Prinzmetal's variant angina. Coronary arteriogram and left ventriculogram during angina attack induced by methacholine

Coronary Artery Spasm: New Insights

Coronary artery spasm (CAS) defined by a severe reversible diffuse or focal vasoconstriction is the most common diagnosis among INOCA (ischemia with no obstructive coronary artery disease) patients irrespective to racial, genetic, and geographic variations. However, the prevalence of CAS tends to decrease in correlation with the increasing use of medicines such as calcium channel blockers, angiotensin converting enzyme inhibitor, and statins, the controlling management of atherosclerotic risk factors, and the decreased habitude to perform a functional reactivity test in highly active cardiac catheterization centers. A wide spectrum of clinical manifestations from silent disease to sudden cardiac death was attributed to this complex entity with unclear pathophysiology. Multiple mechanisms such as the autonomic nervous system, endothelial dysfunction, chronic inflammation, oxidative stress, and smooth muscle hypercontractility are involved. Regardless of the limited benefits proffered by the newly emerged cardiac imaging modalities, the provocative test remains the cornerstone diagnostic tool for CAS. It allows to reproduce CAS and to evaluate reactivity to nitrates. Different invasive and noninvasive therapeutic approaches are approved for the management of CAS. Long-acting nondihydropyridine calcium channel blockers are recommended for first line therapy. Invasive strategies such as PCI (percutaneous coronary intervention) and CABG (coronary artery bypass graft) have shown benefits in CAS with significant atherosclerotic lesions. Combination therapies are proposed for refractory cases.

Incidence and factors associated with mortality in 2,476 patients with variant angina in Korea

This study investigated the incidence and risk factors of mortality in 2,476 patients with variant angina (VA) using the National Health Insurance Service–National Sample Cohort between 2004 and 2011. The risk factors of all-cause and cardiac mortality were investigated using Cox proportional hazards model. Most patients (69.5%) were less than 65 years and 42.9% were women. During the median follow-up duration of 4.9 years, there were 178 (7.2%) and 95 (3.8%) cases of all-cause and cardiac mortality, respectively. Older age, hypertension, diabetes mellitus, poor medication adherence, low household income and tertiary teaching hospitals were independent predictors for all-cause mortality, while older age, hypertension, low household income and tertiary teaching hospitals were independent predictors for cardiac mortality. In conclusion, our findings suggest that traditional risk factor control and continued medication are important to improve VA outcomes, and that household income-level factors should be considered in the assessment of risk of VA patients.

Overview of the pharmacological spasm provocation test: Comparisons between acetylcholine and ergonovine

The spasm provocation tests of ergonovine and acetylcholine have been employed in the cardiac catheterization laboratory. Ergonovine acts through the serotogenic receptors, while acetylcholine acts through the muscarinic cholinergic receptors. Different mediators may have the potential to cause different coronary responses. However, there are few reports concerning the coronary response between ergonovine and acetylcholine in the same patients. Acetylcholine is supersensitive for females; spasm provoked by ergonovine is focal and proximal, whereas provoked spasm by acetylcholine is diffuse and distal. We should use both tests as supplementary in the clinic because ergonovine and acetylcholine have self-limitations to induce coronary spasms during daily life. The maximal pharmacological doses, administration methods, and the angiographical positive definition are remarkably different for each institution in the world. We recommend the pharmacological spasm provocation tests as Class I in the guidelines in patients with vasospastic angina throughout the world.

Overview of the Acetylcholine Spasm Provocation Test

The acetylcholine (ACh) spasm provocation test proposed by Yasue, Okumura et al more than a quarter-century ago has become a popular method for induction of coronary spasm. This test is safe and has a low rate of complications. However, it may be limited in its ability to document attacks in daily life because previously it was the gold-standard method for diagnosing active variant angina. There may be some clinical issues to modify for the next generation of cardiologists. A maximal ACh dose of 50/100 µg in the right coronary artery/left coronary artery is recommended in the Japanese Circulation Society guidelines. We often experienced the usefulness of a maximal ACh dose of 80/200 µg for the induction of coronary spasm in some cases with low or moderate disease activity. It may be necessary to reconsider the maximal ACh dose as a modified method for today's real-world clinical practice. In young patients with rest angina, intracoronary injection of ACh is less sensitive for diagnosis; in these cases, we recommend performing sequential spasm provocation tests. Especially in female patients, to document coronary artery spasm we recommend performing ACh tests first, instead of ergonovine tests, due to the supersensitivity of ACh. We also recommend supplementary use of ACh and ergonovine. This review summarizes our experiences with the ACh spasm provocation test over a period of 24 years. We have found it to be a reliable and useful method for contributing a variety of clinical information and recommend it to the next generation of cardiologists.

Role of coronary spasm in different anginal syndromes

Angina pectoris is a clinical syndrome caused by transient myocardial ischaemia due to an imbalance between myocardial oxygen demand and supply. It is now evident that coronary artery spasm plays an important role in the pathogenesis of various forms of angina pectoris. Angina pectoris that is mainly caused by coronary artery spasm (coronary spastic angina) has one or more of the following characteristics: 1) the attack occurs at rest, 2) the attack is associated with ST-segment elevation in the ECG, 3) the attack has a variable exercise threshold, and 4) the attack is suppressed by Ca-antagonists but not by beta-adrenergic blocking agents. On the other hand, angina pectoris that is caused by increased myocardial oxygen demand in the presence of severe and extensive organic stenosis (organic angina) has the following characteristics: 1) the attack is induced by constant amount of exertion irrespective of hour and day and is relieved by rest, 2) the attack is associated with ST-segment depression in the ECG, and 3) the attack is suppressed by beta-adrenergic blocking agents, which decrease myocardial oxygen demand.

Coronary artery spasm--clinical features, diagnosis, pathogenesis, and treatment

Coronary (artery) spasm plays an important role in the pathogenesis of ischemic heart disease, including stable angina, unstable angina, myocardial infarction, and sudden death. The prevalence of coronary spasm differs among populations, is higher in Japan and Korea than in the Western countries probably due to genetic as well as environmental factors. Coronary spasm occurs most often from midnight to early morning and is usually not induced by exercise in the daytime. The attacks of coronary spasm are associated with either ST segment elevation or depression, or negative U wave on ECG. Patients with multi-vessel coronary spasm may suffer from lethal arrhythmia, including advanced AV block, ventricular tachycardia or fibrillation, or even sudden death, and they are often resistant to conventional medical therapy including Ca-channel blockers (CCBs). Endothelial nitric oxide (NO) activity is reduced and markers of oxidative stress are elevated in patients with coronary spasm. Thrombogenesis is enhanced and plasma levels of hsCRP and P-selection are elevated in patients with coronary spasm. Thus, patients with coronary spasm have endothelial dysfunction and are suffering from a low-grade chronic inflammation. Polymorphisms of endothelial NO synthase, smoking, and low-grade inflammation are the most important risk factors for coronary spasm. Coronary spasm is a hyper-contraction of coronary smooth muscle triggered by an increase of intracellular Ca2+ in the presence of an increased Ca2+ sensitivity. It has been shown that RhoA/ROCK pathway is involved in Ca2+ sensitivity and that the reduced endothelial NO activity results in increased Ca2+ sensitivity through enhanced RhoA/ROCK pathway. Accordingly, it is possible that in addition to CCBs, RhoA/ROCK pathway blockers may prove to be useful for the treatment of coronary spasm.

Relevance of simultaneous ST segment elevation and depression in an exercise treadmill test

Simultaneous ST segment elevation and depression recorded during an exercise treadmill test and its correlation with coronary angiogram is a new finding that does not find a place in medical literature. We conclude that in the presence of simultaneous ST segment elevation and ST segment depression during exercise treadmill test (1) the localizing value of isolated ST elevation is lost and (2) there is severe triple vessel disease warranting early intervention.

Value of the urinary stone promoters/inhibitors ratios in the estimation of the risk of urolithiasis

An imbalance between urinary-promoting and -inhibiting factors has been suggested as more important in urinary stone formation than a disturbance of any single substance. To investigate the value of promoter/inhibitor ratios for estimation of the risk of urolithiasis, urinary citrate/calcium, magnesium/calcium oxalate, and oxalate/citrate x glycosaminoglycans ratios were determined in 30 children with urolithiasis, 36 children with isolated hematuria, and 15 healthy control children. The cutoff points between normal children and children with urolithiasis, accuracy, specificity, and sensitivity for each ratio were determined and compared with those of the 24-h urine calcium and oxalate excretion and urine saturation calculated with the computer program EQUIL 2. The neural network application (aiNET Artificial Neural Network, version 1.25) was used for the determination of the cutoff points for the classification of normal children and the urolithiasis group. The best test for differentiating stone formers from non-stone formers proved the aiNET determined cutoff values of oxalate/citrate x glycosaminoglycans ratio. The method showed 97.78% accuracy, 100% sensitivity, and 93.33% specificity. Two cutoff points between normal and urolithiasis groups were found showing that the children with urolithiasis had ratio values either above 34.00 or less than 10.16. Increased oxalate excretion was linked to the first cutoff value (34.00), and decreased glycosaminoglycans excretion was typical of the second cutoff value (10.16).

123I-MIBG myocardial scintigraphy as a noninvasive screen for the diagnosis of coronary artery spasm

BACKGROUND

It has been suggested that the sympathetic nervous system might play an important role in the development of coronary artery spasm. However, no cardiac imaging modality has been able to demonstrate abnormal sympathetic innervation in patients with coronary artery spasm. The purpose of this study was to assess the presence and location of abnormal sympathetic innervation using iodine 123-metaiodobenzylguanidine (123I-MIBG) single photon emission computed tomography (SPECT) and to evaluate the clinical efficacy of 123I-MIBG SPECT as a noninvasive screening test in patients with coronary artery spasm.

METHODS AND RESULTS

Coronary arteriography and a provocative test with intravenous administration of ergonovine maleate were performed in 26 patients (20 men, 6 women, mean age 48.2+/-12.0 years, range 20 to 67 years) who were suspected of having a coronary artery spasm. The subjects were divided into 2 groups: group 1 (n = 18) comprised subjects with a positive provocative test result, and group 2 (n = 8) comprised subjects with negative provocative test results. Ten healthy subjects served as controls. No abnormal MIBG uptake was observed in the control subjects. Abnormal sympathetic nervous innervation using 123I-MIBG SPECT was observed either as a reduced uptake or a defective pattern in the perfused areas in 13 of the 18 regions supplied by vessels of ergonovine-induced vasospasm. Normal sympathetic innervation, as evidenced by normal 123I-MIBG uptake, was noted in all of the 60 segments of normal vessel territories. Reduced uptake of 123I-MIBG was not detected in the perfused areas of 5 vasospasm-induced vessels (perfusion territory of left anterior descending coronary artery [LAD] and the right coronary artery [RCA] in 2 and 3 patients, respectively). The sensitivity and specificity of 123I-MIBG for detection of coronary artery spasm were 72.2% (95% confidence interval [CI] 55% to 89%) and 100%, respectively. The positive predictive and negative predictive values were 100% and 92.3% (95% CI 91% to 93%), respectively.

CONCLUSION

123I-MIBG SPECT is a feasible method to evaluate noninvasively and localize the territories of coronary arteries with spasm. Invasive diagnostic coronary arteriography with ergonovine provocation test may be unnecessary for diagnosis of coronary artery spasm in patients with typical resting pain, negative exercise test or normal thallium perfusion scan results, but showing abnormalities in 123I-MIBG SPECT.

Determination of urine saturation with computer program EQUIL 2 as a method for estimation of the risk of urolithiasis

To investigate the risk for the development of urolithiasis in 30 children with urolithiasis, 36 children with isolated hematuria, and 15 healthy control children, 24-h urinary excretion of calcium, sodium, oxalate, citrate, sulfate, phosphate, magnesium, urate, chloride, ammonium, and glycosaminoglycans was determined and urine saturation for calcium oxalate was calculated with the computer program EQUIL 2. Compared with controls, children with urolithiasis had significantly increased calcium excretion, oxalate excretion, and urine saturation, whereas children with isolated hematuria had significantly increased calcium excretion only. The best estimation of the relative risk of urolithiasis can be made after urine saturation, using logistic regression. The percentage of patients correctly classified after urine saturation is 85.41% in comparison with 80.95% and 73.81% when the estimation was done by calcium excretion and oxalate excretion, respectively. Using the breakpoint value of 4.29 for urine saturation, it was possible to separate children with increased risk of urolithiasis development from the group of children with isolated hematuria.

Alterations of autonomic nervous activity preceding nocturnal variant angina: sympathetic augmentation with parasympathetic impairment

BACKGROUND

Autonomic nervous discharge has been implicated in the pathogenesis of coronary artery spasm.

METHODS

Cardiac autonomic nervous activities were evaluated from the power of the low-frequency and the high-frequency spectral components of heart rate variability with Holter monitoring in 18 patients with nocturnal variant angina. Samples during the first 512 seconds of each 10-minute period from 60 minutes before to immediately before an anginal attack occurring during the night or at dawn (2:00 to 7:00 AM) were analyzed by fast Fourier transformation.

RESULTS

The R-R interval during the 10- to 0-minute period was significantly shorter than those during the other 10-minute periods. The coefficient of variance of the high-frequency component (0.15 to 0.40 Hz) (CVHF) from the 10- to 0-minute period was not significantly different from the other 10-minute periods. However, both the coefficient of variance of the low-frequency component (0.04 to 0.15 Hz) (CVLF) and the ratio of CVLF and CVHF (CVLF/CVHF) were significantly greater during the 10- to 0-minute period than those during the 30- to 20-minute period, respectively. A significant nighttime fluctuation in the spectral components of heart rate variability with a peak in the CVHF and a nadir in both the CVLF and CVLF/CVHF observed in the control group was blunted in the patients during the attack-free periods while they were medicated with calcium entry blockers.

CONCLUSION

Sympathovagal imbalance, sympathetic activation without parasympathetic augmentation, enhanced in the early morning may play an important role in the genesis of coronary artery spasm in patients with nocturnal variant angina.

Stent placement for recurrent vasospastic angina resistant to medical treatment

The successful stent placement for treatment of recurrent vasospastic angina in a patient with nonstenotic coronary arteries is described. Use of the Palmaz-Schatz stent resulted in successful vasodilation that completely prevented anginal attacks. This procedure represents an alternative treatment for patients with vasospastic angina refractory to aggressive medical therapy.

Coronary artery spasm: a hypothesis on prevention by progesterone

The mechanism of coronary artery spasm has been hypothesized as follows: the dormant gene of the smooth muscle of the human coronary artery is identical or similar to the active gene of the smooth muscle of ductus arteriosus, but can be activated by estrogen. The activation could be preventable by progesterone. The prevention is due to the reduction of the number of estrogen receptors of the smooth muscle of the coronary artery.

Opposing actions of cholinergic agonist and trinitroglycerin on net vascular resistance in perfused rat heart

The effects of cholinergic agonist and nitrovasodilator on transorgan pressure-flow relationships were characterized under antegrade aortic perfusion of the rat heart. Under basal conditions, the preparation exhibited a stable linear dependence of perfusion pressure upon regulated transorgan flow rate from 0 to 9 ml/min with a transorgan vascular resistance of 5 +/- 0.6 mmHg/ml per min. Maximal acetyl-beta-methacholine (10 microM) caused a 3-fold increase in net transorgan vascular resistance to flow of non-cellular perfusate as observed over the range of constant flow rates from 1 to 8 ml/min. Trinitroglycerin (20 microM) reversed cholinergic-induced vasoconstriction. The effects of acetylcholine on transorgan flow were characterized at constant perfusion pressures approximating mean aortic pressures under lethal hypotension (40 mmHg), sublethal hypotension (70 mmHg) and normotension (100 mmHg). Under maximal acetylcholine (5 microM), flow remained adequate at 4.6 ml/min under 100 mmHg aortic pressure, marginally adequate at 1.2 ml/min under 70 mmHg, and sublethally inadequate at 0.4 ml/min under 40 mmHg. It is concluded that acetylcholine is among the factors increasing vascular resistance that can be opposed by nitrovasodilator. It is estimated that inadequate flow might result from maximal cholinergic agonist under hypotensive but apparently not normotensive aortic perfusion pressure as observed in hearts from normal animals.

Autonomic changes associated with spontaneous coronary spasm in patients with variant angina

OBJECTIVES

This study sought to investigate whether changes in nervous autonomic tone may have a role in the mechanisms triggering spontaneous coronary spasm in variant angina.

BACKGROUND

Previous studies have suggested that both sympathetic and vagal activation may act as a trigger of epicardial artery spasm in patients with variant angina, but the actual role of autonomic changes in spontaneous coronary spasm remains unknown.

METHODS

We analyzed the changes in heart rate variability associated with episodes of ST segment elevation detected on Holter monitoring in 23 patients with variant angina (18 men, 5 women; mean [+/-SD] age 59 +/- 12 years). For study purposes, episodes of transmural ischemia lasting > or = 3 min and without any ST segment changes in the previous 40 min were selected for analysis. Heart rate variability indexes were calculated at 2-min intervals, at 30,15,5 and 1 min before ST elevation and at peak ST segment elevation. Ninety-three of 239 total ischemic episodes (39%) fulfilled the inclusion criteria.

RESULTS

The results showed that 1) high frequency (HF) (0.04 to 0.15 Hz), a heart rate variability index specific for vagal activity, decreased in the 2 min preceding ST segment elevation (p < 0.001) and returned to basal levels at peak ST segment elevation; 2) heart rate and low frequency (0.04 to 0.15 Hz), which are partially correlated with sympathetic activity, showed a significant increase at peak ST segment elevation (p < 0.001 for both); 3) the pattern of the HF reduction before ST segment elevation was consistently confirmed in several subgroups of ischemic episodes, including those of patients with or without coronary stenoses, those of patients with anterior or inferior ST segment elevation, those occurring during daily or nightly hours and silent episodes. There were no significant variations in heart rate variability in control periods selected from Holter tapes of patients and before ST segment elevation induced by balloon inflation in 20 patients undergoing coronary angioplasty.

CONCLUSIONS

Our data show that changes in autonomic tone are likely to contribute to trigger or predispose to epicardial spasm. In particular, although not excluding an active role for adrenergic mechanisms, our data suggest that a vagal withdrawal may often be a component of the mechanisms leading to spontaneous coronary vasospasm.

Sympathetic hyperactivity in patients with vasospastic angina--assessment by spectral analysis of heart rate and arterial pressure variabilities

The autonomic nervous system may play an important role in regulating coronary arterial tone. To evaluate the role of autonomic nervous activity in patients with vasospastic angina (VSA), we studied 10 VSA patients with patent coronary artery (mean; 56 yr, range; 44-66 yr) and 8 normal subjects (mean; 58 yr, range; 35-71 yr). ECG and arterial pressure were continuously recorded for 4 min in a supine position at 7:30 am, 10:30 am, and 4:30 pm. Low-frequency (LF; 0.04-0.15 Hz) and high-frequency (HF; 0.20 Hz) components of the beat-to-beat variabilities of the R-R interval (RRI) and systolic arterial pressure (SAP) were then estimated by autoregressive power spectral analysis. The LF-Normalized Power (LF-NP; [LF Power]/[Total Power]-[Direct Current Power]) of both the RRI and SAP variabilities were greater in VSA patients than in normal subjects (RRI: 0.51 +/- 0.07, 0.51 +/- 0.07, 0.53 +/- 0.06, vs 0.25 +/- 0.04, 0.31 +/- 0.05, 0.31 +/- 0.06, at 7:30 am, 10:30 am, and 4:30 pm respectively: p = 0.010, 0.044, 0.018. SAP: 0.62 +/- 0.06, 0.53 +/- 0.06, 0.57 +/- 0.06 vs 0.37 +/- 0.04, 0.30 +/- 0.06, 0.26 +/- 0.07, respectively: p = 0.006, 0.017, 0.003.). The LF-power of SAP variability also tended to be greater in VSA patients. There was no difference in the HF-component coefficient of variance (CCV (%) = 100 x (component power) (1/2)/ mean RR intervals) of the RRI variabilities between the 2 groups. These results indicate that increased sympathetic vasomotor tone and cardiac sympathetic predominance may play an important role in patients with VSA.

Angiotensin converting enzyme as a genetic risk factor for coronary artery spasm. Implication in the pathogenesis of myocardial infarction

It has been reported that individuals with the D allele of an insertion/deletion (I/D) polymorphism of the angiotensin converting enzyme (ACE) gene are at greater risk for myocardial infarction (MI), especially among subjects normally considered to be at low risk. However, little is known about the mechanism by which the ACE polymorphism affects the risk of MI. Coronary artery spasm (CAS) is considered to be one possible mechanism for developing MI. We therefore examined the ACE polymorphism relation to CAS to determine if this was the mechanism by which the DD genotype influences MI. We studied 150 angiographically assessed Japanese males, all more than 60 yr old. CASs were detected using intracoronary injection of ergonovine maleate. Subjects were divided into three groups: those with CAS (group 1), those without CAS, but with fixed organic stenosis (group 2); and those without CAS and no organic stenosis (group 3). DD subjects were significantly represented in group 1 when compared with groups 2 (P = 0.002) and 3 (P = 0.026). These results suggest that the DD genotype relates to the greater risk for MI in the patients with CAS.

Muscarinic receptors and drugs in cardiovascular medicine

The parasympathetic system and its associated muscarinic receptors have been the subject of a renaissance of interest for the following two main reasons: (1) the association of endothelial muscarinic receptors and the nitric oxide (NO) pathway; (2) the discovery of several muscarinic receptor subtypes and drugs interacting with them. In the present survey modern insights into the subdivision of muscarinic receptors have been dealt with as the basis for a description of the muscarinic receptor agonists and antagonists thus far known. There are at least four pharmacologically defined M receptors (M1, M2, M3, M4) in primary tissues, and five muscarinic receptors have been cloned (m1, m2, m3, m4, m5). Selective agonists for M-receptor subtypes hardly exist, and all classical agonists (acetylcholine, carbachol, etc.) are clearly nonselective. A few selective antagonists for M1 (pirenzepine) and M2 receptors (AF-DX 116) have been introduced, although selective M3 receptors are hardly available. Finally, the potential therapeutic use of M-receptor agonists (myocardial ischemia, hypertension) and muscarinic antagonists (certain forms of bradycardia, coronary spasm) has been critically discussed. Although only in a preliminary stage, this development appears to be promising and at least of great fundamental interest.

Cholinergic dysfunction in Shy-Drager syndrome: effect of the parasympathomimetic agent, bethanechol

To determine the frequency, severity and organ distribution of cholinergic dysfunction in the Shy-Drager syndrome, eleven patients were prospectively studied. In addition to documenting adrenergic insufficiency, a battery of twelve tests was employed to assess cholinergic function. Six tests demonstrated pupillary, lacrimal, salivary, urinary bladder, sexual and sudomotor dysfunction in the majority of patients. Cardiac vagal function as studied by the heart rate response to deep breathing, the Valsalva manoeuvre, cold face test, apnoeic facial immersion and atropine test was affected in all patients. Oesophageal motility was abnormal in six patients. Cholinergic dysfunction in patients with the Shy-Drager syndrome was widespread but of variable severity and distribution. Subcutaneous administration of the parasympathomimetic agent bethanechol demonstrated hyperresponsiveness of lacrimal, salivary, oesophageal, bowel, bladder and sudomotor functions. It is suggested that the Shy-Drager syndrome is primarily a preganglionic cholinergic disorder with transsynaptic degeneration accounting for the development of postganglionic cholinergic as well as adrenergic dysfunction.

Bronchial hyperresponsiveness to acetylcholine in patients with vasospastic angina pectoris

STUDY OBJECTIVE

To investigate the similarity between coronary vasospasm and bronchial spasm.

DESIGN

Nonrandomized, case-control study.

SETTING

Referral-based clinics for cardiac and pulmonary disease at one secondary care center.

PATIENTS

Seventeen patients with vasospastic angina pectoris (VSAP) and 14 patients with chest pain syndrome (CPS).

INTERVENTIONS

Medications prohibited: those with known effects on bronchial responsiveness.

MEASUREMENT

Induction of coronary vasospasm: ergonovine maleate (10, 20, 40 micrograms) injection into coronary arteries during coronary angiography. Bronchial responsiveness to acetylcholine (ACh): acetylcholine chloride (0.08 to 20 mg/ml) inhalation and calculation of the provocative concentration of ACh (PC20-ACh) that revealed 20 percent fall in FEV1.

RESULTS

The median value for PC20-ACh in patients with VSAP, 7.80 mg/ml, was significantly lower than that in patients with CPS, > 20.0 mg/ml (p < 0.01 by Mann-Whitney U test). The PC20-ACh in patients with VSAP, however, was correlated neither with the responsive threshold of ergonovine maleate, which induced coronary vasospasm, nor with the duration from the latest angina attack.

CONCLUSION

These results suggest that bronchial responsiveness was increased in most patients with VSAP, but not with CPS. We therefore speculate that patients with VSAP may also have hypercontractibility to ACh of noncoronary systemic smooth muscles.

Comparative studies on the inhibitory effects of calcium antagonists on cytosolic Ca2+ levels increased by high-potassium or glutamate in cultured rat cerebellar granule cells

The inhibitory effects of calcium antagonists on high-potassium or glutamate (Glu) enhanced intracellular calcium ion ([Ca2+]i) levels were studied in cultured cerebellar granule cells. Dosages between 0.5 and 10 microM of flunarizine, nicardipine, SM6586 and SM12565 reduced the rise in [Ca2+]i induced by 50 mM KCl in a dose-dependent manner, although diltiazem, verapamil and nifedipine showed less effects on such [Ca2+]i increases. SM6586, SM12565 and flunarizine at dosages below 10 microM each reduced the magnitude of the [Ca2+]i increase induced by 25 microM Glu, but the other examined calcium antagonists were less effective. These results suggest the dissimilar efficacy of calcium antagonists on the inhibition of [Ca2+]i levels increased by high-potassium and Glu.

Effect of H1 receptor stimulation on coronary artery diameter in patients with variant angina: comparison with effect of acetylcholine

It has been suggested that histamine is involved in the pathogenesis of coronary spasm but its exact role remains unclear. H1 receptor stimulation of the coronary artery was performed with a selective intracoronary infusion of histamine (2 micrograms/min) in 21 patients with variant angina after blockade of the H2 receptor with cimetidine (25 mg/kg) and its effect on the coronary artery diameter was examined. Intracoronary injection of acetylcholine was also performed in 19 of the 21 patients. Ergonovine (0.2 mg) was intravenously administered in one patient. The coronary artery diameter was measured with cinevideodensitometric analysis. A mean plasma histamine concentration in the coronary sinus increased from 4 x 10(-9) to 7 x 10(-8) M 5 min after histamine infusion into the left coronary artery (n = 18). Coronary spasm was induced in 6 patients (29%) with histamine, in 18 (95%) with acetylcholine and in 1 with ergonovine. The effect of histamine on the luminal diameter was analyzed at the site of spasm in the 26 coronary arteries in which spasm was induced by acetylcholine or ergonovine. Of the 20 coronary arteries with a normal arteriogram or a fixed stenosis less than or equal to 50% of luminal diameter, histamine decreased the diameter in 4, increased it in 14 (70%) and caused no change in 2; of the 6 coronary arteries with a fixed stenosis greater than or equal to 75%, histamine decreased the diameter in 5 and increased it in 1. In the coronary arteries in which spasm was not induced by either acetylcholine or ergonovine, histamine increased the diameter, especially in those without advanced atherosclerosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental induction of spasm, sudden progression of organic stenosis and intramural hemorrhage in the epicardial coronary arteries

Pathogenesis of the so-called "heart attack" still remains to be elucidated. The links between stable effort angina and unstable or acute myocardial infarction, and between asymptomatic and spontaneous angina are all missing. In medicine presently, pathophysiology of ischemic heart disease is considered a consequence of i) the progression of atherosclerotic narrowing of the coronary artery, and ii) dynamic and transient obstruction (coronary spasm), but these mechanisms are traditionally believed to be unrelated. This article demonstrates various experimental evidence indicating that these two mechanisms are related. And, this review article describes how to produce experimental coronary spasm in the presence of atherosclerosis, similar to that seen in patients with variant angina, and that coronary spasm can produce sudden progression of coronary atherosclerotic obstruction due to intramural hemorrhage. Establishment of various animal models to elucidate mechanisms related to various stages of ischemic heart disease are needed.

Comparative sensitivity of intracoronary injection of acetylcholine for the induction of coronary spasm in patients with various types of angina pectoris

To elucidate the possible contribution of coronary artery spasm to the pathogenesis of angina pectoris, coronary arterial responses to intracoronary injection of acetylcholine were examined in patients with various types of angina pectoris. Coronary artery spasm with chest pain and/or electrocardiographic ischemic changes was angiographically demonstrated in 50 (85%) of 59 patients with angina pectoris. The sensitivity for coronary spasm was 92% (24 of 26) in patients with rest angina, 100% (16 of 16) in patients with both rest and effort angina, and 59% (10 of 17) in patients with effort angina, while it was only 6% (1 of 16) in patients without coronary artery disease. When patients with effort angina were subdivided according to the variability of anginal threshold for exertional angina, the sensitivity for coronary spasm was as high as 90% (9 out of 10) in patients with variable-threshold angina. In contrast, coronary spasm was less frequently (p less than 0.05) induced in patients with fixed-threshold angina (1 of 7, 14%). These results suggest that coronary arteries in patients with angina pectoris are quite susceptible to acetylcholine except in those patients with stable exercise tolerance or anginal threshold. Thus coronary artery spasm appears to play a significant role for the pathogenesis of angina pectoris in a large proportion of patients with effort angina as well as in patients with rest angina.

Indomethacin attenuates the constriction of canine epicardial coronary arteries to acetylcholine in the absence of endothelium: contribution of platelets to vasoconstriction in vivo

This study was designed to evaluate the in vivo effect of acetylcholine on endothelial-damaged canine epicardial coronary arteries and the potential contribution of platelets to those acetylcholine-induced responses. Changes in left anterior descending artery cross-sectional area were determined by quantitative angiography in the closed chest anesthetized dog. Baseline cross-sectional area of the left anterior descending artery was not changed by removal of the endothelium by balloon-tipped catheter. Increased constrictor tone produced by prostaglandin F2 alpha was comparable in endothelium-intact and endothelium-removed vessels, supporting an endothelium-independent mechanism for prostaglandin F2 alpha in vivo. Acetylcholine produced anterior descending artery vasodilation with the endothelium intact; a comparable maximal dilator response was also obtained in the presence of increased constrictor tone (prostaglandin F2 alpha). In contrast, acetylcholine produced vasoconstriction of the anterior descending artery when the endothelium was removed. To evaluate the mechanism of acetylcholine-induced vasoconstriction in endothelium-removed vessels, the same protocol was completed in the presence of the platelet inhibitor indomethacin. Indomethacin did not alter baseline cross-sectional area or the dilator response to acetylcholine in endothelium-intact vessels. In contrast, the constrictor response in endothelium-removed vessels was antagonized, and a dilator response comparable with that in endothelium-intact vessels was produced by acetylcholine. The results of this study provide an experimental basis for the observations in human studies in which apparently atherosclerotic vessels constrict in response to acetylcholine. Removal of the endothelium in vivo abolishes the dilator response to acetylcholine and converts the acetylcholine response to vasoconstriction or vasospasm.(ABSTRACT TRUNCATED AT 250 WORDS)

Circadian variation of plasma fibrinopeptide A level in patients with variant angina

Plasma levels of fibrinopeptide A (FPA), beta-thromboglobulin (BTG), and platelet factor 4 (PF4) were examined on venous plasma samples taken every 4 hours for 24 hours in 20 patients with variant angina and 20 patients with stable exertional angina together with 24-hour Holter recordings. The mean plasma FPA levels (ng/ml) at 2:00 PM, 6:00 PM, 10:00 PM, 2:00 AM, 6:00 AM, and 10:00 AM were 4.6 +/- 1.0, 3.1 +/- 0.5, 6.1 +/- 1.6, 9.9 +/- 2.4, 8.7 +/- 1.4, and 4.2 +/- 0.8 in patients with variant angina (p less than 0.01) and 1.8 +/- 0.2, 2.3 +/- 0.3, 1.9 +/- 0.3, and 2.3 +/- 0.2 in those with stable exertional angina. In seven patients with variant angina, we also examined the effects of heparin (3,000 units), given subcutaneously at 6:00 PM, 10:00 PM, and 2:00 AM, on the plasma FPA levels and the anginal attacks. Although heparin suppressed the elevation and circadian variation of plasma FPA levels, it did not suppress the attacks and their circadian variation in these patients. Plasma FPA levels increased significantly from 3.7 +/- 0.5 to 12.5 +/- 2.7 ng/ml during or immediately after an attack in the seven patients with no heparin. On the other hand, the plasma levels of BTG and PF4 were increased in patients with variant angina as compared with those with stable exertional angina but did not show a significant circadian variation in both groups. We conclude that 1) plasma levels of FPA, BTG, and PF4 were increased in patients with variant angina as compared with those with stable exertional angina; 2) there was a significant circadian variation in the plasma levels of FPA in parallel with that of the frequency of the attacks with the peak level occurring from midnight to early morning in patients with variant angina; and 3) elevated levels of plasma FPA are the result and not the cause of coronary spasm.

Cholinergic constriction in the general circulation and its role in coronary artery spasm

The release of acetylcholine from autonomic nerves in those tissues that receive a cholinergic innervation is widely believed to dilate blood vessels. Exogenously administered acetylcholine in vivo does dilate vascular beds and produce hypotension; however, this latter effect is indirect and probably the result of liberation of endothelium-derived relaxing factor (EDRF) from endothelial cells. Some blood vessels contain a substantial population of medial constrictor receptors for acetylcholine, and the implications of this presence for vascular control systems has been largely ignored, although it needs to be considered. A survey of the evolution of vasomotor control systems indicates that acetylcholine serves principally as an excitatory transmitter to blood vessels. Neurally mediated cholinergic constriction and not dilation is found in fish, amphibians, reptiles, and birds, with responses initiated by medial muscarinic receptors. Acetylcholine constricts many vascular preparations from these lower animals, but some vessels relax, reflecting the emergence of an EDRF responsive to acetylcholine. An examination of cholinergic responses in mammalian vessels reveals that cholinergic (neurogenic) dilation is limited to a very few vascular beds and to only a few species. Both experimental evidence and evolutionary considerations support the likelihood that cholinergic (neural) constriction operates in some vascular regions in mammals and, in particular, in the coronary circulation of some species, including humans. In fact, constriction, and not dilation, may be the dominant vascular response to activation of the cholinergic axis in most mammals, including humans. The complications and contradictions introduced by the simultaneous presence of both EDRF and a cholinergic constrictor innervation involving medial muscarinic receptors are discussed. A variety of evidence is also presented that implicates cholinergic constriction in at least some instances of coronary artery spasm and sudden death.

Nicorandil: animal pharmacology

Nicorandil, a nicotinamide derivative, is a recently developed, orally active antianginal drug with a cardioprotective activity, and its pharmacologic properties differ from those of conventional antianginal drugs. Nicorandil has the capacity to increase myocardial oxygen supply without increasing oxygen demand by reduction in preload and afterload. In isolated blood-perfused canine heart preparations, when injected into the sinus node, the atrioventricular node or the anterior septal arteries, nicorandil at dose levels doubling blood flow through the respective arteries has virtually no effect on sinus rate, atrioventricular conduction time or contractile force of ventricular muscle. This may indicate that nicorandil possesses a selective effect on the coronary vasculature rather than on the myocardium. Furthermore, the vasospasmolytic activity of nicorandil has been evidenced in in vivo and in vitro experiments. The precise mechanism by which nicorandil develops coronary vasodilating and vasospasmolytic effects remains to be elucidated, but it may be partly inferred by an increase in the potassium conductance in the membrane, a relation with cyclic guanosine monophosphate formation, or inhibition of intracellular calcium ion mobilization in the cell of coronary vascular smooth muscle. Nicorandil possesses a nitrate moiety in its chemical structure. However, it is noted that nicorandil unlike nitrates does not develop tolerance or cross tolerance to other conventional nitrates in terms of blood-pressure lowering effects and coronary vasodilating effects. Thus, nicorandil is likely to have highly beneficial properties in the treatment of angina pectoris.

Comparison of the muscarinic receptors in the coronary artery, cerebral artery and atrium of the pig

The affinity of various muscarinic antagonists for the muscarinic receptors mediating contraction (induced by acetyl-beta-methylcholine) of the isolated pig coronary and basilar artery was determined in order to compare the muscarinic receptor subtype involved in the contractile response of these arteries. In order to identify the muscarinic receptor subtype(s) involved, the affinity of the antagonists for the M2 receptor present in the pig atria was also investigated. The following muscarinic antagonists were used: atropine, pirenzepine, AF-DX 116 (11-2[[2-[(diethylamino)methyl]-1- piperidinyl]acetyl]-5,11-dihydro-6H- pyrido[2,3-b][1,4]benzodiazepin-6-one),4-DAMP(4-diphenylacetoxy-N- methylpiperidine methiodide), HHSiD (hexahydrosiladifenidol), methoctramine (N,N'-bis[6-[(2- methoxybenzyl)amino]hexyl]-1,8-octane-diamine tetrahydrochloride) and ipratropium. The order of affinity of the antagonists with respect to the muscarinic receptor in the coronary artery was clearly different from that for the muscarinic receptor in the basilar artery. The order of affinity established on the basilar artery closely resembled that for the M2 receptor in the atria. It is concluded that the muscarinic receptors on smooth muscle of the coronary and basilar arteries are not identical. The muscarinic receptor involved in the contraction of the basilar artery adheres to the M2 receptor subtype. A comparison of the selectivity of the antagonists suggests that the muscarinic receptor involved in the contraction of the coronary artery belongs to the M3 (like in exocrine glands) or M4 (as found in ileal smooth muscle) receptor subtype.

Coronary artery spasm in the genesis of myocardial ischemia

Angina pectoris that is mainly caused by coronary artery spasm (coronary spastic angina) has 1 or more of the following characteristics: (1) the attack occurs at rest, (2) the attack is associated with ST-segment elevation on the electrocardiogram (not necessarily so in case of old myocardial infarction), (3) the attack has a variable exercise threshold, and (4) the attack is suppressed by calcium antagonists but not by beta-adrenergic blocking agents. By this criteria, coronary artery spasm is involved in the development of most angina pectoris in patients with 1-vessel disease. The role of coronary artery spasm in the development of acute myocardial infarction is still controversial. However, in this study, injection of nitroglycerin, 0.2 mg, into the totally or subtotally occluded coronary artery either released the occlusion or improved the patency in 13 of the 69 patients (18.8%) with acute transmural myocardial infarction in whom coronary arteriography was performed within 4.0 +/- 1.9 hours of the onset of symptoms. Thus, coronary artery spasm appears to play a role in the production of acute myocardial infarction in these patients.

Sensitivity and specificity of intracoronary injection of acetylcholine for the induction of coronary artery spasm

Intracoronary injection of acetylcholine has been shown to induce coronary spasm in patients with variant angina. To examine its sensitivity and specificity, incremental doses of acetylcholine (20, 50 and 100 micrograms into the left coronary artery and 20 and 50 micrograms into the right coronary artery) were injected into the coronary artery or arteries in 70 patients with variant angina (Group 1) (mean age 57 years) and 93 patients without variant angina or angina at rest (Group 2) (mean age 54 years). Forty patients of the latter group had atypical chest pain, 16 cardiomyopathy, 14 arrhythmia, 11 valvular disease, 7 stable effort angina due to advanced coronary artery disease, 3 congenital heart disease and 2 hypertension. A temporary cardiac pacemaker set at 40 to 50 beats/min was positioned in the right ventricle. Coronary spasm was defined as total occlusion or severe vasoconstriction associated with chest pain or ischemic ST changes on the electrocardiogram or both. In Group 1, acetylcholine induced spasm in 63 (90%) of the 70 patients in the artery or arteries predicted to be responsible for spontaneous attacks. In Group 2, acetylcholine induced coronary spasm only in one patient with effort angina and advanced coronary artery disease although lesser degrees of vasoconstriction (less than or equal to 75% of the luminal diameter) occurred in most patients after acetylcholine (specificity of acetylcholine thus was 99%). In conclusion, intracoronary injection of acetylcholine is sensitive and reliable for the induction of coronary spasm.

Effects of perivascular nerve stimulation on the flow rate in isolated epicardial coronary arteries of pigs

The effect of perivascular nerve stimulation on coronary contraction was examined by perfusing the isolated epicardial coronary artery of pigs. Coronary flow decreased in a frequency-dependent manner after electrical stimulation, with a maximum percent flow reduction of 23.8 +/- 1.1% (n = 10) at 20 Hz. The reduction in flow rate was not inhibited by phentolamine nor propranolol but was inhibited by atropine. Neostigmine enhanced the flow reduction induced by nerve stimulation. Acetylcholine reduced the flow rate dose dependently but norepinephrine showed no effect. We conclude that perivascular nerve stimulation of the epicardial coronary artery of pigs causes a modest flow reduction through activation of a cholinergic mechanism.

Relationship between fluctuations in heart rate and asymptomatic nocturnal ischaemia

In order to quantify autonomic changes related to asymptomatic nocturnal myocardial ischaemia, we analyzed heart rate fluctuations recorded during Holter monitoring in 9 subjects with coronary heart disease (21 episodes) and in 11 age-matched controls. R-R interval spectral analysis was computed in sequences of 256 heart beats, taken during the ischaemic episode, 4, 8 and 60 minutes before, and 4 and 60 minutes after. Mean heart rate, R-R interval variability (assessed by R-R interval standard deviation), low and high (respiration-linked) frequency components of R-R interval spectrum were evaluated. Mean heart rate and R-R interval variability increased only during ischaemia (from 62.9 to 73.3 beats/minute, P less than 0.02, and from 39 to 88 msec, P less than 0.01, respectively). While high-frequency components of heart rate variability remained unchanged, low-frequency peak increased during ischaemia (from 9.4 to 43.3 sec2 X 10(-3)/Hz, P less than 0.01) and also 8 minutes (P less than 0.05) and 4 minutes before (P less than 0.05). Despite a moderate increase of heart rate occurring only during ischaemia, the early rearrangement of heart rate fluctuations suggests the occurrence of changes of autonomic tone before the electrocardiographic onset of ischaemia. Due to its limited amount, this phenomenon appears to be a consequence, most likely unspecific, of factors responsible for the genesis of myocardial ischaemia.

Prevention of vasospastic angina by alcohol ingestion: report of 2 cases

The authors report 2 patients with vasospastic angina in whom alcohol ingestion was effective in preventing angina. Coronary angiography revealed no organic coronary stenosis but demonstrated coronary artery spasm during angina attacks. In 1 patient, alcohol ingestion every six hours completely suppressed frequent spontaneous angina. In the other patient, alcohol ingestion markedly prolonged the duration of the exercise on treadmill testing by preventing exercise-induced coronary spasm.

Reactivity of isolated porcine coronary resistance arteries to cholinergic and adrenergic drugs and transmural pressure changes

The reactivity of porcine intramyocardial resistance arteries (223 +/- 7 micron i.d., n = 30) was investigated with a pressurized in vitro preparation. Diameter changes in response to acetylcholine and to adrenergic drugs and dynamic changes in transmural pressure changes were investigated. Acetylcholine produced concentration-dependent constrictions, causing maximal reductions of 71 +/- 3% in lumen diameter, with EC50 values averaging 1.9 X 10(-7) M (n = 7). These responses were inhibited by atropine (10(-7) M) and therefore were mediated by muscarinic receptors. In addition, acetylcholine did not elicit relaxation in nine out of 10 vessels precontracted with U46619 (10(-7) M). Norepinephrine and epinephrine never produced constrictions (n = 6) even in the presence of propranolol (10(-6) M). Both norepinephrine and isoproterenol caused dose-dependent relaxations in acetylcholine-precontracted vessels, with IC50 values of 8.2 X 10(-7) M (n = 5) and 6.6 X 10(-8) M (n = 6), respectively. These relaxations were suppressed by propranolol. Between transmural pressures of 10 and 90 mm Hg, there was no intrinsic myogenic tone (n = 7). In addition, the vessels responded only passively to sudden pressure changes of 40 mm Hg. In all vessels, the functional integrity of the endothelium was verified by relaxations to substance P (10(-8) M) and/or bradykinin (10(-8) M).(ABSTRACT TRUNCATED AT 250 WORDS)

Supersensitivity of coronary arteries in variant angina to spasm induced by intracoronary acetylcholine

Acetylcholine (20 to 100 micrograms) was infused directly into coronary arteries in 10 patients with variant angina (group A), 13 subjects without coronary artery disease (group B) and 8 patients with significant organic coronary artery stenosis (greater than or equal to 50%) but without variant angina (group C) during coronary arteriography, to clarify the action of this agent on coronary arteries. Temporary pacing was performed at a demand heart rate of 40 beats/min while bradyarrhythmia developed. Coronary arteriography after administration of acetylcholine showed coronary vasoconstriction in all 10 patients (100%) of group A. Angina accompanied by electrocardiographic ischemic changes in 9 of 10 (90%, 7 ST-segment elevation and 2 depression) was provoked during this test. In the patients of group B, acetylcholine also induced vasoconstriction in 8 of 22 (36%) coronary arterial systems examined, chest pain in 3 (14%) and ST-segment deviation in none (0%). In the patients of group C, acetylcholine induced vasoconstriction in 3 of 9 (33%), chest pain in 2 (22%) and ST-segment depression in 1 (11%). No definite coronary artery dilation induced by acetylcholine was noted. Coronary vasoconstriction (p less than 0.05), electrocardiographic ischemic findings (p less than 0.01) and chest pain (p less than 0.01) were induced significantly more frequently in group A than in both groups B and group C. No significant difference was found between group B and group C. The coronary arteries in the patients with variant angina seem to be more susceptible to acetylcholine than those of patients without variant angina irrespective of the presence of significant atherosclerosis.

Autonomic control of large coronary arteries and resistance vessels

The resistance coronary vessels as well as the large coronary arteries are regulated to a major extent by autonomic mechanisms. Neural and pharmacologic activation of alpha-adrenergic pathways can reduce coronary blood flow and the cross-sectional area of large coronary arteries, despite concomitant increases in coronary distending pressure. Activation of either beta 1- or beta 2-adrenergic receptors can induce potent dilation of both coronary resistance vessels and large coronary arteries, whereas blockade of these receptors can elicit profound constriction in the presence of elevated beta-adrenergic tone. The regulation of the coronary circulation by parasympathetic mechanism remains the most controversial, likely because of major species differences. Parasympathetic coronary dilation is uniformly observed in the dog, but in primates, important aspects of parasympathetic-mediated coronary vasoconstriction have also been demonstrated.

Findings from long-term electrocardiographic monitoring of patients with variant angina in a coronary care unit

Eleven patients with frequent episodes of variant angina underwent 24-hour electrocardiographic monitoring in a coronary care unit for a total of 70 days to assess circadian variation in ischemic episodes and its correlation with circadian heart rate (HR) rhythm. In each patient a series of 4 to 13 consecutive days, in the absence of therapy, with 8 or more ischemic episodes per day were analyzed. Harmonic regression models were fitted to the hourly number of ischemic episodes and the hourly values of HR. Out of 54 days, with 8 or more episodes per day for a total of 1,357 episodes, a circadian rhythm was observed for 34 days (64%), in at least 1 day in all patients and during the entire period of observation in only 3. Its presence was independent of the number of episodes; the peak of periodic functions occurred at 2.9 +/- 2.7 AM. A cadian rhythm for HR was observed in 61 of the 70 days (87%), consistently in 7 patients; the nadir occurred at 2.4 +/- 1.5 AM; simultaneous cycling in HR and transient ischemia was found on 32 days. The intrapatient difference between the peak and the nadir of the ischemic and the HR function was, on average, 2.6 +/- 3.3 hours. Thus, a circadian rhythm of ischemic episodes was present in all patients although it was not consistently present; simultaneous occurrence of circadian variation in ischemic episodes and HR was observed only in 60% of the days with a sufficiently high number of attacks and when this occurred, a significant phase shift was observed; occasional loss of HR cycling was observed in some patients, without an apparent cause.

Noninvasive demonstration of underlying severe coronary disease in patients with vasospastic angina

Dipyridamole test, isoproterenol test, and treadmill exercise test were performed in two groups of patients with vasospastic angina (Group 1: 10 patients with 70% or greater coronary narrowings, Group 2: 8 patients with narrowings less than 70%. The results were correlated with coronary anatomy. In Group 1, vasodilation of resistance vessels by dipyridamole elicited ischemic episodes in 9 patients and an increase in myocardial oxygen consumption by isoproterenol caused anginal attacks in 7 patients. None of patients of Group 2 showed positive responses to either drug. All patients of Group 1, and 3 patients of Group 2 gave positive responses to treadmill test. These observations show that several different mechanisms are involved in the pathogenesis of myocardial ischemia in patients with vasospastic angina. Pharmacological interventions have higher specificity than exercise tests in predicting coronary anatomy and are useful for the choice of therapy in the patients.

Louis F. Bishop lecture. Role of coronary artery spasm in symptomatic and silent myocardial ischemia

The revival of the concept of coronary spasm has stimulated research into coronary artery disease. Observations in patients with variant angina have substantially contributed to the appreciation of painless myocardial ischemia. However, the presence or absence of pain during ischemic episodes is not related to the cause of ischemia, because painless ischemia can be observed in variant angina (caused by spasm), in effort-induced angina (caused by increased myocardial demand) and in myocardial infarction (caused by thrombosis). Continuous monitoring initially of patients with variant angina and subsequently of patients with unstable and stable angina proved that often painful and painless ischemic episodes are caused by a transient impairment of regional coronary blood flow rather than by an excessive increase of myocardial demand. The transient impairment of coronary flow appears to be caused by dynamic stenosis of epicardial coronary arteries. This most often occurs at the site of atherosclerotic plaques encroaching on the lumen to a variable extent. Dynamic stenosis can be caused by 1) "physiologic" increase of coronary tone, as in stable angina, 2) spasm, as in variant angina, and 3) thrombosis, usually in combination with "physiologic" changes in tone or with spasm, or both, as in unstable angina. The mechanisms of spasm, as typically observed in variant angina, are different from those of "physiologic" increase of tone; they appear to be related to a local alteration that makes a segment of coronary artery hyperreactive to a variety of constrictor stimuli causing only minor degrees of constriction in other coronary arteries. The nature of this abnormality, which may remain stable for months and years, is yet unknown.

Calcium antagonists for Prinzmetal's variant angina, unstable angina and silent myocardial ischemia: therapeutic tool and probe for identification of pathophysiologic mechanisms

The calcium antagonists provide a unique tool to reduce myocardial oxygen demand and prevent increases in coronary vasomotor tone. For patients with Prinzmetal's variant angina, diltiazem, nifedipine and verapamil are extremely effective in preventing episodes of coronary vasospasm and symptoms of ischemia. Unstable angina pectoris is a more complex pathophysiologic syndrome with episodes of ischemia due to increases in coronary vasomotor tone, intermittent platelet aggregation or alterations in the underlying atherosclerotic plaque. Each of the calcium antagonists is effective as monotherapy in decreasing the frequency of angina at rest. Nifedipine is the only calcium antagonist that has been studied in a combination regimen with beta blockers and nitrates for patients with unstable angina, and control of angina is better with the combination regimen than with either form of therapy alone. Although symptoms of myocardial ischemia in unstable angina are reduced by calcium antagonists, these agents do not seem to decrease the incidence of adverse outcomes. Antiplatelet therapy appears to improve morbidity and mortality in patients with unstable angina, suggesting that thrombus formation may play a central role in that disorder. Episodes of silent or asymptomatic myocardial ischemia, identified by ST-segment monitoring, occur in a variety of disorders of coronary disease. Among patients with Prinzmetal's variant angina and unstable angina, episodes of silent ischemia appear to be as frequent as episodes of angina and the calcium antagonists are effective in decreasing episodes of ischemia regardless of the presence or absence of symptoms. Persisting episodes of silent ischemia among patients with unstable angina despite maximal medical therapy identify patients at high risk for an early unfavorable outcome. Among patients with stable exertional angina, episodes of silent ischemia may be up to 5 times as frequent as episodes of angina, and may be due to increases in coronary vasomotor tone, transient platelet aggregation or increases in myocardial oxygen demand. Preliminary experience suggests that calcium antagonists and beta blockers are effective in decreasing episodes of silent ischemia in patients with stable exertional angina and that a combination regimen may be more effective than either form of therapy alone.

Pathogenesis of coronary artery spasm in miniature swine with regional intimal thickening after balloon denudation

Pathogenesis of coronary artery spasm induced by histamine in miniature pigs was studied angiographically in in vivo and in vitro conditions. Endothelial balloon denudation was performed and the animals were fed laboratory chow for 3 months, after which coronary artery spasm was repeatedly provoked by histamine given intracoronarily. Regional hypercontraction of the coronary artery was documented by selective coronary arteriography, and the resulting myocardial ischemia was confirmed by ECG-ST changes. To evaluate coronary artery spasm without the influence of blood constituents and neural control and to quantitate the pharmacophysiological characteristics of histamine-induced coronary constriction in the coronary spasm, the same heart was isolated and perfused with Krebs-Henseleit solution under a constant perfusion pressure of 90 mm Hg. Histamine (10(-5) M) reduced the diameter of the coronary artery of the isolated heart by 29 +/- 4 and 67 +/- 3% (p less than 0.001) in nondenuded and denuded areas, respectively. These figures were similar to data obtained angiographically in vivo after the administration of histamine 10 micrograms/kg. The constriction of the denuded areas in response to histamine was topologically the same in vivo and in vitro. The degree of focal constriction induced by histamine, defined as a percent of stenoses from the mean diameter of the areas of proximal and distal to the spastic site, was similar in in vivo (10 micrograms/kg i.c.) and in vitro (10(-5) M) conditions. KCl (40 mM) reduced both the denuded and nondenuded coronary artery diameter by 67 +/- 3% and 68 +/- 3% (NS), respectively. The dose-response relation of the coronary diameter to histamine was not influenced by pretreatment with the nerve transmitter blockers guanethidine (3 X 10(-6) M), atropine (10(-6) M), and tetrodotoxin (3 X 10(-7) M). Phenylephrine (10(-5) M) did not potentiate constriction of the denuded areas.(ABSTRACT TRUNCATED AT 250 WORDS)