Congestive heart failure

From Felipedia

The failing heart is described as one with reduced myocardial contractility, which can be determined by a reduced force of contraction from any given preload. More objectively, a failing heart can be described as one with a reduced rate of liberation of energy from the breakdown of ATP, or with a reduced velocity of fiber shortening when the heart contracts during the imaginary situation of contracting against no load. It is difficult to directly measure myocardial contractility and to identify a failing heart. Almost any animal with heart disease leading to chamber enlargement or increased wall thickness has a failing heart, but they are usually compensated and do not manifest symptoms; therefore, they are not in heart failure or CHF. This includes probably 95% of the 11% of dogs and cats with heart disease[1].

Heart failure and CHF are clinical syndromes in which an animal manifests signs referable to a complex interaction between a failing heart and the blood vessels. In heart failure, cardiac output is insufficient to perfuse organs with enough oxygenated blood for the organs to function properly either at rest (termed functional class IV heart failure), during mild exertion (class III), during moderate exercise (class II), or during extreme exercise (class I). In CHF, blood dams up in organs—usually the lungs but occasionally in the systemic organs—and causes the congested organs to function abnormally, become edematous, or both. The functional classification of heart failure is expressed when, during graded exercise, the animal shows signs (eg, dyspnea, cough, collapse) due to the heart disease[2].