Variant angina

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Variant angina
Other namesPrinzmetal's angina, vasospastic angina [1]
A man having a Heart Attack.png
Illustration depicting angina
Specialty Cardiology   OOjs UI icon edit-ltr-progressive.svg

Variant angina, also known as Prinzmetal angina,vasospastic angina, angina inversa, coronary vessel spasm, or coronary artery vasospasm, [2] is a syndrome typically consisting of angina (cardiac chest pain). Variant angina differs from stable angina in that it commonly occurs in individuals who are at rest or even asleep, whereas stable angina is generally triggered by exertion or intense exercise. Variant angina is caused by vasospasm, a narrowing of the coronary arteries due to contraction of the heart's smooth muscle tissue in the vessel walls. [3] In comparison, stable angina is caused by the permanent occlusion of these vessels by atherosclerosis, which is the buildup of fatty plaque and hardening of the arteries. [4]

Contents

Signs and symptoms

In contrast to those with angina secondary to atherosclerosis, people with variant angina are generally younger and have fewer risk factors for coronary artery disease with the exception of smoking, which is a common and significant risk factor for both types of angina. Affected people usually have repeated episodes of unexplained (e.g., in the absence of exertion and occurring at sleep or in the early morning hours) chest pain, tightness in throat, chest pressure, light-headedness, excessive sweating, and/or reduced exercise tolerance that, unlike atherosclerosis-related angina, typically does not progress to myocardial infarction (heart attack). Unlike cases of atherosclerosis-related stable angina, these symptoms are often unrelated to exertion and occur in night or early morning hours. [4] However, individuals with atherosclerosis-related unstable angina may similarly exhibit night to early morning hour symptoms that are unrelated to exertion. [5]

Cardiac examination of individuals with variant angina is usually normal in the absence of current symptoms. [2] [6] Two-thirds of these individuals do have concurrent atherosclerosis of a major coronary artery, but this is often mild or not in proportion to the degree of their symptoms. Persons who have atherosclerosis-based occlusion that is ≥70% in a single coronary artery or that involves multiple coronary arteries are predisposed to develop a variant angina form that has a poorer prognosis than most other forms of this disorder. [7] In these individuals but also in a small percentage of individuals without appreciable atherosclerosis of their coronary arteries, attacks of coronary artery spasm can have far more serious presentations such as fainting, shock, and cardiac arrest. Typically, these presentations reflect the development of a heart attack and/or a potentially lethal heart arrhythmia; they require immediate medical intervention as well as consideration for the presence of, and specific treatment regimens for, their disorder. [8] [9]

Variant angina should be suspected by a cardiologist when a) an individual's symptoms occur at rest or during sleep; b) an individual's symptoms occur in clusters; c) an individual with a history of angina does not develop angina during treadmill stress testing (variant angina is exercise tolerant); d) an individual with a history of angina shows no evidence of other forms of cardiac disease; and/or e) an individual without features of coronary artery atherosclerotic heart disease has a history of unexplained fainting. [4] [8]

Complaints of chest pain should be immediately checked for an abnormal electrocardiogram (ECG). ECG changes compatible but not indicative of variant angina include elevations rather than depressions of the ST segment or an elevated ST segment plus a widening of the R wave to create a single, broad QRS complex peak termed the "monophasic curve". [4] Associated with these ECG changes, there may be small elevations in the blood levels of cardiac damage marker enzymes, especially during long attacks. Some individuals with otherwise typical variant angina may show depressions, rather than elevations in the ST segments of their ECGs during angina pain; they may also show new U waves on ECGs during angina attacks. [4]

A significant percentage of those with variant angina have symptom-free episodes of coronary artery spasm. These episodes may be far more frequent than expected, cause myocardial ischemia (i.e. insufficient blood flow to portions of the heart), and be accompanied by potentially serious abnormalities in the rhythm of heart beats, i.e. arrythmias. The only evidence of the presence of totally asymptomatic variant angina would be detection of diagnostic changes on fortuitously conducted ECGs. [4] [9]

Risk factors

The intake of certain agents have been reported to trigger an attack of variant angina. These agents include:

In addition, hyperventilation and virtually any stressful emotional or physical (e.g. cold exposure) event that is suspected of causing significant rises in the blood levels of catecholamines may trigger variant angina. [4] [7]

Mechanism

The mechanism that causes such intense vasospasm, as to cause a clinically significant narrowing of the coronary arteries is so far unknown, but there are three relevant hypotheses:

  1. Enhanced contractility of coronary vascular smooth muscle due to reduced nitric oxide bioavailability caused by a defect in the endothelial nitric oxide synthetase enzyme which leads to endothelial function abnormalities. [7] [10] [11]
    • Acetylcholine is normally released by the parasympathetic nervous system (PSNS) at rest, and causes dilation of the coronary arteries. [12] While acetylcholine induces vasoconstriction of vascular smooth muscle cells through a direct mechanism, acetylcholine also stimulates endothelial cells to produce nitric oxide (NO). NO then diffuses out of the endothelial cells, stimulating relaxation of the nearby smooth muscle cells. In healthy arterial walls, the overall indirect relaxation induced by acetylcholine (via nitric oxide) is of greater effect than any contraction that is induced.
    • When the endothelium is dysfunctional, stimulation with acetylcholine will fail to produce, or produce very little, nitric oxide. Thus, acetylcholine released by the PSNS at rest will simply cause contraction of the vascular smooth muscle.
  2. Thromboxane A2, serotonin, histamine, and endothelin are vasoconstrictor which activated platelets release and/or cause to be released. Abnormal platelet activation (e.g. by lipoprotein(a) interference with fibrinolysis by competing with plasminogen to thereby impair fibrinolysis and promote platelet activation) results in the release of these mediators and coronary vasospasm. [13] [7] [14]
  3. Increased alpha-adrenergic receptor activity in epicardial coronary arteries or the excessive release of the "flight or fight" catecholamines (e.g. norepinephrine) that activate these receptors may lead to coronary vasospasm. [4] [7] [15]

Other factors thought to be associated with the development of variant angina include: intrinsic hypercontractility of coronary artery smooth muscle; existence of significant atherosclerotic coronary artery disease; and reduced activity of the parasympathetic nervous system (which normally functions to dilate blood vessels). [6] [7]

Diagnosis

Prinzmetal angina Prinzmetal angina.png
Prinzmetal angina

Although variant angina has been documented in approximately 2% to 10% of angina patients, it can be overlooked by cardiologists who stop further evaluations after ruling out typical angina. Individuals who develop cardiac chest pain are generally treated empirically as an "acute coronary syndrome", and are immediately tested for elevations in their blood levels of enzymes such as creatine kinase isoenzymes or troponin that are markers for cardiac damage. They are also tested by ECG which may suggest variant angina if it shows elevations in the ST segment or an elevated ST segment plus a widening of the R wave during symptoms that are triggered by a provocative agent (e.g. ergonovine or acetylcholine). The electrocardiogram may show depressions rather than elevations in ST segments but in all diagnosable cases clinical symptoms should be promptly relieved and ECG changes should be promptly reversed by rapidly acting sublingual or intravenous nitroglycerin. However, the gold standard for diagnosing variant angina is to visualize coronary arteries by angiography before and after injection of a provocative agent such as ergonovine, methylergonovine or acetylcholine to precipitate an attack of vasospasm. A positive test to these inducing agents is defined as a ≥90% (some experts require lesser, e.g. ≥70%) constriction of involved arteries. Typically, these constrictions are fully reversed by rapidly acting nitroglycerin. [4] [16]

Individuals with variant angina may have many undocumented episodes of symptom-free coronary artery spasm that are associated with poor blood flow to portions of the heart and subsequent irregular and potentially serious heart arrhythmias. Accordingly, individuals with variant angina should be intermittently evaluated for this using long-term ambulatory cardiac monitoring. [4] [9]

Prevention

Numerous methods are recommended to avoid attacks of variant angina. Affected individuals should not smoke tobacco products. Smoke cessation significantly reduces the incidence of patient-reported variant angina attacks. [7] They should also avoid any trigger known to them to trigger these attacks such as emotional distress, hyperventilation, unnecessary exposure to cold, and early morning exertion. And, they should avoid any of the recreational and therapeutic drugs listed in the above signs and symptoms and risk factors sections as well as blockers of beta receptors such as propranolol which may theoretically worsen vasospasm by inhibiting beta-2 adrenergic receptor's vasodilation effect mediated by these receptors' naturally occurring stimulator i.e. epinephrine. In addition, aspirin should be used with caution and at low doses since at high doses it inhibits the production of the naturally occurring vasodilator, prostacyclin. [4] [16]

Treatment

Acute attacks

During acute attacks, individuals typically respond well to fast-acting sublingual, intravenous, or spray nitroglycerin formulations. The onset of symptom relief in response to intravenous administration, which is used in more severe attacks of angina, occurs almost immediately while sublingual formulations of it act within 1–5 minutes. Spray formulations also require ~1–5 minutes to act. [17]

Maintenance

As maintenance therapy, sublingual nitroglycerin tablets can be taken 3-5 min before conducting activity that causes angina by the small percentage of patients who experience angina infrequently and only when doing such activity. [17] For most affected individuals, antianginals are used as maintenance therapy to avoid attacks of variant angina. Calcium channel blockers of the dihydropyridine class (e.g. nifedipine, amlodipine) [18] or non-dihydropyridine class (e.g. verapamil, diltiazem) are regarded as first-line drugs to avoid angina attacks. Long-acting nitroglycerins such as isosorbide dinitrate or intermittent use of short-acting nitroglycerin (to treat acute symptoms) may be added to the calcium channel blocker regimen in individuals responding sub-optimally to the channel blockers.

However, individuals commonly develop tolerance, or resistance, to the efficacy of continuously used long-acting nitroglycerin formulations. One strategy to avoid this is to schedule nitroglycerin-free periods of between 12 and 14 hours between doses of long-acting nitroglycerin formulations. [17] Individuals whose symptoms are poorly controlled by a calcium blocker may benefit from addition of a long-acting nitroglycerin and/or a second calcium channel blocker of a different class than the blocker already in use. Nevertheless, about 20% of individuals fail to respond adequately to the two-drug calcium blocker plus long-acting nitroglycerin regimen. If these individuals have significant permanent occlusion of their coronary arteries, they may benefit by stenting their occluded arteries. However, coronary stenting is contraindicated in drug-refractory individuals who do not have significant organic occlusion of their coronary arteries. [16]

For drug-refractory individuals without blockage, other, less fully investigated drugs may provide symptom relief. Statins, e.g. fluvastatin, while not evaluated in large-scale double-blind studies, are reportedly helpful in reducing variant angina attacks and should be considered in patients when calcium channel blockers and nitroglycerin fail to achieve good results. [4] There is also interest in using rho-kinase inhibitors, such as fasudil (available in Japan and China but not the USA), [16] and blocker of alpha-1 adrenergic receptors such as prazosin (which when activated cause vasodilation) but studies are needed to support their clinical utility in variant angina. [4] [6]

Emergency

Individuals with certain severe complications of variant angina require immediate therapy. Individuals presenting with potentially lethal irregularities in the rhythm of their heart beating or a history of episodic fainting spells due to such arrhythmias require implantation of an internal defibrillator and/or cardiac pacemaker to stop such arrhythmias and restore normal heart beating. [8] [9] Other rare but severe complications of variant angina, e. g. myocardial infarction, severe congestive heart failure, and cardiogenic shock require the same immediate medical interventions that are used for other causes of these extremis conditions. In all of these emergency cases, percutaneous coronary intervention to stent areas where coronary arteries evidence spasm is only useful in individuals who have concomitant coronary atherosclerosis on coronary angiogram. [4]

Prognosis

Most individuals with variant angina have a favorable prognosis provided they are maintained on calcium channel blockers and/or long-acting nitrates; five-year survival rates in this group are estimated as over 90%. [4] [19] The Japanese Coronary Spasm Association established a clinical risk scoring system to predict outcomes for variant angina. Seven major factors (i.e. history of out of hospital cardiac arrest [score = 4]; smoking, angina at rest, physically obstructive coronary artery disease, and spasm in multiple coronary arteries [score = 2]; and presence of ST segment elevations on ECG and history of using beta blockers [score = 1]) where assigned the indicated scores. Individuals with scores of 0 to 2, 3 to 5, and ≥6 experienced an incidence of a major cardiovascular event in 2.5, 7.0, and 13.0% of cases. [20]

History

Dr. William Heberden is credited with being the first to describe in a 1768 publication the occurrence of chest pain attacks (i.e. angina pectoris) that appeared due to pathologically occluded coronary arteries. These attacks were triggered by exercise or other forms of exertion and relieved by rest and nitroglycerin. In 1959, Dr. Myron Prinzmetal described a type of angina that differed from the classic cases of Heberden angina in that it commonly occurred in the absence of exercise or exertion. Indeed, it often woke patients from their normal sleep. This variant angina differed from the classical angina described by Dr. Heberden in that it appeared due to episodic vasospasm of coronary arteries that were typically not occluded by pathological processes such as atherosclerosis, emboli, or spontaneous dissection (i.e. tears in the walls of coronary arteries). [4] [19] [13] Variant angina had been described twice in the 1930s by other authors [14] [21] and was referred to as cardiac syndrome X (CSX) by Kemp in 1973, in reference to patients with exercise-induced angina who nonetheless had normal coronary angiograms. [22] CSX is now termed microvascular angina, i.e. angina caused by disease of the heart's small arteries. [4]

Some key features of variant angina are chest pain that is concurrently associated with elevations in the ST segment on electrocardiography recordings, that often occurs during the late evening or early morning hours in individuals who are at rest, doing non-strenuous activities, or asleep, and that is not associated with permanent occlusions of their coronary vessels. The disorder seems to occur more often in women than men, has a particularly high incidence in Japanese males as well as females, and affects individuals who may smoke tobacco products but exhibit few other cardiovascular risk factors. [4] [23] However, individuals exhibiting angina symptoms that are associated with depressions in their electrocardiogram ST segments, that are triggered by exertion, and/or who have atherosclerotic coronary artery disease are still considered to have variant angina if their symptoms are caused by coronary artery spasms. Finally, rare cases may exhibit symptom-free coronary artery spasm that is nonetheless associated with cardiac muscle ischemia (i.e. restricted blood flow and poor oxygenation) along with concurrent ischemic electrocardiographic changes. The term vasospastic angina is sometimes used to include all of these atypical cases with the more typical cases of variant angina. [4] Here, variant angina is taken to include typical and atypical cases.

For a portion of patients, variant angina may be a manifestation of a more generalized episodic smooth muscle-contractile disorder such as migraine, Raynaud's phenomenon, or aspirin-induced asthma. [6] Variant angina is also the major complication of eosinophilic coronary periarteritis, an extremely rare disorder caused by extensive eosinophilic infiltration of the adventitia and periadventitia, i.e. the soft tissues, surrounding the coronary arteries. [24] [25] Variant angina also differs from the Kounis syndrome (also termed allergic acute coronary syndrome) in which coronary artery constriction and symptoms are caused by allergic or strong immune reactions to a drug or other substance. Treatment of the Kounis syndrome very much differs from that for variant angina. [26]

See also

Related Research Articles

An antianginal is a drug used in the treatment of angina pectoris, a symptom of ischaemic heart disease.

<span class="mw-page-title-main">Coronary artery disease</span> Reduction of blood flow to the heart

Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), myocardial ischemia, or simply heart disease, involves the reduction of blood flow to the heart muscle due to build-up of atherosclerotic plaque in the arteries of the heart. It is the most common of the cardiovascular diseases. Types include stable angina, unstable angina, and myocardial infarction.

<span class="mw-page-title-main">Angina</span> Chest discomfort due to not enough blood flow to heart muscle

Angina, also known as angina pectoris, is chest pain or pressure, usually caused by insufficient blood flow to the heart muscle (myocardium). It is most commonly a symptom of coronary artery disease.

<span class="mw-page-title-main">Chest pain</span> Discomfort or pain in the chest as a medical symptom

Chest pain is pain or discomfort in the chest, typically the front of the chest. It may be described as sharp, dull, pressure, heaviness or squeezing. Associated symptoms may include pain in the shoulder, arm, upper abdomen, or jaw, along with nausea, sweating, or shortness of breath. It can be divided into heart-related and non-heart-related pain. Pain due to insufficient blood flow to the heart is also called angina pectoris. Those with diabetes or the elderly may have less clear symptoms.

Microvascular angina, previously known as cardiac syndrome X, is angina with signs associated with decreased blood flow to heart tissue but with normal coronary arteries.

<span class="mw-page-title-main">Stenosis</span> Abnormal narrowing of a blood vessel or other tubular organ or structure

Stenosis is the abnormal narrowing of a blood vessel or other tubular organ or structure such as foramina and canals. It is also sometimes called a stricture.

Vasospasm refers to a condition in which an arterial spasm leads to vasoconstriction. This can lead to tissue ischemia and tissue death (necrosis). Cerebral vasospasm may arise in the context of subarachnoid hemorrhage. Symptomatic vasospasm or delayed cerebral ischemia is a major contributor to post-operative stroke and death especially after aneurysmal subarachnoid hemorrhage. Vasospasm typically appears 4 to 10 days after subarachnoid hemorrhage.

<span class="mw-page-title-main">Acute coronary syndrome</span> Medical condition

Acute coronary syndrome (ACS) is a syndrome due to decreased blood flow in the coronary arteries such that part of the heart muscle is unable to function properly or dies. The most common symptom is centrally located pressure-like chest pain, often radiating to the left shoulder or angle of the jaw, and associated with nausea and sweating. Many people with acute coronary syndromes present with symptoms other than chest pain, particularly women, older people, and people with diabetes mellitus.

<span class="mw-page-title-main">Unstable angina</span> Medical condition

Unstable angina is a type of angina pectoris that is irregular or more easily provoked. It is classified as a type of acute coronary syndrome.

Coronary vasospasm refers to when a coronary artery suddenly undergoes either complete or sub-total temporary occlusion.

Coronary artery anomalies are variations of the coronary circulation, affecting <1% of the general population. Symptoms include chest pain, shortness of breath and syncope, although cardiac arrest may be the first clinical presentation. Several varieties are identified, with a different potential to cause sudden cardiac death.

<span class="mw-page-title-main">Takotsubo cardiomyopathy</span> Sudden temporary weakening of the heart muscle

Takotsubo cardiomyopathy or takotsubo syndrome (TTS), also known as stress cardiomyopathy, is a type of non-ischemic cardiomyopathy in which there is a sudden temporary weakening of the muscular portion of the heart. It usually appears after a significant stressor, either physical or emotional; when caused by the latter, the condition is sometimes called broken heart syndrome. Examples of physical stressors that can cause TTS are sepsis, shock, subarachnoid hemorrhage, and pheochromocytoma. Emotional stressors include bereavement, divorce, or the loss of a job. Reviews suggest that of patients diagnosed with the condition, about 70–80% recently experienced a major stressor, including 41–50% with a physical stressor and 26–30% with an emotional stressor. TTS can also appear in patients who have not experienced major stressors.

The following outline is provided as an overview of and topical guide to cardiology, the branch of medicine dealing with disorders of the human heart. The field includes medical diagnosis and treatment of congenital heart defects, coronary artery disease, heart failure, valvular heart disease and electrophysiology. Physicians who specialize in cardiology are called cardiologists.

<span class="mw-page-title-main">Coronary ischemia</span> Medical condition

Coronary ischemia, myocardial ischemia, or cardiac ischemia, is a medical term for a reduced blood flow in the coronary circulation through the coronary arteries. Coronary ischemia is linked to heart disease, and heart attacks. Coronary arteries deliver oxygen-rich blood to the heart muscle. Reduced blood flow to the heart associated with coronary ischemia can result in inadequate oxygen supply to the heart muscle. When oxygen supply to the heart is unable to keep up with oxygen demand from the muscle, the result is the characteristic symptoms of coronary ischemia, the most common of which is chest pain. Chest pain due to coronary ischemia commonly radiates to the arm or neck. Certain individuals such as women, diabetics, and the elderly may present with more varied symptoms. If blood flow through the coronary arteries is stopped completely, cardiac muscle cells may die, known as a myocardial infarction, or heart attack.

<span class="mw-page-title-main">Myocardial infarction</span> Interruption of blood supply to a part of the heart

A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops in one of the coronary arteries of the heart, causing infarction to the heart muscle. The most common symptom is chest pain or discomfort which may travel into the shoulder, arm, back, neck or jaw. Often such pain occurs in the center or left side of the chest and lasts for more than a few minutes. The discomfort may occasionally feel like heartburn.

Roemheld syndrome (RS), or gastrocardiac syndrome, or gastric cardiac syndrome or Roemheld–Techlenburg–Ceconi syndrome or gastric-cardia, was a medical syndrome first coined by Ludwig von Roemheld (1871–1938) describing a cluster of cardiovascular symptoms stimulated by gastrointestinal changes. Although it is currently considered an obsolete medical diagnosis, recent studies have described similar clinical presentations and highlighted potential underlying mechanisms.

<span class="mw-page-title-main">Myocardial bridge</span> Medical condition

A myocardial bridge (MB) is a congenital heart defect in which one of the coronary arteries tunnels through the heart muscle itself (myocardium). In normal patients, the coronary arteries rest on top of the heart muscle and feed blood down into smaller vessels which then take blood into the heart muscle itself. However, if a band of muscle forms around one of the coronary arteries during the fetal stage of development, then a myocardial bridge is formed – a "bridge" of heart muscle over the artery. Each time the heart squeezes to pump blood, the band of muscle exerts pressure and constricts the artery, reducing blood flow to the heart. This defect is present from birth. It is important to note that even a very thin ex. <1 mm and/or short ex. 20 mm MB can cause significant symptoms. MBs can range from a few mm in length to 10 cm or more. The overall prevalence of myocardial bridge is 19%, although its prevalence found by autopsy is much higher (42%).

<span class="mw-page-title-main">Management of acute coronary syndrome</span>

Management of acute coronary syndrome is targeted against the effects of reduced blood flow to the affected area of the heart muscle, usually because of a blood clot in one of the coronary arteries, the vessels that supply oxygenated blood to the myocardium. This is achieved with urgent hospitalization and medical therapy, including drugs that relieve chest pain and reduce the size of the infarct, and drugs that inhibit clot formation; for a subset of patients invasive measures are also employed. Basic principles of management are the same for all types of acute coronary syndrome. However, some important aspects of treatment depend on the presence or absence of elevation of the ST segment on the electrocardiogram, which classifies cases upon presentation to either ST segment elevation myocardial infarction (STEMI) or non-ST elevation acute coronary syndrome (NST-ACS); the latter includes unstable angina and non-ST elevation myocardial infarction (NSTEMI). Treatment is generally more aggressive for STEMI patients, and reperfusion therapy is more often reserved for them. Long-term therapy is necessary for prevention of recurrent events and complications.

Kounis syndrome is defined as acute coronary syndrome caused by an allergic reaction or a strong immune reaction to a drug or other substance. It is a rare syndrome with authentic cases reported in 130 males and 45 females, as reviewed in 2017; however, the disorder is suspected of being commonly overlooked and therefore much more prevalent. Mast cell activation and release of inflammatory cytokines as well as other inflammatory agents from the reaction leads to spasm of the arteries leading to the heart muscle or a plaque breaking free and blocking one or more of those arteries.

Attilio Maseri OMRI KSG was an Italian academic and physician specialized in cardiology, considered a leading researcher in the field of ischemic heart disease. His patients included Queen Elizabeth II and Pope John Paul II.

References

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  18. ↑ "NORVASC- amlodipine besylate tablet". DailyMed. 2019-03-14. Retrieved 2019-12-19. Vasospastic Angina: NORVASC has been demonstrated to block constriction and restore blood flow in coronary arteries and arterioles in response to calcium, potassium epinephrine, serotonin, and thromboxane A2 analog in experimental animal models and in human coronary vessels in vitro. This inhibition of coronary spasm is responsible for the effectiveness of NORVASC in vasospastic (Prinzmetal's or variant) angina.
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  24. ↑ Séguéla PE, Iriart X, Acar P, Montaudon M, Roudaut R, Thambo JB (April 2015). "Eosinophilic cardiac disease: Molecular, clinical and imaging aspects". Archives of Cardiovascular Diseases. 108 (4): 258–68. doi: 10.1016/j.acvd.2015.01.006 . PMID   25858537.
  25. ↑ Kajihara H, Tachiyama Y, Hirose T, Takada A, Takata A, Saito K, Murai T, Yasui W (2013). "Eosinophilic coronary periarteritis (vasospastic angina and sudden death), a new type of coronary arteritis: report of seven autopsy cases and a review of the literature". Virchows Archiv. 462 (2): 239–48. doi:10.1007/s00428-012-1351-7. PMID   23232800. S2CID   32619275.
  26. ↑ Kounis NG (October 2016). "Kounis syndrome: an update on epidemiology, pathogenesis, diagnosis and therapeutic management". Clinical Chemistry and Laboratory Medicine. 54 (10): 1545–59. doi: 10.1515/cclm-2016-0010 . PMID   26966931. S2CID   11386405.
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