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

Sex-specific and ethnicity-specific differences in MINOCA

Suspected myocardial infarction with non-obstructive coronary arteries (MINOCA) has received increasing attention over the past decade. Given the heterogeneity in the mechanisms underlying acute myocardial infarction in the absence of obstructive coronary arteries, the syndrome of MINOCA is considered a working diagnosis that requires further investigation after diagnostic angiography studies have been performed, including coronary magnetic resonance angiography and functional angiography. Although once considered an infrequent and low-risk form of myocardial infarction, recent data have shown that the prognosis of MINOCA is not as benign as previously assumed. However, despite increasing awareness of the condition, many questions remain regarding the diagnosis, risk stratification and treatment of MINOCA. Women seem to be more susceptible to MINOCA, but studies on the sex-specific differences of the disease are scarce. Similarly, ethnicity-specific factors might explain discrepancies in the observed prevalence or underlying pathophysiological mechanisms of MINOCA but data are also scarce. Therefore, in this Review, we provide an update on the latest evidence available on the sex-specific and ethnicity-specific differences in the clinical features, pathophysiological mechanisms, treatment and prognosis of MINOCA.

Coronary Artery Vasospasm in Patients With Eosinophilia

Coronary vasospasm is a relatively well-documented cause for ischemia and myocardial infarction in patients with nonobstructive coronary artery disease. Patients with coexisting eosinophilia present with severe manifestations and are often refractory to traditional therapies. There are few reported cases in the literature. We describe 3 cases occurring within 10 months. (Level of Difficulty: Intermediate.).

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.

Apolipoprotein (a)/Lipoprotein(a)-Induced Oxidative-Inflammatory α7-nAChR/p38 MAPK/IL-6/RhoA-GTP Signaling Axis and M1 Macrophage Polarization Modulate Inflammation-Associated Development of Coronary Artery Spasm

Objective. Apolipoprotein (a)/lipoprotein(a) (Lp(a)), a major carrier of oxidized phospholipids, and α7-nicotinic acetylcholine receptor (α7-nAChR) may play an important role in the development of coronary artery spasm (CAS). In CAS, the association between Lp(a) and the α7-nAChR-modulated inflammatory macrophage polarization and activation and smooth muscle cell dysfunction remains unknown. Methods. We investigated the relevance of Lp(a)/α7-nAChR signaling in patient monocyte-derived macrophages and human coronary artery smooth muscle cells (HCASMCs) using expression profile correlation analyses, fluorescence-assisted cell sorting flow cytometry, immunoblotting, quantitative real-time polymerase chain reaction, and clinicopathological analyses. Results. There are increased serum Lp(a) levels (3.98-fold, $p=0.011$ ) and macrophage population (3.30-fold, $p=0.013$ ) in patients with CAS compared with patients without CAS. Serum Lp(a) level was positively correlated with high-sensitivity C-reactive protein ( $r^2=0.48$ , $p<0.01$ ), IL-6 ( $r^2=0.38$ , $p=0.03$ ), and α7-nAChR ( $r^2=0.45$ , $p<0.01$ ) in patients with CAS, but not in patients without CAS. Compared with untreated or low-density lipoprotein- (LDL-) treated macrophages, Lp(a)-treated macrophages exhibited markedly enhanced α7-nAChR mRNA expression ( $p<0.01$ ) and activity ( $p<0.01$ ), in vitro and ex vivo. Lp(a) but not LDL preferentially induced CD80+ macrophage (M1) polarization and reduced the inducible nitric oxide synthase expression and the subsequent NO production. While shRNA-mediated loss of α7-nAChR function reduced the Lp(a)-induced CD80+ macrophage pool, both shRNA and anti-IL-6 receptor tocilizumab suppressed Lp(a)-upregulated α7-nAChR, p-p38 MAPK, IL-6, and RhoA-GTP protein expression levels in cultures of patient monocyte-derived macrophages and HCASMCs. Conclusions. Elevated Lp(a) levels upregulate α7-nAChR/IL-6/p38 MAPK signaling in macrophages of CAS patients and HCASMC, suggesting that Lp(a)-triggered inflammation mediates CAS through α7-nAChR/p38 MAPK/IL-6/RhoA-GTP signaling induction, macrophage M1 polarization, and HCASMC activation.

Diagnostic and Prognostic Value of Ergonovine Echocardiography for Noninvasive Diagnosis of Coronary Vasospasm

OBJECTIVES

This study sought to obtain large-scale evidence supporting the clinical usefulness of ergonovine echocardiography.

BACKGROUND

The role of noninvasive ergonovine provocation testing with echocardiographic monitoring of ventricular wall motion (ergonovine echocardiography) needs to be defined.

METHODS

Clinical data of patients who underwent ergonovine echocardiography in 3 tertiary referral hospitals in South Korea were analyzed.

RESULTS

Ergonovine echocardiography was performed in 14,012 patients (mean age 52.8 ± 11.1 years; 6,213 [44.3%] women) after exclusion of significant coronary arterial stenosis by functional (treadmill or perfusion scan, n = 9,824) or anatomic test (invasive or computerized tomographic coronary angiography, n = 4,188). Premature termination developed in 0.4% (n = 51), and a positive result was observed in 2,144 patients (15.3%), with variable frequencies according to the diagnosis (acute coronary syndrome [38.2%], variant angina [31.8%], effort angina [14.9%], aborted sudden cardiac death [17.6%], syncope [9.9%]). There was no mortality or development of myocardial infarction during the test. During median follow-up of 11.4 (interquartile range: 7.2 to 15.8) years, death of any cause and cardiovascular death occurred in 494 and 143 patients, respectively. The 10-year overall (96.7 ± 0.2% vs. 91.5 ± 0.6%; p < 0.0001) and cardiovascular mortality-free (99.2 ± 0.1% vs. 96.7 ± 0.4%; p < 0.0001) survival rates were lower in patients with positive ergonovine echocardiography. Regarding patients with positive test results, the functional test group and the anatomic test group did not show a significant difference in the survival rates. After adjustment of age and male sex, a positive test was an independent risk factor associated with all-cause mortality (hazard ratio: 1.879, 95% confidence interval: 1.548 to 2.280; p < 0.001) and cardiovascular death (hazard ratio: 2.903, 95% confidence interval: 2.061 to 4.089; p < 0.001).

CONCLUSIONS

Ergonovine echocardiography for coronary vasospasm diagnosis could be safely performed even without angiographic documentation of fixed coronary stenosis depending on the clinical presentation, and provided important prognostic implication. Ergonovine echocardiography can replace the invasive spasm provocation testing, which has been overlooked unfairly.

Relationship of a thinned medial layer to the attenuated contractile response in atherosclerotic coronary arteries

Coronary arteries with advanced atherosclerosis do not necessarily have greater contractile responses than those with early atherosclerosis. This study aimed to clarify the relationship between thickness of the medial layer and the contractile response to acetylcholine (ACh) in coronary artery using optical coherence tomography (OCT). The OCT and the vasomotor response to ACh in the left anterior descending coronary artery were assessed in 32 patients with previous myocardial infarction. The intimal and medial layer areas were measured by planimetric analysis of the OCT images. The coronary contractile response to ACh had a positive linear relationship with medial area (r = 0.61, P < 0.001). In contrast, the relationship between the coronary contractile response to ACh and intimal area was described by an inverted U-shaped curve that was fitted to a quadratic regression model (R² = 0.35, P = 0.002, y-axis, contraction; x-axis, intimal area). The contractile response increased as the intimal layer thickened up to the inflection point; thereafter, the contractile response declined. The relationship between medial area and intimal area was also described by an inverted U-shaped curve that was fitted to a quadratic regression model (R² = 0.41, P < 0.01, y-axis, medial area; x-axis, intimal area). The medial area increased as the intimal area thickened up to the inflection point; thereafter, the medial area thinned. In conclusion, the thinned medial layer was associated with the attenuated contractile response in a coronary artery with greater atherosclerosis.NEW & NOTEWORTHY This is the first clinical study to show the relationship between the contractile response and the thickness of medial smooth muscle layer in coronary artery of patients with previous myocardial infarction using OCT. The contractile response to acetylcholine was attenuated, and medial layer area was thinned in coronary artery with greater atherosclerosis compared with those in coronary artery with mild or moderate atherosclerosis. The coronary contractile response was positively correlated with thickness of the medial layer in coronary arteries with either mild or greater atherosclerosis. Thus, coronary arteries with advanced atherosclerosis do not necessarily have greater contractile responses than those with early atherosclerosis, which could be related to the thinned medial layer.

Coronary Artery Vasospasm

Coronary artery vasospasm (CVS) is an important mechanism of myocardial ischemia and produces any of the manifestations of coronary artery disease from silent myocardial ischemia, to effort-induced angina and variant angina, to acute coronary syndrome including myocardial infarction or sudden cardiac death. The pathogenesis, characteristic clinical features, diagnosis, and treatment of CVS are summarized. Emphasis is placed on correct diagnosis of CVS using pharmacological spasm provocation test, either during coronary angiography or with echocardiographic monitoring of ventricular wall motion. Current underutilization of pharmacologic provocative test at the time of coronary angiography cannot be justified, as there is no evidence supporting that the incidence of CVS is declining. Physicians' vigilance for objective documentation of CVS is necessary for appropriate management of patients with various clinical presentations of ischemic heart disease.

Sudden cardiac arrest and syncope triggered by coronary spasm

BACKGROUND

Patients with coronary spasm generally have a good prognosis, although it can result in sudden cardiac arrest (SCA) and syncope. We hypothesized that the nature of coronary spasm triggering lethal arrhythmias may be different from that which induces angina-only.

METHODS

Clinical characteristics were examined in patients who had experienced SCA (n = 18) or syncope (n = 28) triggered by coronary spasm. These characteristics were compared to those of patients who had coronary spastic angina-only (n = 52).

RESULTS

SCA and syncope occurred frequently during daytime in 57% and 68%, respectively. Spontaneous ST-segment changes during daytime were recorded more often in patients with SCA (50%) and syncope (39%) than angina-only patients (4%, p < 0.01 for each). Nocturnal angina occurred less frequently in patients with SCA (33%) and syncope (32%) than angina-only patients (83%, p < 0.01 for each). Severe multivessel spasm, daytime ST-segment changes, and younger age were significant predictors of SCA. Daytime ST-segment changes and active smoking were related to syncope.

CONCLUSIONS

The circadian variance of coronary spasm triggering SCA or syncope may be different from that inducing typical coronary spastic angina. The coronary spasm should be evaluated for patients with aborted SCA or recurrent syncope of unknown cause, even though the patients have not experienced the typical nocturnal angina.

Asymptomatic ST-segment depression during exercise testing and the risk of sudden cardiac death in middle-aged men: a population-based follow-up study

AIMS

Silent electrocardiographic ST change predicts future coronary events in patients with coronary heart disease (CHD), but the prognostic significance of asymptomatic ST-segment depression with respect to sudden cardiac death in subjects without apparent CHD is not well known.

METHODS AND RESULTS

We investigated the association between silent ST-segment depression during and after maximal symptom-limited exercise test and the risk of sudden cardiac death in a population-based sample of 1769 men without evident CHD. A total of 72 sudden cardiac death occurred during the median follow-up of 18 years. The risk of sudden cardiac death was increased among men with asymptomatic ST-segment depression during exercise [hazard ratio (HR) 2.1, 95% confidence interval (CI) 1.2-3.9] as well as among those with asymptomatic ST-segment depression during recovery period (HR 3.2, 95% CI 1.7-6.0). Asymptomatic ST-depression during exercise testing was a stronger predictor for the risk of sudden cardiac death especially among smokers as well as in hypercholesterolaemic and hypertensive men than in men without these risk factors.

CONCLUSION

Asymptomatic ST-segment depression was a very strong predictor of sudden cardiac death in men with any conventional risk factor but no previously diagnosed CHD, emphasizing the value of exercise testing to identify asymptomatic high-risk men who could benefit from preventive measures.

Effects of a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, fluvastatin, on coronary spasm after withdrawal of calcium-channel blockers

OBJECTIVES

The purpose of this study was to determine whether a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor (statin) suppresses coronary spasm.

BACKGROUND

Coronary spasm is associated with endothelial dysfunction. Statins have been shown to improve endothelial function.

METHODS

This was a prospective, randomized, open-label, end point study. Sixty-four patients who had no significant organic coronary stenosis and in whom coronary spasm was induced by intracoronary injection of acetylcholine (ACh) were randomly assigned to fluvastatin 30 mg/day plus the conventional calcium-channel blocker (CCB) therapy (31 patients, statin group) or the conventional CCB therapy (33 patients, nonstatin group). After 6 months of treatment, the intracoronary injection of ACh was repeated and the coronary spasm was assessed.

RESULTS

Coronary spasm was suppressed in 16 of the 31 patients (51.5%, p < 0.0001) of the statin group and in 7 of the 33 patients (21.2%, p = 0.0110) of the nonstatin group after 6 months of treatment. Thus, the number of patients with ACh-induced coronary spasm was significantly reduced in the statin group as compared with the nonstatin group (51.6% vs. 21.2%, p = 0.0231) after 6 months of treatment.

CONCLUSIONS

The addition of fluvastatin 30 mg/day to the conventional CCB therapy for 6 months significantly reduced the number of patients with ACh-induced coronary spasm as compared with the conventional CCB therapy. Thus, a statin (fluvastatin) may possibly be a novel therapeutic drug for coronary spasm.

Antianginal actions of beta-adrenoceptor antagonists

Angina pectoris is usually the first clinical sign of underlying myocardial ischemia, which results from an imbalance between oxygen supply and oxygen demand in the heart. This report describes the pharmacology of beta-adrenoceptor antagonists as it relates to the treatment of angina. The beta-adrenoceptor antagonists are widely used in long-term maintenance therapy to prevent acute ischemic episodes in patients with chronic stable angina. Beta-adrenoceptor antagonists competitively inhibit the binding of endogenous catecholamines to beta1-adrenoceptors in the heart. Their anti-ischemic effects are due primarily to a reduction in myocardial oxygen demand. By decreasing heart rate, myocardial contractility and afterload, beta-adrenoceptor antagonists reduce myocardial workload and oxygen consumption at rest as well as during periods of exertion or stress. Predictable adverse effects include bradycardia and cardiac depression, both of which are a direct result of the blockade of cardiac beta1-adrenoceptors, but adverse effects related to the central nervous system (eg, lethargy, sleep disturbances, and depression) may also be bothersome to some patients. Beta-adrenoceptor antagonists must be used cautiously in patients with diabetes mellitus, peripheral vascular disease, heart failure, and asthma or other obstructive airway diseases. Beta-adrenoceptor antagonists may be used in combination with nitrates or calcium channel blockers, which takes advantage of the diverse mechanisms of action of drugs from each pharmacologic category. Moreover, concurrent use of beta-adrenoceptor antagonists may alleviate the reflex tachycardia that sometimes occurs with other antianginal agents.

Association of platelet function in hypertensive patients with left ventricular hypertrophy, transient myocardial ischemia, and coronary artery disease

The aim of the study was to evaluate how platelet aggregation relates to left ventricular hypertrophy, presence of transient myocardial ischemia and coronary atherosclerosis in essential hypertensive patients. For that purpose platelet aggregation, symptom-limited treadmill-test, echocardiography and coronary angiography were performed in 65 male patients with uncomplicated essential hypertension. Aggregation was monitored both by a turbidometric method and by a method based on real-time estimation of mean aggregate size. Platelet function was also studied in 18 male normotensive subjects. Hypertensive patients with transient myocardial ischemia were characterized by increased platelet sensitivity to adenosine diphosphate, thromboxane A2 mimetic-U46619, serotonin, platelet activating factor and by increased spontaneous aggregability of platelets compared with normotensive subjects and to patients without myocardial ischemia. Platelet aggregation induced by low doses of agonists positively correlated with the degree of left ventricular hypertrophy. This study provides evidence that platelets play an important role in myocardial ischemia. Besides, it was found that platelet activity positively correlated with the degree of left ventricular hypertrophy. This may provide an additional link between left ventricular hypertrophy and coronary heart disease in hypertensive patients.

Coronary vasospasm secondary to hypercholinergic crisis: an iatrogenic cause of acute myocardial infarction in myasthenia gravis

Patients with myasthenia gravis undergo lifelong treatment with anticholinesterase agents. While the heart is usually unaffected by this disease, clinicians should bear in mind the potential adverse interaction between cardiac function and the underlying myasthenic disease or its specific medications. In the present article we report, to the best of our knowledge for the first time in the literature, a case of vasospastic acute myocardial infarction due to iatrogenic hypercholinergic crisis secondary to anticholinesterase therapy in an elderly female with myasthenia gravis. This clinical vignette emphasizes the importance of taking into account the potential vasospastic effect of anticholinesterase drugs. Indeed, prompt recognition of the pathophysiology of myocardial ischemia due to iatrogenic hypercholinergic crisis is pivotal to the timely and appropriate management of this medical emergency, as well as prevention of future recurrences.

Hypocapnia reduces the T wave of the electrocardiogram in normal human subjects

During voluntary hyperventilation in unanesthetized humans, hypocapnia causes coronary vasoconstriction and decreased oxygen (O2) supply and availability to the heart. This can induce local epicardial coronary artery spasm in susceptible patients. Its diagnostic potential for detection of early heart disease is unclear. This is because such hypocapnia produces an inconsistent and irreproducible effect on electrocardiogram (ECG) in healthy subjects. To resolve this inconsistency, we have applied two new experimental techniques in normal, healthy subjects to measure the effects of hypocapnia on their ECG: mechanical hyperventilation and averaging of multiple ECG cycles. In 15 normal subjects, we show that hypocapnia (20 ± 1 mmHg) significantly reduced mean T wave amplitude by 0.1 ± 0.0 mV. Hypocapnia also increased mean heart rate by 4 beats/min without significantly altering blood pressure, ionized calcium or potassium levels, or the R wave or other features of the ECG. We therefore provide the first unequivocal demonstration that hypocapnia does consistently reduce T wave amplitude in normal, healthy subjects.

Roles of KATP channels as metabolic sensors in acute metabolic changes

Physiological and pathophysiological roles of K(ATP) channels have been clarified recently in genetically engineered mice. The Kir6.2-containing K(ATP) channels in pancreatic ss-cells and the hypothalamus are essential in the regulation of glucose-induced insulin secretion and hypoglycemia-induced glucagon secretion, respectively, and are involved in glucose uptake in skeletal muscles, thus playing a key role in the maintenance of glucose homeostasis. Disruption of Kir6.1-containing K(ATP) channels in mice leads to spontaneous vascular spasm mimicking vasospastic (Prinzmetal) angina in humans, indicating that the Kir6.1-containing K(ATP) channels in vascular smooth muscles participate in the regulation of vascular tonus, especially in coronary arteries. Together with protective roles of K(ATP) channels against cardiac ischemia and hypoxia-induced seizure propagation, it is now clear that K(ATP) channels, as metabolic sensors, are critical in the maintenance of homeostasis against acute metabolic changes.

Diagnosis of coronary vasospasm by detection of postischemic regional left ventricular delayed relaxation using echocardiographic evaluation with color kinesis

BACKGROUND

Coronary vasospasm has been diagnosed by invasive provocative procedures during coronary arteriography. It would be useful to have a reliable, noninvasive, and safe diagnostic method for coronary vasospasm. Regional left ventricular (LV) diastolic dysfunction may persist without systolic dysfunction after an episode of coronary vasospasm. Color kinesis (CK) has been recently developed to facilitate the echocardiographic evaluation of regional wall motion.

HYPOTHESIS

Color kinesis may be useful for diagnosis of coronary vasospasm by detection of postischemic regional LV diastolic wall motion abnormality.

METHODS

Fifty-one consecutive patients with the last chest symptom within 2 weeks (4 +/- 3 days) were studied echocardiographically. Regional fractional area change during the first 30% of LV filling time in percentage of the segmental end-diastolic area change (CK diastolic index) was used to identify diastolic endocardial motion asynchrony.

RESULTS

After diagnostic coronary arteriography with spasm provocation, 26 patients were diagnosed with coronary spastic angina (CSA) and the other 25 with chest pain syndrome (CPS). Regional delayed relaxation (CK-diastolic index < or = 50%) or diastolic asynchrony had been observed in at least one region in 25 (96%) patients with CSA, whereas it had been noted in 2 (8%) patients with CPS. In 17 (65%) patients with CSA, it had been detected in multiple vascular territories, suggesting multivessel spasm. The diastolic asynchrony disappeared in CSA after a month of angina-free period.

CONCLUSION

Analysis of CK images allows identification of regional LV delayed relaxation or diastolic asynchrony in patients with coronary vasospasm, differentiating them from patients with chest pain syndrome (sensitivity 96%, specificity 92%).

Physiology and pathophysiology of K(ATP) channels in the pancreas and cardiovascular system: a review

K(ATP) channels are present in pancreatic and extrapancreatic tissues such as heart and smooth muscle, and display diverse molecular composition. They contain two different structural subunits: an inwardly rectifying potassium channel subunit (Kir6.x) and a sulfonylurea receptor (SURX). Recent studies on genetically engineered Kir6.2 knockout mice have provided a better understanding of the physiological and pathophysiological roles of Kir6.2-containing K(ATP) channels. Kir6.2/SUR1 has a pivotal role in pancreatic insulin secretion. Kir6.2/SUR2A mediates the effects of K(ATP) channels openers on cardiac excitability and contractility and contributes to ischemic preconditioning. However, controversy remains on the physiological properties of the K(ATP) channels in vascular smooth muscle cells. Kir6.1 knockout mice exhibit sudden cardiac death due to cardiac ischemia, indicating that Kir6.1 rather than Kir6.2 is critical in the regulation of vascular tone. This article summarizes current understanding of the physiology and pathophysiology of Kir6.1- and Kir6.2-containing K(ATP) channels.

Physiological and pathophysiological roles of ATP-sensitive K+ channels

ATP-sensitive potassium (K(ATP)) channels are present in many tissues, including pancreatic islet cells, heart, skeletal muscle, vascular smooth muscle, and brain, in which they couple the cell metabolic state to its membrane potential, playing a crucial role in various cellular functions. The K(ATP) channel is a hetero-octamer comprising two subunits: the pore-forming subunit Kir6.x (Kir6.1 or Kir6.2) and the regulatory subunit sulfonylurea receptor SUR (SUR1 or SUR2). Kir6.x belongs to the inward rectifier K(+) channel family; SUR belongs to the ATP-binding cassette protein superfamily. Heterologous expression of differing combinations of Kir6.1 or Kir6.2 and SUR1 or SUR2 variant (SUR2A or SUR2B) reconstitute different types of K(ATP) channels with distinct electrophysiological properties and nucleotide and pharmacological sensitivities corresponding to the various K(ATP) channels in native tissues. The physiological and pathophysiological roles of K(ATP) channels have been studied primarily using K(ATP) channel blockers and K(+) channel openers, but there is no direct evidence on the role of the K(ATP) channels in many important cellular responses. In addition to the analyses of naturally occurring mutations of the genes in humans, determination of the phenotypes of mice generated by genetic manipulation has been successful in clarifying the function of various gene products. Recently, various genetically engineered mice, including mice lacking K(ATP) channels (knockout mice) and mice expressing various mutant K(ATP) channels (transgenic mice), have been generated. In this review, we focus on the physiological and pathophysiological roles of K(ATP) channels learned from genetic manipulation of mice and naturally occurring mutations in humans.

Prognostic implication of ergonovine echocardiography in patients with near normal coronary angiogram or negative stress test for significant fixed stenosis

OBJECTIVES

The goal of this study was to assess the prognostic value of ergonovine echocardiography (Erg Echo) for diagnosis of coronary vasospasm (CVS) in patients without significant fixed coronary stenosis.

MATERIAL AND METHODS

Medical records of 650 patients who underwent Erg Echo were reviewed. Before Erg Echo, absence of significant fixed coronary stenosis was confirmed by invasive coronary angiography (CAG) in 316 patients (49%) or by noninvasive confirmation of negative treadmill or normal myocardial perfusion scan in 334 patients (51%). The cardiac events after Erg Echo were tabulated and these included cardiac death, myocardial infarction (MI), readmission due to intractable chest pain.

RESULTS

The average age was 54 +/- 10 years, with 223 women and 427 men. Erg Echo was positive in 237 patients (36%), for whom long-acting calcium channel blocker and nitrates were prescribed. During follow-up (46 +/- 23 months), cardiac events developed in 13% (30 of 237) of the positive Erg Echo group and 3% (14 of 413) of the negative Erg Echo group (P <.001). Incidence of cardiac death was higher in the positive Erg Echo group (3.4% vs 0.7%, P =.022). The 5-year survival rate (93% +/- 3% vs 99% +/- 1%, P =.013) and event-free survival rate (94% +/- 2% vs 77% +/- 6%, P <.001) were significantly lower in the positive Erg Echo group. Smoking (hazards ratio 6.3; 95% CI 1.7-23.5) and multivessel spasm (hazards ratio 37.2, 95% CI, 8.1 to 170.4) were independent factors associated with cardiac death and/or MI.

CONCLUSION

Erg Echo for noninvasive diagnosis of CVS in the differential diagnosis of chest pain provides useful prognostic information for patients without significant fixed coronary stenosis and can play a role as a cost-effective diagnostic strategy in these selected patients.

Mouse model of Prinzmetal angina by disruption of the inward rectifier Kir6.1

The inwardly rectifying K(+) channel Kir6.1 forms K(+) channels by coupling with a sulfonylurea receptor in reconstituted systems, but the physiological roles of Kir6.1-containing K(+) channels have not been determined. We report here that mice lacking the gene encoding Kir6.1 (known as Kcnj8) have a high rate of sudden death associated with spontaneous ST elevation followed by atrioventricular block as seen on an electrocardiogram. The K(+) channel opener pinacidil did not induce K(+) currents in vascular smooth-muscle cells of Kir6.1-null mice, and there was no vasodilation response to pinacidil. The administration of methylergometrine, a vasoconstrictive agent, elicited ST elevation followed by cardiac death in Kir6.1-null mice but not in wild-type mice, indicating a phenotype characterized by hypercontractility of coronary arteries and resembling Prinzmetal (or variant) angina in humans. The Kir6.1-containing K(+) channel is critical in the regulation of vascular tonus, especially in the coronary arteries, and its disruption may cause Prinzmetal angina.

Limited role of coronary angioplasty and stenting in coronary spastic angina with organic stenosis

OBJECTIVES

We investigated the efficacy of percutaneous coronary intervention (PCI) in patients with coronary spastic angina (CSA) and severe organic stenosis.

BACKGROUND

Coronary spasm occurs at the site of organic stenosis in most patients with CSA and severe stenosis, whereas multivessel spasm occurs frequently in those with normal coronary arteries. The incidence of multivessel spasm and the efficacy of PCI in patients with CSA and severe stenosis have not been fully elucidated.

METHODS

Forty-five patients with CSA and severe stenosis underwent spasm provocative testing with intracoronary acetylcholine before and 7 +/- 3 months after PCI (20 patients had angioplasty and 25 patients had stenting), when all patients were free of restenosis.

RESULTS

Spasm was induced at the site of severe stenosis in 30 patients (66.7%) with (n = 12) or without (n = 18) spasm induced in another vessel. In the remaining 15 patients, spasm was induced at a different site in the stenotic vessel and/or in another vessel. Repeat provocative tests were performed in 43 of 45 patients. Although spasm was never induced at exactly the same site of the initial stenosis that had been dilated, spasm was induced at a different site in the dilated vessel and/or in another vessel, in 33 (76.7%) of 43 patients. Multivessel spasm occurred in 28 (62.2%) of 45 patients on one or both provocations.

CONCLUSIONS

Spasm was frequently induced at a site different from the initial stenosis, even in the absence of restenosis after PCI. Calcium antagonists should be continued in most patients with CSA who show no restenosis after PCI.

Safety of ergot stress echocardiography for non-invasive detection of coronary vasospasm

BACKGROUND

The safety of ergonovine/ergometrine stress testing for coronary vasospasm when performed outside the cardiac catheterization laboratory (cath lab) has been questioned vigorously.

AIM

To assess the tolerability and safety of ergonovine/ergometrine stress testing performed in the echocardiographic laboratory (echo lab).

METHODS

We retrospectively reviewed the data prospectively collected in the echo lab of the Institute of Clinical Physiology from 1 January 1985 to 1 June 2000, from 587 tests performed on 573 patients (either ergonovine or ergometrine stress echocardiography testing). By selection, all patients had a history of chest pain, consistent with vasospastic angina, negative exercise stress testing or stress echocardiography (with dipyridamole, dobutamine or exercise), and normal or near normal resting left ventricular function. Ergonovine or ergometrine maleate was injected up to a total cumulative dosage of 0.35 mg, under continuous 12-lead electrocardiographic and two-dimensional echocardiographic monitoring.

RESULTS

There were no deaths, myocardial infarctions, ventricular fibrillations or third degree AV blocks. One patient had non-sustained ventricular tachycardia associated with transient ST segment elevation 30 min after the test. Three patients had second degree AV block associated with a positive echocardiography test that was promptly reversed by nitrates administration. Transient regional myocardial dysfunction occurred in 79 patients (13%). Limiting ischaemia-independent side effects were present in 17 patients (3%): hypotension in one, arterial hypertension in five, non-sustained ventricular tachycardia in two and nausea or vomiting in ten. The test was well tolerated and echocardiograms were interpretable in 97% of the tests performed.

CONCLUSION

Pharmacological stress echocardiography with either ergonovine or ergometrine is well tolerated and can be performed with relatively low risk in the echo lab in properly selected patients in whom coronary vasospasm is suspected.

Exercise-induced silent myocardial ischemia and coronary morbidity and mortality in middle-aged men

OBJECTIVES

We investigated the prognostic significance of exercise-induced silent myocardial ischemia in both high and low risk men with no prior coronary heart disease (CHD).

BACKGROUND

Silent ischemia predicts future coronary events in patients with CHD, but there is little evidence of its prognostic significance in subjects free of CHD.

METHODS

We investigated the association of silent ischemia, as defined by ST depression during and after maximal symptom-limited exercise test, with coronary risk in a population-based sample of men with no prior CHD followed for 10 years on average.

RESULTS

Silent ischemia during exercise was associated with a 5.9-fold (95% CI 2.3 to 11.8) CHD mortality in smokers, 3.8-fold (95% CI 1.9 to 7.9) in hypercholesterolemic men and 4.7-fold (95% CI 2.4 to 9.1) in hypertensive men adjusting for other risk factors. The respective relative risks (RRs) of any acute coronary event were 3.0 (95% CI 1.7 to 5.1), 1.9 (95% CI 1.2 to 3.1) and 2.2 (95% CI 1.4 to 3.5). These associations were weaker in men without these risk factors. Furthermore, silent ischemia after exercise was a stronger predictor for the risk of acute coronary events and CHD death in smokers and in hypercholesterolemic and hypertensive men than in men without risk factors.

CONCLUSIONS

Exercise-induced silent myocardial ischemia was a strong predictor of CHD in men with any conventional risk factor, emphasizing the importance of exercise testing to identify asymptomatic high risk men who could benefit from risk reduction and preventive measures.

Polymorphic ventricular tachycardia in patients with vasospastic angina--clinical and electrocardiographic characteristics and long-term outcome

There have been few clinical studies exploring the characteristics of spontaneous polymorphic ventricular tachycardia (VT) during a vasospastic angina attack. During a 4-year recruitment period, Holter ECG recordings were monitored for 42+/-24 h during a drug-free period in 60 consecutive patients with vasospastic angina (VSA) and of these, 8 patients had at least one episode of polymorphic VT during monitoring. Ischemic ST segment elevation was immediately preceded the spontaneous polymorphic VT in all 8 patients, 4 of whom had silent coronary vasospasm. Immediately before the onset of polymorphic VT, both R-on-T and long-short sequences were observed in 4 of the 8 patients and ST wave alternans were recorded in 2 patients. VT exhibited a pattern of torsade de pointes in 4 of the 8 patients. Five patients underwent electrophysiologic testing during a drug-free asymptomatic phase, and polymorphic VT was induced in 2 of the 5 patients, with one developing ventricular fibrillation. During a follow-up period of 73+/-17 months, there was a significant difference in the incidence of sudden death between patients with and without VT (2/8 cases [25%] vs 0/52 [0%]; p<0.01). Thus, vasospastic attacks, even if asymptomatic, that immediately precede the development of polymorphic VT may be associated with a repolarization abnormality and an increased risk of sudden death.

Laser photoablation of experimental post-infarction ventricular tachycardia guided by three dimensional activation mapping

BACKGROUND AND OBJECTIVE

The purpose of this study was to evaluate the efficacy of epicardially delivered laser energy to ablate induced ventricular tachycardia in a post-infarction canine model.

STUDY DESIGN/MATERIALS AND METHODS

In 13 canines, the left anterior wall myocardial infarction was created. Five days later, 240 plunged electrodes were inserted into the heart. Three-dimensional ventricular activation sequences were analyzed on line by a computerized mapping system.

RESULTS

Sixteen sustained monomorphic ventricular tachycardias were reproducibly induced in 10 canines. Epicardially contacted Nd:YAG laser irradiated the areas of the final pathway in macro-reentrant activation and the impulse origin in focal excitation. Linear photocoagulation lesions (11-16 x 50-72 mm) were created. Seven macro-reentrant circuits and six of nine focal origins were eliminated (success rate 81%). Pathology showed that laser photocoagulation involved all surviving subepicardial and intramural fibers.

CONCLUSION

Epicardially delivered laser energy in conjunction with electrical activation mapping has a high probability of ablating post-infarction ventricular tachycardia.

Safety and clinical impact of ergonovine stress echocardiography for diagnosis of coronary vasospasm

OBJECTIVES

We sought to address the issues of safety, feasibility and clinical impact of noninvasive diagnosis of coronary vasospasm (CVS).

BACKGROUND

The safety of ergonovine provocation for CVS performed outside the catheterization laboratory has been questioned.

METHODS

We performed a retrospective analysis of the results of bedside ergonovine provocation testing by monitoring left ventricular regional wall motion abnormalities (RWMAs) using two-dimensional echocardiography (Erg Echo).

RESULTS

After confirming that there was no significant epicardial coronary stenosis, Erg Echo was performed on 1,372 patients from July 1991 to December 1997. Ergonovine echocardiography was terminated prematurely in 13 patients (0.9%) because of limitations caused by side effects unrelated to myocardial ischemia. Among 1,359 completed tests, 31% (n = 421) showed positive results, with development of RWMAs in 412 tests (98%) or ST displacement in electrocardiograms of nine tests (2%). Arrhythmias developed in 1.9% (26/1,372), including transient ventricular tachycardia (n = 2) and atrioventricular block (n = 4), which were promptly reversed with nitroglycerin. There was no mortality or development of myocardial infarction. Based on the angiographic criteria of 218 patients, the sensitivity and specificity of Erg Echo for the diagnosis of CVS were 93% and 91%, respectively. Since 1994, Erg Echo has become a more popular diagnostic method than invasive spasm provocation testing in the catheterization laboratory and has comprised more than 95% of all spasm provocation tests during the last three years. In the outpatient clinic, 453 patients underwent Erg Echo safely.

CONCLUSIONS

Although this is a retrospective study in a single center, we believe that Erg Echo is highly feasible, accurate and safe for the diagnosis of CVS and can replace invasive angiographic spasm provocation testing in the catheterization laboratory.

Occlusions of epicardial arteries might not directly induce symptoms in ischemic heart disease

It is accepted that primary occlusions of epicardial arteries by thromboses, stenotic coronary artery disease (CAD), and spasm directly induce symptoms in ischemic heart disease (IHD). Because of this acceptance, there has been little interest in alternate mechanisms for IHD--as the spasm of resistance vessel (S-RV) concept of IHD, which asserts that S-RV directly induces symptoms in IHD. To stimulate interest in the S-RV concept, evidence against the primacy of occlusions of epicardial arteries was presented, as well as evidence for this position to provide a balanced discussion; while the evidence was mixed, overall findings appeared to weigh significantly against the primacy of occlusions of epicardial arteries. Also, the S-RV concept was discussed; the discussion included presenting the theory's explanations for events in epicardial arteries, with the aim of demonstrating that the concept provides more consistent explanations than the standard position. It is suggested that there is sufficient information to warrant renewed consideration of the S-RV concept.

Coronary artery blood flow: physiologic and pathophysiologic regulation

Acute myocardial ischemia, which results from a significant imbalance between myocardial oxygen demands and myocardial oxygen supply, occurs in as many as six million persons with atherosclerotic coronary artery disease in the United States. Accordingly, a clear understanding of the physiologic and pathophysiologic factors that influence coronary artery blood flow is important to the clinician and provides the basis for the judicious use of medications for the treatment of patients with atherosclerotic coronary artery disease. This review discusses the endothelial, metabolic, myogenic, and neurohumoral mechanisms of coronary blood flow regulation and the interaction of the different mechanisms in the regulation of coronary blood flow. The importance of nitric oxide in coronary blood flow regulation is emphasized. We also discuss the common clinical problems of hyperlipidemia and coronary atherosclerosis, coronary artery spasm, and systemic arterial hypertension that result in coronary artery endothelial dysfunction, the impaired production and increased inactivation of nitric oxide, and impairment in coronary blood flow regulation. This information is important to clinicians because more than forty million people in the United States have atherosclerotic or hypertensive heart disease and therefore are at risk for significant myocardial complications due to impairment of coronary blood flow regulation.

Diagnosis of coronary vasospasm in patients with clinical presentation of unstable angina pectoris using ergonovine echocardiography

Although coronary vasospasm can contribute to the development of unstable angina, the definite diagnostic method has not been established. The purpose of this study was to determine if ergonovine echocardiography (detection of regional wall motion abnormality during bedside ergonovine challenge) after angiographic confirmation of insignificant fixed disease would be useful and safe in detecting coronary vasospasm in patients with unstable angina. After control of chest pain with medications in patients admitted to the coronary care unit under the tentative diagnosis of unstable angina, diagnostic coronary angiography was performed. All patients with normal or insignificant fixed disease underwent ergonovine echocardiography after discontinuation of medications for 4+/-1 days. Among 208 consecutive patients enrolled for this study, 75% (156 of 208) showed significant fixed disease in the angiography. Ergonovine echocardiography was performed in 52 patients with insignificant disease, and coronary vasospasm was documented in 33 (63%, 33 of 52). No serious procedure-related arrhythmia or myocardial infarction occurred. Esophageal motility disorder and hypertrophic cardiomyopathy were diagnosed in 6 and 3 patients, respectively. Chest pain of undetermined etiology was the final diagnosis at discharge in 10 patients (5%, 10 of 208); among them chest pain redeveloped in 2 patients, and repeated ergonovine echocardiography revealed positive results. Our data suggest that among patients with the clinical presentation of unstable angina, coronary vasospasm is the main cause of myocardial ischemia in a considerable number of patients with a normal or near-normal angiogram, and ergonovine echocardiography after confirmation of absence of significant fixed disease is useful and safe for noninvasive diagnosis of coronary vasospasm in this setting.

High thoracic/low cervical, long-term intrathecal (i.t.) infusion of bupivacaine alleviates "refractory" pain in patients with unstable angina pectoris. Report of 2 cases

BACKGROUND

There is no reliable treatment for "refractory" pain from unstable angina pectoris (UAP) when epidural infusion of bupivacaine has failed to relieve it. In two such cases we explored the potential of intrathecal (i.t.) bupivacaine infusion to provide pain relief.

PATIENTS AND METHODS

Two female patients, 70 and 67 years. An 18-G nylon catheter was inserted intrathecally through a 17-G Tuohy needle via the T2-T3 interspace and its tip located at the height of C6-C7 vertebrae. The catheter was connected to a portable, programmable electronic pump filled with bupivacaine 5 mg/ml. The infusion started at rates of 0.1-0.2 ml/h, with optional bolus doses of 0.1-0.2 ml, 4-2 times/h, respectively, by PCA (Patients-Controlled Analgesia), and then adjusted to give the patients satisfactory (80%-100%) pain relief.

RESULTS

Pain relief was obtained with doses of i.t.-bupivacaine ranging from 17 to 45 (mean = 25) mg/d. The pain intensity decreased from VAS (Visual Analogue Score) 9-10 to 0-2 out of 10. The nocturnal sleep improved from 2-4 to 6-7 h. The patients could now ambulate, walking or in a wheel-chair. The i.t.-treatment lasted 700 and 437 d, of which 540 and 343 d (respectively) were spent at home, and was terminated by: (a) the patient's death due to intracranial bleeding (1st case); (b) progressive aggravation of the unstable angina that could not be fully countered by increasing the bupivacaine dose above 1.0 mg/h due to occurrence of cerebral transient ischemic attacks, usually not correlated with orthostatic arterial hypotension but apparently facilitated by microembolization of the cerebral arteries (2nd case).

CONCLUSION

I.t.-bupivacaine infusion may alleviate "refractory" pain in patients with unstable angina pectoris when epidural bupivacaine failed to do so. Its use is apparently limited by the IT-bupivacaine critical dosage (in these patients = 1.0-1.5 mg/h).

Intra- and postoperative myocardial ischemia without significant coronary artery stenosis

A 73-year-old man without a history of coronary artery disease had two episodes of significant ST-segment elevation indicative of inferior myocardial ischemia during the resection of an abdominal aortic aneurysm. During the further course, sudden ST-segment elevations occurred and resolved spontaneously without preceding hemodynamic instability. The patient sustained two episodes of cardiac arrest due to ventricular fibrillation and intermittent third-degree atrioventricular block with ventricular asystole. On cardiac catheterization, coronary arteries had a right dominant pattern. The right coronary artery was entirely patent on multiple injections. Thus, right coronary artery spasm is the only possible explanation for these observations.

Anti-ischemic and anti-anginal effects of thoracic epidural anesthesia versus those of conventional medical therapy in the treatment of severe refractory unstable angina pectoris

BACKGROUND

Cardiac sympathetic blockade by thoracic epidural anesthesia (TEA) dilates stenotic coronary arteries and has been used to control pain in patients with unstable angina. The aim of the present study was to evaluate the potential anti-ischemic effects of cardiac sympathetic blockade by TEA in severe, refractory, unstable angina.

METHODS AND RESULTS

Forty patients with unstable angina refractory to standard anti-anginal therapy were randomized to receive either continuous epidural infusion of bupivacaine (TEA, Th1 to Th5) or to standard anti-anginal therapy including beta-blockers, calcium antagonists, aspirin, heparin, and nitroglycerin infusion (control group). The primary end points were number of anginal attacks and severity of myocardial ischemia assessed by 48-hour ambulatory Holter monitoring. The incidence of myocardial ischemia was lower in the TEA group (22% versus 61%; P<.05). The number of ischemic episodes per patient was 1.0+/-0.6 in the TEA group and 3.6+/-0.9 in the control group (P<.05). The episode duration per patient was 4.1+/-2.5 minutes and 19.7+/-6.2 minutes in the TEA and the control groups, respectively (P<.05). The mean area-under-the-ST-time-curve was 6.8+/-4.3 and 32.2+/-14.3 (mm-min) in the TEA and the control groups, respectively (P<.05). Fifteen anginal attacks were recorded in the control group and one attack in the TEA group (0.83+/-0.21 versus 0.06+/-0.06/patient, respectively, P<.01).

CONCLUSIONS

The anti-ischemic and anti-anginal effects of continuous TEA are superior to those of conventional therapy in the treatment of refractory unstable angina.

Mitogen-activated protein kinase activation: an alternate signaling pathway for sustained vascular smooth muscle contraction

PURPOSE

The vascular smooth muscle determines the dynamic caliber of the blood vessel and hence is the final effector cell in modulating vasomotor tone. Although considerable information is available regarding the physiologic agonists that induce contraction, less is known about the cellular signaling events that lead to long-lasting contractions or vasospasm. We examined the hypothesis that activation of mitogen-activated protein (MAP) kinase may be associated with sustained smooth muscle contractions.

METHODS

Physiologic contractile responses were determined in intact bovine carotid artery smooth muscles in a muscle bath. Corresponding signaling events were determined with immunoblots using antiphosphotyrosine antibodies or immunoprecipitation of whole-cell phosphorylated strips of muscle.

RESULTS

The tyrosine kinase inhibitor, genestein, significantly inhibited the magnitude of contractions induced by phorbol ester, endothelin, angiotensin, and serotonin. In addition, genestein inhibited the sustained phase of contractions induced by serotonin. Serotonin-induced vascular smooth muscle contractions were temporally associated with an increase in the phosphorylation of MAP kinase.

CONCLUSIONS

These data suggest that the activation of MAP kinase is associated with sustained vascular smooth muscle contractions. Pharmacologic manipulation of MAP kinase activation may lead to new approaches to treat pathologic circumstances of increased vasomotor tone such as vasospasm.

Silent myocardial ischaemia in patients undergoing transurethral prostatectomy. A study to evaluate risk scoring and anaesthetic technique with outcome

Ninety four patients undergoing transurethral resection of the prostate underwent Holter electrocardiographic monitoring pre- and postoperatively. There was no difference in silent myocardial ischaemia incidence or load between the spinal (n = 60) and the general anaesthesia (n = 34) groups. Ischaemic heart disease and a higher Detsky score both significantly increased the incidence of silent myocardial ischaemia but not the ischaemic load of those patients that actually demonstrated ischaemia. In this specific surgical population, not undergoing cardiac or vascular surgery, both ischaemic heart disease and cardiac risk scores are poor predictors of ischaemic load. Merely the presence of short duration silent myocardial ischaemia probably has little predictive value for postoperative adverse outcome.

Epicardial vasomotor responses to acetylcholine are not predicted by coronary atherosclerosis as assessed by intracoronary ultrasound

OBJECTIVES

The purpose of this study was to use intravascular ultrasound to determine the morphologic appearance of the coronary arteries, relating the absence, presence and extent of atherosclerosis to the response of the coronary arteries to acetylcholine infusion.

BACKGROUND

Endothelial function plays a major role in the pathophysiology of myocardial ischemia and angina pectoris. The response of the coronary arteries to selective infusion of acetylcholine has been used to examine endothelial function, with vasoconstriction occurring in the absence of intact endothelial function. Vasoconstriction to acetylcholine infusion in humans without overt coronary artery disease has been attributed to early atherosclerosis not detected by coronary angiography.

METHODS

Twenty-nine patients without overt coronary artery disease underwent selective coronary angiography and selective intracoronary infusion of increasing concentrations of acetylcholine (10(-6), 10(-5) and 10(-4) mol/liter), followed by intravascular ultrasound imaging.

RESULTS

The response of the coronary arteries to acetylcholine infusion was not dependent on the absence or presence of atherosclerotic plaque, as detected by intravascular ultrasound. The percent change in epicardial coronary artery diameter during acetylcholine infusion versus baseline was -14 +/- 28% (mean +/- SD) in the seven patients with no visible atherosclerosis on intravascular ultrasound versus -9 +/- 20% in the 22 patients with visible atherosclerosis on intravascular ultrasound (p = NS, confidence interval -14% to 25%). There was a greater vasoconstrictive response to acetylcholine infusion in patients with risk factors for coronary artery disease than in those without risk factors (p = 0.003).

CONCLUSIONS

The vasoreactive response to acetylcholine is not necessarily dependent on ultrasound detection of the presence or absence of atherosclerosis.

Transient myocardial ischemia in patients with chronic angina: relation to heart rate changes and variability in exercise threshold. BAY r 1999 in Chronic Angina Study Group

This study was undertaken to assess the relation of ambulatory myocardial ischemia to heart rate changes and variability in exercise threshold in patients with chronic angina. The study involved 118 patients with chronic angina and proven coronary artery disease who had a 'positive' exercise test result. All patients underwent a first exercise test followed by a 48-h period of ambulatory electrocardiographic monitoring. A second exercise test was performed 4 days later. A total of 101 ischemic episodes were recorded in 35 patients. The heart rate at the appearance of 1-mm ST segment depression during ambulatory electrocardiographic monitoring was > or = 20 beats/min lower than that during exercise testing in 58 ischemic episodes (57%, Group A), 10-19 beats/min lower in 26 (26%, Group B), and < or = 9 beats/min lower or higher in 17 (17%, Group C). Thirty-five percent of the Group A ischemic episodes, 69% of Group B, and 71% of Group C were preceded by an increase in heart rate of > or = 10 beats/min. Thirty patients showed a variable exercise threshold. The prevalence of Group A and B ischemic episodes was not significantly different in patients with fixed or variable exercise threshold, whereas that of Group C episodes was 22% in the former and 0% in the latter (P = 0.036). These results suggest that increased coronary tone may be one of the mechanisms contributing to modulate the occurrence of transient myocardial ischemia in most patients with chronic angina and transient myocardial ischemia at ambulatory electrocardiographic monitoring. This occurs regardless of whether the patients have a variable or fixed exercise threshold.

Concomitant use of nitrates, calcium channel blockers, and beta blockers for optimal antianginal therapy

Despite the introduction of new mechanical techniques for revascularization, pharmacologic therapy continues to be the mainstay of antianginal therapy. The conventional antianginal medications, which include nitrates, beta blockers, and calcium channel blockers, act to correct the imbalance between myocardial supply and demand by increasing coronary blood flow, reducing myocardial oxygen requirements, or both. All three are appropriate for the management of angina caused by a fixed coronary obstruction, but nitrates and calcium channel blockers, which not only reduce demand but also increase supply, are preferred in cases of angina believed to involve a significant increase in vasomotor tone. Because of the different yet complementary mechanisms of action of the three classes of anti-ischemic drugs, use of these agents in combination is a rational approach to the treatment of angina unresponsive to monotherapy. Such combinations have been shown to enhance the therapeutic response achieved with single-agent therapy. In addition, the pharmacologic action of one of the components of the combination regimen may serve to offset side effects typically associated with the other.