Congestive Heart Failure Essays - Circulatory System, Cardiology

Congestive Heart Failure Essays - Circulatory System, Cardiology Congestive Heart Failure Symptomatic myocardial dysfunction responsible for the inability of the heart to pump blood at a rate which is les than the requirement of metabolizing tissue or need a higher end diastolic volume to meet the demand o Systolic heart failure is due to impaired myocardial contractility resulting in reduction of stroke volume, inadequate ventricular emptying, dilatation of heart and elevated ventricular end-diastolic pressure Idiopathic dilated cardiomyopathy is the prototype of systolic heart failure o Diastolic heart failure is characterized by impaired relaxation and filling of ventricle resulting in increased ventricular diastolic pressure at any given diastolic volume- restrictive cardiomyopathies o Concentric hypertrophy of left ventricle in hypertension does cause impaired diastolic relaxation but does not cause failure Normal Ventricular function [pic] o Conditions simulating heart failure > Circulatory insufficiency without myocardial failure ( cardiac temponade or haemorrhagic shock > Circulatory congestion secondary to salt and water retention( renal disease > Sudden increase in myocardial load e.g. accelerated hypertension or rupture of valve cusps Prevalence: o In West, increases with age- 1% at 60 years to 10% after 80 years o In India, rheumatic heart disease is common in young age group and commonly presents with heart failure Etiology and pathogenesis of Heart Failure: [pic] Important causes of heart failure are o Valvular heart disease- common in India o Hypertensive heart disease o Coronary heart disease- responsible for 40-60% heart failure in US o Congenital heart disease o Myocarditis o Cardiomyopathies Pathophysiology of heart failure: o Backward Failure theory: Myocardial Dysfunction ( High End Diastolic Volume of Ventricles ( ( Pressure and volume of atrium and venous system ( ( transudation of fluid from capillaries ( Low circulatory volume ( Activation of Renin-Angiotensin-Aldosterone System ( Salt and Water Retention o Forward Failure Theory Myocardial Dysfunction ( Low Cardiac Output ( Low Renal Perfusion ( Activation of Renin-Angiotensin-Aldosterone System ( Salt and Water Retention o Adaptive mechanisms in heart failure > Frank-Starling mechanism- operated due to increase preload ( increased end-diastolic volume of ventricle ( longer length of myocardial fibers( increased force of contraction > Increased after load ( concentric hypertrophy( restoration of elevated stress on ventricular walls to normal > Redistribution of subnormal cardiac output- less blood flow to skin, muscles and kidney to maintain normal flow to heart and brain > Neuro-hormonal adjustments- increased catecholamines ( increased HR ( maintenance of cardiac output despite low stroke volume > There may be right shift of oxygen dissociation curve to release more oxygen for tissue at lower pO2 levels o Adaptive neuro-hormonal/ cytokine changes in heart failure: > Adrenergic Nervous System- . Increased levels of nor-adrenaline-important in acute heart failure . In chronic heart failure, it may increase after load by increasing peripheral resistance, induce cardiac arrhythmias and may damage myocytes further by causing Ca++ overload . Prognosis of heart failure correlates inversely with levels of nor- adrenaline > Renin -Angiotensin -Aldosterone (RAA) System . Gets activated when there is a fall in cardiac output . Increased angiotensin II causes vasoconstriction and Aldosterone increases retention of Na+ and water and perhaps cases cardiac fibrosis also > Endothelin . A potent vasoconstrictor . Concentration increased in heart failure . Experimental studies indicate benefit of blocking receptors in heart failure > Increased levels of TNF-(- in experiments has been shown to impair systolic function > Vasodilator peptides (Atrial Natriuretic Peptide and Brain Natriuretic Peptide . These hormones released due to stimulation of stretch receptors in atria (ANP & BNP) or ventricles (BNP) and stimulate sodium excretion and urine formation by kidneys . Higher levels correlate with poor prognosis Hypertrophy of ventricles o Pressure overload ( elevated systolic pressure ( parallel addition of myofibrils( concentric hypertrophy o Volume overload ( elevated diastolic pressure( addition of myofibrils in series( eccentric hypertrophy Precipitating Factors for Heart Failure o Infections > Pulmonary infections more likely to occur in the presence of pulmonary vascular congestion > Infections ( fever, tachycardia, ( metabolism and hypoxia ( cardiac overload o Anaemia > Increased oxygen demand of tissue met by increase in cardiac output ( increased cardiac workload o Thyrotoxicosis and pregnancy > Increased cardiac output states ( increased cardiac load o Arrhythmias > In compensated heart disease, arrhythmias are the most important cause of failure > The deleterious effects can be due to following