Adrenergically mediated coronary vasoconstriction in patients with syndrome X

Pharmacotherapy in patients with vasomotor disorders

Background

Anginal symptoms in patients with non-obstructive coronary artery disease are frequently related to vasomotor disorders of the coronary circulation. Although frequently overlooked, a distinct diagnosis of different vasomotor disorders can be made by intracoronary function testing. Early detection and treatment seems beneficial, but little evidence is available for the medical treatment of these disorders. Nevertheless, there are several pharmacotherapeutic options available to treat these patients and improve quality of life.

Methods & findings

We performed an extensive yet non-systematic literature search to explore available pharmacotherapeutic strategies for addressing vasomotor disorders in individuals experiencing angina and non-obstructive coronary artery disease. This article presents a comprehensive overview of therapeutic possibilities for patients exhibiting abnormal vasoconstriction (such as spasm) and abnormal vasodilation (like coronary microvascular dysfunction).

Conclusion

Treatment of vasomotor disorders can be very challenging, but a general treatment algorithm based on the existing evidence and the best available current practice is feasible.

Management of microvascular angina pectoris

Microvascular angina (MVA) is defined as angina pectoris caused by abnormalities of small coronary arteries. In its most typical presentation, MVA is characterized by angina attacks mainly caused by effort, evidence of myocardial ischemia on non-invasive stress tests, but normal coronary arteries at angiography. Patients with stable MVA have excellent long-term prognoses, but often present with persistent and/or worsening of angina symptoms. Treatment of MVA is initially based on standard anti-ischemic drugs (beta-blockers, calcium antagonists, and nitrates), but control of symptoms is often insufficient. In these cases, several additional drugs, with different potential anti-ischemic effects, have been proposed, including ranolazine, ivabradine, angiotensin-converting enzyme (ACE) inhibitors, xanthine derivatives, nicorandil, statins, alpha-blockers and, in perimenopausal women, estrogens. In patients with 'refractory MVA', some further alternative therapies (e.g., spinal cord stimulation, pain-inhibiting substances such as imipramine, rehabilitation programs) have shown favorable results.

Usefulness of impairment of cardiac adrenergic nerve function to predict outcome in patients with cardiac syndrome X

Patients with cardiac syndrome X (CSX) have an excellent long-term prognosis, but a significant number show worsening angina over time. Previous studies have found a significant impairment of cardiac uptake of iodine-123-meta-iodobenzylguanidine (MIBG) on myocardial scintigraphy, indicating abnormal function of cardiac adrenergic nerve fibers. The aim of this study was to assess whether cardiac MIBG results can predict symptomatic outcome in patients with CSX. Cardiac MIBG scintigraphy was performed in 40 patients with CSX (mean age 58 ± 5 years, 14 men). Cardiac MIBG uptake was measured by the heart/mediastinum uptake ratio and a single photon-emission computed tomographic regional uptake score (higher values reflected lower uptake). Clinical findings, exercise stress test parameters, sestamibi stress myocardial scintigraphy, and C-reactive protein serum levels were also assessed. At an average follow-up of 79 months (range 36 to 144), no patient had died or developed acute myocardial infarction. Cardiac MIBG defect score was significantly lower in patients with worsening versus those without worsening of angina status (13 ± 7 vs 38 ± 28, p = 0.001), in those with versus those without hospital readmission because of recurrent chest pain (15 ± 9 vs 35 ± 29, p = 0.01), and in those who underwent versus those who did not undergo repeat coronary angiography (11 ± 7 vs 36 ± 27, p = 0.001). Significant correlations were found between quality of life (as assessed by the EuroQoL scale) and heart/mediastinum ratio (r = 0.48, p = 0.002) and cardiac MIBG uptake score (r = -0.69, p <0.001). No other clinical or laboratory variable showed a significant association with clinical end points. In conclusion, in patients with CSX, abnormal function of cardiac adrenergic nerve fibers, as assessed by an impairment of cardiac MIBG uptake, identifies those with worse symptomatic clinical outcomes.

Cardiac adrenergic nerve function in patients with cardiac syndrome X

BACKGROUND

We previously found a severe impairment of cardiac uptake of I-metaiodobenzylguanidine (MIBG), an analogue of norepinephrine, on myocardial scintigraphy in a small group of patients with cardiac syndrome X (CSX), suggesting a dysfunction of cardiac adrenergic nerve fibres. In this study, we assessed the consistency of these previous findings in a larger group of these patients.

METHODS

Planar and single-photon emission computed tomography MIBG myocardial scintigraphy was performed in 40 CSX patients (58 +/- 7 years, 17 men). Cardiac MIBG uptake was measured by the heart/mediastinum ratio and by a single-photon emission computed tomography regional cardiac MIBG uptake defect score (higher values = lower uptake). As a control group, we studied 20 healthy individuals (56 +/- 6 years, nine men). An exercise stress Tc-SestaMIBI myocardial scintigraphy was performed in 34 CSX patients (85%).

RESULTS

Cardiac MIBG defects were observed in 30 patients (75%), with nine (22.5%) showing no cardiac MIBG uptake at all. Compared with controls, CSX patients showed a significantly lower heart/mediastinum ratio (1.70 +/- 0.35 vs. 2.1 +/- 0.22, P < 0.001) and a higher cardiac MIBG defect score (27 +/- 25 vs. 4.4 +/- 2.5, P < 0.001). No differences were found in lung MIBG uptake between the two groups. Reversible perfusion defects on stress myocardial scintigraphy were found in 17 out of 34 CSX patients (50%), all of whom also had abnormal cardiac MIBG uptake; cardiac MIBG uptake abnormalities were also present in nine of 17 patients with normal perfusion scintigraphic images. Cardiac MIBG uptake findings were similar in our first 12 patients and in the 28 patients studied subsequently.

CONCLUSION

Our data show a relevant impairment of cardiac MIBG uptake in patients with CSX, suggesting that functional abnormalities in cardiac adrenergic nerve function may play a significant role in the mechanisms responsible for the syndrome.

Castration modifies aortic vasoreactivity and serum fatty acids in a sucrose-fed rat model of metabolic syndrome

Levels of testosterone and estradiol influence the incidence of cardiovascular diseases: generally, estrogens in females are protective before menopause; coronaropathies, hypertension, and dyslipidemias in normal men are more frequent at comparable ages. We investigated the modulation by castration of in vitro vasoreactivity, serum lipid content, and systolic blood pressure (SBP) in rats with sucrose-induced metabolic syndrome. The main characteristics of the rat model are: hypertriglyceridemia, moderately high blood pressure, intra-abdominal accumulation of adipose tissue, hyperinsulinemia, nephropathy, increased oxidative stress, and altered vasoreactivity. Male weanling rats received 30% sucrose solution for 16 weeks (metabolic syndrome; MS), controls (C) had plain water; both had commercial rodent chow. They were subdivided into five groups with two subgroups each: Group 1, intact C and MS rats, Groups 2-5, C and MS rats castrated for periods of 16, 12, 8, and 4 weeks. At the end of the study period, systolic blood pressure was measured, and blood and aortas were obtained for fatty acid determination and vasoreactivity assays, respectively. After 16 weeks' sucrose treatment MS aortas showed hypercontractility and decreased vasodilation. Palmitic and palmitoleic acids were increased in MS versus C. Arachidonic acid levels in MS were lower than in intact or castrated C. Long-term castration of 16 weeks normalized the levels of palmitic and oleic acids. With the shorter periods of castration, contractility increased and relaxation decreased in C and MS, but it was more significant in C. Regarding fatty acid composition, long-term castration increased polyunsaturated (arachidonic and eicosapentaenoic) fatty acids. The shorter periods did not modify the fatty acid profile in either C or MS. Metabolic syndrome altered SBP, aortic reactivity, and levels of fatty acids; castration of long duration normalized them in some cases.

Assessment of coronary flow reserve using single photon emission computed tomography with technetium 99m-labeled tracers

The quantitative assessment of coronary flow reserve (CFR) may be useful for the functional evaluation of coronary artery disease (CAD), allowing judgment of its severity, tracking of disease progression, and evaluation of the anti-ischemic efficacy of therapeutic strategies. Invasive techniques, such as intracoronary Doppler ultrasound and the pressure-derived method, which directly assess CFR velocity and fractional flow reserve, have been used for the evaluation of the physiologic significance of coronary lesions. Considerable progress has been made in the improvement of technologies directed toward the noninvasive quantification of myocardial blood flow and CFR. Positron emission tomography has emerged as an accurate technique to quantify CFR. The absolute measurements obtained with this noninvasive approach have been widely validated. Nevertheless, it has not been applied to routine studies because of its high cost and complexity. On the other hand, technetium 99m-labeled tracers have been largely used for the evaluation of myocardial perfusion with single photon emission computed tomography (SPECT) imaging in patients with suspected or known CAD. Recently, attempts to estimate CFR with SPECT tracers have been made to obtain, with noninvasive methods, data for quantitative functional assessment of CAD. This review analyzes the relative merit and limitations of CFR measurements by cardiac SPECT imaging with Tc-99m-labeled tracers and describes the potential clinical applications of this technique.

Myocardial perfusion quantification in patients suspected of cardiac syndrome X with positive and negative exercise testing: a [13N]ammonia positron emission tomography study

BACKGROUND

The combination of angina pectoris, angiographically normal coronary arteries, and a positive exercise stress test (EST) is referred to as cardiac syndrome X. However, a large group of patients suspected of syndrome X reveals a normal exercise stress test and weakens the diagnosis of syndrome X. Previous studies demonstrated an impaired coronary flow reserve on ammonia positron emission tomography (PET) in patients with syndrome X.

AIM

To evaluate the coronary flow reserve in patients suspected of syndrome X with positive and negative EST findings, using [(13)N]ammonia PET as the diagnostic aid.

METHODS

Forty-two patients with chest pain and a normal coronary angiography, were analysed by exercise stress testing (EST) and the dypyridamole stress test (DST) on [(13)N]ammonia PET. Two subgroups were predefined, based on outcome of EST: an EST positive and negative group. A normal control group was used as the reference method.

RESULTS

A total of 24 (57%) out of 42 patients had significant ST-T changes (EST positive). [(13)N]ammonia PET showed a significantly lower rest flow in the EST positive and EST negative group compared to controls (P<0.001 and P=0.0028, respectively). DST [(13)N]ammonia PET perfusion was significantly reduced in flow in both the EST positive and EST negative groups (P<0.001 both), as was the DST/rest [(13)N]ammonia perfusion reserve (P<0.001 for both), compared to normal controls.

CONCLUSION

PET demonstrates a reduced coronary flow reserve in patients suspected of syndrome X, irrespective of the EST findings.

Assessment of coronary flow reserve by sestamibi imaging in patients with typical chest pain and normal coronary arteries

PURPOSE

We assessed coronary flow reserve (CFR) by sestamibi imaging in patients with typical chest pain, positive exercise stress test and normal coronary vessels.

METHODS

Thirty-five patients with typical chest pain and normal angiogram and 12 control subjects with atypical chest pain underwent dipyridamole/rest (99m)Tc-sestamibi imaging. Myocardial blood flow (MBF) was estimated by measuring first transit counts in the pulmonary artery and myocardial counts from SPECT images. Estimated CFR was expressed as the ratio of stress to rest MBF. Rest MBF and CFR were corrected for rate-pressure product (RPP) and expressed as normalised MBF (MBF(n)) and normalised CFR (CFR(n)). Coronary vascular resistances (CVR) were calculated as the ratio between mean arterial pressure and estimated MBF.

RESULTS

At rest, estimated MBF and MBF(n) were lower in controls than in patients (0.98 +/- 0.4 vs 1.30 +/- 0.3 counts/pixel/s and 1.14 +/- 0.5 vs 1.64 +/- 0.6 counts/pixel/s, respectively, both p < 0.02). Stress MBF was not different between controls and patients (2.34 +/- 0.8 vs 2.01 +/- 0.7 counts/pixel/s, p=NS). Estimated CFR was 2.40 +/- 0.3 in controls and 1.54 +/- 0.3 in patients (p < 0.0001). After correction for the RPP, CFR(n) was still higher in controls than in patients (2.1 +/- 0.5 vs 1.29 +/- 0.5, p < 0.0001). At baseline, CVR values were lower (p < 0.01) in patients than in controls. Dipyridamole-induced changes in CVR were greater (p < 0.0001) in controls (-63%) than in patients (-35%). In the overall study population, a significant correlation between dipyridamole-induced changes in CVR and CFR was observed (r = -0.88, p < 0.0001).

CONCLUSION

SPECT might represent a useful non-invasive method for assessing coronary vascular function in patients with angina and a normal coronary angiogram.

Effects of distension of urinary bladder on coronary conduit and resistance vessels in hyperlipidemic patients

BACKGROUND

Distension of the urinary bladder reflexly causes a change of coronary vasomotor response. The effect of such distension on the coronary circulation in hyperlipidemic patients, a condition with impaired endothelial function, remains unknown.

HYPOTHESIS

We tested the hypothesis whether urinary bladder distension caused an exaggerated vasomotor response of epicardial and resistance vasoconstriction in hyperlipidemic patients.

METHODS

Thirty patients with early atherosclerosis (< 50% diameter stenosis) were divided into three groups: Group 1 (n = 10): hyperlipidemia without doxazosin administration; Group 2 (n = 10): hyperlipidemia with pretreatment of alpha1-adrenergic receptor blocker (oral doxazosin 2 mg); and Group 3 (n = 10): normolipidemia. A prospective analysis of the results of quantitative angiograms, intracoronary Doppler flow, and lactate concentrations from aortic root and coronary sinus was performed during distension of urinary bladder.

RESULTS

Bladder distension significantly decreased coronary diameter at the stenotic segments (p = 0.004), coronary blood flow (p = 0.05), and increased coronary resistance (p = 0.006) compared with baseline values, in Group 1 patients. In Group 2 patients during bladder distension, coronary diameter, coronary blood flow, and coronary resistance showed no significant changes compared with baseline values. There were significant differences of stenotic coronary diameter (p = 0.01) between Groups 1 and 3 during bladder distension despite similar changes in rate-pressure product. No significant differences were noted among the groups in the responses of coronary diameter, coronary blood flow, and coronary resistance after nitroglycerin administration.

CONCLUSIONS

The present study showed that urinary bladder distension caused an abnormal vasomotor response of epicardial vasoconstriction and that a concomitant increased coronary resistance involved mechanisms related to alpha1-adrenoceptors. Hyperlipidemia may further impair the response. Pretreated administration of doxazosin had reversed the changes toward baseline. Vasoconstriction during bladder distension can be relieved after nitroglycerin administration, suggesting an unchanged responsiveness of vascular smooth muscle cells to such distension.

Myocardial perfusion in patients with typical chest pain and normal angiogram

BACKGROUND

Approximately 10-30% of patients with typical chest pain present normal epicardial coronaries. In a proportion of these patients, angina is attributed to microvascular dysfunction. Previous studies investigating whether angina is the result of abnormal resting or stress perfusion are controversial but limited by varying inclusion criteria. Therefore, we investigated whether microvascular dysfunction in these patients is associated with perfusion abnormalities at rest or at stress.

PATIENTS AND METHODS

In 58 patients (39 female, 19 male, mean age 58+/-10 years) with angina and normal angiogram as well as 10 control patients with atypical chest pain and normal coronaries (six female, four male, mean age 53+/-11 years) myocardial blood flow (MBF) was measured at rest and under dipyridamole using 13N-ammonia PET. Resting MBF and coronary flow reserve (CFR) as the ratio of hyperaemic to resting MBF were corrected for rate-pressure-product (RPP): normalized resting MBF (MBFn)=MBFx10,000/RPP and CFRn=CFRxRPP/10,000.

RESULTS

Sixteen/58 patients had a normal CFRn (=2.5; group I; CFRn: 3.1+/-0.88); the same as the controls (CFRn: 3.3+/-0.74). Forty-two/58 patients presented a reduced CFRn (group II; CFRn: 1.78+/-0.57). Group II had both a higher MBFn (group II: 1.30+/-0.33 vs. Group I: 1.03+/-0.26; P<0.05 and vs. controls: 1.07+/-0.19; P<0.01) and a lower hyperaemic MBF (group II: 2.25+/-0.76 mL g-1 min-1 vs. Group I: 3.07+/-0.78 mL g-1 min-1; P<0.001 and vs. controls: 3.41+/-0.94 mL g-1 min-1; P<0.0001).

CONCLUSION

Impaired CFRn in patients with typical angina and normal angiogram is owing to both an increased resting and reduced hyperaemic MBF. Therefore, PET represents a prerequisite for further studies to optimize treatment in individuals with anginal pain and normal coronary angiogram.

Abnormal pH-sensing of platelet Na+/H+ exchanger in patients with cardiac syndrome X

An enhanced activity of Na(+)/Li(+) countertransport, studied as a surrogate of Na(+)/H(+) exchanger, has been described in red blood cells of patients with cardiac syndrome X. In this study we investigated whether abnormalities in the activity of platelet Na(+)/H(+) exchanger (NHE) also existed in syndrome X patients and whether such abnormality was associated with platelet activation. Platelet NHE activity was evaluated in 21 syndrome X patients and 18 controls by measuring the pH recovery in platelets after acid loading and/or thrombin stimulation. The linear correlation existing between the initial intracytoplasmic pH (pH(i)) values and the maximal velocity of pH recovery allowed to calculate the values of slope and intercept at pH(i)=6.6 (I(pH6.6)) for each individual. Urinary excretion of the major TXB(2) metabolite, 11-dehydro-TXB(2) was measured in 15 syndrome X patients and 15 controls. The acidification-induced NHE activity resulted significantly higher in syndrome X patients compared to controls. Indeed, slope values were 0.75+/-0.29 and 0.5+/-0.23 min(-1) in patients and controls, respectively (P=0.01), while I(pH6.6) values were 0.24+/-0.1 and 0.17+/-0.1 DeltapH/min (P=0.04). The thrombin-stimulated NHE activity, however, was not different in the two groups and no significant difference in the urinary excretion of 11-dehydro-TXB(2) between patients and controls (median 920 vs. 765 pg/mg creatinine, respectively) (P=0.32) was also found. Thus our data demonstrate an alkaline shift in pH-dependence of platelet NHE of syndrome X patients. This abnormality does not seem to be associated with increased platelet activation.

Cardiac syndrome X. Diagnosis, pathogenesis and management

Patients with cardiac syndrome X (typical chest pain and normal coronary arteriograms) represent a heterogeneous syndrome, which encompasses different pathogenic mechanisms. Although symptoms in most patients with cardiac syndrome X are non-cardiac, a sizable proportion of them have angina pectoris due to transient myocardial ischemia. Thus radionuclide myocardial perfusion defects, coronary sinus oxygen saturation abnormalities and pH changes, myocardial lactate production and stress-induced alterations of cardiac high energy phosphate suggest an ischemic origin of symptoms in at least a proportion of patients with cardiac syndrome X. Microvascular abnormalities, caused by endothelial dysfunction, appear to be responsible for myocardial ischemia in patients with cardiac syndrome X. Endothelial dysfunction is likely to be multifactorial in these patients and it is conceivable that risk factors such as hypertension, hypercholesterolemia, diabetes mellitus and smoking can contribute to its development. Most patients with cardiac syndrome X are postmenopausal women and estrogen deficiency has been therefore proposed as a pathogenic factor in female patients. Additional factors such as abnormal pain perception may contribute to the pathogenesis of chest pain in patients with angina pectoris and normal coronary angiograms. Although prognosis is good regarding survival, patients with cardiac syndrome X have an impaired quality of life. Management of this syndrome represents a major challenge to the treating physician. Understanding the mechanism underlying the condition is of vital importance for patient management. Thus diagnostic tests should aim at identifying the cause of the symptoms in the individual patient, i.e. myocardial ischemia, increased pain perception, abnormalities of adrenergic tone, non-cardiac mechanisms, etc. Moreover, it is important to bear in mind that treatment of cardiac syndrome X should be mainly directed towards improving quality of life, as prognosis is usually good in these patients. Conventional antianginal agents such nitrates, calcium channel antagonists, beta-adrenoceptor antagonists and nicorandil are effective particularly in patients in whom chest pain and ECG changes are clearly suggestive of myocardial ischemia and in those with objective documentation of ischemia. Angiotensin-converting enzyme inhibitors have been shown to be useful in syndrome X patients with increased adrenergic tone, borderline systemic hypertension, and those with documented endothelial dysfunction. Analgesic interventions of different sorts have been proposed based on the hypothesis that somatic and visceral perception of pain is altered in cardiac syndrome X patients. Pharmacological agents such as imipramine and aminophylline, and neural electrical stimulation techniques have been assessed in recent years with encouraging results. Psychological treatment, particularly cognitive therapy, appears to be useful in defined patient subsets. Relaxation techniques such as transcendental meditation have been successfully used in small studies and shown to improve not only chest pain but also exercise-induced ST segment changes. Reports indicate that these techniques improve quality of life.

Recent developments in microvascular angina

Microvascular angina (Syndrome X) is an extremely heterogeneous clinical entity that is the product of genetic, coronary microvascular, metabolic, and clinical factors, which combine together to produce distinct cardiac manifestations and complications. The interactions of these abnormalities remain poorly understood. The diagnosis is considered in patients with anginal symptoms and no epicardial coronary narrowing. Therapy is also problematic, with beta-blockers as first-line pharmacotherapy followed by angiotensin-converting enzyme inhibitors and calcium channel blockers.

Distension of urinary bladder induces exaggerated coronary constriction in smokers with early atherosclerosis

Distension of the urinary bladder causes an increase in efferent sympathetic activity, which can precipitate myocardial ischemia. Smoking has been shown to modulate activities of afferent nerves from the distended urinary bladder and to impair endothelial function in response to sympathetic activation. To assess the effect of bladder distension on coronary dynamics in smokers, we measured epicardial and microvascular responses in 24 patients with early atherosclerosis (< 50% diameter stenosis). Patients were classified into habitual smokers (group 1, n = 14) and nonsmokers (group 2, n = 10). Habitual smokers were randomized into two subgroups on the basis of the use of doxazosin, as follows: subgroup 1A (n = 7), without administration of doxazosin before catheterization; subgroup 1B (n = 7), with dosing doxazosin. In response to bladder distension (mean intravesical pressure 21.5 mmHg), bladder distension significantly decreased coronary diameter at the stenotic segments, coronary blood flow, and increased coronary resistance compared with baseline values, in subgroup 1A patients. In subgroup 1B patients during bladder distension, coronary diameter, coronary blood flow, and coronary resistance did not show significant changes compared with baseline values. There were significant differences of coronary diameter at the stenotic segments, coronary blood flow, and of changes of coronary vascular resistance between subgroup 1A and group 2 during bladder distension, despite similar changes in rate-pressure product. The present study showed that urinary bladder distension caused an abnormal vasomotor response of epicardial vasoconstriction and a concomitant increased coronary resistance, which leads to reduction in coronary blood flow in patients with early atherosclerosis. Smoking may further impair the response, implying that smoking has exaggerated response to sympathetic stimulation of conduit and resistance vessels. The abnormal response was abolished by pretreated administration of doxazosin, suggesting that the involved mechanisms are related to alpha(1)-adrenoceptors.

Acute effects of urinary bladder distention on the coronary circulation in patients with early atherosclerosis

OBJECTIVES

We sought to examine whether distention of the urinary bladder, a physiologic stimulus, could induce impaired coronary circulation in patients with early atherosclerosis.

BACKGROUND

Distention of the urinary bladder reflexively causes an increase in sympathetic activity. The effect of such distention on the coronary circulation in patients with early atherosclerosis remains unknown.

METHODS

To assess the effect of bladder distention on coronary dynamic forces, epicardial and microvascular responses were measured with an intracoronary Doppler flow wire in 40 patients with early atherosclerosis (<50% diameter stenosis). Patients were randomized into two groups according to whether they did not (group 1, n = 20) or did have (group 2, n = 20) pretreatment with an alpha1-adrenergic receptor blocker (oral doxazosin, 2 mg). Coronary flow velocity was monitored by quantitative coronary angiography at baseline, during urinary bladder distention and after intracoronary nitroglycerin injection.

RESULTS

Bladder distention significantly decreased the coronary diameter in the stenotic segments (p<0.001), decreased coronary blood flow (p<0.001) and increased coronary resistance (p<0.001), as compared with baseline values, in group 1 patients. In group 2 patients with bladder distention, the angiographic variables did not show significant changes, as compared with baseline values. No significant differences were noted between the groups in the responses of the angiographic variables after nitroglycerin administration.

CONCLUSIONS

The present study shows, for the first time, that urinary bladder distention caused vasoconstriction of coronary conduit and resistance vessels involved mechanisms related to alpha1 adrenoceptors. Pretreated administration of doxazosin reversed the changes toward baseline. Vasoconstriction during bladder distention can be relieved after nitroglycerin administration, suggesting an unchanged responsiveness of vascular smooth muscle cells to such distention.

Differential coronary hemodynamics and left ventricular contractility in patients with syndrome X

The relationship between coronary hemodynamics and left ventricular contractility was studied in 20 patients with syndrome X. Among them, 10 patients with a resting left ventricular ejection fraction (LVEF, by radionuclide method) equal to or greater than the mean value of the whole group (58%) were defined as having relative increased left ventricular contractility (group H), and another 10 patients with relatively normal contractility (50%</=LVEF<58%) were in group N. Eight subjects with normal contractility, exercise test and coronary angiograms served as the control (group C). Baseline great cardiac venous flow (GCVF) was higher in group N than in group H (P<0.05) and C (P<0.05), but similar between group H and C. After dipyridamole infusion (0.56 mg/kg, i.v., for 4 min), maximum GCVF was less in group H than in group N (P<0.001) and C (P<0.001), but similar between group N and C. As compared to group C (3.09+/-0.35), coronary flow reserve was reduced in both group H (2.34+/-0.55, P=0. 004) and N (2.40+/-0.36, P=0.001). In all syndrome X patients, resting LVEF was negatively correlated to baseline GCVF (P=0.026) and tended to be positively correlated to baseline coronary vascular resistance (P=0.057). Thus, coronary hemodynamics was altered with left ventricular contractility in syndrome X patients. In these patients, coronary flow reserve was similarly reduced with different underlying mechanisms. The limited increase of GCVF after dipyridamole infusion suggests impaired coronary microvascular dilation capacity in patients with relatively increased left ventricular contractility and the increase of baseline GCVF in those with normal contractility is more likely due to an altered basal myocardial metabolism.

alpha-adrenergic coronary vasoconstriction and myocardial ischemia in humans

The use of quantitative coronary angiography, combined with Doppler and PET, has recently been directed at the study of alpha-adrenergic coronary vasomotion in humans. Confirming prior animal experiments, there is no evidence of alpha-adrenergic coronary constrictor tone at rest. Again confirming prior experiments, responses to alpha-adrenoceptor activation are augmented in the presence of coronary endothelial dysfunction and atherosclerosis, involving both alpha(1)- and alpha(2)-adrenoceptors in epicardial conduit arteries and microvessels. Such augmented alpha-adrenergic coronary constriction is observed during exercise and coronary interventions, and it is powerful enough to induce myocardial ischemia and limit myocardial function. Recent studies indicate a genetic determination of alpha(2)-adrenergic coronary constriction.

Effect of alpha1-adrenoceptor blockade on coronary vasodilator reserve in cardiac syndrome X

We sought to test the response of the coronary microcirculation to alpha-adrenoceptor blockade in patients with syndrome X (angina, ischemia-like stress electrocardiogram, and a normal coronary arteriogram). The response of the microcirculation was assessed by quantification of coronary vasodilator reserve (the ratio of hyperemic to resting myocardial blood flow). We investigated 28 patients with syndrome X [18 women, age 54.4 (7.6) years]. Myocardial blood flow was measured at rest and after dipyridamole by using positron emission tomography with H(2)15O. The measurements were made before and after treatment for 10 days with doxazosin (1 mg o.d. for 3 days, followed by 2 mg o.d. for 7 days) or a matched placebo, similarly administered. Patients were randomized to alpha1-blockade or to placebo in double-blind fashion. No significant differences were demonstrable between syndrome X patients treated with doxazosin and those receiving placebo, with respect to resting myocardial blood flow, myocardial blood flow after dipyridamole, or coronary vasodilator reserve (the ratio of the latter two). In addition, no relations were demonstrable among myocardial blood flow, coronary vasodilator reserve, development of chest pain after dipyridamole, or development of ischemia-like ECG changes. Doxazosin had no effect on the perception of chest pain after dipyridamole. No differences were found between the effects of alpha1-blockade with doxazosin or those of placebo with respect to myocardial blood flow in syndrome X. The values obtained for myocardial blood flow and coronary vasodilator reserve for the patients were within the normal range. The data do not support the case for alpha1-mediated vasoconstriction having an etiologic role in the chest pain of syndrome X.

Abnormal cardiac nerve function in syndrome X

Syndrome X is likely to be caused by a dysfunction of small coronary arteries. Several authors suggested that an increased adrenergic activity could be involved in the pathogenesis of syndrome X, but studies investigating this topic by indirect methods led to conflicting results. We directly investigated cardiac sympathetic nerve function in syndrome X by myocardial radionuclide studies with 123I-metaiodobenzylguanidine (MIBG). Twelve syndrome X patients and 10 healthy controls were enrolled in the study. Cardiac MIBG uptake was assessed calculating the heart/mediastinum (H/M) ratio and a semiquantitative MIBG uptake score. Cardiac MIBG images were normal in all but 1 of controls (10%). Conversely, abnormalities in cardiac MIBG uptake were found in 9 syndrome X patients (75%, p < 0.01). In 5 patients the heart was totally or almost totally invisible on radionuclide MIBG images, while regional defects were found in other 4 patients. The H/M ratio was lower and cardiac MIBG uptake score strikingly higher in syndrome X patients. At 3 hours the H/M ratio was 1.70 +/- 0.6 in patients and 2.19 +/- 0.3 in controls (p = 0.03), while MIBG uptake score was 36.7 +/- 31 and 4.0 +/- 2.5 (p = 0.003) in the 4 groups, respectively. There were no differences between patients and controls in lung and salivary MIBG uptake. Reversible perfusion defects on stress thallium scintigraphy were found in 5 syndrome X patients (45%), all of whom also had abnormal MIBG scintigrams, while all 3 patients with normal MIBG scintigraphy also had normal thallium images. Thus, the function of efferent cardiac adrenergic nerve fibers is strongly impaired in the majority (i.e., 75%) of syndrome X patients. This abnormal function likely contributes significantly to the pathophysiologic and clinical features of syndrome X. We speculate that also the increased perception of cardiac pain reported in these patients could be an expression of the abnormal function of cardiac nerves, reflecting alterations of afferent nociceptive cardiac nerve fibers, as the abnormalities in MIBG uptake reflect alterations of efferent cardiac adrenergic nerve fibers.

Enhanced exercise-induced hyperkalemia in patients with syndrome X

OBJECTIVES

The purpose of this study was to determine whether patients with syndrome X have altered potassium metabolism.

BACKGROUND

Patients with syndrome X have angina pectoris and exercise induced ST segment depression on the electrocardiogram despite normal coronary angiograms. Increasing evidence suggests that myocardial ischemia is uncommon in these patients. Altered potassium metabolism causing interstitial potassium accumulation in the myocardium may be an alternative mechanism for chest pain and ST segment depression in syndrome X.

METHODS

We compared the magnitude of exercise-induced hyperkalemia in 16 patients with syndrome X (12 female and four male, mean +/- SD age 53 +/- 6 years) and 15 matched healthy control subjects. The participants underwent a bicycle test at a fixed load of 75 W for 10 min, and blood samples were taken for analysis of potassium, catecholamines and lactate before, during and in the recovery period after exercise. In five patients with syndrome X, the test was repeated during alpha1 adrenoceptor blockade.

RESULTS

Baseline concentrations of serum potassium, plasma catecholamines and plasma lactate were similar in patients and control subjects. The rate of exercise-induced increment of serum potassium was increased in the patients (70 +/- 29 vs. 30 +/- 21 micromol/liter/min in control subjects, p < 0.001). Six patients, who stopped before 10 min of exercise, showed very rapid increments in serum potassium concentration. Compared to the control subjects, patients also demonstrated larger increments in rate-pressure product, plasma norepinephrine and lactate concentrations during exercise. The rate of serum potassium increment correlated with the rate of plasma norepinephrine increment in the patients (r = 0.63, p < 0.02), but not in the control subjects (r = 0.01, p = 0.97). Blockade of alpha1 adrenoceptors decreased systolic blood pressure at baseline, but did not influence the increment of serum potassium, plasma catecholamines and lactate.

CONCLUSIONS

Patients with syndrome X have enhanced exercise induced hyperkalemia in parallel with augmented increases of circulating norepinephrine and lactate. The prevailing mechanisms behind the abnormal potassium handling comprise sources distinct from alpha1-adrenoceptor activation.

Reduced vasodilator capacity in syndrome X related to structure and function of resistance arteries

The combination of angina pectoris, angiographically normal epicardial coronary arteries, and a positive exercise test is referred to as syndrome X. Previous studies have demonstrated an impaired coronary flow reserve and a peripheral vascular dysfunction, suggesting that vascular abnormalities in syndrome X may not be confined to the heart. The aim of this study was to investigate whether any vascular disorder of syndrome X is due to intrinsic structural or functional disturbances in resistance arteries. We compared 16 patients with syndrome X (56.6+/-1.2 years, 3 men) with 15 matched control subjects. Myocardial blood flow was measured with 13N-ammonia positron emission tomography. Forearm blood flow was measured in the brachial artery with high-resolution ultrasound. Gluteal subcutaneous resistance arteries were dissected and mounted on a myograph for measurement of active tension development, lumen diameter, and media thickness. Baseline myocardial blood flow was similar in patients and controls, but dipyridamole-induced hyperemia was decreased in patients (1.67+/-0.13 vs 2.31+/-0.12 ml/ min/g, p <0.01). Patients and controls had similar baseline forearm blood flow, but hyperemic flow after transient occlusion of the brachial artery was impaired in patients (198+/-20 vs 273+/-32 ml/min, p <0.05). Isolated resistance arteries showed no differences in constriction to noradrenaline, or relaxation to acetylcholine, dipyridamole, or nitroglycerin. Furthermore, the ratio between media thickness and lumen diameter were similar in syndrome X patients and controls. Our data show that when compared with a well-matched control group, syndrome X patients have a decreased coronary and peripheral vasodilator capacity. However, this is not reflected by functional abnormalities or structural changes as evaluated in subcutaneous resistance arteries. We conclude that syndrome X is not a generalized intrinsic abnormality of the resistance circulation.

The Effect of Trimetazidine in the Treatment of Microvascular Angina

Although the pathophysiology of microvascular angina is unclear, intracellular metabolic changes are believed to be the main factors. Trimetazidine has an intracellular metabolic effect in coronary insufficiency. The effect of trimetazidine in microvascular angina is unknown. Thirty-five patients (8 men, 27 women, age 36-57 years, mean 43.9 +/- 6.4 years) with microvascular angina were included in this study. The effects of trimetazidine (60 mg daily) were investigated in a placebo-controlled, double-blind study consisting of two 4-week treatment periods. Patients were assessed by symptom-limited exercise testing (Bruce protocol). Heart rate and systolic blood pressure at rest, peak exercise, and the time of 1 mm ST segment depression were not significantly different between placebo and trimetazidine treatment. Trimetazidine prolonged total exercise time and time to 1 mm ST depression compared with placebo. Maximum ST depression was less in patients with trimetazidine therapy than those with placebo. It is concluded that trimetazidine has a beneficial effect in cases with microvascular angina.

Enhanced activity of sodium-lithium countertransport in patients with cardiac syndrome X: a potential link between cardiac and metabolic syndrome X

OBJECTIVES

This study was aimed at assessing both stimulated insulinemia and the sodium-lithium countertransport in a selected group of patients with cardiac syndrome X.

BACKGROUND

Hyperinsulinemia, which is frequently present in patients with cardiac syndrome X, is often associated with an enhanced activity of the sodium-lithium countertransport, an in vitro marker of sodium-hydrogen exchange.

METHODS

Fifteen patients with syndrome X and 14 matched controls were studied. After pharmacological washout, sodium-lithium countertransport was assessed from lithium-loaded red blood cells. Postload insulin levels were evaluated by a double-antibody radioimmunoassay.

RESULTS

Maximal velocity of sodium-lithium countertransport was higher in patients with syndrome X compared to controls (635+/-200 vs. 324+/-49 micromol/liter/h, p = 0.001). Fourteen of the 15 patients with syndrome X (93%) presented sodium-lithium countertransport values higher than the mean +2 SD of the control group. At 120 min, 12 patients with syndrome X (80%) had plasma levels of insulin >420 pmol/liter, which corresponds to the mean value +2 SD of controls (p = 0.006).

CONCLUSIONS

Both enhanced activity of the sodium-lithium countertransport and stimulated hyperinsulinemia are present in the vast majority of patients with cardiac syndrome X. As enhanced activity of the sodium-lithium countertransport has the potential to cause both glucose intolerance and smooth muscle hyperreactivity, it might represent a common cause of the metabolic and vascular alterations frequently found in syndrome X.

Effects of doxazosin on exercise-induced angina pectoris, ST-segment depression, and insulin sensitivity in patients with syndrome X

A significant proportion of patients with cardiac syndrome X have impaired coronary vasodilator capacity, which is thought to be caused by an increased sympathetic drive. The alpha1-adrenoceptor blocker, doxazosin, increases the coronary vasodilator reserve in patients with syndrome X. To study whether the augmentation is associated with clinical improvement in patients, we conducted a double-blind, placebo controlled, crossover study with doxazosin 1 to 4 mg once daily for 10 weeks in 16 patients with syndrome X (14 women and 2 men; mean +/- SD age 56+/-5 years). Time to angina, exercise duration, time to 0.1 mV ST-segment depression, and maximal ST-segment depression during bicycle exercise testing were compared after treatment with doxazosin 2 mg or placebo for 5 weeks and again after treatment with doxazosin 4 mg or placebo for 10 weeks. Insulin sensitivity was assessed by the minimal model after 10 weeks of doxazosin or placebo treatment. Twelve patients completed the protocol. Doxazosin 4 mg/day decreased systolic blood pressure at rest (109+/-16 vs 125+/-18 mm Hg, p <0.05) and increased basal heart rate (85+/-9 vs 76+/-11 beats/min, p <0.05), whereas hemodynamics were unaffected during exercise. Time to angina, exercise duration, time to 0.1 mV ST-segment depression, and maximal ST-segment depression were similar during treatment with doxazosin and placebo irrespective of the doxazosin dose. Insulin sensitivity was not different with doxazosin and placebo. In conclusion, alpha1 blockade does not significantly improve exercise duration, angina pectoris, and ST-segment depression despite a favorable vasodilator effect in patients with syndrome X. The absent clinical efficacy of doxazosin may challenge the use of the coronary vasodilator capacity as an appropriate method to subclassify patients with syndrome X.

Abnormal cardiac adrenergic nerve function in patients with syndrome X detected by [123I]metaiodobenzylguanidine myocardial scintigraphy

BACKGROUND

Previous studies have suggested that an abnormal cardiac adrenergic tone may have a pathophysiological role in syndrome X (effort angina, positive exercise testing, angiographically normal coronary arteries).

METHODS AND RESULTS

To evaluate cardiac adrenergic nerve function, we performed [123I]metaiodobenzylguanidine (MIBG) myocardial scintigraphy in 12 patients with syndrome X and 10 control subjects. Cardiac MIBG uptake was assessed by the heart/mediastinum (H/M) ratio and by an MIBG uptake defect score (higher values=lower uptake). In syndrome X patients, we also correlated MIBG scintigraphic findings with stress myocardial perfusion as assessed by 201Tl scintigraphy. An inferior MIBG defect was observed in only 1 control subject, whereas 9 patients (P<.01) showed MIBG defects. The heart was totally or almost totally invisible on MIBG images in 5 patients, and predominantly regional defects were observed in 4. The H/M ratio was lower (1.70+/-0.6 versus 2.2+/-0.3, P=.03) and MIBG uptake defect score higher (35+/-31 versus 4+/-2, P=.003) in syndrome X patients. Reversible stress thallium perfusion defects were found in 62% of patients with MIBG defects but in no patient with normal MIBG uptake. MIBG defects persisted unchanged in 7 patients at a 5+/-3-month follow-up study.

CONCLUSIONS

In this study, obvious defects in global and/or regional cardiac MIBG uptake, indicating an abnormal cardiac adrenergic nerve function, were detected in 75% of patients with syndrome X. These findings strongly support the cardiac origin of chest pain in syndrome X, although the mechanisms and the pathophysiological meaning of the abnormal cardiac MIBG uptake in these patients deserve further investigation.

Effects of short-term treatment of nicorandil on exercise-induced myocardial ischemia and abnormal cardiac autonomic activity in microvascular angina

The underlying mechanisms of myocardial ischemia in microvascular angina may include endothelial dysfunction, abnormal smooth muscle tone, and abnormal autonomic control of coronary microvasculatures. This randomized, double-blind, placebo-controlled, crossover study was conducted to evaluate the effect of nicorandil (a nitrate-potassium channel opener) therapy on exercise-induced myocardial ischemia and cardiac autonomic activity in 13 patients with microvascular angina. After a 2-week placebo run-in period, patients were randomly assigned to the first 2-week treatment with nicorandil 5 mg tid or placebo, then crossed over to the second 2-week treatment after a 2-week washout period. Treadmill exercise tests and 24-hour ambulatory electrocardiogram monitoring were performed at the end of each treatment phase. The results showed that both time to 1-mm ST depression and total exercise duration were significantly prolonged with nicorandil treatment compared with placebo (p = 0.026 and 0.036, respectively). Maximum exercise ST depression also tended to be less with nicorandil treatment than with placebo (p = 0.083). Compared with 10 healthy control subjects, study patients had significantly reduced heart rate variability in both low- and high-frequency bands while receiving placebo. Nicorandil treatment did not change the altered heart rate variability in either time domain or spectral analysis. Systemic hemodynamics were also unchanged with nicorandil treatment. Thus, 2-week oral nicorandil therapy moderately improved exercise-induced myocardial ischemia without modifying the already altered cardiac autonomic activity, suggesting that nicorandil might have a direct vasodilatory effect on coronary microvasculatures in patients with microvascular angina.

Changes in cardiac autonomic activities in patients with syndrome X. A study of spectral analysis of heart rate variability

The present study was designed to assess cardiac autonomic activities, coronary microvascular function, and their relationship in patients with syndrome X. Control of coronary blood flow is complex, and impaired coronary flow reserve has been attributed as the cause of myocardial ischemia in patients with syndrome X. It is unknown whether cardiac autonomic activities are altered in the presence of coronary microvascular dysfunction in patients with syndrome X. Eighteen patients with syndrome X were studied. Great cardiac vein flow was measured by the thermodilution method and the coronary flow reserve was determined by intravenous dipyridamole (0.56 mg/kg) infusion. Twenty-four-hour ambulatory electrocardiograms were obtained in a drug-free state. Another 14 age- and sex-matched normal subjects served as a control group. The amplitude (in ms) of ultralow (ULF), very-low (VLF), low (LF), and high (HF) frequency bands and total spectra of heart rate variability were measured for twenty-four-hour and every four-hour interval of the day.

Frequency of systemic microvascular dysfunction in syndrome X and in variant angina

In addition to coronary vascular abnormalities, patients with syndrome X and variant angina often have systemic vascular symptoms. To determine whether these patients exhibit a generalized abnormality of vasoreactivity, we used high-resolution ultrasound to compare flow responses and endothelial function in the brachial artery in 21 patients with syndrome X, 15 patients with variant angina, and 20 healthy controls. Arterial diameter was measured at rest, after reactive hyperemia (endothelium-dependent flow-mediated vasodilation), and after sublingual glyceryl trinitrate (endothelium-independent vasodilation). The magnitude of hyperemic flow response was measured after transient forearm occlusion. Flow-mediated dilation in the brachial artery did not differ among patients with syndrome X, variant angina, and controls (2.7 +/- 2.3%, 3.8 +/- 3.5%, and 4.2 +/- 3.0%). Endothelium-independent vasodilation in the brachial artery was similar in the 3 groups (16.0 +/- 7.2%, 12.7 +/- 4.6%, and 14.8 +/- 4.9%). Despite a considerable overlap, reactive hyperemia was lower in patients with syndrome X than in patients with variant angina and controls (342+/-86% vs 466+/-184% and 452+/-104%; p < 0.05). These findings indicate that a substantial proportion of patients with syndrome X have a systemic microvascular abnormality, whereas variant angina is predominantly a segmental disorder of conduit vessels.

Neuronal control of coronary blood flow

Controversies on acetylcholine-induced increases or decreases in coronary blood flow arise from obvious species differences, the role of endothelium in mediating vascular smooth muscle responses, and the marked negative chronotropic and inotropic effects of acetylcholine. In man, there appears to be a predominant dilation of intact epicardial coronary arteries and a constriction of artherosclerotic segments. However, at present there is no evidence for a vagal initiation of myocardial ischemia. Coronary vascular beta-adrenergic receptors mediate dilation, but appear to be functionally insignificant during sympathetic activation. The beta-adrenergic mechanism contributing to myocardial ischemia are indirect, mediated by a tachycardia-related redistribution of blood flow away from the ischemic myocardium. alpha-Adrenergic receptors mediating epicardial coronary artery constriction in experimental studies appear not to be responsible for the initiation of ischemia in patients with angina at rest. However, alpha-adrenergic constriction of coronary resistance vessels resulting in the precipitation of post-stenotic myocardial ischemia was demonstrated in experimental studies and recently confirmed in patients with effort angina. Non-adrenergic, non-cholinergic neurotransmitters exist; however, their role in regulating coronary blood flow remains entirely unclear.

Coronary vasodilator reserve, pain perception, and sex in patients with syndrome X

BACKGROUND

It remains unclear whether myocardial ischemia due to coronary microvascular dysfunction is the cause of chest pain in syndrome X (chest pain, ischemic-like stress ECG despite angiographically normal coronary arteries). To assess the function of the coronary microcirculation and its relation to pain perception, we measured myocardial blood flow (MBF) and coronary vasodilator reserve (CVR) in 29 patients with syndrome X and 20 matched normal control subjects.

METHODS AND RESULTS

MBF at rest and after intravenous dipyridamole (0.56 mg.kg-1 over 4 minutes) was measured using positron emission tomography with H2(15)O. CVR was calculated as MBFdipyridamole/MBFrest. ECG changes and chest pain after dipyridamole in syndrome X were compared with those in 35 patients with coronary artery disease (CAD). Resting and postdipyridamole MBFs were homogeneous throughout the left ventricle in syndrome X patients and control subjects. MBF was 1.05 (0.25), mean (SD) versus 1.00 (0.22) mL.min-1.g-1 (P = NS) at rest and 2.73 (0.81) versus 3.00 (1.00) mL.min-1.g-1 (P = NS) after dipyridamole in patients and control subjects, respectively. CVRs were 2.66 (0.76) and 3.06 (1.08) (P = NS) and after correction of resting MBF for rate-pressure product were 2.35 (0.83) and 2.34 (0.90) (P = NS) in patients and control subjects, respectively. Female syndrome X patients had higher resting MBF than males, at 1.18 (0.20) versus 0.88 (0.19) mL.min-1.g-1 (P < .001). Chest pain after dipyridamole occurred in syndrome X as frequently as in CAD (21/29 versus 22/35, P = NS).

CONCLUSIONS

When patients with syndrome X are compared with control subjects, no differences are found in MBF either at rest or after dipyridamole, despite syndrome X patients experiencing chest pain after dipyridamole to the same extent as patients with CAD. These findings, together with the absence of any relation among MBF, chest pain, and ECG changes under stress, cast further doubt on ischemia as the basis of the chest pain, at least in the majority of syndrome X patients.