Diagnosing heart failure among acutely dyspneic patients with cardiac, inferior vena cava, and lung ultrasonography

Abstract

Background

Rapid diagnosis (dx) of acutely decompensated heart failure (ADHF) may be challenging in the emergency department (ED). Point-of-care ultrasonography (US) allows rapid determination of cardiac function, intravascular volume status, and presence of pulmonary edema. We test the diagnostic test characteristics of these 3 parameters in making the dx of ADHF among acutely dyspneic patients in the ED.

Methods

This was a prospective observational cohort study at an urban academic ED. Inclusion criteria were as follows: dyspneic patients, at least 18 years old and able to consent, whose differential dx included ADHF. Ultrasonography performed by emergency sonologists evaluated the heart for left ventricular ejection fraction (LVEF), the inferior vena cava for collapsibility index (IVC-CI), and the pleura sampled in each of 8 thoracic regions for presence of B-lines. Cutoff values for ADHF were LVEF less than 45%, IVC-CI less than 20%, and at least 10 B-lines. The US findings were compared with the final dx determined by 2 emergency physicians blinded to the US results.

Results

One hundred one participants were enrolled: 52% male, median age 62 (25%-75% interquartile, 53-91). Forty-four (44%) had a final dx of ADHF. Sensitivity and specificity (including 95% confidence interval) for the presence of ADHF were as follows: 74 (65-90) and 74 (62-85) using LVEF less than 45%, 52 (38-67) and 86 (77-95) using IVC-CI less than 20%, and 70 (52-80) and 75 (64-87) using B-lines at least 10. Using all 3 modalities together, the sensitivity and specificity were 36 (22-51) and 100 (95-100). As a comparison, the sensitivity and specificity of brain natriuretic peptide greater than 500 were 75 (55-89) and 83 (67-92).

Conclusion

In this study, US was 100% specific for the dx of ADHF.

Introduction

Congestive heart failure (CHF) is a major public health concern. Approximately 5.7 million patients in the United States carry the diagnosis of CHF with lifetime incidence of 1 in 5 for individuals older than 40 years [1], [2], [3], [4], [5]. Heart failure is the most common hospital discharge diagnosis, and more Medicare dollars are spent for the diagnosis and treatment CHF than for any other diagnosis [1], [6]. The Centers for Medicare and Medicaid Services has targeted heart failure as the disease most worthy of cost-effective management; however, providing cost-effective treatment requires rapid and accurate differentiation of CHF from other causes of dyspnea [7]. Acutely decompensated heart failure (ADHF) is also the most common cause of acute dyspnea among elderly patients in the emergency department (ED) [8]. Although early appropriate diagnosis and therapy are associated with a decreased mortality [8], [9], [10], [11], ADHF is also the most common cause of death among dyspneic patients presenting to the ED [12].

Correctly diagnosing ADHF among acutely dyspneic patients in the ED to provide early appropriate treatment has proven challenging [8], [10], [13], [14], [15], [16], [17], [18]. Traditional diagnostic modalities such as physical examination, plain radiographs, and laboratory studies have variable, and frequently limited, diagnostic utility. The signs and symptoms of ADHF are frequently nonspecific and highly variable as well [15], [18], [19], [20], especially among the increasingly larger group of patients with coexisting respiratory illness such as chronic obstructive pulmonary disease (COPD). Plain chest radiographs have limited correlation with CHF exacerbation [21], [22]; and although natriuretic peptides may lend weight to a suspected diagnosis, they are insufficiently accurate to confirm or exclude the diagnosis of ADHF [1], [11], [16], [23] and have a “gray zone” of values that have little diagnostic value at all [24]. Unfortunately, misdiagnosis is associated with an increase in morbidity and mortality among patients with ADHF [8], [9], [10]. Conversely, treatments for CHF have deleterious effects among patients with noncardiac causes of dyspnea that often present with the same primary physical findings [10], [25].

If the diagnostic accuracy of decompensated heart failure is to be improved in the acute setting, a rapid tool that is more specific for the diagnosis of ADHF must be developed. Such a tool, if positive, would allow treating physicians to begin treating even the most unstable patients with ADHF before the traditional diagnostic tests are available for interpretation without the increased morbidity and mortality associated with misdiagnosis and mistreatment. Furthermore, in less critically ill patients, a highly specific test would aid in making the diagnosis of ADHF when traditional testing is equivocal or delayed. Echocardiography is commonly used to support the diagnosis of CHF, but comprehensive echocardiography is rarely available in the ED and is too time consuming for the acutely decompensating patient. However, limited bedside cardiac and lung ultrasonography (US) is becoming a standard tool in EDs and intensive care units (ICUs). Emergency point-of-care US is ubiquitous among emergency medicine residency training programs, and most emergency residents are graduating with proficiency in limited cardiac US since the American College of Graduate Medical Education began requiring procedural competency in point-of-care US in 2008 [26]. In addition, many emergency physicians (EPs) who graduated before this requirement, as well as many critical care physicians, have also learned limited cardiac US skills. There are 3 point-of-care US modalities that have potential utility in the diagnosis of ADHF: cardiac US (which gives direct visualization of ejection fraction) [27], [28], [29], [30], [31], [32], [33], [34], inferior vena cava (IVC) US (a noninvasive method of estimating intravascular volume status), [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45] and lung US (which can detect the presence of interstitial edema [IE]) [46], [47], [48], [49], [50], [51]. Each of these modalities has been used alone in evaluating for the diagnosis of ADHF; however, when used alone, each one lacks the accuracy needed to definitively make the diagnosis among acutely dyspneic patients in an ED setting—a depressed left ventricular ejection fraction (LVEF) is present in chronic heart failure but does not indicate whether there has been an acute reduction in systolic function, and neither a plethoric IVC nor the presence of IE is specific to ADHF.

Recently, there has been speculation that a combination of the 3 US modalities might yield a tool that is useful in making the diagnosis of ADHF among acutely dyspneic patients in the ED setting. One report has suggested that a focused US examination consisting of point-of-care cardiac, IVC, and lung examinations would be “an ideal tool to rule in or rule out the diagnosis of CHF”; however, this report has no data to support this assumption [52]. Only 1 case report has been published as evidence that this “Triple Scan” could potentially be used to identify the etiology of acute dyspnea in the ED [53]. Another recent study, performed by cardiologists, demonstrated that an echocardiogram, including valvular and IVC interrogation, combined with lung US is more accurate than lung US alone in distinguishing cardiac from noncardiac etiologies of dyspnea [54]. Accordingly, we set out to assess the accuracy of point-of-care US in making the diagnosis of ADHF among acutely dyspneic patients in the ED setting by combining all 3 modalities (cardiac, IVC, and lung US). We also performed a secondary analysis to determine if the combination of any 2 of the 3 modalities would perform as well as all 3 together.