• Clinical science

Principles of coronary heart disease

Abstract

Coronary heart disease (CHD) refers to a mismatch between myocardial oxygen supply and demand. Atherosclerosis is the most important cause. Atherosclerotic changes in coronary vessel walls lead to a narrowing of the lumen and prevent vessels from dilating. As a result, an increase in oxygen demand (e.g., during physical activity) can no longer be satisfied and/or myocardial perfusion at rest is insufficient. Acute retrosternal chest pain (angina) is the cardinal symptom of CHD. Other symptoms include dyspnea, dizziness, anxiety and nausea. If ischemia is severe, myocardial infarction can occur. Coronary heart disease is diagnosed via a cardiac stress test (possibly provoking symptoms and instrumental findings) and/or coronary catheterization (e.g., measurement of coronary blood flow). Management of CHD involves primary and secondary prevention of atherosclerosis (e.g., weight reduction), antianginal treatment (e.g., beta blockers) and, in some cases, revascularization (e.g., PCTA).

This learning card provides a basic overview of coronary heart disease and stable angina. Atherosclerosis and acute coronary syndrome (including myocardial infarction) are discussed in separate learning cards.

Definition

Epidemiology

  • Lifetime risk of coronary heart disease
    • Age 40: 49% in men and 32% in women
    • Age 75: 35% in men and 24% in women
  • Cardiovascular disease is the leading cause of death in the US and the world.

Epidemiological data refers to the US, unless otherwise specified.

Etiology

Pathophysiology

Myocardial oxygen supply and demand

  • Mismatch between the amount of oxygen the myocardium receives and the amount it needs
  • Coronary flow reserve: the ability of the coronary capillaries to dilate and increase blood flow to the myocardium
  • Factors reducing oxygen supply
  • Factors increasing oxygen demand

Increases in heart rate (e.g., during physical exertion) both reduce oxygen supply and increase oxygen demand!

Myocardial ischemia in coronary atherosclerosis

  • Depending on the extent of stenoses (and the corresponding ischemia), patients remain asymptomatic or develop angina and other symptoms. Symptoms usually develop if stenosis is ≥ 70%. If ischemia is severe enough, myocardial infarction can occur.

Effect of vascular stenosis on resistance to blood flow

  • The greater the stenosis, the higher the resistance to blood flow through the blood vessel, provided the length of the vessel and viscosity of blood remain constant.
  • The degree of increased resistance is calculated using the Poiseuille equation: R = 8Lη/(πr4); where R = resistance to flow, L = length of the vessel, η = viscosity of blood, and r = radius of the vessel.
  • When the length of the vessel and viscosity of blood remain constant, the relationship between resistance and the radius of the vessel can be simplified to R ∼ 1/r4.

References:[1][2][3]

Clinical features

Angina

  • Typically retrosternal chest pain or pressure
    • Pain can also radiate to left arm, neck, jaw, epigastric region, or back.
    • Pain does not depend on body position or respiration
    • No chest wall tenderness
    • Angina may be absent, particularly in younger patients
    • Often gradual progression
    • Can also present as gastrointestinal discomfort
  • Dyspnea
  • Dizziness, palpitations
  • Restlessness, anxiety
  • Autonomic symptoms (e.g., diaphoresis, nausea, vomiting, syncope)

Stable angina

  • Symptoms are reproducible/predictable
  • Complaints often subside within minutes; , with rest or after administration of nitroglycerin
  • Common triggers

Unstable angina

  • Symptoms are not reproducible/predictable
  • Usually occurs at rest or with minimal exertion and is usually not relieved by rest or nitroglycerin
  • Every new-onset angina
  • Severe, persistent, and/or worsening angina (crescendo angina)
  • Increasing intensity, frequency, or duration in a patient with a known stable angina

Staging of angina (according to the Canadian Cardiovascular Society)

  • Class I – Angina only during strenuous or prolonged physical activity
  • Class II – Slight limitation, with angina during normal physical activity
  • Class III – Marked limitation with ordinary physical activity
  • Class IV – Inability to perform any activity without angina or angina at rest, i.e, severe limitation

Unstable angina is a form of acute coronary syndrome and may progress to myocardial infarction. Most patients with CHD first become symptomatic with acute myocardial infarction or sudden cardiac death!
References:[4][5][6][7][8][9]

Subtypes and variants

Vasospastic angina

  • Description:
    • Angina caused by transient coronary spasms (usually occurring close to areas of coronary stenosis)
    • Unrelated to exertion and may even occur at rest (classically at night)
  • Etiology: e.g., cigarette smoking, use of stimulants (e.g., cocaine, amphetamines) or sumatriptan, hyperventilation, exposure to cold
  • Epidemiology: average onset around 50 years
  • Diagnostics
    • Reversible ST elevation on ECG
    • No troponin I or T level elevations on serial measurements
    • Coronary spasms on angiography confirm the diagnosis
  • Treatment
  • Prognosis:
    • The five-year survival rate is > 90% (with treatment).
    • Persistence of symptoms is common.

References:[10][11][12]

Diagnostics

Patient history and physical exam

  • History of recurrent angina episodes
  • Signs of atherosclerotic vessel disease (e.g., absent foot pulses, carotid bruit) → see also physical exam in cardiology

Resting ECG

Cardiac stress test

Cardiac stress tests are generally most useful in patients with an intermediate pretest probability of coronary artery disease.

Choosing the most appropriate provocation and detection methods

  • Provocation
    • Able to exercise (and no contraindications for exercise testing): exercise stress test
    • Unable to exercise (and no contraindications to pharmacologic testing): pharmacologic stress test
  • Detection
    • Resting ECG can be interpreted: ECG
    • Resting ECG cannot be interpreted: imaging
  • Example: In a 75-year-old patient with acute aortic dissection, exercise testing would be contraindicated. If he also has atrial fibrillation, imaging would be indicated to monitor the test. Therefore, a pharmacologic stress test with either echocardiography or scintigraphy would be indicated.

Provocation methods

Both types of stress test can be used with ECG, echocardiography, and/or myocardial perfusion imaging. Clinical features, blood pressure, and heart rate are evaluated/recorded simultaneously.

Preparation

Findings in stress-induced ischemia

  • Clinical findings: If one of the following symptoms occurs, the exercise stress should be stopped.
    • New onset/intensification of chest pain
    • Severe dyspnea, cyanosis, pallor, ataxia, or altered mental status
    • Decrease in systolic BP below the resting BP
    • Systolic BP > 250 mm Hg or diastolic BP > 120 mm Hg
  • ECG
  • Imaging
    • The goal is to distinguish between:
    • Echocardiography : Simultaneous evaluation of ventricular size and functional parameters (e.g., EF) and detection of valvular disorders is possible.
    • Radionuclide myocardial perfusion imaging
      • PET:
        • IV administration of 82rubidium or 13Nammonia → visualizes perfusion
        • IV administration of 18FDG (fluorodeoxyglucose, a glucose analog) → visualizes basal metabolic rate
      • SPECT: IV administration of 201thallium or 99mtechnetium) → visualizes perfusion

Patients with new-onset chest pain, ST segment depression, hypotension or arrhythmias should undergo cardiac catheterization!

Cardiac catheterization

  • Indications
    • Persistent symptoms of angina despite appropriate therapy or
    • Pathological result of the non-invasive examination or
    • Noninvasive procedure with ambiguous results and high clinical suspicion of CHD
  • Gold standard of CHD diagnosis

Additional tests

  • Holter monitoring: can detect silent ischemia and arrhythmias and be used to evaluate heart rate variability and pacemaker/ICD function
  • Coronary magnetic resonance imaging (CMRI) or coronary computed tomography angiography (CCTA)

References:[5][13][14][15][16][17][18][19][20][21]

Differential diagnoses

The differential diagnoses listed here are not exhaustive.

Treatment

Approach

Antianginal treatment

Revascularization

References:[22][23][24]

Prognosis

  • Prognostic factors
    • Left ventricular function: increased mortality if EF < 50%
    • Involvement of left main coronary artery or involvement of more than one vessel is associated with a worse prognosis.
  • Stable angina
    • Annual mortality rate: ∼ 5%
    • 25% of patients will suffer an acute MI within the first 5 years.
    • High-grade stenosis is associated with an unfavorable prognosis.

References:[5]

Prevention

Prevention of atherosclerosis

Special considerations in coronary heart disease

References:[23][25][26][27][28]