Cardiovascular · Year 1 · from Cardiovascular

Case 1: Stable Angina Pectoris - Supply-Demand Mismatch

Patient Presentation

Demographics: 62-year-old male

Chief Complaint: Chest discomfort with exertion for 3 months

History of Present Illness: A 62-year-old male with history of hypertension, hyperlipidemia, and type 2 diabetes presents with 3 months of substernal chest pressure that occurs when climbing 2 flights of stairs or walking briskly. The discomfort is described as "tightness" radiating to his left shoulder. Symptoms resolve within 5 minutes of rest. He has been using sublingual nitroglycerin (prescribed by his PCP) with good relief. He denies symptoms at rest.

Physical Examination:

  • Vital Signs: BP 142/88 mmHg, HR 72 bpm, RR 14/min, SpO2 99% on room air
  • General: Overweight, no acute distress at rest
  • Cardiovascular: Regular rhythm, S4 gallop, no murmurs
  • Lungs: Clear
  • Extremities: No edema, pulses 2+ throughout

Workup

  • ECG at rest: Normal sinus rhythm, nonspecific ST-T changes
  • Labs:
  • Fasting glucose: 145 mg/dL
  • HbA1c: 7.8%
  • LDL: 142 mg/dL
  • Total cholesterol: 228 mg/dL
  • Exercise stress ECG:
  • Achieved 7 METs (adequate)
  • Horizontal ST depression 2 mm in V4-V6 at peak exercise
  • Chest discomfort reproduced
  • ST changes resolved with rest
  • Coronary CT angiography: 75% stenosis of mid-LAD, 50% stenosis of proximal RCA

Diagnosis

Chronic stable angina pectoris (Canadian Cardiovascular Society Class II) due to coronary artery disease

Coronary Circulation Correlation:

Myocardial oxygen supply-demand balance:

Oxygen Supply determined by:

  1. Coronary blood flow
  • Occurs primarily in diastole (LV relaxation)
  • Autoregulation maintains flow over perfusion pressures 60-180 mmHg
  1. Oxygen content of blood (hemoglobin, SaO2)

Oxygen Demand (MVO2) determined by:

  1. Heart rate (major determinant)
  2. Wall tension (preload, afterload) - Laplace's law
  3. Contractility
  4. Basal metabolism

Rate-pressure product (RPP): HR × SBP (correlates with MVO2)

Pathophysiology of exertional angina:

  1. Fixed coronary stenosis (75% LAD)
  2. At rest: Adequate flow despite stenosis (autoregulation compensates)
  3. With exertion: ↑ HR, ↑ BP → ↑ MVO2
  4. Stenosis limits flow augmentation → supply cannot meet demand
  5. Ischemia → anaerobic metabolism → lactate → chest pain

Why diastolic perfusion matters:

  • Coronary flow is predominantly diastolic
  • Tachycardia shortens diastole → ↓ perfusion time
  • Elevated LVEDP (from ischemia) → ↓ perfusion gradient

Coronary flow reserve:

  • Normal: Can increase flow 4-5× with demand
  • With 75% stenosis: Flow reserve significantly reduced

Treatment

  1. Anti-anginal medications:
  • Beta-blocker (metoprolol): ↓ HR, ↓ contractility → ↓ MVO2
  • Long-acting nitrate (isosorbide mononitrate): Venodilation (↓ preload), coronary vasodilation
  • Calcium channel blocker if needed (amlodipine)
  1. Aspirin 81 mg daily (antithrombotic)
  2. High-intensity statin (atorvastatin 80 mg)
  3. Risk factor modification:
  • Blood pressure goal <130/80
  • LDL goal <70 mg/dL
  • HbA1c optimization
  • Smoking cessation
  1. Consider invasive evaluation: Coronary angiography ± PCI for refractory symptoms

Clinical Image

Image Description: Coronary angiogram showing significant stenosis (narrowing) of the left anterior descending artery. The stenosis appears as a focal area of reduced contrast filling, indicating reduced blood flow through the affected segment.

Source: Wikimedia Commons - Coronary artery stenosis License: CC BY-SA 3.0 URL: https://commons.wikimedia.org/wiki/File:Coronary_angiography.jpg

All cases for this lecture as Markdown