General Approach to Management of Congestive Heart Failure

It is rarely possible with cardiac disease in small animals to achieve the ideal aim of curing the underlying condition. Closure of a patent ductus arteriosus is probably the closest that we come to curing a cardiac disease. In most other conditions it is difficult to influence the underlying disease process, and we are often left with managing the effects of cardiac disease- the most serious of which is usually congestive heart failure. This means that for many cardiac diseases, no treatment is started until clinical signs develop. The distinction between heart failure and heart disease is therefore important. The heart may be affected by disease without any significant compromise of cardiac function. Examples of this include early degenerative mitral valve disease or mild aortic stenosis, both of which can cause a heart murmur without significantly impairing heart function.

Heart Failure

Congestive heart failure can be defined as abnormal fluid accumulation in the lungs, pleural cavity, abdomen or rarely, in the skin, secondary to increased venous pressures resulting from heart disease. This increase in venous pressures arises partly as a result of abnormal function. If cardiac output is reduced as a result of cardiac disease rather than hypovolemia, then atrial pressures will tend to increase. More importantly, venous pressures are often increased following plasma volume expansion by sodium and water retention.

Neurohormones in heart failure

A reduction in systemic arterial pressures triggers release of neurohormones such as Angiotensin II and aldosterone that promote sodium retention and corresponding water retention. This is an advantageous response where cardiac output falls secondary to hypovolemia or hemorrhage, but fluid retention in the setting of cardiac disease results in hypervolemia and excessive pulmonary and/or systemic venous pressures. The other common effect of neurohormones released in heart failure is to trigger vasoconstriction, which helps restore normal arterial pressures but increases the vascular resistance opposing ejection of blood. Many neurohormones also have direct adverse effects on the myocardium, altering cardiac systolic and diastolic function, and causing ventricular remodeling in association with myocyte death and interstitial fibrosis. [...]