Ischemic Heart Disease (IHD)

Coronary artery disease (CAD) is also referred to as ischemic heart disease (IHD) and is usually due to atherosclerosis of a coronary artery. CAD can be classified as stable or unstable, depending on the clinical manifestations of the disease.

ClassificationTop

1. Classification of CAD:

1) Stable CAD (chronic coronary syndrome):

a) Stable angina pectoris.

b) Vasospastic angina (Prinzmetal variant angina).

c) Microvascular angina (syndrome X).

d) Angina associated with myocardial bridging of coronary arteries.

2) Acute coronary syndromes (ACSs).

2. ACS classification based on initial electrocardiographic (ECG) findings:

1) Non–ST-segment elevation ACS.

2) ST-segment elevation ACS.

3. ACS classification based on clinical manifestations, biochemical markers of myocardial necrosis, and ECG:

1) Unstable angina (UA).

2) Non–ST-segment elevation myocardial infarction (NSTEMI).

3) ST-segment elevation myocardial infarction (STEMI).

4) Unspecified myocardial infarction (MI). ECG abnormalities that do not allow an unequivocal diagnosis of ST-segment elevation: left bundle branch block (acute or preexisting), pacemaker rhythm, or infarction diagnosed on the basis of clinical and biochemical criteria, with ECG performed >24 hours after the onset of symptoms.

5) Sudden cardiac death.

4. Classification of MI based on the evolution of ECG features:

1) Q-wave MI.

2) Non–Q-wave MI.

Etiology and PathogenesisTop

1. Etiology of myocardial ischemia:

1) Most commonly myocardial ischemia is due to coronary atherosclerosis.

2) Less commonly myocardial ischemia is due to coronary artery spasm (Prinzmetal variant angina, illicit drug use [eg, cocaine], or discontinuation of nitrates), coronary artery embolism, vasculitis of the coronary arteries, metabolic disorders affecting the coronary arteries, anatomic defects of the coronary arteries, coronary artery injury, arterial thrombosis due to disorders of hemostasis, reduced oxygen supply in relation to demand (aortic stenosis or regurgitation, hypertrophic cardiomyopathy, carbon monoxide poisoning, decompensated thyrotoxicosis, long-standing hypotension [shock]), anemia, myocardial bridging), or aortic dissection.

2. Etiology of ACS: Imbalance between the myocardial oxygen demand and supply, most frequently due to occlusion of a coronary artery by a thrombus formed on a ruptured atherosclerotic plaque.

1) UA most frequently results from rupture of an eccentric plaque. The resulting thrombus reduces coronary blood flow but occlusion is not complete, so that myocardial necrosis does not occur.

2) NSTEMI is the result of a process similar to UA and is associated with elevation of troponin levels, indicating myocardial necrosis due to subendocardial ischemia.

3) In STEMI the thrombus usually causes a complete and sudden occlusion of a coronary artery. Necrosis starts to develop within 15 to 30 minutes of the cessation of blood flow and spreads from the subendocardium to the epicardium. The rate at which necrosis develops depends on diameter of the occluded artery and collateral circulation.

3. Myocardial injury versus MI: Myocardial injury is defined as elevation of cardiac troponin values >99th percentile. In some situations myocardial injury is associated with MI, as per the definitions specified in the table below (essentially, clinical markers of ischemia must be present; Table 1).

4. Distinction between type 1 and type 2 MI is of particular clinical importance. Although in both of these situations there is a mismatch between oxygen supply and demand, in type 1 MI this occurs secondarily to acute plaque rupture and thrombus formation. In type 2 MI there are many different causes of relative oxygen deficiency (Table 1). Owing to their different mechanisms, type 2 MIs are not amenable to the same antithrombotic therapies as are employed for ACSs. Another important fact is that type 2 MI (demand ischemia) does not exclude an underlying CAD, as patients with non–plaque rupture MIs may still be more susceptible to stresses in the setting of CADs.

TablesTop