Heart failure may occur suddenly, or it may develop gradually. When heart function deteriorates over years, one or more conditions may exist. The strength of muscle contractions may be reduced, and the ability of the heart chambers to fill with blood may be limited by mechanical problems, resulting in less blood to pump out to tissues in the body. Conversely, the pumping chambers may enlarge and fill with too much blood when the heart muscle is not strong enough to pump out all the blood it receives.
In addition, as the architecture of the heart changes as it enlarges, regurgitation of the mitral valve may develop, making the heart failure even worse.
can be immediately life threatening due to lack of time to undergo compensatory adaptations.
may result from cardiopulmonary by-pass surgery, acute infection (sepsis), acute myocardial infarction, valve dysfunction, severe arrhythmias, etc.
can often be managed successfully by pharmacological or surgical interventions.
Chronic heart failure
a long-term condition (months/years) that is associated with the heart undergoing adaptive responses (e.g., dilation, hypertrophy) to a precipitating cause.
These adaptive responses, however, can be deleterious in the long-term and lead to a worsening condition.
Functional classification of Heart Failure by New York Heart Association 03/17/11 Class % of patients Symptoms I 35% No symptoms or limitations in ordinary physical activity II 35% Mild symptoms and slight limitation during ordinary activity III 25% Marked limitation in activity even during minimal activity. Comfortable only at rest IV 5% Severe limitation. Experiences symptoms even at rest
The Frank-Starling law of the heart states that as the ventricular volume increases and stretches the myocardial muscle fibers, the stroke volume increases, up to its maximum capacity. After that point, increasing volume increases pulmonary capillary pressure (and pulmonary congestion), without increasing the stroke volume or cardiac output. The mechanism is the length-force relationships of muscle contraction.
Stroke volume End-Diastolic volume Maximum capacity to produce stroke volume Normal range: stroke volume increases with end-diastolic volume 03/17/11