Coronary Artery Disease (CAD) — Clinical Documentation Guide (2026)

This Clinical Documentation Guide (CDG) provides AAPC/AHIMA-credentialed coders and CDI specialists with comprehensive coding, clinical, and documentation guidance for coronary artery disease (CAD), classified under ICD-10-CM category I25 — Chronic Ischemic Heart Disease. Content reflects FY2026 ICD-10-CM guidelines effective October 1, 2025 through September 30, 2026, incorporates 2026 CPT procedure code updates, and addresses HCC v28 risk adjustment implications fully in effect for payment year 2026. Use this guide to ensure accurate diagnosis code assignment, appropriate CDI query triggers, and defensible documentation across all care settings. For acute myocardial infarction (AMI), see the separate MI Clinical Documentation Guide; I25.2 (Old myocardial infarction) is addressed briefly in Section 8 in the context of chronic CAD history.

🔍 1. Definition

Coronary artery disease (CAD) — also termed ischemic heart disease (IHD) or atherosclerotic heart disease (ASHD) — is a chronic condition characterized by the narrowing or obstruction of one or more coronary arteries due to atherosclerotic plaque accumulation within the arterial wall. The resulting reduction in coronary blood flow produces myocardial ischemia, manifesting clinically as stable angina, unstable angina, acute myocardial infarction, ischemic cardiomyopathy, or sudden cardiac death depending on the severity and acuity of the obstruction, as described by the American Heart Association.

Atherosclerosis — the underlying pathological process — begins with endothelial injury and lipid deposition forming fatty streaks, which progress to complex fibrous plaques. Plaque rupture or erosion triggers thrombosis and can cause acute coronary syndromes (ACS). Stable, obstructive plaques reduce luminal diameter, causing effort-induced angina when oxygen demand exceeds limited supply. Per the 2023 AHA/ACC Chest Pain Guideline, CAD remains the leading cause of morbidity and mortality in the United States, accounting for approximately 1 in 5 deaths annually.

CAD encompasses a spectrum including:

• Atherosclerotic heart disease of native coronary artery (I25.1x series) — the primary CAD category, with or without angina
• Ischemic cardiomyopathy (I25.5) — end-stage CAD with diffuse myocardial dysfunction
• CAD of bypass graft vessels (I25.7xx series) — atherosclerosis developing in surgical bypass conduits
• Chronic total occlusion (CTO) (I25.82) — complete coronary artery occlusion present ≥3 months
• Coronary atherosclerosis due to lipid-rich plaque (I25.83) or calcified coronary lesion (I25.84) — morphologic subtypes with distinct procedural implications

🗂️ 2. Alternative Terminology

Documentation in medical records, operative reports, and discharge summaries employs a wide range of terms that map to the I25 category. The following table summarizes key terminology coders and CDI specialists will encounter:

🩺 3. Signs & Symptoms

The clinical presentation of CAD varies substantially depending on lesion severity, acuity, and patient characteristics. Coders must document the specific manifestation, as it drives code selection:

• Stable angina: Predictable, reproducible chest pressure or tightness brought on by physical exertion or emotional stress; relieved by rest or nitroglycerin within minutes. Typically described as substernal pressure, squeezing, or heaviness, often radiating to the left arm, jaw, or back. Corresponds to I25.118 when CAD is concurrent.
• Unstable angina: New-onset angina, angina at rest, or accelerating angina (increased frequency, duration, or severity); not relieved by usual doses of nitroglycerin; requires urgent evaluation per ACC/AHA guidelines. Corresponds to I25.110 when concurrent CAD is documented.
• Variant/vasospastic angina (Prinzmetal's): Angina occurring at rest, often in the early morning, caused by transient coronary artery spasm; may be associated with ST-segment elevation on ECG. Corresponds to I25.111.
• Dyspnea: Exertional or rest dyspnea may be the anginal equivalent, particularly in diabetic patients with autonomic neuropathy and women, per AHA Circulation (2023).
• Ischemic cardiomyopathy signs: Reduced ejection fraction, biventricular enlargement, symptoms of heart failure (dyspnea, orthopnea, edema, fatigue); I25.5 should be coded along with appropriate heart failure code (I50.xx).
• Chronic total occlusion: May be asymptomatic if collateral circulation has developed; discovered on angiography; I25.82 is an additional code to the primary CAD code.
• Silent ischemia: Objective evidence of ischemia (positive stress test, imaging) without chest pain; I25.6.

🧭 4. Differential Diagnosis

Accurate documentation requires distinguishing CAD from other conditions that mimic its presentation. The following differential diagnoses are commonly encountered in inpatient and outpatient settings:

📋 5. Clinical Indicators for Coders/CDI

The following clinical indicators, when present in the medical record, support assignment of CAD diagnosis codes and should prompt review for specificity:

🦴 6. Anatomy & Pathophysiology

Coronary Anatomy: The coronary circulation consists of two primary arteries arising from the aortic sinuses: the left main coronary artery (LMCA), which divides into the left anterior descending (LAD) and left circumflex (LCx) arteries; and the right coronary artery (RCA). The LAD supplies the anterior wall and interventricular septum; the LCx supplies the lateral wall; the RCA supplies the right ventricle and, in right-dominant systems, the inferior wall and posterior septum, as described by StatPearls — Coronary Artery Anatomy (NCBI).

Atherosclerotic Progression:

1. Endothelial dysfunction: Triggered by risk factors (hypertension, dyslipidemia, smoking, diabetes); increased permeability allows LDL infiltration
2. Foam cell formation: Oxidized LDL is engulfed by macrophages forming foam cells; fatty streak develops
3. Fibrous plaque: Smooth muscle cell migration, extracellular matrix deposition; plaque enlarges, narrowing the lumen
4. Vulnerable plaque: Thin fibrous cap, large lipid core, inflammatory infiltrate; high risk of rupture — coded as I25.83 (lipid-rich plaque)
5. Plaque rupture/erosion: Triggers platelet aggregation and thrombosis → acute coronary syndrome (coded separately as I21.xx for MI)
6. Calcification: Calcium deposits within plaque over time; may paradoxically stabilize some lesions but creates procedural challenges (I25.84)

Coronary Flow Reserve and Ischemia: Clinically significant stenosis (≥70% luminal diameter reduction, or ≥50% with fractional flow reserve [FFR] ≤0.80) impairs the coronary flow reserve — the ability to increase blood flow with increased demand. This produces supply-demand mismatch manifesting as angina with exertion. Chronic total occlusion (I25.82) represents 100% obstruction present ≥3 months; collateral circulation may preserve viability but exercise tolerance remains limited.

Ischemic Cardiomyopathy (I25.5): Chronic ischemia leads to progressive cardiomyocyte loss through necrosis, apoptosis, and hibernating myocardium. The ventricle dilates and systolic function declines, producing a phenotype similar to dilated cardiomyopathy. Per AHA Circulation, ischemic etiology accounts for approximately 60–70% of dilated cardiomyopathy cases. I25.5 should be coded with the appropriate heart failure code (I50.xx) to capture the full clinical picture.

💊 7. Medication Impact / Treatment

Medications for CAD serve dual purposes: symptom relief and secondary prevention of MI and death. Understanding the pharmacologic regimen helps coders identify clinical indicators and CDI specialists recognize documentation opportunities.

Preview ends here. The full guide continues with FY2026 ICD-10-CM code sets, CPT surgical coding, MS-DRG mapping, reimbursement guidance, CDI query templates, and an audit checklist — all available to CCO Members.

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