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Heart Failure - Pathophysiology (view source)
Revision as of 11:47, 3 July 2010
, 11:47, 3 July 2010no edit summary
==Introduction==
==Introduction==
*Class 2: Exercise intolerance or dyspnoea.
*Class 2: Exercise intolerance or dyspnoea.
*Class 3: Marked exercise intolerance.
*Class 3: Marked exercise intolerance.
*Class 4: Cannot exercise, dyspnoea at rest.[[Category:Heart Failure]][[Category:To_Do_-_Cardiovascular]]
*Class 4: Cannot exercise, dyspnoea at rest.
==Introduction==
*The heart pumps unoxygenated blood from the venous circulation into the lungs where it is oxygenated. Newly oxygenated blood then travels to the left atria and ventricle where it is pumped into the arterial circulation to meet the oxygen demands of the body.
*Heart Failure is a condition that begins when the heart is unable to pump enough blood (cardiac output) at normal filling pressures to meet the body’s requirements. Heart Failure is the end result of heart disease (heart abnormality).
*Under normal circumstances the heart can adapt to moderate increases of pressure or volume using its functional reserve capacity. During acute episodes of increased volume or pressure load the dilated heart chambers respond by increasing their force of contraction. This is known as the Frank-Starling Phenomenon. However, in chronic conditions the cardiac chambers hypertrophy. Initially these adaptations are beneficial, but eventually the functional reserve mechanisms lead to heart failure.
*Heart failure can affect the right ventricle, the left ventricle, or both ventricles (biventricular). Clinical signs are characteristic and can help determine which ventricle is affected.
==Etiology of Heart Failure==
The five cardiac impairments that cause heart failure are the following:
===1. Arrhythmias===
'''Problem'''
*Irregularity of cardiac rhythm affects cardiac output
'''Cause'''
*Tachycardia: Increased heart rate does not allow for adequate cardiac filling during diastole and consequently cardiac output drops
*Bradycardia: Decreased heart rate lowers cardiac output by limiting the amount of blood pumped per minute
===2. Diastolic Failure (Restricted Ventricular Filling)===
'''Problem'''
*When the heart is unable to relax fully during diastole (to allow for complete ventricular filling) cardiac output drops
'''Cause'''
*Hypertrophic Cardiomyopathy (increased thickness of the ventricular myocardium reduces lumen size available for diastolic filling)
*Dilated Cardiomyopathy (dilation of the cardiac chambers lowers the contraction force and the cardiac output)
*Pericardial Effusion (increased pressure on the myocardium decreases space for diastolic filling)
===3. Pressure Overload===
'''Problem'''
*Increased pressure in the ventricle causes concentric hypertrophy in an effort to maintain adequate cardiac output. Eventually, high ventricular pressures can result in cardiac failure.
'''Cause'''
*Hypertension (Pulmonary and/or Systemic)
*Outflow tract narrowing (Aortic and/or Pulmonic Stenosis)
===4. Systolic Failure (Myocardial Failure)===
'''Problem'''
*Decreased myocardial contraction during systole causes reduced cardiac output
'''Cause'''
*Primary myocardial diseases (e.g. Dilated cardiomyopathy)
*Complication from another form of heart failure
===5. Volume Overload===
'''Problem'''
*The cardiac ventricles are required to work harder by pumping an increased volume of blood in order to maintain adequate cardiac output. Increased blood volume in the heart causes eccentric hypertrophy in an effort to accommodate the increased blood volume.
'''Cause'''
*Shunting Disorders (e.g. PDA)
*Valvular Regurgitation
*Anemia
[[Category:Heart Failure]][[Category:To_Do_-_Cardiovascular]]