography only. The two data sets were fused and computational methods were applied to determine the SS distribution, using patient derived flow and viscosity data. The intravascular ultrasound data allowed us to measure local WT and remodeling in the main branch.

RESULTS

The lumen reconstruction procedure was successful and it was shown that the impact of the side branch on SS distribution in the main branch diminished within 3mm. Distal to the bifurcation, two continuous regions in the main branch were identified. In the proximal region, we observed lumen preservation, and expansive remodeling. Although a plaque was observed in the low SS region at the non-divider wall, no relationship between SS and WT was found. In the distal region, we observed lumen narrowing and a significant positive relationship between SS and WT.

CONCLUSIONS

A new imaging technique was applied to generate a 3-D reconstruction of a human coronary artery bifurcation in vivo. The observed relationship between SS, WT and remodeling in this specific patient illustrates the spatial heterogeneity of the atherosclerosis in the vicinity of arterial bifurcations.

Association of inflammatory biomarkers and cardiac troponin I with multifocal activation of coronary artery tree in the setting of non-ST-elevation acute myocardial infarction

We evaluated the possible association of the serum levels of C-reactive protein (CRP), serum amyloid A (SAA), fibrinogen, and cardiac troponin I (cTnI) with the presence of complex angiographic characteristics throughout the coronary artery tree in 519 consecutive patients with non-ST-elevation acute myocardial infarction (NSTEMI). Blood samples were obtained in the first 12h of NSTEMI invasion and all patients underwent in-hospital coronary angiography. Coronary lesions were classified as complex lesion (CL) or non-CL according to Ambrose criteria. Serum levels of CRP (p<0.001), SAA (p<0.001), or fibrinogen (p=0.001), but not of cTnI (p=0.9), were significantly related to the presence of multiple (> or =2) CLs. On the contrary, serum levels of cTnI (p<0.001), but not of CRP (p=0.5), SAA (p=0.9), or fibrinogen (p=0.9), were significantly associated with the severity of coronary artery disease. The results of the present study suggest that elevated levels of inflammatory biomarkers are associated with a generalized activation of coronary artery tree while elevated cTnI levels are associated with the severity of coronary artery disease in the setting of NSTEMI. It seems that inflammatory biomarkers and cTnI reflect different aspect of the process involved in unstable coronary artery disease.

Markers of inflammation and multiple complex stenoses (pancoronary plaque vulnerability) in patients with non-ST segment elevation acute coronary syndromes

OBJECTIVE

To assess the relation between markers of inflammation and the presence of multiple vulnerable plaques in patients with non-ST segment elevation acute coronary syndromes.

DESIGN

Prospective cohort study of 55 patients with non-ST segment elevation acute coronary syndromes and angiographically documented coronary disease. Blood samples were obtained at study entry for the assessment of high sensitivity C reactive protein (CRP), neopterin, and neutrophil count. Coronary stenoses were assessed by quantitative computerised angiography and classified as "complex" (irregular borders, ulceration, or filling defects) or "smooth" (absence of complex features). Extent of disease was also assessed by a validated angiographic score.

RESULTS

Neutrophil count (r = 0.36, p = 0.007), CRP concentration (r = 0.33, p = 0.02), and neopterin concentration (r = 0.45, p < 0.001) correlated with the number of complex stenoses. Patients with multiple (three or more) complex stenoses, but not patients with multiple smooth lesions, had a higher neutrophil count (5.9 (1.4) x 10(9)/l v 4.8 (1.4) x 10(9)/l, p = 0.02), CRP concentration (log transformed) (1.08 (0.63) v 0.6 (0.6), p = 0.03), and neopterin concentration (log transformed) (0.94 (0.18) v 0.79 (0.15), p = 0.002). Multiple regression analysis showed that neopterin concentration (B = 4.8, 95% confidence interval (CI) 1.9 to 7.7, p = 0.002) and extent of coronary artery disease (B = 0.6, 95% CI 0.03 to 1.2, p = 0.04) were independently associated with the number of complex stenoses.

CONCLUSIONS

Acute inflammatory markers such as high neutrophil count, CRP concentration, and neopterin concentration correlate with the presence of multiple angiographically complex coronary stenoses. Neopterin concentration was a stronger predictor of multiple complex plaques than were neutrophil count and CRP concentration. These findings suggest that a relation exists between inflammation and pancoronary plaque vulnerability.

Multiple complex stenoses, high neutrophil count and C-reactive protein levels in patients with chronic stable angina

Inflammation plays an important role in atherosclerosis and the genesis of acute coronary syndromes, i.e., atheromatous plaque disruption. Neutrophil count and C-reactive protein (CRP) levels are markers of ongoing inflammation and predictors of cardiovascular risk. We sought to assess whether these inflammatory markers are associated with the presence of multiple complex stenoses in patients with chronic stable angina.

METHODS AND RESULTS

We assessed 150 patients with chronic stable angina, 121 with significant coronary artery stenosis (> or =50% diameter reduction) and 29 without. CRP levels and neutrophil count were assessed at study entry. Stenoses were classified as "complex" (irregular or scalloped borders, ulceration or filling defects) or "smooth" (absence of complex features). Eighty-eight percent of the complex lesions were of type C according to AHA/ACC classification whereas the rest were type B. Patients with > or =3 complex lesions were considered to have multiple complex stenoses. Extent of coronary artery disease was assessed using a validated score. Baseline neutrophil count (4.39 x 10(9) L (-1) +/- 28 versus 3.82 x 10(9) L (-1) +/- 0.77; P = 0.004) and CRP levels (2.15 mg/L (4.6-1) versus 0.39 mg/L (0.69-0.23); P < 0.0001) were higher in patients with significant stenoses compared to patients without. No association was found between disease extent and CRP levels or neutrophil count. Neutrophil count, however (but not CRP) correlated with stenosis complexity (r = 0.28; P = 0.002 ) and was also an independent predictor of the presence of multiple complex stenoses (OR: 4.05; CI 95% (1.9-10.4); P = 0.038).

CONCLUSIONS

CRP levels and neutrophil count are higher in angina patients with coronary stenoses compared to those without. Neutrophil count, but not CRP levels, correlates with angiographic stenosis complexity.

Coronary artery calcium and its relationship to coronary artery disease

Electron-beam computed tomography (EBCT) and the recent generation of multi-slice computed tomography scanners (MSCT) permit high-resolution imaging of the beating heart and the coronary arteries. The visualization of coronary calcium offers the opportunity to non-invasively obtain direct information on coronary anatomy and plaque burden. For clinical purposes, coronary calcium represents the presence of arteriosclerotic plaques. Coronary calcium is deposited in an actively regulated process related to lipid content of and apoptosis within coronary plaques. The amount of coronary calcium is related to the extent of coronary plaque disease, which has substantial diagnostic and prognostic implications. Visualization of coronary calcium by cardiac CT allows to non-invasively detect and localize coronary plaques and describe their distribution in the coronary tree. Approximately 50% to 70% of all plaques are calcified. Calcium cannot be used to reliably identify plaques at risk for developing complications such as rupture or erosion with ensuing thrombus formation. However, data are accumulating that indicate that calcium is an indicator of coronary arteriosclerotic disease activity. A scan negative for coronary calcium has a high negative predictive value indicating absence of stenotic coronary artery disease and an excellent short- to mid-term prognosis. Studies using serial CT scans indicate that the annual progression of coronary calcium varies between 30% to 50% in symptomatic or high-risk individuals and 0% to 20% in patients treated effectively with lipid-lowering medication. An increased rate of progression of coronary calcium seems to indicate a substantially increased risk for adverse cardiac events.

C-reactive protein and multiple complex coronary artery plaques in patients with primary unstable angina

The aim of this study was to investigate the possible association of plasma C-reactive protein (CRP) levels with the presence of angiographically multiple complex lesions (CLs) in patients with primary unstable angina (PUA). For the purpose of this study, 228 consecutive patients with PUA who underwent in-hospital catheterization were evaluated. Plasma CRP levels were measured upon patients' admission. Coronary plaques were classified as CL or non-CL according to Ambrose's criteria. There were 100 (43.9%) patients with no or one CL (</=1) and 128 (56.1%) patients with multiple CLs (>/=2). Tertiles of plasma CRP levels upon admission were significantly associated with the number of CLs on angiographic studies. In particular there was a significant gradual increase in either the number of CLs, or the presence of apparently thrombus-containing CLs with increasing of CRP tertiles. By multivariate analysis CRP was independently associated with the presence of either multiple CLs (R.R.=1.8, 95%CI=1.5-2.2, P<0.001), or angiographically apparent thrombus-containing CLs (R.R.=1.4, 95%CI=1.2-1.7, P=0.03).High plasma levels of CRP may reflect a multifocal activation of the coronary tree in patients with PUA. This finding suggests a generalized inflammatory reaction throughout the coronary tree in these patients.

Considerable time from the onset of plaque rupture and/or thrombi until the onset of acute myocardial infarction in humans: coronary angiographic findings within 1 week before the onset of infarction

BACKGROUND

It has been thought that the thrombi and bleeding in plaques that occur after plaque rupture or endothelial damage from vessels with mild stenosis suddenly occlude the lumen and cause acute myocardial infarction (AMI). However, our hypothesis is that thrombi and bleeding may not suddenly occlude the lumen.

METHODS AND RESULTS

The study group consisted of 20 patients who had coronary angiograms performed within 1 week (3+/-3 days) before AMI and 20 control patients who had coronary angiograms performed 6 to 18 months (282+/-49 days) before AMI. The features of infarct-related coronary segments (IRCS) at 3 days before AMI were the presence of a significant stenosis of >50% (95% in incidence and 71+/-12% diameter stenosis) and Ambrose's type II eccentric lesions (plus multiple irregularities), an indicator of plaque rupture and/or thrombi (60% [70%]), and the features at 1 year before AMI were mild stenosis of <50% (95% incidence and 30+/-18% diameter stenosis) with rare Ambrose's type II eccentric lesions (plus multiple irregularities) (10% [10%]). The same relation was observed in each of the 4 subgroups with Q-wave infarction, non-Q-wave infarction, preceding effort angina within 1 month before AMI, and no preceding effort angina.

CONCLUSIONS

The appearance of marked progression and Ambrose's type II eccentric lesion on coronary angiograms 3 days before AMI suggests the presence of a considerable time from the onset of plaque rupture and/or thrombi until the onset of AMI. These features may be predictors of AMI. The concept provides new insight into the mechanism and prevention of human AMIs.

Usefulness of topography of coronary calcium by electron-beam computed tomography in predicting the natural history of coronary atherosclerosis

Electron-beam computed tomography (EBCT) allows for accurate noninvasive detection and quantification of coronary calcium that is representative of underlying atherosclerotic disease. The present study quantitatively analyzes the topography and establishes the natural history of coronary calcium in patients with variable degrees of coronary atherosclerosis. EBCT was performed in 330 consecutive patients aged 56 +/- 12 years (70% men) with recent (<3 months) onset of signs or symptoms of coronary artery disease (CAD) or who were evaluated because of a presumed high risk. Total calcium scores, computed by the Agatston method, were positive in 269 patients (82%) (mean age 58 +/- 11 years, 73% men). These patients were classified into 4 groups, with total calcium scores ranging between 1 and 30, >30 and 100, >100 and 400, and >400, respectively. The presence and amount of calcium was additionally assessed in 10 major segments of the coronary arterial tree, including the major coronary arteries. Of the 72 patients with calcium of only 1 of the major coronary arteries, the left anterior descending coronary artery was involved in 39 patients (54%) and the right coronary artery in 18 patients (25%). Left main stem calcium was observed in only 10 of 139 patients (7%) with 1- or 2-vessel calcium and in 17 of 77 patients (23%) with 3-vessel calcium. Calcium was consistent most frequently in the proximal left anterior descending coronary artery, followed by the proximal left circumflex and right coronary artery segments. A significant decrease of frequency and amount of calcium from the proximal to distal segments was observed in the left coronary system but not in the right coronary artery, where the distribution was more even. With increasing total calcium scores, segmental scores in the more distal segments were enhanced, but the increase was most pronounced in the proximal segments and particularly in the proximal left anterior descending coronary artery. EBCT-derived coronary calcium shows an axial distribution that appears comparable to that of atherosclerotic lesions observed in pathologic and angiographic studies, highlighting the potential role of EBCT for studying the natural history of CAD.

Improving the Efficacy and Stability of Coronary Reperfusion Following Thrombolysis: Exploring the Thrombin Hypothesis

A major assumption in the treatment of patients with acute myocardial infarction (MI) implies that the speed of coronary arterial reperfusion correlates directly with the overall extent of myocardial salvage, and that the extent of mycardial salvage, in turn, determines the absolute reduction in patient mortality. While a growing experience has made it clear that myocardial salvage-independent (time-independent) mechanisms of benefit also exist, few would argue with the hypothesis that the greatest benefit derived from coronary thrombolysis occurs with early (time-dependent) treatment. Thus, improvements in the efficacy of reperfusion and the stability of reperfusion are likely to have considerable impact on patient outcome.

Current concepts in cardiovascular pathology: the role of LDL cholesterol in plaque rupture and stabilization

Emerging evidence is redefining traditional concepts of coronary atherosclerosis. Recent data indicate that severe stenoses, the traditional focus of attention, do not cause most coronary events. Rather, interest has increased in the often less stenotic but more vulnerable lesions that are characterized by thin fibrous caps, large lipid accumulations, large numbers of macrophages, and depletion of smooth muscle cells. Such lesions appear prone to rupture, which allows the blood to come into contact with the highly thrombogenic material in the lipid core of the plaque, thereby precipitating thrombosis. The fibrous cap may become weakened through decreased synthesis of the extracellular matrix or increased degradation of the matrix. The cytokine interferon-gamma, produced by T-lymphocytes, inhibits the ability of smooth muscle cells to synthesize collagen, a structurally important component of the fibrous cap. A family of enzymes known as matrix metalloproteinases can degrade all major constituents of the vascular extracellular matrix: collagen, elastin, and proteoglycans. Additional studies on the biochemical mechanisms of atherosclerosis may provide a fuller understanding of the ways in which lipid-lowering therapy can confer clinical benefit.

Does the presence and site of myocardial ischemia on perfusion scintigraphy predict the occurrence and site of future myocardial infarction in patients with stable coronary artery disease?

In 47 patients who had undergone myocardial scintigraphy, reversible perfusion abnormality was detected in only 28 segments (60%) that were the site of future acute myocardial infarction.

Changing paradigms in thrombolysis in acute myocardial infarction

Acute myocardial infarction occurs when a ruptured coronary artery plaque causes sudden thrombotic occlusion of a coronary artery and cessation of coronary artery blood flow. This paper reviews the underlying coronary pathology in progressive coronary atherosclerosis, mechanisms of plaque rupture and arterial occlusion and the time relationship between coronary occlusion and myocardial necrosis. Reperfusion can be achieved by chemical thrombolysis with different thrombolytic agents. Early lysis is achieved best by prehospital administration, a transtelephonic monitor, a mobile intensive care unit, active general practitioner treatment or by warning the emergency room of impending arrival of a patient. Thrombolytic therapy may be unsuccessful and not achieve Grade III TIMI flow in less than 4 h (or even 2 h) due to inadequate or intermittent perfusion or reocclusion. Adjuvant therapy includes aspirin and platelet receptor antagonists. Bleeding is a constant danger. Direct percutaneous transluminal coronary angioplasty (PTCA) may be as effective or better than chemical thrombolysis. Reperfusion protects the myocardium and salvages viable tissue. It also improves mechanical remodelling of the ventricle. Long-term follow-up has shown that quantum leaps of fresh coronary occlusion causes step-wise progression in patient disability and that further early, prompt reperfusion can salvage myocardium and prevent this inexorable progress of the disease.

Importance of delaying balloon angioplasty in patients with unstable angina pectoris

Angioplasty in patients with unstable coronary artery disease is associated with higher complication rates compared with patients with stable disease. In this report we describe our results from a group of patients with unstable disease (unstable angina pectoris and postmyocardial infarction) where a strategy of delaying angioplasty for > 5 days after admission was undertaken. Included are 2069 consecutive patients: 1197 treated for stable angina pectoris and 872 treated during admission for unstable angina or myocardial infarction. There was no difference between the two groups in angioplasty success (92.1% stable, 92.3% unstable), failure to dilate without complication (6.4% stable, 6.1% unstable), or in the rate of major complications: death (0.5% stable, 1.1% unstable), Q-wave myocardial infarction (0.9% stable, 1.1% unstable), and emergency coronary artery bypass (0.6% stable, 0.3% unstable). The duration of hospitalization following angioplasty was longer in the unstable group (5.6 +/- 8.1 days vs. 4.2 +/- 4.1 days; p < 0.001) because of longer duration of heparin infusion. There was no difference between groups in minor complications such as groin hematoma and pseudoaneurysm, renal failure, or infections. It was concluded that delaying angioplasty in unstable patients for > 5 days after admission is a safe and effective therapeutic strategy for this group of patients. The need for prolonged heparin infusion after angioplasty is increased in unstable patients and thus the duration of hospitalization after the procedure is longer.

Prognostic significance of maximal exercise testing after myocardial infarction treated with thrombolytic agents: the GISSI-2 data-base. Gruppo Italiano per lo Studio della Sopravvivenza Nell'Infarto

Exercise testing helped in diagnosing postinfarction patients in the prethrombolytic era. Over the past decade acute myocardial infarction treatment has changed because of new thrombolytic therapies and consequently, the value of exercise testing is under debate. The GISSI-2 database allowed us to reevaluate the prognostic role of exercise testing in thrombolysed patients. The exercise test was performed in 6296 patients, on average 28 days after randomisation. The test was not performed in 3923 patients because of contraindications. The test was judged positive for residual ischaemia in 26% of the patients, negative in 38%, and non-diagnostic in 36%. Among the patients with a positive stress test result, 33% had symptoms, whereas 67% had silent myocardial ischaemia. The mortality rate was 7.1% among patients who did not have an exercise test and 1.7% [correction of 7.1%] for those with a positive test, 0.9% for those who had a negative test, and 1.3% for those who did not have a diagnostic test. In the adjusted analysis, symptomatic induced ischaemia, submaximal positive result, low work capacity, and abnormal systolic blood pressure were independent predictors of 6-month mortality (relative risks [RR] 2.54, 95% CI 1.27-5.08, 2.28, 1.17-4.45, 2.05, 1.23-3.42, and 1.86, 1.05-3.31, respectively). However, when these factors were tested simultaneously, only symptomatic induced ischaemia and low work capacity were confirmed as independent predictors of mortality (RR Cox 2.07, 95% CI 1.02-4.23 and 1.78, 1.06-2.99, respectively). Patients with a normal exercise response have an excellent medium-term prognosis and do not need further investigation. However, more evaluation should be devoted to the patients who cannot undergo exercise testing, because the potential to influence outcome appears to be much greater.

Acute myocardial infarction--the angiographic picture: new insights into the pathogenesis of myocardial infarction

The angiographic appearance of the coronary arteries were examined in 302 patients with stable angina pectoris and compared to 308 patients with acute myocardial infarction, who received high-dose intravenous thrombolytic therapy, in order to elucidate the underlying angiopathological picture in the two diseases. In each group coronary lesions were present in proximal segments of the arteries and were closely related to bifurcations. Lesions were more extensively distributed in the coronary tree in patients with stable angina and they had an average of 5.4 lesions per patient, compared to the acute myocardial infarction group who had only 2.4 lesions. Also, in the acute myocardial infarction patients, four-fifths of the culprit arteries were patent, 104 (34%) had a ruptured plaque, 22 (7%) had an ulcerated plaque and in 190 (62%) the lesions were eccentric. The study shows that patients with myocardial infarction who are suitable for thrombolysis have a unique coronary angiographic picture and the acute episode is caused by sudden rupture of a localized atheromatous plaque which initiates an obstructive thrombotic cascade.

Limited usefulness of exercise testing and thallium scintigraphy in evaluation of ambulatory patients several months after recovery from an acute coronary event: implications for management of stable coronary heart disease. Multicenter Myocardial Ischemia Research Group

OBJECTIVES

This study evaluated the value of noninvasive testing to predict cardiac events in patients with stable coronary disease after hospital admission (and risk stratification) for an acute coronary event.

BACKGROUND

Exercise testing with thallium perfusion imaging identifies patients with obstructive coronary artery disease and has been used to stratify patients after myocardial infarction. Its usefulness for predicting cardiac events in patients with stable coronary disease after recovery from an acute coronary event was explored.

METHODS

Nine hundred thirty-six patients were enrolled 1 to 6 months after hospital admission for a coronary event. Patients underwent exercise treadmill testing with planar thallium-201 scintigraphy and were followed up for an average of 23 months (range 6 to 43). End points were 1) unstable angina requiring hospital admission, nonfatal myocardial infarction or cardiac death; 2) nonfatal infarction or cardiac death; or 3) cardiac death alone.

RESULTS

Twelve patients died of cardiac causes (1.2%); 32 had a nonfatal myocardial infarction (3.4%); and 79 patients (8.4%) developed unstable angina in the first year. Exercise testing improved proportional hazards models constructed from clinical variables for all three end points (p < 0.05). The perfusion scan further improved models for the end points (nonfatal infarction or cardiac death and cardiac death alone, p < 0.05). However, the exercise test with or without thallium added little to the overall prediction of primary events (area under the receiver operating curve increased from 0.649 to 0.663), and only 2% to 13% of patients with abnormal results either had a nonfatal infarction or died.

CONCLUSIONS

Thallium-201 scintigraphy and exercise testing variables identify patients at risk for subsequent cardiac events. However, the poor predictive performance of these tests in this group of patients with stable coronary disease severely limits their usefulness. These results suggest a limited role for exercise and thallium testing in predicting cardiac events in patients with known coronary disease.

Lewis A. Conner Memorial Lecture. Mechanisms leading to myocardial infarction: insights from studies of vascular biology

Myocardial infarction is the most frequent cause of mortality in the United States as well as in most western countries. In this review, the processes leading to myocardial infarction are described based on the most recent studies of vascular biology; in addition, evolving strategies for prevention are outlined. The following was specifically discussed. (1) Five phases of the progression of coronary atherosclerosis (phases 1 to 5) and eight morphologically different lesions (types I, II, III, IV, Va, Vb, Vc, and VI) in the various phases are defined. (2) The present understanding of the pathogenesis of each of the phases of progression and of the various lesion types preceding myocardial infarction is described; particular emphasis is placed on the physical, structural, cellular, and chemical characteristics of the "vulnerable or unstable plaques" prone to disruption (types IV and Va lesions). (3) The fate of plaque disruption (type VI lesion) in the genesis of the various coronary syndromes and especially acute myocardial infarction is defined; particular emphasis is placed on the combination of plaque disruption and a high thrombogenic risk profile--local factors (ie, degree of plaque disruption, exposure of lipid-macrophage-rich plaque, etc) and systemic factors (ie, catecholamines, RAS, fibrinogen, etc)--in the genesis of myocardial infarction. (4) Strategies of regression or stabilization of "vulnerable or unstable plaques" for prevention of myocardial infarction are presented within the context of recent favorable experience with risk factor modification and lipid-modifying angiographic trials, beta-blockade and angiotensin-converting enzyme inhibition, antithrombotic strategies, and the possible role of estrogens. The recent past has been very fruitful in yielding a better understanding of the processes leading to myocardial infarction, and the near future appears very promising in terms of preventing the number 1 killer in the western world.

Arterial remodelling after percutaneous transluminal balloon angioplasty

Atheromatous coronary artery disease progresses by atheroma accretion, plaque rupture and thrombus formation, with or without spontaneous fibrinolysis. The natural history may be altered by modifying risk factors in an attempt to induce regression, or treated by mechanical means such as balloon angioplasty, directional coronary atherectomy or drills, or flow modulated by the insertion of an aorto coronary bypass graft with or without endarterectomy. Here we discuss the natural history of the atheromatous disease in a series of 355 patients who underwent at least one PTCA procedure and then underwent a second angiographic study to determine the changes in the dilated and nondilated arteries.