Atherosclerosis (AS) as a
pathophysiological process leading to coronary
artery disease
Content
- Heart is a pump in need of energy!
- Myocardial blood supply & metabolism
- Coronary blood flow
- Risk factors of AS
- Etiopathogenesis of AS
Heart needs a lot of energy (= ATP) to continually
perform as a pump (7,500 L/day,  40 mil beats/year)
SV  f = CO → 70mL  70 bpm =  5 L/min
sympathetic
nervous
system
parasympathetic
nervous
system
venous return (i.e. circulating volume)
synergistic LV contraction
wall integrity
valvular competence
systemic vascular resistance (i.e. blood pressure or valve obstruction)
• quantitatively
• heart rate 70/min
• SV 70ml
• CO 70  70 = 4,900 ml/min  5 L/min at rest
• CO  20 - 25L/min during
exercise!!!!
• influenced by
• autonomic nervous system activity
• hormones
• age
• gender
• genetics
• drugs
• fitness
• anatomy/size of the heart
MYOCARDIAL METABOLISM
Myocardial metabolism – a lot of ATP is needed
• heart is a pump that has to continually perform 2 processes:
• (1) automacy = generation of action potential in order to perform
• (2) contraction
• myocardium thus has a very high demand for ATP even in the resting
state
• for contraction
• actin/myosin – ATP
• Ca2+ handling (Ca2+-ATP-ase, SERCA)
• for repolarisation
• Na+/K+-ATP-ase
• ATP is produced by oxidation of substrates
• FFA - preferentially
• glucose (glycogen)
• ketone bodies and lactate
• since myocardium requires large amounts of O2 it must be, therefore,
well perfused !!
Excitation-contraction coupling in a ventricular cardiomyocyte
• The initial event in the cardiac cycle is membrane depolarization,
which occurs with ion entry through connexin channels from a
neighbouring cardiomyocyte (right) followed by opening of
voltage-gated Na+ channels and Na+ entry (top).
• The resultant rapid depolarization of the membrane inactivates
Na+ channels and opens both K+ channels and Ca2+ channels.
Entry of Ca2+ into the cell triggers the release of Ca2+ from the
sarcoplasmic reticulum through the ryanodine channel.
• Ca2+ then binds to the troponin complex and activates the
contractile apparatus (the sarcomere, bottom).
• Cellular relaxation occurs on removal of Ca2+ from the cytosol by
the Ca2+-uptake pumps of the sarcoplasmic reticulum and by
Na+/Ca2+ exchange with the extracellular fluid.
• Intracellular Na+ homeostasis is achieved by the Na+/K+ pump.
• The molecular components that are required for normal
electrophysiological activity, contractile function and cell–cell
adhesion (the latter mediated by desmosomes) all need to be
positioned correctly within the cell and anchored to each other
and the cytoskeleton.
• Some cardiomyocyte components are not shown (for example,
stretch-activated channels, and ankyrins that target channels and
other proteins to their correct locations within the cell).
• Red stars indicate proteins encoded by genes that are mutated in
primary arrhythmia syndromes; many of these proteins form part
of macromolecular complexes, so mutations in several genes
could be responsible for these syndromes.
• Green stars indicate protein complexes in which mutations in
multiple genes cause cardiomyopathies often associated with
arrhythmias; these complexes include the sarcomere (in
hypertrophic cardiomyopathy), the desmosome (in arrhythmic
right ventricular cardiomyopathy), and the cytoskeleton,
sarcoglycan complex and mitochondrion (in dilated
cardiomyopathy).
Oxygen extraction by various tissues/organs
Organ CaO2 - CvO2 (vol %) % extraction
heart 10 – 12 65 – 70
skeletal muscle (resting) 2 – 5 13 – 30
kidney 2 – 3 13 – 20
intestine 4 – 6 25 – 40
skin 1 – 2 7 – 13
whole body 20 – 30 %
• Theoretically, the maximal amount of oxygen that can be extracted is 20 vol % (if CaO2 = 200 ml O2/l )
• In reality, however, the maximal oxygen extraction is around 15 - 16 vol % because of the kinetics of oxygen
dissociation from haemoglobin
• Therefore, the heart is extracting one-half to two-thirds of the physiologically available oxygen under normal
operating conditions
• Meeting increased demands (during exercise) is only possible by increasing coronary perfusion (= coronary flow
reserve, CFR)
CaO2 - Arterial oxygen content CvO2 Venous oxygen content
Oxygen consumption – quantitative aspects
• amount of oxygen supplied by the coronary blood (VO2):  45 ml O2/min
• VO2 = Qm  CaO2
• myocardial perfusion (Qm) = 210 – 240 ml/min in the resting state
• but 1000 – 1200 ml/min during the exercise
• CaO2 = 200 ml O2/l
• for PaO2 = 13.3 kPa and c[Hb] = 150 g/l
• consumption in the resting state:  30 ml O2/min (60 - 80%)
• very high O2 extraction (A - VO2 difference) compared to other organs
• therefore, the only mechanism increasing the oxygen supply is an increase of
coronary blood flow
• because aorta has a constant pressure, it has to be done by vasodilatation in the
coronary bed = CFR
• small scale neovascularisation is also possible
• majority of oxygen is consumed by LV (generating much larger arterial
pressure compared to right heart supplying pulmonary circulation)
• therefore CBF is a critical determinant of its function (i.e. contractility mainly)
Blood supply of the heart
• demand for O2 and substrates is met by heart blood
vessels - coronary arteries - branching from the
ascendant aorta
• (1) left coronary artery
• (a) left ant. desc. branch
• supplies front part of the LV and RV and front part of the septum
• (b) circumflex branch
• supplies left and back wall of the LV
• (2) right coronary artery
• supplies RV
Vessel morphology related to the function
Physical parameters of circulaction
• flow
• laminar
• normally in majority of circulation
• turbulent
• behind stenosis, bifurcation
• velocity [V]
• Reynold´s number
• perfusion (Ohm´s law)
• flow [F] = pressure [P] / resistance [R]
• resistance (Poiseuille law)
• R = η  L / π  r4
• viscosity [η]
• haematocrit, temperature
• pressure (Laplace law)
• P = tension [T] / diameter [r]
Summary of control mechanisms of coronary microvasculature tone
ENDOTHELIAL DYSFUNCTION AS A TRIGGER OF
ATHEROSCLEROSIS
Endothelium - physiological role of ECs
• (1) vasodilation
• smooth muscle cells (SMC) in blood vessels - notably
arterioles - work in close association with the overlying ECs
• action of hormones, neurotransmitters (ACh) or deformation
of the ECs by flow of blood (shear stress) trigger reactions
that influence associated SMC, these effects operates via
second messenger systems
• phospholipase A2 (PLA2) which activate cyclooxygenase (COX) /
prostacyclin synthase (PCS) to produce prostaglandins (PGI2) which
diffuse readily through the tissue fluids to act on SMC
• alternatively, nitric oxide synthase (L-arginase) (NOS) produces
highly diffusible gaseous "neurotransmitter„ NO acting on SMC
either through G-protein systems or directly on ion channels
• (2) antiadhesive /anti-inflammatory action
• no VCAM, ICAM, selectins, …
• (3) antithrombotic, antiagregant and fibrinolytic action
• heparansulphate
• thrombomodulin
• tPA
NO-mediated vasodilation
• biosynthesis of the key endogenous vasodilator
NO is principally performed by the calciumdependent
endothelial isoform of nitric oxide
synthase (eNOS)
• this is triggered by the binding of agonists or by
shear stress (1) and facilitated by a variety of
cofactors and the molecular chaperone heatshock
protein 90 (HSP90)
• amino acid L-Arg is converted by eNOS into NO
(2), with L-citrulline as a by-product. NO diffuses
into adjacent smooth muscle cells (3) where it
activates its effector enzyme, guanylate cyclase
(GC)
• GC (4) converts GTP into the second messenger
cyclic guanosine monophosphate (cGMP), which
activates protein kinase G (PKG) (5), leading to
modulation of myosin light chain kinase and
smooth muscle relaxation.
• PKG also modulates the activity of potassium
channels (IK; 6), thereby increasing cell membrane
hyperpolarization and causing relaxation
Endothelial dysfunction
• given the essential role of endothelial integrity in
maintenance of normal vessel morphology
endothelial dysfunction act as a pro-atherogenic
factor increasing adhesivity, permeability and
impairing vasodilatation
• causative factors:
• increase BP (hypertension)
• mechanical shear stress
• turbulent flow
• bifurcations
• biochemical abnormalities
• glucose
• modified proteins
• incl. LDL
• homocysteine
• oxidative stress
• oxygen radicals
• formed by smoking
• inflammation
• certain infections
• Chlamydia pneumoniae?
• Helicobacter pylori??
Endothelium - summary
Functional Dysfunctional
constant vasodilation due to mechanical stimuli
(shear stress) and mediators (Ach,
bradykinine) mediated by NO, PGI2 (event.
adenosine)
increased sensitivity to paracrine constrictive
mediators (epinephrine, norepinephrine, AT II,
serotonin) and active formation of
vasoconstrictors (ET-1)
anti-adhezive / anti-inflammatory state (NO,
PGI2), inhibition of expression of adhezive
proteins
expression of adhesive molecules (ICAM,
VCAM, selectins), production of cytokines (e.g.
MCP-1) attracting migration of inflammatory
cells into subendothelial space
constant local anticoagulant production
(heparansulphate, thrombomoduline),
antiagregant and thrombolytic state (tPA)
prothrombotic (vWf, TF), anti-fibrinolytic (PAI-
1) phenotype
CORONARY ATHEROSCLEROSIS
Vessels affected by AS
AS – main facts
• AS is the most common form of arteriosclerosis
• i.e. any form of lowering vessel elasticity, e.g. due to calcification, lipid
accumulation etc.
• 3 forms
• Mönckeberger´s – deposition of calcium in tunica media in elderly
• hyaline arteriolosclerosis in hypertensive subjects
• and classical AS with atheromas (athero = porridge + sclerosis = hardening)
• AS is a degenerative process characterized by chronic inflammation of
the vessel wall
• AS represents multifactorial disease due to endogenous (typically
with significant genetic component) and environmental factors
• AS can theoretically affect any vessel, in reality AS is limited only to
arteries (= arteriosclerosis)
• due to the role of blood pressure and hemodynamic factors in general as a
pathogenic factor
• moreover, not all arteries are equally affected, but most often those in
predilections (bifurcations, non-laminar flow) and here again in a
segmental manner
• coronary aa.
• cerebral bed
• carotid aa.
• renal artery
• lower extremities artery bifurcations
• on the contrary, other sites are typically resistant
• e.g. int. thoracic artery (used as a graft for by-pass surgery)
• a. hepatica
• a. radialis
• main players in the AS etiopathogenesis
• (1) modified lipoproteins (LDL)
• (2) endothelial cells changing their properties (namely adhesivity and
permeability, secreting chemokines)
• (3) monocyte-derived macrophages migrating to intima and forming
„foam“ cells
• (4) normal cells of vessel wall (smooth muscle cells)
• (5) other immune cells (mainly T lymphocytes and mast cells)
• temporal pattern of AS – several pathogenic phases (with variable
time course) and morphology – stages (resp. microscopic findings)
during AS process:
• (1) initiation
• endothelial dysfunction
• fatty streak stage – very early, detected in childhood by section findings
• (2) progression
• diffuse intimal thickening (DIT) due to foam cell accumulation, SMC migration from media and
extracellular matrix expansion
• fibrous plaque (atheroma with fibrous cap)
• calcification
• (3) complication
• vessel remodelling – plaque initially expands towards abluminal diameter (outward), later reduces
vessel lumen – stenosis, clinically ischemia symptoms in a given mal-perfused tissue area
• plaque erosion (superficial thrombus, healing, re-endothelisation)
• fissure, plaques rupture and subsequent thrombosis, vessel occlusion, critical ischemia and tissue
necrosis
AS – main facts
atheroma
(cit. Atherosclerosis: Known and unknown. https://doi.org/10.1111/pin.13202)
Cardiovascular/AS risks
• identification of the main CV risks by
prospective epidemiologic studies
• Framingham study =  TK,  cholesterol, 
triglycerides,  HDL, smoking, obesity,
diabetes, physical inactivity,  age, gender
(male) and psychosocial factors
• original cohort (from 1948)
• 5,209 subjects (aged 32 – 60 yrs) from Framingham,
Massachusetts, USA
• detail examination every 2 years
• II. cohort (from 1971)
• 5,124 adult offspring
• III. cohort
• 3,500 grandchildren of original participants
• identified late clinical manifestation of longterm
untreated / decompensated
hypertension as well:
• heart attack, stroke (→ atherosclerosis)
• heart failure (→ left ventricular hypertrophy)
• renal failure (→ hyperfiltration, nephrosclerosis)
• retinopathy
Risk factors of AS
significantgeneticcontribution
Major
dyslipidaemia ( LDL and VLDL,  HDL)
hypertension
diabetes mellitus
male gender
Minor (20% of CV events occur in subjects without major risks)
 plasma homocysteine
 plasma haemostatic factors (e.g. fibrinogen, PAI, ..)
 Lipoprotein (a) – Lp(a)
chronic inflammation incl. low-grade (hsCRP as a surrogate marker)
e.g. in visceral obesity
clonal haematopoiesis (CHIP)
gut microbiome
non-genetic
Environmental
smoking (major risk!) = ROS and chron. inflammation of airways
physical inactivity
diet
certain infections
components of a
metabolic
syndrome driven
by obesity
(1) Initiation – formation of fatty streak
• LDLs can exist in a native or modified forms
• native LDL is recognised and bound by LDL-R
• modified LDL is up-taken by scavenger receptors
• in vivo LDL is modified by oxidation (acetylation or
glycation) in circulation and in subendothelial space
• minimally at first (mmLDL), extensively later (oxLDL)
• mmLDL and oxLDL are cytotoxic and pro-inflammatory,
they increase expression of adhesive molecules (VCAM,
ICAM, selectins) by EC
• monocytes and T lymphocytes adhere to endothelium
and migrates to subendothelial space, here monocytes
transform to macrophages
• interestingly, neutrophils that are constant cell type
present in inflammatory lessions are completely absent in
AS, finding not entirely understood; it might be because of
the particular cytokine spectrum – expression of MCP-1
(monocyte chemotactic protein) by EC
• macrophages ingest oxLDL via their scavenger receptors
(SR-A and CD36) and form this was so called “foam
cells” (= lipid-laden macropghges)
• macroscopically seen as a yellowish dots or streaks in
subendothelium, hence “fatty streaks”
• free cholesterol from oxLDL in macrophages is again
esterified by ACAT-1 (acyl-CoA cholesterol acyltransferase)
and stored together with lipids, inversely, it
can be transform into soluble form by hormonesensitive
lipase, inbuilt into plasma membrane and
exported from the cell (by transporter ABCA1 and HDL)
• reverse CH transport via HDL is a crucial anti-atherogenic
mechanism
AS pathogenesis – role of risk factors - cholesterol
Risk factors, such as hypercholesterolemia (yellow dots), may upregulate the adhesion molecules of endothelial cells (EC),
which leads to the adherence of monocytes (Mon) and T lymphocytes (Lym) on the surface of intima (left). Furthermore,
these inflammatory cells migrate into the subintimal space under the induction of chemoattractancts, where monocytes
differentiate into macrophages (Mϕ) and uptake accumulated lipids and transform into foam cells (middle). As the lesions
progress, the medial smooth muscle cells (SMC) migrate into the subintima and proliferate (right). Some smooth muscle
cells can take lipids and transfer into foam cells. T lymphocytes may mediate the entire process of the lesion formation
(cit. Atherosclerosis: Known and unknown. https://doi.org/10.1111/pin.13202)
(2) Progression – formation of plaque
• immunologic interaction between
macrophages and T lymphocytes (Th1 and
Th2 sub-population) locally maintains the
chronic inflammation
• production of both pro-atherogenic Th1 cytokines
(MCP-1, IL-6, TNF-α, …) and anti-atherogenic Th2
(IL-4)
• mutual balance between Th1 and Th2 is topically
modified by many factors
• macrophages as antigen-presenting cells help
to activate B lymphocytes to wards
production of auto-antibodies against oxLDL
→ formation of immune complexes →
inflammation
• cytokines stimulate other cells, mainly SMCs
to migrate from media into intima, proliferate
(→ intima thickening) and secrete proteins of
extracelullular matrix (collagen) → fibrose
plaque
• pathologic calcification of atherosclerotic
vessel wall is not a passive consequence but
result of changed gene expression in
macrophages (osteopontin)
Macrophages in advanced AS – role in AS
progression• M in early lesions
• majority of Ch in the form of
esters (enzyme ACAT)
• non-thrombogenic
• HDL reverse transport works
• M in advanced lesion
• accumulation of free Ch (FCH)
• highly thrombogenic
• FCH in membranes of
endoplasmic reticulum changes
its permeability and Ca
concentration inside →
ER stress → apoptosis of
macrophages → more of FCH
extracellularly → increased
thrombogenicity of atheroma
• production of MMPs
(3) Advanced AS plaque
• plaque can grow and slowly obstruct lumen or it
can become unstable and lead to
rupture/fissuration and thrombosis and acute
complete obstruction → “complicated plaque”
• intimal macrophages and SMC die (necrosis and
cytokine-induced apoptosis) and establish necrotic
core of the plaque with accumulated extracellular
CH
• stimulated and hypoxic macrophages produce
proteolytic enzymes degrading extracellular
matrix proteins (matrix metaloproteinases, MMPs)
which further weaken the plaque
• plaque rupture (often eccentric and CH-rich),
typically in the plaque “shoulder” lead to exposure
of accumulated lipids and tissue factors to platelets
and coagulation factors and cause thrombosis
• this can be manifested as a complete vessel
occlusion and thus lead to tissue necrosis (e.g.
myocardial infarction or stroke) or incomplete
occlusion as a consequence of repeated cycles of
rupture → microthrombotisation → fibrinolysis →
healing = “unstable plaque” or angina
• vulnerable plaque (i.e. rupture-prone) vs.
vulnerable patient
• see further
Fate of advanced AS plaque - rupture an thrombosis
• Pathophysiological scenarios
• (1) progressive growth of the plaque
• asymptomatic until >50% of diameter reduction (= >75% crosssectional
area reduction)
• typical cause of stable angina
• (2) superficial erosion
• denudation/apoptosis od ECs – mural platelet thrombi – healing –
further lumen reduction → change in symptom severity = unstable
angina
• (3) plaque rupture and thrombosis
• clinically leads to acute coronary event (MI or sudden death) in
case of total occlusion of the vessel or unstable angina or no
symptoms in case of a healing
• very often happens in haemodynamically insignificant stenosis
• plaque composition rather than plaques size matters
• can happen due to the fracture of the fibrous cap or in the
„shoulder“
• imbalance between forces/mechanical strength
(ad 2) Mechanisms of AS plaque healing
pro zájemce: N Engl J Med 2020; 383:846-857
(ad 3) Vulnerable plaque - thin cap fibroatheroma
• Typical features
• a thin fibrous cap
• extensive inflammatory infiltration by macrophages and
T lymphocytes
• large lipid core
• small numbers of SMCs
• intra-plaque haemorrhage
• inflammation is the most important part of progression
and destabilization of an atherosclerotic plaque
• release of proinflammatory cytokines and matrix
metalloproteinases contributes to degradation of
collagenous components in the fibrous cap of the
atheroma
• apoptosis of collagen synthesizing SMCs
• tissue factor produced by intra-plaque inflammatory cells
• identification of vulnerable plaque (= prone to rupture)
is clinically extremely important
Animal models of AS - mouse
• generally, it is extremely difficult to simulate AS in
animals, even those kept in captivity
• in this aspect Homo sapiens is quite unique in their
susceptibility to damage of vessel wall
• although mice is the most studied model, exp. induced
AS is not entirely similar to man
• exp. model of AS
• induced
• high CH diet + endothelial denudation + hypertension
(ligation of a. renalis)
• spontaneous (knock-out)
• ApoE -/- mouse
• LDL-R -/- mouse
• exp. model spontaneous IM
• induced
• ligation of coronaries
• spontaneous
• comb. apoE/LDL-R -/+
mental stress + hypoxia