Acute and chronic coronary syndromes

Acute and chronic coronary syndromes

Chronic stable angina (Chronic coronary syndrome)

Chronic stable angina is stable situation with symptoms lasting more than one month. It manifests as chest pain brought on by exertion and relieved by rest. It is due to a demand – supply mismatch. Usually it occurs due to reduction of supply of oxygenated blood to a region of the myocardium due to significant narrowing of the coronary artery. Supply side can be affected by anemia which reduces the oxygen carrying capacity of blood. Severe anemia can worsen effort angina.

But chronic stable angina (also known as effort angina) can also occur due to increased demand as in a hypertrophied ventricle in severe aortic stenosis and hypertrophic obstructive cardiomyopathy. Other causes which can increase demand are tachycardia due to fever and hyperthyroidism.

There can be a combination of both mechanisms. For example, a hypertensive patient can have left ventricular hypertrophy along with obstructive coronary artery disease as hypertension is an important risk factor for coronary artery disease.

Chronic ischemia may also manifest as heart failure. Myocardium with chronic ischemia which is reversible on revascularization is known as hibernating myocardium. Large amount of hibernating myocardium can contribute to left ventricular dysfunction and heart failure. Hibernating myocardium will be viable and detectable using tests for myocardial viability like stress echocardiography and positron emission tomography which studies the metabolic activity of the myocardium. Hibernating myocardium has reduced contraction on echocardiography (hypokinesia) which improves with low dose dobutamine stimulation and worsens with high dose dobutamine infusion.

Acute coronary syndrome

 Acute coronary syndrome can be broadly divided into unstable angina and acute myocardial infarction. In unstable angina there is no elevation of biomarkers of myocardial necrosis, while it is elevated in acute myocardial infarction. Two subgroups of acute myocardial infarction are ST elevation myocardial infarction (STEMI) and non ST elevation myocardial infarction (NSTEMI). Non ST elevation myocardial infarction and unstable angina can also be grouped together as non ST elevation acute coronary syndrome (NSTEACS).

Unstable angina

Unstable angina is either rest angina or a recent change in the anginal threshold in effort angina. Thus chronic coronary syndrome can become an acute coronary syndrome, usually by intervention of some precipitating factors like anemia, fever, infection, hyperthyroidism and atrial fibrillation with fast ventricular rate. A combination of factors may work together like atrial fibrillation with fast ventricular rate in hyperthyroidism. Change in the characteristics of the atherosclerotic plaque is often the reason for unstable ischemic syndromes. A plaque with lipid rich core and a thin cap can rupture in response to hemodynamic stress. Clots can form in an ulcerated atherosclerotic plaque which can cause sudden increase in the luminal narrowing. Alternatively hemorrhage into the plaque can also enhance the luminal stenosis. If the lumen gets totally, it usually results in an ST elevation myocardial infarction. Partial occlusions could cause either an unstable angina or non ST elevation myocardial infarction. It may be noted that the former can progress to the latter.

ECG changes in unstable angina: Typical ECG change in unstable angina is a horizontal ST depression, often in the inferior and lateral leads. Downsloping ST depression and T wave inversions may also be noted in unstable angina. Occasionally ECG can be normal in unstable angina. Risk is higher in those with ECG changes than in those without ECG changes. ST elevation during angina, returning back to baseline when angina subsides is classical of Prinzmetal’s vasospastic angina due to coronary vasospasm. It may be noted that Prinzmetal’s angina is associated with obstructive coronary artery disease in two thirds of cases. The prognosis is poorer in those with obstructive coronary artery disease.