Ischemic heart disease (IHD) Flashcards
what is IHD
IHD – group of related syndromes resulting from myocardial ischemia (imbalance between perfusion and demand of the heart for oxygenated blood)
why is IHD known as coronary artery disease
IHD is also known as coronary artery disease (as in over 90% of the cases of IHD are caused by atherosclerotic coronary artery disease)
what are the Clinical manifestations of IHD- 4 syndromes
Myocardial infarction
Angina pectoris
Chronic IHD with heart failure
Sudden cardiac death (due to arrhythmias originating in ischemic myocardium)
what are the clinical manifestations of acute coronary syndromes
1.Unstable angina (periinfarction angina)
2.Acute myocardial infarction and
3.Sudden cardiac death
what is the mechanism of IHD
Mechanism – change of stable atherosclerotic plaque into an unstable atherothrombotic lesion
what is the pathogenesis of IHD
Interaction of many factors lead to diminished perfusion of myocardium resulting in IHD syndromes; these are
Atherosclerotic narrowing of the coronary artery, (dominant factor)
Disruption of plaque (acute plaque changes )
Intraluminal thrombosis overlying the plaque and
Coronary vasospasm .
what is the role of fixed coronory obstruction in IHD
More than 75% reduction in the cross –sectional area of the lumen (critical stenosis) of one or more of the major coronary arteries lead to symptomatic IHD
Chronic fixed obstruction –90% stenosis of lumen can lead to ischemia even at rest
what epicardial coronary artery is obstructed in IHD
Usually, one epicardial coronary artery is obstructed; sometimes 2 or all three are affected; left anterior descending artery (LAD), left circumflex artery (LCX), Right coronary artery RCA
what is the role of acute plaque changes in IHD
Disruption of a partially stenosing plaque precipitate acute coronary syndromes in many patients; The event may be:
Rupture or fissuring, erosion or ulceration –followed by thrombosis,
Hemorrhage into the plaque with enlargement of the plaque
what is the role of coronary thrombosis in IHD
Thrombosis of a disrupted plaque may lead to total /incomplete occlusion of the lumen.
Transmural acute MI –total occlusion
Unstable angina, acute subendocardial infarction and sudden death- incomplete occlusion
Embolization of thrombus- microinfarcts
what is the role of vasoconstriction in IHD
Reduces the lumen size, increases mechanical stress on the plaque
what is vasoconstriction in IHD stimulated by
It is stimulated by:
1.Circulating adrenergic agonists
2. Platelet contents
3.Endothelial dysfunction
4.Mediators from inflammatory cells.
what is angina pectoris
Characterized by paroxysmal and recurrent attacks of substernal or precordial chest pain caused by transient myocardial ischemia (15 seconds-15 minutes).
[note: The duration of ischemia is not sufficient to cause cellular necrosis (infarction)]
what are the three patterns of angina pectoris
stable angina
prinzmetal angina
unstable or preinfraction angina
what is stable angina
Stable angina-occurs with physical activity or emotional excitement and is relieved by rest, caused by chronic stenosing atherosclerosis without plaque disruption
what is prinzmetal angina
Prinzmetal angina- occurs at rest, caused by coronary artery spasm; responds to vasodilators
what is unstable or pre infraction angina
Unstable or pre infarction angina- induced by disruption of plaque with incomplete occlusion of lumen and embolization or vasospasm (or both) ; is usually the prodrome of subsequent MI
what is the leading cause of death in industralized nations
MI ( heart attack)
what are the three patterns of infraction
Transmural/regional-full thickness
subendocardial/circumferential
microscopic infracts
what is the transmural/regional full thickness pattern of infraction
Transmural/ regional-full thickness caused by epicardial vessel occlusion through a combination of chronic atherosclerosis and acute thrombosis; such transmural MIs typically yield ST segment elevations on the electrocardiogram (ECG) (STEMI)
what is the subendocardial/circumferential pattern of infraction
Subendocardial/ circumferential -necrosis limited to inner one third or one half of the ventricular wall in global ischemia as in hypotension (“non–ST elevation infarct”(NSTEMI); ST depression)
what is the microscopic infract pattern of infraction
Microscopic infarcts occur in the setting of small vessel occlusions and may not show any diagnostic ECG changes as in case of vasculitis
what is the pathogenesis of myocardial infraction
Coronary artery occlusion –dynamic interaction among the factors
Atherosclerois, plaque changes, thrombosis and vasospasm in over 90% of MI patients
Other less common causes of myocardial ischemia (in less than 10% of MI patients ) : Emboli, vasculitis, coronary artery aneurysms, hypoxemia, shock and left-sided failure
Myocardial response-irreversible myocyte damage occurs with ischemia lasting at least 20-40 minutes, however typical MI occurs only when severe ischemia lasts for hours, hence early restoration of perfusion may prevent cell death.
whats is the myocardial response to ischemia
Functional alterations-
Rapid loss of contractility, which occurs within a minute or so of the onset of ischemia
Biochemical changes
Within seconds of vascular obstruction, aerobic glycolysis ceases, leading to a drop in adenosine triphosphate (ATP) and accumulation of potentially noxious metabolites (e.g., lactic acid) in the cardiac myocytes.
