23 Heart Failure: Epidemiology, Pathophysiology and Diagnosis John McMurray, Michel Komajda, Stefan Anker and Roy Gardner Introduction Heart failure is the term used to describe a common clinical syndrome arising, in ways that are incompletely understood, as a consequence of reduced cardiac pump function. The term ‘syndrome’ merely describes a con- stellation of symptoms and signs and, therefore, heart failure is not a diagnosis as such. Unfortunately, the typical symptoms (breathlessness and fatigue) and signs (e.g. oedema) of heart failure are relatively non-specific, making clinical confirmation of the syndrome difficult. The syndrome of heart failure itself can arise as a result of almost any abnormality of the structure, mechanical function, or electrical activity of the heart, each of which may require quite different treatments, emphasizing the importance of appropriate investigation of patients with suspected heart failure. Many of the typical clinical symptoms and signs of heart failure do not arise directly as a result of the cardiac abnormality but rather from secondary dysfunction of other organs and tissues, e.g. the kidneys and muscles. These secondary consequences of pump failure are myriad and their causes are not fully elucidated. Dysfunction of tissues and organs remote from the heart cannot, however, be explained solely by reduced perfusion and it is generally believed that other systemic processes (e.g. neurohumoral activation) are involved. In other words, the pathophysiology of heart failure is complex and incompletely understood and, consequently, so is the pathophysiological basis of treatment. It has even proved difficult to agree a simple definition of heart failure (Table 23.1) [1]. The terms used to describe different types of heart failure can also Summary The term ‘heart failure’ describes the common clinical syndrome arising when delivery of oxygen to the metabolizing tissues is impaired because of defective function of the heart as a pump (or, rarely, by extracardiac disorders). The syndrome is characterized by breathlessness, exercise intolerance and sodium and water retention, often manifest as oedema. There are numerous causes of heart failure, the most common of which are myocardial disease and valvular disease. Left ventricular myocardial damage is commonly caused by hypertension, coronary artery disease (usually myocardial infarction) or both. Those disease processes can cause left ventricular systolic dysfunction, diastolic dysfunction or both. The aim of investigation is to establish the underlying cardiac cause of heart failure, quantify ventricular and valvular function, estimate the severity of symptoms and the degree of functional limitation and identify relevant comorbidities. These determine which treatments should and can or cannot be used. A resting 12-lead ECG, transthoracic Doppler echocardiogram, blood chemistry and haematological measurements are essential basic investigations. Investigations also provide information on prognosis which is, to a large extent, determined by left ventricular systolic function and comorbidity, as well as age. The pathophysiology of one type of heart failure, that caused by left ventricular systolic dysfunction, is partially understood. Two key elements are neurohumoral activity and left ventricular remodelling. Untreated, patients with that type of heart failure demonstrate chronic, sustained, neurohumoral activation and show progressive enlargement of the left ventricle with an associated decline in systolic function. The most successful treatments, to date, alter these processes. 685