Is coronary artery disease (CAD) considered a form of ischemic heart disease (IHD)?

Is Coronary Artery Disease Considered Ischemic Heart Disease?

Yes, coronary artery disease (CAD) is considered a subset of ischemic heart disease (IHD), but the relationship is more nuanced than simple equivalence—CAD represents the anatomic disease of the coronary arteries (typically atherosclerotic obstruction), while IHD encompasses the broader clinical spectrum of myocardial oxygen supply-demand imbalance from any cause, including but not limited to obstructive CAD. 1, 2

The Critical Distinction

CAD is defined as impedance or blockage in coronary arteries supplying the heart, usually due to atherosclerosis, whereas IHD represents an imbalance between myocardial oxygen supply and demand that includes both symptomatic and asymptomatic conditions from multiple mechanisms. 2

Why This Matters Clinically

• Obstructive CAD is just "the tip of the iceberg" of ischemic heart disease—this is how the 2024 European Society of Cardiology explicitly describes the relationship 1
• Nearly half of patients with chronic chest pain referred for angiography have no ≥50% stenosis in major epicardial coronary arteries, yet they still have ischemic heart disease 1
• The presence of severe coronary stenosis does not preclude other mechanisms of ischemia—multiple pathways frequently coexist 1

The Evolving Nomenclature Problem

The 2024 Circulation guidelines highlight a critical issue: competing terminologies have created confusion by perpetuating restrictive terms like "coronary" and "disease" that connote only obstructive CAD mechanisms. 1

Historical Terms and Their Limitations

• "Stable coronary artery disease" (older terminology)
• "Stable ischemic heart disease" (SIHD) - used in 2013 ACC/AHA guidelines 1
• "Chronic coronary syndromes" (CCS) - introduced by 2019 ESC guidelines 1
• "Chronic coronary disease" (CCD) - adopted by 2023 American guidelines 1

All these terms are problematic because they overemphasize epicardial coronary obstruction as the sole cause of myocardial ischemia. 1

Non-Obstructive Causes of Ischemic Heart Disease

Ischemic heart disease encompasses multiple mechanisms beyond flow-limiting atherosclerosis: 1

• Coronary microvascular dysfunction (CMD) - impairs myocardial perfusion despite patent epicardial vessels 1, 3
• Coronary artery spasm - both epicardial and microvascular 1, 3
• Myocardial bridging - extramural compression 1
• Diffuse non-obstructive atherosclerosis 1
• INOCA/ANOCA (Ischemia/Angina with Non-Obstructive Coronary Arteries) - now recognized as common, particularly in women 1

Clinical Pitfall to Avoid

Coronary microvascular dysfunction and coronary artery spasm are frequent causes of residual angina after coronary revascularization—assuming that revascularization of obstructive CAD eliminates all ischemia is a major error. 1

Demand Ischemia: IHD Without CAD

Type 2 myocardial infarction represents ischemic heart disease from supply-demand mismatch without acute coronary plaque rupture: 3

• Tachyarrhythmias increasing myocardial workload 3
• Severe hypertension elevating afterload 3
• Hypotension reducing coronary perfusion pressure 3
• Hypoxemia decreasing arterial oxygen content 3
• Anemia reducing oxygen-carrying capacity 3

These patients have ischemic heart disease but may have minimal or no obstructive coronary artery disease. 3, 4

The Proposed Solution: Myocardial Ischemic Syndromes

The 2024 Circulation guidelines propose abandoning "coronary artery disease" and "ischemic heart disease" terminology entirely in favor of "myocardial ischemic syndromes" (acute and non-acute), which better captures all pathogenetic mechanisms. 1

Why "Myocardial Ischemic Syndromes" Is Superior

• Focuses on the target organ (myocardium) rather than just the coronary arteries 1
• Includes both obstructive and non-obstructive mechanisms 1
• Encompasses coronary and non-coronary etiologies 1
• Uses "syndrome" rather than "disease" to reflect the heterogeneous pathophysiology 1

Practical Clinical Framework

When evaluating a patient with suspected ischemia, consider CAD as one potential mechanism within the broader category of ischemic heart disease: 1, 2

1. Assess for obstructive epicardial CAD using stress testing, coronary CT angiography, or invasive angiography 1, 2
2. If obstructive CAD is absent or symptoms persist after revascularization, systematically evaluate for: 1
   • Coronary microvascular dysfunction (requires invasive coronary function testing with coronary flow reserve and index of microcirculatory resistance) 1
   • Coronary vasospasm (requires provocative testing) 1
   • Non-coronary causes of supply-demand mismatch 3

The 2024 ESC guidelines now give a Class I recommendation (Level of Evidence B) for invasive coronary angiography with availability of invasive functional assessment when diagnosis is uncertain after non-invasive testing. 1

Bottom Line for Clinical Practice

Think of the relationship this way: All obstructive CAD causes ischemic heart disease, but not all ischemic heart disease is caused by obstructive CAD. 1, 2 The terms are related but not interchangeable—CAD is anatomic, IHD is functional, and modern practice requires recognizing and treating the full spectrum of mechanisms causing myocardial ischemia. 1, 4