Changes

== Mechanisms of failure  ==

== Mechanisms of failure  ==

'''Myocardial failure '''e.g Dilated cardiomyopathy. Causes a failure in contractility.

'''Myocardial failure ''': Failure of myocardial contraction (systolic dysfunction) e.g. [[Dilated Cardiomyopathy|Dilated Cardiomyopathy]]

'''Volume overload '''e.g. Valve regurgitation and shunts ([[Patent Ductus Arteriosus|PDA]]). Initial response based on the '''Frank-Starling Law''' and stroke volume increases as preload increases and enables the heart to expel the extra blood. Ultimately the heart decompensates and the chamber enlarges. Fluid will build up in the compartment preceding it. For example, failure of the left atrium in this manner due to mitral regurgitation leads to [[Pulmonary Oedema|pulmonary oedema]].  

'''Volume overload ''': Chronic increase in the amount of blood that must be pumped by a given chamber, due to shunting of blood ([[Patent Ductus Arteriosus|PDA]], [[Ventricular Septal Defect|VSD]]), regurgitation of blood ([[Endocardiosis| Degenerative Mitral Valve Disease]]), anaemia or increased metabolic demands ([[Hyperthyroidism]]).  

'''Pressure overload '''e.g. [[Aortic Stenosis|aortic stenosis]] or systemic overload increase afterload so heart muscle hypertrophies. The abnormally thick myocardium may predispose to diastolic failure and [[:Category:Arrhythmia|arrhythmias]].  

'''Pressure overload ''': Increased resistance to chamber emptying. This may be as a result of systemic or pulmonary hypertension, or an outflow obstruction such as [[Aortic Stenosis]] or[[Pulmonic Stenosis]].

'''Compliance failure '''e.g. [[Cardiac Tamponade|cardiac tamponade]] prevents adequate relaxation of the ventricles and doesn't allow sufficient filling therfore results in diastolic failure.  

'''Abnormal rate/rhythm ''': Compromised cardiac output due to an increased or decreased heart rate. Abnormally fast heart rates (tachycardias) result a shorter diastole, therefore impaired filling and reduced stroke volume. Abnormally slow heart rates (bradycardias) limit cardiac output as a direct consequence of reduced heart rate (CO = HR x SV).  

'''Abnormal rate/rhythm '''e.g sustained bradycardia leads to a low output failure.

 

'''Diastolic failure ''':  Impaired ventricular filling with normal systolic function. Examples include [[Cardiac Tamponade|cardiac tamponade]] in [[Pericardial Effusion]], [[Pericarditis, Constrictive| Constrictive Pericarditis]] and [[Hypertrophic Cardiomyopathy|Hypertrophic Cardiomyopathy]] and [[Restrictive Cardiomyopathy|Restrictive Cardiomyopathy]]

== Clinical Signs  ==

== Clinical Signs  ==