Pathophysiology And Functional Impairment In Heart Failure
Pathophysicology of Cardiac Failure
The end systolic volume and diastolic pressure progressively rise when the ejection fraction of the ventricle comes down. Normally, the end diastolic pressure in the ventricles is less then 12 mm Hg. It may fall, remain unchanged or rise with physical exercise but the cardiac output increases. In the failing heart, though the end diastolic pressure goes up with exercise, the cardiac output does not rise, on the other hand it often falls. Venous congestion develops behind the failing chamber. This phenomenon is referred to as "backward failure". Reduction in Cardiac output leads to reduction in tissue perfusion. This is called "Forward failure". Both these mechanisms operate in most of the cases.
As Cardiac failure proceeds hemodynamic alterations take place. Blood supply to vital organs such as the brain and the heart is maintained by diverting the flow from less vital tissues. Rise in venous pressure leads to transudation of fluid into the interstitial spaces. Blood volume in the vascular compartment falls and this stimulates the volume receptors in the atria and carotid arteries resulting in the production of excess of aldosterone, which increases the tubular reabsorption of sodium and therefore salt is retained. The consequent rise in crystalloid osmotic pressure stimulates the osmoreceptors which lead to the release of ADH. Increase ADH activity leads to retention of water. Retention of salt and water favours the development of generalised edema.
Types of Heart Failure
Functionally, heart failure can be divided into right or left heart failure, depending on the side of the chamber which fails initially. In right-sided heart failure, the systolic output of the right ventricle and/or the right atrium falls. Common causes include pulmonary hypertension in mitrial stenosis, atrial septal defect and cor Pulmonale; pericardial diseases, pulmonary stenosis, right sided cardiomyopathy, massive pulmonary embolism and tricuspid stenosis. Right heart failure leads to rise in right atrial pressure (manifested as jugular venous pressure), and systemic venous congestion (manifested as tender hepatomegaly and dependent edema).
Left-sided heart failure is caused by dysfunction of the left ventricle or left atrium. Common causes are acute myocardial infarction, chronic ischemic heart disease, systemic hypertension, aortic valvular disease, mitrial incompetence, and mitrial stenosis. Left sided heart failure leads to pulmonary congestion and pulmonary edema (manifested as orthopnea and paroxysmal nocturnal dyspnea). Persistent left-sided heart failure gives rise to pulmonary hypertension which results in right-sided heart failure as well.
Normal and pathological heart
Other terms of Cardiac Failure
In many cases, both sides fail at the same time. Such combined heart failure may be seen in myocarditis, mitrial stenosis or ischemic heart disease.
Two other terms commonly used are "low output" and "high output" cardiac failure. In the former, the cardiac output is reduced below the average normal and this results in inadequate perfusion of the tissues, e.g mitral stenosis, ischemic heart disease and hypertensive heart disease. In high output failure, the cardiac output is above the average normal, but even here, the cardiac output falls when heart failure sets in, e.g thyrotoxicosis, beri beri, anemia etc.
© 2013 Funom Theophilus Makama