ischemic heart disease 19.9.90
Post on 05-Apr-2018
225 Views
Preview:
TRANSCRIPT
-
7/31/2019 Ischemic Heart Disease 19.9.90
1/27
Ischemic Heart Disease
-
7/31/2019 Ischemic Heart Disease 19.9.90
2/27
Definition
IHD is the generic designation for a group of
pathophysiologically related syndromes
resulting from myocardial ischemiaan
imbalance between the supply (perfusion) and
demand of the heart for oxygenated blood.
Ischemia brings not only an insufficiency of
oxygen, but also reduces the availability ofnutrients and the removal of metabolites
-
7/31/2019 Ischemic Heart Disease 19.9.90
3/27
In more than 90% of cases, the cause of
myocardial ischemia is reduced blood flow due
to obstructive atherosclerotic lesions in the
coronary arteries. Thus, IHD is often termed
coronary artery disease (CAD) or coronary
heart disease
-
7/31/2019 Ischemic Heart Disease 19.9.90
4/27
IHD usually presents as one or more of the
following clinical syndromes:
Myocardial infarction, the most important form ofIHD, in which ischemia causes the death of heartmuscle.
Angina pectoris, in which the ischemia is ofinsufficient severity to cause infarction, but may be aharbinger of MI.
Chronic IHD with heart failure.
Sudden cardiac death.
-
7/31/2019 Ischemic Heart Disease 19.9.90
5/27
Pathogenesis
The dominant cause of the IHD syndromes isinsufficient coronary perfusion relative tomyocardial demand, due to chronic,
progressive atherosclerotic narrowing of theepicardial coronary arteries
Variable degrees of superimposed acuteplaque change
Thrombosis
Vasospasm
-
7/31/2019 Ischemic Heart Disease 19.9.90
6/27
Chronic Atherosclerosis
More than 90% of patients with IHD have
atherosclerosis of one or more of the epicardial
coronary arteries.
A fixed lesion obstructing 75% or greater of the
lumen is generally required to cause symptomatic
ischemia precipitated by exercise (most often
manifested as chest pain, known as angina Obstruction of 90% of the lumen can lead to
inadequate coronary blood flow even at rest
-
7/31/2019 Ischemic Heart Disease 19.9.90
7/27
Acute Plaque Change
The risk of an individual developing clinically important IHDdepends in part on the number, distribution, structure, anddegree of obstruction of atheromatous plaques
However, the varied clinical manifestations of IHD cannot
be explained by the anatomic disease burden alone The acute coronary syndromes are typically initiated by anunpredictable and abrupt conversion of a stableatherosclerotic plaque to an unstable and potentially life-threatening atherothrombotic lesion through rupture,
superficial erosion, ulceration, fissuring, or deephemorrhage
-
7/31/2019 Ischemic Heart Disease 19.9.90
8/27
There are two major methods of in vivo sampling of
coronary atherosclerosis as a surgical specimen:
Percutaneous via catheters
open procedures (surgery).
Coronary atherectomy was at one time a standard treatment
for coronary stenosis, with catheter-based removal of the
plaque
Thrombus Coronary endarterectomy (removal of intimal
disease at open surgery, usually with concomitant bypass
grafting) is not commonly performed because of relatively
high rates ofrestenosis
-
7/31/2019 Ischemic Heart Disease 19.9.90
9/27
luminal narrowing estimation
If accurate measurements of cross-sectionalluminal narrowing are to be undertaken,perfusion fixation is necessary
The coronaries are perfusion fixed with 10%buffered formaldehyde retrograde from theascending aorta at 100 mm Hg pressure for atleast half an hour
The plug is attached to tubing that is connectedto the perfusion chamber that is placed 135 cmabove the specimen, approximately equivalent to100 mm Hg
-
7/31/2019 Ischemic Heart Disease 19.9.90
10/27
luminal narrowing estimation
For correlation with premortem angiography,and for medicolegal civil matters, accuratepercent stenosis is often important to
determine There are two factors limiting accuracy in this
regard:
lack of perfusion fixation( more important)
Subsequent tissue shrinkage during fixationand processing
-
7/31/2019 Ischemic Heart Disease 19.9.90
11/27
This artifact is greatest in eccentric plaques andthose with mild to moderate stenosis
25% lesion could be seen as >90% if the vessel iscollapsed
In reality, because of differential shrinkage ofintimal tissues versus smooth muscle wall, the
effect on percent stenosis is minimal For segments with about 50% stenosis before
processing, there is an increase to about 65%after processing.
However, for 80% stenosis, there is actually adecrease in percent stenosis after processing toalmost 70%
-
7/31/2019 Ischemic Heart Disease 19.9.90
12/27
-
7/31/2019 Ischemic Heart Disease 19.9.90
13/27
-
7/31/2019 Ischemic Heart Disease 19.9.90
14/27
-
7/31/2019 Ischemic Heart Disease 19.9.90
15/27
MORPHOLOGIC FEATURES OF CORONARY
ATHEROTHROMBOSIS
In patients dying after acute myocardial
infarct, thrombi are found in 98% of patients.
The frequency of acute thrombosis in unstable
angina is less than that seen in acute
myocardial infarction and ranges from
-
7/31/2019 Ischemic Heart Disease 19.9.90
16/27
Plaque ruptures
Plaque ruptures are characterized by a luminal
thrombus overlying a lipid-rich fibroatheroma,
often with areas of hemorrhage, usually with
a visibly interrupted cap
The thinned, inflamed fibrous cap
demonstrates an area of discontinuity,
allowing the underlying lipid-rich core tocontact the luminal blood
-
7/31/2019 Ischemic Heart Disease 19.9.90
17/27
Plaque fissure
Plaque fissure is an early form of plaquerupture, in
which there is a break in the fibrous cap
without significant luminal thrombus,resulting in intraplaque fibrin deposits withoutluminal thrombus (Fig. 6.21).
The distinction between plaque fissure andrupture may be difficult and sometimesarbitrary
-
7/31/2019 Ischemic Heart Disease 19.9.90
18/27
-
7/31/2019 Ischemic Heart Disease 19.9.90
19/27
-
7/31/2019 Ischemic Heart Disease 19.9.90
20/27
Plaque erosion
Typically, there is not a prominent necrotic core,in contrast to plaque rupture.
Plaque erosion is characterized by lesser degreesof calcification and overall plaque burden
Histologically, plaque erosion shows denudatedendothelial surface with luminal thrombus
The plaque underlying the thrombus is rich is
proteoglycans and smooth muscle cells There is often a small lipid core near the internal
elastic lamina, but prominent cholesterol crystalsand hemorrhage into plaque are absent
-
7/31/2019 Ischemic Heart Disease 19.9.90
21/27
-
7/31/2019 Ischemic Heart Disease 19.9.90
22/27
-
7/31/2019 Ischemic Heart Disease 19.9.90
23/27
The role of the thrombusmechanism ofaction in ST-segment elevation ACS
Results from stabilization of aplatelet aggregate at site of
plaque rupture by fibrin mesh
platelet
RBCfibrin mesh
GP IIb-IIIa
Generally caused by acompletely occlusive
thrombus in a coronary artery
-
7/31/2019 Ischemic Heart Disease 19.9.90
24/27
The Role of the Platelet: Mechanismof NSTE ACS
Results from cross-linking ofplatelets by fibrinogen at
platelet receptors GP IIb-IIIaat site of plaque rupture
platelet
fibrinogen
Rupturedplaque
GP IIb-IIIa
Generally caused by apartially occlusive, platelet-richthrombus in a coronary artery
Unobstructed
lumen
thrombus
Artery wall
-
7/31/2019 Ischemic Heart Disease 19.9.90
25/27
Not all acute plaque ruptures result in sudden
death or even acute myocardial infarction;
Healed plaque rupturesrepresent a
mechanism of plaque enlargement
-
7/31/2019 Ischemic Heart Disease 19.9.90
26/27
-
7/31/2019 Ischemic Heart Disease 19.9.90
27/27
Factors Influences plaque integrity
The structure and composition of a plaque
(foam cell , fibrous cap , smooth muscle cell)
The balance of synthetic and degradativeactivity of collagen
drugs such as statins
Adrenergic stimulation can elevate systemichypertension or local vasospasm
Intense emotional stress
top related