The prevalence of heart failure is 1–2% in Western countries. It rises sharply in the elderly population, and is estimated to affect more than 10% of people over 70 years old (Mosterd & Hoes, 2007). Its incidence is increasing (annual growth rate almost 2%), mostly due to an ageing population and to improved survival after insults such as acute myocardial infarction (Ambrosy et al., 2014). One study has estimated that the overall lifetime risk of developing heart failure is 33% in men and 28% in women (Bleumink et al., 2004). The number of diagnosed acute heart failure events worldwide is difficult to estimate precisely, but hospitalised heart failure accounts for over 1 million admissions as a primary diagnosis and is the leading cause of hospitalisation in the USA and Europe (Ambrosy et al., 2014). It is estimated that heart failure accounts for about 6.5 million days in hospital per year in the USA. This comes with a significant financial burden with the World Bank estimating that the global economic cost of heart failure is $108 billion a year (Cook et al., 2014).
During the last few decades, improvements in the treatment of heart failure have improved survival and decreased hospitalisation rates. Despite this, its prognosis is still fairly poor: it was recently reported that a European patient population hospitalised for heart failure had a 1-year mortality rate of 17%, and 1-year hospitalisation rate of 44% (Maggioni et al., 2013). Meanwhile, the 2016 UK National Heart Failure Audit identified 56,915 heart failure admissions and observed a 29.6% 1-year mortality rate (Kurmani & Squire, 2017). Similar results were published in 2018 from the Epidemiology of Acute Heart Failure in the Emergency Departments (EAHFE) study which observed trends in acute heart failure over a 10-year period across 41 Spanish hospitals. The study included a total of 13,791 patients with acute heart failure and reported a 1-year all-cause mortality rate of 30.3% (Llorens et al., 2018). Various reasons related to underlying heart, vascular and other diseases contribute to this mortality.
Acute heart failure can be classified in many ways, and it has been divided into the following clinical categories which partly overlap each other (Nieminen et al., 2006):
The European Society of Cardiology Heart Failure Long-Term (ESC-HF-LT) Registry collected data from 6,629 patients admitted with acute heart failure to one of 211 cardiology centres across 21 European countries. The classification of patients in this study were similar to those reported previously with 61.1% presenting with decompensated heart failure, 13.2% with pulmonary oedema, 4.8% with hypertensive heart failure, 2.9% with cardiogenic shock, and 3.5% with right heart failure. Meanwhile, 14.4% presented with acute heart failure with associated acute coronary syndromes (ACS-HF) (Chioncel et al., 2017). A separate study sought to use cluster analysis to identify clinically important phenotypes of acute heart failure. Evaluating 77 clinical variables in 345 patients allowed three clusters to be identified; the first cluster represented vascular failure, with the highest average systolic blood pressure at admission and long congestion with type 2 respiratory failure. The second cluster group represented cardiac and renal failure, having the lowest ejection fraction and worst renal function. The final cluster group was comprised of mostly older patients and had the highest prevalence of atrial fibrillation and preserved ejection fraction. Rates of 1-year mortality or heart failure hospitalisation were highest in cluster group 2 and 3 (Table 1) (Horiuchi et al., 2018).
Table 1. Characteristics of patients within cluster groups (Horiuchi et al., 2018).
It has been reported that acute cardiac dysfunction occurs during or after cardiac surgery in more than 20% of patients. The perioperative low cardiac output syndrome is a substantial risk in cardiac surgery; it occurs in 3–14% of patients undergoing coronary artery bypass surgery, and it is associated with a 10-fold increase in mortality (Mebazaa et al., 2010; Algarni et al., 2012).