Impaired glucose tolerance with late hypersecretion of insulin during oral glucose tolerance test in patients with vasospastic angina

Clinical Characteristics and Major Adverse Cardiovascular Events in Diabetic and Non-Diabetic Patients with Vasospastic Angina

Purpose

The clinical background and prognostic impact of diabetes mellitus (DM) on vasospastic angina (VSA) are unclear; thus, in this retrospective study, we investigated whether they differ based on the presence or absence of DM in patients with VSA.

Patients and Methods

We included 272 Japanese patients with VSA diagnosed by coronary angiography (CAG) and the spasm provocation test (SPT). The diagnosis of DM was determined by measuring fasting blood glucose and hemoglobin A1C and by the patient's current oral medications. On CAG, the presence of atherosclerotic lesions (20%-50%) was checked. On SPT, the coronary spasm was defined as transient coronary vasoconstriction >90% on CAG, accompanied by chest symptoms and/or ST-T changes. Focal spasm was defined as coronary spasm occurring within one segment of the American Heart Association classification on CAG. Blood and urine tests and vascular endothelial function were also evaluated when possible. A major adverse cardiovascular event (MACE), which is defined as cardiac mortality and rehospitalization due to cardiovascular illness, was the basis for determining the prognosis.

Results

There were 49 patients (18%) in the DM group and 223 (82%) in the non-DM group. No significant differences in urinary albumin levels and peripheral vascular function were between groups. On CAG, atherosclerotic lesions were observed significantly more frequently in the DM group (63% vs 46%; P = 0.028). Results of SPT showed a trend toward fewer focal spasms in the DM group (24% vs 39%; P = 0.072). No significant differences in MACE were noted between groups in the primary analysis of DM, whereas sub-analyses of focal spasms showed lower MACE-free survival in the DM group (P = 0.042).

Conclusion

The study results support the hypothesis that DM associated with VSA should be treated appropriately, especially in cases of focal spasm, which may require more attention in treatment.

Spontaneous Multivessel Coronary Spasm During Diagnostic Coronary Angiography

Acute vasospastic angina, formerly known as Prinzmetal angina, is characterized by transient electrocardiographic changes that are not related to exertion. Its atypical presentation makes it difficult to establish the diagnosis, so it is probably underrecognized and therefore mismanaged. We treated a 49-year-old woman who presented with a 2-day history of chest pain associated with palpitations. Abnormal radionuclide stress test results prompted diagnostic coronary angiography, during which the patient reported chest pain and became hemodynamically unstable. Active coronary vasospasm at multiple sites was treated with intracoronary nitroglycerin and nicardipine, leading to immediate recovery. Our case highlights the importance of accurate, timely diagnosis of vasospastic angina, and of early recognition and management of spontaneous coronary spasm during angiography.

Provocative testing for coronary reactivity and spasm

Coronary spasm is an important and often overlooked etiology of chest pain. Although coronary spasm, or Prinzmetal's angina, has been thought of as benign, contemporary studies have shown serious associated adverse outcomes, including acute coronary syndrome, arrhythmia, and death. Definitive diagnosis of coronary spasm can at times be difficult, given the transience of symptoms. Numerous agents have been historically described for provocative testing. We provide a review of published data for the role of provocation testing in the diagnosis of coronary spasm.

Disruption of coronary vasomotor function: the coronary spasm syndrome

Abnormal coronary vasoconstriction, or coronary spasm, can be the result of several factors, including local and neuroendocrine aberrations. It can manifest clinically as a coronary syndrome and plays an important role in the genesis of myocardial ischemia. Over the past half century, coronary angiography allowed the in vivo demonstration of spasm in patients who fit the initial clinical description of the condition as reported by Prinzmetal et al. Several clinical, basic, and more recently, genetic studies have provided insight into the pathogenesis, manifestations, and therapy of this condition. It is not uncommonly encountered in patients with coronary syndromes and absence of clearly pathologic lesions on angiography. Provocation tests utilizing pharmacologic and nonpharmacologic stimuli combined with imaging (echocardiography or coronary angiography) can help make the correct diagnosis. The use of calcium channel blockers and long-acting nitrates is currently considered standard of care and the overall prognosis appears to be good. The recent discovery of genetic abnormalities predisposing to abnormal spasm of the coronaries has stimulated interest in the development of targeted therapies for the management of this condition.

Glucose tolerance status in 510 children and adolescents attending an obesity clinic in Central Italy

Childhood obesity is epidemic in developed countries and is accompanied by an increase in the prevalence of type 2 diabetes (T2DM).

AIMS

Establish prevalence of glucose metabolism alterations in a large sample of overweight/obese children and adolescents from Central Italy.

METHODS

The study group included 510 overweight/obese subjects (3-18 yr). Oral glucose tolerance test (OGTT) was performed with glucose and insulin determination. Homeostatic model assessment of insulin resistance (HOMA-IR) and insulin sensitivity index (ISI) were derived from fasting and OGTT measurements. Beta-cell function was estimated by insulinogenic index. Fat mass was measured by dual-energy x-ray absorptiometry.

RESULTS

Glucose metabolism alterations were detected in 12.4% of patients. Impaired glucose tolerance (IGT) was the most frequent alteration (11.2%), with a higher prevalence in adolescents than in children (14.8 vs. 4.1%, p < 0.001); silent T2DM was identified in two adolescents (0.4%). HOMA-IR and glucose-stimulated insulin levels were higher in patients with IGT than individuals with normal glucose tolerance (HOMA-IR = 4.4 +/- 2.5 vs. 3.4 +/- 2.3, p = 0.001). Fat mass percentage and insulinogenic index were not different between the two groups. In multivariate analysis, age, fasting glucose, and insulin resistance influenced independently plasma glucose at 120 min of OGTT. Individuals with combined impaired fasting glucose/IGT (IFG/IGT) and T2DM were older and had reduced plasma insulin values at OGTT when compared to patients with simple IGT.

CONCLUSIONS

Glucose metabolism alterations are frequently found among children and adolescents with overweight/obesity from Central Italy. Age, fasting glucose, and insulin resistance are main predictors of IGT. We suggest the use of OGTT as a screening tool in obese European adolescents.

Coronary artery spasm and the polymorphisms of the endothelial nitric oxide synthase gene

BACKGROUND

Coronary artery spasm plays an important role in the pathogenesis of vasospastic angina, and contributes to the development of several acute coronary syndromes. Endothelial nitric oxide synthase (ecNOS) catalyzes the synthesis of nitric oxide, which regulates vascular tone, and may be related to coronary vasospasm. The present study investigated whether coronary spasm is related to particular polymorphisms of the ecNOS gene.

METHODS AND RESULTS

Spasm provocation by serial infusions of acetylcholine was performed on 165 patients who were clinically suspected of having angina. In both study patients and healthy controls (n=400), genomic polymorphisms of the ecNOS gene were determined by using polymerase chain reaction. Quantitative luminal diameter measurements of the 3 major coronary arteries were initially obtained before and after acetylcholine injection, and then after isosorbide dinitrate injection, by using a computer-assisted analysis system. Logistic multiple regression analysis identified the a/a or a/b genotype in intron 4 of ecNOS (NOS4a: p=0.0431, odds ratio (OR) 2.43) and diabetes mellitus (p=0.0060, OR 4.88) as significant predictors of coronary spasm. In the patients with NOS4a, both the induced and spontaneous contractions were augmented.

CONCLUSION

The present study results indicated that NOS4a could be a good marker for coronary artery spasm.

The relationship between insulin resistance and polymorphisms of the endothelial nitric oxide synthase gene in patients with coronary artery disease

Nitric oxide (NO) regulates endothelial function and is believed to prevent atherogenesis. In endothelial cells, endothelial nitric oxide synthase (eNOS) is expressed constitutively, and regulates NO synthesis. A mutation of the eNOS gene has been associated with the development of coronary artery disease (CAD). The development of CAD is also influenced by insulin resistance, and recent studies suggest that NO might affect cellular insulin activity. We investigated the association between eNOS polymorphisms and insulin resistance in patients with CAD. We screened 45 patients with a history of myocardial infarction (MI), angina pectoris (AP), or coronary spasm. Genotypes were determined by polymerase chain reaction-restriction fragment-length polymorphism analysis. We examined two polymorphisms of the eNOS gene (The T(-786)-->C variant and the missense Glu298Asp variant). Insulin resistance was measured by determining the plasma immunoreactive insulin concentration at the 120 min time point (IRI 120) of a 75 g oral glucose tolerance test. The IRI 120 of the T(-786)-->C variant group was higher than that for the control group (p<0.05). This finding demonstrates that the T(-786)-->C mutation in the eNOS gene decreases insulin sensitivity.

Hyperinsulinemia as a risk factor for restenosis after coronary balloon angioplasty

The present study evaluated whether hyperinsulinemia is a predictor of restenosis after coronary balloon angioplasty in 69 patients who underwent elective coronary balloon angioplasty; patients were excluded if they were known diabetics being treated with insulin. Quantitative coronary angiography was performed before and after angioplasty and at follow-up. Restenosis was defined as the presence of > or = 50% stenosis at follow-up. Plasma insulin responses before, 30, 60, and 120 min after 75 g glucose load (OGTT) were measured. Plasma insulin levels were higher in patients with restenosis than in patients without restenosis. Minimal lumen diameter at follow-up was smaller, and percent diameter stenosis at follow-up was higher and late loss was greater in the highest sum of insulin levels during OGTT (sigma insulin) quartile (0.95+/-0.15 vs 1.47+/-0.09 mm, p=0.005; 66.3+/-5.8 vs 40.5+/-3.3%, p=0.0003; 0.90+/-0.15 vs 0.49+/-0.08 mm, p=0.02). Even after adjustment for coronary risk factors and administration of angiotensin converting enzyme inhibitors, the association of hyperinsulinemia with restenosis leads to the conclusion that hyperinsulinemia is a strong risk factor for restenosis.

Hyperglycemia reduces coronary collateral blood flow through a nitric oxide-mediated mechanism

We tested the hypothesis that hyperglycemia alters retrograde coronary collateral blood flow by a nitric oxide-mediated mechanism in a canine Ameriod constrictor model of enhanced collateral development. Administration of 15% dextrose to increase blood glucose concentration to 400 or 600 mg/dl decreased retrograde blood flow through the left anterior descending coronary artery to 78 +/- 9 and 82 +/- 8% of baseline values, respectively. In contrast, saline or L-arginine (400 mg x kg(-1) x h(-1)) had no effect on retrograde flow. Coronary hypoperfusion and 1 h of reperfusion decreased retrograde blood flow similarly in saline- or L-arginine-treated dogs (76 +/- 11 and 89 +/- 4% of baseline, respectively), but these decreases were more pronounced in hyperglycemic dogs (47 +/- 10%). L-arginine prevented decreases in retrograde coronary collateral blood flow during hyperglycemia (100 +/- 5 and 95 +/- 6% of baseline at blood glucose concentrations of 400 and 600 mg/dl, respectively) and after coronary hypoperfusion and reperfusion (84 +/- 14%). The results suggest that hyperglycemia decreases retrograde coronary collateral blood flow by adversely affecting nitric oxide availability.

Detection of the "midband" lipoprotein in patients with coronary artery spasm

BACKGROUND

Dyslipidemia in patients with coronary vasospasm has been characterized by a low level of high-density lipoprotein (HDL) cholesterol without elevation of low-density lipoprotein (LDL) cholesterol, distinct from patients with organic coronary artery disease.

HYPOTHESIS

Disordered triglyceride-rich lipoprotein metabolism may be linked to the genesis of coronary artery spasm.

METHODS

The incidence of the "midband" lipoprotein observed between very low-density lipoprotein (VLDL) and LDL bands in the polyacrylamide disc gel electrophoretic analysis was determined in 48 patients with coronary spastic angina (CSA), in 50 patients with stable effort angina and a significant fixed coronary stenosis (SEA), and in 40 control subjects without coronary artery disease (Control).

RESULTS

The incidence was significantly (p<0.05) higher in CSA (71%) than in SEA (50%) and Control (25%). Smoking was significantly (p < 0.05) more prevalent in CSA (77%) than in SEA (50%) and Control (50%). In SEA, serum levels of triglyceride and apoproteins C-II, C-III, and E were all significantly higher, and the serum level of HDL cholesterol was significantly lower in the midband-positive than in the midband-negative subgroup. In CSA, no significant differences were found in these serum levels between the midband-positive and -negative subgroups, except for a significantly (p < 0.05) lower level of HDL cholesterol in the former. However, a significantly (p < 0.05) higher incidence of diabetes mellitus or impaired glucose tolerance was noted in the midband-positive (41%) than in the midband-negative subgroup (7%) in CSA. The incidence of the detected midband lipoprotein was significantly decreased in the blood samples obtained from 20 of CSA after a > 6-month angina-free period (70-->25%, p < 0.05).

CONCLUSIONS

The midband lipoprotein was frequently detected in patients with coronary vasospasm, suggesting that dyslipidemia with disordered triglyceride-rich lipoprotein metabolism may be linked to the genesis of coronary artery spasm.

Women react with more myocardial ischemia and angina pectoris during elective percutaneous transluminal coronary angioplasty

BACKGROUND

Women have been considered to be at higher risk of complications relating to percutaneous transluminal coronary angioplasty (PTCA) than are men. One reason for this sex-related difference could be the ischemic response of myocardium during the procedure.

OBJECTIVE

To investigate whether there are sex-related differences in ischemic response of myocardium during elective PTCA.

METHODS

Consecutive patients (n = 192, of whom 48 were women), were subjected to vectorcardiography during the PTCA procedure. Vectorcardiographic variables, magnitude of ST-segment vector (ST-VM), and magnitude of ST-segment vector change (STC-VM) were studied.

RESULTS

Women were older (63 +/- 10 versus 56 +/- 10 years, P< 0.001) than men in our study and more often had diabetes mellitus and hypertension. Women less often had stents implanted (24 versus 50%, P < 0.01) and they were subjected to fewer balloon inflations (P < 0.001), with a total inflation time shorter than that for men (P< 0.001). Maximum STC-VM was 25% greater for women (P < 0.05). Women reported greater maximum pain (P < 0.05) and nitroglycerine was more frequently used for them during PTCA (P < 0.05). Occurrence of episodes of residual ischemic STC-VM (the difference between total number of episodes and number of balloon inflations) was more common for women (3 +/- 5 versus 1 +/- 3, P< 0.01). Duration of residual ischemic STC-VM episodes (the difference between total duration of episodes and duration of balloon inflations) was longer for women than it was for men (242 +/- 275 versus 148 +/- 233 s, P < 0.05). In a stepwise multivariate analysis and for a matched case-control group, episodes of residual STC-VM and duration of residual STC-VM episodes still indicated that there was an independent sex-related difference (P < 0.01 and P < 0.01, respectively).

CONCLUSIONS

Women more commonly develop vectorcardiographic signs of severe myocardial ischemia, more frequently experience episodes of ischemia and report more severe angina pectoris during elective PTCA than do men.

Management of coronary artery disease: therapeutic options in patients with diabetes

OBJECTIVES

The aim of this review is to discuss the particularities of coronary artery disease (CAD), the effect of intensive medical management and the outcome of percutaneous and surgical revascularization in patients with diabetes mellitus (DM).

BACKGROUND

CAD represents the leading cause of death in patients with DM. Numerous clinical, biological and angiographic risk factors have been shown to be associated with CAD in diabetic patients.

METHODS

Metabolic abnormalities in patients with DM including insulin resistance, hyperglycemia and dyslipidemia are briefly discussed. Then the potential roles of medical management and of percutaneous and surgical coronary revascularization are more extensively reviewed.

RESULTS

More vigorous control of hyperglycemia, hyperlipidemia, hypertension and other risk factors may be of crucial importance for risk reduction. Despite remarkable progress in recent years, the choice of a coronary revascularization strategy remains a challenge in these patients. Diabetic patients with CAD are predisposed to higher cardiovascular events after balloon angioplasty. Whether stenting and new antiplatelet drugs improve the results of percutaneous revascularization in this population needs further evaluation. The superiority of the surgical approach is also not definitely established. Therefore, many aspects of coronary revascularization are still unclear in these patients.

CONCLUSIONS

The results of ongoing randomized trials comparing multiple coronary stents to bypass surgery will likely provide some answers to our questions and additional randomized trials evaluating intensive diabetic control with or without coronary revascularization are needed to determine the best therapeutic approach in these patients.

Coronary artery spasm induced by carotid sinus massage

A 60 year old man with a history of frequent episodes of chest pain and dizziness was referred for evaluation of coronary artery disease. He had no significant coronary artery stenosis at baseline coronary angiography. A carotid sinus massage was performed for evaluation of carotid sinus hypersensitivity in the patient. Both heart rate and blood pressure decreased a little, and returned to baseline level immediately after carotid sinus massage. However, 2.5 minutes after carotid sinus massage, ECG showed ST segment elevation in leads II, III, and aVF. Four minutes after carotid sinus massage, he had chest pain with a progressive elevation in the ST segment in the same leads, when he had 99% focal spasm in the right coronary artery. The vasospasm induced by carotid sinus massage was reproducible over several minutes and resolved spontaneously. Coronary artery spasm may be provoked by the enhanced vagal activation due to carotid sinus massage.

Improvement of endothelial function and insulin sensitivity with vitamin C in patients with coronary spastic angina: possible role of reactive oxygen species

OBJECTIVES

This study was designed to examine the effect of antioxidant supplementation on the endothelial function and insulin sensitivity in patients with coronary spastic angina (CSA).

BACKGROUND

Insulin resistance may play a key role in coronary heart disease, and there is a possible link between acetylcholine-induced coronary vasoconstriction and hyperinsulinemia in patients with CSA. Endothelial dysfunction is present in the systemic arteries in CSA patients, and reactive oxygen species may cause inactivation of nitric oxide in these patients.

METHODS

We measured flow-mediated dilation of the brachial artery using ultrasound technique in 22 patients with CSA and 20 control subjects. We also evaluated glucose tolerance using a 75-g oral glucose tolerance test and insulin sensitivity using steady-state plasma glucose (SSPG) methods in the same patients.

RESULTS

The incidence of impaired glucose tolerance was higher in the CSA group than in the control group. Vitamin C infusion augmented flow-mediated dilation and decreased SSPG levels in the CSA group (from 3.27 +/- 0.77% to 7.00 +/- 0.59% [p < 0.001 by analysis of variance (ANOVA)] and from 177.3 +/- 13.3 to 143.1 +/- 14.9 mg/dl [p = 0.047 by ANOVA], respectively) but not in the control group (from 6.47 +/- 0.66% to 6.80 +/- 0.60% and from 119.8 +/- 11.7 mg/dl to 118.1 +/- 11.3 mg/dl, respectively). The steady-state plasma insulin levels were not affected by vitamin C infusion in either group.

CONCLUSIONS

Vitamin C improves both endothelial function and insulin sensitivity in patients with CSA. Thus, reactive oxygen species and/or decreased nitric oxide bioactivity may play an important role in the genesis of both endothelial dysfunction and insulin resistance in patients with CSA.

Diabetes abolishes ischemic preconditioning: role of glucose, insulin, and osmolality

Recent evidence indicates that hyperglycemia is an important risk factor for the development of cardiovascular disease. We tested the hypothesis that myocardial infarct size is related to blood glucose concentration in the presence or absence of ischemic preconditioning (PC) stimuli in canine models of diabetes mellitus and acute hyperglycemia. Barbiturate-anesthetized dogs were subjected to a 60-min period of coronary artery occlusion and 3-h reperfusion. Infarct size was 24 +/- 2% of the area at risk (AAR) for infarction in control dogs. PC significantly (P < 0.05) decreased the extent of infarction in normal (8 +/- 2% of AAR), but not diabetic (22 +/- 4% of AAR), dogs. Infarct size was linearly related to blood glucose concentration during acute hyperglycemia (r = 0.96; P < 0.001) and during diabetes (r = 0.74; P < 0.002) in the presence or absence of PC stimuli. Increases in serum osmolality caused by administration of raffinose (300 g) did not increase infarct size (11 +/- 3% of AAR) or interfere with the ability of PC to protect against infarction (2 +/- 1% of AAR). The results indicate that hyperglycemia is a major determinant of the extent of myocardial infarction in the dog.

Comparison of insulin response to intravenous glucose in healed myocardial infarction, in "cooled-off" unstable and stable angina pectoris, and in healthy subjects

Fasting and postglucose hyperinsulinemia are recognized risk factors for acute coronary events. The insulin reactivity of patients with acute coronary syndromes, however, has not been carefully compared with that of patients with chronic stable angina. We used Bergman's minimal model to analyze the insulin response to intravenous glucose in 21 subjects: 8 patients with previous (>3 months) acute coronary syndrome but no effort-related angina; 6 patients with stable effort angina but no prior acute event; and 7 healthy controls. Diabetes mellitus, systemic hypertension, dyslipidemias, and obesity were excluded. All patients underwent coronary angiography. Insulin sensitivity, glucose effectiveness, and glucose tolerance were determined from insulin and glucose concentrations measured frequently up to 3 hours after a 0.33 g/kg intravenous glucose bolus. Patients with previous unstable angina or acute myocardial infarction had less extensive disease at angiography than patients with stable angina (p = 0.007). Both patient groups had higher basal and 180-minute insulinemia than controls (p <0.0007). However, patients with stable angina did not differ significantly from controls with regard to early and late insulinemic response to glucose. In contrast, patients with previous acute onset of ischemia had significantly greater 180-minute integrated insulinemia (p = 0.04) and reduced insulin sensitivity (p = 0.05) after the glucose challenge than did the stable angina group. These data suggest that patients with acute presentation of coronary artery disease, compared with patients with uncomplicated chronic stable angina, have an impaired insulin response to glucose despite less extensive coronary disease at angiography.

Enhanced secretion of insulin plays a role in the development of atherosclerosis and restenosis of coronary arteries: elective percutaneous transluminal coronary angioplasty in patients with effort angina

OBJECTIVES

We investigated the relation between insulin and coronary atherosclerosis and restenosis of the coronary arteries, by performing elective percutaneous transluminal coronary angioplasty (PTCA).

BACKGROUND

Insulin is known to promote atherosclerosis of the arteries and has been implicated in the development of restenosis after PTCA.

METHODS

Of 210 angina patients who underwent PTCA, newly detected lesions in 35 consecutive nondiabetic subjects without previous intervention on the same main coronary arteries were analyzed after a 75-g oral glucose tolerance test (OGTT) and follow-up coronary angiography. Atherosclerotic lesions were evaluated by pattern, severity and extent. Restenosis was defined as loss of gain, the percentage of loss of the initial gain in the coronary diameter achieved by PTCA > or = 50%.

RESULTS

Patients with restenosis had a significantly higher extent index (a marker of atherosclerosis), insulin area, ratio of insulin area to glucose area, insulinogenic index and minimal lumen diameter after PTCA than those without restenosis (p=0.001, 0.011, 0.002, 0.016 and 0.041, respectively). Simple regression analysis revealed that only the ratio of insulin area to glucose area (a relative marker of enhanced insulin secretion) significantly correlated with the extent index (p=0.035). Extent index, insulin area, the ratio of insulin area to glucose area and insulinogenic index significantly correlated with loss of gain (p=0.001, 0.010, 0.002 and 0.032, respectively). Stepwise multiple regression analyses revealed that extent index and the ratio of insulin area to glucose area significantly correlated with loss of gain.

CONCLUSIONS

Enhanced secretion of insulin during the OGTT might be useful as a predictor of coronary atherosclerosis and of restenosis after elective PTCA in nondiabetic patients with effort angina.

Enhanced insulin response to oral glucose load in patients with angina pectoris associated with ST segment elevation in the absence of epicardial coronary arterial obstruction

The authors treated 10 patients with microvascular angina (MVA) manifesting angina pectoris, ST segment elevation suggestive of transmural myocardial ischemia, and no epicardial arterial obstruction. Since such patients frequently showed abnormal responses to oral glucose loading, the authors investigated the glucose and insulin responses to glucose loading in 10 MVA patients, 25 patients with vasospastic angina (VAP), 25 patients with effort angina (EAP), and 25 control subjects. Insulinogenic index, peripheral insulin activity [= 10(4)/(peak glucose x insulin at glucose peak)], glucose area, and insulin area were calculated. The MVA group included two patients with impaired glucose tolerance and two newly diagnosed diabetic patients. These proportions were similar to those in the VAP and EAP groups. Glucose levels at 30 to 180 min and insulin levels at 90 to 120 min in the MVA group were higher than in the control group. Peak glucose, glucose area, peak insulin, and insulin area were higher in the MVA group than in the control group (p<0.01). Those in the VAP and EAP groups were also higher. Insulin/glucose ratio at 120 min was higher, peripheral insulin activity, lower, in the disease groups than in the control group (p<0.05). The MVA patients showed a hyperglycemic and hyperinsulinemic response to oral glucose loading, as did the patients with EAP and VAP. Enhanced insulin response to oral glucose loading may also contribute to the pathogenesis of MVA.

Increased QT dispersion in patients with vasospastic angina

BACKGROUND

The risk factors for ventricular arrhythmias in patients with coronary vasospasm have not been identified. We evaluated QT dispersion in patients with vasospastic angina and its relation to susceptibility to ventricular arrhythmias during myocardial ischemia and reperfusion.

METHODS AND RESULTS

We assessed the corrected QT (QTc) dispersion before induction of coronary artery spasm by intracoronary injection of acetylcholine (baseline) and 30 minutes after administration of isosorbide dinitrate in 50 patients with vasospastic angina and 50 patients with atypical chest pain. The baseline QTc dispersion was significantly greater in patients with vasospastic angina than in patients with atypical chest pain (mean+/-SD: 69+/-24 versus 44+/-19 ms, 95% confidence interval of mean difference [CI]: 16 to 33 ms; P<0.001). QTc dispersion decreased significantly, to 48+/-15 ms (CI: 15 to 26 ms; P<0.001 versus baseline), after administration of isosorbide dinitrate in patients with vasospastic angina but did not change significantly in patients with atypical chest pain (mean+/-SD: 41+/-17 ms, CI: -3 to 9 ms). During the provocation test, 24 of 50 patients with vasospastic angina experienced ventricular arrhythmias. The baseline QTc dispersion was significantly greater in patients with than without ventricular arrhythmias (mean+/-SD: 77+/-23 versus 61+/-19 ms, CI: 4 to 26 ms; P<0.05).

CONCLUSIONS

Patients with vasospastic angina exhibited an increased baseline QTc dispersion compared with patients with atypical chest pain, which suggests that inhomogeneity of repolarization and susceptibility to ventricular arrhythmias are increased in patients with vasospastic angina, even when asymptomatic. The association between increased QTc dispersion and ventricular arrhythmias during the provocation test suggests that measurement of QT dispersion may help predict which patients with vasospastic angina are at high risk for ventricular arrhythmias during ischemia.

Insulin and insulin-like growth factor-I cause coronary vasorelaxation in vitro

Insulin and insulin-like growth factor-I (IGF-I) may play a role in the modulation of coronary artery tone, yet there are few data regarding their vasoactive effects on the coronary vascular bed. We evaluated the vasorelaxation effects of insulin and IGF-I on porcine coronary epicardial vessels in vitro and elucidated possible mechanisms. Porcine epicardial arteries were contracted with 10(-7) mol/L endothelin-1 and relaxed with cumulative concentrations of either insulin or IGF-I (10(-12) to 10(-7) mol/L). The above experiments were repeated in vessels without endothelium. Vessels were also incubated with the nitric oxide synthase inhibitor NG-monomethyl-L-arginine (L-NMMA; 10(-4) mol/L) with and without 10(-3.5) mol/L L-arginine, the potassium channel blocker tetraethylammonium (TEA; 10(-2) mol/L), and the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3,-alpha]quinoxalin-1-one (ODQ; 10(-5.5) mol/L); vessels were then contracted with endothelin-1 and relaxed with insulin or IGF-I. Insulin and IGF-I were also added after contraction with 60 mmol/L KCl. Insulin and IGF-I caused a similar decrease in coronary epicardial tension after contraction with endothelin-1 (relaxation of 28+/-4% [n=7] and 25+/-3% [n=8] with insulin and IGF-I, respectively; P<0.0001 for both peptides). Removal of the endothelium did not affect these responses. Incubation with L-NMMA, but not ODQ, attenuated the vasorelaxation response to insulin and IGF in vessels without endothelium. L-Arginine did not reverse this effect of L-NMMA. KCl and TEA attenuated the vasorelaxation effect of both insulin and IGF-I. Thus, both insulin and IGF-I caused non-endothelium-dependent coronary vasorelaxation in vitro, probably through a mechanism involving the activation of potassium channels. These findings suggest that insulin and IGF-I participate in the regulation of coronary vasomotor tone.