Veterinary Clinical Medicine-I (General and Systemic)

PRINCIPLES OF HEART FAILURE

• Heart failure and Shock are both manifestations of circulatory failure.
• Heart failure, a deficit in myocardial performance, is characterized by the inability of the heart to adequately pump the blood presented to it.
• In shock, there is an inadequate venous return to the heart, usually as a result of peripheral circulatory failure.

Functional response to Cardiac Disease

• The circulatory system has multiple responsibilities including the transport of oxygen & nutrients to the tissues; the transport of carbon dioxide & other products of metabolism to the lungs and kidneys; the distribution of hormones and other substances that regulate cell function; and maintaining the adequacy of thermoregulation and urine formation.
• Circulatory control is affected by multiple regulatory systems which generally ensure an adequate capillary blood flow to meet the varying metabolic requirement of various organs, tissues and cells.
• Circulatory adjustments are affected by neural and chemical mechanisms that change the caliber of arterioles and other resistance vessels, that vary the rate and stroke out put of the heart, that increase or decrease blood storage in the capacitance venous vessels, and that in certain specific situations create alterations in the caliber and permeability of capillaries.
• It is readily apparent that other organs of the body are affected when heart function is impaired, even before congestive heart failure becomes clinically apparent. Therefore, many of the signs of congestive heart failure have their basis in organs other than the heart, and the same signs can be produced by other causes when the heart is normal. The involvement of multiple organs in heart disease may be either compensatory functions to maintain homeostasis or functional derangements brought on by circulatory insufficiency.
• In animals with heart disease, the maximal sustainable cardiac output is usually reduced because the cardiovascular reserve capacity is being used even at rest. The importance of the components of the cardiovascular reserve becomes apparent in understanding the functional response to heart disease.