1. Definition
Heart failure is the heart’s inability to adequately increase cardiac output (CO) to meet the body’s demands. At rest, the cardiac output is normal.
2. Causes of heart failure
2.1. Abnormalities of the ventricular filling
- severe hypovolemia
Right ventricle:
- compression of the vena cava
- cirrhosis
- stenosis of the tricuspid valve
- positive intrathoracic or intrapleural pressure (pneumothorax)
- insufficient atrial contraction
Left ventricle:
- right heart failure
- pulmonary embolism
- stenosis or insufficiency of the mitral valve
- left ventricular hypertrophy
- accumulation of pericardial fluid
2.2. Abnormalities of contractility
- ischemia, hypoxia and acidosis
- dilatative cardiomyopathies
- toxins (e.g. alcohol)
- vitamin deficiency – thiamine (B1)
- starvation
- myocardial necrosis
2.3. Abnormalities of afterload (increased TRP)
Right ventricle:
- pulmonary hypertension
- chronic alveolar hypoxia (hypoxic pulmonary vasoconstriction)
- decrease of the capillary diameter (fibrosis, silicosis, emphysema)
- pulmonary embolism
- stenosis or insufficiency of the mitral valve
Left ventricle:
- systemic hypertension
- aortic stenosis or insufficiency
- mitral insufficiency
- polycythemia (high viscosity, increased resistance)
2.4. Abnormalities of heart rate
- extreme bradycardia (e.g. high degree sinoatrial and atrioventricular blocks)
- extreme tachycardia (e.g. supra ventricular or ventricular tachycardias)
3. Classification of heart failure
- chronic
- acute
- forward (right /left)
- backward (right / left)
4. Consequences of acute heart failure
Possible consequences of an acute fall in cardiac output are:
- acute brain hypoxia (death)
- cardiogenic shock
- extreme weakness
- pulmonary edema
- collaps (loss of consciousness)
5. Compensatory mechanism in heart failure
The body employs several mechanisms to increase cardiac output in response to heart failure:
- baroreceptor response: Increases heart rate and contractility via the sympathetic nervous system.
- RAAS activation: Raises blood volume and preload through fluid retention.
- ventricular hypertrophy: Enlarges the heart muscle to maintain output, though it can lead to stiffness over time.