Pathophysiology of Heart Failure Flashcards
Cardiac output varies in response to both physiological and pathological factors: (4)
Preload
Afterload
Contractility
Heart Rate
WHat is Preload (filling pressure)
The left ventricle end-diastolic volume that stretches the ventricle to its greates dimensions.
High Preload = High CO
What is the Afterload?
The pressure against which the heart must work to eject blood during systole (contraction of ventricle)
High afterload = Low CO
How does contractility effect the CO?
This is the ability of the Myocardium to contract. If the contractility increases, the CO increases
How does the Heart rate affect CO?
CO = HR x SV
So if Heart rate increases, the CO increases.
SV = stroke volume (volume pumped from the venticle per beat)
What is responsible for heart failure?
Abnormalities in the Cardiac function causing failure of the heart to pump blood at a rate which meets metabolic demand of tissues.
The symptoms of Heart Failure (HF).
SYmptoms are different for every one and will arise at different times per infividual.
- Excercise intolerance,
- Breathlessness
- Fatigue
- Oedema
What is Acute Heart Failure
Sudden circulatory collapse due to either
- Haemorrhagic shock (lose >20% of blood volume)
- Cardiogenic shock during Acute Myocardial Ifarction
Chronic Heart Failure:
How much of population have this and how much die?
1.5% of whole population
30-40% die within 12 months of diagnosis.
What is likely to be the cause of Chronic HF?
There is usually some form of Cardiomyopathy which is a disease directly affecting the heart.
What are the causes of Inherited Cardiomyopathy (CM)?
- congenital hypertrophic CM (where part of the heart thickens)
- Arrhythmic Right Ventricle CM
What are the causes of Aquired CM?
- Ischaemic CM post Myocardial Infarction
- Overload of pressure due to hypertension
- Valvular disease (often due to pressure)
- Infection or Inflammation (myocarditis)
- Alcoholic CM (direct effect of ethanol)
What is the progression of CM
Gradual reduciton in cardiac function results in symptoms:
Reduced myocardial contractility and reduced CO, causing FATIGUE
Reduced tissue perfusion as blood is sent to vital organs causing WEAKNESS
REduced Venous Return.
Volume Expansion - Retaining water in the kidney LESS URINE
LV failure - pulmonary oedema COUGHING and difficulty breathing
RV failure
WEIGHT LOSS, MUSCLE WASTING, ANOREXIA
What does any Heart Failure likely to be due?
Due to SYSTOLIC dysfunction which is often accompanied by Diastolic dysfunction
What side is most prevelantly associated with Heart Failure?
Left-sided failure is most prevelant, and is the greatest cause of Right-sided failure
What is Biventricular HF?
Left and right Ventricles
WHat is Systolic HF?
Reduced ventricular Contractility
What is Diastolic HF?
Reduced ventricular Filling
What is Compensated HF?
Stable, controlled symptoms
What is Decompensated HF?
Acute, with more symptoms and respiratory deistress.
What is reduction in Cardiac Output?
A neurohormonal reflex.
What does a fall in CO that presents in HF cause?
A physiological response to try to maintain perfusion to vital organs, and is a response similar to that of a big hemorrhage.
What does the Sympathetic NS do in response to reduced CO? (The neurohormonal response)
It is a Baroreceptor reflex that fires from the baroreceptors, Noradrenaline is released to increase the heart rate, to cause venous smooth muscle contraction, vasoconstriction, and increased Myocardium contraction in an effort to increase CO
What is the other system activated by decreased CO?
the neurohormonal response
The renin-angiotensin system: this causes increased renin secretion from the juxoglomerular cells of the kidney leading to increased Angiotensin II production, and therefore more Aldosterone form the adrenal cortex and ADH from the pituitary to increase water reabsrption , increaseing blood Volume
What is the problem with the body’s attempt to increase CO?
It causes further pathology
What will cause remodelling of the heart?
A primary disease, in this case Heart Failure will cause remodelling
What is remodelling of the heart?
Thinning or thickening of the cardial wall causing a decrease in CO.
What is the spiral that tries to increase CO, but causes further pathology?
The remodelling due to primary disease (HF) causes a decrease in CO,
A neurohormonal response is activated- the sympathetic NS and the Renin-Angiotensin System. These result in an increase in blood volume and vasoconstriciton to try to increase CO.
These result in an increased Preload and afterload causing Ventricular Dilation (stretched and thinned ventricle), meaning that the cardiac workload increases, which then decreases the CO. So it is a cycle.
What are the counter-regulating Vasodilators released and why?
These are released to try to counter the increase in Vasoconstriction (by the Sympathetic NS and the renin angiotensin system). Examples are Adrenomedullin and Nitric Oxide. The levels of these give the extent of the disease and also a diagnosis
High levels of counter-regulating vasodilators mean severe disease
