Diagnostic and Prognostic Role of USCOM in Adult Patients With Heart Failure-A Prospective Observational Study

Acute heart failure syndromes (aHFS) cause almost 1 million hospitalizations annually in the United States and are the leading cause of hospitalization in persons aged over 65 years. In 2003, inpatient management of aHFS cost an estimated $12.7 billion in the United States. In 2003, 12.5% of the population in Hong Kong were aged over 65, the third highest proportion of elderly among all countries, and it is postulated that by 2033, the proportion of the elderly in the population will increase to 25%. With the growing elderly population, and the increasing prevalence of hypertension and ischemic heart disease (the major causes of heart failure), heart failure has become a major health care issue globally. In western countries the incidence ranges from 1 to 10 cases/1000/year. Other studies suggest that heart failure is a large and growing public health burden throughout Europe.

Acute exacerbation of heart failure symptoms is a common emergency department (ED) presentation and is known as acute decompensated heart failure (adHF). Acute decompensated heart failure represents the single greatest cost to the US hospitals funded by Medicaid. In Hong Kong (HK), the incidence rate of heart failure was 3-3.8/1000/year rising to 20/1000/year in women over the age of 85 years in recent years. It has been estimated that 7% of all acute medical admissions was due to this condition. In recent years there has been a 10% annual increase in admissions for patients with adHF. Currently in Hong Kong, the vast majority of ED patients with adHF are admitted as inpatients to hospital. In 2005, an audit of outcomes in patients with acute cardiogenic pulmonary oedema, the most severe manifestation of heart failure, presenting to the emergency department at the Prince of Wales Hospital showed that nearly 30% of patients die within 30 days, and a further 30% require readmission within 30 days. Recent evidence from the USA suggests that ED operated observation units are effective in managing low to medium risk adHF patients, reducing length of stay (LOS) for these patients without adversely affecting readmission rate, morbidity and mortality.

2 Dimensional echocardiography (2D-echo) is a conventional standard-of-care tool for non-invasive hemodynamic assessments in adults. In stable settings, heart failure is often characterized and classified according to ejection fraction measured by echocardiography which may be considered a pragmatic gold standard. However, the use of 2D-echo requires highly trained personnel. Obtaining measurements and calculating fundamental cardiovascular parameters such as cardiac output (CO)may take anywhere between 30 to 45 minutes, which is impractical for any setting, let alone an acute care setting. Further, such personnel are frequently not available in emergency departments. The feasibility of real time haemodynamic assessments is therefore limited with 2D-echo. More sophisticated echocardiographic techniques have been developed in an attempt to overcome the problems of sensitivity to preload and particularly afterload, but have achieved little penetration in critical care.

In acute critical care settings, the diagnosis of adHF is based on the history and clinical signs, sometimes aided by echocardiography, chest radiography and blood markers such as B-type Natriuretic Peptide (BNP). The value of BNP over clinical assessment in patients presenting with dyspnoea has been questioned and there is a need for other tools to improve diagnosis. Commencement, dosing, and withdrawal of vasopressors, vasodilators, and inotropes is still largely based on clinical assessment, sometimes assisted by measurement of surrogates of inotropy such as ejection fraction (EF) or aortic ejection velocity, despite the well-known shortcomings of these indices in critical care. This is particularly so in complex surgical patients where vascular tone and fluid loading status are highly variable and changing.

Heart failure is an abnormality of cardiac structure or function leading to failure of the heart to deliver oxygen at a rate commensurate with the requirements of the metabolizing tissues, despite normal filling pressures (or only at the expense of increased filling pressures). The commonest causes are hypertension or ischemic heart disease. If this definition holds, then heart failure should be associated with some measure of reduction in inotropy or oxygen delivery. Until recently there was no simple non-invasive, bedside test that could aid the assessment of patients with heart failure. Whilst inotropy (or myocardial contractility) as a concept is well known to all clinicians, it is seldom thought of as a measurable quantity.