The classification presumes a causal relationship between hypertension and heart involvement and between hypertension and kidney involvement, as the two conditions are linked by the term "with" in the Alphabetic Index. These conditions should be coded as related even in the absence of provider documentation explicitly linking them, unless the documentation clearly states the conditions are unrelated.

ICD-10-CM has combination codes for atherosclerotic heart disease with angina pectoris. The subcategories for these codes are I25.11, Atherosclerotic heart disease of native coronary artery with angina pectoris and I25.7, Atherosclerosis of coronary artery bypass graft(s) and coronary artery of transplanted heart with angina pectoris.

If a patient with coronary artery disease is admitted due to an acute myocardial infarction (AMI), the AMI should be sequenced before the coronary artery disease. See Section I.C.9. Acute myocardial infarction (AMI)

Medical record documentation should clearly specify the cause-and-effect relationship between the medical intervention and the cerebrovascular accident in order to assign a code for intraoperative or postprocedural cerebrovascular accident. Proper code assignment depends on whether it was an infarction or hemorrhage and whether it occurred intraoperatively or postoperatively. If it was a cerebral hemorrhage, code assignment depends on the type of procedure performed.

The ICD-10-CM codes for type 1 acute myocardial infarction (AMI) identify the site, such as anterolateral wall or true posterior wall. Subcategories I21.0-I21.2 and code I21.3 are used for type 1 ST elevation myocardial infarction (STEMI). Code I21.4, Non-ST elevation (NSTEMI) myocardial infarction, is used for type 1 non-ST elevation myocardial infarction (NSTEMI) and nontransmural MIs.

For encounters occurring while the myocardial infarction is equal to, or less than, four weeks old, including transfers to another acute setting or a postacute setting, and the myocardial infarction meets the definition for "other diagnoses" (see Section III, Reporting Additional Diagnoses), codes from category I21 may continue to be reported. For encounters after the 4-week time frame and the patient is still receiving care related to the myocardial infarction, the appropriate aftercare code should be assigned, rather than a code from category I21. For old or healed myocardial infarctions not requiring further care, code I25.2, Old myocardial infarction, may be assigned.

A code from category I22, Subsequent ST elevation (STEMI) and non-ST elevation (NSTEMI) myocardial infarction, is to be used when a patient who has suffered a type 1 or unspecified AMI has a new AMI within the 4 week time frame of the initial AMI. A code from category I22 must be used in conjunction with a code from category I21. The sequencing of the I22 and I21 codes depends on the circumstances of the encounter.

Do not assign code I22 for subsequent myocardial infarctions other than type 1 or unspecified. For subsequent type 2 AMI assign only code I21.A1. For subsequent type 4 or type 5 AMI, assign only code I21.A9.

If a subsequent myocardial infarction of one type occurs within 4 weeks of a myocardial infarction of a different type, assign the appropriate codes from category I21 to identify each type. Do not assign a code from I22. Codes from category I22 should only be assigned if both the initial and subsequent myocardial infarctions are type 1 or unspecified.

The ICD-10-CM provides codes for different types of myocardial infarction. Type 1 myocardial infarctions are assigned to codes I21.0-I21.4. Type 2 myocardial infarction (myocardial infarction due to demand ischemia or secondary to ischemic imbalance) is assigned to code I21.A1, Myocardial infarction type 2 with the underlying cause coded first, if applicable. Do not assign code I24.89, Other forms of acute ischemic heart disease, for the demand ischemia. If a type 2 AMI is described as NSTEMI or STEMI, only assign code I21.A1. Codes I21.01-I21.4 should only be assigned for type 1 AMIs.

Acute myocardial infarctions type 3, 4a, 4b, 4c and 5 are assigned to code I21.A9, Other myocardial infarction type. The "Code also" and "Code first" notes should be followed related to complications, and for coding of postprocedural myocardial infarctions during or following cardiac surgery.

Coronary microvascular dysfunction (CMD) is a condition that impacts the microvasculature by restricting microvascular flow and increasing microvascular resistance. Code I21.B, Myocardial infarction with coronary microvascular dysfunction, is assigned for myocardial infarction with coronary microvascular disease, myocardial infarction with coronary microvascular dysfunction, and myocardial infarction with non-obstructive coronary arteries (MINOCA) with microvascular disease.