Pathophysiology of cardiac disease and congestive heart failure Flashcards
Congestive heart failure is also known as?
Backwards heart failure
What is backwards HF associated with?
Elevated filling pressures and extravasation of fluid (e.g. pulmonary oedema in L-CHF).
Define preload and how does this affect stroke volume?
Venous return to the heart – stretches sarcomeres – more returned the higher the SV
Define afterload
Force of ejection from the heart (of the ventricles) – arterial resistance/pressure
Describe how preload influences cardiac output by the Frank Starling mechanism
Increased the endo diastolic ventricular volume
Sarcomere lengths are increased
Stroke volume of the heart is increased
What are the major consequences of CHF?
- Oedema and Effusions
- Peripheral vasoconstriction
- Tachycardia / Arrhythmias
- Remodelling and fibrosis of the myocardium
How does an increased afterload affect CO?
Increased afterload causes a decreased SV making it harder for the heart to pump
Define heart failure
A clinical syndrome caused by heart diseases resulting in systolic and / or diastolic function severe enough to overwhelm the normal compensatory mechanisms
What are the consequences of forwards HF?
Poor cardiac output and reduced peripheral perfusion
What are the consequences of backwards/congestive HF?
Elevated filling pressures, resulting in oedema and effusions
What is the role of neuro-hormonal activation in the consequences of CHF?
Baroreceptors – increase sympathetic drive in response to a decrease in BP
Sodium and water retention is trying to increase preload but can lead to oedema and effusions if too much
What is endothelin?
potent vasoconstrictor and causes myocardial remodelling and fibrosis
What are the 3 immediate consequences of an increased sympathetic drive in response to decreased blood pressue?
- Increased HR (contractility)
- Vasoconstriction
- Renin release (RAAS)
What is the function of cardiac beta-1 adreno-receptors?
Increased HR - tachycardia
- The aim is to increase cardiac output (CO = SV x HR), but this is detrimental in the
long term, as it increases myocardial oxygen consumption and reduces coronary
perfusion.
What is the function of cardiac alpha-1 adreno-receptors?
Lie on vascular smooth muscle cells and cause vasoconstriction –> increases BP –> increases venous return (preload)
What is the role of angiotensin II within cardiac myocytes?
Results in hypertrophy and fibrosis (cardiac remodelling)
What is the function of vasopressin (ADH)?
Results in water retention
Excessive Sodium and water retention results in Oedema and Effusions.
In heart failure what is released during atrial stretch?
Atrial natriuretic peptide (ANP)
In heart failure what is released due to increased left ventricle pressues?
Brain natriuretic peptide (BNP)
What is used to diagnostically test for HF?
ANP and BNP can be assayed to demonstrate the presence of heart failure, but have a short half-life.
Dogs with CHF have sig. higher levels than normal dogs.
In patients with oedema and effusions what is the aim of treatment?
To increase preload - venous return to the heart
Give examples of mediators of peripheral vasoconstriction
- Alpha-1 receptors in the peripheral NS
- Angiotensin II
- Reduced bradykinin levels
- Vasopressin
- Endothelin
How does Angiotensin II affect filtration pressure in the kidney?
- Angiotensin II causes greater EA constriction than AA.
- This increases glomerular capillary pressure (filtration pressure).
What is the overall function of ACE inhibitors?
Counteract adverse effects of angiotensin II
Which drug can be used to stop aldosterone escape (increased aldosterone levels despite adequate ACE inhibition)?
Spironolactone
Compensatory hypertrophy due to volume overload is an example of … hypertrophy?
Eccentric
What is volume overload of the heart?
One or more chambers of the heart “see” an increased volume of blood. This leads to
chamber dilation and usually compensatory hypertrophy
In which situations would eccentric hypertrophy be seen?
- Mitral regurgitation
- Ventral septal defects
- Patent ductus arteriosus
- Tricuspid regurgitation
What is pressure overload of the heart?
There is increased impedance or increased resistance to outflow of blood from a particular heart chamber (usually a ventricle).
Relative wall thickness increases (walls thick; chamber may be small).
Pressure overload results in … hypertrophy?
Concentric
Examples of pressure overload conditions on the left and right ventricles are:
- Aortic stenosis
- Systemic hypertension
- Pulmonic stenosis
- Pulmonary hypertension
A pressure overload will lead to increased wall stress, how is this compensated for?
By increasing wall thickness (which lowers the chamber radius)
What is the difference in adaptive and maladaptive modelling
Adaptive = initially compensatory Maladaptive = long term compensatory, more harmful than helpful
Myocardial remodelling is associated with?
Fibrosis
Increased wall stress
Myocardial ischaemia
