Cardiac Failure Flashcards
What determines cardiac output?
preload, heart rate, contractility, afterload
What is preload?
The blood that comes in to the heart from venous return - end diastolic volume
What is afterload?
The resistance that the heart has to pump against
Why does an increased preload give an increased force of contraction?
Because the increased volume stretches the muscles and allows them to contract more - necessary to match cardiac output and venous return
What is Starling’s Law?
Increased LVEDV gives increased cardiac output
How can you measure RVEDP?
JVP
How can you measure LVEDP?
pulmonary artery wedge pressure
What is pulmonary artery wedge pressure?
Pressure in the pulmonary vein measured by occluding the pulmonary artery - measured using a Swan-Ganz catheter
What are the starling forces?
The balance of hydrostatic and osmotic pressure across the capillary. Means that the fluid will leak out at the arterial end and leak in at the venous end.
What causes oedema?
An increase in venous pressure - leads to an imbalance in the starling forces and fluid can’t enter the capillaries at the venous end
What are other causes of oedema?
decreased osmotic pressure due to renal or liver failure, blocked lymphatics or increased capillary permeability due to infection or inflammation
What causes pulmonary congestion?
A LVEDP that is over 20-30mmHg
What is cardiac failure?
When the cardiac output is less than the body needs
What causes cardiac failure?
Either decreased cardiac output or increased body needs
What is the response to cardiac failure?
Increase LVEDP to maintain cardiac output by retaining fluid
What is the mechanism of cardiac failure?
- loss of myocardial muscle
- ischaemic heart disease
- cardiomyopathy
- pressure overload
- aortic stenosis
- hypetension
- volume overload
- valve regurgitation
- shunts
What are the pathological causes of cardiac failure?
ischaemic heart disease, valvular heart disease, hypertensive heart disease, congenital heart disease, cor pulmonale, pericardial disease
What are the clinical features of left heart failure?
short of breath, fatigue, tachycardia, crackles
What are the clinical features of right heart failure?
oedema
Why is water retention a response of cardiac failure?
Because of decreased blood supply to the kidney activating the renin-angiotensin-aldosterone system. This leads to greater pressure on the heart.
What is the result of sympathetic nerve activation in cardiac failure?
Causes increased contractility but in the long term also causes arrhythmias, vasoconstriction and has a toxic effect on myocardium
What are the mechanisms for right heart failure?
global heart disease, specific right heart disease or left heart failure
How does left heart failure lead to right heart failure?
Left heart failure leads to pulmonary congestion which leads to hypoxia which leads to pulmonary vasoconstriction which leads to pulmonary arterial hypertension which leads to right heart failure
What is the treatment for cardiac failure?
- reduce fluid and vasodilate
- diuretics, aldosterone antagonists, ACE inhibitors, angiotensin receptor antagonists
- increase contractility
- digoxin
- block effects of NA
- beta blockers
- treat underlying causes