Syndrome X
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Syndrome X On the Web | ||
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
The terms Syndrome X or Metabolic syndrome X may also be referring to metabolic syndrome.
Synonyms and key words: Microvascular angina
Overview
(Cardiac) syndrome X is angina (chest pain) associated with objective evidence of myocardial ischemia in the absence of epicardial coronary artery disease. The disorder has been hypothesized to be a disorder of the coronary microvasculature rather than the large caliber epicardial coronary arteries.
Pathophysiology
In a large percentage of patients, there is coronary microvascular dysfunction. Specifically, the microvasculature cannot dilate to accomadate increased blood flow during exertion to meet the needs of myocardial metabolism. There does not appear to be a systemic abnormality in vasomotor function as brachial artery reactivity is normal[1].
Most likely the underlying pathophysiology is heterogenous, and multiple pathophysiologic mechanisms have been proposed with variable data to support them:
Ischemia is Present in Syndrome X
It has been debated as to whether ischemia is present in patients with Syndrome X. There may be no wall motion abnormalities or coronary sinus lactate production during an episode of ischemic discomfort. This may be due to focal involvement of the myocardium. When coronary sinus samples of more sensitive markers of ischemia reperfusion / oxidative stress are analyzed such as lipid hydroperoxides (ROOHs) and conjugated dienes (CDs) before and after pacing, there is an increase in ROOH and CD levels (from 4.83 +/- 1.18 micromol/l at baseline to 7.88 +/- 1.12 micromol/l and from 0.038 +/- 0.002 to 0.051 +/- 0.003 arbitrary units, respectively, P < 0.01)[2]. In contrast, ROOH and CD levels did not increase in control patients after pacing.
Adenosine as a Cause of Chest Pain
Both endogenous and exogenous adenosine can cause chest discomfort through stimulation of sensory nerves in the heart [3][4]. Huang et al have demonstrated that both A1- and A2-adenosine receptors are present on the cardiac sensory nerve endings of dorsal root ganglion neurons. These sensory neurons are active in the absence of ischemia, but become further activated during myocardial ischemia[4]. In one study in which adenosine was infused, 95% of patients with Syndrome X had chest pain whereas only 40% of control patients experienced chest pain (p<0.001) [5]
An Extension of Dysautonomias
Syndrome X has been associated with dysautonomias and with a greater frequency of autonomic symptoms such as tachycardia, dyspnea, dizziness, and paresthesias [6]. It has therefore been hypothesized that Syndrome X may be an extension of abnormalities of the autonomic nervous system.
"Female Pattern" of Atherosclerosis
It has also been speculated that although the coronary arteriogram may appear normal, there may in fact be diffuse atherosclerosis present in what has been termed "a female pattern" of disease.
Enhanced Pain Sensitivity
Patients with normal coronary arteries and myocardial ischemia have a lower pain threshold and a lower tolerance to pain induced by adenosine [7].
Panic Disorder
Approximately one third of patients with angina pectoris and normal coronary arteries are diagnosed with panic disorder [8].
Epidemiology and Demographics
Syndrome X occurs more often in women. 61.5% of women with Syndrome X are postmenopausal at the time of onset[9]. Some studies have found an increased risk of other vasospastic disorders in syndrome X patients, such as migraine and Raynaud's phenomenon.
Natural history, complications, and prognosis
Syndrome X does not appear to be associated with an excess of major coronary events. In a longitudinal study of 99 patients with Syndorme X over 7 +/- 4 years, left ventricular function was stable: fractional shortening at baseline was 35.4 +/- 4% vs. 35.6 +/- 3% at follow-up and congestive heart failure developed in only one patient[9]. Symptoms did not change in about tho thirds of patients, they improved in 10% of patients, and they were worse in about a quarter of patients [9]
The absence of significant coronary artery disease on coronary angiography is associated with a good prognosis. Among 3,136 patients with normal angiograms, the 7 year survival rate was 96%[10].
Risk Factors
Female gender and left ventricular hypertrophy are associated with an excess risk of Syndrome X. The onset in women often occurs after menopause[9].
Other Conditions to Distinguish Syndrome X From
Syndrome X should be distinguished from Prinzmetal's angina, a disorder which involves spasm of the main epicardial coronary arteries. Syndrome X involves dysfunction of the downstream microvasculature. Syndrome X must also be distinguished from esophageal spasm.
Diagnosis
Symptoms
All 99 patients with Syndrome X in one study had exertional angina, and 41 of them had angina at rest[9]. In patients with syndrome X, the anginal pain tends to last longer after cessation of exertion (> 10 minutes in 53% of patients[9]) than is typical of patients with fixed obstructions of the epicardial arteries (pain generally lasts 2 to 5 minutes). Sublingual nitroglycerine is often not as effective in the patient with Syndrome X as it is in the patient with obstructive epicardial disease, with only 42% of patients reporting relief [9].
Ambulatory Holter Monitoring
Approximately two thirds of patients (64/99 in one study) will experience ST segment depression on ambulatory Holter monitoring[9].
Cardiac Magnetic Resonance Imaging (CMR)
While there is no difference between control patients and patients with Syndrome X in subepicardial perfusion, there is a greater relative magnitude of subendocardial hypoperfusion on CMR during adenosine infusion in patients with Syndrome X. As a result, "the ratio of subendocardial to subepicardial myocardial-perfusion reserve index is significantly lower in patients with syndrome X". [5].
Diagnostic Studies and Criteria for Diagnosis
Syndrome X is often a diagnosis of exclusion. The diagnostic criteria are as follows:
- There must be evidence of myocardial ischemia: Diagnostic studies include an exercise ECG, stress scintigraphy, or stress echocardiography in conjunction with anginal chest discomfort.
- Angina: Angina pectoris must be present. The angina pectoris associated with Syndrome X may last longer that the anginal discomfort associated with the fixed epicardial stenoses of atherosclerotic heart disease.
- Coronary angiogram: There is no narrowing of the epicardial arteries. However, Syndrome X may be associated with a reduction in coronary vasodilator reserve presumably due to abnormalities in the coronary microcirculation. During stress, sampling of the coronary sinus may demonstrate the production of lactate by the myocardium. Intracoronary acetylcholine can be administered to evaluate endothelium-dependent coronary flow reserve.
ESC Guidelines for investigation in patients with Syndrome X (DO NOT EDIT)[11]
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Class I1. Resting echocardiogram in patients with angina and normal or non-obstructed coronary arteries to assess for presence of ventricular hypertrophy and/or diastolic dysfunction. (Level of Evidence: C) Class IIb1. Intracoronary acetylcholine during coronary arteriography, if the arteriogram is visually normal, to assess endothelium-dependent coronary flow reserve, and exclude vasospasm. (Level of Evidence: C) 2. Intracoronary ultrasound, coronary flow reserve, or FFR measurement to exclude missed obstructive lesions, if angiographic appearances are suggestive of a nonobstructive lesion rather than completely normal, and stress imaging techniques identify an extensive area of ischaemia. (Level of Evidence: C) |
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Treatment
The mainstay of treatment in patients with Syndrome X are calcium channel blockers, such as nifedipine and diltiazem. Other therapies include:
- Nitrates. Sublingual nitroglycerine is often not as effective in the patient with Syndrome X as it is in the patient with obstructive epicardial disease, with only 42% of patients reporting relief [9].
- Beta blockers
- Aminophylline - may be effective via inhibition of adenosine receptors.
- Estrogen - may be effective in women.
ESC Guidelines for pharmacological therapy to improve symptoms in patients with Syndrome X (DO NOT EDIT)[11]
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Class I1. Therapy with nitrates, beta blockers, and calcium channel blockers alone or in combination. (Level of Evidence: B) 2. Statin therapy in patients with hyperlipidaemia. (Level of Evidence: B) 3. ACE inhibitors in patients with hypertension. (Level of Evidence: C) Class IIa1. Trial of therapy with other anti-anginals including nicorandil and metabolic agents. (Level of Evidence: C) Class IIb1. Aminophylline for continued pain, despite Class I measures. (Level of Evidence: C) 2. Imipramine for continued pain, despite Class I measures. (Level of Evidence: C) |
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References
- ↑ Bøtker HE, Sonne HS, Sørensen KE (1996) Frequency of systemic microvascular dysfunction in syndrome X and in variant angina. Am J Cardiol 78 (2):182-6. PMID: 8712140
- ↑ Buffon A, Rigattieri S, Santini SA, Ramazzotti V, Crea F, Giardina B et al. (2000) Myocardial ischemia-reperfusion damage after pacing-induced tachycardia in patients with cardiac syndrome X. Am J Physiol Heart Circ Physiol 279 (6):H2627-33. PMID: 11087214
- ↑ http://www.nejm.org/doi/full/10.1056/NEJM200210243471717
- ↑ 4.0 4.1 Huang MH, Sylvén C, Horackova M, Armour JA (1995). "Ventricular sensory neurons in canine dorsal root ganglia: effects of adenosine and substance P.". Am J Physiol. 269 (2 Pt 2): R318–24. PMID 7544544.
- ↑ 5.0 5.1 Panting JR, Gatehouse PD, Yang GZ, Grothues F, Firmin DN, Collins P; et al. (2002). "Abnormal subendocardial perfusion in cardiac syndrome X detected by cardiovascular magnetic resonance imaging". N Engl J Med. 346 (25): 1948–53. doi:10.1056/NEJMoa012369. PMID 12075055.
- ↑ Katon W, Hall ML, Russo J, Cormier L, Hollifield M, Vitaliano PP; et al. (1988). "Chest pain: relationship of psychiatric illness to coronary arteriographic results". Am J Med. 84 (1): 1–9. PMID 3337115.
- ↑ Lagerqvist B, Sylvén C, Waldenström A (1992). "Lower threshold for adenosine-induced chest pain in patients with angina and normal coronary angiograms". Br Heart J. 68 (3): 282–5. PMC 1025071. PMID 1389759.
- ↑ Mukerji V, Beitman BD, Alpert MA, Lamberti JW, DeRosear L, Basha IM (1987). "Panic disorder: a frequent occurrence in patients with chest pain and normal coronary arteries". Angiology. 38 (3): 236–40. PMID 3565851.
- ↑ 9.0 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 Kaski JC, Rosano GM, Collins P, Nihoyannopoulos P, Maseri A, Poole-Wilson PA (1995). "Cardiac syndrome X: clinical characteristics and left ventricular function. Long-term follow-up study". J Am Coll Cardiol. 25 (4): 807–14. doi:10.1016/0735-1097(94)00507-M. PMID 7884081.
- ↑ Kemp HG, Kronmal RA, Vlietstra RE, Frye RL (1986). "Seven year survival of patients with normal or near normal coronary arteriograms: a CASS registry study". J Am Coll Cardiol. 7 (3): 479–83. PMID 3512658.
- ↑ 11.0 11.1 Fox K, Garcia MA, Ardissino D, Buszman P, Camici PG, Crea F; et al. (2006). "Guidelines on the management of stable angina pectoris: executive summary: The Task Force on the Management of Stable Angina Pectoris of the European Society of Cardiology". Eur Heart J. 27 (11): 1341–81. doi:10.1093/eurheartj/ehl001. PMID 16735367.