BySteven Lome, MD

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Coronary Artery Disease - Stable Angina Topic Review

BySteven Lome, MD

Introduction

Atherosclerotic coronary artery disease (CAD) affects the coronary arteries, which deliver blood to the myocardium.

CAD symptoms include stable angina, reviewed here, and acute coronary syndromes (ACS), reviewed in the Unstable Angina/Non-STEMI Topic Review and STEMI Topic Review. CAD also frequently leads to heart failure.

Coronary artery disease is the most common cause of death in the United States. The atherosclerotic process in the coronary arteries may be clinically silent or may be associated with symptoms due to transient or prolonged decreases in oxygen supply to the myocardium. Transient symptoms are referred to as angina pectoris (Latin for “a strangling feeling in the chest”).

Diabetes, tobacco smoking, hypertension, lipid disorders and genetic factors (family history of ischemic heart disease) predispose to the development of atherosclerosis and coronary artery disease; these risk factors are discussed further in the Atherosclerosis Topic Review.

**Atherosclerosis of an artery restricting blood flow**

Pathophysiology – CAD - Stable Angina

The term “ischemic heart disease” implies a physiologically significant myocardial oxygen supply/demand mismatch. The most common cause of this mismatch is flow-limiting atherosclerotic narrowing of the coronary artery, resulting in the potential for inadequate coronary flow. Reduced oxygen carrying capacity, eg, anemia, carbon monoxide poisoning or increased oxygen demand due to tachyarrhythmias, hypertensive emergencies or severe aortic valve stenosis may also precipitate angina.

Three main factors determine myocardial oxygen demand:

Left ventricular (LV) wall stress: This is the force acting against the myocardial cells. It is directly proportional to the LV pressure and radius. Wall stress is indirectly proportional to two times wall thickness. LaPlace’s Law explains the phenomenon:

Left ventricular pressure increases with states that increase afterload (the pressure the heart must overcome to eject blood), including systemic hypertension and aortic valve stenosis.

Left ventricular radius increases as the heart remodels and dilates, for example in valvular heart disease (especially mitral and aortic regurgitation) and with cardiomyopathic processes that cause heart failure with reduced ejection fraction.

Left ventricular wall thickness increases with hypertrophy due to processes like chronic hypertension and aortic valve stenosis, which serves as a compensatory mechanism to decrease wall stress. This decreases oxygen demand, as the stress is distributed over a larger mass. Hypertrophic obstructive cardiomyopathy (HOCM) similarly increases wall thickness. After a myocardial infarction, scarring and fibrosis of the LV wall leads to thinning, thereby increasing wall stress.

Contractility: Contractility is the force of systolic contraction. Sympathetic nervous system activation (eg, during physical exertion or exercise) increases contractility. Beta-blocker therapy, which blocks the sympathetic nervous system, partially decreases contractility and decreases oxygen demand.

Heart rate: Heart rate is a major determinant of myocardial oxygen demand. The greater the number of ventricular contractions per minute, the greater the oxygen requirements. Tachycardia increases oxygen demand significantly. Thus, stable anginal symptoms are typically exertional. Conversely, beta-blocker therapy slows the heart rate and significantly decreases oxygen demand, largely explaining the efficacy of beta-blockers in treating angina.

Etiology – CAD - Stable Angina

Atherosclerosis of the coronary arteries is the most common cause of ischemic heart disease. The five major risk factors for atherosclerotic heart disease include diabetes, tobacco use, hypertension, lipid disorders and genetic factors (family history of ischemic heart disease). States of increased oxygen demand or decreased supply, as described in Pathophysiology, may cause angina. Other causes of angina include coronary spasm, congenital coronary anomalies, vasculitis, increased blood viscosity, coronary aneurysms, severe myocardial bridging, coronary emboli, external compression, coronary fistulas, coronary microvascular dysfunction and anxiety states such as Da Costa’s syndrome (not true angina). These are discussed in Special Situations.

In general, symptoms of stable angina will not develop unless there is flow-limiting stenosis of a major epicardial coronary vessel (left anterior descending, circumflex or right coronary artery). Multiple tandem stenosis may occasionally cause angina, even if the individual obstructions are not flow-limiting.

Angiographic estimation of the severity of coronary luminal stenosis is subjective and somewhat unreliable. Management decisions for patients with CAD should be based, whenever possible, on measurements of coronary flow reserve or objective evidence of ischemia in the distribution of the stenotic epicardial conduit artery. (Chowdhury M, et al. Curr Treat Options Cardiovasc Med. 2020;2a,3a,10a,11a).

Physical Examination – CAD - Stable Angina

Physical examination findings are relatively non-specific and usually only present during the anginal episode, making this a less informative diagnostic modality. When examined during an anginal attack, patients may have elevated heart rate and blood pressure, and an S4 heart sound.

During ischemia, papillary muscle dysfunction can cause mitral regurgitation, resulting in a holosystolic murmur at the cardiac apex radiating to the axilla; see Heart Murmurs Topic Review.

When left ventricular end-diastolic pressure (LVEDP) increases during myocardial ischemia, pulmonary venous pressure increases and may cause veins and into the pulmonary vasculature, causing transient pulmonary congestion that results in dyspnea and rales on lung examination.

Symptoms – CAD - Stable Angina

The primary symptoms of occlusive CAD include chronic stable angina pectoris. Substernal chest pressure upon physical exertion with radiation to the medial portion of the left arm or left jaw is the “textbook” description. Emotional upset/stress or other hemodynamic stresses (eg, hypertensive emergency) may also cause anginal symptoms.

Patients may describe angina as a “tightness,” “discomfort, not pain,” “squeezing,” “indigestion,” “heaviness,” or an “elephant sitting on my chest,” and often describe the sensations of squeezing and tightness by placing a fist in the center of the chest (Levine’s sign). Pain from angina usually begins gradually and lasts for at least 5 minutes. The pain is diffuse and difficult to localize to one part of the chest.

Less common presentations of angina include isolated shoulder pain, pain in both arms, left wrist pain, right-sided chest or jaw pain, radiation to the right arm, mid-thoracic pain, and dyspnea without chest discomfort. Angina pain is rarely described as “sharp.”

Associated symptoms that may occur with the classic anginal symptoms above include dyspnea, diaphoresis (cold sweats), fatigue/weakness, nausea, and dizziness. Women, elderly patients, and patients with diabetes tend to have more atypical presentations of angina.

Many non-cardiac disease states can also cause chest pain. Important features suggestive of non-cardiac causes of chest pain include worsening with inspiration (pleuritic pain), short duration of the pain (below 5 minutes), a small pinpoint area of pain (angina is more diffuse), and lack of relief with nitroglycerin. Note that esophageal spasm — although a relatively uncommon cause of chest pain — can be relieved with nitroglycerine, mimicking angina. Sharp, shooting chest pains lasting a few seconds to a minute are common and usually musculoskeletal in origin.

When an acute coronary syndrome (ACS) with intra-coronary thrombosis occurs, it often produces severe prolonged anginal symptoms at rest; see Acute Coronary Syndromes Topic Review.

Diagnosis – CAD - Stable Angina

Coronary calcium scoring can be helpful in identifying calcified atherosclerotic plaque in intermediate-risk patients without symptoms. For decades, cardiac stress testing has played an important role in the clinical evaluation of patients with chest pain or exertional dyspnea. Recently, coronary computed tomographic angiography (CTA) has gained favor as technology advances. The “gold standard” for diagnosis of coronary disease is invasive coronary angiography.

Differences between stable angina pectoris and unstable angina pectoris, a non-ST segment elevation myocardial infarction (non-STEMI), and an ST segment elevation myocardial infarction (STEMI) are discussed below. The latter three fall in the ACS category and are reviewed in detail elsewhere.

Stable Angina Pectoris

Stable angina pectoris is characterized by recurrent angina relieved by rest or nitroglycerin and occurring on a predictable amount of physical exertion, usually present for weeks to months.

Unstable Angina Pectoris

Unstable angina has three different presentations:

New-onset exertional angina of (even if relieved with rest and requiring a consistent amount of exertion to produce symptoms, angina is considered unstable when it first occurs)
Exertional angina that was previously stable and now occurs with less physical exertion
Anginal symptoms occurring at rest (without physical exertion)

In unstable angina, the cardiac enzymes remain normal or are only very minimally elevated.

Non-ST Segment Elevation Myocardial Infarction

Non-STEMI is characterized by angina at rest associated with myocardial injury, as identified by elevated cardiac biomarkers (see Cardiac Enzymes Topic Review) without ST segment elevation on the 12-lead ECG.

ST Segment Elevation Myocardial Infarction

STEMI is typified by angina at rest with evidence of transmural myocardial injury, as identified by elevated cardiac biomarkers (see Cardiac Enzymes Topic Review) and ST segment elevation on the 12-lead ECG.

Treatment – CAD - Stable Angina

Management of CAD consists of reducing the risk for disease progression, preventing acute coronary syndromes/cardiovascular death and treating symptoms of stable angina. The treatment of ACS is discussed elsewhere.

Reducing Disease Progression Risk

When the diagnosis of CAD is confirmed, treatment directed at the known CV risk factors to prevent progression of disease is critical. This includes lipid management, smoking cessation, BP management, weight loss and dietary/exercise counseling. Regardless of LDL cholesterol levels, all patients with CAD should be taking a HMG-CoA reductase inhibitor (statin) proven to reduce progression of disease. Two small trials showed regression of atherosclerotic plaque in a moderate percentage of patients who were taking high-dose atorvastatin or rosuvastatin.

The 2023 American Heart Association/American College of Cardiology/Multisociety Guideline for the Management of Patients with Chronic Coronary Disease recommends that clinical follow-up should occur once per year for all patients with chronic coronary disease to assess symptoms, change in functional status and adherence to/adequacy of lifestyle and medical interventions. (Virani SS, et al. Circulation. 2023;15a.) However, routine periodic anatomic or ischemic testing is not needed if there has been no change in clinical or functional status. (Virani SS, et al. Circulation. 2023;3b.)

Preventing Acute Coronary Syndromes

All patients with CAD, regardless of risk factors, should be treated with an antiplatelet agent and an HMG-CoA reductase inhibitor (statin) to reduce the risk of acute coronary syndromes/CV death. Controlling hypertension, lipid management and smoking cessation have been shown to prevent not only CAD progression, but also acute coronary syndromes.

Antiplatelet Therapy

Patients with documented coronary artery disease should receive an antiplatelet agent, usually aspirin, for the prevention of acute coronary syndromes. Low-dose aspirin (75 mg-150 mg) is as effective as higher-dose aspirin (162 mg-325 mg) with fewer gastrointestinal bleeding complications. In small studies, clopidogrel was slightly more effective than aspirin at reducing acute coronary syndromes and cardiovascular death. However, cost concerns have precluded its use in the general population for this purpose, since aspirin is cheap and effective. While ticlopidine can help in patients who are not able to tolerate aspirin or clopidogrel, side effects may include thrombotic thrombocytopenic purpura (TTP); it is therefore not recommended as a first- or second-line agent to prevent acute coronary syndromes.

HMG-CoA Reductase Inhibitors

Statins play a pivotal role in reducing CV events and mortality; see HMG-CoA Reductase Inhibitors Topic Review. Statins are recommended for patients with coronary disease, regardless of LDL cholesterol level. Similarly, patients with coronary risk equivalents (peripheral arterial disease or type 2 diabetes) should also receive statins, even with normal LDL levels. Multiple trials have demonstrated significant mortality benefits and reduction of ACS, even in patients with coronary disease and normal LDL levels. The “pleiotropic effects” of statins remain a topic of intense research. Statins have anti-inflammatory properties and plaque stabilization capabilities independent of LDL lowering. The 2018 Guidelines on the Management of Blood Cholesterol recommend a high-intensity statin (atorvastatin 80 mg or rosuvastatin 20 mg) for patients with clinical atherosclerotic cardiovascular disease (ASCVD) who are 75 years of age or younger to achieve a 50% or greater reduction in LDL cholesterol. Depending on the individual patient’s tolerance, atorvastatin can be titrated down to 40 mg and rosuvastatin titrated up to 40 mg per day. A moderate-intensity statin can be used if a high-intensity statin is not tolerated. (Grundy SM, et al. J Am Coll Cardiol. 2019;10a(e294),11a(e295),12a(e296).) For patients between 40 and 75 years of age with LDL cholesterol between 70 and 190 mg/dL and without ASCVD or type 2 diabetes, the 2019 ACC/AHA Guidelines for the Primary Prevention of ASCVD recommend initiating statins based on their 10-year ASCVD risk, as estimated by the ACC/AHA ASCVD Risk Estimator tool. For patients at intermediate risk (≥ 7.5% to < 20% 10-year ASCVD risk), and if the risk estimate and risk enhancers favor statins, a moderate-intensity statin should be initiated to reduce LDL cholesterol by 30-49%. For patients at high risk (≥ 20% 10-year ASCVD risk), statins should be initiated to lower LDL cholesterol by ≥ 50%. (Arnett DK, et al. Circulation. 2019;20a(e196).)

Managing Stable Angina Symptoms

Treatment of chronic stable angina is aimed at increasing myocardial oxygen supply and reducing myocardial oxygen demand, as discussed in Pathophysiology. This can be accomplished with nitrates, beta-blockers, calcium channel blockers, ranolazine and external counterpulsation. As these therapies are discussed, recall that wall stress, heart rate, and contractility determine oxygen demand.

Nitrates

Nitroglycerin is metabolized to form the vasoactive free radical nitric oxide. Systemic venodilation, the predominant mechanism of action of nitroglycerin, results in decreased preload (stretching of the cardiac muscle before contraction), in turn reducing LV pressure and LV volume (decreasing radius). Some arterial vasodilation from smooth muscle relaxation occurs as well, increasing coronary blood flow and oxygen supply, and reducing vasospasm. Importantly, no clinical trial data suggest that nitrates improve survival or reduce the risk for ACS in patients with CAD and chronic angina.

Nitroglycerine is available as a sublingual tablet or spray for acute angina attacks on an as-needed basis. The ACC/AHA Guidelines recommend nitroglycerin (either as sublingual tablets or spray) for immediate relief of angina in patients with stable ischemic heart disease.(Virani SS, et al; Circulation. 2023;51a.) Patients should be advised to take one dose of nitroglycerin (1–2 sprays or 1 tablet) immediately at the onset of an angina attack. A second dose may be taken 5 minutes later if symptoms improve but do not completely subside after the first dose. Patients can also take a third dose 5 minutes after the second dose, but should not take more than 3 doses in a 15-minute period. (Hambrecht R, et al. Circulation. 2013;1a(e643).) Emergency services should be called in the following situations: 1) The symptoms do not improve substantially or if they worsen within 5 minutes of the first nitroglycerin dose; 2) The symptoms do not continue to get better after the second nitroglycerin dose; 3) The symptoms do not completely subside 5 minutes after the third nitroglycerin dose; and 4) The patient took more than the required dose of nitroglycerin. (Hambrecht R, et al. Circulation. 2013;2a(e644).)

Long-acting nitrates are available in a tablet form — isosorbide mononitrate and isosorbide dinitrate — and as a patch to prevent angina from occurring.

Vasodilator-related headache often limits higher doses of nitrates. Hypotension is also common, especially in patients who are “preload dependent”. Hypotension can cause reflex tachycardia, which increases oxygen demand. Tachyphylaxis (drug tolerance resulting in decreased efficacy) occurs with nitrates, requiring drug-free intervals for best results. For example, nitroglycerin patches should be applied in the morning and removed in the evening; when left on all day, tolerance quickly develops, and the clinical benefits decrease significantly.

Phosphodiesterase (PDE) inhibitors (sildenafil, vardenafil, tadalafil), used to treat erectile dysfunction, also enhance nitric oxide production and can cause potentially serious hypotension when used in combination with nitrates. Nitrates and PDE inhibitors should not be used together within 24 hours (sildenafil) or 48 hours (vardenafil, tadalafil) due to this interaction. Interestingly, it was during investigations of phosphodiesterase inhibitors for the treatment of stable angina that researchers noted the improvement in erectile function, and thus redirected their efforts.

Beta-blockers

These drugs block the actions of the sympathetic catecholamines, epinephrine and norepinephrine, leading to reductions in heart rate, contractility, and blood pressure, with significantly decreased myocardial oxygen demand; see Beta-Blockers Topic Review. Dose titration to achieve a resting heart rate of about 60 beats per minute is frequently required for optimal relief of angina. Commonly used beta-blockers include metoprolol, atenolol, propranolol and carvedilol.

Although quite effective in relieving anginal symptoms, beta-blockers have a number of potential side effects and contraindications. Significant bradycardia can occur, leading to fatigue, hypotension and dizziness. “Cardio-selective” beta-blockers target primarily beta-1 receptors. Asthma can be exacerbated, especially with non-cardioselective beta-blockers that antagonize beta-2 receptors. Beta-blocker overdose is treated with glucagon.

The 2023 American Heart Association/American College of Cardiology/Multisociety Guideline for the Management of Patients with Chronic Coronary Disease recommends beta-blockers, calcium channel blockers or long-acting nitrates as first-line antianginal therapy, and states that a second agent from a different class on that list may be added if the patient remains symptomatic after initial treatment. (Virani SS, et al. Circulation. 2023;51a) However, the document does not recommend beta-blocker therapy beyond 1 year in patients with chronic coronary disease who have not had a myocardial infarction in the past year or who have left ventricular ejection fraction more than 50%. (Virani SS, et al. Circulation. 2023;3a)

Calcium Channel Blockers

There are two types of calcium channel blockers. The dihydropyridine calcium channel blockers (amlodipine, nifedipine) act primarily on vascular calcium channels to cause smooth muscle relaxation and arterial vasodilation, decreasing afterload (BP) and reducing oxygen demand. Coronary vasodilation may also reduce vasospasm and improve coronary blood flow. Non-dihydropyridine calcium channel blockers (diltiazem, verapamil) act primarily on myocardial cell calcium channels to decrease heart rate and contractility, thus reducing myocardial oxygen demand.

Sublingual nifedipine, used in the past for angina and hypertensive emergencies, can lead to stroke — likely due to sudden severe drop in blood pressure — as well as myocardial infarction and death. Its use has been abandoned except in autonomic dysreflexia in spinal cord injury.

Ranolazine

A novel agent for angina, ranolazine does not affect hemodynamic parameters (blood pressure, heart rate, vascular tone). The exact mechanism of action is somewhat controversial; however, it likely inhibits sodium channels, eventually reducing intracardiac calcium and causing reduced oxygen consumption. Initially, ranolazine was thought to shift the main energy substrate of myocytes from lipid metabolism to glucose metabolism, but this has not been definitively proven at clinical doses. Ranolazine may be considered for patients with angina who fail nitrates, beta-blockers and calcium channel blockers. Although side effects are relatively uncommon, ranolazine can prolong the QT interval, increasing the risk for polymorphic ventricular tachycardia (torsades de pointes).

The 2023 American Heart Association/American College of Cardiology/Multisociety Guideline for the Management of Patients with Chronic Coronary Disease recommends ranolazine in patients with chronic coronary disease whose angina remains symptomatic despite treatment with beta-blockers, calcium channel blockers or long-acting nitrate therapies. (Virani SS, et al. Circulation. 2023;51a.)

External Counterpulsation

Enhanced external counterpulsation (EECP) is used in the outpatient setting in patients who are refractory to medical therapy. The technique consists of ECG-gated rapid sequential cuff compression of the lower extremities during diastole followed by simultaneous cuff decompression during systole. (Manchanda A, et al. J Am Coll Cardiol. 2007;2a.)

Although the exact mechanism(s) of action of EECP remain unclear, significant anginal relief has been shown in small studies, including the Multicenter Study of Enhanced External Counterpulsation (MUST-EECP) trial. (Manchanda A, et al. J Am Coll Cardiol. 2007;1a, 2b, 3a.)

The 2023 American Heart Association/American College of Cardiology/Multisociety Guideline for the Management of Patients with Chronic Coronary Disease states that enhanced external counterpulsation may be considered in patients with chronic coronary disease, refractory angina and no other treatment options. (Virani SS, et al. Circulation. 2023;52a.)

Percutaneous Coronary Intervention

Percutaneous coronary intervention (PCI), primarily coronary balloon angioplasty with stenting, leads to improvement in angina in a large majority of patients with hemodynamically significant stenosis (> 70%) in a major epicardial coronary vessel. To date, PCI has not improved mortality in CAD patients. The Clinical Outcomes Utilizing Revascularization and Aggressive Drug Evaluation (COURAGE) trial compared medical management to PCI in patients with CAD and stable angina. Patients were randomized to either optimal medical therapy or to coronary revascularization. There was no mortality benefit or reduction in non-fatal myocardial infarction in the PCI group, and medical therapy frequently relieved angina adequately. The ORBITA and ISCHEMIA trials also found revascularization did not improve mortality or CV events in patients with stable ischemic heart disease compared with optimal medical therapy. However, in ISCHEMIA, among patients with frequent angina, those assigned invasive treatment had better symptom relief and quality of life compared with those assigned conservative treatment. (Al-Lamee R, et al. Lancet. 2018;1a; and Maron DJ, et al. N Engl J Med. 2020;1a.)

Coronary Artery Bypass Grafting

Surgical revascularization with coronary artery bypass grafting (CABG) is appropriate for certain candidates. Patients with three-vessel CAD have historically been treated with this approach and a meta-analysis of six large trials supports the concept that surgical revascularization improves outcomes. (Sipahi I, et al. JAMA Intern Med. 2014;1a-b.) Patient characteristics (ie, left main coronary disease, diabetes or LV systolic dysfunction), surgical technique (on- vs. off-pump) and choice of conduits (one or more arterial conduits) have important impact on outcomes.

The 2023 American Heart Association/American College of Cardiology/Multisociety Guideline for the Management of Patients with Chronic Coronary Disease states that revascularization (either PCI or CABG) is recommended in patients with chronic coronary disease and stenoses amenable to revascularization if they have lifestyle-limiting angina despite guideline-directed medical therapy. (Virani SS, et al. Circulation. 2023;53a.)

Special Situations – CAD - Stable Angina

Da Costa’s Syndrome

Also known as “soldier’s heart” or “cardiac neurosis,” Da Costa’s syndrome was first described during the American Civil War. Symptoms are more or less typical of stable angina, but stress testing and angiography show no abnormalities, and typical anginal therapies are not effective. In modern times, Da Costa’s syndrome is considered part of a generalized anxiety disorder. Similar symptoms are sometimes seen as a part of the mitral valve prolapse syndrome. This is physiologically distinct from coronary microvascular dysfunction (formerly known as cardiac “syndrome X”), in which patients can indeed show signs of myocardial ischemia, even with normal coronary arteries and no inducible coronary vasospasm.

Coronary microvascular dysfunction

Coronary microvascular dysfunction (CMD) refers to myocardial ischemia caused by decreased circulatory function in the coronary microvessels. In CMD, the endothelium of coronary arterioles becomes dysfunctional, producing excess H2O2, a pro-inflammatory, pro-proliferative and pro-thrombotic signal that promotes atherosclerosis in conduit arteries, and hypertrophy and fibrosis in cardiomyocytes. By contrast, healthy arteriolar endothelium produces NO, PGI2, and EETs (in addition to low levels of H2O2), which act as anti-inflammatory, anti-proliferative, and anti-thrombotic signals and promote atherostasis and normal function and quiescence in cardiomyocytes. (Gutterman DD, et al. Circ Res. 2016;6a).

CMD was known historically as cardiac syndrome X, and the nomenclature around this disease process remains dynamic (other terms in use include: open artery ischemic heart disease, ischemic heart disease without obstructive coronary artery disease [INOCA] and microvascular angina). Risk factors for CMD are similar to that of other CV diseases, and include type 2 diabetes, hyperlipidemia and hypertension. In some groups (notably women), angina with CMD is more common than angina with CAD, although the two disease processes can also overlap. (Hurst’s the Heart; 2017;35;11a-e, 12a, 13a.)

Hibernating Myocardium

“Hibernating myocardium” refers to chronic regional myocardial dysfunction due to significantly reduced blood flow. Restoration of normal blood flow after PCI or surgical bypass grafting can lead to return of normal function. Viability testing can help to determine if the myocardium in a dysfunctional segment is hibernating or completely infarcted. This testing is best performed using magnetic resonance imaging (MRI) but can also be achieved with positron emission tomography (PET) scanning, thallium myocardial perfusion imaging, and dobutamine stress echocardiography.

Stunned Myocardium

Myocardial stunning occurs when transient ischemia resulting from total or subtotal coronary occlusion, such as during an ACS, results in segmental myocardial dysfunction. When blood flow is restored after coronary revascularization, the dysfunction persists for days or even weeks after the ischemic insult, but the segment eventually recovers normal function.

Collateral Circulation

In the setting of chronic ischemia, collateral circulation may develop to compensate for the reduced blood flow. Collaterals are usually small vessels that connect to an occluded distal vessel from sub-branches of a neighboring, non-occluded coronary vessel. Collateral circulation can sometimes be extensive and may be increased by exercise. Some patients develop more extensive collateral circulation than others, and approaches to enhance the development of coronary collaterals are under investigation.

Walk-through Angina

The walk-through phenomenon occurs when angina at a low level of activity is relieved with continued exercise. On treadmill testing, ST segment depression seen early on may subsequently resolve. The mechanism of this phenomenon is thought to involve the release of endogenous vasodilators, improving flow in collateral circulatory channels and eventually increasing the flow to the ischemic myocardial segment and relieving the symptoms of angina.

Coronary Vasospasm

With sudden increases in arterial tone, coronary vasospasm can occur and result in angina. This is also known as Prinzmetal’s Angina or Variant Angina. Although the coronary arteries may be angiographically normal, advanced imaging techniques demonstrate endothelial erosion and intraluminal thrombus at the sites where vasospasm can be induced by ergonovine or acetylcholine infusion. (Lerman A, et al; JACC Cardiovasc Imaging. 2015;1a). In the absence of severe stenosis, the treatment is dihydropyridine calcium channel blockers. Beta-blockers should be avoided, as beta-blockade leads to “unopposed alpha agonism,” which worsens vasoconstriction.

The ECG during coronary vasospasm can be markedly abnormal, with ST segment elevation mimicking myocardial infarction. The ECG changes resolve once the angina and vasospasm are relieved. Clinically coronary vasospasm is most common in middle-aged women.

Myocardial Bridging

Myocardial bridging occurs when a segment of a coronary vessel does not run along the epicardial surface of the heart, but within the myocardium. During systolic contraction, the coronary vessel can be compressed, as is seen on angiography. Coronary flow occurs in diastole, and is not normally compromised by bridging. (Hurst’s the Heart; 2017;17;25a.) Given the high prevalence of myocardial bridges (MBs; probably up to 25% of unselected individuals) and the fact that coronary flow is essentially limited to diastole, cardiologists advise managing most patients with MBs as having benign normal variants. While the vast majority of MBs are likely asymptomatic, case reports and series have documented an association in some patients between MBs (usually deep and extensive) and angina or anginal‐equivalent symptoms, including exertional chest pain and exertional dyspnea. (Rogers IS, et al. Congenit Heart Dis. 2017;1a-b.) Objective evidence of ischemia should be obtained using advanced imaging techniques before making such a diagnosis.

Coronary Aneurysms

A coronary arterial wall weakened by disease may dilate and form a coronary artery aneurysm. This can occur as post-stenotic dilation with atherosclerotic coronary disease or may occur as a consequence of vasculitis. Kawasaki disease — a form of vasculitis — during childhood can lead to coronary aneurysms in later life that cause ischemic heart disease and angina when the coronary aneurysms are large. The pathophysiologic mechanism of ischemia is thought to be due to microemboli. Current guidelines recommend management based on coronary artery dimensions. (Osborne J, et al; Pediatr Cardiol. 2021;1a). Patients with MBs should be restricted to low-intensity sports and those with a symptomatic MB should be treated with beta-adrenergic blocking agents; surgical correction can be considered if the symptoms are refractory to medical therapy. (Virani SS, et al. Circulation. 2023;62a.)

Congenital Coronary Anomalies

Many types of congenital variations of the coronary arteries exist. Although most are benign, an anomalous coronary artery that passes between the aorta and the pulmonary artery — known as an interarterial course — may be subject to compression, causing myocardial ischemia and angina. Coronary anomalies are the second-leading cause of sudden cardiac death in young athletes, after HOCM. Some examples include the left anterior descending originating from the right coronary cusp, the right coronary artery arising from the left main coronary artery and the circumflex coronary artery arising from the right coronary cusp.