Transcript PATHOPHYSIOLOGY OF HEART FAILURE

PATHOPHYSIOLOGY OF
HEART FAILURE
Prof. J. Hanacek
Technical co-operation: L. Šurinová
Notes to heart physiology
• Essential functions of the heart
•
to cover metabolic needs of body tissue
(oxygen, substrates) by adequate blood supply
• to receive all blood comming back from the tissue
to the heart
• Essential conditions for fulfilling these functions
• normal structure and functions of the heart
• adequate filling of the heart by blood
Essential functions of the heart are secured
by integration of electrical and mechanical
functions of the heart
Cardiac output (CO) = heart rate (HR) x stroke vol.(SV)
- changes of the heart rate
- changes of stroke volume
• Control of HR:
- autonomic nervous system
- hormonal(humoral) control
• Control of SV: - preload
- contractility
- afterload
Adaptive mechanisms of the heart
to increased load
• Frank - Starling mechanism
• Ventricular hypertrophy
– increased mass of contractile elements  strength
of contraction
• Increased sympathetic adrenergic activity
– increased HR, increased contractility
• Incresed activity of R–A–A system
Causes leading to changes of number and size
of cardiomyocytes
Preload
Stretching the myocardial fibers during diastole by increasing enddiastolic volume  force of contraction during systole =
Starling´s law
preload = diastolic muscle sarcomere length leading to increased
tension in muscle before its contraction (Fig.2,3)
- venous return to the heart is important  end-diastolic
volume is influenced
- stretching of the sarcomere maximises the number
of actin-myosin bridges responsible for development of force
- optimal sarcomere length  2.2 m
Myocardial contractility
Contractility of myocardium
Changes in ability of myocardium to develop the force
by contraction that occur independently on the
changes in myocardial fibre length
Mechanisms involved in changes of contractility
•  amount of created cross-bridges in the sarcomere
by  of Ca ++i concentration
- catecholamines  Ca++i  contractility
- inotropic drugs  Ca++i  contractility
 contractility  shifting the entire ventricular function
curve upward and to the left
 contractility  shiffting the entire ventricular function
curve (hypoxia, acidosis) downward and to the right
The pressure – volume loop
• It is the relation between ventricular volume and pressure
• This loop provides a convenient framework for understanding
the response of individual left ventricular contractions
to alterations in preload, afterload, and contractility
• It is composed of 4 phases:
- filling of the ventricle
- isovolumic contraction of ventricle
- isotonic contraction of ventricle(ejection of blood)
- isovolumic relaxation of ventricle
Pressure – volume loops recorded under different
conditions
Afterload
It is expressed as tension which must be developed in the wall
of ventricles during systole to open the semilunar valves and
eject blood to aorta/pulmunary artery
Laplace law:
intraventricular pressure x radius of ventricle
wall tension = -------------------------------------------------------2 x ventricular wall thickness
 afterload: due to - elevation of arterial resistance
-  ventricular size
- myocardial hypotrophy
 afterload: due to -  arterial resistance
- myocardial hypertrophy
-  ventricular size
Heart failure
Definition
It is the pathophysiological process in which
the heart as a pump is unable to meet
the metabolic requirements of the tissue for
oxygen and substrates despite the venous
return to heart is either normal or increased
Explanation of the terms
• Myocardial failure = abnormalities reside in the myocardium and lead
to inability of myocardium to fulfilling its function
• Circulatory failure = any abnormality of the circulation
responsible for the inadequacy in body tissue
perfusion, e.g. decreased blood volume, changes
of vascular tone, heart functiones disorders
• Congestive heart failure = clinical syndrome which is developed
due to accumulation of the blood in front
of the left or right parts of the heart
General pathomechanisms involved in heart
failure development
Cardiac mechanical dysfunction can develop as
a consequence in preload, contractility and afterload
disorders
Disorders of preload
 preload  length of sarcomere is more than optimal 
  strength of contraction
 preload  length of sarcomere is well below the optimal 
  strength of contraction
Important: failing ventricle requires higher end-diastolic volume
to achieve the same improvement of CO that normal
ventricle achieves with lower ventricular volumes
Disorders of contractility
In the most forms of heart failure the contractility of myocardium
is decreased (ischemia, hypoxia, acidosis, inflammation, toxins,
metabolic disorders... )
Disorders of afterload due to:
• fluid retention in the body
•  arterial resistance
• valvular heart diseases ( stenosis )
Characteristic features of systolic dysfunction
(systolic failure)
• ventricular dilatation
• reducing ventricular contractility (either generalized
or localized)
• diminished ejection fraction (i.e., that fraction of end-diastolic
blood volume ejected from the ventricle during each systolic
contraction – les then 45%)
• in failing hearts, the LV end-diastolic volume (or pressure)
may increse as the stroke volume (or CO) decreases
Characteristic features of diastolic dysfunctions
(diastolic failure)
• ventricular cavity size is normal or small
• myocardial contractility is normal or hyperdynamic
• ejection fraction is normal (>50%) or supranormal
• ventricle is usually hypertrophied
• ventricle is filling slowly in early diastole (during the period
of passive filling)
 end-diastolic ventricular pressure is increased
Causes of heart pump failure
A. MECHANICAL ABNORMALITIES
1. Increased pressure load
– central (aortic stenosis, aortic coarctation...)
– peripheral (systemic hypertension)
2. Increased volume load
– valvular regurgitation
– hypervolemia
3. Obstruction to ventricular filling
– valvular stenosis
– pericardial restriction
B. MYOCARDIAL DAMAGE
1. Primary
a) cardiomyopathy
b) myocarditis
c) toxicity (e.g. alcohol)
d) metabolic abnormalities (e.g. hyperthyreoidism)
2. Secondary
a) oxygen deprivation (e.g. coronary heart disease)
b) inflammation (e.g. increased metabolic demands)
c) chronic obstructive lung disease
C. ALTERED CARDIAC RHYTHM
1. ventricular flutter and fibrilation
2. extreme tachycardias
3. extreme bradycardias
Pathomechanisms involved in heart failure
A. Pathomechanisms involved in myocardial failure
1. Damage of cardiomyocytes   contractility,
 compliance
Consequences:
 defect in ATP production and utilisation
 changes in contractile proteins
 uncoupling of excitation – contraction process
  number of cardiomyocytes
 impairment of relaxation of cardiomyocytes with decrease
compliance of myocardium
 impaired of sympato-adrenal system (SAS)   number of
1-adrenergic receptors on the surface of cardiomycytes
2. Changes of neurohumoral control of the heart
function
• Physiology: • SNS   contractility
 HR
 activity of physiologic pacemakers
Mechanism:   sympathetic activity  cAMP 
Ca ++i  contractility
  sympathetic activity  influence
of parasympathetic system on the heart
• Pathophysiology: normal neurohumoral control is
changed and creation of pathologic
neurohumoral mechanisms are present
Chronic heart failure (CHF) is characterized by an imbalance of
neurohumoral adaptive mechanisms with a net results of excessive
vasoconstriction and salt and water retention
Catecholamines : - concentration in blood :
- norepinephrin – 2-3x higher at the rest than in healthy subjects
- circulating norepinephrin is increased much more
during equal load in patients suffering from CHF than
in healthy subject
-  number of beta 1 – adrenergic receptors 
 sensitivity of cardiomyocytes to catecholamines 
  contractility
System rennin – angiotensin – aldosteron
heart failure  CO  kidney perfusion  stim. Of RAA system
Important:
Catecholamines and system RAA = compensatory mechanisms
 heart function and arterial BP
The role of angiotensin II in development of heart
failure
 vasoconstriction ( in resistant vesels)
 retention of Na  blood volume
  releasing of arginin – vasopresin peptide (AVP )
from neurohypophysis
 facilitation of norepinephrine releasing from
sympathetic nerve endings
  sensitivity of vessel wall to norepinephrine
 mitogenic effect on smooth muscles in vessels and
on cardiomyocytes  hypertrophy
 constriction of vas efferens ( in glomerulus )
  sensation of thirst
  secretion of aldosteron from adrenal gland
 mesangial conctraction  glomerular filtration rate
Pathophysiology of diastolic heart failure
 systolic heart failure = failure of ejecting function of the heart
 diastolic heart failure = failure of filling the ventricles,
 resistance to filling of ventricles
Diastolic failure is a widely recognized clinical entity
But, which of the cardiac cycle is real diastole ?
Definition of diastolic heart failure
It is pathophysiological process characterized by symptoms and
signs of congestive heart failure, which is caused by increased filling
resistance of ventricles and increased intraventricular diastolic
pressure
Primary diastolic heart failure
- no signs and symptoms of systolic dysfunction is present
- ! up to 40% of patients suffering from heart failure!
Secondary diastolic heart failure
- diastolic dysfunction is the consequence of primary
systolic dysfunction
Main causes and pathomechanisms of diastolic
heart failure
1. structural disorders passive chamber stiffness
a) intramyocardial
– e.g. myocardial fibrosis, amyloidosis, hypertrophy,
myocardial ischemia...
b) extramyocardial – e.g. constrictive pericarditis
2. functional disorders   relaxation of chambers e. g. myocardial
ischemia, advanced hypertrophy of ventricles,
failing myocardium, asynchrony in heart
functions
Causes and mechanism participating on impaired
ventricular relaxation
a) physiological changes in chamber relaxation due to:
– prolonged ventricular contraction
Relaxation of ventricles is not impaired !
b) pathological changes in chamber relaxation due to:
Impaired relaxation process
 delayed relaxation (retarded)
 incomplete (slowed) relaxation
 Consequences of impaired ventricular relaxation
- filling of ventricles is more dependent on diastasis
and on the systole of atrias than in healthy subjects
Symptoms and signs:
 exercise intolerance = early sign of diastolic failure
  coronary blood flow during diastole
 Causes and mechanisms involved in development
of ventricular stiffness
 ventricular compliance = passive property of ventricle
Source of compliance: cardiomyocytes and other heart
tissue to stretching
 Ventricular compliance is caused by structural abnormalities
localized in myocardium and in extramyocardial tissue
a) Intramyocardial causes : myocardial fibrosis, hypertrophy of
ventricular wall,restrictive cardiomyopathy
b. Extramyocardial causes : constrictive pericarditis
The role of myocardial remodelling in genesis of
heart failure
 adaptive remodelling of the heart
 pathologic remodelling of the heart
Main causes and mechanisms involved in
pathological remodelation of the heart
1.Increased amount and size of myocytes = hypertrophy
Due to: -  volume and/or pressure load
(excentric, concentric hypertrophy)
- hormonal stimulation of cardiomyocytes by
norepinephrine, angiotenzine II
2. Increased % of non-myocytic cells in myocardium
and their influence on structure and function of heart
a. endothelial cells – endothelins : mitogenic ability 
 stimulation growth of smooth muscle cells of vessels, fibroblasts
b. fibroblasts -  production of kolagens
Symptoms and signs of heart failure
1. forward failure:
symptoms result from inability of the heart to pump enough
blood to the periphery (from left heart), or to the lungs (from
the right heart)
a) forward failure of left heart:- muscle weakness, fatigue,
dyspepsia, oliguria....
 general mechanism: tissue hypoperfusion
b) forward failure of right heart: - hypoperfusion of the
lungs  disorders of gas
exchange
- decreased blood supply
to the left heart
2. backward failure:
– symptoms result from inability of the heart to accept
the blood comming from periphery and from lungs
a. backward failure of left heart:
– increased pulmonary capillary pressure  dyspnoea
and tachypnoea, pulmonary edema (cardiac asthma) 
 arterial hypoxemia and hypercapnia....
b. backward failure of right heart:
– increased pressure in systemic venous system 
 peripheral edemas, hepatomegaly, ascites nocturnal diuresis....