Variant angina pectoris. Role of coronary spasm in the development of fixed coronary obstructions

What is the meaning of provoked spasm phenotypes by vasoreactivity testing?

Coronary artery epicardial spasm is involved in the pathogenesis of many cardiac disorders. Vasoreactivity testing, such as intracoronary injection of acetylcholine (ACH) or ergonovine (ER), is the gold standard method for the diagnosis of vasospastic angina. Provoked epicardial spasm phenotypes are classified as focal spasm and diffuse spasm. Multiple factors, including sex, ethnicity, and use of coronary vasoactive stimulators, are related to the provoked phenotypes of epicardial spasm. Diffuse-provoked spasm is often observed in females, where focal-provoked spasm is markedly more common in males. ACH provokes more diffuse and distal spasms, whereas ER induces more focal and proximal spasms. Yellow plaque and coronary thrombi are often observed in lesions with focal spasms, and intimal thickness with a sonolucent zone is significantly more common in lesions with focal spasm. Furthermore, clinical outcomes in patients with focal spasm are unsatisfactory compared with those in patients with diffuse spasm. However, the reproducibility and eternality of provoked spasm phenotypes by vasoreactivity testing is uncertain. Coronary atherosclerosis or endothelial damage may affect coronary vasomotor tone. Although coronary artery spasm may persist in the same coronary artery, provoked coronary spasm phenotypes may exhibit a momentary coronary reaction by intracoronary ACH or ER testing.

Percutaneous coronary intervention in patients with documented coronary vasospasm during long-term follow-up

Objective

Although recurring coronary artery spasm (CAS) may lead to the development of fixed atherosclerotic coronary stenosis (FS), the relationship between coronary atherosclerosis and CAS is still speculative. We evaluated the incidence of FS requiring percutaneous coronary intervention (PCI) in patients with documented CAS during long-term follow-up and analysed their clinical features.

Methods

Clinical data of 3556 patients during a median follow-up of 9.4 years after non-invasive ergonovine spasm provocation testing with echocardiographic monitoring of left ventricular wall motion (erg echo) were analysed.

Results

Erg echo documented CAS in 830 (23.3%) patients, who had higher frequencies of coronary risk factors than those without CAS. Patients with documented CAS on erg echo showed significantly lower 10-year overall (90.5% vs 94.2%, p<0.001) and PCI-free (97.4% vs 98.4%, p=0.002) survival rates than those without CAS. Documented CAS was an independent factor associated with later PCI after adjustment by either Cox regression model or Fine-Gray competing risk model. There was no significant difference in baseline clinical characteristics between patients who needed later PCI and those who did not. Among 28 patients who needed later PCI after documentation of CAS, the original CAS and later PCI territory were concordant in 25 (89.3%), while 3 (10.7%) showed discordance.

Conclusions

CAS is a risk factor for the development of FS requiring PCI during long-term follow-up, and warrants physicians’ vigilance and careful follow-up of patients with documented CAS and insignificant stenosis of major epicardial coronary arteries at the time of initial diagnosis.

Coronary artery spasm: Current knowledge and residual uncertainties

Myocardial ischaemia results from a direct mismatch between oxygen supply and demand, commonly arising as a result of coronary atherosclerosis, microvascular dysfunction or acute thrombosis and luminal obstruction. However, transient ischaemia may also occur due to coronary spasm leading to acute and unexpected myocardial ischaemia without obvious visible coronary pathology. Aside from symptoms of chest pain, coronary spasm can cause infarction, LV impairment, promote life threatening arrhythmias and ultimately sudden cardiac death. While therapeutic options are available, controversies exist around diagnosis, pathology, management and prognosis. This review summarises some of the common questions in this area. In particular we explore and discuss the available evidence for the pharmacological treatment of coronary spasm, and strategies for identification and management of very high risk patients to try and reduce the incidence of sudden premature death.

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Myocardial ischaemia results from a mismatch between oxygen supply and demand.

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Spasm might lead to myocardial ischaemia without visible coronary pathology.

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Coronary spasm can cause infarction, LV impairment and sudden cardiac death.

Insertion/deletion polymorphism in alpha2-adrenergic receptor gene is a genetic risk factor for sudden cardiac death

BACKGROUND

Adrenoceptors mediate contraction of vascular smooth muscle and induce coronary vasoconstriction in humans. A deletion variant of the human alpha(2B)-adrenoreseptor of glutamic acid residues has been associated with impaired receptor desensitization. This receptor variant could, therefore, be involved in cardiovascular diseases associated with enhanced vasoconstriction. Our aim was to study whether an insertion/deletion (I/D) polymorphism in the alpha(2B)-adrenoceptor gene is associated with the risk for sudden cardiac death.

METHODS

This was a prospective population-based study investigating risk factors for cardiovascular diseases in middle-aged men from 42 to 60 years from eastern Finland. The study is based on 1,606 men with complete data on DNA observed for an average time of 17 years.

RESULTS

In this study population, 338 men (21%) had the D/D genotype, 467 (29%) had the I/I genotype, and 801 (50%) had a heterozygous genotype. There were 76 sudden cardiac deaths during follow-up (0.81 deaths/1,000 persons per year). In a Cox model adjusting for other coronary risk factors (age, systolic blood pressure, smoking, diabetes, serum low-density lipoprotein and high-density lipoprotein cholesterol, body mass index, and exercise-induced myocardial ischemia), men with the D/D or I/D genotype had 1.97 times (95% CI 1.08-3.59, P = .026) higher risk to experience sudden cardiac death (20 events for D/D genotype, 13 events for I/I genotype, and 43 events for I/D genotype) compared with men carrying the I/I genotype. In addition, the alpha(2B)-adrenoceptor D/D genotype was associated with the risk of coronary heart disease death and acute coronary events, after adjusting for risk factors.

CONCLUSIONS

The genetic polymorphism of the alpha(2B)-adrenoreceptor is genetic risk predictor for sudden cardiac death.

Intermediate fixed coronary artery stenosis at the site of ergonovine-provoked spasm as a predictor of long-term major adverse cardiac events of patients with coronary spastic angina

BACKGROUND

Organic coronary artery stenosis is a significant prognostic factor in patients with coronary spastic angina (CSA), so the present study was focused on assessing the impact of intermediate fixed stenosis at sites of provoked spasm on the long-term outcomes of CSA patients.

METHODS AND RESULTS

CSA patients diagnosed on the basis of ergonovine-provoked spasm were enrolled and the clinical background and long-term prognosis of CSA patients with intermediate fixed stenosis at the site of provoked spasm (with-fixed-stenosis group, n=37) and those without fixed stenosis (without-fixed-stenosis group, n=126) were retrospectively compared. During the follow-up period (average 4.01 years for with-fixed-stenosis, 4.47 years for without-fixed-stenosis), the with-fixed-stenosis group had a significantly lower event-free survival rate, as well as a higher frequency of admission for unstable angina and percutaneous coronary intervention than the without-fixed-stenosis group, whereas the survival rate did not differ significantly between the 2 groups. In the multivariate analysis, intermediate fixed stenosis at the site of provoked spasm was a predictor of long-term major adverse cardiac events (MACE).

CONCLUSIONS

Intermediate fixed stenosis at the site of ergonovine-provoked spasm is an independent risk factor for MACE during the long-term period in CSA patients.

Lack of association between the insertion/deletion polymorphism of the angiotensin-converting enzyme gene and vasospastic angina

BACKGROUND AND HYPOTHESIS

It has been suggested that the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene is an independent risk factor for coronary atherosclerosis and myocardial infarction, but its relation to vasospastic angina has not been fully proven. In the present study, we investigated the possible relationship between the ACE I/D genotype and vasospastic angina.

METHODS

We explored the distribution of the ACE genotype in 20 patients with vasospastic angina without fixed coronary artery stenosis, 55 angina patients with fixed coronary artery stenosis, and 30 control subjects without coronary artery disease.

RESULTS

The frequency of the DD genotype in patients with vasospastic angina (DD: 30.0%, ID: 20.0%, II: 50.0%) did not differ from that in the control subjects (DD: 23.3%, ID: 26.7%, II: 50.0%), while the frequency in patients with coronary artery stenosis (DD: 43.7%, ID: 21.8%, II: 34.5%) was significantly higher than that in the control subjects. The frequency of the D allele also did not differ between patients with vasospastic angina (0.40) and control subjects (0.37), while the frequency was significantly higher in patients with coronary artery stenosis (0.55).

CONCLUSIONS

These findings suggest that the ACE DD genotype is a potent genetic risk factor for organic coronary artery disease, while it confers no appreciable increase in risk of vasospastic angina. These results also suggest the diversity of the pathogenesis of vascular lesions in these two types of coronary artery disease.

[Up-date of the diagnosis and treatment of vasospastic angina]

Vasospastic or Prinzmetal's variant angina as it is also known is a special type of ischemic heart disease characterized by spontaneous episodes of chest pain accompanied by transitory ST segment elevations during the episodes. These alterations are essential for its diagnosis and it is difficult to diagnose it in their absence. If clinical suspicion is high, it should be confirmed by coronary vasospasm provocation tests, since, on the contrary, there may be cases that are not diagnosed or considered to be other types of diseases. Furthermore, progression of this type of angina to a myocardial infarction due to coronary stenosis is a relatively uncommon event.

Hemodynamic factors and atheromatic plaque rupture in the coronary arteries: from vulnerable plaque to vulnerable coronary segment

Coronary plaque disruption with superimposed thrombosis is the underlying pathology in the acute coronary syndromes and sudden death. Coronary plaques are constantly stressed by a variety of mechanical and hemodynamic forces that may precipitate or 'trigger' disruption of vulnerable or, at extreme conditions, even stable plaques. This paper reviews the exciting new evidence on the hemodynamic factors that may play a role in this process and provides the rationale for the introduction of the concept of the vulnerable coronary segment in the study of acute coronary syndromes.

Contribution of vasoconstriction to the origin of atherosclerosis: a conceptual study

Research during the past century has clearly shown that endothelial injury (EI) and/or endothelial dysfunction (ED) are among the major events determining the onset of atherosclerosis. Included in the events that may elicit endothelial damage, vasoconstriction (VC) has received relatively little attention. This conceptual review attempts to show that in elastic and conduit arteries, VC is not only capable of producing EI/ED, but is also closely associated with many recognized proatherogenic stimuli. Of related interest is the observation that a number of suspected antiatherogenic stimuli oppose VC by their vasodilatory effects, lending further support to this relationship. In addition, recent developments in the knowledge of the molecular basis of VC (including the role of specific inhibitors) are discussed, and their potential for preventing lesion formation and thus becoming novel therapeutic alternatives against the onset of atherosclerosis are highlighted.

Clinical and pharmacological significance of α2-adrenoceptor polymorphisms in cardiovascular diseases

The alpha2-adrenoceptors (alpha2-ARs) are receptors for endogenous catecholamines (norepinephrine and epinephrine) that mediate a number of physiological and pharmacological responses such as hypotension and sedation. Three distinct subtypes, denoted alpha2A-, alpha2B- and alpha2C-AR, have been characterized and cloned. Employment of mutation screening in the study of human populations from various ethnic backgrounds has shown that alpha2-AR genes are polymorphic. The functional and biochemical consequences of these polymorphisms have been analyzed by expressing the wild-type receptors and their respective genetic variants in heterologous systems such as CHO and COS-7 cells. Changes include alteration in G-protein coupling and in agonist-promoted receptor phosphorylation and desensitization. Case-control and population-based studies have shown clinical association with cardiovascular risk. Further investigation of the genetic variants in specialized cells and transgenic animals will provide the molecular basis of cardiovascular disease and may reveal alpha2-AR variants as potential targets for selective pharmacological interventions.

Lesion Severity and Hypercholesterolemia Determine Long-Term Prognosis of Vasospastic Angina Treated With Calcium Channel Antagonists

Although patients with medically treated vasospastic angina have a good outcome, few data exist regarding the role of underlying lesion severity associated with or without hyperlipidemia in the prognosis. Therefore, the aim of the present study was to assess the relationship between the long-term outcome of vasospastic angina and the factors influencing its prognosis. A total of 256 patients (219 men, 37 women; mean age, 54.1+/-9.2) who had coronary spasm with or without underlying lesions and were being treated with calcium channel antagonists were enrolled and followed for 13.6+/-3.7 years. Cardiac events consisted of cardiac death and ischemic events, which included acute myocardial infarction and unstable angina. Cox analysis selected coronary artery stenosis (CAS, >/=50%) and risk factors such as age, hypertension, diabetes mellitus, low-density lipoprotein-cholesterol (LDL-C), sex and smoking. There were 19 cases of cardiac death (7.4%) and 58 of ischemic events (22.7%) during the follow-up period. The presence of significant CAS was an independent predictor of event-free survival (hazard ratio (HR) =2.84, 95% confidence interval (CI) =1.79-4.52, p<0.0001). In 193 patients without significant CAS, there were 10 cases of cardiac death (5.2%, p<0.05) and 34 of ischemic events (17.6%, p<0.01). In that group, high LDL-C was the independent predictor of event-free survival (HR = 3.89, 95% CI = 1.20-12.6, p=0.02). Kaplan-Meier survival analysis revealed significantly lower event-free survival in patients with than in those without lesions (p<0.0001 by log-rank test). These results demonstrate that the most important factor for long-term prognosis of vasospastic angina treated with calcium channel antagonists is significant CAS. High LDL-C, which might alter the underlying coronary endothelial function and/or accelerate atherosclerotic lesions, could also contribute to the occurrence of cardiac events, particularly in patients without significant CAS.

Plaque Morphology at Coronary Sites With Focal Spasm in Variant Angina-Study Using Intravascular Ultrasound-

In the present study, the intravascular ultrasound (IVUS) morphologic appearance of coronary atherosclerotic plaque associated with focal spasm was prospectively studied in 45 patients with or without focal coronary spasm provoked by ergonovine or acetylcholine. The percent plaque area and plaque arc were determined from the IVUS images at the sites of spasm. Calcified lesion was defined as the presence of high-intensity echo with acoustic shadowing. Twenty-three patients had focal coronary spasm defined as angiographic narrowing >75% and IVUS demonstrated atherosclerotic plaque in these 23 sites. In the 22 patients without focal spasm, IVUS demonstrated 18 atherosclerotic lesions in 17 patients and the remaining 5 patients did not have significant lesions. There was no difference in the percent plaque area and plaque arc between plaque lesions with (47+/-10%, 298+/-71 degrees ) and without (39+/-15%, 249+/-83 degrees ) coronary spasm. Interestingly, calcified lesion was less frequently present at the sites with than at those without spasm (p<0.05). These results indicate that the presence of plaque without calcification is likely to be related to the occurrence of focal vasospasm, although the severity and distribution of the disease did not differ between each patient group.

An insertion/deletion polymorphism in the alpha2B-adrenergic receptor gene is a novel genetic risk factor for acute coronary events

OBJECTIVES

Our aim was to study whether an insertion/deletion (I/D) polymorphism in the alpha2B-adrenoceptor gene is associated with the risk for cardiovascular diseases.

BACKGROUND

alpha2-adrenoceptors mediate contraction of vascular smooth muscle and induce coronary vasoconstriction in humans. The alpha2-adrenoceptor subtype B mediates vasoconstriction in mice. A variant of the human alpha2B-adrenoceptor gene that encodes a D of three residues in an intracellular acidic motif has been shown to confer decreased receptor desensitization. This receptor variant could, therefore, be involved in diseases associated with enhanced vasoconstriction.

METHODS

This study was part of a prospective population-based study investigating risk factors for cardiovascular diseases in a cohort of middle-aged men from eastern Finland. Nine hundred twelve men aged 46 to 64 years were followed for an average time of 4.5 years.

RESULTS

In this study population, 192 men (21%) had the D/D genotype; 256 (28%) had the I/I genotype, and 464 (51%) had a heterozygous genotype. In a Cox model adjusting for other coronary risk factors, men with the D/D genotype had 2.2 times (95% confidence interval: 1.1 to 4.4, p = 0.02) the risk to experience an acute coronary event (n = 15 for D/D, 10 for I/I and 12 for I/D) compared with men carrying either of the other two genotypes. The alpha2B-adrenoceptor genotype was not associated with hypertension in this study population.

CONCLUSIONS

The D/D genotype of the alpha2B-adrenoceptor is a novel genetic risk factor for acute coronary events, but not for hypertension.

The protein kinase inhibitor fasudil protects against ischemic myocardial injury induced by endothelin-1 in the rabbit

Endothelin-1 (ET-1) induces severe pathologic conditions such as coronary spasm followed by vasospastic angina pectoris and acute myocardial infarction. The related pathophysiologic mechanisms have remained obscure. Endothelin-1 receptor (ET(A) and ET(B)) is reported to couple with several types of G protein-involved pathways that participate in phospholipase C activation and atrial myofibrils organization into sarcomeric units. Here we demonstrate that ET-1 induces histologic and pathologic dysfunction in the rabbit myocardium and that such pathologic events are prevented by the Rho-kinase inhibitor fasudil. Although the bolus injection of ET-1 (1.4 nmol/kg) via the auricular vein of the rabbit induced only transient T-wave elevation, irreversible, severe histologic changes were observed in papillary muscles of the ventricle, and multifocal myocardial necrosis with infiltration of neutrophils and macrophages in the left ventricle occurred. Oral administration of fasudil (10 mg/kg) significantly reduced the occurrence of myocardial injury determinants, whereas conventional Ca2+ channel blockers (nifedipine, diltiazem) and a K+ channel opener (nicorandil; 10 mg/kg, p.o. each) showed a lesser or no effect on such determinants. These results suggest that ET-1 induces severe myocardial dysfunction based not only on the occurrence of vasospastic ischemia but also on its direct effects on the myocardium.

Plaque disruption and thrombosis. Potential role of inflammation and infection

Considerable data from in vitro and in vivo studies of vascular biology, together with indirect evidence from clinical trials of lipid-lowering or modifying and lifestyle or risk factor modifying interventions, provide strong support for the concept that disruption of atherosclerotic plaque and subsequent thrombosis is a key precipitant of potentially lethal, acute coronary syndromes. Certain characteristics of plaques, including the size and composition of the lipid core, the structure and composition of the fibrous cap, and the presence of a local inflammatory process, predispose the plaque to disruption. Stresses resulting from biomechanical and hemodynamic forces acting on plaques may then trigger disruption, releasing the thrombogenic contents of the lipid core. Alterations in endothelial function may also contribute to vulnerability of plaque rupture and thrombosis. Therefore, interventions aimed at decreasing plaque vulnerability to disruption--all based on the concept of plaque stabilization--may reduce the risk of acute coronary syndromes. Although not yet rigorously validated in humans, plaque stabilization may prove to be an important clinical strategy for preventing the lethal consequences of coronary atherosclerosis.

Racial heterogeneity in coronary artery vasomotor reactivity: differences between Japanese and Caucasian patients

Japanese investigators have provided a substantial contribution in the understanding of coronary vasomotor reactivity. On occasions, their findings have been at variance with those undertaken on caucasian patients, raising speculation that vasomotor differences between races may exist. In a comparative review of the published literature, we evaluated the vasoreactive differences among Japanese and caucasian patients with variant angina or myocardial infarction. In variant angina, Japanese patients appear to have diffusely hyperreactive coronary arteries compared with caucasian people, manifested by their segmental rather than focal spasm, hyperreactive nonspastic vessels and multivessel spasm. These differences may reflect the increased basal tone among Japanese variant angina patients and may relate to controversial differences in endothelial nitric oxide production or autonomic nervous system activity. Provocative vasomotor studies of Japanese patients with a recent myocardial infarction report a higher incidence of inducible spasm than caucasian studies, an observation recently supported by a controlled study. Furthermore, the hyperreactivity was diffuse, occurring in both non-infarct- and infarct-related vessels. These observations support the existence of racial coronary vasomotor reactivity differences but require confirmation in further prospectively conducted studies.

Long lasting spasticity in controlled vasospastic angina

OBJECTIVE

To evaluate changes in coronary artery spasticity in patients with vasospastic angina who had been stable for years under continuous drug treatment.

METHODS

Follow up coronary angiography was performed under intracoronary ergonovine provocation in 27 well controlled patients with vasospastic angina and no organic stenosis; the tests were done > 24 months after the initial coronary angiography, in which occlusive spasm had been induced by the same regimen of ergonovine provocation.

RESULTS

The mean (SD) follow up period was 47.2 (21.6) months. All patients had been free from angina attack for more than 24 months under treatment with antianginal drugs. During this follow up period, organic stenosis developed in only one case. Occlusive spasm was observed during follow up coronary angiography in 23 patients. Spasm with 90% narrowing was observed in three other patients, and diffuse significant narrowing was seen in the final patient. No significant difference was found in spasticity (p = 0.75) between the initial and the follow up tests.

CONCLUSIONS

Repeated ergonovine provocation during coronary angiography after a controlled period of several years showed that coronary spasm remains inducible in most patients. Discontinuance of drug treatment during the remission from anginal attacks achieved by medication may put the patient at high risk.

Role of inflammation and metalloproteinases in plaque disruption and thrombosis

Numerous pathological, clinical, angiographic and angioscopic studies have demonstrated that acute coronary syndromes (unstable angina, acute myocardial infarction and ischemic sudden death) are most frequently the consequence of plaque disruption (plaque rupture or superficial plaque erosion) and consequent coronary thrombosis. Several serial angiographic studies have demonstrated that nearly 60-70% of acute coronary syndromes evolve from mildly to moderately obstructive atherosclerotic plaques. Coronary plaque disruption appears to be a function of both the composition of the plaque (plaque vulnerability ) as well as extrinsic triggers that may precipitate plaque disruption in a vulnerable plaque. Vulnerability for plaque disruption appears to be largely determined by the size of the lipid-rich atheromatous core, the thickness of the fibrous cap covering the core, and the presence of ongoing inflammation within and underneath the cap. Inflammatory cells may play a critical role in plaque disruption through the elaboration of matrix degrading metalloproteinases or MMPs (collagenases, gelatinases, stromelysins and matrilysin) and by inhibition of function and survival of matrix-synthesizing smooth muscle cells. Inflammatory cells may also play a critical role in triggering thrombosis following plaque disruption through the tissue factor pathway. In addition, stresses resulting from hemodynamic and mechanical forces may precipitate plaque disruption, particularly at points where the fibrous cap is weakest, such as at its shoulders. The degree of thrombosis following plaque disruption is determined by the thrombogenicity of the disrupted plaque, disturbed local rheology and systemic thrombotic-thrombolytic milieu. Surges in sympathetic activity provoked by sudden vigorous exercise, emotional stress -- including anger, or cold weather, may also trigger plaque disruption. These observations have led to the concept of plaque stabilization as a new clinical strategy for the prevention of acute coronary syndromes. Plaque stabilization can be achieved through pharmacologic and lifestyle-modifying interventions that reduce vulnerability to plaque disruption by altering plaque composition and/or inflammatory activity within the plaque.

Histological evaluation of coronary plaque in patients with variant angina: relationship between vasospasm and neointimal hyperplasia in primary coronary lesions

OBJECTIVES

This study was designed to determine whether coronary vasospasm in patients with variant angina pectoris (VAP) may produce focal organic lesions at the site of vasospasm that would contribute to disease progression.

BACKGROUND

Recent clinical angiographic and experimental studies have demonstrated the potential role of vasospasm in the worsening of organic coronary stenosis.

METHODS

We studied histologically the coronary plaques obtained at atherectomy in 202 patients with moderate to severe coronary stenosis. This population included 22 patients with VAP, 100 patients with chronic stable angina and 80 patients with restenosis following angioplasty or atherectomy. Diagnosis of VAP was based on both the clinical feature of angina at rest associated with ST elevation and a positive response to acetylcholine provocation test.

RESULTS

The most common histological appearance in 92% of patients with stable angina was hypocellular fibroatheromatous plaques, whereas neointimal hyperplasia was the characteristic feature of the plaque observed in 90% of patients with restenosis. The coronary specimens at the site of spasm in 15 of the 22 patients (68%) with VAP demonstrated intimal injuries such as neointimal hyperplasia (15), thrombus formation (2), and intimal hemorrhage (3). Neointimal hyperplasia was significantly more common in the patients with VAP as compared with those with stable angina (68% vs. 8%; p < 0.0001). A rapid progression of organic stenosis within three years was angiographically found in 5 of the 22 patients with variant angina. In all five cases, neointimal hyperplasia was the main contributor to the worsening of the organic lesion at the site of spasm. These histological findings in patients with VAP extremely resembled those in restenosis. Except for vasospasm, no factors significantly predicted the presence of neointimal formations in primary coronary lesions.

CONCLUSIONS

Coronary vasospasm may provoke vascular injury that leads to the formation of neointima in VAP patients similar to that seen with restenosis. Coronary spasm may thus play a key role in the rapid coronary stenosis progression in certain patients with VAP.

New insights into the pathogenesis and prevention of acute coronary syndromes

Several recent studies have shown that 60-70% of coronary occlusions that cause acute coronary syndromes (such as unstable angina, myocardial infarction, or sudden ischemic death) evolve from atherosclerotic plaques that are only mildly to moderately obstructive. Numerous studies have demonstrated that coronary thrombosis, the immediate cause of acute coronary syndromes, is a consequence of plaque disruption. Most thrombotic events are related to deep plaque fissure, while superficial plaque erosion is the cause in a significant minority of cases. Thus, the mechanisms by which stable coronary artery disease (CAD) evolves into an unstable and potentially lethal acute coronary syndrome are related to plaque disruption and thrombosis. The vulnerability of a plaque to disruption appears to be determined by the presence of a large lipid-rich core, a thin fibrous cap, and an inflammatory cellular infiltrate, rather than by the size of the plaque or the severity of stenosis caused by a plaque before disruption. In addition to plaque disruption and thrombosis, enhanced vasoconstriction--a characteristic feature of CAD and dyslipidemia-may contribute to the clinical manifestations of CAD. Angiographic studies have demonstrated that risk factor modification produces a disproportionately greater reduction in ischemic clinical events than in anatomic regression of plaque, suggesting "plaque stabilization" may be the major mechanism of such clinical benefit. The relatively rapid attenuation of endothelial-mediated vasomotor dysfunction with the treatment of dyslipidemia lends credence to this concept.

Ergonovine echocardiography as a screening test for diagnosis of vasospastic angina before coronary angiography

OBJECTIVES

In patients with chest pain suggestive of variant angina, we performed this prospective study to test the specificity and diagnostic validity of ergonovine echocardiography (detection of regional wall motion abnormality during bedside ergonovine challenge) as a screening procedure before coronary angiography.

BACKGROUND

Spasm provocation test outside the catheterization room has generally not been accepted as a safe diagnostic method.

METHODS

Ergonovine echocardiography was performed in 80 consecutive patients with chest pain syndrome after confirmation of negative treadmill or normal stress myocardial perfusion scan results using thallium-201. A bolus of ergonovine maleate was injected at 5-min intervals up to a total cumulative dosage of 0.35 mg with echocardiographic monitoring of left ventricular wall motion. A 12-lead electrocardiogram (ECG) was also recorded every 3 min after each ergonovine injection. Positive test results were development of regional wall motion abnormalities or transient ST segment elevation or depression >0.1 mV in any single lead of the 12-lead ECG. Coronary angiography was undertaken within 2 +/- 4 days (mean +/- SD) after ergonovine echocardiography, and the spasm provocation test with acetylcholine or ergonovine was performed in patients with normal angiographic findings or lumen diameter narrowing <70%.

RESULTS

On the basis of angiographic criteria, 56 patients had coronary vasospasm; this finding was later ruled out in 19 patients with near-normal angiographic results by a negative response on the spasm provocation test. In the remaining five patients, coronary spasm provocation was not performed because they revealed a high degree of fixed stenosis (lumen diameter narrowing 97 +/- 4%). Ergonovine echocardiography could diagnose coronary vasospasm before angiography, with a sensitivity of 91% (51 of 56 patients, 95% confidence interval [CI] 84% TO 98%) and specificity of 88% (21 of 24 patients, 95% CI 75% to 100%). Of 53 patients showing regional wall motion abnormalities during ergonovine echocardiography, characteristic ST segment elevation in the simultaneously recorded ECG was observed in only 20 (38%). There were no complications, including myocardial infarction or fatal arrhythmia, during the test.

CONCLUSIONS

Ergonovine echocardiography before coronary angiography is safe and can be used as a reliable diagnostic screening test for coronary vasospasm in patients with negative treadmill or normal stress myocardial perfusion scan results. These findings suggest that invasive coronary angiography can be avoided in selected patients for the diagnosis of vasospastic angina.

Pathophysiology of plaque rupture and the concept of plaque stabilization

Atherosclerosis complicated by plaque rupture or disruption and thrombosis is primarily responsible for the potentially lethal acute coronary syndromes. Plaques with a large extracellular lipid-rich core, thin fibrous cap with reduced collagen content and smooth muscle density, and increased numbers of activated macrophages and mast cells appear to be most vulnerable to rupture. Plaque disruption tends to occur at points at which the plaque surface is weakest and most vulnerable, which coincide with points at which stresses, resulting from biomechanical and hemodynamic forces acting on plaques, are concentrated. Reduced matrix synthesis as well as increased matrix degradation may predispose fibrous caps to rupture spontaneously or in response to extrinsic mechanical or hemodynamic stresses. Modification of endothelial dysfunction and reduction of vulnerability to plaque rupture and thrombosis may lead to plaque stabilization resulting in reduction of the frequency of acute coronary syndromes. This putative concept of plaque stabilization, although attractive, has not yet been rigorously validated in humans. Indirect data from clinical trials involving lipid lowering/modification and lifestyle/risk factor modification, however, provide strong support for this new paradigm. Thus, plaque stabilization may prove to be an important modality for reduction of lethal consequences of coronary atherosclerosis.

Fluctuation of spastic location in patients with vasospastic angina: a quantitative angiographic study

OBJECTIVES

This study sought to determine whether the location of coronary spastic activity may change over time in patients with persistent variant angina.

BACKGROUND

Although electrocardiographic studies have provided indirect evidence to indicate that the location of ischemia may change in patients with variant angina, it has not been tested by quantitative angiography whether the location of vasospastic activity may change over time.

METHODS

Paired ergonovine provocation tests and coronary angiography were performed at a mean (+/- SD) interval of 43 +/- 13 months apart in patients with persistent symptoms of vasospastic angina in the absence of significant atherosclerosis. A total of 87 spastic and nonspastic segments of 87 major vessels in 29 patients were analyzed by quantitative angiography at baseline, after the administration of ergonovine and after isosorbide dinitrate at the initial and follow-up tests.

RESULTS

In 13 patients (group 1), coronary spasm was observed in the same 16 coronary segments at both the initial and follow-up ergonovine provocation tests. In 16 patients (group 2), the following angiographic changes occurred between the initial and follow-up tests in 48 major vessels: Of the 23 segments that developed spasm at the initial test, 10 did not have spasm at the follow-up test; of the 25 vessels that did not demonstrate spasm on the initial test, 12 demonstrated spasm on the follow-up test (a new site of spasm). Thus, in 22 (46%) of 48 vessels, fluctuation of spastic location was observed at follow-up.

CONCLUSIONS

Quantitative coronary angiography and repeated ergonovine tests revealed that some patients with persistent vasospastic angina demonstrate fluctuation of vasospastic location, whereas others exhibit a fixed location of vasospasm. Vasospastic angina may not only be a transient disease restricted in location, but may also be a persistent and variable condition involving multiple vessels over many years.