Coronary vasomotor tone during static and dynamic exercise

Beta-1 vs. beta-2 adrenergic control of coronary blood flow during isometric handgrip exercise in humans

During exercise, β-adrenergic receptors are activated throughout the body. In healthy humans, the net effect of β-adrenergic stimulation is an increase in coronary blood flow. However, the role of vascular β1 vs. β2 receptors in coronary exercise hyperemia is not clear. In this study, we simultaneously measured noninvasive indexes of myocardial oxygen supply (i.e., blood velocity in the left anterior descending coronary artery; Doppler echocardiography) and demand [i.e., rate pressure product (RPP) = heart rate × systolic blood pressure) and tested the hypothesis that β1 blockade with esmolol improves coronary exercise hyperemia compared with nonselective β-blockade with propranolol. Eight healthy young men received intravenous infusions of esmolol, propranolol, and saline on three separate days in a single-blind, randomized, crossover design. During each infusion, subjects performed isometric handgrip exercise until fatigue. Blood pressure, heart rate, and coronary blood velocity (CBV) were measured continuously, and RPP was calculated. Changes in parameters from baseline were compared with paired t-tests. Esmolol (Δ = 3296 ± 1204) and propranolol (Δ = 2997 ± 699) caused similar reductions in peak RPP compared with saline (Δ = 5384 ± 1865). In support of our hypothesis, ΔCBV with esmolol was significantly greater than with propranolol (7.3 ± 2.4 vs. 4.5 ± 1.6 cm/s; P = 0.002). This effect was also evident when normalizing ΔCBV to ΔRPP. In summary, not only does selective β1 blockade reduce myocardial oxygen demand during exercise, but it also unveils β2-receptor-mediated coronary exercise hyperemia.NEW & NOTEWORTHY In this study, we evaluated the role of vascular β1 vs. β2 receptors in coronary exercise hyperemia in a single-blind, randomized, crossover study in healthy men. In response to isometric handgrip exercise, blood flow velocity in the left anterior descending coronary artery was significantly greater with esmolol compared with propranolol. These findings increase our understanding of the individual and combined roles of coronary β1 and β2 adrenergic receptors in humans.

Effect of adrenergic agonists on coronary blood flow: a laboratory study in healthy volunteers

Myocardial oxygen supply and demand mismatch is fundamental to the pathophysiology of ischemia and infarction. The sympathetic nervous system, through α‐adrenergic receptors and β‐adrenergic receptors, influences both myocardial oxygen supply and demand. In animal models, mechanistic studies have established that adrenergic receptors contribute to coronary vascular tone. The purpose of this laboratory study was to noninvasively quantify coronary responses to adrenergic receptor stimulation in humans. Fourteen healthy volunteers (11 men and 3 women) performed isometric handgrip exercise to fatigue followed by intravenous infusion of isoproterenol. A subset of individuals also received infusions of phenylephrine (n = 6), terbutaline (n = 10), and epinephrine (n = 4); all dosages were based on fat‐free mass and were infused slowly to achieve steady‐state. The left anterior descending coronary artery was visualized using Doppler echocardiography. Beat‐by‐beat heart rate (HR), blood pressure (BP), peak diastolic coronary velocity (CBVpeak), and coronary velocity time integral were calculated. Data are presented as M ± SD. Isometric handgrip elicited significant increases in BP, HR, and CBVpeak (from 23.3 ± 5.3 to 34.5 ± 9.9 cm/sec). Isoproterenol raised HR and CBVpeak (from 22.6 ± 4.8 to 43.9 ± 12.4 cm/sec). Terbutaline and epinephrine evoked coronary hyperemia whereas phenylephrine did not significantly alter CBVpeak. Different indices of coronary hyperemia (changes in CBVpeak and velocity time integral) were significantly correlated (R = 0.803). The current data indicate that coronary hyperemia occurs in healthy humans in response to isometric handgrip exercise and low‐dose, steady‐state infusions of isoproterenol, terbutaline, and epinephrine. The contribution of β1 versus β2 receptors to coronary hyperemia remains to be determined. In this echocardiographic study, we demonstrate that coronary blood flow increases when β‐adrenergic receptors are stimulated (i.e., during exercise and different intravenous infusions). Our infusion paradigms and beat‐by‐beat imaging methodologies can be used in future studies to evaluate age‐, sex‐, and disease‐ differences in adrenergic control of coronary blood flow.

Cardiorespiratory Fitness and Atherosclerosis: Recent Data and Future Directions

Historically, the relationship between exercise and the cardiovascular system was viewed as unidirectional, with a disease resulting in exercise limitation and hazard. This article reviews and explores the bidirectional nature, delineating the effects, generally positive, on the cardiovascular system and atherosclerosis. Exercise augments eNOS, affects redox potential, and favorably affects mediators of atherosclerosis including lipids, glucose homeostasis, and inflammation. There are direct effects on the vasculature as well as indirect benefits related to exercise-induced changes in body composition and skeletal muscle. Application of aerobic exercise to specific populations is described, with the hope that this knowledge will move the science forward and improve individual patient outcome.

Sirolimus-Eluting Stents Associated With Paradoxic Coronary Vasoconstriction

OBJECTIVES

The purpose of the present study was to assess coronary vasomotor response to exercise after sirolimus-eluting stent (SES) implantation.

BACKGROUND

Sirolimus-eluting stents have been shown to markedly reduce the incidence of angiographic and clinical restenosis. However, long-term effects of sirolimus on endothelial function are unknown.

METHODS

Coronary vasomotion was evaluated with biplane quantitative coronary angiography at rest and during supine bicycle exercise in 25 patients with coronary artery disease. Eleven patients were treated with a bare-metal stent (BMS) (control group) and 14 patients underwent SES implantation (sirolimus group) for de novo coronary artery lesions. Both groups were studied 6 +/- 1 month after the intervention. Minimal luminal diameter; stent diameter; and proximal, distal, and reference vessel diameter were determined.

RESULTS

The reference vessel showed exercise-induced vasodilation (+13 +/- 4%) in both groups. Vasomotion within the stented vessel segments was abolished. In controls, the adjacent segments proximal and distal to the stent showed exercise-induced vasodilation (+15 +/- 3% and +17 +/- 4%, respectively). In contrast, there was exercise-induced vasoconstriction of the proximal and distal vessel segments adjacent to SESs (-12 +/- 4% and -15 +/- 6%, respectively; p < 0.001 vs. corresponding segments of controls). Sublingual nitroglycerin was associated with maximal vasodilation of the proximal and distal vessel segments in both groups.

CONCLUSIONS

Implantation of a BMS does not affect physiologic response to exercise proximal and distal to the stent. However, SESs are associated with exercise-induced paradoxic coronary vasoconstriction of the adjacent vessel segments, although vasodilatory response to nitroglycerin is maintained. These observations suggest (drug-induced) endothelial dysfunction as the underlying mechanism.

Impact of exercise-induced coronary vasomotion on anti-ischemic therapy

Coronary vasomotion has an important role in the regulation of myocardial perfusion. During dynamic exercise, normal coronary arteries dilate, whereas stenotic arteries constrict. This exercise-induced vasoconstriction has been associated with the occurrence of myocardial ischemia and has been believed to be the result of endothelial dysfunction, with a reduced release or production of EDRF, increased sympathetic stimulation, enhanced platelet aggregation with release of thromboxane A2 and serotonin, or a passive collapse of the disease-free wall segment within the stenosis (the Bernoulli effect), or a combination of any of these. More recently, it has been realized that pharmacological treatment might prevent exercise-induced vasoconstriction and, thus, reduce myocardial ischemia and the occurrence of angina pectoris. Vasodilators such as nitrates, calcium antagonists or alpha-receptor blockers dilate the coronary arteries and prevent coronary stenosis narrowing during exercise. In contrast, beta-blocking agents are associated with coronary vasoconstriction at rest, but--conversely--can induce coronary vasodilatation during exercise. Pharmacological treatment in patients with stable angina pectoris may improve myocardial ischemia by reducing pre- and afterload, myocardial contractility, oxygen consumption, and vasomotor tone. However, coronary collateral perfusion can modify these effects by shunting blood from the non-ischemic to the ischemic region (collateral flow) or by shunting blood from the ischemic to the non-ischemic zone (coronary steal phenomenon). Typically, a steal phenomenon has been reported in patients receiving either dipyridamole or calcium antagonists, whereas a reversed steal has been described after beta-blockade, with an increase in contralateral tone shunting blood from the non-ischemic to the ischemic zone (reverse steal phenomenon).

Coronary artery dimensions in primary and secondary left ventricular hypertrophy

BACKGROUND

Coronary artery enlargement has been previously described in left ventricular hypertrophy.

OBJECTIVES

We sought to assess coronary artery dimensions and their relation to left ventricular muscle mass in primary and secondary hypertrophy.

METHODS

Cross-sectional area of the left and right coronary arteries was determined by quantitative coronary angiography in 52 patients: 12 control subjects and 40 patients (13 with hypertrophic cardiomyopathy, 12 with dilated cardiomyopathy and 15 with aortic valve disease). As a measure of left ventricular hypertrophy, angiographic left ventricular mass and equatorial cross-sectional muscle area were determined.

RESULTS

Cross-sectional area of both the left and right coronary arteries is increased in left ventricular hypertrophy (p < 0.05 vs. values in control subjects). There is a curvilinear relation between left coronary artery size and left ventricular muscle mass (r = 0.76) or cross-sectional muscle area (r = 0.75). However, normalization of coronary cross-sectional area for left ventricular muscle mass or muscle area shows insufficient enlargement of the coronary arteries in both primary and secondary hypertrophy.

CONCLUSIONS

1) Coronary artery size increases as left ventricular mass increases in both primary and secondary hypertrophy. 2) The enlargement of left coronary cross-sectional area is independent of the cause of the increase in left ventricular mass. 3) The size of the coronary arteries is inappropriate with regard to left ventricular hypertrophy. Thus, the stimulus for growth of the coronary arteries is not influenced by the underlying disease but appears to depend on the degree of left ventricular hypertrophy.

Relation of basal coronary tone and vasospastic activity in patients with variant angina

OBJECTIVE

To examine the vasoconstrictor response to ergonovine and the vasodilator response to isosorbide dinitrate in spastic and non-spastic coronary segments from 31 patients undergoing serial angiographic follow up of variant angina.

METHODS

Coronary angiograms and ergonovine provocation tests were repeated at an interval of 45 (SD 15) months apart. While all 31 patients showed a positive response to ergonovine initially, vasospastic responsiveness persisted in only 16 patients at follow up (group 1) and not in the other 15 patients in whom symptoms of variant angina had resolved (group 2). Mean luminal diameter of 170 normal or near normal entire coronary segments (American Heart Association classification) were measured (a) at baseline, (b) after the administration of ergonovine, and (c) after the administration of isosorbide dinitrate, during both the initial and follow up angiograms using a computer based quantitative angiography analysis system (CAAS II).

RESULTS

In vasospastic patients (initial and follow up angiograms in group 1, and initial angiogram in group 2), basal tone was significantly higher in spastic segments compared to adjacent segments or segments in non-spastic vessels. The diagnostic sensitivity and specificity at 20% increase in basal coronary tone for the prediction of vasospasm were 77% and 73%, respectively.

CONCLUSIONS

Coronary artery tone may change in proportion to the activity of variant angina over several years. Contrary to some previous reports, the estimation of basal coronary tone may be useful in the assessment of vasospastic activity in patients with variant angina.

Coronary vasomotion during dynamic exercise: influence of intravenous and intracoronary nicardipine

OBJECTIVES

Our aim was to evaluate the influence of a calcium channel blocking agent of the dihydropyridine group (nicardipine) on coronary vasomotion during dynamic exercise.

BACKGROUND

Coronary vasomotion plays an important role in the pathophysiology of myocardial ischemia.

METHODS

Twenty-nine patients with coronary artery disease were studied at rest and during bicycle exercise with the use of biplane quantitative coronary angiography. Twelve patients without pretreatment (group 1) served as control subjects. Seventeen patients (group 2) received nicardipine, either 0.2 mg by intracoronary injection (n = 9) or 2.5 mg intravenously (n = 8) before exercise.

RESULTS

In the control group there was exercise-induced vasoconstriction (-29%, p < 0.001) of the stenotic segment but coronary vasodilation (+22%, p < 0.05) of the normal vessel segment. In group 2, nicardipine induced coronary vasodilation of both the normal (+16%, p < 0.001) and the stenotic vessel segment (+35%). During subsequent exercise there was some additional vasodilation of normal (+4%, p = NS) and stenotic arteries (+5%, p = NS). There was no difference between either intracoronary or intravenous nicardipine with regard to vasodilation. Application of sublingual nitroglycerin was associated with significant vasodilation of the normal vessel segment in groups 1 (+18%, p < 0.05) and 2 (+15%, p < 0.001). The stenotic vessels showed a significant increase in percent cross-sectional area after nitroglycerin in groups 1 (+12%, p = NS) and 2 (+51%, p < 0.001). Exertional angina pectoris occurred less frequently in group 2 (18%) than in group 1 (67% [p < 0.005 vs. group 2]); group 2 also had a smaller increase in mean pulmonary artery pressure (+14 vs. +21 mm Hg, p < 0.05).

CONCLUSIONS

Exercise induces vasoconstriction of stenotic, but vasodilation of normal, coronary vessel segments. Intravenous and intracoronary nicardipine prevent vasoconstriction of stenotic coronary arteries during exercise and exert a significant anti-ischemic effect. The combination of two anti-ischemic drugs, nitroglycerin and nicardipine, has an additive effect on coronary vasomotion that is seen only in the stenotic vessel segment. Thus, the anti-ischemic action of nicardipine is mainly due to a primary effect on coronary vasomotor response rather than to secondary effects such as changes in loading conditions.

Lipid lowering and plaque regression. New insights into prevention of plaque disruption and clinical events in coronary disease

The consensus of evidence from angiographic trials demonstrates both coronary artery and clinical benefits from lowering of lipids by a variety of regimens. The findings of reduced arterial disease progression and increased regression have been convincing but, at best, modest in their magnitude. For example, among those treated intensively in FATS, the mean improvement in proximal stenosis severity per patient was < 1% stenosis, and only 12% of all lesions showed convincing regression. In view of these modest arterial benefits, the associated reductions in cardiovascular events have been surprisingly great. For example, coronary events were reduced 75% in FATS; this was entirely a result of a 93% reduction in the likelihood that a mildly or moderately diseased arterial segment would experience substantial progression to a severe lesion at the time of a clinical event. We believe that the magnitude of the clinical benefit is best explained in terms of this observation, according to the following lines of reasoning. Clinical events most commonly spring from lesions that are initially of mild or moderate severity and then abruptly undergo a disruptive transformation to a severe culprit lesion. The process of plaque fissuring, leading to plaque disruption and thrombosis, triggers most clinical coronary events. Fissuring is predicted by a large accumulation of core lipid in the plaque and by a high density of lipid-laden macrophages in its thinned fibrous cap. Lesions with these characteristics constitute only 10-20% of the overall lesion population but account for 80-90% of the acute clinical events. In the experimental setting, normalization of an atherogenic lipid profile substantially decreases the number of lipid-laden intimal macrophages (foam cells) and depletes cholesterol from the core lipid pool. In the clinical setting, intensive lipid lowering virtually halts the progression of mild and moderate lesions to clinical events. Thus, the reduction in clinical events observed in these trials appears to be best explained by the relation of the lipid and foam cell content of the plaque to its likelihood of fissuring and by the effects of lipid-lowering therapy on these "high-risk" features of plaque morphology. The composite of data presented here supports the hypothesis that lipid-lowering therapy selectively depletes (regresses) that relatively small but dangerous subgroup of fatty lesions containing a large lipid core and dense clusters of intimal macrophages. By doing so, these lesions are effectively stabilized and clinical event rate is accordingly decreased.

Normalization of coronary vasomotion after percutaneous transluminal coronary angioplasty?

BACKGROUND

Coronary vasomotion was evaluated at rest and during bicycle exercise in 33 patients (age, 53 +/- 7 years) with coronary artery disease. In a first group of patients (n = 15), vasomotion was studied before and 4.3 +/- 2.3 months (early) after percutaneous transluminal coronary angioplasty (PTCA), whereas in a second group (n = 18), exercise coronary arteriography was performed 30 +/- 11 months (late) after successful PTCA. Patients with restenosis (percent area stenosis greater than or equal to 75% or percent diameter stenosis greater than or equal to 50%) were excluded.

METHODS AND RESULTS

Luminal areas of a normal segment and the stenotic segment were determined at rest, during supine bicycle exercise, and 5 minutes after sublingual nitrate administration by using biplane quantitative coronary arteriography. Work loads before and early after PTCA were identical in group 1 and similar late after PTCA in group 2. Percent area stenosis decreased from 86% to 36% (p less than 0.001) in group 1 and from 93% to 46% (p less than 0.001) in group 2. Normal coronary arteries showed mild vasodilation during exercise before (+3%, NS versus rest), early (+7%, NS versus rest), and late after (+10%, p less than 0.05 versus rest) PTCA. Administration of sublingual nitrate was associated with significant vasodilation of the normal vessel segment before (+27%, p less than 0.001 versus rest), early (+31%, p less than 0.001 versus rest), and late (+21%, p less than 0.001 versus rest) after PTCA. In contrast, the stenotic vessel segments showed coronary vasoconstriction during exercise before PTCA (-25%, p less than 0.001 versus rest), whereas minimal vasomotion was observed early (+2%; NS versus rest) as well as late (+5%; NS versus rest) after PTCA. Individual post-PTCA (early and late) exercise data elicited vasodilation in 19, no vasomotion in four, and vasoconstriction in 10 instances. Sublingual administration of nitrate was associated with a significant increase in minimal luminal area before (+18%, p less than 0.05 versus rest), early (+24%, p less than 0.01 versus rest), and late (+16%, p less than 0.001 versus rest) after PTCA. An inverse linear correlation was found between the percent change in minimal luminal area during peak exercise and percent area stenosis at rest (r = 0.77, p less than 0.001).

CONCLUSIONS

Exercise-induced stenosis narrowing is observed before PTCA but normal vasomotion is reestablished in two thirds of all patients early and late after PTCA. In one third, an abnormal reaction to exercise (i.e., vasoconstriction) persisted after PTCA, mainly in those patients with a residual area stenosis of 50% (percent diameter stenosis of 30%) or more. Thus, PTCA appears to have a salutary effect on coronary vasomotion during exercise, which, however, remains dependent on the severity of the residual stenosis.

Moderate hypothermia in the management of resistant automatic tachycardias in children

BACKGROUND

Automatic focus tachycardias are often resistant to electrical and pharmacological treatment. Moderate systemic hypothermia (32-34 degrees C) may reduce the tachycardia rate in children with His bundle tachycardia after cardiac surgery.

METHODS

The case notes of seven children with automatic focus tachycardias treated with hypothermia were reviewed. Six had His bundle tachycardia after cardiac surgery and one had ectopic atrial tachycardia; all had signs of low cardiac output.

RESULTS

Hypothermia led to a reduction in heart rate in all patients (from 211 (28) (mean (SD] to 146 (5) beats/minute, p less than 0.001), with rises in systolic blood pressure (from 74 (14) mm Hg to 97 (10) mm Hg, p less than 0.01) and hourly urine output (from 0.5 (0.4) ml/kg to 4.6 (2.8) ml/kg, p less than 0.02). No direct adverse effects were noted. The arrhythmia did not resolve in three children, who died (two with His bundle tachycardia after Fontan procedures and one with ectopic atrial tachycardia); the other four regained sinus rhythm which was maintained at follow up of 3-13 (mean 9) months.

CONCLUSIONS

Moderate systemic hypothermia led to slowing of the arrhythmia rate and an improvement in cardiac output in patients with resistant automatic focus tachycardias. It can be used to improve the haemodynamic condition while other measures of arrhythmia control are being pursued or until spontaneous recovery of normal rhythm.

The poststenotic vessel segment during dynamic exercise: effect of oral isosorbide-dinitrate

Coronary vasomotion of normal, stenotic, and poststenotic vessel segments was studied in 18 patients with coronary artery disease at rest, during submaximal bicycle exercise, and 5 min after sublingual nitroglycerin or oral isosorbide-dinitrate (ISDN) spray. Patients were divided into two groups: group 1 consisted of 10 patients with no premedication prior to exercise, and group 2 consisted of 8 patients receiving 120 mg long-acting ISDN orally 1 h before the procedure. Quantitative coronary arteriography was carried out in biplane projection using a semi-automatic computer system. The normal vessel segment showed a trend toward a small increase in cross-sectional area during exercise in both groups (+3% in group 1 and +4% in group 2, both NS). After sublingual nitroglycerin following exercise, there was a significant increase in group 1 (+29%, p less than 0.001 vs rest) but not after ISDN spray in group 2 (+5%, NS vs rest). The stenotic vessel segment showed exercise-induced stenosis narrowing in group 1 (-31%, p less than 0.01 vs rest) which was prevented by oral ISDN (+6%, NS vs rest). After exercise, sublingual administration of nitroglycerin or ISDN spray was associated with no significant change in stenosis area in either group. The poststenotic vessel segment showed no significant vasomotion during exercise in both groups (area change +6% in group 1 and +7% in group 2), but poststenotic luminal area increased after sublingual nitroglycerin (group 1: +15%, p less than 0.01 vs rest) or ISDN spray (group 2: +15%, p less than 0.05 vs rest). The mean pulmonary artery pressure increased during exercise from 22 to 39 mmHg (p less than 0.001) in group 1 and from 14 to 27 mmHg (p less than 0.001) in group 2. At rest (p less than 0.001) and during exercise (p less than 0.01) mean pulmonary pressure was lower in group 2 than in group 1. Thus, it is concluded that coronary vasomotion of the poststenotic vessel segment is only minimal during exercise and is not affected by coronary vasomotion of the stenotic vessel segment. Pretreatment with oral ISDN did not influence coronary vasomotion of the poststenotic vessel segment, but prevented exercise-induced stenosis narrowing. In the untreated patients, vasoconstriction of the stenotic vessel segment is limited to the site of the stenosis, and it appears that there is no release of vasoactive substances with vasoconstrictive influences on the poststenotic segment.

Coronary vasomotor tone in large epicardial coronary arteries with special emphasis on beta-adrenergic vasomotion, effects of beta-blockade

Changes in coronary vasomotor tone of large epicardial coronary arteries today can be assessed quite accurately by exact measurements of coronary diameters applying computer assisted systems. The effect of various vasodilators (nitrates, calcium antagonists, EDRF-dependent compounds) was tested in this way. It appears that normal coronary artery segments reach a maximum of dilator reserve with an increase of luminal diameter of approximately 30-40%; different patterns of kinetics were, however, encountered. beta-Blocking agents, both non-selective (propranolol) and selective (atenolol), were found to lead to a gradual vasoconstriction, i.e., a decrease in diameter by approximately 20-25% over 20 min, an effect which is overcome by nitrates. New beta-blocking compounds with vasodilator properties, such as celiprolol, show no constriction. The vasoconstrictor effect of propranolol and atenolol may not only be due to the decrease of flow following the drop in myocardial oxygen consumption, but could also reflect an unopposed alpha-adrenergic tone. The clinical aspects of this observation are discussed.